Add ZMQ_REQ_SEND_RESETS option.

This allows making a new request on a REQ socket by sending a new
message. Without the option set, calling send() after the first message
is done will continue to return an EFSM error.

It's useful for when a REQ is not getting a response. Previously that
meant creating a new socket or switching to DEALER.

.gitignore

@@ -59,6 +59,7 @@ tests/test_spec_rep
 tests/test_spec_req
 tests/test_spec_router
 tests/test_req_request_ids
+tests/test_req_send_resets
 src/platform.hpp*
 src/stamp-h1
 perf/local_lat

doc/zmq_setsockopt.txt

@@ -13,10 +13,10 @@ SYNOPSIS
 *int zmq_setsockopt (void '*socket', int 'option_name', const void '*option_value', size_t 'option_len');*
 
 Caution: All options, with the exception of ZMQ_SUBSCRIBE, ZMQ_UNSUBSCRIBE,
-ZMQ_LINGER, ZMQ_ROUTER_MANDATORY, ZMQ_PROBE_ROUTER, ZMQ_XPUB_VERBOSE only 
-take effect for subsequent socket bind/connects. Specifically, security 
-options take effect for subsequent binds/connects and can be changed at any 
-time to affect subsequent binds and/or connects.
+ZMQ_LINGER, ZMQ_ROUTER_MANDATORY, ZMQ_PROBE_ROUTER, ZMQ_XPUB_VERBOSE,
+ZMQ_REQ_SEND_RESETS only take effect for subsequent socket bind/connects.
+Specifically, security options take effect for subsequent binds/connects and can be
+changed at any time to affect subsequent binds and/or connects.
 
 DESCRIPTION
 -----------
@@ -476,6 +476,28 @@ Default value:: 0
 Applicable socket types:: ZMQ_REQ
 
 
+ZMQ_REQ_SEND_RESETS: reset request-reply sequence by sending another message
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When set to 0, a REQ socket does not allow initiating a new request with
+_zmq_send(3)_ until the reply to the previous one has been received. 
+When set to 1, sending another message is allowed and has the effect of
+disconnecting the underlying connection to the peer from which the reply was
+expected, triggering a reconnection attempt on transports that support it.
+The request-reply state machine is reset and a new request is sent to the
+next available peer.
+
+When this option is enabled, also enable ZMQ_REQ_REQUEST_IDS to ensure correct
+matching of requests and replies. Otherwise a late reply to an aborted request
+can be reported as the reply to the superseding request.
+
+[horizontal]
+Option value type:: int
+Option value unit:: 0, 1
+Default value:: 0
+Applicable socket types:: ZMQ_REQ
+
+
 ZMQ_TCP_KEEPALIVE: Override SO_KEEPALIVE socket option
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

include/zmq.h

@@ -277,6 +277,7 @@ ZMQ_EXPORT int zmq_msg_set (zmq_msg_t *msg, int option, int optval);
 #define ZMQ_CURVE_SERVERKEY 50
 #define ZMQ_PROBE_ROUTER 51
 #define ZMQ_REQ_REQUEST_IDS 52
+#define ZMQ_REQ_SEND_RESETS 53
 
 /*  Message options                                                           */
 #define ZMQ_MORE 1

src/req.cpp

@@ -30,7 +30,8 @@ zmq::req_t::req_t (class ctx_t *parent_, uint32_t tid_, int sid_) :
     message_begins (true),
     reply_pipe (NULL),
     request_id_frames_enabled (false),
-    request_id (generate_random())
+    request_id (generate_random()),
+    send_resets (false)
 {
     options.type = ZMQ_REQ;
 }
@@ -42,12 +43,19 @@ zmq::req_t::~req_t ()
 int zmq::req_t::xsend (msg_t *msg_)
 {
     //  If we've sent a request and we still haven't got the reply,
-    //  we can't send another request.
+    //  we can't send another request unless the send_resets option is enabled.
     if (receiving_reply) {
+        if (!send_resets) {
             errno = EFSM;
             return -1;
         }
 
+        if (reply_pipe)
+            reply_pipe->terminate (false);
+        receiving_reply = false;
+        message_begins = true;
+    }
+
     //  First part of the request is the request identity.
     if (message_begins) {
         reply_pipe = NULL;
@@ -197,6 +205,13 @@ int zmq::req_t::xsetsockopt(int option_, const void *optval_, size_t optvallen_)
             }
             break;
 
+        case ZMQ_REQ_SEND_RESETS:
+            if (is_int && value >= 0) {
+                send_resets = value;
+                return 0;
+            }
+            break;
+
         default:
             break;
     }

src/req.hpp

@@ -43,7 +43,7 @@ namespace zmq
         int xrecv (zmq::msg_t *msg_);
         bool xhas_in ();
         bool xhas_out ();
-        int xsetsockopt(int option_, const void *optval_, size_t optvallen_);
+        int xsetsockopt (int option_, const void *optval_, size_t optvallen_);
 
     protected:
 
@@ -71,8 +71,9 @@ namespace zmq
         //  request is sent.
         uint32_t request_id;
 
