fixed default values of TCP_SNDLOWAT and TCP_SNDQUEUELOWAT for small windows (bug #34176 select after non-blocking send times out)

CHANGELOG

@@ -69,6 +69,10 @@ HISTORY
 
  ++ Bugfixes:
 
+  2011-10-18: Simon Goldschmidt
+  * opt.h: fixed default values of TCP_SNDLOWAT and TCP_SNDQUEUELOWAT for small
+    windows (bug #34176 select after non-blocking send times out)
+
   2011-10-18: Simon Goldschmidt
   * tcp_impl.h, tcp_out.c: fixed bug #34587: TCP_BUILD_MSS_OPTION doesn't
     consider netif->mtu, causes slow network

src/include/lwip/opt.h

@@ -989,7 +989,7 @@
  * TCP snd_buf for select to return writable (combined with TCP_SNDQUEUELOWAT).
  */
 #ifndef TCP_SNDLOWAT
-#define TCP_SNDLOWAT                    ((TCP_SND_BUF)/2)
+#define TCP_SNDLOWAT                    LWIP_MAX(((TCP_SND_BUF)/2), (2 * TCP_MSS) + 1)
 #endif
 
 /**
@@ -998,7 +998,7 @@
  * this number, select returns writable (combined with TCP_SNDLOWAT).
  */
 #ifndef TCP_SNDQUEUELOWAT
-#define TCP_SNDQUEUELOWAT               ((TCP_SND_QUEUELEN)/2)
+#define TCP_SNDQUEUELOWAT               LWIP_MAX(((TCP_SND_QUEUELEN)/2), 5)
 #endif
 
 /**