pg_backup_tar.c

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/*-------------------------------------------------------------------------
 *
 * pg_backup_tar.c
 *
 *  This file is copied from the 'files' format file, but dumps data into
 *  one temp file then sends it to the output TAR archive.
 *
 *  The tar format also includes a 'restore.sql' script which is there for
 *  the benefit of humans. This script is never used by pg_restore.
 *
 *  NOTE: If you untar the created 'tar' file, the resulting files are
 *  compatible with the 'directory' format. Please keep the two formats in
 *  sync.
 *
 *  See the headers to pg_backup_directory & 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
 *  result from its use.
 *
 *
 * IDENTIFICATION
 *      src/bin/pg_dump/pg_backup_tar.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres_fe.h"
 
#include <sys/stat.h>
#include <ctype.h>
#include <limits.h>
#include <unistd.h>
 
#include "common/file_utils.h"
#include "fe_utils/string_utils.h"
#include "pg_backup_archiver.h"
#include "pg_backup_tar.h"
#include "pg_backup_utils.h"
#include "pgtar.h"
 
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 _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 _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);
 
#define K_STD_BUF_SIZE 1024
 
 
typedef struct
{
    FILE       *nFH;
    FILE       *tarFH;
    FILE       *tmpFH;
    char       *targetFile;
    char        mode;
    pgoff_t     pos;
    pgoff_t     fileLen;
    ArchiveHandle *AH;
} TAR_MEMBER;
 
typedef struct
{
    int         hasSeek;
    pgoff_t     filePos;
    TAR_MEMBER *loToc;
    FILE       *tarFH;
    pgoff_t     tarFHpos;
    pgoff_t     tarNextMember;
    TAR_MEMBER *FH;
    int         isSpecialScript;
    TAR_MEMBER *scriptTH;
} lclContext;
 
typedef struct
{
    TAR_MEMBER *TH;
    char       *filename;
} lclTocEntry;
 
static void _LoadLOs(ArchiveHandle *AH, TocEntry *te);
 
static TAR_MEMBER *tarOpen(ArchiveHandle *AH, const char *filename, char mode);
static void tarClose(ArchiveHandle *AH, TAR_MEMBER *th);
 
#ifdef __NOT_USED__
static char *tarGets(char *buf, size_t len, TAR_MEMBER *th);
#endif
static int  tarPrintf(TAR_MEMBER *th, const char *fmt,...) pg_attribute_printf(2, 3);
 
static void _tarAddFile(ArchiveHandle *AH, TAR_MEMBER *th);
static TAR_MEMBER *_tarPositionTo(ArchiveHandle *AH, const char *filename);
static size_t tarRead(void *buf, size_t len, TAR_MEMBER *th);
static size_t tarWrite(const void *buf, size_t len, TAR_MEMBER *th);
static void _tarWriteHeader(TAR_MEMBER *th);
static int  _tarGetHeader(ArchiveHandle *AH, TAR_MEMBER *th);
static size_t _tarReadRaw(ArchiveHandle *AH, void *buf, size_t len, TAR_MEMBER *th, FILE *fh);
 
static size_t _scriptOut(ArchiveHandle *AH, const void *buf, size_t len);
 
/*
 *  Initializer
 */
void
InitArchiveFmt_Tar(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 = NULL;
    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->ClonePtr = NULL;
    AH->DeClonePtr = NULL;
 
    AH->WorkerJobDumpPtr = NULL;
    AH->WorkerJobRestorePtr = NULL;
 
    /*
     * Set up some special context used in compressing data.
     */
    ctx = pg_malloc0_object(lclContext);
    AH->formatData = ctx;
    ctx->filePos = 0;
    ctx->isSpecialScript = 0;
 
    /*
     * Now open the tar file, and load the TOC if we're in read mode.
     */
    if (AH->mode == archModeWrite)
    {
        if (AH->fSpec && strcmp(AH->fSpec, "") != 0)
        {
            ctx->tarFH = fopen(AH->fSpec, PG_BINARY_W);
            if (ctx->tarFH == NULL)
                pg_fatal("could not open TOC file \"%s\" for output: %m",
                         AH->fSpec);
        }
        else
        {
            ctx->tarFH = stdout;
            if (ctx->tarFH == NULL)
                pg_fatal("could not open TOC file for output: %m");
        }
 
        ctx->tarFHpos = 0;
 
