civetweb/mongoose.c

// Copyright (c) 2004-2011 Sergey Lyubka
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

#if defined(_WIN32)
#define _CRT_SECURE_NO_WARNINGS // Disable deprecation warning in VS2005
#else
#define _XOPEN_SOURCE 600     // For flockfile() on Linux
#define _LARGEFILE_SOURCE     // Enable 64-bit file offsets
#define __STDC_FORMAT_MACROS  // <inttypes.h> wants this for C++
#define __STDC_LIMIT_MACROS   // C++ wants that for INT64_MAX
#endif

#if defined(__SYMBIAN32__)
#define NO_SSL // SSL is not supported
#define NO_CGI // CGI is not supported
#define PATH_MAX FILENAME_MAX
#endif // __SYMBIAN32__

#ifndef _WIN32_WCE // Some ANSI #includes are not available on Windows CE
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <signal.h>
#include <fcntl.h>
#endif // !_WIN32_WCE

#include <time.h>
#include <stdlib.h>
#include <stdarg.h>
#include <assert.h>
#include <string.h>
#include <ctype.h>
#include <limits.h>
#include <stddef.h>
#include <stdio.h>

#if defined(_WIN32) && !defined(__SYMBIAN32__) // Windows specific
#define _WIN32_WINNT 0x0400 // To make it link in VS2005
#include <windows.h>

#ifndef PATH_MAX
#define PATH_MAX MAX_PATH
#endif

#ifndef _WIN32_WCE
#include <process.h>
#include <direct.h>
#include <io.h>
#else // _WIN32_WCE
#include <winsock2.h>
#include <ws2tcpip.h>
#define NO_CGI // WinCE has no pipes

typedef long off_t;
#define BUFSIZ  4096

#define errno   GetLastError()
#define strerror(x)  _ultoa(x, (char *) _alloca(sizeof(x) *3 ), 10)
#endif // _WIN32_WCE

#define MAKEUQUAD(lo, hi) ((uint64_t)(((uint32_t)(lo)) | \
      ((uint64_t)((uint32_t)(hi))) << 32))
#define RATE_DIFF 10000000 // 100 nsecs
#define EPOCH_DIFF MAKEUQUAD(0xd53e8000, 0x019db1de)
#define SYS2UNIX_TIME(lo, hi) \
  (time_t) ((MAKEUQUAD((lo), (hi)) - EPOCH_DIFF) / RATE_DIFF)

// Visual Studio 6 does not know __func__ or __FUNCTION__
// The rest of MS compilers use __FUNCTION__, not C99 __func__
// Also use _strtoui64 on modern M$ compilers
#if defined(_MSC_VER) && _MSC_VER < 1300
#define STRX(x) #x
#define STR(x) STRX(x)
#define __func__ "line " STR(__LINE__)
#define strtoull(x, y, z) strtoul(x, y, z)
#define strtoll(x, y, z) strtol(x, y, z)
#else
#define __func__  __FUNCTION__
#define strtoull(x, y, z) _strtoui64(x, y, z)
#define strtoll(x, y, z) _strtoi64(x, y, z)
#endif // _MSC_VER

#define ERRNO   GetLastError()
#define NO_SOCKLEN_T
#define SSL_LIB   "ssleay32.dll"
#define CRYPTO_LIB  "libeay32.dll"
#define DIRSEP '\\'
#define IS_DIRSEP_CHAR(c) ((c) == '/' || (c) == '\\')
#define O_NONBLOCK  0
#if !defined(EWOULDBLOCK)
#define EWOULDBLOCK  WSAEWOULDBLOCK
#endif // !EWOULDBLOCK
#define _POSIX_
#define INT64_FMT  "I64d"

#define WINCDECL __cdecl
#define SHUT_WR 1
#define snprintf _snprintf
#define vsnprintf _vsnprintf
#define mg_sleep(x) Sleep(x)

#define pipe(x) _pipe(x, BUFSIZ, _O_BINARY)
#define popen(x, y) _popen(x, y)
#define pclose(x) _pclose(x)
#define close(x) _close(x)
#define dlsym(x,y) GetProcAddress((HINSTANCE) (x), (y))
#define RTLD_LAZY  0
#define fseeko(x, y, z) fseek((x), (y), (z))
#define fdopen(x, y) _fdopen((x), (y))
#define write(x, y, z) _write((x), (y), (unsigned) z)
#define read(x, y, z) _read((x), (y), (unsigned) z)
#define flockfile(x) EnterCriticalSection(&global_log_file_lock)
#define funlockfile(x) LeaveCriticalSection(&global_log_file_lock)

#if !defined(fileno)
#define fileno(x) _fileno(x)
#endif // !fileno MINGW #defines fileno

typedef HANDLE pthread_mutex_t;
typedef struct {HANDLE signal, broadcast;} pthread_cond_t;
typedef DWORD pthread_t;
#define pid_t HANDLE // MINGW typedefs pid_t to int. Using #define here.

struct timespec {
  long tv_nsec;
  long tv_sec;
};

static int pthread_mutex_lock(pthread_mutex_t *);
static int pthread_mutex_unlock(pthread_mutex_t *);
static FILE *mg_fopen(const char *path, const char *mode);

#if defined(HAVE_STDINT)
#include <stdint.h>
#else
typedef unsigned int  uint32_t;
typedef unsigned short  uint16_t;
typedef unsigned __int64 uint64_t;
typedef __int64   int64_t;
#define INT64_MAX  9223372036854775807
#endif // HAVE_STDINT

// POSIX dirent interface
struct dirent {
  char d_name[PATH_MAX];
};

typedef struct DIR {
  HANDLE   handle;
  WIN32_FIND_DATAW info;
  struct dirent  result;
} DIR;

#else    // UNIX  specific
#include <sys/wait.h>
#include <sys/socket.h>
#include <sys/select.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/time.h>
#include <stdint.h>
#include <inttypes.h>
#include <netdb.h>

#include <pwd.h>
#include <unistd.h>
#include <dirent.h>
#if !defined(NO_SSL_DL) && !defined(NO_SSL)
#include <dlfcn.h>
#endif
#include <pthread.h>
#if defined(__MACH__)
#define SSL_LIB   "libssl.dylib"
#define CRYPTO_LIB  "libcrypto.dylib"
#else
#if !defined(SSL_LIB)
#define SSL_LIB   "libssl.so"
#endif
#if !defined(CRYPTO_LIB)
#define CRYPTO_LIB  "libcrypto.so"
#endif
#endif
#define DIRSEP   '/'
#define IS_DIRSEP_CHAR(c) ((c) == '/')
#ifndef O_BINARY
#define O_BINARY  0
#endif // O_BINARY
#define closesocket(a) close(a)
#define mg_fopen(x, y) fopen(x, y)
#define mg_mkdir(x, y) mkdir(x, y)
#define mg_remove(x) remove(x)
#define mg_rename(x, y) rename(x, y)
#define mg_sleep(x) usleep((x) * 1000)
#define ERRNO errno
#define INVALID_SOCKET (-1)
#define INT64_FMT PRId64
typedef int SOCKET;
#define WINCDECL

#endif // End of Windows and UNIX specific includes

#include "mongoose.h"

#define MONGOOSE_VERSION "3.2"
#define PASSWORDS_FILE_NAME ".htpasswd"
#define CGI_ENVIRONMENT_SIZE 4096
#define MAX_CGI_ENVIR_VARS 64
#define ARRAY_SIZE(array) (sizeof(array) / sizeof(array[0]))

#ifdef _WIN32
static CRITICAL_SECTION global_log_file_lock;
static pthread_t pthread_self(void) {
  return GetCurrentThreadId();
}
#endif // _WIN32

#if defined(DEBUG)
#define DEBUG_TRACE(x) do { \
  flockfile(stdout); \
  printf("*** %lu.%p.%s.%d: ", \
         (unsigned long) time(NULL), (void *) pthread_self(), \
         __func__, __LINE__); \
  printf x; \
  putchar('\n'); \
  fflush(stdout); \
  funlockfile(stdout); \
} while (0)
#else
#define DEBUG_TRACE(x)
#endif // DEBUG

// Darwin prior to 7.0 and Win32 do not have socklen_t
#ifdef NO_SOCKLEN_T
typedef int socklen_t;
#endif // NO_SOCKLEN_T

#if !defined(MSG_NOSIGNAL)
#define MSG_NOSIGNAL 0
#endif

static const char *http_500_error = "Internal Server Error";

// Snatched from OpenSSL includes. I put the prototypes here to be independent
// from the OpenSSL source installation. Having this, mongoose + SSL can be
// built on any system with binary SSL libraries installed.
typedef struct ssl_st SSL;
typedef struct ssl_method_st SSL_METHOD;
typedef struct ssl_ctx_st SSL_CTX;

#define SSL_ERROR_WANT_READ 2
#define SSL_ERROR_WANT_WRITE 3
#define SSL_FILETYPE_PEM 1
#define CRYPTO_LOCK  1

#if defined(NO_SSL_DL)
extern void SSL_free(SSL *);
extern int SSL_accept(SSL *);
extern int SSL_connect(SSL *);
extern int SSL_read(SSL *, void *, int);
extern int SSL_write(SSL *, const void *, int);
extern int SSL_get_error(const SSL *, int);
extern int SSL_set_fd(SSL *, int);
extern SSL *SSL_new(SSL_CTX *);
extern SSL_CTX *SSL_CTX_new(SSL_METHOD *);
extern SSL_METHOD *SSLv23_server_method(void);
extern int SSL_library_init(void);
extern void SSL_load_error_strings(void);
extern int SSL_CTX_use_PrivateKey_file(SSL_CTX *, const char *, int);
extern int SSL_CTX_use_certificate_file(SSL_CTX *, const char *, int);
extern int SSL_CTX_use_certificate_chain_file(SSL_CTX *, const char *);
extern void SSL_CTX_set_default_passwd_cb(SSL_CTX *, mg_callback_t);
extern void SSL_CTX_free(SSL_CTX *);
extern unsigned long ERR_get_error(void);
extern char *ERR_error_string(unsigned long, char *);
extern int CRYPTO_num_locks(void);
extern void CRYPTO_set_locking_callback(void (*)(int, int, const char *, int));
extern void CRYPTO_set_id_callback(unsigned long (*)(void));
#else
// Dynamically loaded SSL functionality
struct ssl_func {
  const char *name;   // SSL function name
  void  (*ptr)(void); // Function pointer
};

#define SSL_free (* (void (*)(SSL *)) ssl_sw[0].ptr)
#define SSL_accept (* (int (*)(SSL *)) ssl_sw[1].ptr)
#define SSL_connect (* (int (*)(SSL *)) ssl_sw[2].ptr)
#define SSL_read (* (int (*)(SSL *, void *, int)) ssl_sw[3].ptr)
#define SSL_write (* (int (*)(SSL *, const void *,int)) ssl_sw[4].ptr)
#define SSL_get_error (* (int (*)(SSL *, int)) ssl_sw[5].ptr)
#define SSL_set_fd (* (int (*)(SSL *, SOCKET)) ssl_sw[6].ptr)
#define SSL_new (* (SSL * (*)(SSL_CTX *)) ssl_sw[7].ptr)
#define SSL_CTX_new (* (SSL_CTX * (*)(SSL_METHOD *)) ssl_sw[8].ptr)
#define SSLv23_server_method (* (SSL_METHOD * (*)(void)) ssl_sw[9].ptr)
#define SSL_library_init (* (int (*)(void)) ssl_sw[10].ptr)
#define SSL_CTX_use_PrivateKey_file (* (int (*)(SSL_CTX *, \
        const char *, int)) ssl_sw[11].ptr)
#define SSL_CTX_use_certificate_file (* (int (*)(SSL_CTX *, \
        const char *, int)) ssl_sw[12].ptr)
#define SSL_CTX_set_default_passwd_cb \
  (* (void (*)(SSL_CTX *, mg_callback_t)) ssl_sw[13].ptr)
#define SSL_CTX_free (* (void (*)(SSL_CTX *)) ssl_sw[14].ptr)
#define SSL_load_error_strings (* (void (*)(void)) ssl_sw[15].ptr)
#define SSL_CTX_use_certificate_chain_file \
  (* (int (*)(SSL_CTX *, const char *)) ssl_sw[16].ptr)

#define CRYPTO_num_locks (* (int (*)(void)) crypto_sw[0].ptr)
#define CRYPTO_set_locking_callback \
  (* (void (*)(void (*)(int, int, const char *, int))) crypto_sw[1].ptr)
#define CRYPTO_set_id_callback \
  (* (void (*)(unsigned long (*)(void))) crypto_sw[2].ptr)
#define ERR_get_error (* (unsigned long (*)(void)) crypto_sw[3].ptr)
#define ERR_error_string (* (char * (*)(unsigned long,char *)) crypto_sw[4].ptr)

// set_ssl_option() function updates this array.
// It loads SSL library dynamically and changes NULLs to the actual addresses
// of respective functions. The macros above (like SSL_connect()) are really
// just calling these functions indirectly via the pointer.
static struct ssl_func ssl_sw[] = {
  {"SSL_free",   NULL},
  {"SSL_accept",   NULL},
  {"SSL_connect",   NULL},
  {"SSL_read",   NULL},
  {"SSL_write",   NULL},
  {"SSL_get_error",  NULL},
  {"SSL_set_fd",   NULL},
  {"SSL_new",   NULL},
  {"SSL_CTX_new",   NULL},
  {"SSLv23_server_method", NULL},
  {"SSL_library_init",  NULL},
  {"SSL_CTX_use_PrivateKey_file", NULL},
  {"SSL_CTX_use_certificate_file",NULL},
  {"SSL_CTX_set_default_passwd_cb",NULL},
  {"SSL_CTX_free",  NULL},
  {"SSL_load_error_strings", NULL},
  {"SSL_CTX_use_certificate_chain_file", NULL},
  {NULL,    NULL}
};

// Similar array as ssl_sw. These functions could be located in different lib.
#if !defined(NO_SSL)
static struct ssl_func crypto_sw[] = {
  {"CRYPTO_num_locks",  NULL},
  {"CRYPTO_set_locking_callback", NULL},
  {"CRYPTO_set_id_callback", NULL},
  {"ERR_get_error",  NULL},
  {"ERR_error_string", NULL},
  {NULL,    NULL}
};
#endif // NO_SSL
#endif // NO_SSL_DL

static const char *month_names[] = {
  "Jan", "Feb", "Mar", "Apr", "May", "Jun",
  "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
};

// Unified socket address. For IPv6 support, add IPv6 address structure
// in the union u.
union usa {
  struct sockaddr sa;
  struct sockaddr_in sin;
#if defined(USE_IPV6)
  struct sockaddr_in6 sin6;
#endif
};

// Describes a string (chunk of memory).
struct vec {
  const char *ptr;
  size_t len;
};

// Structure used by mg_stat() function. Uses 64 bit file length.
struct mgstat {
  int is_directory;  // Directory marker
  int64_t size;      // File size
  time_t mtime;      // Modification time
};

// Describes listening socket, or socket which was accept()-ed by the master
// thread and queued for future handling by the worker thread.
struct socket {
  struct socket *next;  // Linkage
  SOCKET sock;          // Listening socket
  union usa lsa;        // Local socket address
  union usa rsa;        // Remote socket address
  int is_ssl;           // Is socket SSL-ed
};

enum {
  CGI_EXTENSIONS, CGI_ENVIRONMENT, PUT_DELETE_PASSWORDS_FILE, CGI_INTERPRETER,
  PROTECT_URI, AUTHENTICATION_DOMAIN, SSI_EXTENSIONS, ACCESS_LOG_FILE,
  SSL_CHAIN_FILE, ENABLE_DIRECTORY_LISTING, ERROR_LOG_FILE,
  GLOBAL_PASSWORDS_FILE, INDEX_FILES,
  ENABLE_KEEP_ALIVE, ACCESS_CONTROL_LIST, MAX_REQUEST_SIZE,
  EXTRA_MIME_TYPES, LISTENING_PORTS,
  DOCUMENT_ROOT, SSL_CERTIFICATE, NUM_THREADS, RUN_AS_USER, REWRITE,
  NUM_OPTIONS
};

static const char *config_options[] = {
  "C", "cgi_pattern", "**.cgi$|**.pl$|**.php$",
  "E", "cgi_environment", NULL,
  "G", "put_delete_passwords_file", NULL,
  "I", "cgi_interpreter", NULL,
  "P", "protect_uri", NULL,
  "R", "authentication_domain", "mydomain.com",
  "S", "ssi_pattern", "**.shtml$|**.shtm$",
  "a", "access_log_file", NULL,
  "c", "ssl_chain_file", NULL,
  "d", "enable_directory_listing", "yes",
  "e", "error_log_file", NULL,
  "g", "global_passwords_file", NULL,
  "i", "index_files", "index.html,index.htm,index.cgi,index.shtml,index.php",
  "k", "enable_keep_alive", "no",
  "l", "access_control_list", NULL,
  "M", "max_request_size", "16384",
  "m", "extra_mime_types", NULL,
  "p", "listening_ports", "8080",
  "r", "document_root",  ".",
  "s", "ssl_certificate", NULL,
  "t", "num_threads", "10",
  "u", "run_as_user", NULL,
  "w", "url_rewrite_patterns", NULL,
  NULL
};
#define ENTRIES_PER_CONFIG_OPTION 3

struct mg_context {
  volatile int stop_flag;       // Should we stop event loop
  SSL_CTX *ssl_ctx;             // SSL context
  char *config[NUM_OPTIONS];    // Mongoose configuration parameters
  mg_callback_t user_callback;  // User-defined callback function
  void *user_data;              // User-defined data

  struct socket *listening_sockets;

  volatile int num_threads;  // Number of threads
  pthread_mutex_t mutex;     // Protects (max|num)_threads
  pthread_cond_t  cond;      // Condvar for tracking workers terminations

  struct socket queue[20];   // Accepted sockets
  volatile int sq_head;      // Head of the socket queue
  volatile int sq_tail;      // Tail of the socket queue
  pthread_cond_t sq_full;    // Singaled when socket is produced
  pthread_cond_t sq_empty;   // Signaled when socket is consumed
};

struct mg_connection {
  struct mg_request_info request_info;
  struct mg_context *ctx;
  SSL *ssl;                   // SSL descriptor
  struct socket client;       // Connected client
  time_t birth_time;          // Time connection was accepted
  int64_t num_bytes_sent;     // Total bytes sent to client
  int64_t content_len;        // Content-Length header value
  int64_t consumed_content;   // How many bytes of content is already read
  char *buf;                  // Buffer for received data
  char *path_info;            // PATH_INFO part of the URL
  int must_close;             // 1 if connection must be closed
  int buf_size;               // Buffer size
  int request_len;            // Size of the request + headers in a buffer
  int data_len;               // Total size of data in a buffer
};

const char **mg_get_valid_option_names(void) {
  return config_options;
}

static void *call_user(struct mg_connection *conn, enum mg_event event) {
  conn->request_info.user_data = conn->ctx->user_data;
  return conn->ctx->user_callback == NULL ? NULL :
    conn->ctx->user_callback(event, conn, &conn->request_info);
}

static int get_option_index(const char *name) {
  int i;

  for (i = 0; config_options[i] != NULL; i += ENTRIES_PER_CONFIG_OPTION) {
    if (strcmp(config_options[i], name) == 0 ||
        strcmp(config_options[i + 1], name) == 0) {
      return i / ENTRIES_PER_CONFIG_OPTION;
    }
  }
  return -1;
}

const char *mg_get_option(const struct mg_context *ctx, const char *name) {
  int i;
  if ((i = get_option_index(name)) == -1) {
    return NULL;
  } else if (ctx->config[i] == NULL) {
    return "";
  } else {
    return ctx->config[i];
  }
}

static void sockaddr_to_string(char *buf, size_t len,
                                     const union usa *usa) {
  buf[0] = '\0';
#if defined(USE_IPV6)
  inet_ntop(usa->sa.sa_family, usa->sa.sa_family == AF_INET ?
            (void *) &usa->sin.sin_addr :
            (void *) &usa->sin6.sin6_addr, buf, len);
#elif defined(_WIN32)
  // Only Windoze Vista (and newer) have inet_ntop()
  strncpy(buf, inet_ntoa(usa->sin.sin_addr), len);
#else
  inet_ntop(usa->sa.sa_family, (void *) &usa->sin.sin_addr, buf, len);
#endif
}

