Avoid crashing when restoring a saved GUC session_authorization value

that refers to a now-deleted userid.  Per gripe from Chris Ochs.

src/backend/commands/variable.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/variable.c,v 1.98 2004/07/01 00:50:12 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/variable.c,v 1.99 2004/08/11 21:10:36 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -591,31 +591,37 @@ assign_client_encoding(const char *value, bool doit, GucSource source)
  * lookups.  Hence, the stored form of the value must provide a numeric userid
  * that can be re-used directly.  We store the string in the form of
  * NAMEDATALEN 'x's, followed by T or F to indicate superuserness, followed
- * by the numeric userid --- this cannot conflict with any valid user name,
- * because of the NAMEDATALEN limit on names.
+ * by the numeric userid, followed by a comma, followed by the user name.
+ * This cannot be confused with a plain user name because of the NAMEDATALEN
+ * limit on names, so we can tell whether we're being passed an initial
+ * username or a saved/restored value.
  */
+extern char *session_authorization_string; /* in guc.c */
+
 const char *
 assign_session_authorization(const char *value, bool doit, GucSource source)
 {
 	AclId		usesysid = 0;
 	bool		is_superuser = false;
+	const char *actual_username = NULL;
 	char	   *result;
 
 	if (strspn(value, "x") == NAMEDATALEN &&
 		(value[NAMEDATALEN] == 'T' || value[NAMEDATALEN] == 'F'))
 	{
-		/* might be a saved numeric userid */
+		/* might be a saved userid string */
+		AclId		savedsysid;
 		char	   *endptr;
 
-		usesysid = (AclId) strtoul(value + NAMEDATALEN + 1, &endptr, 10);
+		savedsysid = (AclId) strtoul(value + NAMEDATALEN + 1, &endptr, 10);
 
-		if (endptr != value + NAMEDATALEN + 1 && *endptr == '\0')
+		if (endptr != value + NAMEDATALEN + 1 && *endptr == ',')
 		{
-			/* syntactically valid, so use the numeric user ID and flag */
+			/* syntactically valid, so break out the data */
+			usesysid = savedsysid;
 			is_superuser = (value[NAMEDATALEN] == 'T');
+			actual_username = endptr + 1;
 		}
-		else
-			usesysid = 0;
 	}
 
 	if (usesysid == 0)
@@ -647,6 +653,7 @@ assign_session_authorization(const char *value, bool doit, GucSource source)
 
 		usesysid = ((Form_pg_shadow) GETSTRUCT(userTup))->usesysid;
 		is_superuser = ((Form_pg_shadow) GETSTRUCT(userTup))->usesuper;
+		actual_username = value;
 
 		ReleaseSysCache(userTup);
 	}
@@ -654,15 +661,16 @@ assign_session_authorization(const char *value, bool doit, GucSource source)
 	if (doit)
 		SetSessionAuthorization(usesysid, is_superuser);
 
-	result = (char *) malloc(NAMEDATALEN + 32);
+	result = (char *) malloc(NAMEDATALEN + 32 + strlen(actual_username));
 	if (!result)
 		return NULL;
 
 	memset(result, 'x', NAMEDATALEN);
 
-	snprintf(result + NAMEDATALEN, 32, "%c%lu",
-			 is_superuser ? 'T' : 'F',
-			 (unsigned long) usesysid);
+	sprintf(result + NAMEDATALEN, "%c%lu,%s",
+			is_superuser ? 'T' : 'F',
+			(unsigned long) usesysid,
+			actual_username);
 
 	return result;
 }
@@ -671,8 +679,19 @@ const char *
 show_session_authorization(void)
 {
 	/*
-	 * We can't use the stored string; see comments for
+	 * Extract the user name from the stored string; see
 	 * assign_session_authorization
 	 */
-	return GetUserNameFromId(GetSessionUserId());
+	const char *value = session_authorization_string;
+	AclId		savedsysid;
+	char	   *endptr;
+
+	Assert(strspn(value, "x") == NAMEDATALEN &&
+		   (value[NAMEDATALEN] == 'T' || value[NAMEDATALEN] == 'F'));
+
+	savedsysid = (AclId) strtoul(value + NAMEDATALEN + 1, &endptr, 10);
+
+	Assert(endptr != value + NAMEDATALEN + 1 && *endptr == ',');
+
+	return endptr + 1;
 }

src/backend/utils/misc/guc.c

@@ -10,7 +10,7 @@
  * Written by Peter Eisentraut <peter_e@gmx.net>.
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.230 2004/08/08 20:17:36 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.231 2004/08/11 21:10:37 tgl Exp $
  *
  *--------------------------------------------------------------------
  */
@@ -175,7 +175,6 @@ static char *locale_ctype;
 static char *regex_flavor_string;
 static char *server_encoding_string;
 static char *server_version_string;
-static char *session_authorization_string;
 static char *timezone_string;
 static char *XactIsoLevel_string;
 static char *custom_variable_classes;
@@ -184,6 +183,8 @@ static int	max_index_keys;
 static int	max_identifier_length;
 static int	block_size;
 static bool integer_datetimes;
+/* should be static, but commands/variable.c needs to get at it */
+char *session_authorization_string;
 
 
 /*