refactored ZMQ_ROUTER_ANNOUNCE_SELF code. renamed it to ZMQ_PROBE_NEW_PEERS.

implement it for DEALER tocket.
+documentation

doc/zmq_setsockopt.txt

@@ -421,6 +421,21 @@ Default value:: 0
 Applicable socket types:: ZMQ_ROUTER
 
 
+ZMQ_PROBE_NEW_PEERS: automatically send empty packet to every established connection
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Sets the 'ROUTER' & 'DEALER' sockets behavior to automatically send an empty packet
+to any new connection made (or accepted) by socket. It could help sockets to
+auto discovery themself. It especially important in 'ROUTER' <-> 'ROUTER' connections
+where it solves 'who will write first' problems.
+
+[horizontal]
+Option value type:: int
+Option value unit:: 0, 1
+Default value:: 0
+Applicable socket types:: ZMQ_ROUTER, ZMQ_DEALER
+
+
 ZMQ_XPUB_VERBOSE: provide all subscription messages on XPUB sockets
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

include/zmq.h

@@ -274,7 +274,7 @@ ZMQ_EXPORT int zmq_msg_set (zmq_msg_t *msg, int option, int optval);
 #define ZMQ_CURVE_SERVER 47
 #define ZMQ_CURVE_PUBLICKEY 48
 #define ZMQ_CURVE_SERVERKEY 49
-#define ZMQ_ROUTER_ANNOUNCE_SELF 50
+#define ZMQ_PROBE_NEW_PEERS 50
 
 /*  Message options                                                           */
 #define ZMQ_MORE 1

src/dealer.cpp

@@ -22,7 +22,8 @@
 #include "msg.hpp"
 
 zmq::dealer_t::dealer_t (class ctx_t *parent_, uint32_t tid_, int sid_) :
-    socket_base_t (parent_, tid_, sid_)
+    socket_base_t (parent_, tid_, sid_),
+    probe_new_peers(false)
 {
     options.type = ZMQ_DEALER;
 }
@@ -37,10 +38,48 @@ void zmq::dealer_t::xattach_pipe (pipe_t *pipe_, bool icanhasall_)
     (void) icanhasall_;
 
     zmq_assert (pipe_);
+
+    if (probe_new_peers) {
+        int rc, ok;
+        msg_t probe_msg_;
+
+        rc = probe_msg_.init ();
+        errno_assert (rc == 0);
+
+        ok = pipe_->write (&probe_msg_);
+        zmq_assert (ok);
+        pipe_->flush ();
+
+        rc = probe_msg_.close ();
+        errno_assert (rc == 0);
+    }
+
     fq.attach (pipe_);
     lb.attach (pipe_);
 }
 
+int zmq::dealer_t::xsetsockopt (int option_, const void *optval_,
+    size_t optvallen_)
+{
+    bool is_int = (optvallen_ == sizeof (int));
+    int value = is_int? *((int *) optval_): 0;
+
+    switch (option_) {
+        case ZMQ_PROBE_NEW_PEERS:
+            if (is_int && value >= 0) {
+                probe_new_peers = value;
+                return 0;
+            }
+            break;
+
+        default:
+            break;
+    }
+
+    errno = EINVAL;
+    return -1;
+}
+
 int zmq::dealer_t::xsend (msg_t *msg_)
 {
     return lb.send (msg_);

src/dealer.hpp

@@ -46,6 +46,7 @@ namespace zmq
 
         //  Overloads of functions from socket_base_t.
         void xattach_pipe (zmq::pipe_t *pipe_, bool icanhasall_);
+        int xsetsockopt (int option_, const void *optval_, size_t optvallen_);
         int xsend (zmq::msg_t *msg_);
         int xrecv (zmq::msg_t *msg_);
         bool xhas_in ();
@@ -61,6 +62,9 @@ namespace zmq
         fq_t fq;
         lb_t lb;
 
+        // if true, send an empty message to every connected peer
+        bool probe_new_peers;
+
         dealer_t (const dealer_t&);
         const dealer_t &operator = (const dealer_t&);
     };

src/router.cpp

@@ -34,7 +34,7 @@ zmq::router_t::router_t (class ctx_t *parent_, uint32_t tid_, int sid_) :
     next_peer_id (generate_random ()),
     mandatory(false),
     raw_sock(false),
-    announce_self(false)
+    probe_new_peers(false)
 {
     options.type = ZMQ_ROUTER;
     options.recv_identity = true;
@@ -85,7 +85,7 @@ int zmq::router_t::xsetsockopt (int option_, const void *optval_,
             //  DEBUGGING PROBLEM WITH TRAVIS CI
             printf ("E: invalid option value (int=%d value=%d)\n", is_int, value);
             break;
-        
+
         case ZMQ_ROUTER_MANDATORY:
             if (is_int && value >= 0) {
                 mandatory = value;
@@ -94,14 +94,14 @@ int zmq::router_t::xsetsockopt (int option_, const void *optval_,
             //  DEBUGGING PROBLEM WITH TRAVIS CI
             printf ("E: invalid option value (int=%d value=%d)\n", is_int, value);
             break;
-            
-        case ZMQ_ROUTER_ANNOUNCE_SELF:
+
+        case ZMQ_PROBE_NEW_PEERS:
             if (is_int && value >= 0) {
-                announce_self = value;
+                probe_new_peers = value;
                 return 0;
             }
             break;
-            
+
         default:
             break;
     }
@@ -397,14 +397,23 @@ bool zmq::router_t::identify_peer (pipe_t *pipe_)
     ok = outpipes.insert (outpipes_t::value_type (identity, outpipe)).second;
     zmq_assert (ok);
 
-    if (announce_self) {
-        msg_t tmp_;
-        tmp_.init ();
-        ok = pipe_->write (&tmp_);
-        zmq_assert (ok);
+    if (probe_new_peers) {
+        int rc;
+        msg_t probe_msg_;
+
+        rc = probe_msg_.init ();
+        errno_assert (rc == 0);
+
+        ok = pipe_->write (&probe_msg_);
         pipe_->flush ();
-        tmp_.close ();
-    };
+
+        rc = probe_msg_.close ();
+        errno_assert (rc == 0);
+
+        //  Ignore not probed peers
+        if (!ok)
+            return false;
+    }
 
     return true;
 }

src/router.hpp

@@ -47,8 +47,8 @@ namespace zmq
         //  Overloads of functions from socket_base_t.
         void xattach_pipe (zmq::pipe_t *pipe_, bool icanhasall_);
         int xsetsockopt (int option_, const void *optval_, size_t optvallen_);
-        int xsend (msg_t *msg_);
-        int xrecv (msg_t *msg_);
+        int xsend (zmq::msg_t *msg_);
+        int xrecv (zmq::msg_t *msg_);
         bool xhas_in ();
         bool xhas_out ();
         void xread_activated (zmq::pipe_t *pipe_);
@@ -112,8 +112,8 @@ namespace zmq
         bool mandatory;
         bool raw_sock;
 
-        // if true, send an empty message to every connected peer to solve 'who will write first' race condition
-        bool announce_self;
+        // if true, send an empty message to every connected peer to solve 'who will write first?' auto discovery problem
+        bool probe_new_peers;
 
         router_t (const router_t&);
         const router_t &operator = (const router_t&);