Problem: cannot use new pre-allocated FD with IPC

Solution: parse the value set by the ZMQ_PRE_ALLOCATED_FD sockopt
when creating a new IPC socket and use it if valid.
Add new tests/test_pre_allocated_fd_ipc.cpp unit test.

.gitignore

@@ -125,6 +125,7 @@ test_timers
 test_radio_dish
 test_udp
 test_large_msg
+test_pre_allocated_fd_ipc
 tests/test*.log
 tests/test*.trs
 src/platform.hpp*

Makefile.am

@@ -617,6 +617,7 @@ test_apps += \
 	tests/test_shutdown_stress \
 	tests/test_pair_ipc \
 	tests/test_reqrep_ipc \
+	tests/test_pre_allocated_fd_ipc \
 	tests/test_timeo \
 	tests/test_filter_ipc
 
@@ -639,6 +640,11 @@ tests_test_timeo_LDADD = src/libzmq.la
 tests_test_filter_ipc_SOURCES = tests/test_filter_ipc.cpp
 tests_test_filter_ipc_LDADD = src/libzmq.la
 
+tests_test_pre_allocated_fd_ipc_SOURCES = \
+	tests/test_pre_allocated_fd_ipc.cpp \
+	tests/testutil.hpp
+tests_test_pre_allocated_fd_ipc_LDADD = src/libzmq.la
+
 if HAVE_FORK
 test_apps += tests/test_fork
 

src/ipc_listener.cpp

@@ -155,7 +155,12 @@ int zmq::ipc_listener_t::set_address (const char *addr_)
 
     //  Get rid of the file associated with the UNIX domain socket that
     //  may have been left behind by the previous run of the application.
-    ::unlink (addr.c_str());
+    //  MUST NOT unlink if the FD is managed by the user, or it will stop
+    //  working after the first client connects. The user will take care of
+    //  cleaning up the file after the service is stopped.
+    if (options.pre_allocated_fd == -1) {
+        ::unlink (addr.c_str());
+    }
     filename.clear ();
 
     //  Initialise the address structure.
@@ -164,26 +169,30 @@ int zmq::ipc_listener_t::set_address (const char *addr_)
     if (rc != 0)
         return -1;
 
-    //  Create a listening socket.
-    s = open_socket (AF_UNIX, SOCK_STREAM, 0);
-    if (s == -1)
-        return -1;
-
     address.to_string (endpoint);
 
-    //  Bind the socket to the file path.
-    rc = bind (s, address.addr (), address.addrlen ());
-    if (rc != 0)
-        goto error;
+    if (options.pre_allocated_fd != -1) {
+        s = options.pre_allocated_fd;
+    } else {
+        //  Create a listening socket.
+        s = open_socket (AF_UNIX, SOCK_STREAM, 0);
+        if (s == -1)
+            return -1;
+
+        //  Bind the socket to the file path.
+        rc = bind (s, address.addr (), address.addrlen ());
+        if (rc != 0)
+            goto error;
+
+        //  Listen for incoming connections.
+        rc = listen (s, options.backlog);
+        if (rc != 0)
+            goto error;
+    }
 
     filename.assign (addr.c_str());
     has_file = true;
 
-    //  Listen for incoming connections.
-    rc = listen (s, options.backlog);
-    if (rc != 0)
-        goto error;
-
     socket->event_listening (endpoint, s);
     return 0;
 
@@ -204,7 +213,10 @@ int zmq::ipc_listener_t::close ()
 
     //  If there's an underlying UNIX domain socket, get rid of the file it
     //  is associated with.
-    if (has_file && !filename.empty ()) {
+    //  MUST NOT unlink if the FD is managed by the user, or it will stop
+    //  working after the first client connects. The user will take care of
+    //  cleaning up the file after the service is stopped.
+    if (has_file && !filename.empty () && options.pre_allocated_fd == -1) {
         rc = ::unlink(filename.c_str ());
         if (rc != 0) {
             socket->event_close_failed (endpoint, zmq_errno());

tests/CMakeLists.txt

@@ -90,6 +90,7 @@ if(NOT WIN32)
           test_stream_exceeds_buffer
           test_router_mandatory_hwm
           test_term_endpoint_tipc
+          test_pre_allocated_fd_ipc
   )
   if(HAVE_FORK)
     list(APPEND tests test_fork)

