ZMQ_FILTER socket option added

This option is a performance tweak. In devices XSUB socket filters
the messages just to send them to XPUB socket which filters them
once more. Setting ZMQ_FILTER option to 0 allows to switch the
filtering in XSUB socket off.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

doc/zmq_getsockopt.txt

@@ -297,7 +297,7 @@ Applicable socket types:: all
 ZMQ_MULTICAST_HOPS: Maximum network hops for multicast packets
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-The option shell retrieve time-to-live used for outbound multicast packets.
+The option shall retrieve time-to-live used for outbound multicast packets.
 The default of 1 means that the multicast packets don't leave the local network.
 
 [horizontal]
@@ -307,6 +307,23 @@ Default value:: 1
 Applicable socket types:: all, when using multicast transports
 
 
+ZMQ_FILTER: Switches message filtering on or off
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The option shall retrieve the filtering behaiour of the socket.
+If 1, messages are filtered according to subcriptions as expected.
+If 0, messages are not filtered. This is a performance tweak. If a device
+receives a message from XSUB socket and it is about to send it to XPUB socket
+immediately, filtering would be done twice. We can thus turn off filtering in
+XSUB socket and rely on filtering in XPUB socket.
+
+[horizontal]
+Option value type:: int
+Option value unit:: boolean
+Default value:: 1
+Applicable socket types:: ZMQ_SUB, ZMQ_XSUB
+
+
 ZMQ_FD: Retrieve file descriptor associated with the socket
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 The 'ZMQ_FD' option shall retrieve the file descriptor associated with the

doc/zmq_setsockopt.txt

@@ -284,6 +284,7 @@ Option value unit:: connections
 Default value:: 100
 Applicable socket types:: all, only for connection-oriented transports.
 
+
 ZMQ_MAXMSGSIZE: Maximum acceptable inbound message size
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -296,6 +297,7 @@ Option value unit:: bytes
 Default value:: -1
 Applicable socket types:: all
 
+
 ZMQ_MULTICAST_HOPS: Maximum network hops for multicast packets
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -309,6 +311,23 @@ Option value unit:: network hops
 Default value:: 1
 Applicable socket types:: all, when using multicast transports
 
+
+ZMQ_FILTER: Switches message filtering on or off
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If set to 1, messages are filtered according to subcriptions as expected.
+If set to 0, messages are not filtered. This is a performance tweak. If a device
+receives a message from XSUB socket and it is about to send it to XPUB socket
+immediately, filtering would be done twice. We can thus turn off filtering in
+XSUB socket and rely on filtering in XPUB socket.
+
+[horizontal]
+Option value type:: int
+Option value unit:: boolean
+Default value:: 1
+Applicable socket types:: ZMQ_SUB, ZMQ_XSUB
+
+
 RETURN VALUE
 ------------
 The _zmq_setsockopt()_ function shall return zero if successful. Otherwise it

include/zmq.h

@@ -180,6 +180,7 @@ ZMQ_EXPORT int zmq_term (void *context);
 #define ZMQ_SNDHWM 23
 #define ZMQ_RCVHWM 24
 #define ZMQ_MULTICAST_HOPS 25
+#define ZMQ_FILTER 26
     
 /*  Send/recv options.                                                        */
 #define ZMQ_DONTWAIT 1

src/options.cpp

@@ -38,6 +38,7 @@ zmq::options_t::options_t () :
     reconnect_ivl_max (0),
     backlog (100),
     maxmsgsize (-1),
+    filter (1),
     immediate_connect (true)
 {
 }
@@ -172,6 +173,15 @@ int zmq::options_t::setsockopt (int option_, const void *optval_,
         multicast_hops = *((int*) optval_);
         return 0;
 
+    case ZMQ_FILTER:
+        if (optvallen_ != sizeof (int) || (*((int*) optval_) != 0 &&
+                *((int*) optval_) != 1)) {
+            errno = EINVAL;
+            return -1;
+        }
+        filter = *((int*) optval_);
+        return 0;
+
     }
 
     errno = EINVAL;
@@ -317,6 +327,15 @@ int zmq::options_t::getsockopt (int option_, void *optval_, size_t *optvallen_)
         *optvallen_ = sizeof (int);
         return 0;
 
+    case ZMQ_FILTER:
+        if (*optvallen_ < sizeof (int)) {
+            errno = EINVAL;
+            return -1;
+        }
+        *((int*) optval_) = filter;
+        *optvallen_ = sizeof (int);
+        return 0;
+
     }
 
     errno = EINVAL;

src/options.hpp

@@ -75,6 +75,9 @@ namespace zmq
         //  Maximal size of message to handle.
         int64_t maxmsgsize;
 
+        //  If 1, (X)SUB socket should filter the messages. If 0, it should not.
+        int filter;
+
         //  If true, when connecting, pipes are created immediately without
         //  waiting for the connection to be established. That way the socket
         //  is not aware of the peer's identity, however, it is able to send

src/xsub.cpp

@@ -133,7 +133,7 @@ int zmq::xsub_t::xrecv (msg_t *msg_, int flags_)
 
         //  Check whether the message matches at least one subscription.
         //  Non-initial parts of the message are passed 
-        if (more || match (msg_)) {
+        if (more || !options.filter || match (msg_)) {
             more = msg_->flags () & msg_t::more;
             return 0;
         }
@@ -173,7 +173,7 @@ bool zmq::xsub_t::xhas_in ()
         }
 
         //  Check whether the message matches at least one subscription.
-        if (match (&message)) {
+        if (!options.filter || match (&message)) {
             has_message = true;
             return true;
         }