compress_gzip.c

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/*-------------------------------------------------------------------------
 *
 * compress_gzip.c
 *   Routines for archivers to read or write a gzip compressed data stream.
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *     src/bin/pg_dump/compress_gzip.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres_fe.h"
#include <unistd.h>
 
#include "compress_gzip.h"
#include "pg_backup_utils.h"
 
#ifdef HAVE_LIBZ
#include <zlib.h>
 
/*
 * We don't use the gzgetc() macro, because zlib's configuration logic is not
 * robust enough to guarantee that the macro will have the same ideas about
 * struct field layout as the library itself does; see for example
 * https://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=59711
 * Instead, #undef the macro and fall back to the underlying function.
 */
#undef gzgetc
 
/*----------------------
 * Compressor API
 *----------------------
 */
typedef struct GzipCompressorState
{
    z_streamp   zp;
 
    void       *outbuf;
    size_t      outsize;
} GzipCompressorState;
 
/* Private routines that support gzip compressed data I/O */
static void DeflateCompressorInit(CompressorState *cs);
static void DeflateCompressorEnd(ArchiveHandle *AH, CompressorState *cs);
static void DeflateCompressorCommon(ArchiveHandle *AH, CompressorState *cs,
                                    bool flush);
static void EndCompressorGzip(ArchiveHandle *AH, CompressorState *cs);
static void WriteDataToArchiveGzip(ArchiveHandle *AH, CompressorState *cs,
                                   const void *data, size_t dLen);
static void ReadDataFromArchiveGzip(ArchiveHandle *AH, CompressorState *cs);
 
static void
DeflateCompressorInit(CompressorState *cs)
{
    GzipCompressorState *gzipcs;
    z_streamp   zp;
 
    gzipcs = (GzipCompressorState *) pg_malloc0(sizeof(GzipCompressorState));
    zp = gzipcs->zp = (z_streamp) pg_malloc(sizeof(z_stream));
    zp->zalloc = Z_NULL;
    zp->zfree = Z_NULL;
    zp->opaque = Z_NULL;
 
    /*
     * outsize 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.
     */
    gzipcs->outsize = DEFAULT_IO_BUFFER_SIZE;
    gzipcs->outbuf = pg_malloc(gzipcs->outsize + 1);
 
    /* -Z 0 uses the "None" compressor -- not zlib with no compression */
    Assert(cs->compression_spec.level != 0);
 
    if (deflateInit(zp, cs->compression_spec.level) != Z_OK)
        pg_fatal("could not initialize compression library: %s", zp->msg);
 
    /* Just be paranoid - maybe End is called after Start, with no Write */
    zp->next_out = gzipcs->outbuf;
    zp->avail_out = gzipcs->outsize;
 
    /* Keep track of gzipcs */
    cs->private_data = gzipcs;
}
 
static void
DeflateCompressorEnd(ArchiveHandle *AH, CompressorState *cs)
{
    GzipCompressorState *gzipcs = (GzipCompressorState *) cs->private_data;
    z_streamp   zp;
 
    zp = gzipcs->zp;
    zp->next_in = NULL;
    zp->avail_in = 0;
 
    /* Flush any remaining data from zlib buffer */
    DeflateCompressorCommon(AH, cs, true);
 
    if (deflateEnd(zp) != Z_OK)
        pg_fatal("could not close compression stream: %s", zp->msg);
 
    pg_free(gzipcs->outbuf);
    pg_free(gzipcs->zp);
    pg_free(gzipcs);
    cs->private_data = NULL;
}
 
static void
DeflateCompressorCommon(ArchiveHandle *AH, CompressorState *cs, bool flush)
{
    GzipCompressorState *gzipcs = (GzipCompressorState *) cs->private_data;
    z_streamp   zp = gzipcs->zp;
    void       *out = gzipcs->outbuf;
    int         res = Z_OK;
 
    while (gzipcs->zp->avail_in != 0 || flush)
    {
        res = deflate(zp, flush ? Z_FINISH : Z_NO_FLUSH);
        if (res == Z_STREAM_ERROR)
            pg_fatal("could not compress data: %s", zp->msg);
        if ((flush && (zp->avail_out < gzipcs->outsize))
            || (zp->avail_out == 0)
            || (zp->avail_in != 0)
            )
        {
            /*
             * Extra paranoia: avoid zero-length chunks, since a zero length
             * chunk is the EOF marker in the custom format. This should never
             * happen but ...
             */
            if (zp->avail_out < gzipcs->outsize)
            {
                /*
                 * Any write function should do its own error checking but to
                 * make sure we do a check here as well ...
                 */
                size_t      len = gzipcs->outsize - zp->avail_out;
 
