From 48e55b1e5d43843d1bcfec2410db0c2ccc732fe6 Mon Sep 17 00:00:00 2001
From: goldsimon <goldsimon@gmx.de>
Date: Thu, 29 Jun 2017 08:43:59 +0200
Subject: [PATCH] tcp_output: slightly move the jump target 'output_done': when
 nothing is to send, pcb->unsent cannot be NULL; add a

---
 src/core/tcp_out.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/core/tcp_out.c b/src/core/tcp_out.c
index 1ea65144..a5000572 100644
--- a/src/core/tcp_out.c
+++ b/src/core/tcp_out.c
@@ -1089,6 +1089,12 @@ tcp_output(struct tcp_pcb *pcb)
                  lwip_ntohl(seg->tcphdr->seqno), pcb->lastack));
   }
 #endif /* TCP_CWND_DEBUG */
+
+  if (seg == NULL) {
+    /* nothing to send: shortcut out of here */
+    goto output_done;
+  }
+
   /* Check if we need to start the persistent timer when the next unsent segment
    * does not fit within the remaining send window and RTO timer is not running (we
    * have no in-flight data). A traditional approach would fill the remaining window
@@ -1187,7 +1193,6 @@ tcp_output(struct tcp_pcb *pcb)
     }
     seg = pcb->unsent;
   }
-output_done:
 #if TCP_OVERSIZE
   if (pcb->unsent == NULL) {
     /* last unsent has been removed, reset unsent_oversize */
@@ -1195,6 +1200,7 @@ output_done:
   }
 #endif /* TCP_OVERSIZE */
 
+output_done:
   pcb->flags &= ~TF_NAGLEMEMERR;
   return ERR_OK;
 }