postgres/src/bin/pg_dump/pg_backup_custom.c

/*-------------------------------------------------------------------------
 *
 * pg_backup_custom.c
 *
 *	Implements the custom output format.
 *
 *	The comments with the routined in this code are a good place to
 *	understand how to write a new format.
 *
 *	See the headers to pg_restore for more details.
 *
 * Copyright (c) 2000, Philip Warner
 *		Rights are granted to use this software in any way so long
 *		as this notice is not removed.
 *
 *	The author is not responsible for loss or damages that may
 *	and any liability will be limited to the time taken to fix any
 *	related bug.
 *
 *
 * IDENTIFICATION
 *		$PostgreSQL: pgsql/src/bin/pg_dump/pg_backup_custom.c,v 1.38 2007/03/18 16:50:44 neilc Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "pg_backup_archiver.h"

/*--------
 * Routines in the format interface
 *--------
 */

static void _ArchiveEntry(ArchiveHandle *AH, TocEntry *te);
static void _StartData(ArchiveHandle *AH, TocEntry *te);
static size_t _WriteData(ArchiveHandle *AH, const void *data, size_t dLen);
static void _EndData(ArchiveHandle *AH, TocEntry *te);
static int	_WriteByte(ArchiveHandle *AH, const int i);
static int	_ReadByte(ArchiveHandle *);
static size_t _WriteBuf(ArchiveHandle *AH, const void *buf, size_t len);
static size_t _ReadBuf(ArchiveHandle *AH, void *buf, size_t len);
static void _CloseArchive(ArchiveHandle *AH);
static void _PrintTocData(ArchiveHandle *AH, TocEntry *te, RestoreOptions *ropt);
static void _WriteExtraToc(ArchiveHandle *AH, TocEntry *te);
static void _ReadExtraToc(ArchiveHandle *AH, TocEntry *te);
static void _PrintExtraToc(ArchiveHandle *AH, TocEntry *te);

static void _PrintData(ArchiveHandle *AH);
static void _skipData(ArchiveHandle *AH);
static void _skipBlobs(ArchiveHandle *AH);

static void _StartBlobs(ArchiveHandle *AH, TocEntry *te);
static void _StartBlob(ArchiveHandle *AH, TocEntry *te, Oid oid);
static void _EndBlob(ArchiveHandle *AH, TocEntry *te, Oid oid);
static void _EndBlobs(ArchiveHandle *AH, TocEntry *te);
static void _LoadBlobs(ArchiveHandle *AH);

/*------------
 * Buffers used in zlib compression and extra data stored in archive and
 * in TOC entries.
 *------------
 */
#define zlibOutSize 4096
#define zlibInSize	4096

typedef struct
{
	z_streamp	zp;
	char	   *zlibOut;
	char	   *zlibIn;
	size_t		inSize;
	int			hasSeek;
	pgoff_t		filePos;
	pgoff_t		dataStart;
} lclContext;

typedef struct
{
	int			dataState;
	pgoff_t		dataPos;
} lclTocEntry;


/*------
 * Static declarations
 *------
 */
static void _readBlockHeader(ArchiveHandle *AH, int *type, int *id);
static void _StartDataCompressor(ArchiveHandle *AH, TocEntry *te);
static void _EndDataCompressor(ArchiveHandle *AH, TocEntry *te);
static pgoff_t _getFilePos(ArchiveHandle *AH, lclContext *ctx);
static int	_DoDeflate(ArchiveHandle *AH, lclContext *ctx, int flush);

static const char *modulename = gettext_noop("custom archiver");



/*
 *	Init routine required by ALL formats. This is a global routine
 *	and should be declared in pg_backup_archiver.h
 *
 *	It's task is to create any extra archive context (using AH->formatData),
 *	and to initialize the supported function pointers.
 *
 *	It should also prepare whatever it's input source is for reading/writing,
 *	and in the case of a read mode connection, it should load the Header & TOC.
 */
void
InitArchiveFmt_Custom(ArchiveHandle *AH)
{
	lclContext *ctx;