// Print error message to the opened error log stream.
static void cry(struct mg_connection *conn, const char *fmt, ...) {
  char buf[BUFSIZ], src_addr[20];
  va_list ap;
  FILE *fp;
  time_t timestamp;

  va_start(ap, fmt);
  (void) vsnprintf(buf, sizeof(buf), fmt, ap);
  va_end(ap);

  // Do not lock when getting the callback value, here and below.
  // I suppose this is fine, since function cannot disappear in the
  // same way string option can.
  conn->request_info.log_message = buf;
  if (call_user(conn, MG_EVENT_LOG) == NULL) {
    fp = conn->ctx->config[ERROR_LOG_FILE] == NULL ? NULL :
      mg_fopen(conn->ctx->config[ERROR_LOG_FILE], "a+");

    if (fp != NULL) {
      flockfile(fp);
      timestamp = time(NULL);

      sockaddr_to_string(src_addr, sizeof(src_addr), &conn->client.rsa);
      fprintf(fp, "[%010lu] [error] [client %s] ", (unsigned long) timestamp,
              src_addr);

      if (conn->request_info.request_method != NULL) {
        fprintf(fp, "%s %s: ", conn->request_info.request_method,
                conn->request_info.uri);
      }

      (void) fprintf(fp, "%s", buf);
      fputc('\n', fp);
      funlockfile(fp);
      if (fp != stderr) {
        fclose(fp);
      }
    }
  }
  conn->request_info.log_message = NULL;
}

// Return fake connection structure. Used for logging, if connection
// is not applicable at the moment of logging.
static struct mg_connection *fc(struct mg_context *ctx) {
  static struct mg_connection fake_connection;
  fake_connection.ctx = ctx;
  return &fake_connection;
}

const char *mg_version(void) {
  return MONGOOSE_VERSION;
}

static void mg_strlcpy(register char *dst, register const char *src, size_t n) {
  for (; *src != '\0' && n > 1; n--) {
    *dst++ = *src++;
  }
  *dst = '\0';
}

static int lowercase(const char *s) {
  return tolower(* (const unsigned char *) s);
}

static int mg_strncasecmp(const char *s1, const char *s2, size_t len) {
  int diff = 0;

  if (len > 0)
    do {
      diff = lowercase(s1++) - lowercase(s2++);
    } while (diff == 0 && s1[-1] != '\0' && --len > 0);

  return diff;
}

static int mg_strcasecmp(const char *s1, const char *s2) {
  int diff;

  do {
    diff = lowercase(s1++) - lowercase(s2++);
  } while (diff == 0 && s1[-1] != '\0');

  return diff;
}

static char * mg_strndup(const char *ptr, size_t len) {
  char *p;

  if ((p = (char *) malloc(len + 1)) != NULL) {
    mg_strlcpy(p, ptr, len + 1);
  }

  return p;
}

static char * mg_strdup(const char *str) {
  return mg_strndup(str, strlen(str));
}

// Like snprintf(), but never returns negative value, or the value
// that is larger than a supplied buffer.
// Thanks to Adam Zeldis to pointing snprintf()-caused vulnerability
// in his audit report.
static int mg_vsnprintf(struct mg_connection *conn, char *buf, size_t buflen,
                        const char *fmt, va_list ap) {
  int n;

  if (buflen == 0)
    return 0;

  n = vsnprintf(buf, buflen, fmt, ap);

  if (n < 0) {
    cry(conn, "vsnprintf error");
    n = 0;
  } else if (n >= (int) buflen) {
    cry(conn, "truncating vsnprintf buffer: [%.*s]",
        n > 200 ? 200 : n, buf);
    n = (int) buflen - 1;
  }
  buf[n] = '\0';

  return n;
}

static int mg_snprintf(struct mg_connection *conn, char *buf, size_t buflen,
                       const char *fmt, ...) {
  va_list ap;
  int n;

  va_start(ap, fmt);
  n = mg_vsnprintf(conn, buf, buflen, fmt, ap);
  va_end(ap);

  return n;
}

// Skip the characters until one of the delimiters characters found.
// 0-terminate resulting word. Skip the delimiter and following whitespaces if any.
// Advance pointer to buffer to the next word. Return found 0-terminated word.
// Delimiters can be quoted with quotechar.
static char *skip_quoted(char **buf, const char *delimiters,
                         const char *whitespace, char quotechar) {
  char *p, *begin_word, *end_word, *end_whitespace;

  begin_word = *buf;
  end_word = begin_word + strcspn(begin_word, delimiters);

  // Check for quotechar
  if (end_word > begin_word) {
    p = end_word - 1;
    while (*p == quotechar) {
      // If there is anything beyond end_word, copy it
      if (*end_word == '\0') {
        *p = '\0';
        break;
      } else {
        size_t end_off = strcspn(end_word + 1, delimiters);
        memmove (p, end_word, end_off + 1);
        p += end_off; // p must correspond to end_word - 1
        end_word += end_off + 1;
      }
    }
    for (p++; p < end_word; p++) {
      *p = '\0';
    }
  }

  if (*end_word == '\0') {
    *buf = end_word;
  } else {
    end_whitespace = end_word + 1 + strspn(end_word + 1, whitespace);

    for (p = end_word; p < end_whitespace; p++) {
      *p = '\0';
    }

    *buf = end_whitespace;
  }

  return begin_word;
}

// Simplified version of skip_quoted without quote char
// and whitespace == delimiters
static char *skip(char **buf, const char *delimiters) {
  return skip_quoted(buf, delimiters, delimiters, 0);
}


// Return HTTP header value, or NULL if not found.
static const char *get_header(const struct mg_request_info *ri,
                              const char *name) {
  int i;

  for (i = 0; i < ri->num_headers; i++)
    if (!mg_strcasecmp(name, ri->http_headers[i].name))
      return ri->http_headers[i].value;

  return NULL;
}

const char *mg_get_header(const struct mg_connection *conn, const char *name) {
  return get_header(&conn->request_info, name);
}

// A helper function for traversing comma separated list of values.
// It returns a list pointer shifted to the next value, of NULL if the end
// of the list found.
// Value is stored in val vector. If value has form "x=y", then eq_val
// vector is initialized to point to the "y" part, and val vector length
// is adjusted to point only to "x".
static const char *next_option(const char *list, struct vec *val,
                               struct vec *eq_val) {
  if (list == NULL || *list == '\0') {
    // End of the list
    list = NULL;
  } else {
    val->ptr = list;
    if ((list = strchr(val->ptr, ',')) != NULL) {
      // Comma found. Store length and shift the list ptr
      val->len = list - val->ptr;
      list++;
    } else {
      // This value is the last one
      list = val->ptr + strlen(val->ptr);
      val->len = list - val->ptr;
    }

    if (eq_val != NULL) {
      // Value has form "x=y", adjust pointers and lengths
      // so that val points to "x", and eq_val points to "y".
      eq_val->len = 0;
      eq_val->ptr = (const char *) memchr(val->ptr, '=', val->len);
      if (eq_val->ptr != NULL) {
        eq_val->ptr++;  // Skip over '=' character
        eq_val->len = val->ptr + val->len - eq_val->ptr;
        val->len = (eq_val->ptr - val->ptr) - 1;
      }
    }
  }

  return list;
}

static int match_prefix(const char *pattern, int pattern_len, const char *str) {
  const char *or_str;
  int i, j, len, res;

  if ((or_str = (const char *) memchr(pattern, '|', pattern_len)) != NULL) {
    res = match_prefix(pattern, or_str - pattern, str);
    return res > 0 ? res :
        match_prefix(or_str + 1, (pattern + pattern_len) - (or_str + 1), str);
  }

  i = j = 0;
  res = -1;
  for (; i < pattern_len; i++, j++) {
    if (pattern[i] == '?' && str[j] != '\0') {
      continue;
    } else if (pattern[i] == '$') {
      return str[j] == '\0' ? j : -1;
    } else if (pattern[i] == '*') {
      i++;
      if (pattern[i] == '*') {
        i++;
        len = strlen(str + j);
      } else {
        len = strcspn(str + j, "/");
      }
      if (i == pattern_len) {
        return j + len;
      }
      do {
        res = match_prefix(pattern + i, pattern_len - i, str + j + len);
      } while (res == -1 && len-- > 0);
      return res == -1 ? -1 : j + res + len;
    } else if (pattern[i] != str[j]) {
      return -1;
    }
  }
  return j;
}

// HTTP 1.1 assumes keep alive if "Connection:" header is not set
// This function must tolerate situations when connection info is not
// set up, for example if request parsing failed.
static int should_keep_alive(const struct mg_connection *conn) {
  const char *http_version = conn->request_info.http_version;
  const char *header = mg_get_header(conn, "Connection");
  if (conn->must_close ||
      conn->request_info.status_code == 401 ||
      mg_strcasecmp(conn->ctx->config[ENABLE_KEEP_ALIVE], "yes") != 0 ||
      (header != NULL && mg_strcasecmp(header, "keep-alive") != 0) ||
      (header == NULL && http_version && strcmp(http_version, "1.1"))) {
    return 0;
  }
  return 1;
}

static const char *suggest_connection_header(const struct mg_connection *conn) {
  return should_keep_alive(conn) ? "keep-alive" : "close";
}

static void send_http_error(struct mg_connection *conn, int status,
                            const char *reason, const char *fmt, ...) {
  char buf[BUFSIZ];
  va_list ap;
  int len;

  conn->request_info.status_code = status;

  if (call_user(conn, MG_HTTP_ERROR) == NULL) {
    buf[0] = '\0';
    len = 0;

    // Errors 1xx, 204 and 304 MUST NOT send a body
    if (status > 199 && status != 204 && status != 304) {
      len = mg_snprintf(conn, buf, sizeof(buf), "Error %d: %s", status, reason);
      cry(conn, "%s", buf);
      buf[len++] = '\n';

      va_start(ap, fmt);
      len += mg_vsnprintf(conn, buf + len, sizeof(buf) - len, fmt, ap);
      va_end(ap);
    }
    DEBUG_TRACE(("[%s]", buf));

    mg_printf(conn, "HTTP/1.1 %d %s\r\n"
              "Content-Type: text/plain\r\n"
              "Content-Length: %d\r\n"
              "Connection: %s\r\n\r\n", status, reason, len,
              suggest_connection_header(conn));
    conn->num_bytes_sent += mg_printf(conn, "%s", buf);
  }
}

#if defined(_WIN32) && !defined(__SYMBIAN32__)
static int pthread_mutex_init(pthread_mutex_t *mutex, void *unused) {
  unused = NULL;
  *mutex = CreateMutex(NULL, FALSE, NULL);
  return *mutex == NULL ? -1 : 0;
}

static int pthread_mutex_destroy(pthread_mutex_t *mutex) {
  return CloseHandle(*mutex) == 0 ? -1 : 0;
}

static int pthread_mutex_lock(pthread_mutex_t *mutex) {
  return WaitForSingleObject(*mutex, INFINITE) == WAIT_OBJECT_0? 0 : -1;
}

static int pthread_mutex_unlock(pthread_mutex_t *mutex) {
  return ReleaseMutex(*mutex) == 0 ? -1 : 0;
}

static int pthread_cond_init(pthread_cond_t *cv, const void *unused) {
  unused = NULL;
  cv->signal = CreateEvent(NULL, FALSE, FALSE, NULL);
  cv->broadcast = CreateEvent(NULL, TRUE, FALSE, NULL);
  return cv->signal != NULL && cv->broadcast != NULL ? 0 : -1;
}

static int pthread_cond_wait(pthread_cond_t *cv, pthread_mutex_t *mutex) {
  HANDLE handles[] = {cv->signal, cv->broadcast};
  ReleaseMutex(*mutex);
  WaitForMultipleObjects(2, handles, FALSE, INFINITE);
  return WaitForSingleObject(*mutex, INFINITE) == WAIT_OBJECT_0? 0 : -1;
}

static int pthread_cond_signal(pthread_cond_t *cv) {
  return SetEvent(cv->signal) == 0 ? -1 : 0;
}

static int pthread_cond_broadcast(pthread_cond_t *cv) {
  // Implementation with PulseEvent() has race condition, see
  // http://www.cs.wustl.edu/~schmidt/win32-cv-1.html
  return PulseEvent(cv->broadcast) == 0 ? -1 : 0;
}

static int pthread_cond_destroy(pthread_cond_t *cv) {
  return CloseHandle(cv->signal) && CloseHandle(cv->broadcast) ? 0 : -1;
}

// For Windows, change all slashes to backslashes in path names.
static void change_slashes_to_backslashes(char *path) {
  int i;

  for (i = 0; path[i] != '\0'; i++) {
    if (path[i] == '/')
      path[i] = '\\';
    // i > 0 check is to preserve UNC paths, like \\server\file.txt
    if (path[i] == '\\' && i > 0)
      while (path[i + 1] == '\\' || path[i + 1] == '/')
        (void) memmove(path + i + 1,
            path + i + 2, strlen(path + i + 1));
  }
}

// Encode 'path' which is assumed UTF-8 string, into UNICODE string.
// wbuf and wbuf_len is a target buffer and its length.
static void to_unicode(const char *path, wchar_t *wbuf, size_t wbuf_len) {
  char buf[PATH_MAX], buf2[PATH_MAX], *p;

  mg_strlcpy(buf, path, sizeof(buf));
  change_slashes_to_backslashes(buf);

  // Point p to the end of the file name
  p = buf + strlen(buf) - 1;

  // Trim trailing backslash character
  while (p > buf && *p == '\\' && p[-1] != ':') {
    *p-- = '\0';
  }

   // Protect from CGI code disclosure.
   // This is very nasty hole. Windows happily opens files with
   // some garbage in the end of file name. So fopen("a.cgi    ", "r")
   // actually opens "a.cgi", and does not return an error!
  if (*p == 0x20 ||               // No space at the end
      (*p == 0x2e && p > buf) ||  // No '.' but allow '.' as full path
      *p == 0x2b ||               // No '+'
      (*p & ~0x7f)) {             // And generally no non-ascii chars
    (void) fprintf(stderr, "Rejecting suspicious path: [%s]", buf);
    wbuf[0] = L'\0';
  } else {
    // Convert to Unicode and back. If doubly-converted string does not
    // match the original, something is fishy, reject.
    memset(wbuf, 0, wbuf_len * sizeof(wchar_t));
    MultiByteToWideChar(CP_UTF8, 0, buf, -1, wbuf, (int) wbuf_len);
    WideCharToMultiByte(CP_UTF8, 0, wbuf, (int) wbuf_len, buf2, sizeof(buf2),
                        NULL, NULL);
    if (strcmp(buf, buf2) != 0) {
      wbuf[0] = L'\0';
    }
  }
}

#if defined(_WIN32_WCE)
static time_t time(time_t *ptime) {
  time_t t;
  SYSTEMTIME st;
  FILETIME ft;

  GetSystemTime(&st);
  SystemTimeToFileTime(&st, &ft);
  t = SYS2UNIX_TIME(ft.dwLowDateTime, ft.dwHighDateTime);

  if (ptime != NULL) {
    *ptime = t;
  }

  return t;
}

static struct tm *localtime(const time_t *ptime, struct tm *ptm) {
  int64_t t = ((int64_t) *ptime) * RATE_DIFF + EPOCH_DIFF;
  FILETIME ft, lft;
  SYSTEMTIME st;
  TIME_ZONE_INFORMATION tzinfo;

  if (ptm == NULL) {
    return NULL;
  }

  * (int64_t *) &ft = t;
  FileTimeToLocalFileTime(&ft, &lft);
  FileTimeToSystemTime(&lft, &st);
  ptm->tm_year = st.wYear - 1900;
  ptm->tm_mon = st.wMonth - 1;
  ptm->tm_wday = st.wDayOfWeek;
  ptm->tm_mday = st.wDay;
  ptm->tm_hour = st.wHour;
  ptm->tm_min = st.wMinute;
  ptm->tm_sec = st.wSecond;
  ptm->tm_yday = 0; // hope nobody uses this
  ptm->tm_isdst =
    GetTimeZoneInformation(&tzinfo) == TIME_ZONE_ID_DAYLIGHT ? 1 : 0;

  return ptm;
}

static struct tm *gmtime(const time_t *ptime, struct tm *ptm) {
  // FIXME(lsm): fix this.
  return localtime(ptime, ptm);
}

static size_t strftime(char *dst, size_t dst_size, const char *fmt,
                       const struct tm *tm) {
  (void) snprintf(dst, dst_size, "implement strftime() for WinCE");
  return 0;
}
#endif

static int mg_rename(const char* oldname, const char* newname) {
  wchar_t woldbuf[PATH_MAX];
  wchar_t wnewbuf[PATH_MAX];

  to_unicode(oldname, woldbuf, ARRAY_SIZE(woldbuf));
  to_unicode(newname, wnewbuf, ARRAY_SIZE(wnewbuf));

  return MoveFileW(woldbuf, wnewbuf) ? 0 : -1;
}


static FILE *mg_fopen(const char *path, const char *mode) {
  wchar_t wbuf[PATH_MAX], wmode[20];

  to_unicode(path, wbuf, ARRAY_SIZE(wbuf));
  MultiByteToWideChar(CP_UTF8, 0, mode, -1, wmode, ARRAY_SIZE(wmode));

  return _wfopen(wbuf, wmode);
}

static int mg_stat(const char *path, struct mgstat *stp) {
  int ok = -1; // Error
  wchar_t wbuf[PATH_MAX];
  WIN32_FILE_ATTRIBUTE_DATA info;

  to_unicode(path, wbuf, ARRAY_SIZE(wbuf));

  if (GetFileAttributesExW(wbuf, GetFileExInfoStandard, &info) != 0) {
    stp->size = MAKEUQUAD(info.nFileSizeLow, info.nFileSizeHigh);
    stp->mtime = SYS2UNIX_TIME(info.ftLastWriteTime.dwLowDateTime,
                               info.ftLastWriteTime.dwHighDateTime);
    stp->is_directory =
      info.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY;
    ok = 0;  // Success
  }

  return ok;
}

static int mg_remove(const char *path) {
  wchar_t wbuf[PATH_MAX];
  to_unicode(path, wbuf, ARRAY_SIZE(wbuf));
  return DeleteFileW(wbuf) ? 0 : -1;
}

static int mg_mkdir(const char *path, int mode) {
  char buf[PATH_MAX];
  wchar_t wbuf[PATH_MAX];

  mode = 0; // Unused
  mg_strlcpy(buf, path, sizeof(buf));
  change_slashes_to_backslashes(buf);

  (void) MultiByteToWideChar(CP_UTF8, 0, buf, -1, wbuf, sizeof(wbuf));

  return CreateDirectoryW(wbuf, NULL) ? 0 : -1;
}

// Implementation of POSIX opendir/closedir/readdir for Windows.
static DIR * opendir(const char *name) {
  DIR *dir = NULL;
  wchar_t wpath[PATH_MAX];
  DWORD attrs;

  if (name == NULL) {
    SetLastError(ERROR_BAD_ARGUMENTS);
  } else if ((dir = (DIR *) malloc(sizeof(*dir))) == NULL) {
    SetLastError(ERROR_NOT_ENOUGH_MEMORY);
  } else {
    to_unicode(name, wpath, ARRAY_SIZE(wpath));
    attrs = GetFileAttributesW(wpath);
    if (attrs != 0xFFFFFFFF &&
        ((attrs & FILE_ATTRIBUTE_DIRECTORY) == FILE_ATTRIBUTE_DIRECTORY)) {
      (void) wcscat(wpath, L"\\*");
      dir->handle = FindFirstFileW(wpath, &dir->info);
      dir->result.d_name[0] = '\0';
    } else {
      free(dir);
      dir = NULL;
    }
  }

  return dir;
}

static int closedir(DIR *dir) {
  int result = 0;

  if (dir != NULL) {
    if (dir->handle != INVALID_HANDLE_VALUE)
      result = FindClose(dir->handle) ? 0 : -1;

    free(dir);
  } else {
    result = -1;
    SetLastError(ERROR_BAD_ARGUMENTS);
  }

  return result;
}

static struct dirent *readdir(DIR *dir) {
  struct dirent *result = 0;

  if (dir) {
    if (dir->handle != INVALID_HANDLE_VALUE) {
      result = &dir->result;
      (void) WideCharToMultiByte(CP_UTF8, 0,
          dir->info.cFileName, -1, result->d_name,
          sizeof(result->d_name), NULL, NULL);

      if (!FindNextFileW(dir->handle, &dir->info)) {
        (void) FindClose(dir->handle);
        dir->handle = INVALID_HANDLE_VALUE;
      }

