[Patches] [ python-Patches-900744 ] catch invalid chunk length in httplib read routine

Tue Mar 13 22:47:22 CET 2007

Patches item #900744, was opened at 2004-02-19 23:14
Message generated for change (Comment added) made by gbrandl
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Category: Library (Lib)
Group: Python 2.5
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Wummel (calvin)
Assigned to: Georg Brandl (gbrandl)
Summary: catch invalid chunk length in httplib read routine

Initial Comment:
In HTTPResponse._read_chunked the chunk length is not
checked to be a valid integer, and a ValueError will be
raised in such a case.
The attached patch catches ValueError (which should not
normally happen, so this try:except: is reasonably
fast), and raises IncompleteRead exception instead.
I have no test case for this yet, but am trying to
construct one :)

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>Comment By: Georg Brandl (gbrandl)
Date: 2007-03-13 21:47

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See also #1486335.

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Comment By: Martin v. Löwis (loewis)
Date: 2007-02-19 16:05

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I meant to suggest that your patch (based on agwego's recommendation)
should be accepted. Now that you ask, I'm not so sure anymore: errors
should never pass silently.

So I now think, that it should raise IncompleteRead, based also on the
observation that these methods can *already* raise IncompleteRead, and that
this already carries the data that we received.

OTOH, IIUC, the error also means that we lost protocol synchronisation
with the server, so we should in any case close the connection. So merging
these changes is probably the right thing :-) Withdrawing my acceptance
again, and hoping that somebody can produce a complete patch (which
includes the test case in a style that works with regrtest)

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Comment By: Georg Brandl (gbrandl)
Date: 2007-02-19 12:10

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Martin: which patch? Mine, which returns what was read so far, or
calvin's, which raises IncompleteRead?

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Comment By: Martin v. Löwis (loewis)
Date: 2007-02-18 08:39

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Georg, the patch is fine for 2.6, please apply (for 2.5, I would be
cautious because of the behaviour change).

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Comment By: Wummel (calvin)
Date: 2006-02-01 22:16

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I attached a simple testcase that triggers the bug. IMHO
this patch should be applied for Python 2.5.

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Comment By: Raymond Hettinger (rhettinger)
Date: 2005-07-19 01:07

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Technically, the patch is fine and it is the way the code
should have been written in the first place.

Please bring-up on python-dev to determine whether it should
be done.  I can imagine that a fair amount of existing code
has through trial and error discovered the ValueError and
chosen to catch that.  Changing the exception may
unnecessarily break people's code.  Sometimes we  take that
step when it needs to be done, but there should be a good
pay-off and, in this case, I don't see it.

You may also want to mention it on comp.lang.python to see
if anyone cares

If the patch goes forward, see if you can mock-up a test
that triggers the exception so we have a good unittest.

In anycase, this should not be backported (we avoid giving
people reasons to not upgrade).

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Comment By: Georg Brandl (birkenfeld)
Date: 2005-07-18 19:34

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Attaching patch which does what agwego said
(httplib-chunked.diff).

Please review.

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Comment By: agwego (agwego)
Date: 2005-02-28 16:53

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I've run into this problem in conjunction with mod_python
3.1.4 (and although the problem is caused in mod_python) my
python skills aren't up to the task. Which leaves me with
fixing httplib. Although the above patch works when it comes
to end of file situations, I think it would be better to
return what has been consumed so far and leave it at that. A
few lines down there's a comment about consuming trailers,
this is the case that is tripping up httplib as far as I can
tell. This is happening in Python 2.3.4.

--- packages/Python-2.3.4/Lib/httplib.py        Sun Nov  2
11:51:38 2003
+++ httplib.py  Mon Feb 28 11:26:48 2005
@@ -423,7 +423,11 @@
                 i = line.find(';')
                 if i >= 0:
                     line = line[:i] # strip chunk-extensions
-                chunk_left = int(line, 16)
+                try:
+                    chunk_left = int(line, 16)
+                except ValueError, msg:
+                    self.close()
+                    return value
                 if chunk_left == 0:
                     break
             if amt is None:




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