Fix a couple of contrib/dblink bugs.

dblink_exec leaked temporary database connections if any error occurred
after connection setup, for example
	SELECT dblink_exec('...connect string...', 'select 1/0');
Add a PG_TRY block to ensure PQfinish gets done when it is needed.
(dblink_record_internal is on the hairy edge of needing similar treatment,
but seems not to be actively broken at the moment.)

Also, in 9.0 and up, only one of the three functions using tuplestore
return mode was properly checking that the query context would allow
a tuplestore result.

Noted while reviewing dblink patch.  Back-patch to all supported branches.

Author: tglsfdc

contrib/dblink/dblink.c

@@ -67,6 +67,7 @@ typedef struct remoteConn
  * Internal declarations
  */
 static Datum dblink_record_internal(FunctionCallInfo fcinfo, bool is_async);
+static void prepTuplestoreResult(FunctionCallInfo fcinfo);
 static void materializeResult(FunctionCallInfo fcinfo, PGresult *res);
 static remoteConn *getConnectionByName(const char *name);
 static HTAB *createConnHash(void);
@@ -495,7 +496,6 @@ PG_FUNCTION_INFO_V1(dblink_fetch);
 Datum
 dblink_fetch(PG_FUNCTION_ARGS)
 {
-	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
 	PGresult   *res = NULL;
 	char	   *conname = NULL;
 	remoteConn *rconn = NULL;
@@ -505,6 +505,8 @@ dblink_fetch(PG_FUNCTION_ARGS)
 	int			howmany = 0;
 	bool		fail = true;	/* default to backward compatible */
 
+	prepTuplestoreResult(fcinfo);
+
 	DBLINK_INIT;
 
 	if (PG_NARGS() == 4)
@@ -551,11 +553,6 @@ dblink_fetch(PG_FUNCTION_ARGS)
 	if (!conn)
 		DBLINK_CONN_NOT_AVAIL;
 
-	/* let the caller know we're sending back a tuplestore */
-	rsinfo->returnMode = SFRM_Materialize;
-	rsinfo->setResult = NULL;
-	rsinfo->setDesc = NULL;
-
 	initStringInfo(&buf);
 	appendStringInfo(&buf, "FETCH %d FROM %s", howmany, curname);
 
@@ -632,7 +629,6 @@ dblink_get_result(PG_FUNCTION_ARGS)
 static Datum
 dblink_record_internal(FunctionCallInfo fcinfo, bool is_async)
 {
-	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
 	char	   *msg;
 	PGresult   *res = NULL;
 	PGconn	   *conn = NULL;
@@ -643,16 +639,7 @@ dblink_record_internal(FunctionCallInfo fcinfo, bool is_async)
 	bool		fail = true;	/* default to backward compatible */
 	bool		freeconn = false;
 
-	/* check to see if caller supports us returning a tuplestore */
-	if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
-		ereport(ERROR,
-				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("set-valued function called in context that cannot accept a set")));
-	if (!(rsinfo->allowedModes & SFRM_Materialize))
-		ereport(ERROR,
-				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("materialize mode required, but it is not " \
-						"allowed in this context")));
+	prepTuplestoreResult(fcinfo);
 
 	DBLINK_INIT;
 
@@ -712,11 +699,6 @@ dblink_record_internal(FunctionCallInfo fcinfo, bool is_async)
 	if (!conn)
 		DBLINK_CONN_NOT_AVAIL;
 
-	/* let the caller know we're sending back a tuplestore */
-	rsinfo->returnMode = SFRM_Materialize;
-	rsinfo->setResult = NULL;
-	rsinfo->setDesc = NULL;
-
 	/* synchronous query, or async result retrieval */
 	if (!is_async)
 		res = PQexec(conn, sql);
@@ -745,14 +727,45 @@ dblink_record_internal(FunctionCallInfo fcinfo, bool is_async)
 }
 
