pg_backup_custom.c

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/*-------------------------------------------------------------------------
 *
 * 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
 *      src/bin/pg_dump/pg_backup_custom.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres_fe.h"

#include "compress_io.h"
#include "parallel.h"
#include "pg_backup_utils.h"
#include "common/file_utils.h"

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

static void _ArchiveEntry(ArchiveHandle *AH, TocEntry *te);
static void _StartData(ArchiveHandle *AH, TocEntry *te);
static void _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 void _WriteBuf(ArchiveHandle *AH, const void *buf, size_t len);
static void _ReadBuf(ArchiveHandle *AH, void *buf, size_t len);
static void _CloseArchive(ArchiveHandle *AH);
static void _ReopenArchive(ArchiveHandle *AH);
static void _PrintTocData(ArchiveHandle *AH, TocEntry *te);
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, bool drop);
static void _Clone(ArchiveHandle *AH);
static void _DeClone(ArchiveHandle *AH);

static int  _WorkerJobRestoreCustom(ArchiveHandle *AH, TocEntry *te);

typedef struct
{
    CompressorState *cs;
    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 pgoff_t _getFilePos(ArchiveHandle *AH, lclContext *ctx);

static void _CustomWriteFunc(ArchiveHandle *AH, const char *buf, size_t len);
static size_t _CustomReadFunc(ArchiveHandle *AH, char **buf, size_t *buflen);

/* translator: this is a module name */
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->ReopenPtr = _ReopenArchive;
    AH->PrintTocDataPtr = _PrintTocData;
    AH->ReadExtraTocPtr = _ReadExtraToc;
    AH->WriteExtraTocPtr = _WriteExtraToc;
    AH->PrintExtraTocPtr = _PrintExtraToc;

    AH->StartBlobsPtr = _StartBlobs;
    AH->StartBlobPtr = _StartBlob;
    AH->EndBlobPtr = _EndBlob;
    AH->EndBlobsPtr = _EndBlobs;
    AH->ClonePtr = _Clone;
    AH->DeClonePtr = _DeClone;

    /* no parallel dump in the custom archive, only parallel restore */
    AH->WorkerJobDumpPtr = NULL;
    AH->WorkerJobRestorePtr = _WorkerJobRestoreCustom;

    /* Set up a private area. */
    ctx = (lclContext *) pg_malloc0(sizeof(lclContext));
    AH->formatData = (void *) ctx;

    /* Initialize LO buffering */
    AH->lo_buf_size = LOBBUFSIZE;
    AH->lo_buf = (void *) pg_malloc(LOBBUFSIZE);

    ctx->filePos = 0;

    /*
     * Now open the file
     */
    if (AH->mode == archModeWrite)
    {
        if (AH->fSpec && strcmp(AH->fSpec, "") != 0)
        {
            AH->FH = fopen(AH->fSpec, PG_BINARY_W);
            if (!AH->FH)
                exit_horribly(modulename, "could not open output file \"%s\": %s\n",
                              AH->fSpec, strerror(errno));
        }
        else
        {
            AH->FH = stdout;
            if (!AH->FH)
                exit_horribly(modulename, "could not open output file: %s\n",
                              strerror(errno));
        }

        ctx->hasSeek = checkSeek(AH->FH);
    }
    else
    {
        if (AH->fSpec && strcmp(AH->fSpec, "") != 0)
        {
            AH->FH = fopen(AH->fSpec, PG_BINARY_R);
            if (!AH->FH)
                exit_horribly(modulename, "could not open input file \"%s\": %s\n",
                              AH->fSpec, strerror(errno));
        }
        else
        {
            AH->FH = stdin;
            if (!AH->FH)
                exit_horribly(modulename, "could not open input file: %s\n",
                              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 extract format-related TOC data.
*/
static void
_ArchiveEntry(ArchiveHandle *AH, TocEntry *te)
{
    lclTocEntry *ctx;

    ctx = (lclTocEntry *) pg_malloc0(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 should also
 * use the Archiver input routines.
 */
static void
_ReadExtraToc(ArchiveHandle *AH, TocEntry *te)
{
    lclTocEntry *ctx = (lclTocEntry *) te->formatData;

