fe-exec.c

关系型数据库 Postgresql 6.5.2

/*-------------------------------------------------------------------------
 *
 * fe-exec.c
 *	  functions related to sending a query down to the backend
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /usr/local/cvsroot/pgsql/src/interfaces/libpq/fe-exec.c,v 1.81 1999/05/28 01:54:53 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "libpq-fe.h"
#include "libpq-int.h"
#include "postgres.h"

#ifdef WIN32
#include "win32.h"
#else
#if !defined(NO_UNISTD_H)
#include <unistd.h>
#endif
#endif
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <ctype.h>


/* keep this in same order as ExecStatusType in libpq-fe.h */
const char *const pgresStatus[] = {
	"PGRES_EMPTY_QUERY",
	"PGRES_COMMAND_OK",
	"PGRES_TUPLES_OK",
	"PGRES_COPY_OUT",
	"PGRES_COPY_IN",
	"PGRES_BAD_RESPONSE",
	"PGRES_NONFATAL_ERROR",
	"PGRES_FATAL_ERROR"
};


#define DONOTICE(conn,message) \
	((*(conn)->noticeHook) ((conn)->noticeArg, (message)))


static int	addTuple(PGresult *res, PGresAttValue *tup);
static void parseInput(PGconn *conn);
static void handleSendFailure(PGconn *conn);
static int	getRowDescriptions(PGconn *conn);
static int	getAnotherTuple(PGconn *conn, int binary);
static int	getNotify(PGconn *conn);
static int	getNotice(PGconn *conn);


/* ----------------
 * Space management for PGresult.
 *
 * Formerly, libpq did a separate malloc() for each field of each tuple
 * returned by a query.  This was remarkably expensive --- malloc/free
 * consumed a sizable part of the application's runtime.  And there is
 * no real need to keep track of the fields separately, since they will
 * all be freed together when the PGresult is released.  So now, we grab
 * large blocks of storage from malloc and allocate space for query data
 * within these blocks, using a trivially simple allocator.  This reduces
 * the number of malloc/free calls dramatically, and it also avoids
 * fragmentation of the malloc storage arena.
 * The PGresult structure itself is still malloc'd separately.  We could
 * combine it with the first allocation block, but that would waste space
 * for the common case that no extra storage is actually needed (that is,
 * the SQL command did not return tuples).
 * We also malloc the top-level array of tuple pointers separately, because
 * we need to be able to enlarge it via realloc, and our trivial space
 * allocator doesn't handle that effectively.  (Too bad the FE/BE protocol
 * doesn't tell us up front how many tuples will be returned.)
 * All other subsidiary storage for a PGresult is kept in PGresult_data blocks
 * of size PGRESULT_DATA_BLOCKSIZE.  The overhead at the start of each block
 * is just a link to the next one, if any.	Free-space management info is
 * kept in the owning PGresult.
 * A query returning a small amount of data will thus require three malloc
 * calls: one for the PGresult, one for the tuples pointer array, and one
 * PGresult_data block.
 * Only the most recently allocated PGresult_data block is a candidate to
 * have more stuff added to it --- any extra space left over in older blocks
 * is wasted.  We could be smarter and search the whole chain, but the point
 * here is to be simple and fast.  Typical applications do not keep a PGresult
 * around very long anyway, so some wasted space within one is not a problem.
 *
 * Tuning constants for the space allocator are:
 * PGRESULT_DATA_BLOCKSIZE: size of a standard allocation block, in bytes
 * PGRESULT_ALIGN_BOUNDARY: assumed alignment requirement for binary data
 * PGRESULT_SEP_ALLOC_THRESHOLD: objects bigger than this are given separate
 *	 blocks, instead of being crammed into a regular allocation block.
 * Requirements for correct function are:
 * PGRESULT_ALIGN_BOUNDARY must be a multiple of the alignment requirements
 *		of all machine data types.	(Currently this is set from configure
 *		tests, so it should be OK automatically.)
 * PGRESULT_SEP_ALLOC_THRESHOLD + PGRESULT_BLOCK_OVERHEAD <=
 *			PGRESULT_DATA_BLOCKSIZE
 *		pqResultAlloc assumes an object smaller than the threshold will fit
 *		in a new block.
 * The amount of space wasted at the end of a block could be as much as
 * PGRESULT_SEP_ALLOC_THRESHOLD, so it doesn't pay to make that too large.
 * ----------------
 */

#ifdef MAX
#undef MAX
#endif
#define MAX(a,b)  ((a) > (b) ? (a) : (b))

#define PGRESULT_DATA_BLOCKSIZE		2048
#define PGRESULT_ALIGN_BOUNDARY		MAXIMUM_ALIGNOF		/* from configure */
#define PGRESULT_BLOCK_OVERHEAD		MAX(sizeof(PGresult_data), PGRESULT_ALIGN_BOUNDARY)
#define PGRESULT_SEP_ALLOC_THRESHOLD	(PGRESULT_DATA_BLOCKSIZE / 2)


