Client connections sending SIGPIPE

[stonier]

@jakan2 says that the ecl socket server is getting killed when the client connection breaks. The relevant ecl code:

long SocketServer::write(const char *s, unsigned long n) ecl_debug_throw_decl(StandardException) {
    int bytes_written = ::send(client_socket_fd,s,n,0);
    if ( bytes_written < 0 ) {
        switch(errno) {
            case ( EPIPE ) : {
                close();
                return ConnectionHungUp;
            }
            default : {
                ecl_debug_throw( devices::send_exception(LOC) );
                error_handler = devices::send_error();
                return ConnectionProblem;
            }
        }
    }
}

So it seems we already had handling for exactly this in our old use cases, but this no longer works. Look up the man pages:

   EPIPE  The  local  end  has been shut down on a connection oriented socket.  In this case the process will also receive a SIGPIPE unless MSG_NOSIGNAL is set.

So SIGPIPE is getting sent which kills the server. The 'fix' would be to do this:

  int bytes_written = ::send(client_socket_fd,s,n,0);
  int bytes_written = ::send(client_socket_fd,s,n,MSG_NOSIGNAL);

The question is....why is this code falling over now and not before? If we know this, then we can know that we're not introducing another problem.

[stonier]

@jakan2 - I think I found the reason. From the man pages:

POSIX.1-2001 only describes the MSG_OOB and MSG_EOR flags.  POSIX.1-2008 adds a specification of MSG_NOSIGNAL.

Probably the linux operating systems we were using did not have POSIX.1-2008 implementations.

[stonier]

We should handle cases where the signal is not defined - I updated the server code appropriately.

#ifdef MSG_NOSIGNAL
    int bytes_written = ::send(client_socket_fd,s,n,0|MSG_NOSIGNAL);
#else
    int bytes_written = ::send(client_socket_fd,s,n,0);
#endif