    } else {
      SetLastError(ERROR_FILE_NOT_FOUND);
    }
  } else {
    SetLastError(ERROR_BAD_ARGUMENTS);
  }

  return result;
}

#define set_close_on_exec(fd) // No FD_CLOEXEC on Windows

int mg_start_thread(mg_thread_func_t f, void *p) {
  return _beginthread((void (__cdecl *)(void *)) f, 0, p) == -1L ? -1 : 0;
}

static HANDLE dlopen(const char *dll_name, int flags) {
  wchar_t wbuf[PATH_MAX];
  flags = 0; // Unused
  to_unicode(dll_name, wbuf, ARRAY_SIZE(wbuf));
  return LoadLibraryW(wbuf);
}

#if !defined(NO_CGI)
#define SIGKILL 0
static int kill(pid_t pid, int sig_num) {
  (void) TerminateProcess(pid, sig_num);
  (void) CloseHandle(pid);
  return 0;
}

static pid_t spawn_process(struct mg_connection *conn, const char *prog,
                           char *envblk, char *envp[], int fd_stdin,
                           int fd_stdout, const char *dir) {
  HANDLE me;
  char *p, *interp, cmdline[PATH_MAX], buf[PATH_MAX];
  FILE *fp;
  STARTUPINFOA si = { sizeof(si) };
  PROCESS_INFORMATION pi = { 0 };

  envp = NULL; // Unused

  // TODO(lsm): redirect CGI errors to the error log file
  si.dwFlags = STARTF_USESTDHANDLES | STARTF_USESHOWWINDOW;
  si.wShowWindow = SW_HIDE;

  me = GetCurrentProcess();
  (void) DuplicateHandle(me, (HANDLE) _get_osfhandle(fd_stdin), me,
      &si.hStdInput, 0, TRUE, DUPLICATE_SAME_ACCESS);
  (void) DuplicateHandle(me, (HANDLE) _get_osfhandle(fd_stdout), me,
      &si.hStdOutput, 0, TRUE, DUPLICATE_SAME_ACCESS);

  // If CGI file is a script, try to read the interpreter line
  interp = conn->ctx->config[CGI_INTERPRETER];
  if (interp == NULL) {
    buf[2] = '\0';
    mg_snprintf(conn, cmdline, sizeof(cmdline), "%s%c%s", dir, DIRSEP, prog);
    if ((fp = fopen(cmdline, "r")) != NULL) {
      (void) fgets(buf, sizeof(buf), fp);
      if (buf[0] != '#' || buf[1] != '!') {
        // First line does not start with "#!". Do not set interpreter.
        buf[2] = '\0';
      } else {
        // Trim whitespaces in interpreter name
        for (p = &buf[strlen(buf) - 1]; p > buf && isspace(*p); p--) {
          *p = '\0';
        }
      }
      (void) fclose(fp);
    }
    interp = buf + 2;
  }

  (void) mg_snprintf(conn, cmdline, sizeof(cmdline), "%s%s%s%c%s",
                     interp, interp[0] == '\0' ? "" : " ", dir, DIRSEP, prog);

  DEBUG_TRACE(("Running [%s]", cmdline));
  if (CreateProcessA(NULL, cmdline, NULL, NULL, TRUE,
        CREATE_NEW_PROCESS_GROUP, envblk, dir, &si, &pi) == 0) {
    cry(conn, "%s: CreateProcess(%s): %d",
        __func__, cmdline, ERRNO);
    pi.hProcess = (pid_t) -1;
  } else {
    (void) close(fd_stdin);
    (void) close(fd_stdout);
  }

  (void) CloseHandle(si.hStdOutput);
  (void) CloseHandle(si.hStdInput);
  (void) CloseHandle(pi.hThread);

  return (pid_t) pi.hProcess;
}
#endif // !NO_CGI

static int set_non_blocking_mode(SOCKET sock) {
  unsigned long on = 1;
  return ioctlsocket(sock, FIONBIO, &on);
}

#else
static int mg_stat(const char *path, struct mgstat *stp) {
  struct stat st;
  int ok;

  if (stat(path, &st) == 0) {
    ok = 0;
    stp->size = st.st_size;
    stp->mtime = st.st_mtime;
    stp->is_directory = S_ISDIR(st.st_mode);
  } else {
    ok = -1;
  }

  return ok;
}

static void set_close_on_exec(int fd) {
  (void) fcntl(fd, F_SETFD, FD_CLOEXEC);
}

int mg_start_thread(mg_thread_func_t func, void *param) {
  pthread_t thread_id;
  pthread_attr_t attr;

  (void) pthread_attr_init(&attr);
  (void) pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
  // TODO(lsm): figure out why mongoose dies on Linux if next line is enabled
  // (void) pthread_attr_setstacksize(&attr, sizeof(struct mg_connection) * 5);

  return pthread_create(&thread_id, &attr, func, param);
}

#ifndef NO_CGI
static pid_t spawn_process(struct mg_connection *conn, const char *prog,
                           char *envblk, char *envp[], int fd_stdin,
                           int fd_stdout, const char *dir) {
  pid_t pid;
  const char *interp;

  envblk = NULL; // Unused

  if ((pid = fork()) == -1) {
    // Parent
    send_http_error(conn, 500, http_500_error, "fork(): %s", strerror(ERRNO));
  } else if (pid == 0) {
    // Child
    if (chdir(dir) != 0) {
      cry(conn, "%s: chdir(%s): %s", __func__, dir, strerror(ERRNO));
    } else if (dup2(fd_stdin, 0) == -1) {
      cry(conn, "%s: dup2(%d, 0): %s", __func__, fd_stdin, strerror(ERRNO));
    } else if (dup2(fd_stdout, 1) == -1) {
      cry(conn, "%s: dup2(%d, 1): %s", __func__, fd_stdout, strerror(ERRNO));
    } else {
      (void) dup2(fd_stdout, 2);
      (void) close(fd_stdin);
      (void) close(fd_stdout);

      // Execute CGI program. No need to lock: new process
      interp = conn->ctx->config[CGI_INTERPRETER];
      if (interp == NULL) {
        (void) execle(prog, prog, NULL, envp);
        cry(conn, "%s: execle(%s): %s", __func__, prog, strerror(ERRNO));
      } else {
        (void) execle(interp, interp, prog, NULL, envp);
        cry(conn, "%s: execle(%s %s): %s", __func__, interp, prog,
            strerror(ERRNO));
      }
    }
    exit(EXIT_FAILURE);
  } else {
    // Parent. Close stdio descriptors
    (void) close(fd_stdin);
    (void) close(fd_stdout);
  }

  return pid;
}
#endif // !NO_CGI

static int set_non_blocking_mode(SOCKET sock) {
  int flags;

  flags = fcntl(sock, F_GETFL, 0);
  (void) fcntl(sock, F_SETFL, flags | O_NONBLOCK);

  return 0;
}
#endif // _WIN32

// Write data to the IO channel - opened file descriptor, socket or SSL
// descriptor. Return number of bytes written.
static int64_t push(FILE *fp, SOCKET sock, SSL *ssl, const char *buf,
                    int64_t len) {
  int64_t sent;
  int n, k;

  sent = 0;
  while (sent < len) {

    // How many bytes we send in this iteration
    k = len - sent > INT_MAX ? INT_MAX : (int) (len - sent);

    if (ssl != NULL) {
      n = SSL_write(ssl, buf + sent, k);
    } else if (fp != NULL) {
      n = fwrite(buf + sent, 1, (size_t) k, fp);
      if (ferror(fp))
        n = -1;
    } else {
      n = send(sock, buf + sent, (size_t) k, MSG_NOSIGNAL);
    }

    if (n < 0)
      break;

    sent += n;
  }

  return sent;
}

// Read from IO channel - opened file descriptor, socket, or SSL descriptor.
// Return number of bytes read.
static int pull(FILE *fp, SOCKET sock, SSL *ssl, char *buf, int len) {
  int nread;

  if (ssl != NULL) {
    nread = SSL_read(ssl, buf, len);
  } else if (fp != NULL) {
    // Use read() instead of fread(), because if we're reading from the CGI
    // pipe, fread() may block until IO buffer is filled up. We cannot afford
    // to block and must pass all read bytes immediately to the client.
    nread = read(fileno(fp), buf, (size_t) len);
    if (ferror(fp))
      nread = -1;
  } else {
    nread = recv(sock, buf, (size_t) len, 0);
  }

  return nread;
}

int mg_read(struct mg_connection *conn, void *buf, size_t len) {
  int n, buffered_len, nread;
  const char *buffered;

  assert((conn->content_len == -1 && conn->consumed_content == 0) ||
         conn->consumed_content <= conn->content_len);
  DEBUG_TRACE(("%p %zu %lld %lld", buf, len,
               conn->content_len, conn->consumed_content));
  nread = 0;
  if (conn->consumed_content < conn->content_len) {

    // Adjust number of bytes to read.
    int64_t to_read = conn->content_len - conn->consumed_content;
    if (to_read < (int64_t) len) {
      len = (int) to_read;
    }

    // How many bytes of data we have buffered in the request buffer?
    buffered = conn->buf + conn->request_len + conn->consumed_content;
    buffered_len = conn->data_len - conn->request_len;
    assert(buffered_len >= 0);

    // Return buffered data back if we haven't done that yet.
    if (conn->consumed_content < (int64_t) buffered_len) {
      buffered_len -= (int) conn->consumed_content;
      if (len < (size_t) buffered_len) {
        buffered_len = len;
      }
      memcpy(buf, buffered, (size_t)buffered_len);
      len -= buffered_len;
      buf = (char *) buf + buffered_len;
      conn->consumed_content += buffered_len;
      nread = buffered_len;
    }

    // We have returned all buffered data. Read new data from the remote socket.
    while (len > 0) {
      n = pull(NULL, conn->client.sock, conn->ssl, (char *) buf, (int) len);
      if (n <= 0) {
        break;
      }
      buf = (char *) buf + n;
      conn->consumed_content += n;
      nread += n;
      len -= n;
    }
  }
  return nread;
}

int mg_write(struct mg_connection *conn, const void *buf, size_t len) {
  return (int) push(NULL, conn->client.sock, conn->ssl, (const char *) buf,
                    (int64_t) len);
}

int mg_printf(struct mg_connection *conn, const char *fmt, ...) {
  char buf[BUFSIZ];
  int len;
  va_list ap;

  va_start(ap, fmt);
  len = mg_vsnprintf(conn, buf, sizeof(buf), fmt, ap);
  va_end(ap);

  return mg_write(conn, buf, (size_t)len);
}

// URL-decode input buffer into destination buffer.
// 0-terminate the destination buffer. Return the length of decoded data.
// form-url-encoded data differs from URI encoding in a way that it
// uses '+' as character for space, see RFC 1866 section 8.2.1
// http://ftp.ics.uci.edu/pub/ietf/html/rfc1866.txt
static size_t url_decode(const char *src, size_t src_len, char *dst,
                         size_t dst_len, int is_form_url_encoded) {
  size_t i, j;
  int a, b;
#define HEXTOI(x) (isdigit(x) ? x - '0' : x - 'W')

  for (i = j = 0; i < src_len && j < dst_len - 1; i++, j++) {
    if (src[i] == '%' &&
        isxdigit(* (const unsigned char *) (src + i + 1)) &&
        isxdigit(* (const unsigned char *) (src + i + 2))) {
      a = tolower(* (const unsigned char *) (src + i + 1));
      b = tolower(* (const unsigned char *) (src + i + 2));
      dst[j] = (char) ((HEXTOI(a) << 4) | HEXTOI(b));
      i += 2;
    } else if (is_form_url_encoded && src[i] == '+') {
      dst[j] = ' ';
    } else {
      dst[j] = src[i];
    }
  }

  dst[j] = '\0'; // Null-terminate the destination

  return j;
}

// Scan given buffer and fetch the value of the given variable.
// It can be specified in query string, or in the POST data.
// Return NULL if the variable not found, or allocated 0-terminated value.
// It is caller's responsibility to free the returned value.
int mg_get_var(const char *buf, size_t buf_len, const char *name,
               char *dst, size_t dst_len) {
  const char *p, *e, *s;
  size_t name_len, len;

  name_len = strlen(name);
  e = buf + buf_len;
  len = -1;
  dst[0] = '\0';

  // buf is "var1=val1&var2=val2...". Find variable first
  for (p = buf; p != NULL && p + name_len < e; p++) {
    if ((p == buf || p[-1] == '&') && p[name_len] == '=' &&
        !mg_strncasecmp(name, p, name_len)) {

      // Point p to variable value
      p += name_len + 1;

      // Point s to the end of the value
      s = (const char *) memchr(p, '&', (size_t)(e - p));
      if (s == NULL) {
        s = e;
      }
      assert(s >= p);

      // Decode variable into destination buffer
      if ((size_t) (s - p) < dst_len) {
        len = url_decode(p, (size_t)(s - p), dst, dst_len, 1);
      }
      break;
    }
  }

  return len;
}

int mg_get_cookie(const struct mg_connection *conn, const char *cookie_name,
                  char *dst, size_t dst_size) {
  const char *s, *p, *end;
  int name_len, len = -1;

  dst[0] = '\0';
  if ((s = mg_get_header(conn, "Cookie")) == NULL) {
    return 0;
  }

  name_len = strlen(cookie_name);
  end = s + strlen(s);

  for (; (s = strstr(s, cookie_name)) != NULL; s += name_len)
    if (s[name_len] == '=') {
      s += name_len + 1;
      if ((p = strchr(s, ' ')) == NULL)
        p = end;
      if (p[-1] == ';')
        p--;
      if (*s == '"' && p[-1] == '"' && p > s + 1) {
        s++;
        p--;
      }
      if ((size_t) (p - s) < dst_size) {
        len = (p - s) + 1;
        mg_strlcpy(dst, s, (size_t)len);
      }
      break;
    }

  return len;
}

static int convert_uri_to_file_name(struct mg_connection *conn, char *buf,
                                    size_t buf_len, struct mgstat *st) {
  struct vec a, b;
  const char *rewrite, *uri = conn->request_info.uri;
  char *p;
  int match_len, stat_result;

  buf_len--;  // This is because memmove() for PATH_INFO may shift part
              // of the path one byte on the right.
  mg_snprintf(conn, buf, buf_len, "%s%s", conn->ctx->config[DOCUMENT_ROOT],
              uri);

  rewrite = conn->ctx->config[REWRITE];
  while ((rewrite = next_option(rewrite, &a, &b)) != NULL) {
    if ((match_len = match_prefix(a.ptr, a.len, uri)) > 0) {
      mg_snprintf(conn, buf, buf_len, "%.*s%s", b.len, b.ptr, uri + match_len);
      break;
    }
  }

#if defined(_WIN32) && !defined(__SYMBIAN32__)
  //change_slashes_to_backslashes(buf);
#endif // _WIN32

  if ((stat_result = mg_stat(buf, st)) != 0) {
    // Support PATH_INFO for CGI scripts.
    for (p = buf + strlen(buf); p > buf + 1; p--) {
      if (*p == '/') {
        *p = '\0';
        if (match_prefix(conn->ctx->config[CGI_EXTENSIONS],
                         strlen(conn->ctx->config[CGI_EXTENSIONS]), buf) > 0 &&
            (stat_result = mg_stat(buf, st)) == 0) {
          // Shift PATH_INFO block one character right, e.g.
          //  "/x.cgi/foo/bar\x00" => "/x.cgi\x00/foo/bar\x00"
          // conn->path_info is pointing to the local variable "path" declared
          // in handle_request(), so PATH_INFO not valid after
          // handle_request returns.
          conn->path_info = p + 1;
          memmove(p + 2, p + 1, strlen(p + 1) + 1);  // +1 is for trailing \0
          p[1] = '/';
          break;
        } else {
          *p = '/';
          stat_result = -1;
        }
      }
    }
  }

  return stat_result;
}

static int sslize(struct mg_connection *conn, int (*func)(SSL *)) {
  return (conn->ssl = SSL_new(conn->ctx->ssl_ctx)) != NULL &&
    SSL_set_fd(conn->ssl, conn->client.sock) == 1 &&
    func(conn->ssl) == 1;
}

// Check whether full request is buffered. Return:
//   -1  if request is malformed
//    0  if request is not yet fully buffered
//   >0  actual request length, including last \r\n\r\n
static int get_request_len(const char *buf, int buflen) {
  const char *s, *e;
  int len = 0;

  DEBUG_TRACE(("buf: %p, len: %d", buf, buflen));
  for (s = buf, e = s + buflen - 1; len <= 0 && s < e; s++)
    // Control characters are not allowed but >=128 is.
    if (!isprint(* (const unsigned char *) s) && *s != '\r' &&
        *s != '\n' && * (const unsigned char *) s < 128) {
      len = -1;
    } else if (s[0] == '\n' && s[1] == '\n') {
      len = (int) (s - buf) + 2;
    } else if (s[0] == '\n' && &s[1] < e &&
        s[1] == '\r' && s[2] == '\n') {
      len = (int) (s - buf) + 3;
    }

  return len;
}

// Convert month to the month number. Return -1 on error, or month number
static int get_month_index(const char *s) {
  size_t i;

  for (i = 0; i < ARRAY_SIZE(month_names); i++)
    if (!strcmp(s, month_names[i]))
      return (int) i;

  return -1;
}

// Parse UTC date-time string, and return the corresponding time_t value.
static time_t parse_date_string(const char *datetime) {
  static const unsigned short days_before_month[] = {
    0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
  };
  char month_str[32];
  int second, minute, hour, day, month, year, leap_days, days;
  time_t result = (time_t) 0;

  if (((sscanf(datetime, "%d/%3s/%d %d:%d:%d",
               &day, month_str, &year, &hour, &minute, &second) == 6) ||
       (sscanf(datetime, "%d %3s %d %d:%d:%d",
               &day, month_str, &year, &hour, &minute, &second) == 6) ||
       (sscanf(datetime, "%*3s, %d %3s %d %d:%d:%d",
               &day, month_str, &year, &hour, &minute, &second) == 6) ||
       (sscanf(datetime, "%d-%3s-%d %d:%d:%d",
               &day, month_str, &year, &hour, &minute, &second) == 6)) &&
      year > 1970 &&
      (month = get_month_index(month_str)) != -1) {
    year -= 1970;
    leap_days = year / 4 - year / 100 + year / 400;
    days = year * 365 + days_before_month[month] + (day - 1) + leap_days;
    result = days * 24 * 3600 + hour * 3600 + minute * 60 + second;
  }

  return result;
}

// Protect against directory disclosure attack by removing '..',
// excessive '/' and '\' characters
static void remove_double_dots_and_double_slashes(char *s) {
  char *p = s;

  while (*s != '\0') {
    *p++ = *s++;
    if (IS_DIRSEP_CHAR(s[-1])) {
      // Skip all following slashes and backslashes
      while (IS_DIRSEP_CHAR(s[0])) {
        s++;
      }