	/* Assuming static functions, this can be copied for each format. */
	AH->ArchiveEntryPtr = _ArchiveEntry;
	AH->StartDataPtr = _StartData;
	AH->WriteDataPtr = _WriteData;
	AH->EndDataPtr = _EndData;
	AH->WriteBytePtr = _WriteByte;
	AH->ReadBytePtr = _ReadByte;
	AH->WriteBufPtr = _WriteBuf;
	AH->ReadBufPtr = _ReadBuf;
	AH->ClosePtr = _CloseArchive;
	AH->PrintTocDataPtr = _PrintTocData;
	AH->ReadExtraTocPtr = _ReadExtraToc;
	AH->WriteExtraTocPtr = _WriteExtraToc;
	AH->PrintExtraTocPtr = _PrintExtraToc;

	AH->StartBlobsPtr = _StartBlobs;
	AH->StartBlobPtr = _StartBlob;
	AH->EndBlobPtr = _EndBlob;
	AH->EndBlobsPtr = _EndBlobs;

	/*
	 * Set up some special context used in compressing data.
	 */
	ctx = (lclContext *) calloc(1, sizeof(lclContext));
	if (ctx == NULL)
		die_horribly(AH, modulename, "out of memory\n");
	AH->formatData = (void *) ctx;

	ctx->zp = (z_streamp) malloc(sizeof(z_stream));
	if (ctx->zp == NULL)
		die_horribly(AH, modulename, "out of memory\n");

	/* Initialize LO buffering */
	AH->lo_buf_size = LOBBUFSIZE;
	AH->lo_buf = (void *) malloc(LOBBUFSIZE);
	if (AH->lo_buf == NULL)
		die_horribly(AH, modulename, "out of memory\n");

	/*
	 * zlibOutSize is the buffer size we tell zlib it can output to.  We
	 * actually allocate one extra byte because some routines want to append a
	 * trailing zero byte to the zlib output.  The input buffer is expansible
	 * and is always of size ctx->inSize; zlibInSize is just the initial
	 * default size for it.
	 */
	ctx->zlibOut = (char *) malloc(zlibOutSize + 1);
	ctx->zlibIn = (char *) malloc(zlibInSize);
	ctx->inSize = zlibInSize;
	ctx->filePos = 0;

	if (ctx->zlibOut == NULL || ctx->zlibIn == NULL)
		die_horribly(AH, modulename, "out of memory\n");

	/*
	 * Now open the file
	 */
	if (AH->mode == archModeWrite)
	{
		if (AH->fSpec && strcmp(AH->fSpec, "") != 0)
			AH->FH = fopen(AH->fSpec, PG_BINARY_W);
		else
			AH->FH = stdout;

		if (!AH->FH)
			die_horribly(AH, modulename, "could not open output file \"%s\": %s\n", AH->fSpec, strerror(errno));

		ctx->hasSeek = checkSeek(AH->FH);
	}
	else
	{
		if (AH->fSpec && strcmp(AH->fSpec, "") != 0)
			AH->FH = fopen(AH->fSpec, PG_BINARY_R);
		else
			AH->FH = stdin;
		if (!AH->FH)
			die_horribly(AH, modulename, "could not open input file \"%s\": %s\n", AH->fSpec, strerror(errno));

		ctx->hasSeek = checkSeek(AH->FH);

		ReadHead(AH);
		ReadToc(AH);
		ctx->dataStart = _getFilePos(AH, ctx);
	}

}

/*
 * Called by the Archiver when the dumper creates a new TOC entry.
 *
 * Optional.
 *
 * Set up extrac format-related TOC data.
*/
static void
_ArchiveEntry(ArchiveHandle *AH, TocEntry *te)
{
	lclTocEntry *ctx;

	ctx = (lclTocEntry *) calloc(1, sizeof(lclTocEntry));
	if (te->dataDumper)
		ctx->dataState = K_OFFSET_POS_NOT_SET;
	else
		ctx->dataState = K_OFFSET_NO_DATA;

	te->formatData = (void *) ctx;
}

/*
 * Called by the Archiver to save any extra format-related TOC entry
 * data.
 *
 * Optional.
 *
 * Use the Archiver routines to write data - they are non-endian, and
 * maintain other important file information.
 */
static void
_WriteExtraToc(ArchiveHandle *AH, TocEntry *te)
{
	lclTocEntry *ctx = (lclTocEntry *) te->formatData;

