ROUTER socket blocks on SNDHWM

Till now the message was droppen in such case.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

src/router.cpp

@@ -129,40 +129,44 @@ int zmq::router_t::xsend (msg_t *msg_, int flags_)
     if (!more_out) {
         zmq_assert (!current_out);
 
-        //  If we have malformed message (prefix with no subsequent message)
-        //  then just silently ignore it.
-        //  TODO: The connections should be killed instead.
-        if (msg_->flags () & msg_t::label) {
-
-            more_out = true;
-
-            //  Find the pipe associated with the peer ID stored in the prefix.
-            if (unlikely (msg_->size () != 4)) {
-                errno = ECANTROUTE;
-                return -1;
-            }
-            uint32_t peer_id = get_uint32 ((unsigned char*) msg_->data ());
-            outpipes_t::iterator it = outpipes.find (peer_id);
-            if (unlikely (it == outpipes.end ())) {
-                errno = ECANTROUTE;
-                return -1;
-            }
-
-            //  Check whether the pipe is available for writing.
-            current_out = it->second.pipe;
-            msg_t empty;
-            int rc = empty.init ();
-            errno_assert (rc == 0);
-            if (!current_out->check_write (&empty)) {
-                it->second.active = false;
-                more_out = false;
-                current_out = NULL;
-            }
+        //  The first message part has to be label.
+        if (unlikely (!(msg_->flags () & msg_t::label))) {
+            errno = EFSM;
+            return -1;
+        }
+
+        //  Find the pipe associated with the peer ID stored in the message.
+        if (unlikely (msg_->size () != 4)) {
+            errno = ECANTROUTE;
+            return -1;
+        }
+        uint32_t peer_id = get_uint32 ((unsigned char*) msg_->data ());
+        outpipes_t::iterator it = outpipes.find (peer_id);
+        if (unlikely (it == outpipes.end ())) {
+            errno = ECANTROUTE;
+            return -1;
+        }
+
+        //  Check whether the pipe is available for writing.
+        msg_t empty;
+        int rc = empty.init ();
+        errno_assert (rc == 0);
+        if (!it->second.pipe->check_write (&empty)) {
             rc = empty.close ();
             errno_assert (rc == 0);
+            it->second.active = false;
+            errno = EAGAIN;
+            return -1;
         }
+        rc = empty.close ();
+        errno_assert (rc == 0);
 
-        int rc = msg_->close ();
+        //  Mark the pipe to send the message to.
+        current_out = it->second.pipe;
+        more_out = true;
+        
+        //  Clean up the message object.
+        rc = msg_->close ();
         errno_assert (rc == 0);
         rc = msg_->init ();
         errno_assert (rc == 0);