      // Skip all double-dots
      while (*s == '.' && s[1] == '.') {
        s += 2;
      }
    }
  }
  *p = '\0';
}

static const struct {
  const char *extension;
  size_t ext_len;
  const char *mime_type;
  size_t mime_type_len;
} builtin_mime_types[] = {
  {".html", 5, "text/html",   9},
  {".htm", 4, "text/html",   9},
  {".shtm", 5, "text/html",   9},
  {".shtml", 6, "text/html",   9},
  {".css", 4, "text/css",   8},
  {".js",  3, "application/x-javascript", 24},
  {".ico", 4, "image/x-icon",   12},
  {".gif", 4, "image/gif",   9},
  {".jpg", 4, "image/jpeg",   10},
  {".jpeg", 5, "image/jpeg",   10},
  {".png", 4, "image/png",   9},
  {".svg", 4, "image/svg+xml",  13},
  {".torrent", 8, "application/x-bittorrent", 24},
  {".wav", 4, "audio/x-wav",   11},
  {".mp3", 4, "audio/x-mp3",   11},
  {".mid", 4, "audio/mid",   9},
  {".m3u", 4, "audio/x-mpegurl",  15},
  {".ram", 4, "audio/x-pn-realaudio",  20},
  {".xml", 4, "text/xml",   8},
  {".xslt", 5, "application/xml",  15},
  {".ra",  3, "audio/x-pn-realaudio",  20},
  {".doc", 4, "application/msword",  19},
  {".exe", 4, "application/octet-stream", 24},
  {".zip", 4, "application/x-zip-compressed", 28},
  {".xls", 4, "application/excel",  17},
  {".tgz", 4, "application/x-tar-gz",  20},
  {".tar", 4, "application/x-tar",  17},
  {".gz",  3, "application/x-gunzip",  20},
  {".arj", 4, "application/x-arj-compressed", 28},
  {".rar", 4, "application/x-arj-compressed", 28},
  {".rtf", 4, "application/rtf",  15},
  {".pdf", 4, "application/pdf",  15},
  {".swf", 4, "application/x-shockwave-flash",29},
  {".mpg", 4, "video/mpeg",   10},
  {".mpeg", 5, "video/mpeg",   10},
  {".mp4", 4, "video/mp4", 9},
  {".m4v", 4, "video/x-m4v", 11},
  {".asf", 4, "video/x-ms-asf",  14},
  {".avi", 4, "video/x-msvideo",  15},
  {".bmp", 4, "image/bmp",   9},
  {NULL,  0, NULL,    0}
};

// Look at the "path" extension and figure what mime type it has.
// Store mime type in the vector.
static void get_mime_type(struct mg_context *ctx, const char *path,
                          struct vec *vec) {
  struct vec ext_vec, mime_vec;
  const char *list, *ext;
  size_t i, path_len;

  path_len = strlen(path);

  // Scan user-defined mime types first, in case user wants to
  // override default mime types.
  list = ctx->config[EXTRA_MIME_TYPES];
  while ((list = next_option(list, &ext_vec, &mime_vec)) != NULL) {
    // ext now points to the path suffix
    ext = path + path_len - ext_vec.len;
    if (mg_strncasecmp(ext, ext_vec.ptr, ext_vec.len) == 0) {
      *vec = mime_vec;
      return;
    }
  }

  // Now scan built-in mime types
  for (i = 0; builtin_mime_types[i].extension != NULL; i++) {
    ext = path + (path_len - builtin_mime_types[i].ext_len);
    if (path_len > builtin_mime_types[i].ext_len &&
        mg_strcasecmp(ext, builtin_mime_types[i].extension) == 0) {
      vec->ptr = builtin_mime_types[i].mime_type;
      vec->len = builtin_mime_types[i].mime_type_len;
      return;
    }
  }

  // Nothing found. Fall back to "text/plain"
  vec->ptr = "text/plain";
  vec->len = 10;
}

#ifndef HAVE_MD5
typedef struct MD5Context {
  uint32_t buf[4];
  uint32_t bits[2];
  unsigned char in[64];
} MD5_CTX;

#if defined(__BYTE_ORDER) && (__BYTE_ORDER == 1234)
#define byteReverse(buf, len) // Do nothing
#else
static void byteReverse(unsigned char *buf, unsigned longs) {
  uint32_t t;
  do {
    t = (uint32_t) ((unsigned) buf[3] << 8 | buf[2]) << 16 |
      ((unsigned) buf[1] << 8 | buf[0]);
    *(uint32_t *) buf = t;
    buf += 4;
  } while (--longs);
}
#endif

#define F1(x, y, z) (z ^ (x & (y ^ z)))
#define F2(x, y, z) F1(z, x, y)
#define F3(x, y, z) (x ^ y ^ z)
#define F4(x, y, z) (y ^ (x | ~z))

#define MD5STEP(f, w, x, y, z, data, s) \
  ( w += f(x, y, z) + data,  w = w<<s | w>>(32-s),  w += x )

// Start MD5 accumulation.  Set bit count to 0 and buffer to mysterious
// initialization constants.
static void MD5Init(MD5_CTX *ctx) {
  ctx->buf[0] = 0x67452301;
  ctx->buf[1] = 0xefcdab89;
  ctx->buf[2] = 0x98badcfe;
  ctx->buf[3] = 0x10325476;

  ctx->bits[0] = 0;
  ctx->bits[1] = 0;
}

static void MD5Transform(uint32_t buf[4], uint32_t const in[16]) {
  register uint32_t a, b, c, d;

  a = buf[0];
  b = buf[1];
  c = buf[2];
  d = buf[3];

  MD5STEP(F1, a, b, c, d, in[0] + 0xd76aa478, 7);
  MD5STEP(F1, d, a, b, c, in[1] + 0xe8c7b756, 12);
  MD5STEP(F1, c, d, a, b, in[2] + 0x242070db, 17);
  MD5STEP(F1, b, c, d, a, in[3] + 0xc1bdceee, 22);
  MD5STEP(F1, a, b, c, d, in[4] + 0xf57c0faf, 7);
  MD5STEP(F1, d, a, b, c, in[5] + 0x4787c62a, 12);
  MD5STEP(F1, c, d, a, b, in[6] + 0xa8304613, 17);
  MD5STEP(F1, b, c, d, a, in[7] + 0xfd469501, 22);
  MD5STEP(F1, a, b, c, d, in[8] + 0x698098d8, 7);
  MD5STEP(F1, d, a, b, c, in[9] + 0x8b44f7af, 12);
  MD5STEP(F1, c, d, a, b, in[10] + 0xffff5bb1, 17);
  MD5STEP(F1, b, c, d, a, in[11] + 0x895cd7be, 22);
  MD5STEP(F1, a, b, c, d, in[12] + 0x6b901122, 7);
  MD5STEP(F1, d, a, b, c, in[13] + 0xfd987193, 12);
  MD5STEP(F1, c, d, a, b, in[14] + 0xa679438e, 17);
  MD5STEP(F1, b, c, d, a, in[15] + 0x49b40821, 22);

  MD5STEP(F2, a, b, c, d, in[1] + 0xf61e2562, 5);
  MD5STEP(F2, d, a, b, c, in[6] + 0xc040b340, 9);
  MD5STEP(F2, c, d, a, b, in[11] + 0x265e5a51, 14);
  MD5STEP(F2, b, c, d, a, in[0] + 0xe9b6c7aa, 20);
  MD5STEP(F2, a, b, c, d, in[5] + 0xd62f105d, 5);
  MD5STEP(F2, d, a, b, c, in[10] + 0x02441453, 9);
  MD5STEP(F2, c, d, a, b, in[15] + 0xd8a1e681, 14);
  MD5STEP(F2, b, c, d, a, in[4] + 0xe7d3fbc8, 20);
  MD5STEP(F2, a, b, c, d, in[9] + 0x21e1cde6, 5);
  MD5STEP(F2, d, a, b, c, in[14] + 0xc33707d6, 9);
  MD5STEP(F2, c, d, a, b, in[3] + 0xf4d50d87, 14);
  MD5STEP(F2, b, c, d, a, in[8] + 0x455a14ed, 20);
  MD5STEP(F2, a, b, c, d, in[13] + 0xa9e3e905, 5);
  MD5STEP(F2, d, a, b, c, in[2] + 0xfcefa3f8, 9);
  MD5STEP(F2, c, d, a, b, in[7] + 0x676f02d9, 14);
  MD5STEP(F2, b, c, d, a, in[12] + 0x8d2a4c8a, 20);

  MD5STEP(F3, a, b, c, d, in[5] + 0xfffa3942, 4);
  MD5STEP(F3, d, a, b, c, in[8] + 0x8771f681, 11);
  MD5STEP(F3, c, d, a, b, in[11] + 0x6d9d6122, 16);
  MD5STEP(F3, b, c, d, a, in[14] + 0xfde5380c, 23);
  MD5STEP(F3, a, b, c, d, in[1] + 0xa4beea44, 4);
  MD5STEP(F3, d, a, b, c, in[4] + 0x4bdecfa9, 11);
  MD5STEP(F3, c, d, a, b, in[7] + 0xf6bb4b60, 16);
  MD5STEP(F3, b, c, d, a, in[10] + 0xbebfbc70, 23);
  MD5STEP(F3, a, b, c, d, in[13] + 0x289b7ec6, 4);
  MD5STEP(F3, d, a, b, c, in[0] + 0xeaa127fa, 11);
  MD5STEP(F3, c, d, a, b, in[3] + 0xd4ef3085, 16);
  MD5STEP(F3, b, c, d, a, in[6] + 0x04881d05, 23);
  MD5STEP(F3, a, b, c, d, in[9] + 0xd9d4d039, 4);
  MD5STEP(F3, d, a, b, c, in[12] + 0xe6db99e5, 11);
  MD5STEP(F3, c, d, a, b, in[15] + 0x1fa27cf8, 16);
  MD5STEP(F3, b, c, d, a, in[2] + 0xc4ac5665, 23);

  MD5STEP(F4, a, b, c, d, in[0] + 0xf4292244, 6);
  MD5STEP(F4, d, a, b, c, in[7] + 0x432aff97, 10);
  MD5STEP(F4, c, d, a, b, in[14] + 0xab9423a7, 15);
  MD5STEP(F4, b, c, d, a, in[5] + 0xfc93a039, 21);
  MD5STEP(F4, a, b, c, d, in[12] + 0x655b59c3, 6);
  MD5STEP(F4, d, a, b, c, in[3] + 0x8f0ccc92, 10);
  MD5STEP(F4, c, d, a, b, in[10] + 0xffeff47d, 15);
  MD5STEP(F4, b, c, d, a, in[1] + 0x85845dd1, 21);
  MD5STEP(F4, a, b, c, d, in[8] + 0x6fa87e4f, 6);
  MD5STEP(F4, d, a, b, c, in[15] + 0xfe2ce6e0, 10);
  MD5STEP(F4, c, d, a, b, in[6] + 0xa3014314, 15);
  MD5STEP(F4, b, c, d, a, in[13] + 0x4e0811a1, 21);
  MD5STEP(F4, a, b, c, d, in[4] + 0xf7537e82, 6);
  MD5STEP(F4, d, a, b, c, in[11] + 0xbd3af235, 10);
  MD5STEP(F4, c, d, a, b, in[2] + 0x2ad7d2bb, 15);
  MD5STEP(F4, b, c, d, a, in[9] + 0xeb86d391, 21);

  buf[0] += a;
  buf[1] += b;
  buf[2] += c;
  buf[3] += d;
}

static void MD5Update(MD5_CTX *ctx, unsigned char const *buf, unsigned len) {
  uint32_t t;

  t = ctx->bits[0];
  if ((ctx->bits[0] = t + ((uint32_t) len << 3)) < t)
    ctx->bits[1]++;
  ctx->bits[1] += len >> 29;

  t = (t >> 3) & 0x3f;

  if (t) {
    unsigned char *p = (unsigned char *) ctx->in + t;

    t = 64 - t;
    if (len < t) {
      memcpy(p, buf, len);
      return;
    }
    memcpy(p, buf, t);
    byteReverse(ctx->in, 16);
    MD5Transform(ctx->buf, (uint32_t *) ctx->in);
    buf += t;
    len -= t;
  }

  while (len >= 64) {
    memcpy(ctx->in, buf, 64);
    byteReverse(ctx->in, 16);
    MD5Transform(ctx->buf, (uint32_t *) ctx->in);
    buf += 64;
    len -= 64;
  }

  memcpy(ctx->in, buf, len);
}

static void MD5Final(unsigned char digest[16], MD5_CTX *ctx) {
  unsigned count;
  unsigned char *p;

  count = (ctx->bits[0] >> 3) & 0x3F;

  p = ctx->in + count;
  *p++ = 0x80;
  count = 64 - 1 - count;
  if (count < 8) {
    memset(p, 0, count);
    byteReverse(ctx->in, 16);
    MD5Transform(ctx->buf, (uint32_t *) ctx->in);
    memset(ctx->in, 0, 56);
  } else {
    memset(p, 0, count - 8);
  }
  byteReverse(ctx->in, 14);

  ((uint32_t *) ctx->in)[14] = ctx->bits[0];
  ((uint32_t *) ctx->in)[15] = ctx->bits[1];

  MD5Transform(ctx->buf, (uint32_t *) ctx->in);
  byteReverse((unsigned char *) ctx->buf, 4);
  memcpy(digest, ctx->buf, 16);
  memset((char *) ctx, 0, sizeof(*ctx));
}
#endif // !HAVE_MD5

// Stringify binary data. Output buffer must be twice as big as input,
// because each byte takes 2 bytes in string representation
static void bin2str(char *to, const unsigned char *p, size_t len) {
  static const char *hex = "0123456789abcdef";

  for (; len--; p++) {
    *to++ = hex[p[0] >> 4];
    *to++ = hex[p[0] & 0x0f];
  }
  *to = '\0';
}

// Return stringified MD5 hash for list of vectors. Buffer must be 33 bytes.
void mg_md5(char *buf, ...) {
  unsigned char hash[16];
  const char *p;
  va_list ap;
  MD5_CTX ctx;

  MD5Init(&ctx);

  va_start(ap, buf);
  while ((p = va_arg(ap, const char *)) != NULL) {
    MD5Update(&ctx, (const unsigned char *) p, (unsigned) strlen(p));
  }
  va_end(ap);

  MD5Final(hash, &ctx);
  bin2str(buf, hash, sizeof(hash));
}

// Check the user's password, return 1 if OK
static int check_password(const char *method, const char *ha1, const char *uri,
                          const char *nonce, const char *nc, const char *cnonce,
                          const char *qop, const char *response) {
  char ha2[32 + 1], expected_response[32 + 1];

  // Some of the parameters may be NULL
  if (method == NULL || nonce == NULL || nc == NULL || cnonce == NULL ||
      qop == NULL || response == NULL) {
    return 0;
  }

  // NOTE(lsm): due to a bug in MSIE, we do not compare the URI
  // TODO(lsm): check for authentication timeout
  if (// strcmp(dig->uri, c->ouri) != 0 ||
      strlen(response) != 32
      // || now - strtoul(dig->nonce, NULL, 10) > 3600
      ) {
    return 0;
  }

  mg_md5(ha2, method, ":", uri, NULL);
  mg_md5(expected_response, ha1, ":", nonce, ":", nc,
      ":", cnonce, ":", qop, ":", ha2, NULL);

  return mg_strcasecmp(response, expected_response) == 0;
}

// Use the global passwords file, if specified by auth_gpass option,
// or search for .htpasswd in the requested directory.
static FILE *open_auth_file(struct mg_connection *conn, const char *path) {
  struct mg_context *ctx = conn->ctx;
  char name[PATH_MAX];
  const char *p, *e;
  struct mgstat st;
  FILE *fp;

  if (ctx->config[GLOBAL_PASSWORDS_FILE] != NULL) {
    // Use global passwords file
    fp =  mg_fopen(ctx->config[GLOBAL_PASSWORDS_FILE], "r");
    if (fp == NULL)
      cry(fc(ctx), "fopen(%s): %s",
          ctx->config[GLOBAL_PASSWORDS_FILE], strerror(ERRNO));
  } else if (!mg_stat(path, &st) && st.is_directory) {
    (void) mg_snprintf(conn, name, sizeof(name), "%s%c%s",
        path, DIRSEP, PASSWORDS_FILE_NAME);
    fp = mg_fopen(name, "r");
  } else {
     // Try to find .htpasswd in requested directory.
    for (p = path, e = p + strlen(p) - 1; e > p; e--)
      if (IS_DIRSEP_CHAR(*e))
        break;
    (void) mg_snprintf(conn, name, sizeof(name), "%.*s%c%s",
        (int) (e - p), p, DIRSEP, PASSWORDS_FILE_NAME);
    fp = mg_fopen(name, "r");
  }

  return fp;
}

// Parsed Authorization header
struct ah {
  char *user, *uri, *cnonce, *response, *qop, *nc, *nonce;
};

static int parse_auth_header(struct mg_connection *conn, char *buf,
                             size_t buf_size, struct ah *ah) {
  char *name, *value, *s;
  const char *auth_header;

  if ((auth_header = mg_get_header(conn, "Authorization")) == NULL ||
      mg_strncasecmp(auth_header, "Digest ", 7) != 0) {
    return 0;
  }

  // Make modifiable copy of the auth header
  (void) mg_strlcpy(buf, auth_header + 7, buf_size);

  s = buf;
  (void) memset(ah, 0, sizeof(*ah));

  // Parse authorization header
  for (;;) {
    // Gobble initial spaces
    while (isspace(* (unsigned char *) s)) {
      s++;
    }
    name = skip_quoted(&s, "=", " ", 0);
    // Value is either quote-delimited, or ends at first comma or space.
    if (s[0] == '\"') {
      s++;
      value = skip_quoted(&s, "\"", " ", '\\');
      if (s[0] == ',') {
        s++;
      }
    } else {
      value = skip_quoted(&s, ", ", " ", 0);  // IE uses commas, FF uses spaces
    }
    if (*name == '\0') {
      break;
    }

    if (!strcmp(name, "username")) {
      ah->user = value;
    } else if (!strcmp(name, "cnonce")) {
      ah->cnonce = value;
    } else if (!strcmp(name, "response")) {
      ah->response = value;
    } else if (!strcmp(name, "uri")) {
      ah->uri = value;
    } else if (!strcmp(name, "qop")) {
      ah->qop = value;
    } else if (!strcmp(name, "nc")) {
      ah->nc = value;
    } else if (!strcmp(name, "nonce")) {
      ah->nonce = value;
    }
  }

  // CGI needs it as REMOTE_USER
  if (ah->user != NULL) {
    conn->request_info.remote_user = mg_strdup(ah->user);
  } else {
    return 0;
  }

  return 1;
}

// Authorize against the opened passwords file. Return 1 if authorized.
static int authorize(struct mg_connection *conn, FILE *fp) {
  struct ah ah;
  char line[256], f_user[256], ha1[256], f_domain[256], buf[BUFSIZ];

  if (!parse_auth_header(conn, buf, sizeof(buf), &ah)) {
    return 0;
  }

  // Loop over passwords file
  while (fgets(line, sizeof(line), fp) != NULL) {
    if (sscanf(line, "%[^:]:%[^:]:%s", f_user, f_domain, ha1) != 3) {
      continue;
    }

    if (!strcmp(ah.user, f_user) &&
        !strcmp(conn->ctx->config[AUTHENTICATION_DOMAIN], f_domain))
      return check_password(
            conn->request_info.request_method,
            ha1, ah.uri, ah.nonce, ah.nc, ah.cnonce, ah.qop,
            ah.response);
  }

  return 0;
}

// Return 1 if request is authorised, 0 otherwise.
static int check_authorization(struct mg_connection *conn, const char *path) {
  FILE *fp;
  char fname[PATH_MAX];
  struct vec uri_vec, filename_vec;
  const char *list;
  int authorized;

  fp = NULL;
  authorized = 1;

  list = conn->ctx->config[PROTECT_URI];
  while ((list = next_option(list, &uri_vec, &filename_vec)) != NULL) {
    if (!memcmp(conn->request_info.uri, uri_vec.ptr, uri_vec.len)) {
      (void) mg_snprintf(conn, fname, sizeof(fname), "%.*s",
          filename_vec.len, filename_vec.ptr);
      if ((fp = mg_fopen(fname, "r")) == NULL) {
        cry(conn, "%s: cannot open %s: %s", __func__, fname, strerror(errno));
      }
      break;
    }
  }

  if (fp == NULL) {
    fp = open_auth_file(conn, path);
  }

  if (fp != NULL) {
    authorized = authorize(conn, fp);
    (void) fclose(fp);
  }

  return authorized;
}

static void send_authorization_request(struct mg_connection *conn) {
  conn->request_info.status_code = 401;
  (void) mg_printf(conn,
      "HTTP/1.1 401 Unauthorized\r\n"
      "Content-Length: 0\r\n"
      "WWW-Authenticate: Digest qop=\"auth\", "
      "realm=\"%s\", nonce=\"%lu\"\r\n\r\n",
      conn->ctx->config[AUTHENTICATION_DOMAIN],
      (unsigned long) time(NULL));
}

static int is_authorized_for_put(struct mg_connection *conn) {
  FILE *fp;
  int ret = 0;

  fp = conn->ctx->config[PUT_DELETE_PASSWORDS_FILE] == NULL ? NULL :
    mg_fopen(conn->ctx->config[PUT_DELETE_PASSWORDS_FILE], "r");

  if (fp != NULL) {
    ret = authorize(conn, fp);
    (void) fclose(fp);
  }

  return ret;
}

int mg_modify_passwords_file(const char *fname, const char *domain,
                             const char *user, const char *pass) {
  int found;
  char line[512], u[512], d[512], ha1[33], tmp[PATH_MAX];
  FILE *fp, *fp2;

  found = 0;
  fp = fp2 = NULL;