/*
 * PQmakeEmptyPGresult
 *	 returns a newly allocated, initialized PGresult with given status.
 *	 If conn is not NULL and status indicates an error, the conn's
 *	 errorMessage is copied.
 *
 * Note this is exported --- you wouldn't think an application would need
 * to build its own PGresults, but this has proven useful in both libpgtcl
 * and the Perl5 interface, so maybe it's not so unreasonable.
 */

PGresult   *
PQmakeEmptyPGresult(PGconn *conn, ExecStatusType status)
{
	PGresult   *result;

	result = (PGresult *) malloc(sizeof(PGresult));

	result->conn = conn;		/* might be NULL */
	result->ntups = 0;
	result->numAttributes = 0;
	result->attDescs = NULL;
	result->tuples = NULL;
	result->tupArrSize = 0;
	result->resultStatus = status;
	result->cmdStatus[0] = '\0';
	result->binary = 0;
	result->errMsg = NULL;
	result->null_field[0] = '\0';
	result->curBlock = NULL;
	result->curOffset = 0;
	result->spaceLeft = 0;

	if (conn)					/* consider copying conn's errorMessage */
	{
		switch (status)
		{
			case PGRES_EMPTY_QUERY:
			case PGRES_COMMAND_OK:
			case PGRES_TUPLES_OK:
			case PGRES_COPY_OUT:
			case PGRES_COPY_IN:
				/* non-error cases */
				break;
			default:
				pqSetResultError(result, conn->errorMessage);
				break;
		}
	}
	return result;
}

/*
 * pqResultAlloc -
 *		Allocate subsidiary storage for a PGresult.
 *
 * nBytes is the amount of space needed for the object.
 * If isBinary is true, we assume that we need to align the object on
 * a machine allocation boundary.
 * If isBinary is false, we assume the object is a char string and can
 * be allocated on any byte boundary.
 */
void *
pqResultAlloc(PGresult *res, int nBytes, int isBinary)
{
	char	   *space;
	PGresult_data *block;

	if (!res)
		return NULL;

	if (nBytes <= 0)
		return res->null_field;

	/*
	 * If alignment is needed, round up the current position to an
	 * alignment boundary.
	 */
	if (isBinary)
	{
		int			offset = res->curOffset % PGRESULT_ALIGN_BOUNDARY;

		if (offset)
		{
			res->curOffset += PGRESULT_ALIGN_BOUNDARY - offset;
			res->spaceLeft -= PGRESULT_ALIGN_BOUNDARY - offset;
		}
	}

	/* If there's enough space in the current block, no problem. */
	if (nBytes <= res->spaceLeft)
	{
		space = res->curBlock->space + res->curOffset;
		res->curOffset += nBytes;
		res->spaceLeft -= nBytes;
		return space;
	}

	/*
	 * If the requested object is very large, give it its own block; this
	 * avoids wasting what might be most of the current block to start a
	 * new block.  (We'd have to special-case requests bigger than the
	 * block size anyway.)	The object is always given binary alignment in
	 * this case.
	 */
	if (nBytes >= PGRESULT_SEP_ALLOC_THRESHOLD)
	{
		block = (PGresult_data *) malloc(nBytes + PGRESULT_BLOCK_OVERHEAD);
		if (!block)
			return NULL;
		space = block->space + PGRESULT_BLOCK_OVERHEAD;
		if (res->curBlock)
		{

			/*
			 * Tuck special block below the active block, so that we don't
			 * have to waste the free space in the active block.
			 */
			block->next = res->curBlock->next;
			res->curBlock->next = block;
		}
		else
		{
			/* Must set up the new block as the first active block. */
			block->next = NULL;
			res->curBlock = block;
			res->spaceLeft = 0; /* be sure it's marked full */
		}
		return space;
	}

	/* Otherwise, start a new block. */
	block = (PGresult_data *) malloc(PGRESULT_DATA_BLOCKSIZE);
	if (!block)
		return NULL;
	block->next = res->curBlock;
	res->curBlock = block;
	if (isBinary)
	{
		/* object needs full alignment */
		res->curOffset = PGRESULT_BLOCK_OVERHEAD;
		res->spaceLeft = PGRESULT_DATA_BLOCKSIZE - PGRESULT_BLOCK_OVERHEAD;
	}
	else
	{
		/* we can cram it right after the overhead pointer */
		res->curOffset = sizeof(PGresult_data);
		res->spaceLeft = PGRESULT_DATA_BLOCKSIZE - sizeof(PGresult_data);
	}

	space = block->space + res->curOffset;
	res->curOffset += nBytes;
	res->spaceLeft -= nBytes;
	return space;
}

/*
 * pqResultStrdup -
 *		Like strdup, but the space is subsidiary PGresult space.
 */
char *
pqResultStrdup(PGresult *res, const char *str)
{
	char	   *space = (char *) pqResultAlloc(res, strlen(str) + 1, FALSE);

	if (space)
		strcpy(space, str);
	return space;
}

/*
 * pqSetResultError -
 *		assign a new error message to a PGresult
 */
void
pqSetResultError(PGresult *res, const char *msg)
{
	if (!res)
		return;
	if (msg && *msg)
		res->errMsg = pqResultStrdup(res, msg);
	else
		res->errMsg = NULL;
}

