pg_backup_custom.c

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/*-------------------------------------------------------------------------
 *
 * pg_backup_custom.c
 *
 *  Implements the custom output format.
 *
 *  The comments with the routines 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 "common/file_utils.h"
#include "compress_io.h"
#include "pg_backup_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 *AH);
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 _skipLOs(ArchiveHandle *AH);
 
static void _StartLOs(ArchiveHandle *AH, TocEntry *te);
static void _StartLO(ArchiveHandle *AH, TocEntry *te, Oid oid);
static void _EndLO(ArchiveHandle *AH, TocEntry *te, Oid oid);
static void _EndLOs(ArchiveHandle *AH, TocEntry *te);
static void _LoadLOs(ArchiveHandle *AH, bool drop);
 
static void _PrepParallelRestore(ArchiveHandle *AH);
static void _Clone(ArchiveHandle *AH);
static void _DeClone(ArchiveHandle *AH);
 
static int  _WorkerJobRestoreCustom(ArchiveHandle *AH, TocEntry *te);
 
typedef struct
{
    CompressorState *cs;
    int         hasSeek;
    /* lastFilePos is used only when reading, and may be invalid if !hasSeek */
    pgoff_t     lastFilePos;    /* position after last data block we've read */
} lclContext;
 
typedef struct
{
    int         dataState;
    pgoff_t     dataPos;        /* valid only if dataState=K_OFFSET_POS_SET */
} 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);
 
 
/*
 *  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 its 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->StartLOsPtr = _StartLOs;
    AH->StartLOPtr = _StartLO;
    AH->EndLOPtr = _EndLO;
    AH->EndLOsPtr = _EndLOs;
 
    AH->PrepParallelRestorePtr = _PrepParallelRestore;
    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 = ctx;
 
    /*
     * 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)
                pg_fatal("could not open output file \"%s\": %m", AH->fSpec);
        }
        else
        {
            AH->FH = stdout;
            if (!AH->FH)
                pg_fatal("could not open output file: %m");
        }
 
        ctx->hasSeek = checkSeek(AH->FH);
    }
    else
    {
        if (AH->fSpec && strcmp(AH->fSpec, "") != 0)
        {
            AH->FH = fopen(AH->fSpec, PG_BINARY_R);
            if (!AH->FH)
                pg_fatal("could not open input file \"%s\": %m", AH->fSpec);
        }
        else
        {
            AH->FH = stdin;
            if (!AH->FH)
                pg_fatal("could not open input file: %m");
        }
 
        ctx->hasSeek = checkSeek(AH->FH);
 
        ReadHead(AH);
        ReadToc(AH);
 
        /*
         * Remember location of first data block (i.e., the point after TOC)
         * in case we have to search for desired data blocks.
         */
        ctx->lastFilePos = _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 = 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 = 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);
    if (tctx->dataPos >= 0)
        tctx->dataState = K_OFFSET_POS_SET;
 
    _WriteByte(AH, BLK_DATA);   /* Block type */
    WriteInt(AH, te->dumpId);   /* For sanity check */
 
    ctx->cs = AllocateCompressor(AH->compression_spec,
                                 NULL,
                                 _CustomWriteFunc);
}
 
/*
 * Called by archiver when dumper calls WriteData. This routine is
 * called for both LO and table data; it is the responsibility of
 * the format to manage each kind of data using StartLO/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)
        /* writeData() internally throws write errors */
        cs->writeData(AH, cs, data, dLen);
}
 
/*
 * Called by the archiver when a dumper's 'DataDumper' routine has
 * finished.
 *
 * Mandatory.
 */
static void
_EndData(ArchiveHandle *AH, TocEntry *te)
{
    lclContext *ctx = (lclContext *) AH->formatData;
 
    EndCompressor(AH, ctx->cs);
    ctx->cs = NULL;
 
