Read timeout using either urllib2 or any other http library
Solution 1:
It's not possible for any library to do this without using some kind of asynchronous timer through threads or otherwise. The reason is that the timeout
parameter used in httplib
, urllib2
and other libraries sets the timeout
on the underlying socket
. And what this actually does is explained in the documentation.
SO_RCVTIMEO
Sets the timeout value that specifies the maximum amount of time an input function waits until it completes. It accepts a timeval structure with the number of seconds and microseconds specifying the limit on how long to wait for an input operation to complete. If a receive operation has blocked for this much time without receiving additional data, it shall return with a partial count or errno set to [EAGAIN] or [EWOULDBLOCK] if no data is received.
The bolded part is key. A socket.timeout
is only raised if not a single byte has been received for the duration of the timeout
window. In other words, this is a timeout
between received bytes.
A simple function using threading.Timer
could be as follows.
import httplib
import socket
import threading
def download(host, path, timeout = 10):
content = None
http = httplib.HTTPConnection(host)
http.request('GET', path)
response = http.getresponse()
timer = threading.Timer(timeout, http.sock.shutdown, [socket.SHUT_RD])
timer.start()
try:
content = response.read()
except httplib.IncompleteRead:
pass
timer.cancel() # cancel on triggered Timer is safe
http.close()
return content
>>> host = 'releases.ubuntu.com'
>>> content = download(host, '/15.04/ubuntu-15.04-desktop-amd64.iso', 1)
>>> print content is None
True
>>> content = download(host, '/15.04/MD5SUMS', 1)
>>> print content is None
False
Other than checking for None
, it's also possible to catch the httplib.IncompleteRead
exception not inside the function, but outside of it. The latter case will not work though if the HTTP request doesn't have a Content-Length
header.
Solution 2:
I found in my tests (using the technique described here) that a timeout set in the urlopen()
call also effects the read()
call:
import urllib2 as u
c = u.urlopen('http://localhost/', timeout=5.0)
s = c.read(1<<20)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python2.7/socket.py", line 380, in read
data = self._sock.recv(left)
File "/usr/lib/python2.7/httplib.py", line 561, in read
s = self.fp.read(amt)
File "/usr/lib/python2.7/httplib.py", line 1298, in read
return s + self._file.read(amt - len(s))
File "/usr/lib/python2.7/socket.py", line 380, in read
data = self._sock.recv(left)
socket.timeout: timed out
Maybe it's a feature of newer versions? I'm using Python 2.7 on a 12.04 Ubuntu straight out of the box.
Solution 3:
One possible (imperfect) solution is to set the global socket timeout, explained in more detail here:
import socket
import urllib2
# timeout in seconds
socket.setdefaulttimeout(10)
# this call to urllib2.urlopen now uses the default timeout
# we have set in the socket module
req = urllib2.Request('http://www.voidspace.org.uk')
response = urllib2.urlopen(req)
However, this only works if you're willing to globally modify the timeout for all users of the socket module. I'm running the request from within a Celery task, so doing this would mess up timeouts for the Celery worker code itself.
I'd be happy to hear any other solutions...
Solution 4:
I'd expect this to be a common problem, and yet - no answers to be found anywhere... Just built a solution for this using timeout signal:
import urllib2
import socket
timeout = 10
socket.setdefaulttimeout(timeout)
import time
import signal
def timeout_catcher(signum, _):
raise urllib2.URLError("Read timeout")
signal.signal(signal.SIGALRM, timeout_catcher)
def safe_read(url, timeout_time):
signal.setitimer(signal.ITIMER_REAL, timeout_time)
url = 'http://uberdns.eu'
content = urllib2.urlopen(url, timeout=timeout_time).read()
signal.setitimer(signal.ITIMER_REAL, 0)
# you should also catch any exceptions going out of urlopen here,
# set the timer to 0, and pass the exceptions on.
The credit for the signal part of the solution goes here btw: python timer mystery