        /*
         * Make unbuffered since we will dup() it, and the buffers screw each
         * other
         */
        /* setvbuf(ctx->tarFH, NULL, _IONBF, 0); */
 
        ctx->hasSeek = checkSeek(ctx->tarFH);
 
        /*
         * We don't support compression because reading the files back is not
         * possible since gzdopen uses buffered IO which totally screws file
         * positioning.
         */
        if (AH->compression_spec.algorithm != PG_COMPRESSION_NONE)
            pg_fatal("compression is not supported by tar archive format");
    }
    else
    {                           /* Read Mode */
        if (AH->fSpec && strcmp(AH->fSpec, "") != 0)
        {
            ctx->tarFH = fopen(AH->fSpec, PG_BINARY_R);
            if (ctx->tarFH == NULL)
                pg_fatal("could not open TOC file \"%s\" for input: %m",
                         AH->fSpec);
        }
        else
        {
            ctx->tarFH = stdin;
            if (ctx->tarFH == NULL)
                pg_fatal("could not open TOC file for input: %m");
        }
 
        /*
         * Make unbuffered since we will dup() it, and the buffers screw each
         * other
         */
        /* setvbuf(ctx->tarFH, NULL, _IONBF, 0); */
 
        ctx->tarFHpos = 0;
 
        ctx->hasSeek = checkSeek(ctx->tarFH);
 
        ctx->FH = tarOpen(AH, "toc.dat", 'r');
        ReadHead(AH);
        ReadToc(AH);
        tarClose(AH, ctx->FH);  /* Nothing else in the file... */
    }
}
 
/*
 * - Start a new TOC entry
 *   Setup the output file name.
 */
static void
_ArchiveEntry(ArchiveHandle *AH, TocEntry *te)
{
    lclTocEntry *ctx;
    char        fn[K_STD_BUF_SIZE];
 
    ctx = pg_malloc0_object(lclTocEntry);
    if (te->dataDumper != NULL)
    {
        snprintf(fn, sizeof(fn), "%d.dat", te->dumpId);
        ctx->filename = pg_strdup(fn);
    }
    else
    {
        ctx->filename = NULL;
        ctx->TH = NULL;
    }
    te->formatData = ctx;
}
 
static void
_WriteExtraToc(ArchiveHandle *AH, TocEntry *te)
{
    lclTocEntry *ctx = (lclTocEntry *) te->formatData;
 
    if (ctx->filename)
        WriteStr(AH, ctx->filename);
    else
        WriteStr(AH, "");
}
 
static void
_ReadExtraToc(ArchiveHandle *AH, TocEntry *te)
{
    lclTocEntry *ctx = (lclTocEntry *) te->formatData;
 
    if (ctx == NULL)
    {
        ctx = pg_malloc0_object(lclTocEntry);
        te->formatData = ctx;
    }
 
    ctx->filename = ReadStr(AH);
    if (strlen(ctx->filename) == 0)
    {
        free(ctx->filename);
        ctx->filename = NULL;
    }
    ctx->TH = NULL;
}
 
static void
_PrintExtraToc(ArchiveHandle *AH, TocEntry *te)
{
    lclTocEntry *ctx = (lclTocEntry *) te->formatData;
 
    if (AH->public.verbose && ctx->filename != NULL)
        ahprintf(AH, "-- File: %s\n", ctx->filename);
}
 
static void
_StartData(ArchiveHandle *AH, TocEntry *te)
{
    lclTocEntry *tctx = (lclTocEntry *) te->formatData;
 
    tctx->TH = tarOpen(AH, tctx->filename, 'w');
}
 
static TAR_MEMBER *
tarOpen(ArchiveHandle *AH, const char *filename, char mode)
{
    lclContext *ctx = (lclContext *) AH->formatData;
    TAR_MEMBER *tm;
 
    if (mode == 'r')
    {
        tm = _tarPositionTo(AH, filename);
        if (!tm)                /* Not found */
        {
            if (filename)
            {
                /*
                 * Couldn't find the requested file. Future: do SEEK(0) and
                 * retry.
                 */
                pg_fatal("could not find file \"%s\" in archive", filename);
            }
            else
            {
                /* Any file OK, none left, so return NULL */
                return NULL;
            }
        }
 
        if (AH->compression_spec.algorithm == PG_COMPRESSION_NONE)
            tm->nFH = ctx->tarFH;
        else
            pg_fatal("compression is not supported by tar archive format");
    }
    else
    {
        int         old_umask;
 
        tm = pg_malloc0_object(TAR_MEMBER);
 
