Five Pitfalls of Linux Sockets Programming (developerWorks) [LWN.net]

Five Pitfalls of Linux Sockets Programming (developerWorks)

Posted Sep 21, 2005 14:38 UTC (Wed) by RobSeace (subscriber, #4435)
In reply to: Five Pitfalls of Linux Sockets Programming (developerWorks) by hppnq
Parent article: Five Pitfalls of Linux Sockets Programming (developerWorks)

There is no other possible scenario where a return value of 0 could
occur (other than a passed-in length of 0), that I'm aware of... If
the socket is blocking, and there is no room in the queue for any more
data at all, then send()/write() will block... If the socket is
non-blocking, and there is no room in the queue for any more data at all,
then send()/write() will return -1 with errno set to EAGAIN... In all
other cases, there is room for at least 1 byte of data in the send queue,
and hence the return value will be at least 1... I can conceive of no
situation, short of passing in a length of 0, where send()/write() could
ever possibly return 0...

(Log in to post comments)

Five Pitfalls of Linux Sockets Programming (developerWorks)

Posted Sep 21, 2005 15:09 UTC (Wed) by RobSeace (subscriber, #4435) [Link]

That example I would expect to return -1 with an errno of EFAULT, since
the NULL pointer is invalid... Alternatively, it might simply crash the
app with SIGSEGV... But, I certainly would never expect it to return 0...
Really, there is no other notion of "actual length of the data" than the
length you pass in to send()/write()... It has no other way of knowing
any other length than what you tell it... (Short of running off the end of
your valid address space, causing either EFAULT or SIGSEGV...)

Five Pitfalls of Linux Sockets Programming (developerWorks)

Posted Sep 21, 2005 15:29 UTC (Wed) by hppnq (guest, #14462) [Link]

EFAULT seems appropriate, yes; SIGSEGV would be disappointing.

Though, looking up a few send(2) manpages I cannot really conclude that NULL would be an invalid address (I consulted a Solaris manpage before my first comment * bangs head on table * and apparently Solaris doesn't care about EFAULT at all ;-).

But it's trivial to find out of course what Linux does in this case, I'll let you know unless you beat me to it. ;-)

Five Pitfalls of Linux Sockets Programming (developerWorks)

Posted Sep 21, 2005 16:24 UTC (Wed) by RobSeace (subscriber, #4435) [Link]

It does indeed fail with EFAULT on both Linux (2.4.x, at least) and QNX4.2x
(the only other system I have access to, at the moment)... On any system
where it didn't fail so, I'd expect the seg-fault... It's the only other
rational choice...

Five Pitfalls of Linux Sockets Programming (developerWorks)

Posted Sep 21, 2005 17:12 UTC (Wed) by hppnq (guest, #14462) [Link]

Alright, common sense rules. ;-) Cheers Rob!