Defend against crash while processing Describe Statement or Describe Portal

messages, when client attempts to execute these outside a transaction (start
one) or in a failed transaction (reject message, except for COMMIT/ROLLBACK
statements which we can handle).  Per report from Francisco Figueiredo Jr.

1 files changed, 25 insertions, 1 deletions

diff --git a/src/backend/commands/prepare.c b/src/backend/commands/prepare.c
index dc84f57506a..1ee955ebe14 100644
--- a/src/backend/commands/prepare.c
+++ b/src/backend/commands/prepare.c
@@ -10,7 +10,7 @@
  * Copyright (c) 2002-2005, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/prepare.c,v 1.43 2005/11/29 01:25:49 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/prepare.c,v 1.44 2005/12/14 17:06:27 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -448,6 +448,30 @@ FetchPreparedStatementResultDesc(PreparedStatement *stmt)
 }
 
 /*
+ * Given a prepared statement, determine whether it will return tuples.
+ *
+ * Note: this is used rather than just testing the result of
+ * FetchPreparedStatementResultDesc() because that routine can fail if
+ * invoked in an aborted transaction.  This one is safe to use in any
+ * context.  Be sure to keep the two routines in sync!
+ */
+bool
+PreparedStatementReturnsTuples(PreparedStatement *stmt)
+{
+	switch (ChoosePortalStrategy(stmt->query_list))
+	{
+		case PORTAL_ONE_SELECT:
+		case PORTAL_UTIL_SELECT:
+			return true;
+
+		case PORTAL_MULTI_QUERY:
+			/* will not return tuples */
+			break;
+	}
+	return false;
+}
+
+/*
  * Given a prepared statement that returns tuples, extract the query
  * targetlist.	Returns NIL if the statement doesn't have a determinable
  * targetlist.