  // Regard empty password as no password - remove user record.
  if (pass != NULL && pass[0] == '\0') {
    pass = NULL;
  }

  (void) snprintf(tmp, sizeof(tmp), "%s.tmp", fname);

  // Create the file if does not exist
  if ((fp = mg_fopen(fname, "a+")) != NULL) {
    (void) fclose(fp);
  }

  // Open the given file and temporary file
  if ((fp = mg_fopen(fname, "r")) == NULL) {
    return 0;
  } else if ((fp2 = mg_fopen(tmp, "w+")) == NULL) {
    fclose(fp);
    return 0;
  }

  // Copy the stuff to temporary file
  while (fgets(line, sizeof(line), fp) != NULL) {
    if (sscanf(line, "%[^:]:%[^:]:%*s", u, d) != 2) {
      continue;
    }

    if (!strcmp(u, user) && !strcmp(d, domain)) {
      found++;
      if (pass != NULL) {
        mg_md5(ha1, user, ":", domain, ":", pass, NULL);
        fprintf(fp2, "%s:%s:%s\n", user, domain, ha1);
      }
    } else {
      (void) fprintf(fp2, "%s", line);
    }
  }

  // If new user, just add it
  if (!found && pass != NULL) {
    mg_md5(ha1, user, ":", domain, ":", pass, NULL);
    (void) fprintf(fp2, "%s:%s:%s\n", user, domain, ha1);
  }

  // Close files
  (void) fclose(fp);
  (void) fclose(fp2);

  // Put the temp file in place of real file
  (void) mg_remove(fname);
  (void) mg_rename(tmp, fname);

  return 1;
}

struct de {
  struct mg_connection *conn;
  char *file_name;
  struct mgstat st;
};

static void url_encode(const char *src, char *dst, size_t dst_len) {
  static const char *dont_escape = "._-$,;~()";
  static const char *hex = "0123456789abcdef";
  const char *end = dst + dst_len - 1;

  for (; *src != '\0' && dst < end; src++, dst++) {
    if (isalnum(*(const unsigned char *) src) ||
        strchr(dont_escape, * (const unsigned char *) src) != NULL) {
      *dst = *src;
    } else if (dst + 2 < end) {
      dst[0] = '%';
      dst[1] = hex[(* (const unsigned char *) src) >> 4];
      dst[2] = hex[(* (const unsigned char *) src) & 0xf];
      dst += 2;
    }
  }

  *dst = '\0';
}

static void print_dir_entry(struct de *de) {
  char size[64], mod[64], href[PATH_MAX];

  if (de->st.is_directory) {
    (void) mg_snprintf(de->conn, size, sizeof(size), "%s", "[DIRECTORY]");
  } else {
     // We use (signed) cast below because MSVC 6 compiler cannot
     // convert unsigned __int64 to double. Sigh.
    if (de->st.size < 1024) {
      (void) mg_snprintf(de->conn, size, sizeof(size),
          "%lu", (unsigned long) de->st.size);
    } else if (de->st.size < 1024 * 1024) {
      (void) mg_snprintf(de->conn, size, sizeof(size),
          "%.1fk", (double) de->st.size / 1024.0);
    } else if (de->st.size < 1024 * 1024 * 1024) {
      (void) mg_snprintf(de->conn, size, sizeof(size),
          "%.1fM", (double) de->st.size / 1048576);
    } else {
      (void) mg_snprintf(de->conn, size, sizeof(size),
          "%.1fG", (double) de->st.size / 1073741824);
    }
  }
  (void) strftime(mod, sizeof(mod), "%d-%b-%Y %H:%M", localtime(&de->st.mtime));
  url_encode(de->file_name, href, sizeof(href));
  de->conn->num_bytes_sent += mg_printf(de->conn,
      "<tr><td><a href=\"%s%s%s\">%s%s</a></td>"
      "<td>&nbsp;%s</td><td>&nbsp;&nbsp;%s</td></tr>\n",
      de->conn->request_info.uri, href, de->st.is_directory ? "/" : "",
      de->file_name, de->st.is_directory ? "/" : "", mod, size);
}

// This function is called from send_directory() and used for
// sorting directory entries by size, or name, or modification time.
// On windows, __cdecl specification is needed in case if project is built
// with __stdcall convention. qsort always requires __cdels callback.
static int WINCDECL compare_dir_entries(const void *p1, const void *p2) {
  const struct de *a = (const struct de *) p1, *b = (const struct de *) p2;
  const char *query_string = a->conn->request_info.query_string;
  int cmp_result = 0;

  if (query_string == NULL) {
    query_string = "na";
  }

  if (a->st.is_directory && !b->st.is_directory) {
    return -1;  // Always put directories on top
  } else if (!a->st.is_directory && b->st.is_directory) {
    return 1;   // Always put directories on top
  } else if (*query_string == 'n') {
    cmp_result = strcmp(a->file_name, b->file_name);
  } else if (*query_string == 's') {
    cmp_result = a->st.size == b->st.size ? 0 :
      a->st.size > b->st.size ? 1 : -1;
  } else if (*query_string == 'd') {
    cmp_result = a->st.mtime == b->st.mtime ? 0 :
      a->st.mtime > b->st.mtime ? 1 : -1;
  }

  return query_string[1] == 'd' ? -cmp_result : cmp_result;
}

static int scan_directory(struct mg_connection *conn, const char *dir,
                          void *data, void (*cb)(struct de *, void *)) {
  char path[PATH_MAX];
  struct dirent *dp;
  DIR *dirp;
  struct de de;

  if ((dirp = opendir(dir)) == NULL) {
    return 0;
  } else {
    de.conn = conn;

    while ((dp = readdir(dirp)) != NULL) {
      // Do not show current dir and passwords file
      if (!strcmp(dp->d_name, ".") ||
          !strcmp(dp->d_name, "..") ||
          !strcmp(dp->d_name, PASSWORDS_FILE_NAME))
        continue;

      mg_snprintf(conn, path, sizeof(path), "%s%c%s", dir, DIRSEP, dp->d_name);

      // If we don't memset stat structure to zero, mtime will have
      // garbage and strftime() will segfault later on in
      // print_dir_entry(). memset is required only if mg_stat()
      // fails. For more details, see
      // http://code.google.com/p/mongoose/issues/detail?id=79
      if (mg_stat(path, &de.st) != 0) {
        memset(&de.st, 0, sizeof(de.st));
      }
      de.file_name = dp->d_name;

      cb(&de, data);
    }
    (void) closedir(dirp);
  }
  return 1;
}

struct dir_scan_data {
  struct de *entries;
  int num_entries;
  int arr_size;
};

static void dir_scan_callback(struct de *de, void *data) {
  struct dir_scan_data *dsd = (struct dir_scan_data *) data;

  if (dsd->entries == NULL || dsd->num_entries >= dsd->arr_size) {
    dsd->arr_size *= 2;
    dsd->entries = (struct de *) realloc(dsd->entries, dsd->arr_size *
                                         sizeof(dsd->entries[0]));
  }
  if (dsd->entries == NULL) {
    // TODO(lsm): propagate an error to the caller
    dsd->num_entries = 0;
  } else {
    dsd->entries[dsd->num_entries].file_name = mg_strdup(de->file_name);
    dsd->entries[dsd->num_entries].st = de->st;
    dsd->entries[dsd->num_entries].conn = de->conn;
    dsd->num_entries++;
  }
}

static void handle_directory_request(struct mg_connection *conn,
                                     const char *dir) {
  int i, sort_direction;
  struct dir_scan_data data = { NULL, 0, 128 };

  if (!scan_directory(conn, dir, &data, dir_scan_callback)) {
    send_http_error(conn, 500, "Cannot open directory",
                    "Error: opendir(%s): %s", dir, strerror(ERRNO));
    return;
  }

  sort_direction = conn->request_info.query_string != NULL &&
    conn->request_info.query_string[1] == 'd' ? 'a' : 'd';

  conn->must_close = 1;
  mg_printf(conn, "%s",
            "HTTP/1.1 200 OK\r\n"
            "Connection: close\r\n"
            "Content-Type: text/html; charset=utf-8\r\n\r\n");

  conn->num_bytes_sent += mg_printf(conn,
      "<html><head><title>Index of %s</title>"
      "<style>th {text-align: left;}</style></head>"
      "<body><h1>Index of %s</h1><pre><table cellpadding=\"0\">"
      "<tr><th><a href=\"?n%c\">Name</a></th>"
      "<th><a href=\"?d%c\">Modified</a></th>"
      "<th><a href=\"?s%c\">Size</a></th></tr>"
      "<tr><td colspan=\"3\"><hr></td></tr>",
      conn->request_info.uri, conn->request_info.uri,
      sort_direction, sort_direction, sort_direction);

  // Print first entry - link to a parent directory
  conn->num_bytes_sent += mg_printf(conn,
      "<tr><td><a href=\"%s%s\">%s</a></td>"
      "<td>&nbsp;%s</td><td>&nbsp;&nbsp;%s</td></tr>\n",
      conn->request_info.uri, "..", "Parent directory", "-", "-");

  // Sort and print directory entries
  qsort(data.entries, (size_t) data.num_entries, sizeof(data.entries[0]),
        compare_dir_entries);
  for (i = 0; i < data.num_entries; i++) {
    print_dir_entry(&data.entries[i]);
    free(data.entries[i].file_name);
  }
  free(data.entries);

  conn->num_bytes_sent += mg_printf(conn, "%s", "</table></body></html>");
  conn->request_info.status_code = 200;
}

// Send len bytes from the opened file to the client.
static void send_file_data(struct mg_connection *conn, FILE *fp, int64_t len) {
  char buf[BUFSIZ];
  int to_read, num_read, num_written;

  while (len > 0) {
    // Calculate how much to read from the file in the buffer
    to_read = sizeof(buf);
    if ((int64_t) to_read > len)
      to_read = (int) len;

    // Read from file, exit the loop on error
    if ((num_read = fread(buf, 1, (size_t)to_read, fp)) == 0)
      break;

    // Send read bytes to the client, exit the loop on error
    if ((num_written = mg_write(conn, buf, (size_t)num_read)) != num_read)
      break;

    // Both read and were successful, adjust counters
    conn->num_bytes_sent += num_written;
    len -= num_written;
  }
}

static int parse_range_header(const char *header, int64_t *a, int64_t *b) {
  return sscanf(header, "bytes=%" INT64_FMT "-%" INT64_FMT, a, b);
}

static void gmt_time_string(char *buf, size_t buf_len, time_t *t) {
  strftime(buf, buf_len, "%a, %d %b %Y %H:%M:%S GMT", gmtime(t));
}

static void handle_file_request(struct mg_connection *conn, const char *path,
                                struct mgstat *stp) {
  char date[64], lm[64], etag[64], range[64];
  const char *msg = "OK", *hdr;
  time_t curtime = time(NULL);
  int64_t cl, r1, r2;
  struct vec mime_vec;
  FILE *fp;
  int n;

  get_mime_type(conn->ctx, path, &mime_vec);
  cl = stp->size;
  conn->request_info.status_code = 200;
  range[0] = '\0';

  if ((fp = mg_fopen(path, "rb")) == NULL) {
    send_http_error(conn, 500, http_500_error,
        "fopen(%s): %s", path, strerror(ERRNO));
    return;
  }
  set_close_on_exec(fileno(fp));

  // If Range: header specified, act accordingly
  r1 = r2 = 0;
  hdr = mg_get_header(conn, "Range");
  if (hdr != NULL && (n = parse_range_header(hdr, &r1, &r2)) > 0) {
    conn->request_info.status_code = 206;
    (void) fseeko(fp, (off_t) r1, SEEK_SET);
    cl = n == 2 ? r2 - r1 + 1: cl - r1;
    (void) mg_snprintf(conn, range, sizeof(range),
        "Content-Range: bytes "
        "%" INT64_FMT "-%"
        INT64_FMT "/%" INT64_FMT "\r\n",
        r1, r1 + cl - 1, stp->size);
    msg = "Partial Content";
  }

  // Prepare Etag, Date, Last-Modified headers. Must be in UTC, according to
  // http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3.3
  gmt_time_string(date, sizeof(date), &curtime);
  gmt_time_string(lm, sizeof(lm), &stp->mtime);
  (void) mg_snprintf(conn, etag, sizeof(etag), "%lx.%lx",
      (unsigned long) stp->mtime, (unsigned long) stp->size);

  (void) mg_printf(conn,
      "HTTP/1.1 %d %s\r\n"
      "Date: %s\r\n"
      "Last-Modified: %s\r\n"
      "Etag: \"%s\"\r\n"
      "Content-Type: %.*s\r\n"
      "Content-Length: %" INT64_FMT "\r\n"
      "Connection: %s\r\n"
      "Accept-Ranges: bytes\r\n"
      "%s\r\n",
      conn->request_info.status_code, msg, date, lm, etag, (int) mime_vec.len,
      mime_vec.ptr, cl, suggest_connection_header(conn), range);

  if (strcmp(conn->request_info.request_method, "HEAD") != 0) {
    send_file_data(conn, fp, cl);
  }
  (void) fclose(fp);
}

void mg_send_file(struct mg_connection *conn, const char *path) {
  struct mgstat st;
  if (mg_stat(path, &st) == 0) {
    handle_file_request(conn, path, &st);
  } else {
    send_http_error(conn, 404, "Not Found", "%s", "File not found");
  }
}


// Parse HTTP headers from the given buffer, advance buffer to the point
// where parsing stopped.
static void parse_http_headers(char **buf, struct mg_request_info *ri) {
  int i;

  for (i = 0; i < (int) ARRAY_SIZE(ri->http_headers); i++) {
    ri->http_headers[i].name = skip_quoted(buf, ":", " ", 0);
    ri->http_headers[i].value = skip(buf, "\r\n");
    if (ri->http_headers[i].name[0] == '\0')
      break;
    ri->num_headers = i + 1;
  }
}

static int is_valid_http_method(const char *method) {
  return !strcmp(method, "GET") || !strcmp(method, "POST") ||
    !strcmp(method, "HEAD") || !strcmp(method, "CONNECT") ||
    !strcmp(method, "PUT") || !strcmp(method, "DELETE") ||
    !strcmp(method, "OPTIONS") || !strcmp(method, "PROPFIND");
}

// Parse HTTP request, fill in mg_request_info structure.
// This function modifies the buffer with HTTP request by nul-terminating
// HTTP request components, header names and header values.
static int parse_http_message(char *buf, int len, struct mg_request_info *ri) {
  int request_length = get_request_len(buf, len);
  if (request_length > 0) {
    // Reset attributes. DO NOT TOUCH is_ssl, remote_ip, remote_port
    ri->remote_user = ri->request_method = ri->uri = ri->http_version = NULL;
    ri->num_headers = 0;
    ri->status_code = -1;

    buf[request_length - 1] = '\0';

    // RFC says that all initial whitespaces should be ingored
    while (*buf != '\0' && isspace(* (unsigned char *) buf)) {
      buf++;
    }
    ri->request_method = skip(&buf, " ");
    ri->uri = skip(&buf, " ");
    ri->http_version = skip(&buf, "\r\n");
    parse_http_headers(&buf, ri);
  }
  return request_length;
}

static int parse_http_request(char *buf, int len, struct mg_request_info *ri) {
  int result = parse_http_message(buf, len, ri);
  if (result > 0 &&
      is_valid_http_method(ri->request_method) &&
      !strncmp(ri->http_version, "HTTP/", 5)) {
    ri->http_version += 5;   // Skip "HTTP/"
  } else {
    result = -1;
  }
  return result;
}

static int parse_http_response(char *buf, int len, struct mg_request_info *ri) {
  int result = parse_http_message(buf, len, ri);
  return result > 0 && !strncmp(ri->request_method, "HTTP/", 5) ? result : -1;
}

// Keep reading the input (either opened file descriptor fd, or socket sock,
// or SSL descriptor ssl) into buffer buf, until \r\n\r\n appears in the
// buffer (which marks the end of HTTP request). Buffer buf may already
// have some data. The length of the data is stored in nread.
// Upon every read operation, increase nread by the number of bytes read.
static int read_request(FILE *fp, SOCKET sock, SSL *ssl, char *buf, int bufsiz,
                        int *nread) {
  int request_len, n = 0;

  do {
    request_len = get_request_len(buf, *nread);
    if (request_len == 0 &&
        (n = pull(fp, sock, ssl, buf + *nread, bufsiz - *nread)) > 0) {
      *nread += n;
    }
  } while (*nread <= bufsiz && request_len == 0 && n > 0);

  return request_len;
}

// For given directory path, substitute it to valid index file.
// Return 0 if index file has been found, -1 if not found.
// If the file is found, it's stats is returned in stp.
static int substitute_index_file(struct mg_connection *conn, char *path,
                                 size_t path_len, struct mgstat *stp) {
  const char *list = conn->ctx->config[INDEX_FILES];
  struct mgstat st;
  struct vec filename_vec;
  size_t n = strlen(path);
  int found = 0;

  // The 'path' given to us points to the directory. Remove all trailing
  // directory separator characters from the end of the path, and
  // then append single directory separator character.
  while (n > 0 && IS_DIRSEP_CHAR(path[n - 1])) {
    n--;
  }
  path[n] = DIRSEP;

  // Traverse index files list. For each entry, append it to the given
  // path and see if the file exists. If it exists, break the loop
  while ((list = next_option(list, &filename_vec, NULL)) != NULL) {

    // Ignore too long entries that may overflow path buffer
    if (filename_vec.len > path_len - (n + 2))
      continue;

    // Prepare full path to the index file
    (void) mg_strlcpy(path + n + 1, filename_vec.ptr, filename_vec.len + 1);

    // Does it exist?
    if (mg_stat(path, &st) == 0) {
      // Yes it does, break the loop
      *stp = st;
      found = 1;
      break;
    }
  }

