Mark Eichin submitted bug report #1480821

(http://curl.haxx.se/bug/view.cgi?id=1480821) He found and identified a
problem with how libcurl dealt with GnuTLS and a case where gnutls returned
GNUTLS_E_AGAIN indicating it would block. It would then return an unexpected
return code, making Curl_ssl_send() confuse the upper layer - causing random
28 bytes trash data to get inserted in the transfered stream.

The proper fix was to make the Curl_gtls_send() function return the proper
return codes that the callers would expect. The Curl_ossl_send() function
already did this.

lib/gtls.c

@@ -458,6 +458,12 @@ int Curl_gtls_send(struct connectdata *conn,
   int rc;
   rc = gnutls_record_send(conn->ssl[sockindex].session, mem, len);
 
+  if(rc < 0 ) {
+    if(rc == GNUTLS_E_AGAIN)
+      return 0; /* EWOULDBLOCK equivalent */
+    rc = -1; /* generic error code for send failure */
+  }
+
   return rc;
 }