    /* Send the end marker */
    WriteInt(AH, 0);
}
 
/*
 * Called by the archiver when starting to save BLOB DATA (not schema).
 * This routine should save whatever format-specific information is needed
 * to read the LOs back into memory.
 *
 * It is called just prior to the dumper's DataDumper routine.
 *
 * Optional, but strongly recommended.
 */
static void
_StartLOs(ArchiveHandle *AH, TocEntry *te)
{
    lclContext *ctx = (lclContext *) AH->formatData;
    lclTocEntry *tctx = (lclTocEntry *) te->formatData;
 
    tctx->dataPos = _getFilePos(AH, ctx);
    if (tctx->dataPos >= 0)
        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 StartLO.
 *
 * Mandatory.
 *
 * Must save the passed OID for retrieval at restore-time.
 */
static void
_StartLO(ArchiveHandle *AH, TocEntry *te, Oid oid)
{
    lclContext *ctx = (lclContext *) AH->formatData;
 
    if (oid == 0)
        pg_fatal("invalid OID for large object");
 
    WriteInt(AH, oid);
 
    ctx->cs = AllocateCompressor(AH->compression_spec,
                                 NULL,
                                 _CustomWriteFunc);
}
 
/*
 * Called by the archiver when the dumper calls EndLO.
 *
 * Optional.
 */
static void
_EndLO(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 BLOB DATA.
 *
 * Optional.
 */
static void
_EndLOs(ArchiveHandle *AH, TocEntry *te)
{
    /* Write out a fake zero OID to mark end-of-LOs. */
    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.  Remember the
         * positions of skipped-over blocks, so that if we later decide we
         * need to read one, we'll be able to seek to it.
         *
         * When our input file is seekable, we can do the search starting from
         * the point after the last data block we scanned in previous
         * iterations of this function.
         */
        if (ctx->hasSeek)
        {
            if (fseeko(AH->FH, ctx->lastFilePos, SEEK_SET) != 0)
                pg_fatal("error during file seek: %m");
        }
 
        for (;;)
        {
            pgoff_t     thisBlkPos = _getFilePos(AH, ctx);
 
            _readBlockHeader(AH, &blkType, &id);
 
            if (blkType == EOF || id == te->dumpId)
                break;
 
            /* Remember the block position, if we got one */
            if (thisBlkPos >= 0)
            {
                TocEntry   *otherte = getTocEntryByDumpId(AH, id);
 
                if (otherte && otherte->formatData)
                {
                    lclTocEntry *othertctx = (lclTocEntry *) otherte->formatData;
 
                    /*
                     * Note: on Windows, multiple threads might access/update
                     * the same lclTocEntry concurrently, but that should be
                     * safe as long as we update dataPos before dataState.
                     * Ideally, we'd use pg_write_barrier() to enforce that,
                     * but the needed infrastructure doesn't exist in frontend
                     * code.  But Windows only runs on machines with strong
                     * store ordering, so it should be okay for now.
                     */
                    if (othertctx->dataState == K_OFFSET_POS_NOT_SET)
                    {
                        othertctx->dataPos = thisBlkPos;
                        othertctx->dataState = K_OFFSET_POS_SET;
                    }
                    else if (othertctx->dataPos != thisBlkPos ||
                             othertctx->dataState != K_OFFSET_POS_SET)
                    {
                        /* sanity check */
                        pg_log_warning("data block %d has wrong seek position",
                                       id);
                    }
                }
            }
 
            switch (blkType)
            {
                case BLK_DATA:
                    _skipData(AH);
                    break;
 
                case BLK_BLOBS:
                    _skipLOs(AH);
                    break;
 
                default:        /* Always have a default */
                    pg_fatal("unrecognized data block type (%d) while searching archive",
                             blkType);
                    break;
            }
        }
    }
    else
    {
        /* We can just seek to the place we need to be. */
        if (fseeko(AH->FH, tctx->dataPos, SEEK_SET) != 0)
            pg_fatal("error during file seek: %m");
 
        _readBlockHeader(AH, &blkType, &id);
    }
 
    /*
     * If we reached EOF without finding the block we want, then either it
     * doesn't exist, or it does but we lack the ability to seek back to it.
     */
    if (blkType == EOF)
    {
        if (!ctx->hasSeek)
            pg_fatal("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",
                     te->dumpId);
        else
            pg_fatal("could not find block ID %d in archive -- "
                     "possibly corrupt archive",
                     te->dumpId);
    }
 
