Add ZMQ_REQ_REQUEST_IDS option.

* Documentation:
The default behavior of REQ sockets is to rely on the ordering of messages
to match requests and responses and that is usually sufficient. When this option
is set to 1, the REQ socket will prefix outgoing messages with an extra frame
containing a request id. That means the full message is (request id, 0,
user frames...). The REQ socket will discard all incoming messages that don't
begin with these two frames.

* Behavior change: When a REQ socket gets an invalid reply, it used to
  discard the message and return EAGAIN. REQ sockets still discard
  invalid messages, but keep looking at the next one automatically
  until a good one is found or there are no more messages.
* Add test_req_request_ids.

.gitignore

@@ -58,6 +58,7 @@ tests/test_spec_pushpull
 tests/test_spec_rep
 tests/test_spec_req
 tests/test_spec_router
+tests/test_req_request_ids
 src/platform.hpp*
 src/stamp-h1
 perf/local_lat

doc/zmq_setsockopt.txt

@@ -459,6 +459,23 @@ Default value:: 0
 Applicable socket types:: ZMQ_XPUB
 
 
+ZMQ_REQ_REQUEST_IDS: enable extra request identity frames
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The default behavior of REQ sockets is to rely on the ordering of messages
+to match requests and responses and that is usually sufficient. When this option
+is set to 1, the REQ socket will prefix outgoing messages with an extra frame
+containing a request id. That means the full message is (request id, 0,
+user frames...). The REQ socket will discard all incoming messages that don't
+begin with these two frames.
+
+[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

@@ -276,6 +276,7 @@ ZMQ_EXPORT int zmq_msg_set (zmq_msg_t *msg, int option, int optval);
 #define ZMQ_CURVE_SECRETKEY 49
 #define ZMQ_CURVE_SERVERKEY 50
 #define ZMQ_PROBE_ROUTER 51
+#define ZMQ_REQ_REQUEST_IDS 52
 
 /*  Message options                                                           */
 #define ZMQ_MORE 1

src/req.cpp

@@ -28,7 +28,9 @@ zmq::req_t::req_t (class ctx_t *parent_, uint32_t tid_, int sid_) :
     dealer_t (parent_, tid_, sid_),
     receiving_reply (false),
     message_begins (true),
-    reply_pipe (NULL)
+    reply_pipe (NULL),
+    request_id_frames_enabled (false),
+    request_id (generate_random())
 {
     options.type = ZMQ_REQ;
 }
@@ -48,16 +50,31 @@ int zmq::req_t::xsend (msg_t *msg_)
 
     //  First part of the request is the request identity.
     if (message_begins) {
+        reply_pipe = NULL;
+
+        if (request_id_frames_enabled) {
+            request_id++;
+
+            msg_t id;
+            int rc = id.init_data (&request_id, sizeof (request_id), NULL, NULL);
+            errno_assert (rc == 0);
+            id.set_flags (msg_t::more);
+
+            rc = dealer_t::sendpipe (&id, &reply_pipe);
+            if (rc != 0)
+                return -1;
+        }
+
         msg_t bottom;
         int rc = bottom.init ();
         errno_assert (rc == 0);
         bottom.set_flags (msg_t::more);
 
-        reply_pipe = NULL;
         rc = dealer_t::sendpipe (&bottom, &reply_pipe);
         if (rc != 0)
             return -1;
         assert (reply_pipe);
+
         message_begins = false;
 
         // Eat all currently avaliable messages before the request is fully
@@ -99,24 +116,39 @@ int zmq::req_t::xrecv (msg_t *msg_)
         return -1;
     }
 
-    //  First part of the reply should be the original request ID.
-    if (message_begins) {
+    //  Skip messages until one with the right first frames is found.
+    while (message_begins) {
+        //  If enabled, the first frame must have the correct request_id.
+        if (request_id_frames_enabled) {
+            int rc = recv_reply_pipe (msg_);
+            if (rc != 0)
+                return rc;
+
+            if (unlikely (!(msg_->flags () & msg_t::more) ||
+                          msg_->size () != sizeof (request_id) ||
+                          *static_cast<uint32_t *> (msg_->data ()) != request_id)) {
+                //  Skip the remaining frames and try the next message
+                while (msg_->flags () & msg_t::more) {
+                    rc = recv_reply_pipe (msg_);
+                    errno_assert (rc == 0);
+                }
+                continue;
+            }
+        }
+
+        //  The next frame must be 0.
+        // TODO: Failing this check should also close the connection with the peer!
         int rc = recv_reply_pipe (msg_);
         if (rc != 0)
             return rc;
 