	WriteOffset(AH, ctx->dataPos, ctx->dataState);
}

/*
 * Called by the Archiver to read any extra format-related TOC data.
 *
 * Optional.
 *
 * Needs to match the order defined in _WriteExtraToc, and sould also
 * use the Archiver input routines.
 */
static void
_ReadExtraToc(ArchiveHandle *AH, TocEntry *te)
{
	int			junk;
	lclTocEntry *ctx = (lclTocEntry *) te->formatData;

	if (ctx == NULL)
	{
		ctx = (lclTocEntry *) calloc(1, sizeof(lclTocEntry));
		te->formatData = (void *) ctx;
	}

	ctx->dataState = ReadOffset(AH, &(ctx->dataPos));

	/*
	 * Prior to V1.7 (pg7.3), we dumped the data size as an int now we don't
	 * dump it at all.
	 */
	if (AH->version < K_VERS_1_7)
		junk = ReadInt(AH);
}

/*
 * Called by the Archiver when restoring an archive to output a comment
 * that includes useful information about the TOC entry.
 *
 * Optional.
 *
 */
static void
_PrintExtraToc(ArchiveHandle *AH, TocEntry *te)
{
	lclTocEntry *ctx = (lclTocEntry *) te->formatData;

	if (AH->public.verbose)
		ahprintf(AH, "-- Data Pos: " INT64_FORMAT "\n",
				 (int64) ctx->dataPos);
}

/*
 * Called by the archiver when saving TABLE DATA (not schema). This routine
 * should save whatever format-specific information is needed to read
 * the archive back.
 *
 * It is called just prior to the dumper's 'DataDumper' routine being called.
 *
 * Optional, but strongly recommended.
 *
 */
static void
_StartData(ArchiveHandle *AH, TocEntry *te)
{
	lclContext *ctx = (lclContext *) AH->formatData;
	lclTocEntry *tctx = (lclTocEntry *) te->formatData;

	tctx->dataPos = _getFilePos(AH, ctx);
	tctx->dataState = K_OFFSET_POS_SET;

	_WriteByte(AH, BLK_DATA);	/* Block type */
	WriteInt(AH, te->dumpId);	/* For sanity check */

	_StartDataCompressor(AH, te);
}

/*
 * Called by archiver when dumper calls WriteData. This routine is
 * called for both BLOB and TABLE data; it is the responsibility of
 * the format to manage each kind of data using StartBlob/StartData.
 *
 * It should only be called from within a DataDumper routine.
 *
 * Mandatory.
 */
static size_t
_WriteData(ArchiveHandle *AH, const void *data, size_t dLen)
{
	lclContext *ctx = (lclContext *) AH->formatData;
	z_streamp	zp = ctx->zp;

	zp->next_in = (void *) data;
	zp->avail_in = dLen;

	while (zp->avail_in != 0)
	{
		/* printf("Deflating %lu bytes\n", (unsigned long) dLen); */
		_DoDeflate(AH, ctx, 0);
	}
	return dLen;
}

/*
 * Called by the archiver when a dumper's 'DataDumper' routine has
 * finished.
 *
 * Optional.
 *
 */
static void
_EndData(ArchiveHandle *AH, TocEntry *te)
{
/*	lclContext *ctx = (lclContext *) AH->formatData; */
/*	lclTocEntry *tctx = (lclTocEntry *) te->formatData; */

	_EndDataCompressor(AH, te);
}

/*
 * Called by the archiver when starting to save all BLOB DATA (not schema).
 * This routine should save whatever format-specific information is needed
 * to read the BLOBs back into memory.
 *
 * It is called just prior to the dumper's DataDumper routine.
 *
 * Optional, but strongly recommended.
 */
static void
_StartBlobs(ArchiveHandle *AH, TocEntry *te)
{
	lclContext *ctx = (lclContext *) AH->formatData;
	lclTocEntry *tctx = (lclTocEntry *) te->formatData;

	tctx->dataPos = _getFilePos(AH, ctx);
	tctx->dataState = K_OFFSET_POS_SET;

	_WriteByte(AH, BLK_BLOBS);	/* Block type */
	WriteInt(AH, te->dumpId);	/* For sanity check */
}

