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dest.c

/*-------------------------------------------------------------------------
 *
 * dest.c
 *      support for communication destinations
 *
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *      $PostgreSQL: pgsql/src/backend/tcop/dest.c,v 1.75.2.1 2010/01/30 20:09:59 tgl 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 "commands/copy.h"
#include "executor/executor.h"
#include "executor/functions.h"
#include "executor/tstoreReceiver.h"
#include "libpq/libpq.h"
#include "libpq/pqformat.h"
#include "utils/portal.h"


/* ----------------
 *          dummy DestReceiver functions
 * ----------------
 */
static void
donothingReceive(TupleTableSlot *slot, DestReceiver *self)
{
}

static void
donothingStartup(DestReceiver *self, int operation, TupleDesc typeinfo)
{
}

static void
donothingCleanup(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,
      DestNone
};

static DestReceiver debugtupDR = {
      debugtup, debugStartup, donothingCleanup, donothingCleanup,
      DestDebug
};

static DestReceiver spi_printtupDR = {
      spi_printtup, spi_dest_startup, donothingCleanup, donothingCleanup,
      DestSPI
};

/* Globally available receiver for DestNone */
DestReceiver *None_Receiver = &donothingDR;


/* ----------------
 *          BeginCommand - initialize the destination at start of command
 * ----------------
 */
void
BeginCommand(const char *commandTag, CommandDest dest)
{
      /* Nothing to do at present */
}

/* ----------------
 *          CreateDestReceiver - return appropriate receiver function set for dest
 * ----------------
 */
DestReceiver *
CreateDestReceiver(CommandDest dest)
{
      switch (dest)
      {
            case DestRemote:
            case DestRemoteExecute:
                  return printtup_create_DR(dest);

            case DestNone:
                  return &donothingDR;

            case DestDebug:
                  return &debugtupDR;

            case DestSPI:
                  return &spi_printtupDR;

            case DestTuplestore:
                  return CreateTuplestoreDestReceiver();

            case DestIntoRel:
                  return CreateIntoRelDestReceiver();

            case DestCopyOut:
                  return CreateCopyDestReceiver();

            case DestSQLFunction:
                  return CreateSQLFunctionDestReceiver();
      }

      /* should never get here */
      return &donothingDR;
}

/* ----------------
 *          EndCommand - clean up the destination at end of command
 * ----------------
 */
void
EndCommand(const char *commandTag, CommandDest dest)
{
      switch (dest)
      {
            case DestRemote:
            case DestRemoteExecute:
                  /*
                   * We assume the commandTag is plain ASCII and therefore
                   * requires no encoding conversion.
                   */
                  pq_putmessage('C', commandTag, strlen(commandTag) + 1);
                  break;

            case DestNone:
            case DestDebug:
            case DestSPI:
            case DestTuplestore:
            case DestIntoRel:
            case DestCopyOut:
            case DestSQLFunction:
                  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.
 * ----------------
 */
void
NullCommand(CommandDest dest)
{
      switch (dest)
      {
            case DestRemote:
            case DestRemoteExecute:

                  /*
                   * 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_putmessage('I', "", 1);
                  break;

            case DestNone:
            case DestDebug:
            case DestSPI:
            case DestTuplestore:
            case DestIntoRel:
            case DestCopyOut:
            case DestSQLFunction:
                  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.
 * ----------------
 */
void
ReadyForQuery(CommandDest dest)
{
      switch (dest)
      {
            case DestRemote:
            case DestRemoteExecute:
                  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 DestNone:
            case DestDebug:
            case DestSPI:
            case DestTuplestore:
            case DestIntoRel:
            case DestCopyOut:
            case DestSQLFunction:
                  break;
      }
}

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