-        // TODO: This should also close the connection with the peer!
         if (unlikely (!(msg_->flags () & msg_t::more) || msg_->size () != 0)) {
-            while (true) {
-                int rc = dealer_t::xrecv (msg_);
+            //  Skip the remaining frames and try the next message
+            while (msg_->flags () & msg_t::more) {
+                rc = recv_reply_pipe (msg_);
                 errno_assert (rc == 0);
-                if (!(msg_->flags () & msg_t::more))
-                    break;
             }
-            msg_->close ();
-            msg_->init ();
-            errno = EAGAIN;
-            return -1;
+            continue;
         }
 
         message_begins = false;
@@ -153,6 +185,25 @@ bool zmq::req_t::xhas_out ()
     return dealer_t::xhas_out ();
 }
 
+int zmq::req_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_REQ_REQUEST_IDS:
+            if (is_int && value >= 0) {
+                request_id_frames_enabled = value;
+                return 0;
+            }
+            break;
+
+        default:
+            break;
+    }
+
+    return dealer_t::xsetsockopt(option_, optval_, optvallen_);
+}
+
 int zmq::req_t::recv_reply_pipe (msg_t *msg_)
 {
     while (true) {

src/req.hpp

@@ -43,6 +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_);
 
     protected:
 
@@ -63,6 +64,17 @@ namespace zmq
         //  The pipe the request was sent to and where the reply is expected.
         zmq::pipe_t *reply_pipe;
 
+        //  Whether request id frames shall be sent and expected.
+        bool request_id_frames_enabled;
+
+        //  The current request id. It is incremented every time before a new
+        //  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.
+        bool send_resets;
+
         req_t (const req_t&);
         const req_t &operator = (const req_t&);
     };

tests/Makefile.am

@@ -29,7 +29,8 @@ noinst_PROGRAMS = test_pair_inproc \
                   test_spec_rep \
                   test_spec_dealer \
                   test_spec_router \
-                  test_spec_pushpull
+                  test_spec_pushpull \
+                  test_req_request_ids
 
 if !ON_MINGW
 noinst_PROGRAMS += test_shutdown_stress \
@@ -65,6 +66,7 @@ test_spec_rep_SOURCES = test_spec_rep.cpp
 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
 if !ON_MINGW
 test_shutdown_stress_SOURCES = test_shutdown_stress.cpp
 test_pair_ipc_SOURCES = test_pair_ipc.cpp testutil.hpp

