Problem: use of TCP loopback fastpath not available for user sockets

Solution: add socket option

include/zmq.h

@@ -584,6 +584,7 @@ ZMQ_EXPORT void zmq_threadclose (void *thread);
 #define ZMQ_GSSAPI_SERVICE_PRINCIPAL_NAMETYPE 91
 #define ZMQ_BINDTODEVICE 92
 #define ZMQ_ZAP_ENFORCE_DOMAIN 93
+#define ZMQ_LOOPBACK_FASTPATH 94
 
 /*  DRAFT 0MQ socket events and monitoring                                    */
 /*  Unspecified system errors during handshake. Event value is an errno.      */

src/options.cpp

@@ -90,7 +90,8 @@ zmq::options_t::options_t () :
     heartbeat_interval (0),
     heartbeat_timeout (-1),
     use_fd (-1),
-    zap_enforce_domain (false)
+    zap_enforce_domain (false),
+    loopback_fastpath (false)
 {
     memset (curve_public_key, 0, CURVE_KEYSIZE);
     memset (curve_secret_key, 0, CURVE_KEYSIZE);
@@ -627,6 +628,13 @@ int zmq::options_t::setsockopt (int option_,
             }
             break;
 
+        case ZMQ_LOOPBACK_FASTPATH:
+            if (is_int) {
+                loopback_fastpath = (value != 0);
+                return 0;
+            }
+            break;
+
 
         default:
 #if defined(ZMQ_ACT_MILITANT)
@@ -1064,6 +1072,13 @@ int zmq::options_t::getsockopt (int option_,
             }
             break;
 
+        case ZMQ_LOOPBACK_FASTPATH:
+            if (is_int) {
+                *value = loopback_fastpath;
+                return 0;
+            }
+            break;
+
         default:
 #if defined(ZMQ_ACT_MILITANT)
             malformed = false;

src/options.hpp

@@ -248,6 +248,9 @@ struct options_t
 
     //  Enforce a non-empty ZAP domain requirement for PLAIN auth
     bool zap_enforce_domain;
+
+    // Use of loopback fastpath.
+    bool loopback_fastpath;
 };
 }
 

src/signaler.cpp

@@ -65,6 +65,7 @@
 #include "err.hpp"
 #include "fd.hpp"
 #include "ip.hpp"
+#include "tcp.hpp"
 
 #if defined ZMQ_HAVE_EVENTFD
 #include <sys/eventfd.h>
@@ -392,22 +393,7 @@ static void tune_socket (const SOCKET socket)
                          (char *) &tcp_nodelay, sizeof tcp_nodelay);
     wsa_assert (rc != SOCKET_ERROR);
 
-    int sio_loopback_fastpath = 1;
-    DWORD numberOfBytesReturned = 0;
-
-    rc = WSAIoctl (socket, SIO_LOOPBACK_FAST_PATH, &sio_loopback_fastpath,
-                   sizeof sio_loopback_fastpath, NULL, 0,
-                   &numberOfBytesReturned, 0, 0);
-
-    if (SOCKET_ERROR == rc) {
-        DWORD lastError = ::WSAGetLastError ();
-
-        if (WSAEOPNOTSUPP == lastError) {
-            // This system is not Windows 8 or Server 2012, and the call is not supported.
-        } else {
-            wsa_assert (false);
-        }
-    }
+    zmq::tcp_tune_loopback_fast_path (socket);
 }
 #endif
 

src/tcp.cpp

@@ -332,3 +332,27 @@ void zmq::tcp_assert_tuning_error (zmq::fd_t s_, int rc_)
     }
 #endif
 }
+
+void zmq::tcp_tune_loopback_fast_path (const fd_t socket_)
+{
+#if defined ZMQ_HAVE_WINDOWS
+    int sio_loopback_fastpath = 1;
+    DWORD numberOfBytesReturned = 0;
+
+    int rc = WSAIoctl (socket_, SIO_LOOPBACK_FAST_PATH, &sio_loopback_fastpath,
+                       sizeof sio_loopback_fastpath, NULL, 0,
+                       &numberOfBytesReturned, 0, 0);
+
+    if (SOCKET_ERROR == rc) {
+        DWORD lastError = ::WSAGetLastError ();
+
+        if (WSAEOPNOTSUPP == lastError) {
+            // This system is not Windows 8 or Server 2012, and the call is not supported.
+        } else {
+            wsa_assert (false);
+        }
+    }
+#else
+    LIBZMQ_UNUSED (socket_);
+#endif
+}

