[ python-Bugs-1411097 ] httplib patch to make _read_chunked() more robust

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Mon Feb 6 02:24:58 CET 2006


Bugs item #1411097, was opened at 2006-01-20 20:26
Message generated for change (Comment added) made by jjlee
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Category: Python Library
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: John J Lee (jjlee)
Assigned to: Nobody/Anonymous (nobody)
Summary: httplib patch to make _read_chunked() more robust

Initial Comment:
To reproduce:

import urllib2
print urllib2.urlopen("http://66.117.37.13/").read()


The attached patch "fixes" the hang, but that patch is
not acceptable because it also removes the .readline()
and .readlines() methods on the response object
returned by urllib2.urlopen().

The patch seems to demonstrate that the problem is
caused by the (ab)use of socket._fileobject in
urllib2.AbstractHTTPHandler (I believe this hack was
introduced when urllib2 switched to using
httplib.HTTPConnection).

Not sure yet what the actual problem is...


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>Comment By: John J Lee (jjlee)
Date: 2006-02-06 01:24

Message:
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Oops, fixed chunk.patch to .strip() before comparing to "".

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Comment By: John J Lee (jjlee)
Date: 2006-02-06 00:38

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First, expanding a bit on what I wrote on 2006-01-21: The
problem does relate to chunked encoding, and is unrelated to
urllib2's use of _fileobject.  My hack to remove use of
socket._fileobject from urllib2 merely breaks handling of
chunked encoding by cutting httplib.HTTPResponse out of the
picture.  The problem is seen in urllib2 in recent Pythons
thanks to urllib2 switching to use of httplib.HTTPConnection
and HTTP/1.1, hence chunked encoding is allowed.  urllib
still uses httplib.HTTP, hence HTTP/1.0, so is unaffected.
To reproduce with httplib:
import httplib
conn = httplib.HTTPConnection("66.117.37.13")
conn.request("GET", "/", headers={"Connection": "close"})
r1 = conn.getresponse()
print r1.read()
The Connection: close is required -- if it's not there the
server doesn't use chunked transfer-encoding.
I verified with a packet sniffer that the problem is that
this server does not send the final trailing CRLF required
by section 3.6.1 of RFC 2616.  However, that section also
says that trailers (trailing HTTP headers) MUST NOT be sent
by the server unless either a TE header was present and
indicated that trailers are acceptable (httplib does not
send the TE header), or the trailers are optional metadata
and may be discarded by the client.  So, I propose the
attached patch to httplib (chunk.patch) as a work-around.


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Comment By: John J Lee (jjlee)
Date: 2006-01-21 22:10

Message:
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In fact the commit message for rev 36871 states the real
reason _fileobject is used (handling chunked encoding),
showing my workaround is even more harmful than I thought. 
Moreover, doing a urlopen on 66.117.37.13 shows the response
*is* chunked.

The problem seems to be caused by httplib failing to find a
CRLF at the end of the chunked response, so the loop at the
end of _read_chunked() never terminates.  Haven't looked in
detail yet, but I'm guessing a) it's the server's fault and
b) httplib should work around it.


Here's the commit message from 36871:


Fix urllib2.urlopen() handling of chunked content encoding.

The change to use the newer httplib interface admitted the
possibility
that we'd get an HTTP/1.1 chunked response, but the code
didn't handle
it correctly.  The raw socket object can't be pass to
addinfourl(),
because it would read the undecoded response.  Instead,
addinfourl()
must call HTTPResponse.read(), which will handle the decoding.

One extra wrinkle is that the HTTPReponse object can't be
passed to
addinfourl() either, because it doesn't implement readline() or
readlines().  As a quick hack, use socket._fileobject(), which
implements those methods on top of a read buffer. 
(suggested by mwh)

Finally, add some tests based on test_urllibnet.

Thanks to Andrew Sawyers for originally reporting the
chunked problem.


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