  // If no index file exists, restore directory path
  if (!found) {
    path[n] = '\0';
  }

  return found;
}

// Return True if we should reply 304 Not Modified.
static int is_not_modified(const struct mg_connection *conn,
                           const struct mgstat *stp) {
  const char *ims = mg_get_header(conn, "If-Modified-Since");
  return ims != NULL && stp->mtime <= parse_date_string(ims);
}

static int forward_body_data(struct mg_connection *conn, FILE *fp,
                             SOCKET sock, SSL *ssl) {
  const char *expect, *buffered;
  char buf[BUFSIZ];
  int to_read, nread, buffered_len, success = 0;

  expect = mg_get_header(conn, "Expect");
  assert(fp != NULL);

  if (conn->content_len == -1) {
    send_http_error(conn, 411, "Length Required", "");
  } else if (expect != NULL && mg_strcasecmp(expect, "100-continue")) {
    send_http_error(conn, 417, "Expectation Failed", "");
  } else {
    if (expect != NULL) {
      (void) mg_printf(conn, "%s", "HTTP/1.1 100 Continue\r\n\r\n");
    }

    buffered = conn->buf + conn->request_len;
    buffered_len = conn->data_len - conn->request_len;
    assert(buffered_len >= 0);
    assert(conn->consumed_content == 0);

    if (buffered_len > 0) {
      if ((int64_t) buffered_len > conn->content_len) {
        buffered_len = (int) conn->content_len;
      }
      push(fp, sock, ssl, buffered, (int64_t) buffered_len);
      conn->consumed_content += buffered_len;
    }

    while (conn->consumed_content < conn->content_len) {
      to_read = sizeof(buf);
      if ((int64_t) to_read > conn->content_len - conn->consumed_content) {
        to_read = (int) (conn->content_len - conn->consumed_content);
      }
      nread = pull(NULL, conn->client.sock, conn->ssl, buf, to_read);
      if (nread <= 0 || push(fp, sock, ssl, buf, nread) != nread) {
        break;
      }
      conn->consumed_content += nread;
    }

    if (conn->consumed_content == conn->content_len) {
      success = 1;
    }

    // Each error code path in this function must send an error
    if (!success) {
      send_http_error(conn, 577, http_500_error, "");
    }
  }

  return success;
}

#if !defined(NO_CGI)
// This structure helps to create an environment for the spawned CGI program.
// Environment is an array of "VARIABLE=VALUE\0" ASCIIZ strings,
// last element must be NULL.
// However, on Windows there is a requirement that all these VARIABLE=VALUE\0
// strings must reside in a contiguous buffer. The end of the buffer is
// marked by two '\0' characters.
// We satisfy both worlds: we create an envp array (which is vars), all
// entries are actually pointers inside buf.
struct cgi_env_block {
  struct mg_connection *conn;
  char buf[CGI_ENVIRONMENT_SIZE]; // Environment buffer
  int len; // Space taken
  char *vars[MAX_CGI_ENVIR_VARS]; // char **envp
  int nvars; // Number of variables
};

// Append VARIABLE=VALUE\0 string to the buffer, and add a respective
// pointer into the vars array.
static char *addenv(struct cgi_env_block *block, const char *fmt, ...) {
  int n, space;
  char *added;
  va_list ap;

  // Calculate how much space is left in the buffer
  space = sizeof(block->buf) - block->len - 2;
  assert(space >= 0);

  // Make a pointer to the free space int the buffer
  added = block->buf + block->len;

  // Copy VARIABLE=VALUE\0 string into the free space
  va_start(ap, fmt);
  n = mg_vsnprintf(block->conn, added, (size_t) space, fmt, ap);
  va_end(ap);

  // Make sure we do not overflow buffer and the envp array
  if (n > 0 && n < space &&
      block->nvars < (int) ARRAY_SIZE(block->vars) - 2) {
    // Append a pointer to the added string into the envp array
    block->vars[block->nvars++] = block->buf + block->len;
    // Bump up used length counter. Include \0 terminator
    block->len += n + 1;
  }

  return added;
}

static void prepare_cgi_environment(struct mg_connection *conn,
                                    const char *prog,
                                    struct cgi_env_block *blk) {
  const char *s, *slash;
  struct vec var_vec;
  char *p, src_addr[20];
  int  i;

  blk->len = blk->nvars = 0;
  blk->conn = conn;
  sockaddr_to_string(src_addr, sizeof(src_addr), &conn->client.rsa);

  addenv(blk, "SERVER_NAME=%s", conn->ctx->config[AUTHENTICATION_DOMAIN]);
  addenv(blk, "SERVER_ROOT=%s", conn->ctx->config[DOCUMENT_ROOT]);
  addenv(blk, "DOCUMENT_ROOT=%s", conn->ctx->config[DOCUMENT_ROOT]);

  // Prepare the environment block
  addenv(blk, "%s", "GATEWAY_INTERFACE=CGI/1.1");
  addenv(blk, "%s", "SERVER_PROTOCOL=HTTP/1.1");
  addenv(blk, "%s", "REDIRECT_STATUS=200"); // For PHP

  // TODO(lsm): fix this for IPv6 case
  addenv(blk, "SERVER_PORT=%d", ntohs(conn->client.lsa.sin.sin_port));

  addenv(blk, "REQUEST_METHOD=%s", conn->request_info.request_method);
  addenv(blk, "REMOTE_ADDR=%s", src_addr);
  addenv(blk, "REMOTE_PORT=%d", conn->request_info.remote_port);
  addenv(blk, "REQUEST_URI=%s", conn->request_info.uri);

  // SCRIPT_NAME
  assert(conn->request_info.uri[0] == '/');
  slash = strrchr(conn->request_info.uri, '/');
  if ((s = strrchr(prog, '/')) == NULL)
    s = prog;
  addenv(blk, "SCRIPT_NAME=%.*s%s", slash - conn->request_info.uri,
         conn->request_info.uri, s);

  addenv(blk, "SCRIPT_FILENAME=%s", prog);
  addenv(blk, "PATH_TRANSLATED=%s", prog);
  addenv(blk, "HTTPS=%s", conn->ssl == NULL ? "off" : "on");

  if ((s = mg_get_header(conn, "Content-Type")) != NULL)
    addenv(blk, "CONTENT_TYPE=%s", s);

  if (conn->request_info.query_string != NULL)
    addenv(blk, "QUERY_STRING=%s", conn->request_info.query_string);

  if ((s = mg_get_header(conn, "Content-Length")) != NULL)
    addenv(blk, "CONTENT_LENGTH=%s", s);

  if ((s = getenv("PATH")) != NULL)
    addenv(blk, "PATH=%s", s);

  if (conn->path_info != NULL) {
    addenv(blk, "PATH_INFO=%s", conn->path_info);
  }

#if defined(_WIN32)
  if ((s = getenv("COMSPEC")) != NULL) {
    addenv(blk, "COMSPEC=%s", s);
  }
  if ((s = getenv("SYSTEMROOT")) != NULL) {
    addenv(blk, "SYSTEMROOT=%s", s);
  }
  if ((s = getenv("SystemDrive")) != NULL) {
    addenv(blk, "SystemDrive=%s", s);
  }
#else
  if ((s = getenv("LD_LIBRARY_PATH")) != NULL)
    addenv(blk, "LD_LIBRARY_PATH=%s", s);
#endif // _WIN32

  if ((s = getenv("PERLLIB")) != NULL)
    addenv(blk, "PERLLIB=%s", s);

  if (conn->request_info.remote_user != NULL) {
    addenv(blk, "REMOTE_USER=%s", conn->request_info.remote_user);
    addenv(blk, "%s", "AUTH_TYPE=Digest");
  }

  // Add all headers as HTTP_* variables
  for (i = 0; i < conn->request_info.num_headers; i++) {
    p = addenv(blk, "HTTP_%s=%s",
        conn->request_info.http_headers[i].name,
        conn->request_info.http_headers[i].value);

    // Convert variable name into uppercase, and change - to _
    for (; *p != '=' && *p != '\0'; p++) {
      if (*p == '-')
        *p = '_';
      *p = (char) toupper(* (unsigned char *) p);
    }
  }

  // Add user-specified variables
  s = conn->ctx->config[CGI_ENVIRONMENT];
  while ((s = next_option(s, &var_vec, NULL)) != NULL) {
    addenv(blk, "%.*s", var_vec.len, var_vec.ptr);
  }

  blk->vars[blk->nvars++] = NULL;
  blk->buf[blk->len++] = '\0';

  assert(blk->nvars < (int) ARRAY_SIZE(blk->vars));
  assert(blk->len > 0);
  assert(blk->len < (int) sizeof(blk->buf));
}

static void handle_cgi_request(struct mg_connection *conn, const char *prog) {
  int headers_len, data_len, i, fd_stdin[2], fd_stdout[2];
  const char *status, *status_text;
  char buf[16384], *pbuf, dir[PATH_MAX], *p;
  struct mg_request_info ri;
  struct cgi_env_block blk;
  FILE *in, *out;
  pid_t pid;

  prepare_cgi_environment(conn, prog, &blk);

  // CGI must be executed in its own directory. 'dir' must point to the
  // directory containing executable program, 'p' must point to the
  // executable program name relative to 'dir'.
  (void) mg_snprintf(conn, dir, sizeof(dir), "%s", prog);
  if ((p = strrchr(dir, DIRSEP)) != NULL) {
    *p++ = '\0';
  } else {
    dir[0] = '.', dir[1] = '\0';
    p = (char *) prog;
  }

  pid = (pid_t) -1;
  fd_stdin[0] = fd_stdin[1] = fd_stdout[0] = fd_stdout[1] = -1;
  in = out = NULL;

  if (pipe(fd_stdin) != 0 || pipe(fd_stdout) != 0) {
    send_http_error(conn, 500, http_500_error,
        "Cannot create CGI pipe: %s", strerror(ERRNO));
    goto done;
  } else if ((pid = spawn_process(conn, p, blk.buf, blk.vars,
          fd_stdin[0], fd_stdout[1], dir)) == (pid_t) -1) {
    goto done;
  } else if ((in = fdopen(fd_stdin[1], "wb")) == NULL ||
      (out = fdopen(fd_stdout[0], "rb")) == NULL) {
    send_http_error(conn, 500, http_500_error,
        "fopen: %s", strerror(ERRNO));
    goto done;
  }

  setbuf(in, NULL);
  setbuf(out, NULL);

  // spawn_process() must close those!
  // If we don't mark them as closed, close() attempt before
  // return from this function throws an exception on Windows.
  // Windows does not like when closed descriptor is closed again.
  fd_stdin[0] = fd_stdout[1] = -1;

  // Send POST data to the CGI process if needed
  if (!strcmp(conn->request_info.request_method, "POST") &&
      !forward_body_data(conn, in, INVALID_SOCKET, NULL)) {
    goto done;
  }

  // Now read CGI reply into a buffer. We need to set correct
  // status code, thus we need to see all HTTP headers first.
  // Do not send anything back to client, until we buffer in all
  // HTTP headers.
  data_len = 0;
  headers_len = read_request(out, INVALID_SOCKET, NULL,
                             buf, sizeof(buf), &data_len);
  if (headers_len <= 0) {
    send_http_error(conn, 500, http_500_error,
                    "CGI program sent malformed HTTP headers: [%.*s]",
                    data_len, buf);
    goto done;
  }
  pbuf = buf;
  buf[headers_len - 1] = '\0';
  parse_http_headers(&pbuf, &ri);

  // Make up and send the status line
  status_text = "OK";
  if ((status = get_header(&ri, "Status")) != NULL) {
    conn->request_info.status_code = atoi(status);
    status_text = status;
    while (isdigit(* (unsigned char *) status_text) || *status_text == ' ') {
      status_text++;
    }
  } else if (get_header(&ri, "Location") != NULL) {
    conn->request_info.status_code = 302;
  } else {
    conn->request_info.status_code = 200;
  }
  if (get_header(&ri, "Connection") != NULL &&
      !mg_strcasecmp(get_header(&ri, "Connection"), "keep-alive")) {
    conn->must_close = 1;
  }
  (void) mg_printf(conn, "HTTP/1.1 %d %s\r\n", conn->request_info.status_code,
                   status_text);

  // Send headers
  for (i = 0; i < ri.num_headers; i++) {
    mg_printf(conn, "%s: %s\r\n",
              ri.http_headers[i].name, ri.http_headers[i].value);
  }
  (void) mg_write(conn, "\r\n", 2);

  // Send chunk of data that may be read after the headers
  conn->num_bytes_sent += mg_write(conn, buf + headers_len,
                                   (size_t)(data_len - headers_len));

  // Read the rest of CGI output and send to the client
  send_file_data(conn, out, INT64_MAX);

done:
  if (pid != (pid_t) -1) {
    kill(pid, SIGKILL);
  }
  if (fd_stdin[0] != -1) {
    (void) close(fd_stdin[0]);
  }
  if (fd_stdout[1] != -1) {
    (void) close(fd_stdout[1]);
  }

  if (in != NULL) {
    (void) fclose(in);
  } else if (fd_stdin[1] != -1) {
    (void) close(fd_stdin[1]);
  }

  if (out != NULL) {
    (void) fclose(out);
  } else if (fd_stdout[0] != -1) {
    (void) close(fd_stdout[0]);
  }
}
#endif // !NO_CGI

// For a given PUT path, create all intermediate subdirectories
// for given path. Return 0 if the path itself is a directory,
// or -1 on error, 1 if OK.
static int put_dir(const char *path) {
  char buf[PATH_MAX];
  const char *s, *p;
  struct mgstat st;
  int len, res = 1;

  for (s = p = path + 2; (p = strchr(s, DIRSEP)) != NULL; s = ++p) {
    len = p - path;
    if (len >= (int) sizeof(buf)) {
      res = -1;
      break;
    }
    memcpy(buf, path, len);
    buf[len] = '\0';

    // Try to create intermediate directory
    DEBUG_TRACE(("mkdir(%s)", buf));
    if (mg_stat(buf, &st) == -1 && mg_mkdir(buf, 0755) != 0) {
      res = -1;
      break;
    }

    // Is path itself a directory?
    if (p[1] == '\0') {
      res = 0;
    }
  }

  return res;
}

static void put_file(struct mg_connection *conn, const char *path) {
  struct mgstat st;
  const char *range;
  int64_t r1, r2;
  FILE *fp;
  int rc;

  conn->request_info.status_code = mg_stat(path, &st) == 0 ? 200 : 201;

  if ((rc = put_dir(path)) == 0) {
    mg_printf(conn, "HTTP/1.1 %d OK\r\n\r\n", conn->request_info.status_code);
  } else if (rc == -1) {
    send_http_error(conn, 500, http_500_error,
        "put_dir(%s): %s", path, strerror(ERRNO));
  } else if ((fp = mg_fopen(path, "wb+")) == NULL) {
    send_http_error(conn, 500, http_500_error,
        "fopen(%s): %s", path, strerror(ERRNO));
  } else {
    set_close_on_exec(fileno(fp));
    range = mg_get_header(conn, "Content-Range");
    r1 = r2 = 0;
    if (range != NULL && parse_range_header(range, &r1, &r2) > 0) {
      conn->request_info.status_code = 206;
      // TODO(lsm): handle seek error
      (void) fseeko(fp, (off_t) r1, SEEK_SET);
    }
    if (forward_body_data(conn, fp, INVALID_SOCKET, NULL))
      (void) mg_printf(conn, "HTTP/1.1 %d OK\r\n\r\n",
          conn->request_info.status_code);
    (void) fclose(fp);
  }
}

static void send_ssi_file(struct mg_connection *, const char *, FILE *, int);

static void do_ssi_include(struct mg_connection *conn, const char *ssi,
                           char *tag, int include_level) {
  char file_name[BUFSIZ], path[PATH_MAX], *p;
  FILE *fp;

  // sscanf() is safe here, since send_ssi_file() also uses buffer
  // of size BUFSIZ to get the tag. So strlen(tag) is always < BUFSIZ.
  if (sscanf(tag, " virtual=\"%[^\"]\"", file_name) == 1) {
    // File name is relative to the webserver root
    (void) mg_snprintf(conn, path, sizeof(path), "%s%c%s",
        conn->ctx->config[DOCUMENT_ROOT], DIRSEP, file_name);
  } else if (sscanf(tag, " file=\"%[^\"]\"", file_name) == 1) {
    // File name is relative to the webserver working directory
    // or it is absolute system path
    (void) mg_snprintf(conn, path, sizeof(path), "%s", file_name);
  } else if (sscanf(tag, " \"%[^\"]\"", file_name) == 1) {
    // File name is relative to the currect document
    (void) mg_snprintf(conn, path, sizeof(path), "%s", ssi);
    if ((p = strrchr(path, DIRSEP)) != NULL) {
      p[1] = '\0';
    }
    (void) mg_snprintf(conn, path + strlen(path),
        sizeof(path) - strlen(path), "%s", file_name);
  } else {
    cry(conn, "Bad SSI #include: [%s]", tag);
    return;
  }

  if ((fp = mg_fopen(path, "rb")) == NULL) {
    cry(conn, "Cannot open SSI #include: [%s]: fopen(%s): %s",
        tag, path, strerror(ERRNO));
  } else {
    set_close_on_exec(fileno(fp));
    if (match_prefix(conn->ctx->config[SSI_EXTENSIONS],
                     strlen(conn->ctx->config[SSI_EXTENSIONS]), path) > 0) {
      send_ssi_file(conn, path, fp, include_level + 1);
    } else {
      send_file_data(conn, fp, INT64_MAX);
    }
    (void) fclose(fp);
  }
}

#if !defined(NO_POPEN)
static void do_ssi_exec(struct mg_connection *conn, char *tag) {
  char cmd[BUFSIZ];
  FILE *fp;

  if (sscanf(tag, " \"%[^\"]\"", cmd) != 1) {
    cry(conn, "Bad SSI #exec: [%s]", tag);
  } else if ((fp = popen(cmd, "r")) == NULL) {
    cry(conn, "Cannot SSI #exec: [%s]: %s", cmd, strerror(ERRNO));
  } else {
    send_file_data(conn, fp, INT64_MAX);
    (void) pclose(fp);
  }
}
#endif // !NO_POPEN

static void send_ssi_file(struct mg_connection *conn, const char *path,
                          FILE *fp, int include_level) {
  char buf[BUFSIZ];
  int ch, len, in_ssi_tag;

  if (include_level > 10) {
    cry(conn, "SSI #include level is too deep (%s)", path);
    return;
  }

  in_ssi_tag = 0;
  len = 0;

  while ((ch = fgetc(fp)) != EOF) {
    if (in_ssi_tag && ch == '>') {
      in_ssi_tag = 0;
      buf[len++] = (char) ch;
      buf[len] = '\0';
      assert(len <= (int) sizeof(buf));
      if (len < 6 || memcmp(buf, "<!--#", 5) != 0) {
        // Not an SSI tag, pass it
        (void) mg_write(conn, buf, (size_t)len);
      } else {
        if (!memcmp(buf + 5, "include", 7)) {
          do_ssi_include(conn, path, buf + 12, include_level);
#if !defined(NO_POPEN)
        } else if (!memcmp(buf + 5, "exec", 4)) {
          do_ssi_exec(conn, buf + 9);
#endif // !NO_POPEN
        } else {
          cry(conn, "%s: unknown SSI " "command: \"%s\"", path, buf);
        }
      }
      len = 0;
    } else if (in_ssi_tag) {
      if (len == 5 && memcmp(buf, "<!--#", 5) != 0) {
        // Not an SSI tag
        in_ssi_tag = 0;
      } else if (len == (int) sizeof(buf) - 2) {
        cry(conn, "%s: SSI tag is too large", path);
        len = 0;
      }
      buf[len++] = ch & 0xff;
    } else if (ch == '<') {
      in_ssi_tag = 1;
      if (len > 0) {
        (void) mg_write(conn, buf, (size_t)len);
      }
      len = 0;
      buf[len++] = ch & 0xff;
    } else {
      buf[len++] = ch & 0xff;
      if (len == (int) sizeof(buf)) {
        (void) mg_write(conn, buf, (size_t)len);
        len = 0;
      }
    }
  }

  // Send the rest of buffered data
  if (len > 0) {
    (void) mg_write(conn, buf, (size_t)len);
  }
}

static void handle_ssi_file_request(struct mg_connection *conn,
                                    const char *path) {
  FILE *fp;

  if ((fp = mg_fopen(path, "rb")) == NULL) {
    send_http_error(conn, 500, http_500_error, "fopen(%s): %s", path,
                    strerror(ERRNO));
  } else {
    conn->must_close = 1;
    set_close_on_exec(fileno(fp));
    mg_printf(conn, "HTTP/1.1 200 OK\r\n"
              "Content-Type: text/html\r\nConnection: %s\r\n\r\n",
              suggest_connection_header(conn));
    send_ssi_file(conn, path, fp, 0);
    (void) fclose(fp);
  }
}

static void send_options(struct mg_connection *conn) {
  conn->request_info.status_code = 200;

