Don't send messages on down networks.

message.c

@@ -534,6 +534,9 @@ ensure_space(struct network *net, int space)
 static void
 start_message(struct network *net, int type, int len)
 {
+    if(!net->up)
+        return;
+
     if(net->bufsize - net->buffered < len + 2)
         flushbuf(net);
     net->sendbuf[net->buffered++] = type;
@@ -541,7 +544,11 @@ start_message(struct network *net, int type, int len)
 }
 
 static void
-end_message(struct network *net, int type, int bytes) {
+end_message(struct network *net, int type, int bytes)
+{
+    if(!net->up)
+        return;
+
     assert(net->buffered >= bytes + 2 &&
            net->sendbuf[net->buffered - bytes - 2] == type &&
            net->sendbuf[net->buffered - bytes - 1] == bytes);
@@ -551,12 +558,18 @@ end_message(struct network *net, int type, int bytes) {
 static void
 accumulate_byte(struct network *net, unsigned char value)
 {
+    if(!net->up)
+        return;
+
     net->sendbuf[net->buffered++] = value;
 }
 
 static void
 accumulate_short(struct network *net, unsigned short value)
 {
+    if(!net->up)
+        return;
+
     DO_HTONS(net->sendbuf + net->buffered, value);
     net->buffered += 2;
 }
@@ -565,6 +578,9 @@ static void
 accumulate_bytes(struct network *net,
                  const unsigned char *value, unsigned len)
 {
+    if(!net->up)
+        return;
+
     memcpy(net->sendbuf + net->buffered, value, len);
     net->buffered += len;
 }