Handle corner cases correctly in psql's reconnection logic.

tglsfdc · tglsfdc · commit 89535db970b0 · 2019-09-02T14:02:46.000-04:00
After an unexpected connection loss and successful reconnection, psql neglected to resynchronize its internal state about the server, such as server version. Ordinarily we'd be reconnecting to the same server and so this isn't really necessary, but there are scenarios where we do need to update --- one example is where we have a list of possible connection targets and they're not all alike. Define "resynchronize" as including connection_warnings(), so that this case acts the same as \connect. This seems useful; for example, if the server version did change, the user might wish to know that. An attuned user might also notice that the new connection isn't SSL-encrypted, for example, though this approach isn't especially in-your-face about such changes. Although this part is a behavioral change, it only affects interactive sessions, so it should not break any applications. Also, in do_connect, make sure that we desynchronize correctly when abandoning an old connection in non-interactive mode. These problems evidently are the result of people patching only one of the two places where psql deals with connection changes, so insert some cross-referencing comments in hopes of forestalling future bugs of the same ilk. Lastly, in Windows builds, issue codepage mismatch warnings only at startup, not during reconnections. psql's codepage can't change during a reconnect, so complaining about it again seems like useless noise. Peter Billen and Tom Lane. Back-patch to all supported branches. Discussion: https://postgr.es/m/CAMTXbE8e6U=EBQfNSe01Ej17CBStGiudMAGSOPaw-ALxM-5jXg@mail.gmail.com
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
@@ -1793,8 +1793,14 @@ do_connect(enum trivalue reuse_previous_specification,
 			psql_error("\\connect: %s", PQerrorMessage(n_conn));
 			if (o_conn)
 			{
+				/*
+				 * Transition to having no connection.  Keep this bit in sync
+				 * with CheckConnection().
+				 */
 				PQfinish(o_conn);
 				pset.db = NULL;
+				ResetCancelConn();
+				UnsyncVariables();
 			}
 		}
 
@@ -1808,7 +1814,8 @@ do_connect(enum trivalue reuse_previous_specification,
 
 	/*
 	 * Replace the old connection with the new one, and update
-	 * connection-dependent variables.
+	 * connection-dependent variables.  Keep the resynchronization logic in
+	 * sync with CheckConnection().
 	 */
 	PQsetNoticeProcessor(n_conn, NoticeProcessor, NULL);
 	pset.db = n_conn;
@@ -1885,7 +1892,8 @@ connection_warnings(bool in_startup)
 										 sverbuf, sizeof(sverbuf)));
 
 #ifdef WIN32
-		checkWin32Codepage();
+		if (in_startup)
+			checkWin32Codepage();
 #endif
 		printSSLInfo();
 	}
diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
@@ -299,13 +299,27 @@ CheckConnection(void)
 		if (!OK)
 		{
 			psql_error("Failed.\n");
+
+			/*
+			 * Transition to having no connection.  Keep this bit in sync with
+			 * do_connect().
+			 */
 			PQfinish(pset.db);
 			pset.db = NULL;
 			ResetCancelConn();
 			UnsyncVariables();
 		}
 		else
+		{
 			psql_error("Succeeded.\n");
+
+			/*
+			 * Re-sync, just in case anything changed.  Keep this in sync with
+			 * do_connect().
+			 */
+			SyncVariables();
+			connection_warnings(false); /* Must be after SyncVariables */
+		}
 	}
 
 	return OK;