/*
 * Called by the archiver when the dumper calls StartBlob.
 *
 * Mandatory.
 *
 * Must save the passed OID for retrieval at restore-time.
 */
static void
_StartBlob(ArchiveHandle *AH, TocEntry *te, Oid oid)
{
	if (oid == 0)
		die_horribly(AH, modulename, "invalid OID for large object\n");

	WriteInt(AH, oid);
	_StartDataCompressor(AH, te);
}

/*
 * Called by the archiver when the dumper calls EndBlob.
 *
 * Optional.
 */
static void
_EndBlob(ArchiveHandle *AH, TocEntry *te, Oid oid)
{
	_EndDataCompressor(AH, te);
}

/*
 * Called by the archiver when finishing saving all BLOB DATA.
 *
 * Optional.
 */
static void
_EndBlobs(ArchiveHandle *AH, TocEntry *te)
{
	/* Write out a fake zero OID to mark end-of-blobs. */
	WriteInt(AH, 0);
}

/*
 * Print data for a given TOC entry
 */
static void
_PrintTocData(ArchiveHandle *AH, TocEntry *te, RestoreOptions *ropt)
{
	lclContext *ctx = (lclContext *) AH->formatData;
	int			id;
	lclTocEntry *tctx = (lclTocEntry *) te->formatData;
	int			blkType;
	int			found = 0;

	if (tctx->dataState == K_OFFSET_NO_DATA)
		return;

	if (!ctx->hasSeek || tctx->dataState == K_OFFSET_POS_NOT_SET)
	{
		/* Skip over unnecessary blocks until we get the one we want. */

		found = 0;

		_readBlockHeader(AH, &blkType, &id);

		while (id != te->dumpId)
		{
			if ((TocIDRequired(AH, id, ropt) & REQ_DATA) != 0)
				die_horribly(AH, modulename,
							 "dumping a specific TOC data block out of order is not supported"
					  " without ID on this input stream (fseek required)\n");

			switch (blkType)
			{
				case BLK_DATA:
					_skipData(AH);
					break;

				case BLK_BLOBS:
					_skipBlobs(AH);
					break;

				default:		/* Always have a default */
					die_horribly(AH, modulename,
								 "unrecognized data block type (%d) while searching archive\n",
								 blkType);
					break;
			}
			_readBlockHeader(AH, &blkType, &id);
		}
	}
	else
	{
		/* Grab it */
		if (fseeko(AH->FH, tctx->dataPos, SEEK_SET) != 0)
			die_horribly(AH, modulename, "error during file seek: %s\n", strerror(errno));

		_readBlockHeader(AH, &blkType, &id);
	}

	/* Are we sane? */
	if (id != te->dumpId)
		die_horribly(AH, modulename, "found unexpected block ID (%d) when reading data -- expected %d\n",
					 id, te->dumpId);

	switch (blkType)
	{
		case BLK_DATA:
			_PrintData(AH);
			break;

		case BLK_BLOBS:
			_LoadBlobs(AH);
			break;

		default:				/* Always have a default */
			die_horribly(AH, modulename, "unrecognized data block type %d while restoring archive\n",
						 blkType);
			break;
	}
}

/*
 * Print data from current file position.
*/
static void
_PrintData(ArchiveHandle *AH)
{
	lclContext *ctx = (lclContext *) AH->formatData;
	z_streamp	zp = ctx->zp;
	size_t		blkLen;
	char	   *in = ctx->zlibIn;
	size_t		cnt;

#ifdef HAVE_LIBZ
	int			res;
	char	   *out = ctx->zlibOut;
#endif

#ifdef HAVE_LIBZ

	res = Z_OK;

	if (AH->compression != 0)
	{
		zp->zalloc = Z_NULL;
		zp->zfree = Z_NULL;
		zp->opaque = Z_NULL;

		if (inflateInit(zp) != Z_OK)
			die_horribly(AH, modulename, "could not initialize compression library: %s\n", zp->msg);
	}
#endif

	blkLen = ReadInt(AH);
	while (blkLen != 0)
	{
		if (blkLen + 1 > ctx->inSize)
		{
			free(ctx->zlibIn);
			ctx->zlibIn = NULL;
			ctx->zlibIn = (char *) malloc(blkLen + 1);
			if (!ctx->zlibIn)
				die_horribly(AH, modulename, "out of memory\n");

			ctx->inSize = blkLen + 1;
			in = ctx->zlibIn;
		}

		cnt = fread(in, 1, blkLen, AH->FH);
		if (cnt != blkLen)
		{
			if (feof(AH->FH))
				die_horribly(AH, modulename,
							 "could not read from input file: end of file\n");
			else
				die_horribly(AH, modulename,
					"could not read from input file: %s\n", strerror(errno));
		}

		ctx->filePos += blkLen;

		zp->next_in = (void *) in;
		zp->avail_in = blkLen;