        /*
         * POSIX does not require, but permits, tmpfile() to restrict file
         * permissions.  Given an OS crash after we write data, the filesystem
         * might retain the data but forget tmpfile()'s unlink().  If so, the
         * file mode protects confidentiality of the data written.
         */
        old_umask = umask(S_IRWXG | S_IRWXO);
 
#ifndef WIN32
        tm->tmpFH = tmpfile();
#else
 
        /*
         * On WIN32, tmpfile() generates a filename in the root directory,
         * which requires administrative permissions on certain systems. Loop
         * until we find a unique file name we can create.
         */
        while (1)
        {
            char       *name;
            int         fd;
 
            name = _tempnam(NULL, "pg_temp_");
            if (name == NULL)
                break;
            fd = open(name, O_RDWR | O_CREAT | O_EXCL | O_BINARY |
                      O_TEMPORARY, S_IRUSR | S_IWUSR);
            free(name);
 
            if (fd != -1)       /* created a file */
            {
                tm->tmpFH = fdopen(fd, "w+b");
                break;
            }
            else if (errno != EEXIST)   /* failure other than file exists */
                break;
        }
#endif
 
        if (tm->tmpFH == NULL)
            pg_fatal("could not generate temporary file name: %m");
 
        umask(old_umask);
 
        if (AH->compression_spec.algorithm == PG_COMPRESSION_NONE)
            tm->nFH = tm->tmpFH;
        else
            pg_fatal("compression is not supported by tar archive format");
 
        tm->AH = AH;
        tm->targetFile = pg_strdup(filename);
    }
 
    tm->mode = mode;
    tm->tarFH = ctx->tarFH;
 
    return tm;
}
 
static void
tarClose(ArchiveHandle *AH, TAR_MEMBER *th)
{
    if (AH->compression_spec.algorithm != PG_COMPRESSION_NONE)
        pg_fatal("compression is not supported by tar archive format");
 
    if (th->mode == 'w')
        _tarAddFile(AH, th);    /* This will close the temp file */
 
    /*
     * else Nothing to do for normal read since we don't dup() normal file
     * handle, and we don't use temp files.
     */
 
    free(th->targetFile);
 
    th->nFH = NULL;
}
 
#ifdef __NOT_USED__
static char *
tarGets(char *buf, size_t len, TAR_MEMBER *th)
{
    char       *s;
    size_t      cnt = 0;
    char        c = ' ';
    int         eof = 0;
 
    /* Can't read past logical EOF */
    if (len > (th->fileLen - th->pos))
        len = th->fileLen - th->pos;
 
    while (cnt < len && c != '\n')
    {
        if (_tarReadRaw(th->AH, &c, 1, th, NULL) <= 0)
        {
            eof = 1;
            break;
        }
        buf[cnt++] = c;
    }
 
    if (eof && cnt == 0)
        s = NULL;
    else
    {
        buf[cnt++] = '\0';
        s = buf;
    }
 
    if (s)
    {
        len = strlen(s);
        th->pos += len;
    }
 
    return s;
}
#endif
 
/*
 * Just read bytes from the archive. This is the low level read routine
 * that is used for ALL reads on a tar file.
 */
static size_t
_tarReadRaw(ArchiveHandle *AH, void *buf, size_t len, TAR_MEMBER *th, FILE *fh)
{
    lclContext *ctx = (lclContext *) AH->formatData;
    size_t      avail;
    size_t      used = 0;
    size_t      res = 0;
 
    Assert(th || fh);
 
    avail = AH->lookaheadLen - AH->lookaheadPos;
    if (avail > 0)
    {
        /* We have some lookahead bytes to use */
        if (avail >= len)       /* Just use the lookahead buffer */
            used = len;
        else
            used = avail;
 
