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Re: multi interface proxy issue

From: Daniel Stenberg <>
Date: Fri, 23 May 2014 22:46:02 +0200 (CEST)

On Wed, 21 May 2014, Thomas Herchek wrote:

> One of our customers is having an issue traversing an HTTP authenticated
> proxy using our application. We are using libcurl 7.33.0 and specify
> CURL_AUTH_ANY for proxy authentication.

So this is just a problem that happens for that particular user and not
something you can otherwise repeat?

> Our application uses both the multi and non-multi libcurl interfaces. The
> code that does not use the multi interface has no problem authenticating to
> the proxy and reaching the Internet. From the logs I can see it is using
> NTLM for the auth. But the code that uses the multi interface just hangs
> for 30 minutes when traversing the proxy before timing out. The customer is
> using a Forefront TMG proxy.

We did have a few of those bugs before. The strange thing is that already with
7.33.0 the easy interface code uses the multi interface internally, so the
curl_easy_perform is just a wrapper wround multi code, meaning both interfaces
run almost the exact same code.

I'd be interesting to see if a later version also have this problem but I
realize it might not be that easy for you to just test run the latest version
at your customer's place.

> I see there is Known Bug 65 that says “libcurl will fail if the (passive)
> TCP connection for the data transfer isn’t more or less instant because it
> doesn’t wait for a connect confirmation”. Is that the likely issue?

No. I don't even think that KNOWN_BUG is still present. The test 564 which is
mentioned there also works fine...

> Do you have any debugging suggestions or work arounds?

1) Figure out exactly in which condition it hangs and why
2) Run the latest libcurl version
3) Try to force the problem to happen to allow debugging


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Received on 2014-05-23