Cygwin: connect: implement resetting a connected DGRAM socket

Following POSIX and Linux, allow a connected DGRAM socket's connection
to be reset (so that the socket becomes unconnected).  This is done by
calling connect and specifing an address whose family is AF_UNSPEC.

winsup/cygwin/fhandler_socket_inet.cc

@@ -781,8 +781,20 @@ int
 fhandler_socket_inet::connect (const struct sockaddr *name, int namelen)
 {
   struct sockaddr_storage sst;
+  bool reset = (name->sa_family == AF_UNSPEC
+		&& get_socket_type () == SOCK_DGRAM);
 
-  if (get_inet_addr_inet (name, namelen, &sst, &namelen) == SOCKET_ERROR)
+  if (reset)
+    {
+      if (connect_state () == unconnected)
+	return 0;
+      /* To reset a connected DGRAM socket, call Winsock's connect
+	 function with the address member of the sockaddr structure
+	 filled with zeroes. */
+      memset (&sst, 0, sizeof sst);
+      sst.ss_family = get_addr_family ();
+    }
+  else if (get_inet_addr_inet (name, namelen, &sst, &namelen) == SOCKET_ERROR)
     return SOCKET_ERROR;
 
   /* Initialize connect state to "connect_pending".  In the SOCK_STREAM
@@ -804,7 +816,12 @@ fhandler_socket_inet::connect (const struct sockaddr *name, int namelen)
 
   int res = ::connect (get_socket (), (struct sockaddr *) &sst, namelen);
   if (!res)
+    {
+      if (reset)
+	connect_state (unconnected);
+      else
 	connect_state (connected);
+    }
   else if (!is_nonblocking ()
       && res == SOCKET_ERROR
       && WSAGetLastError () == WSAEWOULDBLOCK)

winsup/cygwin/fhandler_socket_local.cc

@@ -894,18 +894,33 @@ fhandler_socket_local::connect (const struct sockaddr *name, int namelen)
 {
   struct sockaddr_storage sst;
   int type = 0;
+  bool reset = (name->sa_family == AF_UNSPEC
+		&& get_socket_type () == SOCK_DGRAM);
 
-  if (get_inet_addr_local (name, namelen, &sst, &namelen, &type, connect_secret)
+  if (reset)
-      == SOCKET_ERROR)
+    {
+      if (connect_state () == unconnected)
+	return 0;
+      /* To reset a connected DGRAM socket, call Winsock's connect
+	 function with the address member of the sockaddr structure
+	 filled with zeroes. */
+      memset (&sst, 0, sizeof sst);
+      sst.ss_family = get_addr_family ();
+    }
+  else if (get_inet_addr_local (name, namelen, &sst, &namelen, &type,
+				connect_secret) == SOCKET_ERROR)
     return SOCKET_ERROR;
 
-  if (get_socket_type () != type)
+  if (get_socket_type () != type && !reset)
     {
       WSASetLastError (WSAEPROTOTYPE);
       set_winsock_errno ();
       return SOCKET_ERROR;
     }
 
+  if (reset)
+    set_peer_sun_path (NULL);
+  else
     set_peer_sun_path (name->sa_data);
 
   /* Don't move af_local_set_cred into af_local_connect which may be called
@@ -933,7 +948,12 @@ fhandler_socket_local::connect (const struct sockaddr *name, int namelen)
 
   int res = ::connect (get_socket (), (struct sockaddr *) &sst, namelen);
   if (!res)
+    {
+      if (reset)
+	connect_state (unconnected);
+      else
 	connect_state (connected);
+    }
   else if (!is_nonblocking ()
       && res == SOCKET_ERROR
       && WSAGetLastError () == WSAEWOULDBLOCK)

winsup/cygwin/fhandler_socket_unix.cc

@@ -1696,6 +1696,13 @@ fhandler_socket_unix::connect (const struct sockaddr *name, int namelen)
       conn_unlock ();
       return -1;
     }
+  if (name->sa_family == AF_UNSPEC && get_socket_type () == SOCK_DGRAM)
+    {
+      connect_state (unconnected);
+      peer_sun_path (NULL);
+      conn_unlock ();
+      return 0;
+    }
   connect_state (connect_pending);
   conn_unlock ();
   /* Check validity of name */

winsup/cygwin/release/3.2.1

@@ -28,3 +28,8 @@ Bug Fixes
 
 - Fix a bug in recognizing a successful completion of connect(2) on a
   datagram socket.
+
+- Fix connect(2) when called with an address structure whose family is
+  AF_UNSPEC.  As specified by POSIX and Linux, this is allowed on
+  datagram sockets, and its effect is to reset the socket's peer
+  address.