Bugs item #2080222, was opened at 2008-08-28 10:45
Message generated for change (Comment added) made by bagder
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Category: http
Group: bad behaviour
Status: Open
Resolution: None
Priority: 6
Private: No
Submitted By: vila-sf (vila-sf)
Assigned to: Daniel Stenberg (bagder)
Summary: race condition while POSTing to HTTP/1.0 servers

Initial Comment:
As explained at https://bugs.launchpad.net/bzr/+bug/225020, it seems that in rare occurrences curl/libcurl try to send the body of a POST request while the server has already sent a 403 response.

The version used is:
curl 7.18.0 (i486-pc-linux-gnu) libcurl/7.18.0 OpenSSL/0.9.8g zlib/1.2.3.3 libidn/1.1 on ubuntu hardy.

It occurs rarely and only with HTTP/1.0 servers.

It has been mentioned that a change in socket behaviour in the kernel may be provoking this bug.

The link above provides a wireshark capture of the transaction.

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>Comment By: Daniel Stenberg (bagder)
Date: 2008-08-29 10:48

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There have been other POST-related issues fixed since 7.18.0 so I would
rather argue that you should run at least 7.18.2. But that said, it's easy
to adapt the patch for 7.18.0:

--- transfer.c~ 2008-01-16 13:24:00.000000000 +0100
+++ transfer.c 2008-08-29 10:46:14.000000000 +0200
@@ -1396,6 +1396,16 @@

       } while(data_pending(conn));

+ if(((k->keepon & (KEEP_READ|KEEP_WRITE)) == KEEP_WRITE) &&
+ conn->bits.close ) {
+ /* When we've read the entire thing and the close bit is set,
the
+ server may now close the connection. If there's now any kind
of
+ sending going on from our side, we need to stop that
+ immediately. */
+ infof(data, "we are done reading and this is set to close, stop
send\n");
+ k->keepon &= ~KEEP_WRITE; /* no writing anymore either */
+ }
+
     } /* if( read from socket ) */

     /* If we still have writing to do, we check if we have a writable

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Comment By: vila-sf (vila-sf)
Date: 2008-08-29 10:32

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I have version 7-18.0 here and I would like to validate your patch since I
have a test suite to exercise it against.

Unfortunately the patch doesn't apply cleanly :-/

Could you provide a patch against:

 * $Id: transfer.c,v 1.381 2008-01-16 12:24:00 bagder Exp $

In this file, there is a single occurrence of 'while(data_pending(conn));'
but the following line is not 'return CURLE_OK;', not at all :-/

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Comment By: Daniel Stenberg (bagder)
Date: 2008-08-28 13:00

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Here's my first shot. This is a diff against current CVS but I think it
can be adjusted to older libcurls fairly easy:

--- lib/transfer.c 26 Aug 2008 21:28:57 -0000 1.404
+++ lib/transfer.c 28 Aug 2008 11:00:09 -0000
@@ -656,6 +656,15 @@

   } while(data_pending(conn));

+ if(((k->keepon & (KEEP_READ|KEEP_WRITE)) == KEEP_WRITE) &&
+ conn->bits.close ) {
+ /* When we've read the entire thing and the close bit is set, the
server may
+ now close the connection. If there's now any kind of sending going
on from
+ our side, we need to stop that immediately. */
+ infof(data, "we are done reading and this is set to close, stop
send\n");
+ k->keepon &= ~KEEP_WRITE; /* no writing anymore either */
+ }
+
   return CURLE_OK;
 }

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Comment By: Daniel Stenberg (bagder)
Date: 2008-08-28 11:44

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I've now (locally) modified the curl test suite so that I was possible to
write up a test case that repeats this behavior. I'll now see what I can do
to make it behave...

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Comment By: vila-sf (vila-sf)
Date: 2008-08-28 11:29

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I can confirm that if curl wasn't trying to send the body when a 403
response has been received, it will indeed fix my use case. Thanks to
badger for linking to the other bug.

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Comment By: Daniel Stenberg (bagder)
Date: 2008-08-28 10:58

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This looks related to the previous mentions of libcurl not properly
stopping the sending when 400+ codes are received:

http://curl.haxx.se/mail/archive-2008-08/0138.html

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Received on 2008-08-29