On Thu, 16 Feb 2017, Philippe Daouadi wrote:

I am using curl multi with a boost asio backend. On windows only, when I open a connection that's supposed to be refused (my test connects to, curl never signals me that the socket couldn't connect.

It seems to work for me on Linux. When we build curl debug-enabled, it also builds a version of the main loop that uses the event-based system internally and I can then try that URL like this:

  $ ./src/curl --test-event
  curl: (7) Failed to connect to port 1: Connection refused

I am not sure where the bug is, but I think it is in curl. From what I saw in curl's code, curl does an asychronous connect() and sets a timer (through the multi's timer callback) to 200ms.

That's the happy eyeballs timeout. It is not really there to detect connect problems per se, but sure it should make you call libcurl again after 200 ms.

After those 200ms, curl checks that the socket is indeed connected (CURLM_STATE_WAITCONNECT in multi_runsingle() in multi.c),

The state machine will stay in that state until a connect is verified or failed, so yes. But for a failed connect, the socket should get a signal too and the regular "monitoring" of the socket should get triggered, libcurl should get called again and the failed connection attempt get noticed.

and for some reason windows doesn't return the "connection refused" error yet. Then nothing more happens, curl doesn't set a new timer to check the connection again. In the end, the timeout set on the request (if there is one) triggers and we get a connection timeout error.

Yeah, there's actually an internal "max time limit" for connections (300 seconds), but for some reason this isn't set to an actual timer! (There's a historical reason for that, but we should probably fix it.)

What I don't understand is why you need a timeout. The failed connection should get noticed on the socket descriptor itself. That's the actual reason for this problem.


 / daniel.haxx.se
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