Add missing functions for wolfssl integration #583

WolfSSL´s OpenSSL emulation misses some functions.
For details see https://github.com/civetweb/civetweb/issues/583

src/civetweb.c

@@ -1586,6 +1586,13 @@ typedef struct SSL_CTX SSL_CTX;
 #include <openssl/dh.h>
 #include <openssl/bn.h>
 #include <openssl/opensslv.h>
+
+#ifdef WOLFSSL_VERSION
+/* Additional defines for WolfSSL, see
+ * https://github.com/civetweb/civetweb/issues/583 */
+#include "wolfssl_extras.inl"
+#endif
+
 #else
 
 /* SSL loaded dynamically from DLL.

src/wolfssl_extras.inl

@@ -0,0 +1,77 @@
+/* Additional defines for WolfSSL, see
+ * https://github.com/civetweb/civetweb/issues/583 */
+
+
+/* Required for WOLFSSL_X509 */
+#include <openssl/../internal.h>
+
+
+#define i2d_X509 cw_i2d_X509
+#define EVP_Digest cw_EVP_Digest
+
+
+/* i2d_X509 has no valid implementation in wolfssl
+ *
+ * The letters i and d in for example i2d_X509 stand for "internal" (that is an
+ *internal C structure)
+ * and " DER ". So that i2d_X509 converts from internal to DER.
+ *
+ * For OpenSSL 0.9.7 and later if *out is NULL memory will be allocated for a
+ *buffer and the encoded
+ * data written to it. In this case *out is not incremented and it points to the
+ *start of the data
+ * just written.
+ */
+int
+cw_i2d_X509(struct WOLFSSL_X509 *x, unsigned char **out)
+{
+	if (!x || !x->derCert) {
+		return -1;
+	}
+
+	const int ret = (int)x->derCert->length;
+
+	if (out && (ret > 0)) {
+		if (*out == NULL) {
+			*out = mg_malloc(ret);
+		}
+		if (*out != NULL) {
+			memcpy(*out, x->derCert->buffer, ret);
+		}
+	}
+
+	return ret;
+}
+
+
+/* EVP_Digest not in wolfssl */
+int
+cw_EVP_Digest(const void *data,
+              size_t count,
+              unsigned char *md,
+              unsigned int *size,
+              const EVP_MD *type,
+              ENGINE *impl)
+{
+	EVP_MD_CTX *ctx = EVP_MD_CTX_new();
+	int ret;
+
+	if (ctx == NULL)
+		return 0;
+
+	/* EVP_MD_CTX_set_flags(ctx, EVP_MD_CTX_FLAG_ONESHOT); */
+	ret = EVP_DigestInit_ex(ctx, type, impl)
+	      && EVP_DigestUpdate(ctx, data, count)
+	      && EVP_DigestFinal_ex(ctx, md, size);
+	EVP_MD_CTX_free(ctx);
+
+	return ret;
+}
+
+
+/*
+ * the variable SSL_OP_NO_TLSv1_1 is not defined within the context of
+ * wolfssl but since the methods using the value are all stubs, we can
+ * define it arbitrarily and it will not have any consequences
+ */
+#define SSL_OP_NO_TLSv1_1 (0x10000000L)