  (void) mg_printf(conn,
      "HTTP/1.1 200 OK\r\n"
      "Allow: GET, POST, HEAD, CONNECT, PUT, DELETE, OPTIONS\r\n"
      "DAV: 1\r\n\r\n");
}

// Writes PROPFIND properties for a collection element
static void print_props(struct mg_connection *conn, const char* uri,
                        struct mgstat* st) {
  char mtime[64];
  gmt_time_string(mtime, sizeof(mtime), &st->mtime);
  conn->num_bytes_sent += mg_printf(conn,
      "<d:response>"
       "<d:href>%s</d:href>"
       "<d:propstat>"
        "<d:prop>"
         "<d:resourcetype>%s</d:resourcetype>"
         "<d:getcontentlength>%" INT64_FMT "</d:getcontentlength>"
         "<d:getlastmodified>%s</d:getlastmodified>"
        "</d:prop>"
        "<d:status>HTTP/1.1 200 OK</d:status>"
       "</d:propstat>"
      "</d:response>\n",
      uri,
      st->is_directory ? "<d:collection/>" : "",
      st->size,
      mtime);
}

static void print_dav_dir_entry(struct de *de, void *data) {
  char href[PATH_MAX];
  struct mg_connection *conn = (struct mg_connection *) data;
  mg_snprintf(conn, href, sizeof(href), "%s%s",
              conn->request_info.uri, de->file_name);
  print_props(conn, href, &de->st);
}

static void handle_propfind(struct mg_connection *conn, const char* path,
                            struct mgstat* st) {
  const char *depth = mg_get_header(conn, "Depth");

  conn->must_close = 1;
  conn->request_info.status_code = 207;
  mg_printf(conn, "HTTP/1.1 207 Multi-Status\r\n"
            "Connection: close\r\n"
            "Content-Type: text/xml; charset=utf-8\r\n\r\n");

  conn->num_bytes_sent += mg_printf(conn,
      "<?xml version=\"1.0\" encoding=\"utf-8\"?>"
      "<d:multistatus xmlns:d='DAV:'>\n");

  // Print properties for the requested resource itself
  print_props(conn, conn->request_info.uri, st);

  // If it is a directory, print directory entries too if Depth is not 0
  if (st->is_directory &&
      !mg_strcasecmp(conn->ctx->config[ENABLE_DIRECTORY_LISTING], "yes") &&
      (depth == NULL || strcmp(depth, "0") != 0)) {
    scan_directory(conn, path, conn, &print_dav_dir_entry);
  }

  conn->num_bytes_sent += mg_printf(conn, "%s\n", "</d:multistatus>");
}

// This is the heart of the Mongoose's logic.
// This function is called when the request is read, parsed and validated,
// and Mongoose must decide what action to take: serve a file, or
// a directory, or call embedded function, etcetera.
static void handle_request(struct mg_connection *conn) {
  struct mg_request_info *ri = &conn->request_info;
  char path[PATH_MAX];
  int stat_result, uri_len;
  struct mgstat st;

  if ((conn->request_info.query_string = strchr(ri->uri, '?')) != NULL) {
    * conn->request_info.query_string++ = '\0';
  }
  uri_len = strlen(ri->uri);
  url_decode(ri->uri, (size_t)uri_len, ri->uri, (size_t)(uri_len + 1), 0);
  remove_double_dots_and_double_slashes(ri->uri);
  stat_result = convert_uri_to_file_name(conn, path, sizeof(path), &st);

  DEBUG_TRACE(("%s", ri->uri));
  if (!check_authorization(conn, path)) {
    send_authorization_request(conn);
  } else if (call_user(conn, MG_NEW_REQUEST) != NULL) {
    // Do nothing, callback has served the request
  } else if (!strcmp(ri->request_method, "OPTIONS")) {
    send_options(conn);
  } else if (strstr(path, PASSWORDS_FILE_NAME)) {
    // Do not allow to view passwords files
    send_http_error(conn, 403, "Forbidden", "Access Forbidden");
  } else if (conn->ctx->config[DOCUMENT_ROOT] == NULL) {
    send_http_error(conn, 404, "Not Found", "Not Found");
  } else if ((!strcmp(ri->request_method, "PUT") ||
        !strcmp(ri->request_method, "DELETE")) &&
      (conn->ctx->config[PUT_DELETE_PASSWORDS_FILE] == NULL ||
       !is_authorized_for_put(conn))) {
    send_authorization_request(conn);
  } else if (!strcmp(ri->request_method, "PUT")) {
    put_file(conn, path);
  } else if (!strcmp(ri->request_method, "DELETE")) {
    if (mg_remove(path) == 0) {
      send_http_error(conn, 200, "OK", "");
    } else {
      send_http_error(conn, 500, http_500_error, "remove(%s): %s", path,
                      strerror(ERRNO));
    }
  } else if (stat_result != 0) {
    send_http_error(conn, 404, "Not Found", "%s", "File not found");
  } else if (st.is_directory && ri->uri[uri_len - 1] != '/') {
    (void) mg_printf(conn,
        "HTTP/1.1 301 Moved Permanently\r\n"
        "Location: %s/\r\n\r\n", ri->uri);
  } else if (!strcmp(ri->request_method, "PROPFIND")) {
    handle_propfind(conn, path, &st);
  } else if (st.is_directory &&
             !substitute_index_file(conn, path, sizeof(path), &st)) {
    if (!mg_strcasecmp(conn->ctx->config[ENABLE_DIRECTORY_LISTING], "yes")) {
      handle_directory_request(conn, path);
    } else {
      send_http_error(conn, 403, "Directory Listing Denied",
          "Directory listing denied");
    }
#if !defined(NO_CGI)
  } else if (match_prefix(conn->ctx->config[CGI_EXTENSIONS],
                          strlen(conn->ctx->config[CGI_EXTENSIONS]),
                          path) > 0) {
    if (strcmp(ri->request_method, "POST") &&
        strcmp(ri->request_method, "GET")) {
      send_http_error(conn, 501, "Not Implemented",
                      "Method %s is not implemented", ri->request_method);
    } else {
      handle_cgi_request(conn, path);
    }
#endif // !NO_CGI
  } else if (match_prefix(conn->ctx->config[SSI_EXTENSIONS],
                          strlen(conn->ctx->config[SSI_EXTENSIONS]),
                          path) > 0) {
    handle_ssi_file_request(conn, path);
  } else if (is_not_modified(conn, &st)) {
    send_http_error(conn, 304, "Not Modified", "");
  } else {
    handle_file_request(conn, path, &st);
  }
}

static void close_all_listening_sockets(struct mg_context *ctx) {
  struct socket *sp, *tmp;
  for (sp = ctx->listening_sockets; sp != NULL; sp = tmp) {
    tmp = sp->next;
    (void) closesocket(sp->sock);
    free(sp);
  }
}

// Valid listening port specification is: [ip_address:]port[s]
// Examples: 80, 443s, 127.0.0.1:3128,1.2.3.4:8080s
// TODO(lsm): add parsing of the IPv6 address
static int parse_port_string(const struct vec *vec, struct socket *so) {
  int a, b, c, d, port, len;

  // MacOS needs that. If we do not zero it, subsequent bind() will fail.
  // Also, all-zeroes in the socket address means binding to all addresses
  // for both IPv4 and IPv6 (INADDR_ANY and IN6ADDR_ANY_INIT).
  memset(so, 0, sizeof(*so));

  if (sscanf(vec->ptr, "%d.%d.%d.%d:%d%n", &a, &b, &c, &d, &port, &len) == 5) {
    // Bind to a specific IPv4 address
    so->lsa.sin.sin_addr.s_addr = htonl((a << 24) | (b << 16) | (c << 8) | d);
  } else if (sscanf(vec->ptr, "%d%n", &port, &len) != 1 ||
             len <= 0 ||
             len > (int) vec->len ||
             (vec->ptr[len] && vec->ptr[len] != 's' && vec->ptr[len] != ',')) {
    return 0;
  }

  so->is_ssl = vec->ptr[len] == 's';
#if defined(USE_IPV6)
  so->lsa.sin6.sin6_family = AF_INET6;
  so->lsa.sin6.sin6_port = htons((uint16_t) port);
#else
  so->lsa.sin.sin_family = AF_INET;
  so->lsa.sin.sin_port = htons((uint16_t) port);
#endif

  return 1;
}

static int set_ports_option(struct mg_context *ctx) {
  const char *list = ctx->config[LISTENING_PORTS];
  int on = 1, success = 1;
  SOCKET sock;
  struct vec vec;
  struct socket so, *listener;

  while (success && (list = next_option(list, &vec, NULL)) != NULL) {
    if (!parse_port_string(&vec, &so)) {
      cry(fc(ctx), "%s: %.*s: invalid port spec. Expecting list of: %s",
          __func__, vec.len, vec.ptr, "[IP_ADDRESS:]PORT[s|p]");
      success = 0;
    } else if (so.is_ssl && ctx->ssl_ctx == NULL) {
      cry(fc(ctx), "Cannot add SSL socket, is -ssl_certificate option set?");
      success = 0;
    } else if ((sock = socket(so.lsa.sa.sa_family, SOCK_STREAM, 6)) ==
               INVALID_SOCKET ||
#if !defined(_WIN32)
               // On Windows, SO_REUSEADDR is recommended only for
               // broadcast UDP sockets
               setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &on,
                          sizeof(on)) != 0 ||
#endif // !_WIN32
               // Set TCP keep-alive. This is needed because if HTTP-level
               // keep-alive is enabled, and client resets the connection,
               // server won't get TCP FIN or RST and will keep the connection
               // open forever. With TCP keep-alive, next keep-alive
               // handshake will figure out that the client is down and
               // will close the server end.
               // Thanks to Igor Klopov who suggested the patch.
               setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (void *) &on,
                          sizeof(on)) != 0 ||
               bind(sock, &so.lsa.sa, sizeof(so.lsa)) != 0 ||
               listen(sock, 100) != 0) {
      closesocket(sock);
      cry(fc(ctx), "%s: cannot bind to %.*s: %s", __func__,
          vec.len, vec.ptr, strerror(ERRNO));
      success = 0;
    } else if ((listener = (struct socket *)
                calloc(1, sizeof(*listener))) == NULL) {
      closesocket(sock);
      cry(fc(ctx), "%s: %s", __func__, strerror(ERRNO));
      success = 0;
    } else {
      *listener = so;
      listener->sock = sock;
      set_close_on_exec(listener->sock);
      listener->next = ctx->listening_sockets;
      ctx->listening_sockets = listener;
    }
  }

  if (!success) {
    close_all_listening_sockets(ctx);
  }

  return success;
}

static void log_header(const struct mg_connection *conn, const char *header,
                       FILE *fp) {
  const char *header_value;

  if ((header_value = mg_get_header(conn, header)) == NULL) {
    (void) fprintf(fp, "%s", " -");
  } else {
    (void) fprintf(fp, " \"%s\"", header_value);
  }
}

static void log_access(const struct mg_connection *conn) {
  const struct mg_request_info *ri;
  FILE *fp;
  char date[64], src_addr[20];

  fp = conn->ctx->config[ACCESS_LOG_FILE] == NULL ?  NULL :
    mg_fopen(conn->ctx->config[ACCESS_LOG_FILE], "a+");

  if (fp == NULL)
    return;

  strftime(date, sizeof(date), "%d/%b/%Y:%H:%M:%S %z",
           localtime(&conn->birth_time));

  ri = &conn->request_info;
  flockfile(fp);

  sockaddr_to_string(src_addr, sizeof(src_addr), &conn->client.rsa);
  fprintf(fp, "%s - %s [%s] \"%s %s HTTP/%s\" %d %" INT64_FMT,
          src_addr, ri->remote_user == NULL ? "-" : ri->remote_user, date,
          ri->request_method ? ri->request_method : "-",
          ri->uri ? ri->uri : "-", ri->http_version,
          conn->request_info.status_code, conn->num_bytes_sent);
  log_header(conn, "Referer", fp);
  log_header(conn, "User-Agent", fp);
  fputc('\n', fp);
  fflush(fp);

  funlockfile(fp);
  fclose(fp);
}

static int isbyte(int n) {
  return n >= 0 && n <= 255;
}

// Verify given socket address against the ACL.
// Return -1 if ACL is malformed, 0 if address is disallowed, 1 if allowed.
static int check_acl(struct mg_context *ctx, const union usa *usa) {
  int a, b, c, d, n, mask, allowed;
  char flag;
  uint32_t acl_subnet, acl_mask, remote_ip;
  struct vec vec;
  const char *list = ctx->config[ACCESS_CONTROL_LIST];

  if (list == NULL) {
    return 1;
  }

  (void) memcpy(&remote_ip, &usa->sin.sin_addr, sizeof(remote_ip));

  // If any ACL is set, deny by default
  allowed = '-';

  while ((list = next_option(list, &vec, NULL)) != NULL) {
    mask = 32;

    if (sscanf(vec.ptr, "%c%d.%d.%d.%d%n", &flag, &a, &b, &c, &d, &n) != 5) {
      cry(fc(ctx), "%s: subnet must be [+|-]x.x.x.x[/x]", __func__);
      return -1;
    } else if (flag != '+' && flag != '-') {
      cry(fc(ctx), "%s: flag must be + or -: [%s]", __func__, vec.ptr);
      return -1;
    } else if (!isbyte(a)||!isbyte(b)||!isbyte(c)||!isbyte(d)) {
      cry(fc(ctx), "%s: bad ip address: [%s]", __func__, vec.ptr);
      return -1;
    } else if (sscanf(vec.ptr + n, "/%d", &mask) == 0) {
      // Do nothing, no mask specified
    } else if (mask < 0 || mask > 32) {
      cry(fc(ctx), "%s: bad subnet mask: %d [%s]", __func__, n, vec.ptr);
      return -1;
    }

    acl_subnet = (a << 24) | (b << 16) | (c << 8) | d;
    acl_mask = mask ? 0xffffffffU << (32 - mask) : 0;

    if (acl_subnet == (ntohl(remote_ip) & acl_mask)) {
      allowed = flag;
    }
  }

  return allowed == '+';
}

static void add_to_set(SOCKET fd, fd_set *set, int *max_fd) {
  FD_SET(fd, set);
  if (fd > (SOCKET) *max_fd) {
    *max_fd = (int) fd;
  }
}

#if !defined(_WIN32)
static int set_uid_option(struct mg_context *ctx) {
  struct passwd *pw;
  const char *uid = ctx->config[RUN_AS_USER];
  int success = 0;

  if (uid == NULL) {
    success = 1;
  } else {
    if ((pw = getpwnam(uid)) == NULL) {
      cry(fc(ctx), "%s: unknown user [%s]", __func__, uid);
    } else if (setgid(pw->pw_gid) == -1) {
      cry(fc(ctx), "%s: setgid(%s): %s", __func__, uid, strerror(errno));
    } else if (setuid(pw->pw_uid) == -1) {
      cry(fc(ctx), "%s: setuid(%s): %s", __func__, uid, strerror(errno));
    } else {
      success = 1;
    }
  }

  return success;
}
#endif // !_WIN32

#if !defined(NO_SSL)
static pthread_mutex_t *ssl_mutexes;

// Return OpenSSL error message
static const char *ssl_error(void) {
  unsigned long err;
  err = ERR_get_error();
  return err == 0 ? "" : ERR_error_string(err, NULL);
}

static void ssl_locking_callback(int mode, int mutex_num, const char *file,
                                 int line) {
  line = 0;    // Unused
  file = NULL; // Unused

  if (mode & CRYPTO_LOCK) {
    (void) pthread_mutex_lock(&ssl_mutexes[mutex_num]);
  } else {
    (void) pthread_mutex_unlock(&ssl_mutexes[mutex_num]);
  }
}

static unsigned long ssl_id_callback(void) {
  return (unsigned long) pthread_self();
}

#if !defined(NO_SSL_DL)
static int load_dll(struct mg_context *ctx, const char *dll_name,
                    struct ssl_func *sw) {
  union {void *p; void (*fp)(void);} u;
  void  *dll_handle;
  struct ssl_func *fp;

  if ((dll_handle = dlopen(dll_name, RTLD_LAZY)) == NULL) {
    cry(fc(ctx), "%s: cannot load %s", __func__, dll_name);
    return 0;
  }

  for (fp = sw; fp->name != NULL; fp++) {
#ifdef _WIN32
    // GetProcAddress() returns pointer to function
    u.fp = (void (*)(void)) dlsym(dll_handle, fp->name);
#else
    // dlsym() on UNIX returns void *. ISO C forbids casts of data pointers to
    // function pointers. We need to use a union to make a cast.
    u.p = dlsym(dll_handle, fp->name);
#endif // _WIN32
    if (u.fp == NULL) {
      cry(fc(ctx), "%s: %s: cannot find %s", __func__, dll_name, fp->name);
      return 0;
    } else {
      fp->ptr = u.fp;
    }
  }

  return 1;
}
#endif // NO_SSL_DL

// Dynamically load SSL library. Set up ctx->ssl_ctx pointer.
static int set_ssl_option(struct mg_context *ctx) {
  struct mg_request_info request_info;
  SSL_CTX *CTX;
  int i, size;
  const char *pem = ctx->config[SSL_CERTIFICATE];
  const char *chain = ctx->config[SSL_CHAIN_FILE];

  if (pem == NULL) {
    return 1;
  }

#if !defined(NO_SSL_DL)
  if (!load_dll(ctx, SSL_LIB, ssl_sw) ||
      !load_dll(ctx, CRYPTO_LIB, crypto_sw)) {
    return 0;
  }
#endif // NO_SSL_DL

  // Initialize SSL crap
  SSL_library_init();
  SSL_load_error_strings();

  if ((CTX = SSL_CTX_new(SSLv23_server_method())) == NULL) {
    cry(fc(ctx), "SSL_CTX_new error: %s", ssl_error());
  } else if (ctx->user_callback != NULL) {
    memset(&request_info, 0, sizeof(request_info));
    request_info.user_data = ctx->user_data;
    ctx->user_callback(MG_INIT_SSL, (struct mg_connection *) CTX,
                       &request_info);
  }

  if (CTX != NULL && SSL_CTX_use_certificate_file(CTX, pem,
        SSL_FILETYPE_PEM) == 0) {
    cry(fc(ctx), "%s: cannot open %s: %s", __func__, pem, ssl_error());
    return 0;
  } else if (CTX != NULL && SSL_CTX_use_PrivateKey_file(CTX, pem,
        SSL_FILETYPE_PEM) == 0) {
    cry(fc(ctx), "%s: cannot open %s: %s", NULL, pem, ssl_error());
    return 0;
  }

  if (CTX != NULL && chain != NULL &&
      SSL_CTX_use_certificate_chain_file(CTX, chain) == 0) {
    cry(fc(ctx), "%s: cannot open %s: %s", NULL, chain, ssl_error());
    return 0;
  }

  // Initialize locking callbacks, needed for thread safety.
  // http://www.openssl.org/support/faq.html#PROG1
  size = sizeof(pthread_mutex_t) * CRYPTO_num_locks();
  if ((ssl_mutexes = (pthread_mutex_t *) malloc((size_t)size)) == NULL) {
    cry(fc(ctx), "%s: cannot allocate mutexes: %s", __func__, ssl_error());
    return 0;
  }

  for (i = 0; i < CRYPTO_num_locks(); i++) {
    pthread_mutex_init(&ssl_mutexes[i], NULL);
  }

  CRYPTO_set_locking_callback(&ssl_locking_callback);
  CRYPTO_set_id_callback(&ssl_id_callback);

