fixed bug #43192 tcp_enqueue_flags() should not check TCP_SND_QUEUELEN when sending FIN

CHANGELOG

@@ -127,6 +127,10 @@ HISTORY
 
   ++ Bugfixes:
 
+  2014-09-16: Simon Goldschmidt
+  * tcp_out.c: fixed bug #43192 tcp_enqueue_flags() should not check TCP_SND_QUEUELEN
+    when sending FIN
+
   2014-09-03: Simon Goldschmidt
   * msg_in.c: fixed bug #39355 SNMP Memory Leak in case of error
 

src/core/tcp_out.c

@@ -745,8 +745,9 @@ tcp_enqueue_flags(struct tcp_pcb *pcb, u8_t flags)
   LWIP_ASSERT("tcp_enqueue_flags: need either TCP_SYN or TCP_FIN in flags (programmer violates API)",
               (flags & (TCP_SYN | TCP_FIN)) != 0);
 
-  /* check for configured max queuelen and possible overflow */
-  if ((pcb->snd_queuelen >= TCP_SND_QUEUELEN) || (pcb->snd_queuelen > TCP_SNDQUEUELEN_OVERFLOW)) {
+  /* check for configured max queuelen and possible overflow (FIN flag should always come through!) */
+  if (((pcb->snd_queuelen >= TCP_SND_QUEUELEN) || (pcb->snd_queuelen > TCP_SNDQUEUELEN_OVERFLOW)) &&
+      ((flags & TCP_FIN) == 0)) {
     LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 3, ("tcp_enqueue_flags: too long queue %"U16_F" (max %"U16_F")\n",
                                        pcb->snd_queuelen, TCP_SND_QUEUELEN));
     TCP_STATS_INC(tcp.memerr);