tests/test_req_request_ids.cpp

@@ -0,0 +1,179 @@
+/*
+    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);
+
+    void *router = zmq_socket (ctx, ZMQ_ROUTER);
+    assert (router);
+
+    int enabled = 1;
+    int rc = zmq_setsockopt (req, ZMQ_REQ_REQUEST_IDS, &enabled, sizeof (int));
+    assert (rc == 0);
+
+    int rcvtimeo = 100;
+    rc = zmq_setsockopt (req, ZMQ_RCVTIMEO, &rcvtimeo, sizeof (int));
+    assert (rc == 0);
+
+    rc = zmq_connect (req, "tcp://localhost:5555");
+    assert (rc == 0);
+
+    rc = zmq_bind (router, "tcp://*:5555");
+    assert (rc == 0);
+
+    // Send a multi-part request.
+    s_send_seq (req, "ABC", "DEF", SEQ_END);
+
+    zmq_msg_t msg;
+    zmq_msg_init (&msg);
+
+    // Receive peer identity
+    rc = zmq_msg_recv (&msg, router, 0);
+    assert (rc != -1);
+    assert (zmq_msg_size (&msg) > 0);
+    zmq_msg_t peer_id_msg;
+    zmq_msg_init (&peer_id_msg);
+    zmq_msg_copy (&peer_id_msg, &msg);
+
+    int more = 0;
+    size_t more_size = sizeof (more);
+    rc = zmq_getsockopt (router, ZMQ_RCVMORE, &more, &more_size);
+    assert (rc == 0);
+    assert (more);
+
+    // Receive request id 1
+    rc = zmq_msg_recv (&msg, router, 0);
+    assert (rc != -1);
+    assert (zmq_msg_size (&msg) == sizeof(uint32_t));
+    uint32_t req_id = *static_cast<uint32_t *> (zmq_msg_data (&msg));
+    zmq_msg_t req_id_msg;
+    zmq_msg_init (&req_id_msg);
+    zmq_msg_copy (&req_id_msg, &msg);
+
+    more = 0;
+    more_size = sizeof (more);
+    rc = zmq_getsockopt (router, ZMQ_RCVMORE, &more, &more_size);
+    assert (rc == 0);
+    assert (more);
+
+    // Receive the rest.
+    s_recv_seq (router, 0, "ABC", "DEF", SEQ_END);
+
+    // Send back a bad reply: correct req id
+    zmq_msg_copy (&msg, &peer_id_msg);
+    rc = zmq_msg_send (&msg, router, ZMQ_SNDMORE);
+    assert (rc != -1);
+    zmq_msg_copy (&msg, &req_id_msg);
+    rc = zmq_msg_send (&msg, router, 0);
+    assert (rc != -1);
+
+    // Send back a bad reply: wrong req id
+    zmq_msg_copy (&msg, &peer_id_msg);
+    rc = zmq_msg_send (&msg, router, ZMQ_SNDMORE);
+    assert (rc != -1);
+    uint32_t bad_req_id = req_id + 1;
+    zmq_msg_init_data (&msg, &bad_req_id, sizeof (uint32_t), NULL, NULL);
+    rc = zmq_msg_send (&msg, router, 0);
+    assert (rc != -1);
+
+    // Send back a bad reply: correct req id, 0
+    zmq_msg_copy (&msg, &peer_id_msg);
+    rc = zmq_msg_send (&msg, router, ZMQ_SNDMORE);
+    assert (rc != -1);
+    zmq_msg_copy (&msg, &req_id_msg);
+    rc = zmq_msg_send (&msg, router, ZMQ_SNDMORE);
+    assert (rc != -1);
+    s_send_seq (router, 0, SEQ_END);
+
+    // Send back a bad reply: correct req id, garbage
+    zmq_msg_copy (&msg, &peer_id_msg);
+    rc = zmq_msg_send (&msg, router, ZMQ_SNDMORE);
+    assert (rc != -1);
+    zmq_msg_copy (&msg, &req_id_msg);
+    rc = zmq_msg_send (&msg, router, ZMQ_SNDMORE);
+    assert (rc != -1);
+    s_send_seq (router, "FOO", SEQ_END);
+
+    // Send back a bad reply: wrong req id, 0
+    zmq_msg_copy (&msg, &peer_id_msg);
+    rc = zmq_msg_send (&msg, router, ZMQ_SNDMORE);
+    assert (rc != -1);
+    zmq_msg_init_data (&msg, &bad_req_id, sizeof (uint32_t), NULL, NULL);
+    rc = zmq_msg_send (&msg, router, ZMQ_SNDMORE);
+    assert (rc != -1);
+    s_send_seq (router, 0, SEQ_END);
+
+    // Send back a bad reply: correct req id, garbage, data
+    zmq_msg_copy (&msg, &peer_id_msg);
+    rc = zmq_msg_send (&msg, router, ZMQ_SNDMORE);
+    assert (rc != -1);
+    zmq_msg_copy (&msg, &req_id_msg);
+    rc = zmq_msg_send (&msg, router, ZMQ_SNDMORE);
+    assert (rc != -1);
+    s_send_seq (router, "FOO", "DATA", SEQ_END);
+
+    // Send back a bad reply: wrong req id, 0, data
+    zmq_msg_copy (&msg, &peer_id_msg);
+    rc = zmq_msg_send (&msg, router, ZMQ_SNDMORE);
+    assert (rc != -1);
+    zmq_msg_init_data (&msg, &bad_req_id, sizeof (uint32_t), NULL, NULL);
+    rc = zmq_msg_send (&msg, router, ZMQ_SNDMORE);
+    assert (rc != -1);
+    s_send_seq (router, 0, "DATA", SEQ_END);
+
+    // Send back a good reply.
+    zmq_msg_copy (&msg, &peer_id_msg);
+    rc = zmq_msg_send (&msg, router, ZMQ_SNDMORE);
+    assert (rc != -1);
+    zmq_msg_copy (&msg, &req_id_msg);
+    rc = zmq_msg_send (&msg, router, ZMQ_SNDMORE);
+    assert (rc != -1);
+    s_send_seq (router, 0, "GHI", SEQ_END);
+
+    // Receive reply. If any of the other messages got through, we wouldn't see
+    // this particular data.
+    s_recv_seq (req, "GHI", SEQ_END);
+
+    rc = zmq_msg_close (&msg);
+    assert (rc == 0);
+
+    rc = zmq_msg_close (&peer_id_msg);
+    assert (rc == 0);
+
+    rc = zmq_msg_close (&req_id_msg);
+    assert (rc == 0);
+
+    close_zero_linger (req);
+    close_zero_linger (router);
+
+    rc = zmq_ctx_term (ctx);
+    assert (rc == 0);
+
+    return 0;
+}