unix,win: implement uv_udp_open_ex

Fixes: https://github.com/libuv/libuv/issues/4551
Signed-off-by: Juan José Arboleda <soyjuanarbol@gmail.com>

docs/src/udp.rst

@@ -173,6 +173,22 @@ API
     .. versionadded:: 1.7.0
     .. versionchanged:: 1.37.0 added the `UV_UDP_RECVMMSG` flag.
 
+.. c:function:: int uv_udp_open_ex(uv_udp_t* handle, uv_os_sock_t sock, unsigned int flags)
+
+    Opens an existing file descriptor or Windows SOCKET as a UDP handle.
+
+    :param handle: UDP handle. Should have been initialized with
+        :c:func:`uv_udp_init`.
+
+    :param sock: An existing socket to associate with the handle.
+
+    :param flags: Flags that control socket behavior,
+        ``UV_UDP_REUSEADDR``, and ``UV_UDP_REUSEPORT`` are supported.
+
+    :returns: 0 on success, or an error code < 0 on failure.
+
+    .. versionadded:: 1.52.0
+
 .. c:function:: int uv_udp_open(uv_udp_t* handle, uv_os_sock_t sock)
 
     Opens an existing file descriptor or Windows SOCKET as a UDP handle.
@@ -189,6 +205,10 @@ API
         The passed file descriptor or SOCKET is not checked for its type, but
         it's required that it represents a valid datagram socket.
 
+        Internally sets the SO_REUSEADDR socket option unconditionally. This
+        means the reuse flag is always enabled, regardless of user intent. For
+        more control use :c:func:`uv_udp_open_ex`.
+
 .. c:function:: int uv_udp_bind(uv_udp_t* handle, const struct sockaddr* addr, unsigned int flags)
 
     Bind the UDP handle to an IP address and port.

include/uv.h

@@ -746,6 +746,9 @@ struct uv_udp_send_s {
 UV_EXTERN int uv_udp_init(uv_loop_t*, uv_udp_t* handle);
 UV_EXTERN int uv_udp_init_ex(uv_loop_t*, uv_udp_t* handle, unsigned int flags);
 UV_EXTERN int uv_udp_open(uv_udp_t* handle, uv_os_sock_t sock);
+UV_EXTERN int uv_udp_open_ex(uv_udp_t* handle,
+                             uv_os_sock_t sock,
+                             unsigned int flags);
 UV_EXTERN int uv_udp_bind(uv_udp_t* handle,
                           const struct sockaddr* addr,
                           unsigned int flags);

src/unix/udp.c

@@ -897,9 +897,13 @@ int uv_udp_using_recvmmsg(const uv_udp_t* handle) {
 }
 
 
-int uv_udp_open(uv_udp_t* handle, uv_os_sock_t sock) {
+int uv_udp_open_ex(uv_udp_t* handle, uv_os_sock_t sock, unsigned int flags) {
   int err;
 
+  /* Check for bad flags. */
+  if (flags & ~(UV_UDP_REUSEADDR | UV_UDP_REUSEPORT))
+    return UV_EINVAL;
+
   /* Check for already active socket. */
   if (handle->io_watcher.fd != -1)
     return UV_EBUSY;
@@ -911,9 +915,17 @@ int uv_udp_open(uv_udp_t* handle, uv_os_sock_t sock) {
   if (err)
     return err;
 
-  err = uv__sock_reuseaddr(sock);
-  if (err)
-    return err;
+  if (flags & UV_UDP_REUSEADDR) {
+    err = uv__sock_reuseaddr(sock);
+    if (err)
+      return err;
+  }
+
+  if (flags & UV_UDP_REUSEPORT) {
+    err = uv__sock_reuseport(sock);
+    if (err)
+      return err;
+  }
 
   handle->io_watcher.fd = sock;
   if (uv__udp_is_connected(handle))
@@ -923,6 +935,15 @@ int uv_udp_open(uv_udp_t* handle, uv_os_sock_t sock) {
 }
 
 
+int uv_udp_open(uv_udp_t* handle, uv_os_sock_t sock) {
+  /*
+   * Keep backward compatibility, always set REUSEADDR.
+   * Refs: https://github.com/libuv/libuv/issues/4551
+   */
+  return uv_udp_open_ex(handle, sock, UV_UDP_REUSEADDR);
+}
+
+
 int uv_udp_set_membership(uv_udp_t* handle,
                           const char* multicast_addr,
                           const char* interface_addr,

src/win/udp.c

@@ -204,7 +204,7 @@ static int uv__udp_maybe_bind(uv_udp_t* handle,
    * so we just return an error directly when UV_UDP_REUSEPORT is requested
    * for binding the socket. */
   if (flags & UV_UDP_REUSEPORT)
-    return ERROR_NOT_SUPPORTED;
+    return UV_ENOTSUP;
 
   if ((flags & UV_UDP_IPV6ONLY) && addr->sa_family != AF_INET6) {
     /* UV_UDP_IPV6ONLY is supported only for IPV6 sockets */
@@ -908,11 +908,15 @@ int uv__udp_is_bound(uv_udp_t* handle) {
 }
 
 
-int uv_udp_open(uv_udp_t* handle, uv_os_sock_t sock) {
+int uv_udp_open_ex(uv_udp_t* handle, uv_os_sock_t sock, unsigned int flags) {
   WSAPROTOCOL_INFOW protocol_info;
   int opt_len;
   int err;
 
+  /* Check for bad flags. */
+  if (flags & ~(UV_UDP_REUSEADDR | UV_UDP_REUSEPORT))
+    return UV_EINVAL;
+
   /* Detect the address family of the socket. */
   opt_len = (int) sizeof protocol_info;
   if (getsockopt(sock,
@@ -930,6 +934,25 @@ int uv_udp_open(uv_udp_t* handle, uv_os_sock_t sock) {
   if (err)
     return uv_translate_sys_error(err);
 
+  /* There is no SO_REUSEPORT on Windows, Windows only knows SO_REUSEADDR.
+   * so we just return an error directly when UV_UDP_REUSEPORT is requested
+   * for binding the socket. */
+  if (flags & UV_UDP_REUSEPORT)
+    return UV_ENOTSUP;
+
+  if (flags & UV_UDP_REUSEADDR) {
+    DWORD yes = 1;
+    /* Set SO_REUSEADDR on the socket. */
+    if (setsockopt(handle->socket,
+                   SOL_SOCKET,
+                   SO_REUSEADDR,
+                   (char*) &yes,
+                   sizeof yes) == SOCKET_ERROR) {
+      err = WSAGetLastError();
+      return uv_translate_sys_error(err);
+    }
+  }
+
   if (uv__udp_is_bound(handle))
     handle->flags |= UV_HANDLE_BOUND;
 
@@ -940,6 +963,11 @@ int uv_udp_open(uv_udp_t* handle, uv_os_sock_t sock) {
 }
 
 
+int uv_udp_open(uv_udp_t* handle, uv_os_sock_t sock) {
+  return uv_udp_open_ex(handle, sock, 0);
+}
+
+
 #define SOCKOPT_SETTER(name, option4, option6, validate)                      \
   int uv_udp_set_##name(uv_udp_t* handle, int value) {                        \
     DWORD optval = (DWORD) value;                                             \