        /* Copy, and adjust buffer pos */
        memcpy(buf, AH->lookahead + AH->lookaheadPos, used);
        AH->lookaheadPos += used;
 
        /* Adjust required length */
        len -= used;
    }
 
    /* Read the file if len > 0 */
    if (len > 0)
    {
        if (fh)
        {
            res = fread(&((char *) buf)[used], 1, len, fh);
            if (res != len && !feof(fh))
                READ_ERROR_EXIT(fh);
        }
        else if (th)
        {
            res = fread(&((char *) buf)[used], 1, len, th->nFH);
            if (res != len && !feof(th->nFH))
                READ_ERROR_EXIT(th->nFH);
        }
    }
 
    ctx->tarFHpos += res + used;
 
    return (res + used);
}
 
static size_t
tarRead(void *buf, size_t len, TAR_MEMBER *th)
{
    size_t      res;
 
    if (th->pos + len > th->fileLen)
        len = th->fileLen - th->pos;
 
    if (len <= 0)
        return 0;
 
    res = _tarReadRaw(th->AH, buf, len, th, NULL);
 
    th->pos += res;
 
    return res;
}
 
static size_t
tarWrite(const void *buf, size_t len, TAR_MEMBER *th)
{
    size_t      res;
 
    res = fwrite(buf, 1, len, th->nFH);
 
    th->pos += res;
    return res;
}
 
static void
_WriteData(ArchiveHandle *AH, const void *data, size_t dLen)
{
    lclTocEntry *tctx = (lclTocEntry *) AH->currToc->formatData;
 
    if (tarWrite(data, dLen, tctx->TH) != dLen)
        WRITE_ERROR_EXIT;
}
 
static void
_EndData(ArchiveHandle *AH, TocEntry *te)
{
    lclTocEntry *tctx = (lclTocEntry *) te->formatData;
 
    /* Close the file */
    tarClose(AH, tctx->TH);
    tctx->TH = NULL;
}
 
/*
 * Print data for a given file
 */
static void
_PrintFileData(ArchiveHandle *AH, char *filename)
{
    lclContext *ctx = (lclContext *) AH->formatData;
    char        buf[4096];
    size_t      cnt;
    TAR_MEMBER *th;
 
    if (!filename)
        return;
 
    th = tarOpen(AH, filename, 'r');
    ctx->FH = th;
 
    while ((cnt = tarRead(buf, 4095, th)) > 0)
    {
        buf[cnt] = '\0';
        ahwrite(buf, 1, cnt, AH);
    }
 
    tarClose(AH, th);
}
 
 
/*
 * 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         pos1;
 
    if (!tctx->filename)
        return;
 
    /*
     * If we're writing the special restore.sql script, emit a suitable
     * command to include each table's data from the corresponding file.
     *
     * In the COPY case this is a bit klugy because the regular COPY command
     * was already printed before we get control.
     */
    if (ctx->isSpecialScript)
    {
        if (te->copyStmt)
        {
            /* Abort the COPY FROM stdin */
            ahprintf(AH, "\\.\n");
 
            /*
             * The COPY statement should look like "COPY ... FROM stdin;\n",
             * see dumpTableData().
             */
            pos1 = (int) strlen(te->copyStmt) - 13;
            if (pos1 < 6 || strncmp(te->copyStmt, "COPY ", 5) != 0 ||
                strcmp(te->copyStmt + pos1, " FROM stdin;\n") != 0)
                pg_fatal("unexpected COPY statement syntax: \"%s\"",
                         te->copyStmt);
 
            /* Emit all but the FROM part ... */
            ahwrite(te->copyStmt, 1, pos1, AH);
            /* ... and insert modified FROM */
            ahprintf(AH, " FROM '$$PATH$$/%s';\n\n", tctx->filename);
        }
        else
        {
            /* --inserts mode, no worries, just include the data file */
            ahprintf(AH, "\\i $$PATH$$/%s\n\n", tctx->filename);
        }
 
        return;
    }
 
    if (strcmp(te->desc, "BLOBS") == 0)
        _LoadLOs(AH, te);
    else
        _PrintFileData(AH, tctx->filename);
}
 
static void
_LoadLOs(ArchiveHandle *AH, TocEntry *te)
{
    Oid         oid;
    lclContext *ctx = (lclContext *) AH->formatData;
    TAR_MEMBER *th;
    size_t      cnt;
    bool        foundLO = false;
    char        buf[4096];
 