#ifdef HAVE_LIBZ

		if (AH->compression != 0)
		{
			while (zp->avail_in != 0)
			{
				zp->next_out = (void *) out;
				zp->avail_out = zlibOutSize;
				res = inflate(zp, 0);
				if (res != Z_OK && res != Z_STREAM_END)
					die_horribly(AH, modulename, "could not uncompress data: %s\n", zp->msg);

				out[zlibOutSize - zp->avail_out] = '\0';
				ahwrite(out, 1, zlibOutSize - zp->avail_out, AH);
			}
		}
		else
		{
#endif
			in[zp->avail_in] = '\0';
			ahwrite(in, 1, zp->avail_in, AH);
			zp->avail_in = 0;

#ifdef HAVE_LIBZ
		}
#endif
		blkLen = ReadInt(AH);
	}

#ifdef HAVE_LIBZ
	if (AH->compression != 0)
	{
		zp->next_in = NULL;
		zp->avail_in = 0;
		while (res != Z_STREAM_END)
		{
			zp->next_out = (void *) out;
			zp->avail_out = zlibOutSize;
			res = inflate(zp, 0);
			if (res != Z_OK && res != Z_STREAM_END)
				die_horribly(AH, modulename, "could not uncompress data: %s\n", zp->msg);

			out[zlibOutSize - zp->avail_out] = '\0';
			ahwrite(out, 1, zlibOutSize - zp->avail_out, AH);
		}
		if (inflateEnd(zp) != Z_OK)
			die_horribly(AH, modulename, "could not close compression library: %s\n", zp->msg);
	}
#endif
}

static void
_LoadBlobs(ArchiveHandle *AH)
{
	Oid			oid;

	StartRestoreBlobs(AH);

	oid = ReadInt(AH);
	while (oid != 0)
	{
		StartRestoreBlob(AH, oid);
		_PrintData(AH);
		EndRestoreBlob(AH, oid);
		oid = ReadInt(AH);
	}

	EndRestoreBlobs(AH);
}

/*
 * Skip the BLOBs from the current file position.
 * BLOBS are written sequentially as data blocks (see below).
 * Each BLOB is preceded by it's original OID.
 * A zero OID indicated the end of the BLOBS
 */
static void
_skipBlobs(ArchiveHandle *AH)
{
	Oid			oid;

	oid = ReadInt(AH);
	while (oid != 0)
	{
		_skipData(AH);
		oid = ReadInt(AH);
	}
}

/*
 * Skip data from current file position.
 * Data blocks are formatted as an integer length, followed by data.
 * A zero length denoted the end of the block.
*/
static void
_skipData(ArchiveHandle *AH)
{
	lclContext *ctx = (lclContext *) AH->formatData;
	size_t		blkLen;
	char	   *in = ctx->zlibIn;
	size_t		cnt;

	blkLen = ReadInt(AH);
	while (blkLen != 0)
	{
		if (blkLen > ctx->inSize)
		{
			free(ctx->zlibIn);
			ctx->zlibIn = (char *) malloc(blkLen);
			ctx->inSize = blkLen;
			in = ctx->zlibIn;
		}
		cnt = fread(in, 1, blkLen, AH->FH);
		if (cnt != blkLen)
		{
			if (feof(AH->FH))
				die_horribly(AH, modulename,
							 "could not read from input file: end of file\n");
			else
				die_horribly(AH, modulename,
					"could not read from input file: %s\n", strerror(errno));
		}

		ctx->filePos += blkLen;

		blkLen = ReadInt(AH);
	}
}

/*
 * Write a byte of data to the archive.
 *
 * Mandatory.
 *
 * Called by the archiver to do integer & byte output to the archive.
 * These routines are only used to read & write headers & TOC.
 *
 */
static int
_WriteByte(ArchiveHandle *AH, const int i)
{
	lclContext *ctx = (lclContext *) AH->formatData;
	int			res;

	res = fputc(i, AH->FH);
	if (res != EOF)
		ctx->filePos += 1;
	else
		die_horribly(AH, modulename, "could not write byte: %s\n", strerror(errno));
	return res;
}