    /* Are we sane? */
    if (id != te->dumpId)
        pg_fatal("found unexpected block ID (%d) when reading data -- expected %d",
                 id, te->dumpId);
 
    switch (blkType)
    {
        case BLK_DATA:
            _PrintData(AH);
            break;
 
        case BLK_BLOBS:
            _LoadLOs(AH, AH->public.ropt->dropSchema);
            break;
 
        default:                /* Always have a default */
            pg_fatal("unrecognized data block type %d while restoring archive",
                     blkType);
            break;
    }
 
    /*
     * If our input file is seekable but lacks data offsets, update our
     * knowledge of where to start future searches from.  (Note that we did
     * not update the current TE's dataState/dataPos.  We could have, but
     * there is no point since it will not be visited again.)
     */
    if (ctx->hasSeek && tctx->dataState == K_OFFSET_POS_NOT_SET)
    {
        pgoff_t     curPos = _getFilePos(AH, ctx);
 
        if (curPos > ctx->lastFilePos)
            ctx->lastFilePos = curPos;
    }
}
 
/*
 * Print data from current file position.
*/
static void
_PrintData(ArchiveHandle *AH)
{
    CompressorState *cs;
 
    cs = AllocateCompressor(AH->compression_spec,
                            _CustomReadFunc, NULL);
    cs->readData(AH, cs);
    EndCompressor(AH, cs);
}
 
static void
_LoadLOs(ArchiveHandle *AH, bool drop)
{
    Oid         oid;
 
    StartRestoreLOs(AH);
 
    oid = ReadInt(AH);
    while (oid != 0)
    {
        StartRestoreLO(AH, oid, drop);
        _PrintData(AH);
        EndRestoreLO(AH, oid);
        oid = ReadInt(AH);
    }
 
    EndRestoreLOs(AH);
}
 
/*
 * Skip the LOs from the current file position.
 * LOs are written sequentially as data blocks (see below).
 * Each LO is preceded by its original OID.
 * A zero OID indicates the end of the LOs.
 */
static void
_skipLOs(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 indicates the end of the block.
*/
static void
_skipData(ArchiveHandle *AH)
{
    lclContext *ctx = (lclContext *) AH->formatData;
    size_t      blkLen;
    char       *buf = NULL;
    int         buflen = 0;
 
    blkLen = ReadInt(AH);
    while (blkLen != 0)
    {
        if (ctx->hasSeek)
        {
            if (fseeko(AH->FH, blkLen, SEEK_CUR) != 0)
                pg_fatal("error during file seek: %m");
        }
        else
        {
            if (blkLen > buflen)
            {
                free(buf);
                buf = (char *) pg_malloc(blkLen);
                buflen = blkLen;
            }
            if (fread(buf, 1, blkLen, AH->FH) != blkLen)
            {
                if (feof(AH->FH))
                    pg_fatal("could not read from input file: end of file");
                else
                    pg_fatal("could not read from input file: %m");
            }
        }
 
        blkLen = ReadInt(AH);
    }
 
    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)
{
    if (fputc(i, AH->FH) == EOF)
        WRITE_ERROR_EXIT;
 
    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)
{
    int         res;
 
    res = getc(AH->FH);
    if (res == EOF)
        READ_ERROR_EXIT(AH->FH);
    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)
{
    if (fwrite(buf, 1, len, AH->FH) != len)
        WRITE_ERROR_EXIT;
}
 
/*
 * 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)
{
    if (fread(buf, 1, len, AH->FH) != len)
        READ_ERROR_EXIT(AH->FH);
}
 
/*
 * 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 & LOs.
 *
 */
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)
            pg_fatal("could not determine seek position in archive file: %m");
        WriteToc(AH);
        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).  We can skip this
         * step if we're not dumping any data; there are no offsets to update
         * in that case.
         */
        if (ctx->hasSeek && AH->public.dopt->dumpData &&
            fseeko(AH->FH, tpos, SEEK_SET) == 0)
            WriteToc(AH);
    }
 
    if (fclose(AH->FH) != 0)
        pg_fatal("could not close archive file: %m");
 
    /* Sync the output file if one is defined */
    if (AH->dosync && AH->mode == archModeWrite && AH->fSpec)
        (void) fsync_fname(AH->fSpec, false);
 
    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)
        pg_fatal("can only reopen input archives");
 
