ZMQII-34: ensure that poll won't return POLLIN event when the message will be filtered out anyway (POSIX)

src/sub.cpp

@@ -26,14 +26,17 @@
 
 zmq::sub_t::sub_t (class app_thread_t *parent_) :
     socket_base_t (parent_),
-    all_count (0)
+    all_count (0),
+    has_message (false)
 {
     options.requires_in = true;
     options.requires_out = false;
+    zmq_msg_init (&message);
 }
 
 zmq::sub_t::~sub_t ()
 {
+    zmq_msg_close (&message);
 }
 
 void zmq::sub_t::xattach_pipes (class reader_t *inpipe_,
@@ -115,16 +118,72 @@ int zmq::sub_t::xflush ()
 
 int zmq::sub_t::xrecv (zmq_msg_t *msg_, int flags_)
 {
-    //  Get a message using fair queueing algorithm.
-    int rc = fq.recv (msg_, flags_);
+    //  If there's already a message prepared by a previous call to zmq_poll,
+    //  return it straight ahead.
+    if (has_message) {
+        zmq_msg_move (msg_, &message);
+        has_message = false;
+        return 0;
+    }
 
-    //  If there's no message available, return immediately.
-    if (rc != 0 && errno == EAGAIN)
-        return -1;
+    //  TODO: This can result in infinite loop in the case of continuous
+    //  stream of non-matching messages which breaks the non-blocking recv
+    //  semantics.
+    while (true) {
 
+        //  Get a message using fair queueing algorithm.
+        int rc = fq.recv (msg_, flags_);
+
+        //  If there's no message available, return immediately.
+        //  The same when error occurs.
+        if (rc != 0)
+            return -1;
+
+        //  Check whether the message matches at least one subscription.
+        if (match (msg_))
+            return 0;
+    }
+}
+
+bool zmq::sub_t::xhas_in ()
+{
+    //  If there's already a message prepared by a previous call to zmq_poll,
+    //  return straight ahead.
+    if (has_message)
+        return true;
+
+    //  TODO: This can result in infinite loop in the case of continuous
+    //  stream of non-matching messages.
+    while (true) {
+
+        //  Get a message using fair queueing algorithm.
+        int rc = fq.recv (&message, ZMQ_NOBLOCK);
+
+        //  If there's no message available, return immediately.
+        //  The same when error occurs.
+        if (rc != 0) {
+            zmq_assert (errno == EAGAIN);
+            return false;
+        }
+
+        //  Check whether the message matches at least one subscription.
+        if (match (&message)) {
+            has_message = true;
+            return true;
+        }
+    }
+}
+
+bool zmq::sub_t::xhas_out ()
+{
+    return false;
+}
+
+bool zmq::sub_t::match (zmq_msg_t *msg_)
+{
     //  If there is at least one * subscription, the message matches.
     if (all_count)
-        return 0;
+        return true;
 
     //  Check whether the message matches at least one prefix subscription.
     //  TODO: Make this efficient - O(log(n)) where n is number of characters in
@@ -135,25 +194,8 @@ int zmq::sub_t::xrecv (zmq_msg_t *msg_, int flags_)
         size_t sub_size = it->size ();
         if (sub_size <= msg_size &&
               memcmp (zmq_msg_data (msg_), it->data (), sub_size) == 0)
-            return 0;
+            return true;
     }
 
-    //  The message did not pass the filter. Trim it.
-    //  Note that we are returning a different error code so that the caller
-    //  knows there are more messages available. We cannot loop here as
-    //  a stream of non-matching messages would create a DoS situation.
-    zmq_msg_close (msg_);
-    zmq_msg_init (msg_);
-    errno = EINPROGRESS;
-    return -1;
-}
-
-bool zmq::sub_t::xhas_in ()
-{
-    return fq.has_in ();
-}
-
-bool zmq::sub_t::xhas_out ()
-{
     return false;
 }