/*
 * Read a byte of data from the archive.
 *
 * Mandatory
 *
 * Called by the archiver to read bytes & integers from the archive.
 * These routines are only used to read & write headers & TOC.
 *
 */
static int
_ReadByte(ArchiveHandle *AH)
{
	lclContext *ctx = (lclContext *) AH->formatData;
	int			res;

	res = fgetc(AH->FH);
	if (res != EOF)
		ctx->filePos += 1;
	return res;
}

/*
 * Write a buffer of data to the archive.
 *
 * Mandatory.
 *
 * Called by the archiver to write a block of bytes to the archive.
 * These routines are only used to read & write headers & TOC.
 *
 */
static size_t
_WriteBuf(ArchiveHandle *AH, const void *buf, size_t len)
{
	lclContext *ctx = (lclContext *) AH->formatData;
	size_t		res;

	res = fwrite(buf, 1, len, AH->FH);

	if (res != len)
		die_horribly(AH, modulename,
					 "could not write to output file: %s\n", strerror(errno));

	ctx->filePos += res;
	return res;
}

/*
 * Read a block of bytes from the archive.
 *
 * Mandatory.
 *
 * Called by the archiver to read a block of bytes from the archive
 * These routines are only used to read & write headers & TOC.
 *
 */
static size_t
_ReadBuf(ArchiveHandle *AH, void *buf, size_t len)
{
	lclContext *ctx = (lclContext *) AH->formatData;
	size_t		res;

	res = fread(buf, 1, len, AH->FH);
	ctx->filePos += res;

	return res;
}

/*
 * Close the archive.
 *
 * Mandatory.
 *
 * When writing the archive, this is the routine that actually starts
 * the process of saving it to files. No data should be written prior
 * to this point, since the user could sort the TOC after creating it.
 *
 * If an archive is to be written, this toutine must call:
 *		WriteHead			to save the archive header
 *		WriteToc			to save the TOC entries
 *		WriteDataChunks		to save all DATA & BLOBs.
 *
 */
static void
_CloseArchive(ArchiveHandle *AH)
{
	lclContext *ctx = (lclContext *) AH->formatData;
	pgoff_t		tpos;

	if (AH->mode == archModeWrite)
	{
		WriteHead(AH);
		tpos = ftello(AH->FH);
		WriteToc(AH);
		ctx->dataStart = _getFilePos(AH, ctx);
		WriteDataChunks(AH);

		/*
		 * This is not an essential operation - it is really only needed if we
		 * expect to be doing seeks to read the data back - it may be ok to
		 * just use the existing self-consistent block formatting.
		 */
		if (ctx->hasSeek)
		{
			fseeko(AH->FH, tpos, SEEK_SET);
			WriteToc(AH);
		}
	}

	if (fclose(AH->FH) != 0)
		die_horribly(AH, modulename, "could not close archive file: %s\n", strerror(errno));

	AH->FH = NULL;
}

/*--------------------------------------------------
 * END OF FORMAT CALLBACKS
 *--------------------------------------------------
 */

/*
 * Get the current position in the archive file.
 */
static pgoff_t
_getFilePos(ArchiveHandle *AH, lclContext *ctx)
{
	pgoff_t		pos;

	if (ctx->hasSeek)
	{
		pos = ftello(AH->FH);
		if (pos != ctx->filePos)
		{
			write_msg(modulename, "WARNING: ftell mismatch with expected position -- ftell used\n");

			/*
			 * Prior to 1.7 (pg7.3) we relied on the internally maintained
			 * pointer. Now we rely on pgoff_t always. pos = ctx->filePos;
			 */
		}
	}
	else
		pos = ctx->filePos;
	return pos;
}

/*
 * Read a data block header. The format changed in V1.3, so we
 * put the code here for simplicity.
 */
static void
_readBlockHeader(ArchiveHandle *AH, int *type, int *id)
{
	if (AH->version < K_VERS_1_3)
		*type = BLK_DATA;
	else
		*type = _ReadByte(AH);

