civetweb/examples/websocket.c

// Copyright (c) 2004-2012 Sergey Lyubka
// This file is a part of mongoose project, http://github.com/valenok/mongoose

#include <stdio.h>
#include <string.h>
#include "mongoose.h"

static void *callback(enum mg_event event, struct mg_connection *conn) {
  if (event == MG_WEBSOCKET_READY) {
    unsigned char buf[40];
    buf[0] = 0x81;
    buf[1] = snprintf((char *) buf + 2, sizeof(buf) - 2, "%s", "server ready");
    mg_write(conn, buf, 2 + buf[1]);
    return "";  // MG_WEBSOCKET_READY return value is ignored
  } else if (event == MG_WEBSOCKET_MESSAGE) {
    unsigned char buf[200], reply[200];
    int n, i, mask_len, xor, msg_len, len;

    // Read message from the client.
    // Accept only small (<126 bytes) messages.
    len = 0;
    msg_len = mask_len = 0;
    for (;;) {
      if ((n = mg_read(conn, buf + len, sizeof(buf) - len)) <= 0) {
        return "";  // Read error, close websocket
      }
      len += n;
      if (len >= 2) {
        msg_len = buf[1] & 127;
        mask_len = (buf[1] & 128) ? 4 : 0;
        if (msg_len > 125) {
          return ""; // Message is too long, close websocket
        }
        // If we've buffered the whole message, exit the loop
        if (len >= 2 + mask_len + msg_len) {
          break;
        }
      }
    }

    // Prepare frame
    reply[0] = 0x81;  // text, FIN set
    reply[1] = msg_len;

    // Copy message from request to reply, applying the mask if required.
    for (i = 0; i < msg_len; i++) {
      xor = mask_len == 0 ? 0 : buf[2 + (i % 4)];
      reply[i + 2] = buf[i + 2 + mask_len] ^ xor;
    }

    // Echo the message back to the client
    mg_write(conn, reply, 2 + msg_len);

    // Return non-NULL means stoping websocket conversation.
    // Close the conversation if client has sent us "exit" string.
    return memcmp(reply + 2, "exit", 4) == 0 ? "" : NULL;
  } else {
    return NULL;
  }
}

int main(void) {
  struct mg_context *ctx;
  const char *options[] = {
    "listening_ports", "8080",
    "document_root", "websocket_html_root",
    NULL
  };

  ctx = mg_start(&callback, NULL, options);
  getchar();  // Wait until user hits "enter"
  mg_stop(ctx);

  return 0;
}