[sock] flush / handle lines during input handling when a telnet SB (r…

…enegotation) is received (#84)

This is needed to properly keep GMCP/ATCP handling inline against the incoming
socket data lines.  Otherwise the SB attributes get handled first whilst
the normal data is queued into the line buffer, and then the line buffer
is handled at the end.

I don't like doing the socket flush here though.  Ugh.

Co-authored-by: Adrian Chadd <[email protected]>
Co-authored-by: Karol Lassak <[email protected]>

src/socket.c

@@ -3530,6 +3530,24 @@ static int handle_socket_input(const char *simbuffer, int simlen, const char *en
                 continue;  /* avoid non-telnet processing */
 
             } else if (xsock->fsastate == TN_SB) {
+                    /*
+                     * Flush existing data before handling subnegotiation.
+                     *
+                     * This is needed for the handful of situations where
+                     * things like GMCP/ATCP messages happen to be wrapping
+                     * the incoming text lines rather than a purely out of
+                     * band notification.
+                     *
+                     * Ideally the server would send an EOR or GA here,
+                     * but MUDs use that to terminate the prompt line.
+                     */
+#if WIDECHAR
+		    inbound_decode_str(xsock->buffer, incomingposttelnet,
+                        incomingFSM, 0);
+#endif
+		    handle_socket_input_queue_lines(xsock);
+		    flushxsock();
+
 		if (xsock->subbuffer->len > RECEIVELIMIT) {
 		    /* It shouldn't take this long; server is broken.  Abort. */
 		    SStringcat(xsock->buffer, CS(xsock->subbuffer));