- Michael Goffioul filed bug report #2107377 "Problem with mutli + GnuTLS +

proxy" (http://curl.haxx.se/bug/view.cgi?id=2107377) that showed how a multi
  interface using program didn't work when built with GnuTLS and a CONNECT
  request was done over a proxy (basically test 502 over a proxy to a HTTPS
  site). It turned out the ssl connect function would get called twice which
  caused the second call to fail.

CHANGES

@@ -6,6 +6,14 @@
 
                                   Changelog
 
+Daniel Stenberg (22 Sep 2008)
+- Michael Goffioul filed bug report #2107377 "Problem with mutli + GnuTLS +
+  proxy" (http://curl.haxx.se/bug/view.cgi?id=2107377) that showed how a multi
+  interface using program didn't work when built with GnuTLS and a CONNECT
+  request was done over a proxy (basically test 502 over a proxy to a HTTPS
+  site). It turned out the ssl connect function would get called twice which
+  caused the second call to fail.
+
 Daniel Fandrich (22 Sep 2008)
 - Fixed test 539 to handle an out of memory condition that shows up now
   that memdebug.h is included in the test programs.

RELEASE-NOTES

@@ -22,6 +22,7 @@ This release includes the following bugfixes:
  o cookie with invalid expire dates are now considered expired
  o HTTP pipelining over proxy
  o fix regression in configure script which affected OpenSSL builds on MSYS
+ o GnuTLS-based multi interface doing HTTPS over proxy failed
 
 This release includes the following known bugs:
 
@@ -36,6 +37,6 @@ advice from friends like these:
 
  Keith Mok, Yang Tse, Daniel Fandrich, Guenter Knauf, Dmitriy Sergeyev,
  Linus Nielsen Feltzing, Martin Drasar, Stefan Krause, Dmitry Kurochkin,
- Mike Revi, Andres Garcia
+ Mike Revi, Andres Garcia, Michael Goffioul
 
         Thanks! (and sorry if I forgot to mention someone)

lib/http.c

@@ -1814,6 +1814,13 @@ static CURLcode https_connecting(struct connectdata *conn, bool *done)
   CURLcode result;
   DEBUGASSERT((conn) && (conn->protocol & PROT_HTTPS));
 
+  if(conn->ssl[FIRSTSOCKET].use) {
+    /* in some circumstances, this already has SSL enabled and then we don't
+       need to connect SSL again */
+    *done = TRUE;
+    return CURLE_OK;
+  }
+
   /* perform SSL initialization for this socket */
   result = Curl_ssl_connect_nonblocking(conn, FIRSTSOCKET, done);
   if(result) {