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RE: cURL on Windows with _WIN32_WINNT=0x0600 suffers from WSAPoll bug

From: Jan Koen Annot <>
Date: Fri, 3 Aug 2012 08:15:16 +0000

On Wednesday, August 01, 2012, Daniel Stenberg wrote:

> Is there any official documentation or recognition of this flaw somewhere? A
> question from 2008 in a forum post is not the most comforting source.

On August 1, I opened a case for this to Microsoft Premier Online (
The support engineer handling my case wrote that the case description is quite clear.
He will try to reproduce the issue and then proceed with troubleshooting it.

> What's your suggested fix?

1. For a user of the cURL library on Windows: do not use _WIN32_WINNT=0x0600, but use _WIN32_WINNT=0x0502.
2. For the developers of the cURL library:
        2.1 Remove the usage of WSAPoll (see file select.h of the curl library source code; I am using curl-7.26.0)
        2.2 Work around the bug in WSAPoll, for example by using short timeouts only and calling getsockopt(SO_ERROR) explicitly for sockets for which WSAPoll doesn't signal activity.
3. For Microsoft: repair the bug and publish an update to be installed

Jan Koen Annot

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Received on 2012-08-03