[newlib-cygwin] Cygwin: connect: implement resetting a connected DGRAM socket

[Ken Brown <kbrown@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=3b0ba6535218631b1ab467cd29d36b1eae4a0af6

commit 3b0ba6535218631b1ab467cd29d36b1eae4a0af6
Author: Ken Brown <kbrown@cornell.edu>
Date:   Fri Apr 23 18:17:57 2021 -0400

    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.

Diff:
---
 winsup/cygwin/fhandler_socket_inet.cc  | 21 +++++++++++++++++++--
 winsup/cygwin/fhandler_socket_local.cc | 30 +++++++++++++++++++++++++-----
 winsup/cygwin/fhandler_socket_unix.cc  |  7 +++++++
 winsup/cygwin/release/3.2.1            |  5 +++++
 4 files changed, 56 insertions(+), 7 deletions(-)

diff --git a/winsup/cygwin/fhandler_socket_inet.cc b/winsup/cygwin/fhandler_socket_inet.cc
index f6bb8c503..30eab4099 100644
--- a/winsup/cygwin/fhandler_socket_inet.cc
+++ b/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)
-    connect_state (connected);
+    {
+      if (reset)
+	connect_state (unconnected);
+      else
+	connect_state (connected);
+    }
   else if (!is_nonblocking ()
       && res == SOCKET_ERROR
       && WSAGetLastError () == WSAEWOULDBLOCK)
diff --git a/winsup/cygwin/fhandler_socket_local.cc b/winsup/cygwin/fhandler_socket_local.cc
index 1c8d48b58..bd4081622 100644
--- a/winsup/cygwin/fhandler_socket_local.cc
+++ b/winsup/cygwin/fhandler_socket_local.cc
@@ -894,19 +894,34 @@ 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)
-      == 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_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;
     }
 
-  set_peer_sun_path (name->sa_data);
+  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
      via select, possibly running under another identity.  Call early here,
@@ -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)
-    connect_state (connected);
+    {
+      if (reset)
+	connect_state (unconnected);
+      else
+	connect_state (connected);
+    }
   else if (!is_nonblocking ()
       && res == SOCKET_ERROR
       && WSAGetLastError () == WSAEWOULDBLOCK)
diff --git a/winsup/cygwin/fhandler_socket_unix.cc b/winsup/cygwin/fhandler_socket_unix.cc
index 252bcd9a9..a2428e952 100644
--- a/winsup/cygwin/fhandler_socket_unix.cc
+++ b/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 */
diff --git a/winsup/cygwin/release/3.2.1 b/winsup/cygwin/release/3.2.1
index 7662c7114..6ebe68fa6 100644
--- a/winsup/cygwin/release/3.2.1
+++ b/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.