unix, win: add uv_udp_try_send

The function returns UV_EAGAIN if the queue is not empty and
the message couldn't be sent immediately.

Makefile.am

@@ -214,6 +214,7 @@ test_run_tests_SOURCES = test/blackhole-server.c \
                          test/test-udp-open.c \
                          test/test-udp-options.c \
                          test/test-udp-send-and-recv.c \
+                         test/test-udp-try-send.c \
                          test/test-walk-handles.c \
                          test/test-watcher-cross-stop.c
 test_run_tests_LDADD = libuv.la

include/uv.h

@@ -901,12 +901,12 @@ typedef void (*uv_udp_recv_cb)(uv_udp_t* handle,
 struct uv_udp_s {
   UV_HANDLE_FIELDS
   /* read-only */
-  /* Total size of buffers queued for sending. May send
-   * actually less since udp packets are truncated to the MTU size.
+  /* number of bytes queued for sending, ay send
+   * actually less since udp packets are truncated to the MTU size
    */
   size_t send_queue_size;
-  /* Total count of sends currently in the queue awaiting to
-   * be processed.
+  /* number of send requests currently in the queue awaiting to
+   * be processed
    */
   size_t send_queue_count;
   UV_UDP_PRIVATE_FIELDS
@@ -1076,6 +1076,19 @@ UV_EXTERN int uv_udp_send(uv_udp_send_t* req,
                           const struct sockaddr* addr,
                           uv_udp_send_cb send_cb);
 
+/*
+ * Same as `uv_udp_send()`, but won't queue a send request if it can't be completed
+ * immediately.
+ * Will return either:
+ * - >= 0: number of bytes written (can be less than the supplied buffer size if the
+ *         packet is truncated)
+ * - < 0: negative error code (UV_EAGAIN is returned when the message can't be sent
+ *        immediately)
+ */
+UV_EXTERN int uv_udp_try_send(uv_udp_t* handle,
+                              const uv_buf_t bufs[],
+                              unsigned int nbufs,
+                              const struct sockaddr* addr);
 /*
  * Receive data. If the socket has not previously been bound with `uv_udp_bind`
  * it is bound to 0.0.0.0 (the "all interfaces" address) and a random

src/unix/udp.c

@@ -448,6 +448,46 @@ int uv__udp_send(uv_udp_send_t* req,
 }
 
 
+int uv__udp_try_send(uv_udp_t* handle,
+                     const uv_buf_t bufs[],
+                     unsigned int nbufs,
+                     const struct sockaddr* addr,
+                     unsigned int addrlen) {
+  int err;
+  struct msghdr h;
+  ssize_t size;
+
+  assert(nbufs > 0);
+
+  /* already sending a message */
+  if (handle->send_queue_count != 0)
+    return -EAGAIN;
+
+  err = uv__udp_maybe_deferred_bind(handle, addr->sa_family, 0);
+  if (err)
+    return err;
+
+  memset(&h, 0, sizeof h);
+  h.msg_name = (struct sockaddr*) addr;
+  h.msg_namelen = addrlen;
+  h.msg_iov = (struct iovec*) bufs;
+  h.msg_iovlen = nbufs;
+
+  do {
+    size = sendmsg(handle->io_watcher.fd, &h, 0);
+  } while (size == -1 && errno == EINTR);
+
+  if (size == -1) {
+    if (errno == EAGAIN || errno == EWOULDBLOCK)
+      return -EAGAIN;
+    else
+      return -errno;
+  }
+
+  return size;
+}
+
+
 static int uv__udp_set_membership4(uv_udp_t* handle,
                                    const struct sockaddr_in* multicast_addr,
                                    const char* interface_addr,

src/uv-common.c

@@ -233,6 +233,26 @@ int uv_udp_send(uv_udp_send_t* req,
 }
 
 
+int uv_udp_try_send(uv_udp_t* handle,
+                    const uv_buf_t bufs[],
+                    unsigned int nbufs,
+                    const struct sockaddr* addr) {
+  unsigned int addrlen;
+
+  if (handle->type != UV_UDP)
+    return UV_EINVAL;
+
+  if (addr->sa_family == AF_INET)
+    addrlen = sizeof(struct sockaddr_in);
+  else if (addr->sa_family == AF_INET6)
+    addrlen = sizeof(struct sockaddr_in6);
+  else
+    return UV_EINVAL;
+
+  return uv__udp_try_send(handle, bufs, nbufs, addr, addrlen);
+}
+
+
 int uv_udp_recv_start(uv_udp_t* handle,
                       uv_alloc_cb alloc_cb,
                       uv_udp_recv_cb recv_cb) {

src/uv-common.h

@@ -83,6 +83,12 @@ int uv__udp_send(uv_udp_send_t* req,
                  unsigned int addrlen,
                  uv_udp_send_cb send_cb);
 