  // Done with everything. Save the context.
  ctx->ssl_ctx = CTX;

  return 1;
}

static void uninitialize_ssl(struct mg_context *ctx) {
  int i;
  if (ctx->ssl_ctx != NULL) {
    CRYPTO_set_locking_callback(NULL);
    for (i = 0; i < CRYPTO_num_locks(); i++) {
      pthread_mutex_destroy(&ssl_mutexes[i]);
    }
    CRYPTO_set_locking_callback(NULL);
    CRYPTO_set_id_callback(NULL);
  }
}
#endif // !NO_SSL

static int set_gpass_option(struct mg_context *ctx) {
  struct mgstat mgstat;
  const char *path = ctx->config[GLOBAL_PASSWORDS_FILE];
  return path == NULL || mg_stat(path, &mgstat) == 0;
}

static int set_acl_option(struct mg_context *ctx) {
  union usa fake;
  return check_acl(ctx, &fake) != -1;
}

static void reset_per_request_attributes(struct mg_connection *conn) {
  conn->path_info = NULL;
  conn->num_bytes_sent = conn->consumed_content = 0;
  conn->content_len = -1;
  conn->request_len = conn->data_len = 0;
  conn->must_close = 0;
}

static void close_socket_gracefully(SOCKET sock) {
  char buf[BUFSIZ];
  struct linger linger;
  int n;

  // Set linger option to avoid socket hanging out after close. This prevent
  // ephemeral port exhaust problem under high QPS.
  linger.l_onoff = 1;
  linger.l_linger = 1;
  setsockopt(sock, SOL_SOCKET, SO_LINGER, (void *) &linger, sizeof(linger));

  // Send FIN to the client
  (void) shutdown(sock, SHUT_WR);
  set_non_blocking_mode(sock);

  // Read and discard pending data. If we do not do that and close the
  // socket, the data in the send buffer may be discarded. This
  // behaviour is seen on Windows, when client keeps sending data
  // when server decide to close the connection; then when client
  // does recv() it gets no data back.
  do {
    n = pull(NULL, sock, NULL, buf, sizeof(buf));
  } while (n > 0);

  // Now we know that our FIN is ACK-ed, safe to close
  (void) closesocket(sock);
}

static void close_connection(struct mg_connection *conn) {
  if (conn->ssl) {
    SSL_free(conn->ssl);
    conn->ssl = NULL;
  }

  if (conn->client.sock != INVALID_SOCKET) {
    close_socket_gracefully(conn->client.sock);
  }
}

struct mg_connection *mg_connect(struct mg_context *ctx,
                                 const char *host, int port, int use_ssl) {
  struct mg_connection *newconn = NULL;
  struct sockaddr_in sin;
  struct hostent *he;
  int sock;

  if (ctx->ssl_ctx == NULL && use_ssl) {
    cry(fc(ctx), "%s: SSL is not initialized", __func__);
  } else if ((he = gethostbyname(host)) == NULL) {
    cry(fc(ctx), "%s: gethostbyname(%s): %s", __func__, host, strerror(ERRNO));
  } else if ((sock = socket(PF_INET, SOCK_STREAM, 0)) == INVALID_SOCKET) {
    cry(fc(ctx), "%s: socket: %s", __func__, strerror(ERRNO));
  } else {
    sin.sin_family = AF_INET;
    sin.sin_port = htons((uint16_t) port);
    sin.sin_addr = * (struct in_addr *) he->h_addr_list[0];
    if (connect(sock, (struct sockaddr *) &sin, sizeof(sin)) != 0) {
      cry(fc(ctx), "%s: connect(%s:%d): %s", __func__, host, port,
          strerror(ERRNO));
      closesocket(sock);
    } else if ((newconn = (struct mg_connection *)
                calloc(1, sizeof(*newconn))) == NULL) {
      cry(fc(ctx), "%s: calloc: %s", __func__, strerror(ERRNO));
      closesocket(sock);
    } else {
      newconn->client.sock = sock;
      newconn->client.rsa.sin = sin;
      newconn->client.is_ssl = use_ssl;
      if (use_ssl) {
        sslize(newconn, SSL_connect);
      }
    }
  }

  return newconn;
}

FILE *mg_fetch(struct mg_context *ctx, const char *url, const char *path,
               struct mg_request_info *ri) {
  struct mg_connection *newconn;
  int n, req_length, data_length = 0, port = 80;
  char host[1025], proto[10], buf[16384];
  FILE *fp = NULL;

  if (sscanf(url, "%9[htps]://%1024[^:]:%d/%n", proto, host, &port, &n) != 3 &&
      sscanf(url, "%9[htps]://%1024[^/]/%n", proto, host, &n) != 2) {
    cry(fc(ctx), "%s: invalid URL: [%s]", __func__, url);
  } else if ((newconn = mg_connect(ctx, host, port,
                                   !strcmp(proto, "https"))) == NULL) {
    cry(fc(ctx), "%s: mg_connect(%s): %s", __func__, url, strerror(ERRNO));
  } else {
    mg_printf(newconn, "GET /%s HTTP/1.0\r\n\r\n", url + n);
    req_length = read_request(NULL, newconn->client.sock,
                              newconn->ssl, buf, sizeof(buf), &data_length);
    if (req_length <= 0) {
      cry(fc(ctx), "%s(%s): invalid HTTP reply", __func__, url);
    } else if (parse_http_response(buf, req_length, ri) <= 0) {
      cry(fc(ctx), "%s(%s): cannot parse HTTP headers", __func__, url);
    } else if ((fp = fopen(path, "w+b")) == NULL) {
      cry(fc(ctx), "%s: fopen(%s): %s", __func__, path, strerror(ERRNO));
    } else {
      data_length -= req_length;
      memmove(buf, buf + req_length, data_length);
      do {
        if (fwrite(buf, 1, data_length, fp) != (size_t) data_length) {
          fclose(fp);
          fp = NULL;
          break;
        }
        data_length = mg_read(newconn, buf, sizeof(buf));
      } while (data_length > 0);
    }
    close_connection(newconn);
    free(newconn);
  }

  return fp;
}



static void discard_current_request_from_buffer(struct mg_connection *conn) {
  char *buffered;
  int buffered_len, body_len;

  buffered = conn->buf + conn->request_len;
  buffered_len = conn->data_len - conn->request_len;
  assert(buffered_len >= 0);

  if (conn->content_len <= 0) {
    // Protect from negative Content-Length, too
    body_len = 0;
  } else if (conn->content_len < (int64_t) buffered_len) {
    body_len = (int) conn->content_len;
  } else {
    body_len = buffered_len;
  }

  conn->data_len -= conn->request_len + body_len;
  memmove(conn->buf, conn->buf + conn->request_len + body_len,
          (size_t) conn->data_len);
}

static int is_valid_uri(const char *uri) {
  // Conform to http://www.w3.org/Protocols/rfc2616/rfc2616-sec5.html#sec5.1.2
  // URI can be an asterisk (*) or should start with slash.
  return uri[0] == '/' || (uri[0] == '*' && uri[1] == '\0');
}

static void process_new_connection(struct mg_connection *conn) {
  struct mg_request_info *ri = &conn->request_info;
  int keep_alive_enabled;
  const char *cl;

  keep_alive_enabled = !strcmp(conn->ctx->config[ENABLE_KEEP_ALIVE], "yes");

  do {
    reset_per_request_attributes(conn);
    conn->request_len = read_request(NULL, conn->client.sock, conn->ssl,
                                     conn->buf, conn->buf_size,
                                     &conn->data_len);
    assert(conn->data_len >= conn->request_len);
    if (conn->request_len == 0 && conn->data_len == conn->buf_size) {
      send_http_error(conn, 413, "Request Too Large", "");
      return;
    } if (conn->request_len <= 0) {
      return;  // Remote end closed the connection
    }

    if (parse_http_request(conn->buf, conn->buf_size, ri) <= 0 ||
        !is_valid_uri(ri->uri)) {
      // Do not put garbage in the access log, just send it back to the client
      send_http_error(conn, 400, "Bad Request",
          "Cannot parse HTTP request: [%.*s]", conn->data_len, conn->buf);
    } else if (strcmp(ri->http_version, "1.0") &&
               strcmp(ri->http_version, "1.1")) {
      // Request seems valid, but HTTP version is strange
      send_http_error(conn, 505, "HTTP version not supported", "");
      log_access(conn);
    } else {
      // Request is valid, handle it
      cl = get_header(ri, "Content-Length");
      conn->content_len = cl == NULL ? -1 : strtoll(cl, NULL, 10);
      conn->birth_time = time(NULL);
      handle_request(conn);
      call_user(conn, MG_REQUEST_COMPLETE);
      log_access(conn);
      discard_current_request_from_buffer(conn);
    }
    if (ri->remote_user != NULL) {
      free((void *) ri->remote_user);
    }
  } while (conn->ctx->stop_flag == 0 &&
           keep_alive_enabled &&
           should_keep_alive(conn));
}

// Worker threads take accepted socket from the queue
static int consume_socket(struct mg_context *ctx, struct socket *sp) {
  (void) pthread_mutex_lock(&ctx->mutex);
  DEBUG_TRACE(("going idle"));

  // If the queue is empty, wait. We're idle at this point.
  while (ctx->sq_head == ctx->sq_tail && ctx->stop_flag == 0) {
    pthread_cond_wait(&ctx->sq_full, &ctx->mutex);
  }

  // If we're stopping, sq_head may be equal to sq_tail.
  if (ctx->sq_head > ctx->sq_tail) {
    // Copy socket from the queue and increment tail
    *sp = ctx->queue[ctx->sq_tail % ARRAY_SIZE(ctx->queue)];
    ctx->sq_tail++;
    DEBUG_TRACE(("grabbed socket %d, going busy", sp->sock));

    // Wrap pointers if needed
    while (ctx->sq_tail > (int) ARRAY_SIZE(ctx->queue)) {
      ctx->sq_tail -= ARRAY_SIZE(ctx->queue);
      ctx->sq_head -= ARRAY_SIZE(ctx->queue);
    }
  }

  (void) pthread_cond_signal(&ctx->sq_empty);
  (void) pthread_mutex_unlock(&ctx->mutex);

  return !ctx->stop_flag;
}

static void worker_thread(struct mg_context *ctx) {
  struct mg_connection *conn;
  int buf_size = atoi(ctx->config[MAX_REQUEST_SIZE]);

  conn = (struct mg_connection *) calloc(1, sizeof(*conn) + buf_size);
  if (conn == NULL) {
    cry(fc(ctx), "%s", "Cannot create new connection struct, OOM");
    return;
  }
  conn->buf_size = buf_size;
  conn->buf = (char *) (conn + 1);

  // Call consume_socket() even when ctx->stop_flag > 0, to let it signal
  // sq_empty condvar to wake up the master waiting in produce_socket()
  while (consume_socket(ctx, &conn->client)) {
    conn->birth_time = time(NULL);
    conn->ctx = ctx;

    // Fill in IP, port info early so even if SSL setup below fails,
    // error handler would have the corresponding info.
    // Thanks to Johannes Winkelmann for the patch.
    // TODO(lsm): Fix IPv6 case
    conn->request_info.remote_port = ntohs(conn->client.rsa.sin.sin_port);
    memcpy(&conn->request_info.remote_ip,
           &conn->client.rsa.sin.sin_addr.s_addr, 4);
    conn->request_info.remote_ip = ntohl(conn->request_info.remote_ip);
    conn->request_info.is_ssl = conn->client.is_ssl;

    if (!conn->client.is_ssl ||
        (conn->client.is_ssl && sslize(conn, SSL_accept))) {
      process_new_connection(conn);
    }

    close_connection(conn);
  }
  free(conn);

  // Signal master that we're done with connection and exiting
  (void) pthread_mutex_lock(&ctx->mutex);
  ctx->num_threads--;
  (void) pthread_cond_signal(&ctx->cond);
  assert(ctx->num_threads >= 0);
  (void) pthread_mutex_unlock(&ctx->mutex);

  DEBUG_TRACE(("exiting"));
}

// Master thread adds accepted socket to a queue
static void produce_socket(struct mg_context *ctx, const struct socket *sp) {
  (void) pthread_mutex_lock(&ctx->mutex);

  // If the queue is full, wait
  while (ctx->stop_flag == 0 &&
         ctx->sq_head - ctx->sq_tail >= (int) ARRAY_SIZE(ctx->queue)) {
    (void) pthread_cond_wait(&ctx->sq_empty, &ctx->mutex);
  }

  if (ctx->sq_head - ctx->sq_tail < (int) ARRAY_SIZE(ctx->queue)) {
    // Copy socket to the queue and increment head
    ctx->queue[ctx->sq_head % ARRAY_SIZE(ctx->queue)] = *sp;
    ctx->sq_head++;
    DEBUG_TRACE(("queued socket %d", sp->sock));
  }

  (void) pthread_cond_signal(&ctx->sq_full);
  (void) pthread_mutex_unlock(&ctx->mutex);
}

static void accept_new_connection(const struct socket *listener,
                                  struct mg_context *ctx) {
  struct socket accepted;
  char src_addr[20];
  socklen_t len;
  int allowed;

  len = sizeof(accepted.rsa);
  accepted.lsa = listener->lsa;
  accepted.sock = accept(listener->sock, &accepted.rsa.sa, &len);
  if (accepted.sock != INVALID_SOCKET) {
    allowed = check_acl(ctx, &accepted.rsa);
    if (allowed) {
      // Put accepted socket structure into the queue
      DEBUG_TRACE(("accepted socket %d", accepted.sock));
      accepted.is_ssl = listener->is_ssl;
      produce_socket(ctx, &accepted);
    } else {
      sockaddr_to_string(src_addr, sizeof(src_addr), &accepted.rsa);
      cry(fc(ctx), "%s: %s is not allowed to connect", __func__, src_addr);
      (void) closesocket(accepted.sock);
    }
  }
}

static void master_thread(struct mg_context *ctx) {
  fd_set read_set;
  struct timeval tv;
  struct socket *sp;
  int max_fd;

  // Increase priority of the master thread
#if defined(_WIN32)
  SetThreadPriority(GetCurrentThread(), THREAD_PRIORITY_ABOVE_NORMAL);
#endif
  
#if defined(ISSUE_317)
  struct sched_param sched_param;
  sched_param.sched_priority = sched_get_priority_max(SCHED_RR);
  pthread_setschedparam(pthread_self(), SCHED_RR, &sched_param);
#endif

  while (ctx->stop_flag == 0) {
    FD_ZERO(&read_set);
    max_fd = -1;

    // Add listening sockets to the read set
    for (sp = ctx->listening_sockets; sp != NULL; sp = sp->next) {
      add_to_set(sp->sock, &read_set, &max_fd);
    }

    tv.tv_sec = 0;
    tv.tv_usec = 200 * 1000;

    if (select(max_fd + 1, &read_set, NULL, NULL, &tv) < 0) {
#ifdef _WIN32
      // On windows, if read_set and write_set are empty,
      // select() returns "Invalid parameter" error
      // (at least on my Windows XP Pro). So in this case, we sleep here.
      mg_sleep(1000);
#endif // _WIN32
    } else {
      for (sp = ctx->listening_sockets; sp != NULL; sp = sp->next) {
        if (ctx->stop_flag == 0 && FD_ISSET(sp->sock, &read_set)) {
          accept_new_connection(sp, ctx);
        }
      }
    }
  }
  DEBUG_TRACE(("stopping workers"));

  // Stop signal received: somebody called mg_stop. Quit.
  close_all_listening_sockets(ctx);

  // Wakeup workers that are waiting for connections to handle.
  pthread_cond_broadcast(&ctx->sq_full);

  // Wait until all threads finish
  (void) pthread_mutex_lock(&ctx->mutex);
  while (ctx->num_threads > 0) {
    (void) pthread_cond_wait(&ctx->cond, &ctx->mutex);
  }
  (void) pthread_mutex_unlock(&ctx->mutex);

  // All threads exited, no sync is needed. Destroy mutex and condvars
  (void) pthread_mutex_destroy(&ctx->mutex);
  (void) pthread_cond_destroy(&ctx->cond);
  (void) pthread_cond_destroy(&ctx->sq_empty);
  (void) pthread_cond_destroy(&ctx->sq_full);

#if !defined(NO_SSL)
  uninitialize_ssl(ctx);
#endif

  // Signal mg_stop() that we're done
  ctx->stop_flag = 2;

  DEBUG_TRACE(("exiting"));
}

static void free_context(struct mg_context *ctx) {
  int i;

  // Deallocate config parameters
  for (i = 0; i < NUM_OPTIONS; i++) {
    if (ctx->config[i] != NULL)
      free(ctx->config[i]);
  }

  // Deallocate SSL context
  if (ctx->ssl_ctx != NULL) {
    SSL_CTX_free(ctx->ssl_ctx);
  }
#ifndef NO_SSL
  if (ssl_mutexes != NULL) {
    free(ssl_mutexes);
  }
#endif // !NO_SSL

  // Deallocate context itself
  free(ctx);
}

void mg_stop(struct mg_context *ctx) {
  ctx->stop_flag = 1;

  // Wait until mg_fini() stops
  while (ctx->stop_flag != 2) {
    mg_sleep(10);
  }
  free_context(ctx);

#if defined(_WIN32) && !defined(__SYMBIAN32__)
  (void) WSACleanup();
#endif // _WIN32
}

struct mg_context *mg_start(mg_callback_t user_callback, void *user_data,
                            const char **options) {
  struct mg_context *ctx;
  const char *name, *value, *default_value;
  int i;

#if defined(_WIN32) && !defined(__SYMBIAN32__)
  WSADATA data;
  WSAStartup(MAKEWORD(2,2), &data);
  InitializeCriticalSection(&global_log_file_lock);
#endif // _WIN32

  // Allocate context and initialize reasonable general case defaults.
  // TODO(lsm): do proper error handling here.
  ctx = (struct mg_context *) calloc(1, sizeof(*ctx));
  ctx->user_callback = user_callback;
  ctx->user_data = user_data;

  while (options && (name = *options++) != NULL) {
    if ((i = get_option_index(name)) == -1) {
      cry(fc(ctx), "Invalid option: %s", name);
      free_context(ctx);
      return NULL;
    } else if ((value = *options++) == NULL) {
      cry(fc(ctx), "%s: option value cannot be NULL", name);
      free_context(ctx);
      return NULL;
    }
    if (ctx->config[i] != NULL) {
      cry(fc(ctx), "%s: duplicate option", name);
    }
    ctx->config[i] = mg_strdup(value);
    DEBUG_TRACE(("[%s] -> [%s]", name, value));
  }

  // Set default value if needed
  for (i = 0; config_options[i * ENTRIES_PER_CONFIG_OPTION] != NULL; i++) {
    default_value = config_options[i * ENTRIES_PER_CONFIG_OPTION + 2];
    if (ctx->config[i] == NULL && default_value != NULL) {
      ctx->config[i] = mg_strdup(default_value);
      DEBUG_TRACE(("Setting default: [%s] -> [%s]",
                   config_options[i * ENTRIES_PER_CONFIG_OPTION + 1],
                   default_value));
    }
  }

  // NOTE(lsm): order is important here. SSL certificates must
  // be initialized before listening ports. UID must be set last.
  if (!set_gpass_option(ctx) ||
#if !defined(NO_SSL)
      !set_ssl_option(ctx) ||
#endif
      !set_ports_option(ctx) ||
#if !defined(_WIN32)
      !set_uid_option(ctx) ||
#endif
      !set_acl_option(ctx)) {
    free_context(ctx);
    return NULL;
  }

#if !defined(_WIN32) && !defined(__SYMBIAN32__)
  // Ignore SIGPIPE signal, so if browser cancels the request, it
  // won't kill the whole process.
  (void) signal(SIGPIPE, SIG_IGN);
  // Also ignoring SIGCHLD to let the OS to reap zombies properly.
  (void) signal(SIGCHLD, SIG_IGN);
#endif // !_WIN32

  (void) pthread_mutex_init(&ctx->mutex, NULL);
  (void) pthread_cond_init(&ctx->cond, NULL);
  (void) pthread_cond_init(&ctx->sq_empty, NULL);
  (void) pthread_cond_init(&ctx->sq_full, NULL);

  // Start master (listening) thread
  mg_start_thread((mg_thread_func_t) master_thread, ctx);

  // Start worker threads
  for (i = 0; i < atoi(ctx->config[NUM_THREADS]); i++) {
    if (mg_start_thread((mg_thread_func_t) worker_thread, ctx) != 0) {
      cry(fc(ctx), "Cannot start worker thread: %d", ERRNO);
    } else {
      ctx->num_threads++;
    }
  }

  return ctx;
}