    if (ctx == NULL)
    {
        ctx = (lclTocEntry *) pg_malloc0(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)
        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 */

    ctx->cs = AllocateCompressor(AH->compression, _CustomWriteFunc);
}

/*
 * 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 void
_WriteData(ArchiveHandle *AH, const void *data, size_t dLen)
{
    lclContext *ctx = (lclContext *) AH->formatData;
    CompressorState *cs = ctx->cs;

    if (dLen > 0)
        /* WriteDataToArchive() internally throws write errors */
        WriteDataToArchive(AH, cs, data, dLen);

    return;
}

/*
 * 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;

    EndCompressor(AH, ctx->cs);
    /* Send the end marker */
    WriteInt(AH, 0);
}

/*
 * 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)
{
    lclContext *ctx = (lclContext *) AH->formatData;

    if (oid == 0)
        exit_horribly(modulename, "invalid OID for large object\n");

    WriteInt(AH, oid);

    ctx->cs = AllocateCompressor(AH->compression, _CustomWriteFunc);
}

/*
 * Called by the archiver when the dumper calls EndBlob.
 *
 * Optional.
 */
static void
_EndBlob(ArchiveHandle *AH, TocEntry *te, Oid oid)
{
    lclContext *ctx = (lclContext *) AH->formatData;

    EndCompressor(AH, ctx->cs);
    /* Send the end marker */
    WriteInt(AH, 0);
}

/*
 * 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)
{
    lclContext *ctx = (lclContext *) AH->formatData;
    lclTocEntry *tctx = (lclTocEntry *) te->formatData;
    int         blkType;
    int         id;

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

    if (!ctx->hasSeek || tctx->dataState == K_OFFSET_POS_NOT_SET)
    {
        /*
         * We cannot seek directly to the desired block.  Instead, skip over
         * block headers until we find the one we want.  This could fail if we
         * are asked to restore items out-of-order.
         */
        _readBlockHeader(AH, &blkType, &id);

        while (blkType != EOF && id != te->dumpId)
        {
            switch (blkType)
            {
                case BLK_DATA:
                    _skipData(AH);
                    break;

                case BLK_BLOBS:
                    _skipBlobs(AH);
                    break;

                default:        /* Always have a default */
                    exit_horribly(modulename,
                                  "unrecognized data block type (%d) while searching archive\n",
                                  blkType);
                    break;
            }
            _readBlockHeader(AH, &blkType, &id);
        }
    }
    else
    {
        /* We can just seek to the place we need to be. */
        if (fseeko(AH->FH, tctx->dataPos, SEEK_SET) != 0)
            exit_horribly(modulename, "error during file seek: %s\n",
                          strerror(errno));

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

    /* Produce suitable failure message if we fell off end of file */
    if (blkType == EOF)
    {
        if (tctx->dataState == K_OFFSET_POS_NOT_SET)
            exit_horribly(modulename, "could not find block ID %d in archive -- "
                          "possibly due to out-of-order restore request, "
                          "which cannot be handled due to lack of data offsets in archive\n",
                          te->dumpId);
        else if (!ctx->hasSeek)
            exit_horribly(modulename, "could not find block ID %d in archive -- "
                          "possibly due to out-of-order restore request, "
                          "which cannot be handled due to non-seekable input file\n",
                          te->dumpId);
        else                    /* huh, the dataPos led us to EOF? */
            exit_horribly(modulename, "could not find block ID %d in archive -- "
                          "possibly corrupt archive\n",
                          te->dumpId);
    }

    /* Are we sane? */
    if (id != te->dumpId)
        exit_horribly(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, AH->public.ropt->dropSchema);
            break;

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

/*
 * Print data from current file position.
*/
static void
_PrintData(ArchiveHandle *AH)
{
    ReadDataFromArchive(AH, AH->compression, _CustomReadFunc);
}

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

    StartRestoreBlobs(AH);

    oid = ReadInt(AH);
    while (oid != 0)
    {
        StartRestoreBlob(AH, oid, drop);
        _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       *buf = NULL;
    int         buflen = 0;
    size_t      cnt;