    StartRestoreLOs(AH);
 
    /*
     * The blobs_NNN.toc or blobs.toc file is fairly useless to us because it
     * will appear only after the associated blob_NNN.dat files.  For archive
     * versions >= 16 we can look at the BLOBS entry's te->tag to discover the
     * OID of the first blob we want to restore, and then search forward to
     * find the appropriate blob_<oid>.dat file.  For older versions we rely
     * on the knowledge that there was only one BLOBS entry and just search
     * for the first blob_<oid>.dat file.  Once we find the first blob file to
     * restore, restore all blobs until we reach the blobs[_NNN].toc file.
     */
    if (AH->version >= K_VERS_1_16)
    {
        /* We rely on atooid to not complain about nnnn..nnnn tags */
        oid = atooid(te->tag);
        snprintf(buf, sizeof(buf), "blob_%u.dat", oid);
        th = tarOpen(AH, buf, 'r'); /* Advance to first desired file */
    }
    else
        th = tarOpen(AH, NULL, 'r');    /* Open next file */
 
    while (th != NULL)
    {
        ctx->FH = th;
 
        if (strncmp(th->targetFile, "blob_", 5) == 0)
        {
            oid = atooid(&th->targetFile[5]);
            if (oid != 0)
            {
                pg_log_info("restoring large object with OID %u", oid);
 
                StartRestoreLO(AH, oid, AH->public.ropt->dropSchema);
 
                while ((cnt = tarRead(buf, 4095, th)) > 0)
                {
                    buf[cnt] = '\0';
                    ahwrite(buf, 1, cnt, AH);
                }
                EndRestoreLO(AH, oid);
                foundLO = true;
            }
            tarClose(AH, th);
        }
        else
        {
            tarClose(AH, th);
 
            /*
             * Once we have found the first LO, stop at the first non-LO entry
             * (which will be 'blobs[_NNN].toc').  This coding would eat all
             * the rest of the archive if there are no LOs ... but this
             * function shouldn't be called at all in that case.
             */
            if (foundLO)
                break;
        }
 
        th = tarOpen(AH, NULL, 'r');
    }
    EndRestoreLOs(AH);
}
 
 
static int
_WriteByte(ArchiveHandle *AH, const int i)
{
    lclContext *ctx = (lclContext *) AH->formatData;
    char        b = i;          /* Avoid endian problems */
 
    if (tarWrite(&b, 1, ctx->FH) != 1)
        WRITE_ERROR_EXIT;
 
    ctx->filePos += 1;
    return 1;
}
 
static int
_ReadByte(ArchiveHandle *AH)
{
    lclContext *ctx = (lclContext *) AH->formatData;
    size_t      res;
    unsigned char c;
 
    res = tarRead(&c, 1, ctx->FH);
    if (res != 1)
        /* We already would have exited for errors on reads, must be EOF */
        pg_fatal("could not read from input file: end of file");
    ctx->filePos += 1;
    return c;
}
 
static void
_WriteBuf(ArchiveHandle *AH, const void *buf, size_t len)
{
    lclContext *ctx = (lclContext *) AH->formatData;
 
    if (tarWrite(buf, len, ctx->FH) != len)
        WRITE_ERROR_EXIT;
 
    ctx->filePos += len;
}
 
static void
_ReadBuf(ArchiveHandle *AH, void *buf, size_t len)
{
    lclContext *ctx = (lclContext *) AH->formatData;
 
    if (tarRead(buf, len, ctx->FH) != len)
        /* We already would have exited for errors on reads, must be EOF */
        pg_fatal("could not read from input file: end of file");
 
    ctx->filePos += len;
}
 
static void
_CloseArchive(ArchiveHandle *AH)
{
    lclContext *ctx = (lclContext *) AH->formatData;
    TAR_MEMBER *th;
    RestoreOptions *ropt;
    RestoreOptions *savRopt;
    DumpOptions *savDopt;
    int         savVerbose,
                i;
 
    if (AH->mode == archModeWrite)
    {
        /*
         * Write the Header & TOC to the archive FIRST
         */
        th = tarOpen(AH, "toc.dat", 'w');
        ctx->FH = th;
        WriteHead(AH);
        WriteToc(AH);
        tarClose(AH, th);       /* Not needed any more */
 
