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This queue is for tickets about the libwww-perl CPAN distribution.

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Id: 82408
Status: resolved
Priority: 0/
Queue: libwww-perl

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Owner: Nobody in particular
Requestors: zefram [...] fysh.org
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Subject: pipelined response deadlock
Date: Fri, 4 Jan 2013 15:21:08 +0000
To: bug-libwww-perl [...] rt.cpan.org
From: Zefram <zefram [...] fysh.org>
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LWP::Protocol::http has some logic to abort sending a request body if it's received the entire response header already. It assumes that the server has a complete response that doesn't depend on any part of the request body. It breaks if the server is only able to send the headers early and will need to see the request body in order to generate the response body. Obviously that's an unusual condition. RFC 2616 doesn't explicitly address this form of pipelining, but section 8.1.1 does say "HTTP requests and responses can be pipelined on a connection", which could be construed as general permission. The failure mode is somewhat nasty: because LWP just stops sending data, and doesn't close that half of the connection, the server and LWP are liable to wait for each other indefinitely. This failure actually arises, subject to a race condition, in the test suite for mod_perl. Attached patch fixes, trivially, by dropping that branch of the code. Note that the similar logic to abort if the server closes the connection remains. That will presumably take effect in many of the situations that the removed logic was trying to address. -zefram
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