	*id = ReadInt(AH);
}

/*
 * If zlib is available, then startit up. This is called from
 * StartData & StartBlob. The buffers are setup in the Init routine.
 */
static void
_StartDataCompressor(ArchiveHandle *AH, TocEntry *te)
{
	lclContext *ctx = (lclContext *) AH->formatData;
	z_streamp	zp = ctx->zp;

#ifdef HAVE_LIBZ

	if (AH->compression < 0 || AH->compression > 9)
		AH->compression = Z_DEFAULT_COMPRESSION;

	if (AH->compression != 0)
	{
		zp->zalloc = Z_NULL;
		zp->zfree = Z_NULL;
		zp->opaque = Z_NULL;

		if (deflateInit(zp, AH->compression) != Z_OK)
			die_horribly(AH, modulename, "could not initialize compression library: %s\n", zp->msg);
	}
#else

	AH->compression = 0;
#endif

	/* Just be paranoid - maybe End is called after Start, with no Write */
	zp->next_out = (void *) ctx->zlibOut;
	zp->avail_out = zlibOutSize;
}

/*
 * Send compressed data to the output stream (via ahwrite).
 * Each data chunk is preceded by it's length.
 * In the case of Z0, or no zlib, just write the raw data.
 *
 */
static int
_DoDeflate(ArchiveHandle *AH, lclContext *ctx, int flush)
{
	z_streamp	zp = ctx->zp;

#ifdef HAVE_LIBZ
	char	   *out = ctx->zlibOut;
	int			res = Z_OK;

	if (AH->compression != 0)
	{
		res = deflate(zp, flush);
		if (res == Z_STREAM_ERROR)
			die_horribly(AH, modulename, "could not compress data: %s\n", zp->msg);

		if (((flush == Z_FINISH) && (zp->avail_out < zlibOutSize))
			|| (zp->avail_out == 0)
			|| (zp->avail_in != 0)
			)
		{
			/*
			 * Extra paranoia: avoid zero-length chunks since a zero length
			 * chunk is the EOF marker. This should never happen but...
			 */
			if (zp->avail_out < zlibOutSize)
			{
				/*
				 * printf("Wrote %lu byte deflated chunk\n", (unsigned long)
				 * (zlibOutSize - zp->avail_out));
				 */
				WriteInt(AH, zlibOutSize - zp->avail_out);
				if (fwrite(out, 1, zlibOutSize - zp->avail_out, AH->FH) != (zlibOutSize - zp->avail_out))
					die_horribly(AH, modulename, "could not write to output file: %s\n", strerror(errno));
				ctx->filePos += zlibOutSize - zp->avail_out;
			}
			zp->next_out = (void *) out;
			zp->avail_out = zlibOutSize;
		}
	}
	else
#endif
	{
		if (zp->avail_in > 0)
		{
			WriteInt(AH, zp->avail_in);
			if (fwrite(zp->next_in, 1, zp->avail_in, AH->FH) != zp->avail_in)
				die_horribly(AH, modulename, "could not write to output file: %s\n", strerror(errno));
			ctx->filePos += zp->avail_in;
			zp->avail_in = 0;
		}
		else
		{
#ifdef HAVE_LIBZ
			if (flush == Z_FINISH)
				res = Z_STREAM_END;
#endif
		}
	}

#ifdef HAVE_LIBZ
	return res;
#else
	return 1;
#endif
}

/*
 * Terminate zlib context and flush it's buffers. If no zlib
 * then just return.
 *
 */
static void
_EndDataCompressor(ArchiveHandle *AH, TocEntry *te)
{

#ifdef HAVE_LIBZ
	lclContext *ctx = (lclContext *) AH->formatData;
	z_streamp	zp = ctx->zp;
	int			res;

	if (AH->compression != 0)
	{
		zp->next_in = NULL;
		zp->avail_in = 0;

		do
		{
			/* printf("Ending data output\n"); */
			res = _DoDeflate(AH, ctx, Z_FINISH);
		} while (res != Z_STREAM_END);

		if (deflateEnd(zp) != Z_OK)
			die_horribly(AH, modulename, "could not close compression stream: %s\n", zp->msg);
	}
#endif

	/* Send the end marker */
	WriteInt(AH, 0);
}