        /*
         * Now send the data (tables & LOs)
         */
        WriteDataChunks(AH, NULL);
 
        /*
         * Now this format wants to append a script which does a full restore
         * if the files have been extracted.
         */
        th = tarOpen(AH, "restore.sql", 'w');
 
        tarPrintf(th, "--\n"
                  "-- NOTE:\n"
                  "--\n"
                  "-- File paths need to be edited. Search for $$PATH$$ and\n"
                  "-- replace it with the path to the directory containing\n"
                  "-- the extracted data files.\n"
                  "--\n");
 
        AH->CustomOutPtr = _scriptOut;
 
        ctx->isSpecialScript = 1;
        ctx->scriptTH = th;
 
        ropt = NewRestoreOptions();
        memcpy(ropt, AH->public.ropt, sizeof(RestoreOptions));
        ropt->filename = NULL;
        ropt->dropSchema = 1;
        ropt->superuser = NULL;
        ropt->suppressDumpWarnings = true;
 
        savDopt = AH->public.dopt;
        savRopt = AH->public.ropt;
 
        SetArchiveOptions((Archive *) AH, NULL, ropt);
 
        savVerbose = AH->public.verbose;
        AH->public.verbose = 0;
 
        RestoreArchive((Archive *) AH, false);
 
        SetArchiveOptions((Archive *) AH, savDopt, savRopt);
 
        AH->public.verbose = savVerbose;
 
        tarClose(AH, th);
 
        ctx->isSpecialScript = 0;
 
        /*
         * EOF marker for tar files is two blocks of NULLs.
         */
        for (i = 0; i < TAR_BLOCK_SIZE * 2; i++)
        {
            if (fputc(0, ctx->tarFH) == EOF)
                WRITE_ERROR_EXIT;
        }
 
        /* Sync the output file if one is defined */
        if (AH->dosync && AH->fSpec)
            (void) fsync_fname(AH->fSpec, false);
    }
 
    AH->FH = NULL;
}
 
static size_t
_scriptOut(ArchiveHandle *AH, const void *buf, size_t len)
{
    lclContext *ctx = (lclContext *) AH->formatData;
 
    return tarWrite(buf, len, ctx->scriptTH);
}
 
/*
 * Large Object support
 */
 
/*
 * 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;
    char        fname[K_STD_BUF_SIZE];
 
    sprintf(fname, "blobs_%d.toc", te->dumpId);
    ctx->loToc = tarOpen(AH, fname, 'w');
}
 
/*
 * 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;
    lclTocEntry *tctx = (lclTocEntry *) te->formatData;
    char        fname[255];
 
    if (oid == 0)
        pg_fatal("invalid OID for large object (%u)", oid);
 
    if (AH->compression_spec.algorithm != PG_COMPRESSION_NONE)
        pg_fatal("compression is not supported by tar archive format");
 
    sprintf(fname, "blob_%u.dat", oid);
 
    tarPrintf(ctx->loToc, "%u %s\n", oid, fname);
 
    tctx->TH = tarOpen(AH, fname, 'w');
}
 
/*
 * Called by the archiver when the dumper calls EndLO.
 *
 * Optional.
 *
 */
static void
_EndLO(ArchiveHandle *AH, TocEntry *te, Oid oid)
{
    lclTocEntry *tctx = (lclTocEntry *) te->formatData;
 
    tarClose(AH, tctx->TH);
}
 
/*
 * Called by the archiver when finishing saving BLOB DATA.
 *
 * Optional.
 *
 */
static void
_EndLOs(ArchiveHandle *AH, TocEntry *te)
{
    lclContext *ctx = (lclContext *) AH->formatData;
 
    /* Write out a fake zero OID to mark end-of-LOs. */
    /* WriteInt(AH, 0); */
 
    tarClose(AH, ctx->loToc);
}
 
 
 
/*------------
 * TAR Support
 *------------
 */
 
static int
tarPrintf(TAR_MEMBER *th, const char *fmt,...)
{
    int         save_errno = errno;
    char       *p;
    size_t      len = 128;      /* initial assumption about buffer size */
    size_t      cnt;
 
    for (;;)
    {
        va_list     args;
 
