[ python-Bugs-1728403 ] reading from malformed big5 document hangs cpython

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Bugs item #1728403, was opened at 2007-05-30 10:36
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Category: Python Interpreter Core
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: tsuraan (tsuraan3)
Assigned to: Nobody/Anonymous (nobody)
Summary: reading from malformed big5 document hangs cpython

Initial Comment:
Python enters some sort of infinite loop when attempting to read data from a malformed file that is big5 encoded (using the codecs library).  This behaviour can be observed under Linux and FreeBSD, using Python 2.4 and 2.5 .  A really simple example illustrating the bug follows:

Python 2.4.4 (#1, May 15 2007, 13:33:55)
[GCC 4.1.1 (Gentoo 4.1.1-r3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import codecs
>>> fname='out'      
>>> outfd=open(fname,'w')
>>> outfd.write(chr(243))
>>> outfd.close()
>>>
>>> infd= codecs.open(fname, encoding='big5')
>>> infd.read(1024)

And then, it hangs forever.  If I instead use the following code:

Python 2.5 (r25:51908, Jan  8 2007, 19:09:28)
[GCC 3.4.5 (Gentoo 3.4.5-r1, ssp-3.4.5-1.0, pie-8.7.9)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import codecs, signal
>>> fname='out'
>>> def handler(*args):
...   raise Exception("boo!")
...
>>> signal.signal(signal.SIGALRM, handler)
0
>>> outfd=open(fname, 'w')
>>> outfd.write (chr(243))
>>> outfd.close()
>>>
>>> infd=codecs.open(fname, encoding='big5')
>>> signal.alarm(5)
0
>>> infd.read(1024)

The program still hangs forever.  The program can be made to crash if I don't install a signal handler at all, but that's pretty lame.  It looks like the entire interpreter is being locked up by this read, so I don't think there's likely to be a pure-python workaround, but I thought it would be a good but to have out there so a future version of python can (hopefully) fix this. 

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