Don't crash if cursor_to_xmlschema is used on a non-data-returning Portal.

cursor_to_xmlschema() assumed that any Portal must have a tupDesc,
which is not so.  Add a defensive check.

It's plausible that this mistake occurred because of the rather
poorly chosen name of the lookup function SPI_cursor_find(),
which in such cases is returning something that isn't very much
like a cursor.  Add some documentation to try to forestall future
errors of the same ilk.

Report and patch by Boyu Yang (docs changes by me).  Back-patch
to all supported branches.

Discussion: https://postgr.es/m/dd343010-c637-434c-a8cb-418f53bda3b8[email protected]

diff --git a/doc/src/sgml/spi.sgml b/doc/src/sgml/spi.sgml
index 16c3ab71e8505f322b5993960873468eab65c86e..47f4b5b43171c5315fe83c6bee5802907cc1624b 100644 (file)
--- a/doc/src/sgml/spi.sgml
+++ b/doc/src/sgml/spi.sgml
@@ -2727,6 +2727,19 @@ Portal SPI_cursor_find(const char * name)
    NULL if none was found
   
  
+
+ 
+  Notes
+
+  
+   Beware that this function can return a Portal object
+   that does not have cursor-like properties; for example it might not
+   return tuples.  If you simply pass the Portal pointer
+   to other SPI functions, they can defend themselves against such
+   cases, but caution is appropriate when directly inspecting
+   the Portal.
+  
+ 
 
 
 

diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c
index 866d0d649a4a2da294bdd5b8bbe9ef0617fe6364..2300c7ebf340c0034da17a26e1018404fabc3f49 100644 (file)
--- a/src/backend/utils/adt/xml.c
+++ b/src/backend/utils/adt/xml.c
@@ -3012,6 +3012,10 @@ cursor_to_xmlschema(PG_FUNCTION_ARGS)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_CURSOR),
                 errmsg("cursor \"%s\" does not exist", name)));
+   if (portal->tupDesc == NULL)
+       ereport(ERROR,
+               (errcode(ERRCODE_INVALID_CURSOR_STATE),
+                errmsg("portal \"%s\" does not return tuples", name)));
 
    xmlschema = _SPI_strdup(map_sql_table_to_xmlschema(portal->tupDesc,
                                                       InvalidOid, nulls,