        /* Allocate work buffer. */
        p = (char *) pg_malloc(len);
 
        /* Try to format the data. */
        errno = save_errno;
        va_start(args, fmt);
        cnt = pvsnprintf(p, len, fmt, args);
        va_end(args);
 
        if (cnt < len)
            break;              /* success */
 
        /* Release buffer and loop around to try again with larger len. */
        free(p);
        len = cnt;
    }
 
    cnt = tarWrite(p, cnt, th);
    free(p);
    return (int) cnt;
}
 
bool
isValidTarHeader(char *header)
{
    int         sum;
    int         chk = tarChecksum(header);
 
    sum = read_tar_number(&header[TAR_OFFSET_CHECKSUM], 8);
 
    if (sum != chk)
        return false;
 
    /* POSIX tar format */
    if (memcmp(&header[TAR_OFFSET_MAGIC], "ustar\0", 6) == 0 &&
        memcmp(&header[TAR_OFFSET_VERSION], "00", 2) == 0)
        return true;
    /* GNU tar format */
    if (memcmp(&header[TAR_OFFSET_MAGIC], "ustar  \0", 8) == 0)
        return true;
    /* not-quite-POSIX format written by pre-9.3 pg_dump */
    if (memcmp(&header[TAR_OFFSET_MAGIC], "ustar00\0", 8) == 0)
        return true;
 
    return false;
}
 
/* Given the member, write the TAR header & copy the file */
static void
_tarAddFile(ArchiveHandle *AH, TAR_MEMBER *th)
{
    lclContext *ctx = (lclContext *) AH->formatData;
    FILE       *tmp = th->tmpFH;    /* Grab it for convenience */
    char        buf[32768];
    size_t      cnt;
    pgoff_t     len = 0;
    size_t      res;
    size_t      i,
                pad;
 
    /*
     * Find file len & go back to start.
     */
    if (fseeko(tmp, 0, SEEK_END) != 0)
        pg_fatal("error during file seek: %m");
    th->fileLen = ftello(tmp);
    if (th->fileLen < 0)
        pg_fatal("could not determine seek position in archive file: %m");
    if (fseeko(tmp, 0, SEEK_SET) != 0)
        pg_fatal("error during file seek: %m");
 
    _tarWriteHeader(th);
 
    while ((cnt = fread(buf, 1, sizeof(buf), tmp)) > 0)
    {
        if ((res = fwrite(buf, 1, cnt, th->tarFH)) != cnt)
            WRITE_ERROR_EXIT;
        len += res;
    }
    if (!feof(tmp))
        READ_ERROR_EXIT(tmp);
 
    if (fclose(tmp) != 0)       /* This *should* delete it... */
        pg_fatal("could not close temporary file: %m");
 
    if (len != th->fileLen)
        pg_fatal("actual file length (%lld) does not match expected (%lld)",
                 (long long) len, (long long) th->fileLen);
 
    pad = tarPaddingBytesRequired(len);
    for (i = 0; i < pad; i++)
    {
        if (fputc('\0', th->tarFH) == EOF)
            WRITE_ERROR_EXIT;
    }
 
    ctx->tarFHpos += len + pad;
}
 
/* Locate the file in the archive, read header and position to data */
static TAR_MEMBER *
_tarPositionTo(ArchiveHandle *AH, const char *filename)
{
    lclContext *ctx = (lclContext *) AH->formatData;
    TAR_MEMBER *th = pg_malloc0_object(TAR_MEMBER);
    char        c;
    char        header[TAR_BLOCK_SIZE];
    size_t      i,
                len,
                blks;
    int         id;
 
    th->AH = AH;
 
    /* Go to end of current file, if any */
    if (ctx->tarFHpos != 0)
    {
        pg_log_debug("moving from position %lld to next member at file position %lld",
                     (long long) ctx->tarFHpos, (long long) ctx->tarNextMember);
 
        while (ctx->tarFHpos < ctx->tarNextMember)
            _tarReadRaw(AH, &c, 1, NULL, ctx->tarFH);
    }
 
    pg_log_debug("now at file position %lld", (long long) ctx->tarFHpos);
 