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

        ctx->filePos += blkLen;

        blkLen = ReadInt(AH);
    }

    if (buf)
        free(buf);
}

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

    if ((res = fputc(i, AH->FH)) == EOF)
        WRITE_ERROR_EXIT;
    ctx->filePos += 1;

    return 1;
}

/*
 * Read a byte of data from the archive.
 *
 * Mandatory
 *
 * Called by the archiver to read bytes & integers from the archive.
 * EOF should be treated as a fatal error.
 */
static int
_ReadByte(ArchiveHandle *AH)
{
    lclContext *ctx = (lclContext *) AH->formatData;
    int         res;

    res = getc(AH->FH);
    if (res == EOF)
        READ_ERROR_EXIT(AH->FH);
    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.
 */
static void
_WriteBuf(ArchiveHandle *AH, const void *buf, size_t len)
{
    lclContext *ctx = (lclContext *) AH->formatData;

    if (fwrite(buf, 1, len, AH->FH) != len)
        WRITE_ERROR_EXIT;
    ctx->filePos += len;

    return;
}

/*
 * Read a block of bytes from the archive.
 *
 * Mandatory.
 *
 * Called by the archiver to read a block of bytes from the archive
 */
static void
_ReadBuf(ArchiveHandle *AH, void *buf, size_t len)
{
    lclContext *ctx = (lclContext *) AH->formatData;

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

    return;
}

/*
 * 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 routine 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);
        /* Remember TOC's seek position for use below */
        tpos = ftello(AH->FH);
        if (tpos < 0 && ctx->hasSeek)
            exit_horribly(modulename, "could not determine seek position in archive file: %s\n",
                          strerror(errno));
        WriteToc(AH);
        ctx->dataStart = _getFilePos(AH, ctx);
        WriteDataChunks(AH, NULL);

        /*
         * If possible, re-write the TOC in order to update the data offset
         * information.  This is not essential, as pg_restore can cope in most
         * cases without it; but it can make pg_restore significantly faster
         * in some situations (especially parallel restore).
         */
        if (ctx->hasSeek &&
            fseeko(AH->FH, tpos, SEEK_SET) == 0)
            WriteToc(AH);
    }

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

    /* Sync the output file if one is defined */
    if (AH->dosync && AH->mode == archModeWrite && AH->fSpec)
        (void) fsync_fname(AH->fSpec, false, progname);

    AH->FH = NULL;
}

/*
 * Reopen the archive's file handle.
 *
 * We close the original file handle, except on Windows.  (The difference
 * is because on Windows, this is used within a multithreading context,
 * and we don't want a thread closing the parent file handle.)
 */
static void
_ReopenArchive(ArchiveHandle *AH)
{
    lclContext *ctx = (lclContext *) AH->formatData;
    pgoff_t     tpos;

    if (AH->mode == archModeWrite)
        exit_horribly(modulename, "can only reopen input archives\n");

    /*
     * These two cases are user-facing errors since they represent unsupported
     * (but not invalid) use-cases.  Word the error messages appropriately.
     */
    if (AH->fSpec == NULL || strcmp(AH->fSpec, "") == 0)
        exit_horribly(modulename, "parallel restore from standard input is not supported\n");
    if (!ctx->hasSeek)
        exit_horribly(modulename, "parallel restore from non-seekable file is not supported\n");

    tpos = ftello(AH->FH);
    if (tpos < 0)
        exit_horribly(modulename, "could not determine seek position in archive file: %s\n",
                      strerror(errno));

#ifndef WIN32
    if (fclose(AH->FH) != 0)
        exit_horribly(modulename, "could not close archive file: %s\n",
                      strerror(errno));
#endif

    AH->FH = fopen(AH->fSpec, PG_BINARY_R);
    if (!AH->FH)
        exit_horribly(modulename, "could not open input file \"%s\": %s\n",
                      AH->fSpec, strerror(errno));

    if (fseeko(AH->FH, tpos, SEEK_SET) != 0)
        exit_horribly(modulename, "could not set seek position in archive file: %s\n",
                      strerror(errno));
}

