c - What causes the Broken Pipe Error?

Question

I know that broken pipe error is thrown when the socket on the peer side is closed.

But, in my test I have noted that an immediate 'send' call on this side when the peer side is closed doesn't always lead to a broken pipe error.

E.g.:

After closing the socket on peer side (I have tried clean closing by calling close and also abnormal closing by killing the peer), if I try to send 40 bytes, then I don't get a broken pipe, but, if I try to send 40000 bytes then it immediately gives broken pipe error.

What exactly causes broken pipe and can it's behavior be predicted?

Answer 1

It can take time for the network close to be observed - the total time is nominally about 2 minutes (yes, minutes!) after a close before the packets destined for the port are all assumed to be dead. The error condition is detected at some point. With a small write, you are inside the MTU of the system, so the message is queued for sending. With a big write, you are bigger than the MTU and the system spots the problem quicker. If you ignore the SIGPIPE signal, then the functions will return EPIPE error on a broken pipe - at some point when the broken-ness of the connection is detected.