Programming

I have client and server connected.
client write and read from csock.
server write and read from ssock
suppose the server does :
....
close(ssock); //send FIN to client
othertask();
....

READ ERROR


if after the server close() the client does:
...
read(csock,...);
...
read(csock,...);
...
close(csock,...);
...
read(csock,...);
...


first read return 0 (read FIN)


second read also return 0.


third read return -1 with errno set to EBADF.


QUESTION 1:
Indeed if after the server close() the client does:
....
write(csock, "hello", 6); //server send RST
...
read(csock,...);
...
write(csock, ...);


first write return 6 without signaling nothing.


read return:
0 if the client read before the RST arrives.
-1 with errno set to ECONNRESET otherwise.


second write comports the SIGPIPE signal.
if it is ignored write return -1 and errno=EPIPE, otherwise it
comports the client termination.
is ok?


IS THE SITUATION THE SAME WHEN THE SERVER CRASH BEFORE THE CLIENT'S
FIRST WRITE?


QUESTION 2:
when read fails with errno=ENOTCONN?


QUESTION 3:
In general if I don't set the timeout option, is possible that a
read() fails with errno=ETIMEDOUT?


WRITE ERROR


when write fails and errno =ECONNRESET??

Here are some examples of when these errors occur:
write(..) on a socket that has been closed at the other end will cause a SIGPIPE.

read on a remotely closed socket will return 0 (EOF) or ECONNRESET in some cases, see the last part of this reply.

read(..) or write(..) on a socket that was never connected will return ENOTCONN.

read(..) or write(..) on a locally closed socket will return EBADF

I'm referring to [comp.unix.programmer] Unix-socket-faq for network programming when answering the question regarding read returning 0 or ECONNRESET:

"If the peer calls close() or exits, without having messed with
SO_LINGER, then our calls to read() should return 0. It is less clear
what happens to write() calls in this case; I would expect EPIPE, not
on the next call, but the one after.

If the peer reboots, or sets l_onoff = 1, l_linger = 0 and then
closes, then we should get ECONNRESET (eventually) from read(), or
EPIPE from write()."

/Kristofer

close() closes the file descriptor hence your EBADF for the following read.

As a suggestion, once you use close, actually or mentally put -1 into the file descriptor variable. This also acts as a massive hint that the file descriptor is no longer valid.

Did you really mean "shutdown()" ?