On Windows, also call shutdown() while closing the client socket.

tglsfdc · tglsfdc · commit a8a983e8299a · 2021-12-07T13:34:19.000-05:00
Further experimentation shows that commit 6051857 is not sufficient when using (some versions of?) OpenSSL. The reason is obscure, but calling shutdown(socket, SD_SEND) improves matters. Per testing by Andrew Dunstan and Alexander Lakhin. Back-patch as before. Discussion: https://postgr.es/m/af5e0bf3-6a61-bb97-6cba-061ddf22ff6b@dunslane.net
diff --git a/src/backend/libpq/pqcomm.c b/src/backend/libpq/pqcomm.c
@@ -294,14 +294,16 @@ socket_close(int code, Datum arg)
 		 * not yet sent to the client.  (This is a flat-out violation of the
 		 * TCP RFCs, but count on Microsoft not to care about that.)  To get
 		 * the spec-compliant "graceful shutdown" behavior, we must invoke
-		 * closesocket() explicitly.
+		 * closesocket() explicitly.  When using OpenSSL, it seems that clean
+		 * shutdown also requires an explicit shutdown() call.
 		 *
 		 * This code runs late enough during process shutdown that we should
 		 * have finished all externally-visible shutdown activities, so that
 		 * in principle it's good enough to act as a synchronous close on
 		 * Windows too.  But it's a lot more fragile than the other way.
 		 */
 #ifdef WIN32
+		shutdown(MyProcPort->sock, SD_SEND);
 		closesocket(MyProcPort->sock);
 #endif
 