 /*
- * Materialize the PGresult to return them as the function result.
- * The res will be released in this function.
+ * Verify function caller can handle a tuplestore result, and set up for that.
+ *
+ * Note: if the caller returns without actually creating a tuplestore, the
+ * executor will treat the function result as an empty set.
+ */
+static void
+prepTuplestoreResult(FunctionCallInfo fcinfo)
+{
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+
+	/* check to see if query supports us returning a tuplestore */
+	if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("set-valued function called in context that cannot accept a set")));
+	if (!(rsinfo->allowedModes & SFRM_Materialize))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("materialize mode required, but it is not allowed in this context")));
+
+	/* let the executor know we're sending back a tuplestore */
+	rsinfo->returnMode = SFRM_Materialize;
+
+	/* caller must fill these to return a non-empty result */
+	rsinfo->setResult = NULL;
+	rsinfo->setDesc = NULL;
+}
+
+/*
+ * Copy the contents of the PGresult into a tuplestore to be returned
+ * as the result of the current function.
+ * The PGresult will be released in this function.
  */
 static void
 materializeResult(FunctionCallInfo fcinfo, PGresult *res)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
 
+	/* prepTuplestoreResult must have been called previously */
 	Assert(rsinfo->returnMode == SFRM_Materialize);
 
 	PG_TRY();
@@ -1004,85 +1017,97 @@ PG_FUNCTION_INFO_V1(dblink_exec);
 Datum
 dblink_exec(PG_FUNCTION_ARGS)
 {
-	char	   *msg;
-	PGresult   *res = NULL;
-	text	   *sql_cmd_status = NULL;
-	PGconn	   *conn = NULL;
-	char	   *connstr = NULL;
-	char	   *sql = NULL;
-	char	   *conname = NULL;
-	remoteConn *rconn = NULL;
-	bool		freeconn = false;
-	bool		fail = true;	/* default to backward compatible behavior */
+	text	   *volatile sql_cmd_status = NULL;
+	PGconn	   *volatile conn = NULL;
+	volatile bool freeconn = false;
 
 	DBLINK_INIT;
 
-	if (PG_NARGS() == 3)
-	{
-		/* must be text,text,bool */
-		DBLINK_GET_CONN;
-		sql = text_to_cstring(PG_GETARG_TEXT_PP(1));
-		fail = PG_GETARG_BOOL(2);
-	}
-	else if (PG_NARGS() == 2)
+	PG_TRY();
 	{
-		/* might be text,text or text,bool */
-		if (get_fn_expr_argtype(fcinfo->flinfo, 1) == BOOLOID)
+		char	   *msg;
+		PGresult   *res = NULL;
+		char	   *connstr = NULL;
+		char	   *sql = NULL;
+		char	   *conname = NULL;
+		remoteConn *rconn = NULL;
+		bool		fail = true;	/* default to backward compatible behavior */
+
+		if (PG_NARGS() == 3)
+		{
+			/* must be text,text,bool */
+			DBLINK_GET_CONN;
+			sql = text_to_cstring(PG_GETARG_TEXT_PP(1));
+			fail = PG_GETARG_BOOL(2);
+		}
+		else if (PG_NARGS() == 2)
+		{
+			/* might be text,text or text,bool */
+			if (get_fn_expr_argtype(fcinfo->flinfo, 1) == BOOLOID)
+			{
+				conn = pconn->conn;
+				sql = text_to_cstring(PG_GETARG_TEXT_PP(0));
+				fail = PG_GETARG_BOOL(1);
+			}
+			else
+			{
+				DBLINK_GET_CONN;
+				sql = text_to_cstring(PG_GETARG_TEXT_PP(1));
+			}
+		}
+		else if (PG_NARGS() == 1)
 		{
+			/* must be single text argument */
 			conn = pconn->conn;
 			sql = text_to_cstring(PG_GETARG_TEXT_PP(0));
-			fail = PG_GETARG_BOOL(1);
 		}
 		else
-		{
-			DBLINK_GET_CONN;
-			sql = text_to_cstring(PG_GETARG_TEXT_PP(1));
-		}
-	}
-	else if (PG_NARGS() == 1)
-	{
-		/* must be single text argument */
-		conn = pconn->conn;
-		sql = text_to_cstring(PG_GETARG_TEXT_PP(0));
-	}
-	else
-		/* shouldn't happen */
-		elog(ERROR, "wrong number of arguments");
+			/* shouldn't happen */
+			elog(ERROR, "wrong number of arguments");
 