    /* We are at the start of the file, or at the next member */
 
    /* Get the header */
    if (!_tarGetHeader(AH, th))
    {
        if (filename)
            pg_fatal("could not find header for file \"%s\" in tar archive", filename);
        else
        {
            /*
             * We're just scanning the archive for the next file, so return
             * null
             */
            free(th);
            return NULL;
        }
    }
 
    while (filename != NULL && strcmp(th->targetFile, filename) != 0)
    {
        pg_log_debug("skipping tar member %s", th->targetFile);
 
        id = atoi(th->targetFile);
        if ((TocIDRequired(AH, id) & REQ_DATA) != 0)
            pg_fatal("restoring data out of order is not supported in this archive format: "
                     "\"%s\" is required, but comes before \"%s\" in the archive file.",
                     th->targetFile, filename);
 
        /* Header doesn't match, so read to next header */
        len = th->fileLen;
        len += tarPaddingBytesRequired(th->fileLen);
        blks = len / TAR_BLOCK_SIZE;    /* # of tar blocks */
 
        for (i = 0; i < blks; i++)
            _tarReadRaw(AH, &header[0], TAR_BLOCK_SIZE, NULL, ctx->tarFH);
 
        if (!_tarGetHeader(AH, th))
            pg_fatal("could not find header for file \"%s\" in tar archive", filename);
    }
 
    ctx->tarNextMember = ctx->tarFHpos + th->fileLen
        + tarPaddingBytesRequired(th->fileLen);
    th->pos = 0;
 
    return th;
}
 
/* Read & verify a header */
static int
_tarGetHeader(ArchiveHandle *AH, TAR_MEMBER *th)
{
    lclContext *ctx = (lclContext *) AH->formatData;
    char        h[TAR_BLOCK_SIZE];
    char        tag[100 + 1];
    int         sum,
                chk;
    pgoff_t     len;
    pgoff_t     hPos;
    bool        gotBlock = false;
 
    while (!gotBlock)
    {
        /* Save the pos for reporting purposes */
        hPos = ctx->tarFHpos;
 
        /* Read the next tar block, return EOF, exit if short */
        len = _tarReadRaw(AH, h, TAR_BLOCK_SIZE, NULL, ctx->tarFH);
        if (len == 0)           /* EOF */
            return 0;
 
        if (len != TAR_BLOCK_SIZE)
            pg_fatal(ngettext("incomplete tar header found (%lu byte)",
                              "incomplete tar header found (%lu bytes)",
                              len),
                     (unsigned long) len);
 
        /* Calc checksum */
        chk = tarChecksum(h);
        sum = read_tar_number(&h[TAR_OFFSET_CHECKSUM], 8);
 
        /*
         * If the checksum failed, see if it is a null block. If so, silently
         * continue to the next block.
         */
        if (chk == sum)
            gotBlock = true;
        else
        {
            int         i;
 
            for (i = 0; i < TAR_BLOCK_SIZE; i++)
            {
                if (h[i] != 0)
                {
                    gotBlock = true;
                    break;
                }
            }
        }
    }
 
    /* Name field is 100 bytes, might not be null-terminated */
    strlcpy(tag, &h[TAR_OFFSET_NAME], 100 + 1);
 
    len = read_tar_number(&h[TAR_OFFSET_SIZE], 12);
 
    pg_log_debug("TOC Entry %s at %llu (length %llu, checksum %d)",
                 tag, (unsigned long long) hPos, (unsigned long long) len, sum);
 
    if (chk != sum)
        pg_fatal("corrupt tar header found in %s (expected %d, computed %d) file position %llu",
                 tag, sum, chk, (unsigned long long) ftello(ctx->tarFH));
 
    th->targetFile = pg_strdup(tag);
    th->fileLen = len;
 
    return 1;
}
 
 
static void
_tarWriteHeader(TAR_MEMBER *th)
{
    char        h[TAR_BLOCK_SIZE];
 
    tarCreateHeader(h, th->targetFile, NULL, th->fileLen,
                    0600, 04000, 02000, time(NULL));
 
    /* Now write the completed header. */
    if (fwrite(h, 1, TAR_BLOCK_SIZE, th->tarFH) != TAR_BLOCK_SIZE)
        WRITE_ERROR_EXIT;
}