+int uv__udp_try_send(uv_udp_t* handle,
+                     const uv_buf_t bufs[],
+                     unsigned int nbufs,
+                     const struct sockaddr* addr,
+                     unsigned int addrlen);
+
 int uv__udp_recv_start(uv_udp_t* handle, uv_alloc_cb alloccb,
                        uv_udp_recv_cb recv_cb);
 

src/win/udp.c

@@ -869,3 +869,12 @@ int uv__udp_send(uv_udp_send_t* req,
 
   return 0;
 }
+
+
+int uv__udp_try_send(uv_udp_t* handle,
+                     const uv_buf_t bufs[],
+                     unsigned int nbufs,
+                     const struct sockaddr* addr,
+                     unsigned int addrlen) {
+  return UV_ENOSYS;
+}

test/test-list.h

@@ -95,6 +95,7 @@ TEST_DECLARE   (udp_ipv6_only)
 TEST_DECLARE   (udp_options)
 TEST_DECLARE   (udp_no_autobind)
 TEST_DECLARE   (udp_open)
+TEST_DECLARE   (udp_try_send)
 TEST_DECLARE   (pipe_bind_error_addrinuse)
 TEST_DECLARE   (pipe_bind_error_addrnotavail)
 TEST_DECLARE   (pipe_bind_error_inval)
@@ -376,6 +377,7 @@ TASK_LIST_START
   TEST_ENTRY  (udp_multicast_join)
   TEST_ENTRY  (udp_multicast_join6)
   TEST_ENTRY  (udp_multicast_ttl)
+  TEST_ENTRY  (udp_try_send)
 
   TEST_ENTRY  (udp_open)
   TEST_HELPER (udp_open, udp4_echo_server)

test/test-udp-try-send.c

@@ -0,0 +1,133 @@
+/* Copyright Joyent, Inc. and other Node contributors. All rights reserved.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include "uv.h"
+#include "task.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#ifdef _WIN32
+
+TEST_IMPL(udp_try_send) {
+
+  MAKE_VALGRIND_HAPPY();
+  return 0;
+}
+
+#else  /* !_WIN32 */
+
+#define CHECK_HANDLE(handle) \
+  ASSERT((uv_udp_t*)(handle) == &server || (uv_udp_t*)(handle) == &client)
+
+static uv_udp_t server;
+static uv_udp_t client;
+
+static int sv_recv_cb_called;
+
+static int close_cb_called;
+
+
+static void alloc_cb(uv_handle_t* handle,
+                     size_t suggested_size,
+                     uv_buf_t* buf) {
+  static char slab[65536];
+  CHECK_HANDLE(handle);
+  ASSERT(suggested_size <= sizeof(slab));
+  buf->base = slab;
+  buf->len = sizeof(slab);
+}
+
+
+static void close_cb(uv_handle_t* handle) {
+  CHECK_HANDLE(handle);
+  ASSERT(uv_is_closing(handle));
+  close_cb_called++;
+}
+
+
+static void sv_recv_cb(uv_udp_t* handle,
+                       ssize_t nread,
+                       const uv_buf_t* rcvbuf,
+                       const struct sockaddr* addr,
+                       unsigned flags) {
+  ASSERT(nread > 0);
+
+  if (nread == 0) {
+    ASSERT(addr == NULL);
+    return;
+  }
+
+  ASSERT(nread == 4);
+  ASSERT(addr != NULL);
+
+  ASSERT(memcmp("EXIT", rcvbuf->base, nread) == 0);
+  uv_close((uv_handle_t*) handle, close_cb);
+  uv_close((uv_handle_t*) &client, close_cb);
+
+  sv_recv_cb_called++;
+}
+
+
+TEST_IMPL(udp_try_send) {
+  struct sockaddr_in addr;
+  static char buffer[64 * 1024];
+  uv_buf_t buf;
+  int r;
+
+  ASSERT(0 == uv_ip4_addr("0.0.0.0", TEST_PORT, &addr));
+
+  r = uv_udp_init(uv_default_loop(), &server);
+  ASSERT(r == 0);
+
+  r = uv_udp_bind(&server, (const struct sockaddr*) &addr, 0);
+  ASSERT(r == 0);
+
+  r = uv_udp_recv_start(&server, alloc_cb, sv_recv_cb);
+  ASSERT(r == 0);
+
+  ASSERT(0 == uv_ip4_addr("127.0.0.1", TEST_PORT, &addr));
+
+  r = uv_udp_init(uv_default_loop(), &client);
+  ASSERT(r == 0);
+
+  buf = uv_buf_init(buffer, sizeof(buffer));
+  r = uv_udp_try_send(&client, &buf, 1, (const struct sockaddr*) &addr);
+  ASSERT(r == UV_EMSGSIZE);
+
+  buf = uv_buf_init("EXIT", 4);
+  r = uv_udp_try_send(&client, &buf, 1, (const struct sockaddr*) &addr);
+  ASSERT(r == 4);
+
+  uv_run(uv_default_loop(), UV_RUN_DEFAULT);
+
+  ASSERT(close_cb_called == 2);
+  ASSERT(sv_recv_cb_called == 1);
+
+  ASSERT(client.send_queue_size == 0);
+  ASSERT(server.send_queue_size == 0);
+
+  MAKE_VALGRIND_HAPPY();
+  return 0;
+}
+
+#endif  /* !_WIN32 */

uv.gyp

@@ -402,6 +402,7 @@
         'test/test-ip6-addr.c',
         'test/test-udp-multicast-interface.c',
         'test/test-udp-multicast-interface6.c',
+        'test/test-udp-try-send.c',
       ],
       'conditions': [
         [ 'OS=="win"', {