-        //  If true, send() will reset its internal state instead of failing if
-        //  a previous request is still pending.
+        //  If true, send() will reset its internal state and terminate the
+        //  reply_pipe's connection instead of failing if a previous request is
+        //  still pending.
         bool send_resets;
 
         req_t (const req_t&);

tests/Makefile.am

@@ -30,7 +30,8 @@ noinst_PROGRAMS = test_pair_inproc \
                   test_spec_dealer \
                   test_spec_router \
                   test_spec_pushpull \
-                  test_req_request_ids
+                  test_req_request_ids \
+                  test_req_send_resets
 
 if !ON_MINGW
 noinst_PROGRAMS += test_shutdown_stress \
@@ -67,6 +68,7 @@ test_spec_dealer_SOURCES = test_spec_dealer.cpp
 test_spec_router_SOURCES = test_spec_router.cpp
 test_spec_pushpull_SOURCES = test_spec_pushpull.cpp
 test_req_request_ids_SOURCES = test_req_request_ids.cpp
+test_req_send_resets_SOURCES = test_req_send_resets.cpp
 if !ON_MINGW
 test_shutdown_stress_SOURCES = test_shutdown_stress.cpp
 test_pair_ipc_SOURCES = test_pair_ipc.cpp testutil.hpp

tests/test_req_send_resets.cpp

+/*
+    Copyright (c) 2007-2013 Contributors as noted in the AUTHORS file
+
+    This file is part of 0MQ.
+
+    0MQ is free software; you can redistribute it and/or modify it under
+    the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    0MQ is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <stdio.h>
+#include <unistd.h>
+#include <time.h>
+#include "testutil.hpp"
+
+int main (void)
+{
+    void *ctx = zmq_ctx_new ();
+    assert (ctx);
+
+    void *req = zmq_socket (ctx, ZMQ_REQ);
+    assert (req);
+
+    int enabled = 1;
+    int rc = zmq_setsockopt (req, ZMQ_REQ_SEND_RESETS, &enabled, sizeof (int));
+    assert (rc == 0);
+
+    rc = zmq_setsockopt (req, ZMQ_REQ_REQUEST_IDS, &enabled, sizeof (int));
+    assert (rc == 0);
+
+    rc = zmq_bind (req, "tcp://*:5555");
+    assert (rc == 0);
+
+    const size_t services = 5;
+    void *rep [services];
+    for (size_t peer = 0; peer < services; peer++) {
+        rep [peer] = zmq_socket (ctx, ZMQ_REP);
+        assert (rep [peer]);
+
+        int timeout = 100;
+        rc = zmq_setsockopt (rep [peer], ZMQ_RCVTIMEO, &timeout, sizeof (int));
+        assert (rc == 0);
+
+        rc = zmq_connect (rep [peer], "tcp://localhost:5555");
+        assert (rc == 0);
+    }
+    //  We have to give the connects time to finish otherwise the requests
+    //  will not properly round-robin. We could alternatively connect the
+    //  REQ sockets to the REP sockets.
+    struct timespec t = { 0, 250 * 1000000 };
+    nanosleep (&t, NULL);
+
+
+    //  Case 1: Second send() before a reply arrives in a pipe.
+
+    //  Send a request, ensure it arrives, don't send a reply
+    s_send_seq (req, "A", "B", SEQ_END);
+    s_recv_seq (rep [0], "A", "B", SEQ_END);
+
+    //  Send another request on the REQ socket
+    s_send_seq (req, "C", "D", SEQ_END);
+    s_recv_seq (rep [1], "C", "D", SEQ_END);
+
+    //  Send a reply to the first request - that should be discarded by the REQ
+    s_send_seq (rep [0], "WRONG", SEQ_END);
+
+    //  Send the expected reply
+    s_send_seq (rep [1], "OK", SEQ_END);
+    s_recv_seq (req, "OK", SEQ_END);
+
+
+    //  Another standard req-rep cycle, just to check
+    s_send_seq (req, "E", SEQ_END);
+    s_recv_seq (rep [2], "E", SEQ_END);
+    s_send_seq (rep [2], "F", "G", SEQ_END);
+    s_recv_seq (req, "F", "G", SEQ_END);
+
+
+    //  Case 2: Second send() after a reply is already in a pipe on the REQ.
+
+    //  Send a request, ensure it arrives, send a reply
+    s_send_seq (req, "H", SEQ_END);
+    s_recv_seq (rep [3], "H", SEQ_END);
+    s_send_seq (rep [3], "BAD", SEQ_END);
+
+    // Wait for message to be there.
+    rc = zmq_poll (0, 0, 100);
+    assert (rc == 0);
+
+    //  Without receiving that reply, send another request on the REQ socket
+    s_send_seq (req, "I", SEQ_END);
+    s_recv_seq (rep [4], "I", SEQ_END);
+
+    //  Send the expected reply
+    s_send_seq (rep [4], "GOOD", SEQ_END);
+    s_recv_seq (req, "GOOD", SEQ_END);
+
+
+    close_zero_linger (req);
+    for (size_t peer = 0; peer < services; peer++)
+        close_zero_linger (rep [peer]);
+
+    // Wait for disconnects.
+    rc = zmq_poll (0, 0, 100);
+    assert (rc == 0);
+
+    rc = zmq_ctx_term (ctx);
+    assert (rc == 0);
+
+    return 0 ;
+}