tests/test_pre_allocated_fd_ipc.cpp

@@ -0,0 +1,213 @@
+/*
+    Copyright (c) 2007-2016 Contributors as noted in the AUTHORS file
+
+    This file is part of libzmq, the ZeroMQ core engine in C++.
+
+    libzmq is free software; you can redistribute it and/or modify it under
+    the terms of the GNU Lesser General Public License (LGPL) as published
+    by the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    As a special exception, the Contributors give you permission to link
+    this library with independent modules to produce an executable,
+    regardless of the license terms of these independent modules, and to
+    copy and distribute the resulting executable under terms of your choice,
+    provided that you also meet, for each linked independent module, the
+    terms and conditions of the license of that module. An independent
+    module is a module which is not derived from or based on this library.
+    If you modify this library, you must extend this exception to your
+    version of the library.
+
+    libzmq 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 <sys/types.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include "testutil.hpp"
+
+void pre_allocate_sock (void *zmq_socket, const char *path)
+{
+    struct sockaddr_un addr;
+    addr.sun_family = AF_UNIX;
+    strcpy (addr.sun_path, path);
+
+    unlink (path);
+
+    int s_pre = socket (AF_UNIX, SOCK_STREAM, 0);
+    assert (s_pre != -1);
+
+    int rc = bind (s_pre, (struct sockaddr *) &addr,
+            sizeof (struct sockaddr_un));
+    assert (rc == 0);
+
+    rc = listen (s_pre, SOMAXCONN);
+    assert (rc == 0);
+
+    rc = zmq_setsockopt (zmq_socket, ZMQ_PRE_ALLOCATED_FD, &s_pre,
+            sizeof (s_pre));
+    assert(rc == 0);
+}
+
+void test_req_rep ()
+{
+    void *ctx = zmq_ctx_new ();
+    assert (ctx);
+
+    void *sb = zmq_socket (ctx, ZMQ_REP);
+    assert (sb);
+
+    pre_allocate_sock(sb, "/tmp/tester");
+
+    int rc = zmq_bind (sb, "ipc:///tmp/tester");
+    assert (rc == 0);
+
+    void *sc = zmq_socket (ctx, ZMQ_REQ);
+    assert (sc);
+    rc = zmq_connect (sc, "ipc:///tmp/tester");
+    assert (rc == 0);
+
+    bounce (sb, sc);
+
+    rc = zmq_close (sc);
+    assert (rc == 0);
+
+    rc = zmq_close (sb);
+    assert (rc == 0);
+
+    rc = zmq_ctx_term (ctx);
+    assert (rc == 0);
+
+    rc = unlink ("/tmp/tester");
+    assert (rc == 0);
+}
+
+void test_pair ()
+{
+    void *ctx = zmq_ctx_new ();
+    assert (ctx);
+
+    void *sb = zmq_socket (ctx, ZMQ_PAIR);
+    assert (sb);
+
+    pre_allocate_sock(sb, "/tmp/tester");
+
+    int rc = zmq_bind (sb, "ipc:///tmp/tester");
+    assert (rc == 0);
+
+    void *sc = zmq_socket (ctx, ZMQ_PAIR);
+    assert (sc);
+    rc = zmq_connect (sc, "ipc:///tmp/tester");
+    assert (rc == 0);
+
+    bounce (sb, sc);
+
+    rc = zmq_close (sc);
+    assert (rc == 0);
+
+    rc = zmq_close (sb);
+    assert (rc == 0);
+
+    rc = zmq_ctx_term (ctx);
+    assert (rc == 0);
+
+    rc = unlink ("/tmp/tester");
+    assert (rc == 0);
+}
+
+void test_client_server ()
+{
+    void *ctx = zmq_ctx_new ();
+    assert (ctx);
+
+    void *sb = zmq_socket (ctx, ZMQ_SERVER);
+    assert (sb);
+
+    pre_allocate_sock(sb, "/tmp/tester");
+
+    int rc = zmq_bind (sb, "ipc:///tmp/tester");
+    assert (rc == 0);
+
+    void *sc = zmq_socket (ctx, ZMQ_CLIENT);
+    assert (sc);
+    rc = zmq_connect (sc, "ipc:///tmp/tester");
+    assert (rc == 0);
+
+    zmq_msg_t msg;
+    rc = zmq_msg_init_size (&msg, 1);
+    assert (rc == 0);
+
+    char *data = (char *) zmq_msg_data (&msg);
+    data [0] = 1;
+
+    rc = zmq_msg_send (&msg, sc, ZMQ_SNDMORE);
+    assert (rc == -1);
+
+    rc = zmq_msg_send (&msg, sc, 0);
+    assert (rc == 1);
+
+    rc = zmq_msg_init (&msg);
+    assert (rc == 0);
+
+    rc = zmq_msg_recv (&msg, sb, 0);
+    assert (rc == 1);
+
+    uint32_t routing_id = zmq_msg_routing_id (&msg);
+    assert (routing_id != 0);
+
+    rc = zmq_msg_close (&msg);
+    assert (rc == 0);
+
+    rc = zmq_msg_init_size (&msg, 1);
+    assert (rc == 0);
+
+    data = (char *)zmq_msg_data (&msg);
+    data[0] = 2;
+
+    rc = zmq_msg_set_routing_id (&msg, routing_id);
+    assert (rc == 0);
+
+    rc = zmq_msg_send (&msg, sb, ZMQ_SNDMORE);
+    assert (rc == -1);
+
+    rc = zmq_msg_send (&msg, sb, 0);
+    assert (rc == 1);
+
+    rc = zmq_msg_recv (&msg, sc, 0);
+    assert (rc == 1);
+
+    routing_id = zmq_msg_routing_id (&msg);
+    assert (routing_id == 0);
+
+    rc = zmq_msg_close (&msg);
+    assert (rc == 0);
+
+    rc = zmq_close (sc);
+    assert (rc == 0);
+
+    rc = zmq_close (sb);
+    assert (rc == 0);
+
+    rc = zmq_ctx_term (ctx);
+    assert (rc == 0);
+
+    rc = unlink ("/tmp/tester");
+    assert (rc == 0);
+}
+
+int main (void)
+{
+    setup_test_environment();
+
+    test_req_rep();
+    test_pair();
+    test_client_server();
+
+    return 0 ;
+}