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Date: Thu, 22 Oct 2009 21:11:14 +0100
Message-ID: <416096c60910221311n5f3d5f4m673dacebdc89833e@mail.gmail.com>
Subject: Re: Python throws error when closing /dev/urandom
From: Andy Koppe <andy.koppe@gmail.com>
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> 2009/10/22 Topher Cawlfield
>> I'm not sure if this is the right place to post such problems, but I ran=
 into
>> this problem when trying to use the paramiko library with python 2.5.2 i=
n Cygwin.
>>
>> Ultimately the problem is that an IOError is generated when opening
>> /dev/urandom, reading some bytes from it (doesn't seem to matter how muc=
h),
>> and closing the file. =C2=A0If you don't read from the file there is no =
error upon
>> closing.
>>
>> $ python
>> Python 2.5.2 (r252:60911, Dec =C2=A02 2008, 09:26:14)
>> [GCC 3.4.4 (cygming special, gdc 0.12, using dmd 0.125)] on cygwin
>> Type "help", "copyright", "credits" or "license" for more information.
>> .>>> f =3D open("/dev/urandom")
>> .>>> f.close()
>>
>> Note: no problem just opening and closing the special file. =C2=A0But:
>>
>> .>>> f =3D open("/dev/urandom")
>> .>>> f.read(8)
>> '\xf9"\xb7\'E\xf8Q\xa0'
>> .>>> f.close()
>> Traceback (most recent call last):
>> =C2=A0File "<stdin>", line 1, in <module>
>> IOError: [Errno 0] Error
>> .>>>
>
> Reproduced the issue with this C test:
>
> #include <stdlib.h>
> #include <stdio.h>
>
> int main(void) {
> =C2=A0FILE *f =3D fopen("/dev/urandom", "r");
> =C2=A0if (!f) {
> =C2=A0 =C2=A0puts("fopen failed");
> =C2=A0 =C2=A0return 1;
> =C2=A0}
> =C2=A0char buf[8];
> =C2=A0printf("read %i bytes\n", fread(buf, 1, sizeof buf, f));
> =C2=A0if (fclose(f)) {
> =C2=A0 =C2=A0puts("fclose failed");
> =C2=A0 =C2=A0return 1;
> =C2=A0}
> =C2=A0return 0;
> }
>
> The fclose fails on Cygwin, but succeeds on Debian.

ps: Same issue with /dev/zero, /dev/full, and also /dev/clipboard.

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