/*------------------------------------------------------------------------- * * dest.c *	  support for communication destinations * * * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION *	  $Header: /cvsroot/pgsql/src/backend/tcop/dest.c,v 1.61 2003/08/04 02:40:04 momjian Exp $ * *------------------------------------------------------------------------- *//* *	 INTERFACE ROUTINES *		BeginCommand - initialize the destination at start of command *		CreateDestReceiver - create tuple receiver object for destination *		EndCommand - clean up the destination at end of command *		NullCommand - tell dest that an empty query string was recognized *		ReadyForQuery - tell dest that we are ready for a new query * *	 NOTES *		These routines do the appropriate work before and after *		tuples are returned by a query to keep the backend and the *		"destination" portals synchronized. */#include "postgres.h"#include "access/printtup.h"#include "access/xact.h"#include "executor/tstoreReceiver.h"#include "libpq/libpq.h"#include "libpq/pqformat.h"#include "utils/portal.h"/* ---------------- *		dummy DestReceiver functions * ---------------- */static voiddonothingReceive(HeapTuple tuple, TupleDesc typeinfo, DestReceiver *self){}static voiddonothingStartup(DestReceiver *self, int operation, TupleDesc typeinfo){}static voiddonothingCleanup(DestReceiver *self){	/* this is used for both shutdown and destroy methods */}/* ---------------- *		static DestReceiver structs for dest types needing no local state * ---------------- */static DestReceiver donothingDR = {	donothingReceive, donothingStartup, donothingCleanup, donothingCleanup,	None};static DestReceiver debugtupDR = {	debugtup, debugStartup, donothingCleanup, donothingCleanup,	Debug};static DestReceiver spi_printtupDR = {	spi_printtup, spi_dest_startup, donothingCleanup, donothingCleanup,	SPI};/* Globally available receiver for None */DestReceiver *None_Receiver = &donothingDR;/* ---------------- *		BeginCommand - initialize the destination at start of command * ---------------- */voidBeginCommand(const char *commandTag, CommandDest dest){	/* Nothing to do at present */}/* ---------------- *		CreateDestReceiver - return appropriate receiver function set for dest * * Note: a Portal must be specified for destinations Remote, RemoteExecute, * and Tuplestore.	It can be NULL for the others. * ---------------- */DestReceiver *CreateDestReceiver(CommandDest dest, Portal portal){	switch (dest)	{		case Remote:		case RemoteExecute:			if (portal == NULL)				elog(ERROR, "no portal specified for Remote receiver");			return printtup_create_DR(dest, portal);		case None:			return &donothingDR;		case Debug:			return &debugtupDR;		case SPI:			return &spi_printtupDR;		case Tuplestore:			if (portal == NULL)				elog(ERROR, "no portal specified for Tuplestore receiver");			if (portal->holdStore == NULL ||				portal->holdContext == NULL)				elog(ERROR, "portal has no holdStore");			return CreateTuplestoreDestReceiver(portal->holdStore,												portal->holdContext);	}	/* should never get here */	return &donothingDR;}/* ---------------- *		EndCommand - clean up the destination at end of command * ---------------- */voidEndCommand(const char *commandTag, CommandDest dest){	switch (dest)	{		case Remote:		case RemoteExecute:			pq_puttextmessage('C', commandTag);			break;		case None:		case Debug:		case SPI:		case Tuplestore:			break;	}}/* ---------------- *		NullCommand - tell dest that an empty query string was recognized * *		In FE/BE protocol version 1.0, this hack is necessary to support *		libpq's crufty way of determining whether a multiple-command *		query string is done.  In protocol 2.0 it's probably not really *		necessary to distinguish empty queries anymore, but we still do it *		for backwards compatibility with 1.0.  In protocol 3.0 it has some *		use again, since it ensures that there will be a recognizable end *		to the response to an Execute message. * ---------------- */voidNullCommand(CommandDest dest){	switch (dest)	{		case Remote:		case RemoteExecute:			/*			 * tell the fe that we saw an empty query string.  In			 * protocols before 3.0 this has a useless empty-string			 * message body.			 */			if (PG_PROTOCOL_MAJOR(FrontendProtocol) >= 3)				pq_putemptymessage('I');			else				pq_puttextmessage('I', "");			break;		case None:		case Debug:		case SPI:		case Tuplestore:			break;	}}/* ---------------- *		ReadyForQuery - tell dest that we are ready for a new query * *		The ReadyForQuery message is sent in protocol versions 2.0 and up *		so that the FE can tell when we are done processing a query string. *		In versions 3.0 and up, it also carries a transaction state indicator. * *		Note that by flushing the stdio buffer here, we can avoid doing it *		most other places and thus reduce the number of separate packets sent. * ---------------- */voidReadyForQuery(CommandDest dest){	switch (dest)	{		case Remote:		case RemoteExecute:			if (PG_PROTOCOL_MAJOR(FrontendProtocol) >= 3)			{				StringInfoData buf;				pq_beginmessage(&buf, 'Z');				pq_sendbyte(&buf, TransactionBlockStatusCode());				pq_endmessage(&buf);			}			else if (PG_PROTOCOL_MAJOR(FrontendProtocol) >= 2)				pq_putemptymessage('Z');			/* Flush output at end of cycle in any case. */			pq_flush();			break;		case None:		case Debug:		case SPI:		case Tuplestore:			break;	}}