/*
 * Clone format-specific fields during parallel restoration.
 */
static void
_Clone(ArchiveHandle *AH)
{
    lclContext *ctx = (lclContext *) AH->formatData;

    AH->formatData = (lclContext *) pg_malloc(sizeof(lclContext));
    memcpy(AH->formatData, ctx, sizeof(lclContext));
    ctx = (lclContext *) AH->formatData;

    /* sanity check, shouldn't happen */
    if (ctx->cs != NULL)
        exit_horribly(modulename, "compressor active\n");

    /*
     * Note: we do not make a local lo_buf because we expect at most one BLOBS
     * entry per archive, so no parallelism is possible.  Likewise,
     * TOC-entry-local state isn't an issue because any one TOC entry is
     * touched by just one worker child.
     */
}

static void
_DeClone(ArchiveHandle *AH)
{
    lclContext *ctx = (lclContext *) AH->formatData;

    free(ctx);
}

/*
 * This function is executed in the child of a parallel restore from a
 * custom-format archive and restores the actual data for one TOC entry.
 */
static int
_WorkerJobRestoreCustom(ArchiveHandle *AH, TocEntry *te)
{
    return parallel_restore(AH, te);
}

/*--------------------------------------------------
 * 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)
    {
        /*
         * Prior to 1.7 (pg7.3) we relied on the internally maintained
         * pointer.  Now we rely on ftello() always, unless the file has been
         * found to not support it.  For debugging purposes, print a warning
         * if the internal pointer disagrees, so that we're more likely to
         * notice if something's broken about the internal position tracking.
         */
        pos = ftello(AH->FH);
        if (pos < 0)
            exit_horribly(modulename, "could not determine seek position in archive file: %s\n",
                          strerror(errno));

        if (pos != ctx->filePos)
            write_msg(modulename, "WARNING: ftell mismatch with expected position -- ftell used\n");
    }
    else
        pos = ctx->filePos;
    return pos;
}

/*
 * Read a data block header. The format changed in V1.3, so we
 * centralize the code here for simplicity.  Returns *type = EOF
 * if at EOF.
 */
static void
_readBlockHeader(ArchiveHandle *AH, int *type, int *id)
{
    lclContext *ctx = (lclContext *) AH->formatData;
    int         byt;

    /*
     * Note: if we are at EOF with a pre-1.3 input file, we'll exit_horribly
     * inside ReadInt rather than returning EOF.  It doesn't seem worth
     * jumping through hoops to deal with that case better, because no such
     * files are likely to exist in the wild: only some 7.1 development
     * versions of pg_dump ever generated such files.
     */
    if (AH->version < K_VERS_1_3)
        *type = BLK_DATA;
    else
    {
        byt = getc(AH->FH);
        *type = byt;
        if (byt == EOF)
        {
            *id = 0;            /* don't return an uninitialized value */
            return;
        }
        ctx->filePos += 1;
    }

    *id = ReadInt(AH);
}

/*
 * Callback function for WriteDataToArchive. Writes one block of (compressed)
 * data to the archive.
 */
static void
_CustomWriteFunc(ArchiveHandle *AH, const char *buf, size_t len)
{
    /* never write 0-byte blocks (this should not happen) */
    if (len > 0)
    {
        WriteInt(AH, len);
        _WriteBuf(AH, buf, len);
    }
    return;
}

/*
 * Callback function for ReadDataFromArchive. To keep things simple, we
 * always read one compressed block at a time.
 */
static size_t
_CustomReadFunc(ArchiveHandle *AH, char **buf, size_t *buflen)
{
    size_t      blkLen;

    /* Read length */
    blkLen = ReadInt(AH);
    if (blkLen == 0)
        return 0;

    /* If the caller's buffer is not large enough, allocate a bigger one */
    if (blkLen > *buflen)
    {
        free(*buf);
        *buf = (char *) pg_malloc(blkLen);
        *buflen = blkLen;
    }

    /* exits app on read errors */
    _ReadBuf(AH, *buf, blkLen);

    return blkLen;
}