/*
 * PQclear -
 *	  free's the memory associated with a PGresult
 */
void
PQclear(PGresult *res)
{
	PGresult_data *block;

	if (!res)
		return;

	/* Free all the subsidiary blocks */
	while ((block = res->curBlock) != NULL)
	{
		res->curBlock = block->next;
		free(block);
	}

	/* Free the top-level tuple pointer array */
	if (res->tuples)
		free(res->tuples);

	/* Free the PGresult structure itself */
	free(res);
}

/*
 * Handy subroutine to deallocate any partially constructed async result.
 */

void
pqClearAsyncResult(PGconn *conn)
{
	if (conn->result)
		PQclear(conn->result);
	conn->result = NULL;
	conn->curTuple = NULL;
}


/*
 * addTuple
 *	  add a row pointer to the PGresult structure, growing it if necessary
 *	  Returns TRUE if OK, FALSE if not enough memory to add the row
 */
static int
addTuple(PGresult *res, PGresAttValue *tup)
{
	if (res->ntups >= res->tupArrSize)
	{

		/*
		 * Try to grow the array.
		 *
		 * We can use realloc because shallow copying of the structure is
		 * okay.  Note that the first time through, res->tuples is NULL.
		 * While ANSI says that realloc() should act like malloc() in that
		 * case, some old C libraries (like SunOS 4.1.x) coredump instead.
		 * On failure realloc is supposed to return NULL without damaging
		 * the existing allocation. Note that the positions beyond
		 * res->ntups are garbage, not necessarily NULL.
		 */
		int			newSize = (res->tupArrSize > 0) ? res->tupArrSize * 2 : 128;
		PGresAttValue **newTuples;

		if (res->tuples == NULL)
			newTuples = (PGresAttValue **)
				malloc(newSize * sizeof(PGresAttValue *));
		else
			newTuples = (PGresAttValue **)
				realloc(res->tuples, newSize * sizeof(PGresAttValue *));
		if (!newTuples)
			return FALSE;		/* malloc or realloc failed */
		res->tupArrSize = newSize;
		res->tuples = newTuples;
	}
	res->tuples[res->ntups] = tup;
	res->ntups++;
	return TRUE;
}


/*
 * PQsendQuery
 *	 Submit a query, but don't wait for it to finish
 *
 * Returns: 1 if successfully submitted
 *			0 if error (conn->errorMessage is set)
 */

int
PQsendQuery(PGconn *conn, const char *query)
{
	if (!conn)
		return 0;
	if (!query)
	{
		sprintf(conn->errorMessage, "PQsendQuery() -- query pointer is null.");
		return 0;
	}
	/* check to see if the query string is too long */
	if (strlen(query) > MAX_MESSAGE_LEN - 2)
	{
		sprintf(conn->errorMessage, "PQsendQuery() -- query is too long.  "
				"Maximum length is %d\n", MAX_MESSAGE_LEN - 2);
		return 0;
	}

	/* Don't try to send if we know there's no live connection. */
	if (conn->status != CONNECTION_OK)
	{
		sprintf(conn->errorMessage, "PQsendQuery() -- There is no connection "
				"to the backend.\n");
		return 0;
	}
	/* Can't send while already busy, either. */
	if (conn->asyncStatus != PGASYNC_IDLE)
	{
		sprintf(conn->errorMessage,
				"PQsendQuery() -- another query already in progress.");
		return 0;
	}

	/* clear the error string */
	conn->errorMessage[0] = '\0';

	/* initialize async result-accumulation state */
	conn->result = NULL;
	conn->curTuple = NULL;

	/* send the query to the backend; */
	/* the frontend-backend protocol uses 'Q' to designate queries */
	if (pqPutnchar("Q", 1, conn) ||
		pqPuts(query, conn) ||
		pqFlush(conn))
	{
		handleSendFailure(conn);
		return 0;
	}

	/* OK, it's launched! */
	conn->asyncStatus = PGASYNC_BUSY;
	return 1;
}

/*
 * handleSendFailure: try to clean up after failure to send command.
 *
 * Primarily, what we want to accomplish here is to process an async
 * NOTICE message that the backend might have sent just before it died.
 *
 * NOTE: this routine should only be called in PGASYNC_IDLE state.
 */

static void
handleSendFailure(PGconn *conn)
{
	/* Preserve the error message emitted by the failing output routine */
	char * svErrMsg = strdup(conn->errorMessage);

	/*
	 * Accept any available input data, ignoring errors.  Note that if
	 * pqReadData decides the backend has closed the channel, it will
	 * close our side of the socket --- that's just what we want here.
	 */
	while (pqReadData(conn) > 0)
		/* loop until no more data readable */ ;

	/*
	 * Parse any available input messages.  Since we are in PGASYNC_IDLE
	 * state, only NOTICE and NOTIFY messages will be eaten.
	 */
	parseInput(conn);

	/* Restore error message generated by output routine, if any. */
	if (*svErrMsg != '\0')
		strcpy(conn->errorMessage, svErrMsg);
	free(svErrMsg);