Python FTP timeout value not effective


J

John Nagle

I'm reading files from an FTP server at the U.S. Securities and
Exchange Commission. This code has been running successfully for
years. Recently, they imposed a consistent connection delay
of 20 seconds at FTP connection, presumably because they're having
some denial of service attack. Python 2.7 urllib2 doesn't
seem to use the timeout specified. After 20 seconds, it
gives up and times out.

Here's the traceback:

Internal error in EDGAR update: <urlopen error ftp error: [Errno 110]
Connection timed out>
.....
File "./edgar/edgarnetutil.py", line 53, in urlopen
return(urllib2.urlopen(url,timeout=timeout))
File "/opt/python27/lib/python2.7/urllib2.py", line 126, in urlopen
return _opener.open(url, data, timeout)
File "/opt/python27/lib/python2.7/urllib2.py", line 394, in open
response = self._open(req, data)
File "/opt/python27/lib/python2.7/urllib2.py", line 412, in _open
'_open', req)
File "/opt/python27/lib/python2.7/urllib2.py", line 372, in _call_chain
result = func(*args)
File "/opt/python27/lib/python2.7/urllib2.py", line 1379, in ftp_open
fw = self.connect_ftp(user, passwd, host, port, dirs, req.timeout)
File "/opt/python27/lib/python2.7/urllib2.py", line 1400, in connect_ftp
fw = ftpwrapper(user, passwd, host, port, dirs, timeout)
File "/opt/python27/lib/python2.7/urllib.py", line 860, in __init__
self.init()
File "/opt/python27/lib/python2.7/urllib.py", line 866, in init
self.ftp.connect(self.host, self.port, self.timeout)
File "/opt/python27/lib/python2.7/ftplib.py", line 132, in connect
self.sock = socket.create_connection((self.host, self.port),
self.timeout)
File "/opt/python27/lib/python2.7/socket.py", line 571, in
create_connection
raise err
URLError: <urlopen error ftp error: [Errno 110] Connection timed out>

Periodic update completed in 21.1 seconds.
----------------------------------------------

Here's the relevant code:

TIMEOUTSECS = 60 ## give up waiting for server after 60 seconds
....
def urlopen(url,timeout=TIMEOUTSECS) :
if url.endswith(".gz") : # gzipped file, must decompress first
nd = urllib2.urlopen(url,timeout=timeout) # get connection
... # (NOT .gz FILE, DOESN'T TAKE THIS PATH)
else :
return(urllib2.urlopen(url,timeout=timeout)) # (OPEN FAILS)


TIMEOUTSECS used to be 20 seconds, and I increased it to 60. It didn't
help.

This isn't an OS problem. The above traceback was on a Linux system.
On Windows 7, it fails with

"URLError: <urlopen error ftp error: [Errno 10060] A connection attempt
failed because the connected party did not properly respond after a
period of time, or established connection failed because connected host
has failed to respond>"

But in both cases, the command line FTP client will work, after a
consistent 20 second delay before the login prompt. So the
Python timeout parameter isn't working.

John Nagle
 
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D

David Bolen

John Nagle said:
Here's the relevant code:

TIMEOUTSECS = 60 ## give up waiting for server after 60 seconds
...
def urlopen(url,timeout=TIMEOUTSECS) :
if url.endswith(".gz") : # gzipped file, must decompress first
nd = urllib2.urlopen(url,timeout=timeout) # get connection
... # (NOT .gz FILE, DOESN'T TAKE THIS PATH)
else :
return(urllib2.urlopen(url,timeout=timeout)) # (OPEN FAILS)


TIMEOUTSECS used to be 20 seconds, and I increased it to 60. It didn't
help.

I apologize if it's an obvious question, but is there any possibility that
the default value to urlopen is not being used, but some other timeout is
being supplied? Or that somehow TIMEOUTSECS is being redefined before
being used by the urlopen definition? Can you (or have you) verified the
actual timeout parameter value being supplied to urllib2.urlopen?

The fact that you seem to still be timing out very close to the prior 20s
timeout value seems a little curious, since there's no timeout by default
(barring an application level global socket default), so it feels like a
value being supplied.