    /*
     * 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)
        pg_fatal("parallel restore from standard input is not supported");
    if (!ctx->hasSeek)
        pg_fatal("parallel restore from non-seekable file is not supported");
 
    tpos = ftello(AH->FH);
    if (tpos < 0)
        pg_fatal("could not determine seek position in archive file: %m");
 
#ifndef WIN32
    if (fclose(AH->FH) != 0)
        pg_fatal("could not close archive file: %m");
#endif
 
    AH->FH = fopen(AH->fSpec, PG_BINARY_R);
    if (!AH->FH)
        pg_fatal("could not open input file \"%s\": %m", AH->fSpec);
 
    if (fseeko(AH->FH, tpos, SEEK_SET) != 0)
        pg_fatal("could not set seek position in archive file: %m");
}
 
/*
 * Prepare for parallel restore.
 *
 * The main thing that needs to happen here is to fill in TABLE DATA and BLOBS
 * TOC entries' dataLength fields with appropriate values to guide the
 * ordering of restore jobs.  The source of said data is format-dependent,
 * as is the exact meaning of the values.
 *
 * A format module might also choose to do other setup here.
 */
static void
_PrepParallelRestore(ArchiveHandle *AH)
{
    lclContext *ctx = (lclContext *) AH->formatData;
    TocEntry   *prev_te = NULL;
    lclTocEntry *prev_tctx = NULL;
    TocEntry   *te;
 
    /*
     * Knowing that the data items were dumped out in TOC order, we can
     * reconstruct the length of each item as the delta to the start offset of
     * the next data item.
     */
    for (te = AH->toc->next; te != AH->toc; te = te->next)
    {
        lclTocEntry *tctx = (lclTocEntry *) te->formatData;
 
        /*
         * Ignore entries without a known data offset; if we were unable to
         * seek to rewrite the TOC when creating the archive, this'll be all
         * of them, and we'll end up with no size estimates.
         */
        if (tctx->dataState != K_OFFSET_POS_SET)
            continue;
 
        /* Compute previous data item's length */
        if (prev_te)
        {
            if (tctx->dataPos > prev_tctx->dataPos)
                prev_te->dataLength = tctx->dataPos - prev_tctx->dataPos;
        }
 
        prev_te = te;
        prev_tctx = tctx;
    }
 
    /* If OK to seek, we can determine the length of the last item */
    if (prev_te && ctx->hasSeek)
    {
        pgoff_t     endpos;
 
        if (fseeko(AH->FH, 0, SEEK_END) != 0)
            pg_fatal("error during file seek: %m");
        endpos = ftello(AH->FH);
        if (endpos > prev_tctx->dataPos)
            prev_te->dataLength = endpos - prev_tctx->dataPos;
    }
}
 
/*
 * Clone format-specific fields during parallel restoration.
 */
static void
_Clone(ArchiveHandle *AH)
{
    lclContext *ctx = (lclContext *) AH->formatData;
 
    /*
     * Each thread must have private lclContext working state.
     */
    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)
        pg_fatal("compressor active");
 
    /*
     * We intentionally do not clone TOC-entry-local state: it's useful to
     * share knowledge about where the data blocks are across threads.
     * _PrintTocData has to be careful about the order of operations on that
     * state, though.
     */
}
 
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.
 *
 * With a non-seekable archive file, we may not be able to obtain the
 * file position.  If so, just return -1.  It's not too important in
 * that case because we won't be able to rewrite the TOC to fill in
 * data block offsets anyway.
 */
static pgoff_t
_getFilePos(ArchiveHandle *AH, lclContext *ctx)
{
    pgoff_t     pos;
 
    pos = ftello(AH->FH);
    if (pos < 0)
    {
        /* Not expected if we found we can seek. */
        if (ctx->hasSeek)
            pg_fatal("could not determine seek position in archive file: %m");
    }
    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)
{
    int         byt;
 
    /*
     * Note: if we are at EOF with a pre-1.3 input file, we'll pg_fatal()
     * 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;
        }
    }
 
    *id = ReadInt(AH);
}
 
/*
 * Callback function for writeData. 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);
    }
}
 
/*
 * Callback function for readData. 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;
}