src/tcp.hpp

@@ -66,6 +66,8 @@ int tcp_read (fd_t s_, void *data_, size_t size_);
 //  Asserts that an internal error did not occur.  Does not assert
 //  on network errors such as reset or aborted connections.
 void tcp_assert_tuning_error (fd_t s_, int rc_);
+
+void tcp_tune_loopback_fast_path (fd_t socket_);
 }
 
 #endif

src/tcp_connecter.cpp

@@ -302,6 +302,10 @@ int zmq::tcp_connecter_t::open ()
     // Set the socket to non-blocking mode so that we get async connect().
     unblock_socket (s);
 
+    // Set the socket to loopback fastpath if configured.
+    if (options.loopback_fastpath)
+        tcp_tune_loopback_fast_path (s);
+
     //  Set the socket buffer limits for the underlying socket.
     if (options.sndbuf >= 0)
         set_tcp_send_buffer (s, options.sndbuf);

src/tcp_listener.cpp

@@ -216,6 +216,10 @@ int zmq::tcp_listener_t::set_address (const char *addr_)
     if (options.tos != 0)
         set_ip_type_of_service (s, options.tos);
 
+    // Set the socket to loopback fastpath if configured.
+    if (options.loopback_fastpath)
+        tcp_tune_loopback_fast_path (s);
+
     // Bind the socket to a device if applicable
     if (!options.bound_device.empty ())
         bind_to_device (s, options.bound_device);

src/zmq_draft.h

@@ -55,6 +55,7 @@ unsigned long zmq_stopwatch_intermediate (void *watch_);
 #define ZMQ_GSSAPI_SERVICE_PRINCIPAL_NAMETYPE 91
 #define ZMQ_BINDTODEVICE 92
 #define ZMQ_ZAP_ENFORCE_DOMAIN 93
+#define ZMQ_LOOPBACK_FASTPATH 94
 
 /*  DRAFT 0MQ socket events and monitoring                                    */
 /*  Unspecified system errors during handshake. Event value is an errno.      */

tests/test_pair_tcp.cpp

@@ -29,9 +29,20 @@
 
 #include "testutil.hpp"
 
-int main (void)
+typedef void (*extra_func_t) (void *socket);
+
+#ifdef ZMQ_BUILD_DRAFT
+void set_sockopt_fastpath (void *socket)
+{
+    int value = 1;
+    int rc =
+      zmq_setsockopt (socket, ZMQ_LOOPBACK_FASTPATH, &value, sizeof value);
+    assert (rc == 0);
+}
+#endif
+
+void test_pair_tcp (extra_func_t extra_func = NULL)
 {
-    setup_test_environment ();
     size_t len = MAX_SOCKET_STRING;
     char my_endpoint[MAX_SOCKET_STRING];
     void *ctx = zmq_ctx_new ();
@@ -39,6 +50,10 @@ int main (void)
 
     void *sb = zmq_socket (ctx, ZMQ_PAIR);
     assert (sb);
+
+    if (extra_func)
+        extra_func (sb);
+
     int rc = zmq_bind (sb, "tcp://127.0.0.1:*");
     assert (rc == 0);
     rc = zmq_getsockopt (sb, ZMQ_LAST_ENDPOINT, my_endpoint, &len);
@@ -46,6 +61,9 @@ int main (void)
 
     void *sc = zmq_socket (ctx, ZMQ_PAIR);
     assert (sc);
+    if (extra_func)
+        extra_func (sc);
+
     rc = zmq_connect (sc, my_endpoint);
     assert (rc == 0);
 
@@ -59,6 +77,16 @@ int main (void)
 
     rc = zmq_ctx_term (ctx);
     assert (rc == 0);
+}
+
+int main (void)
+{
+    setup_test_environment ();
+
+    test_pair_tcp ();
+#ifdef ZMQ_BUILD_DRAFT
+    test_pair_tcp (set_sockopt_fastpath);
+#endif
 
     return 0;
 }