Not sure which 2.7 you're using, but I tried the below with both 2.7.3 and
2.7.5 on Linux since they were handy, and the timeout parameter seems to be
working properly at least in a case I can simulate (xxx is a firewalled
host so the connection attempt just gets black-holed until the timeout):
... print time.ctime()
... try:
... urllib2.urlopen('ftp://xxx', timeout=timeout)
... except:
... print 'Error'
... print time.ctime()
...Mon Sep 2 17:36:15 2013
Error
Mon Sep 2 17:36:20 2013Mon Sep 2 17:36:23 2013
Error
Mon Sep 2 17:36:44 2013Mon Sep 2 17:36:50 2013
Error
Mon Sep 2 17:37:50 2013

It's tougher to simulate a host that artificially delays the connection
attempt but then succeeds, so maybe it's an issue related specifically to
that implementation. Depending on how the delay is implemented (delaying
SYN response versus accepting the connection but just delaying the welcome
banner, for example), I suppose it may be tickling some very specific bug.

Since all communication essentially boils down to I/O over the socket, it
seems to me likely that those cases should still fail over time periods
related to the timeout supplied, unlike your actual results, which makes me
wonder about the actual urllib2.urlopen timeout parameter.

-- David
 
C

Chris Angelico

"URLError: <urlopen error ftp error: [Errno 10060] A connection attempt
failed because the connected party did not properly respond after a
period of time, or established connection failed because connected host
has failed to respond>"

But in both cases, the command line FTP client will work, after a
consistent 20 second delay before the login prompt. So the
Python timeout parameter isn't working.

That's a socket timeout, not an FTP timeout - that's why the timeout
parameter isn't doing anything. Are you sure it's just a 20-second
delay there? Check if there's something else blocking the connection
somehow. Can you telnet to that computer on port 21?

ChrisA
 
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T

Terry Reedy

I'm reading files from an FTP server at the U.S. Securities and
Exchange Commission. This code has been running successfully for
years. Recently, they imposed a consistent connection delay
of 20 seconds at FTP connection, presumably because they're having
some denial of service attack. Python 2.7 urllib2 doesn't
seem to use the timeout specified. After 20 seconds, it
gives up and times out.

Here's the traceback:

Internal error in EDGAR update: <urlopen error ftp error: [Errno 110]
Connection timed out>
....
File "./edgar/edgarnetutil.py", line 53, in urlopen

File "/opt/python27/lib/python2.7/socket.py", line 571, in
create_connection ....
raise err
URLError: <urlopen error ftp error: [Errno 110] Connection timed out>

Periodic update completed in 21.1 seconds.
----------------------------------------------

Here's the relevant code:

TIMEOUTSECS = 60 ## give up waiting for server after 60 seconds
...
def urlopen(url,timeout=TIMEOUTSECS) :
if url.endswith(".gz") : # gzipped file, must decompress first
nd = urllib2.urlopen(url,timeout=timeout) # get connection
... # (NOT .gz FILE, DOESN'T TAKE THIS PATH)
else :
return(urllib2.urlopen(url,timeout=timeout)) # (OPEN FAILS)

I looked at the 3.3 urllib.retrieve.urlopen code and timeout is passed
through a couple of layers but is it hard to see if it reaches the
socket connection call. I would also try python3.3 as timeout may have
been changed a bit.

There are some 'timeout' issues on the tracker, such as
http://bugs.python.org/issue4079
http://bugs.python.org/issue18417
but these do not obviously apply to an explicitly passed timeout

I would also try using ftplib, which cuts out lots of the general
purpose layers urlopen. FTP.__init__ stores timeout in self.timeout and
calls connect(), which passes self.timeout to socket.create_connection.
'230-Anonymous access granted, restrictions apply\n \n Please read the
file README.txt\n230 it was last modified on Tue Aug 15 14:29:31 2000
- 4765 days ago'"214-The following commands are recognized (* =>'s unimplemented):\n CWD
XCWD CDUP XCUP SMNT* QUIT PORT PASV \n EPRT
EPSV ALLO* RNFR RNTO DELE MDTM RMD \n XRMD MKD
XMKD PWD XPWD SIZE SYST HELP \n NOOP FEAT
OPTS AUTH* CCC* CONF* ENC* MIC* \n PBSZ* PROT* TYPE
STRU MODE RETR STOR STOU \n APPE REST ABOR
USER PASS ACCT* REIN* LIST \n NLST STAT SITE MLSD
MLST \n214 Direct comments to (e-mail address removed)"

I tried to read 'README.txt but I do not know how to use the commands or
local FTP methods.
TIMEOUTSECS used to be 20 seconds, and I increased it to 60. It didn't
help.

This isn't an OS problem. The above traceback was on a Linux system.
On Windows 7, it fails with

"URLError: <urlopen error ftp error: [Errno 10060] A connection attempt
failed because the connected party did not properly respond after a
period of time, or established connection failed because connected host
has failed to respond>"

But in both cases, the command line FTP client will work, after a
consistent 20 second delay before the login prompt. So the
Python timeout parameter isn't working.
 

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