-	if (!conn)
-		DBLINK_CONN_NOT_AVAIL;
+		if (!conn)
+			DBLINK_CONN_NOT_AVAIL;
 
-	res = PQexec(conn, sql);
-	if (!res ||
-		(PQresultStatus(res) != PGRES_COMMAND_OK &&
-		 PQresultStatus(res) != PGRES_TUPLES_OK))
-	{
-		dblink_res_error(conname, res, "could not execute command", fail);
+		res = PQexec(conn, sql);
+		if (!res ||
+			(PQresultStatus(res) != PGRES_COMMAND_OK &&
+			 PQresultStatus(res) != PGRES_TUPLES_OK))
+		{
+			dblink_res_error(conname, res, "could not execute command", fail);
 
-		/*
-		 * and save a copy of the command status string to return as our
-		 * result tuple
-		 */
-		sql_cmd_status = cstring_to_text("ERROR");
-	}
-	else if (PQresultStatus(res) == PGRES_COMMAND_OK)
-	{
-		/*
-		 * and save a copy of the command status string to return as our
-		 * result tuple
-		 */
-		sql_cmd_status = cstring_to_text(PQcmdStatus(res));
-		PQclear(res);
+			/*
+			 * and save a copy of the command status string to return as our
+			 * result tuple
+			 */
+			sql_cmd_status = cstring_to_text("ERROR");
+		}
+		else if (PQresultStatus(res) == PGRES_COMMAND_OK)
+		{
+			/*
+			 * and save a copy of the command status string to return as our
+			 * result tuple
+			 */
+			sql_cmd_status = cstring_to_text(PQcmdStatus(res));
+			PQclear(res);
+		}
+		else
+		{
+			PQclear(res);
+			ereport(ERROR,
+				  (errcode(ERRCODE_S_R_E_PROHIBITED_SQL_STATEMENT_ATTEMPTED),
+				   errmsg("statement returning results not allowed")));
+		}
 	}
-	else
+	PG_CATCH();
 	{
-		PQclear(res);
-		ereport(ERROR,
-				(errcode(ERRCODE_S_R_E_PROHIBITED_SQL_STATEMENT_ATTEMPTED),
-				 errmsg("statement returning results not allowed")));
+		/* if needed, close the connection to the database */
+		if (freeconn)
+			PQfinish(conn);
+		PG_RE_THROW();
 	}
+	PG_END_TRY();
 
-	/* if needed, close the connection to the database and cleanup */
+	/* if needed, close the connection to the database */
 	if (freeconn)
 		PQfinish(conn);
 
@@ -1503,13 +1528,15 @@ dblink_get_notify(PG_FUNCTION_ARGS)
 	MemoryContext per_query_ctx;
 	MemoryContext oldcontext;
 
+	prepTuplestoreResult(fcinfo);
+
 	DBLINK_INIT;
 	if (PG_NARGS() == 1)
 		DBLINK_GET_NAMED_CONN;
 	else
 		conn = pconn->conn;
 
-	/* create the tuplestore */
+	/* create the tuplestore in per-query memory */
 	per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
 	oldcontext = MemoryContextSwitchTo(per_query_ctx);
 
@@ -1522,7 +1549,6 @@ dblink_get_notify(PG_FUNCTION_ARGS)
 					   TEXTOID, -1, 0);
 
 	tupstore = tuplestore_begin_heap(true, false, work_mem);
-	rsinfo->returnMode = SFRM_Materialize;
 	rsinfo->setResult = tupstore;
 	rsinfo->setDesc = tupdesc;