Writing to a closed, local TCP socket not failing

Question

I seem to be having a problem with my sockets. Below, you will see some code which forks a server and a client. The server opens a TCP socket, and the client connects to i

Answer 1

You have two sockets - one for the client and another for the server. Now your client is doing the active close.This means TCP's conection termination has been started by the client ( A tcp FIN segment has been sent from the client send).

At this stage you see the client socket in FIN_WAIT1 state. Now what is the state of the server socket now? It is in CLOSE_WAIT state.So the server socket is not closed.

The FIN from the server has not been sent yet. (Why - since the application has not closed the socket). At this stage you are writing over the server socket so you are not getting an error.

Now if you want to see the error just write close(client_fd) before writing over the socket.

close(client_fd);
printf( "Write result: %d\n", write( client_fd, "123", 3 ) );

Here the server socket is no more in CLOSE_WAIT state so you can see return value of write is -ve to indicate the error. I hope this clarifies.