Throw suitable error for COPY TO STDOUT/FROM STDIN in a SQL function.

A client copy can't work inside a function because the FE/BE wire protocol
doesn't support nesting of a COPY operation within query results.  (Maybe
it could, but the protocol spec doesn't suggest that clients should support
this, and libpq for one certainly doesn't.)

In most PLs, this prohibition is enforced by spi.c, but SQL functions don't
use SPI.  A comparison of _SPI_execute_plan() and init_execution_state()
shows that rejecting client COPY is the only discrepancy in what they
allow, so there's no other similar bugs.

This is an astonishingly ancient oversight, so back-patch to all supported
branches.

Report: https://postgr.es/m/BY2PR05MB2309EABA3DEFA0143F50F0D593780@BY2PR05MB2309.namprd05.prod.outlook.com

diff --git a/src/backend/executor/functions.c b/src/backend/executor/functions.c
index a14053e8425b2170036aecbc1577d856b74ec81f..a3642e28dd5ccf8ff35479ac82e92057ec1d6d1c 100644 (file)
--- a/src/backend/executor/functions.c
+++ b/src/backend/executor/functions.c
@@ -497,7 +497,16 @@ init_execution_state(List *queryTree_list,
                        else
                                stmt = (Node *) pg_plan_query(queryTree, 0, NULL);
 
-                       /* Precheck all commands for validity in a function */
+                       /*
+                        * Precheck all commands for validity in a function.  This should
+                        * generally match the restrictions spi.c applies.
+                        */
+                       if (IsA(stmt, CopyStmt) &&
+                               ((CopyStmt *) stmt)->filename == NULL)
+                               ereport(ERROR,
+                                               (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+                                       errmsg("cannot COPY to/from client in a SQL function")));
+
                        if (IsA(stmt, TransactionStmt))
                                ereport(ERROR,
                                                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),