New submission from Cory Benfield:
Initially reported on the requests bug list at
https://github.com/kennethreitz/requests/issues/2467
In cases when a remote web server sends a non-chunked response that does not
have a content length, it is possible to get http.client to hang on a read. To
hit it requires a specific set of circumstances:
- Python 3 (this bug is not seen on Python 2 in my testing)
- HTTPS (using plaintext HTTP resolves the problem)
- A socket timeout must be set (leaving it unset, i.e. leaving the socket in
blocking mode, resolves this problem)
- The server must not send a content-length or set Transfer-Coding: chunked.
- The reads must not be an even divisor of the content's length.
- The timeout must be longer than the time the server is willing to keep the
connection open (otherwise an exception is thrown).
The following code can be used as a sample to demonstrate the bug:
import http.client
import time
def test(connection_class=http.client.HTTPSConnection, timeout=10, read_size=7):
start = time.time()
c = connection_class('sleepy-reaches-6892.herokuapp.com')
c.connect()
if timeout is not None:
c.sock.settimeout(timeout)
c.request('GET', '/test')
r = c.getresponse()
while True:
data = r.read(read_size)
if not data:
break
print('Finished in {}'.format(time.time() - start))
Below are the results from several different runs:
test(): Finished in 4.8294830322265625
test(connection_class=http.client.HTTPConnection): Finished in
0.3060309886932373
test(timeout=None): Finished in 0.6070599555969238
test(read_size=2): Finished in 0.6600658893585205
As you can see, only this particular set of features causes the bug. Note that
if you change the URL to one that does return a Content-Length (e.g.
http2bin.org/get), this bug also goes away.
This is a really weird edge case bug. There's some extensive investigation over
at the requests bug report, but I've not been able to convincingly point at the
problem yet.
----------
components: Library (Lib)
messages: 237151
nosy: Lukasa
priority: normal
severity: normal
status: open
title: HTTPS reads can block when content length not available and timeout set.
versions: Python 3.4
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Python tracker <[email protected]>
<http://bugs.python.org/issue23576>
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