Re: Fix potential hang in https handshake.

From: Jeff King <peff@peff.net>
Date: Oct 19, 2012, 20:27 UTC
Message-ID: <20121019202723.GA24184@sigill.intra.peff.net>
In-Reply-To: <CAJo=hJvWV0WPN5rCYK-JxfaEPWp7syUM1H0w4=Eb27=50+pXjg@mail.gmail.com>

On Fri, Oct 19, 2012 at 07:10:46AM -0700, Shawn O. Pearce wrote:

Show 9 quoted lines

> > IOW, it seems like we are _already_ following the advice referenced in
> > curl's manpage. Is there some case I am missing? Confused...
> 
> The issue with the current code is sometimes when libcurl is opening a
> CONNECT style connection through an HTTP proxy it returns a crazy high
> timeout (>240 seconds) and no fds. In this case Git waits forever.
> Stefan observed that using a timeout of 50 ms in this situation to
> poll libcurl is better, as it figures out a lot more quickly that it
> is connected to the proxy and can issue the request.

Ah. That sounds like a bug in curl to me. But either way, if we want to work around it, wouldn't the right thing be to override curl's timeout in that instance? Like:

diff --git a/http.c b/http.c
index df9bb71..cd07cdf 100644
--- a/http.c
+++ b/http.c
@@ -631,6 +631,19 @@ void run_active_slot(struct active_request_slot *slot)
 			FD_ZERO(&excfds);
 			curl_multi_fdset(curlm, &readfds, &writefds, &excfds, &max_fd);
 
+			/*
+			 * Sometimes curl will give a really long timeout for a
+			 * CONNECT when there are no fds to read, but we can
+			 * get better results by running curl_multi_perform
+			 * more frequently.
+			 */
+			if (maxfd < 0 &&
+			    (select_timeout.tv_sec > 0 ||
+			     select_timeout.tv_usec > 50000)) {
+				select_timeout.tv_sec = 0;
+				select_timeout.tv_usec = 50000;
+			}
+
 			select(max_fd+1, &readfds, &writefds, &excfds, &select_timeout);
 		}
 	}

-Peff