                cs->writeF(AH, out, len);
            }
            zp->next_out = out;
            zp->avail_out = gzipcs->outsize;
        }
 
        if (res == Z_STREAM_END)
            break;
    }
}
 
static void
EndCompressorGzip(ArchiveHandle *AH, CompressorState *cs)
{
    /* If deflation was initialized, finalize it */
    if (cs->private_data)
        DeflateCompressorEnd(AH, cs);
}
 
static void
WriteDataToArchiveGzip(ArchiveHandle *AH, CompressorState *cs,
                       const void *data, size_t dLen)
{
    GzipCompressorState *gzipcs = (GzipCompressorState *) cs->private_data;
 
    gzipcs->zp->next_in = data;
    gzipcs->zp->avail_in = dLen;
    DeflateCompressorCommon(AH, cs, false);
}
 
static void
ReadDataFromArchiveGzip(ArchiveHandle *AH, CompressorState *cs)
{
    z_streamp   zp;
    char       *out;
    int         res = Z_OK;
    size_t      cnt;
    char       *buf;
    size_t      buflen;
 
    zp = (z_streamp) pg_malloc(sizeof(z_stream));
    zp->zalloc = Z_NULL;
    zp->zfree = Z_NULL;
    zp->opaque = Z_NULL;
 
    buflen = DEFAULT_IO_BUFFER_SIZE;
    buf = pg_malloc(buflen);
 
    out = pg_malloc(DEFAULT_IO_BUFFER_SIZE + 1);
 
    if (inflateInit(zp) != Z_OK)
        pg_fatal("could not initialize compression library: %s",
                 zp->msg);
 
    /* no minimal chunk size for zlib */
    while ((cnt = cs->readF(AH, &buf, &buflen)))
    {
        zp->next_in = (void *) buf;
        zp->avail_in = cnt;
 
        while (zp->avail_in > 0)
        {
            zp->next_out = (void *) out;
            zp->avail_out = DEFAULT_IO_BUFFER_SIZE;
 
            res = inflate(zp, 0);
            if (res != Z_OK && res != Z_STREAM_END)
                pg_fatal("could not uncompress data: %s", zp->msg);
 
            out[DEFAULT_IO_BUFFER_SIZE - zp->avail_out] = '\0';
            ahwrite(out, 1, DEFAULT_IO_BUFFER_SIZE - zp->avail_out, AH);
        }
    }
 
    zp->next_in = NULL;
    zp->avail_in = 0;
    while (res != Z_STREAM_END)
    {
        zp->next_out = (void *) out;
        zp->avail_out = DEFAULT_IO_BUFFER_SIZE;
        res = inflate(zp, 0);
        if (res != Z_OK && res != Z_STREAM_END)
            pg_fatal("could not uncompress data: %s", zp->msg);
 
        out[DEFAULT_IO_BUFFER_SIZE - zp->avail_out] = '\0';
        ahwrite(out, 1, DEFAULT_IO_BUFFER_SIZE - zp->avail_out, AH);
    }
 
    if (inflateEnd(zp) != Z_OK)
        pg_fatal("could not close compression library: %s", zp->msg);
 
    free(buf);
    free(out);
    free(zp);
}
 
/* Public routines that support gzip compressed data I/O */
void
InitCompressorGzip(CompressorState *cs,
                   const pg_compress_specification compression_spec)
{
    cs->readData = ReadDataFromArchiveGzip;
    cs->writeData = WriteDataToArchiveGzip;
    cs->end = EndCompressorGzip;
 
    cs->compression_spec = compression_spec;
 
    /*
     * If the caller has defined a write function, prepare the necessary
     * state.  Note that if the data is empty, End may be called immediately
     * after Init, without ever calling Write.
     */
    if (cs->writeF)
        DeflateCompressorInit(cs);
}
 
 
/*----------------------
 * Compress File API
 *----------------------
 */
 
static size_t
Gzip_read(void *ptr, size_t size, CompressFileHandle *CFH)
{
    gzFile      gzfp = (gzFile) CFH->private_data;
    int         gzret;
 
    /* Reading zero bytes must be a no-op */
    if (size == 0)
        return 0;
 
    gzret = gzread(gzfp, ptr, size);
 
    /*
     * gzread returns zero on EOF as well as some error conditions, and less
     * than zero on other error conditions, so we need to inspect for EOF on
     * zero.
     */
    if (gzret <= 0)
    {
        int         errnum;
        const char *errmsg;
 
        if (gzret == 0 && gzeof(gzfp))
            return 0;
 
        errmsg = gzerror(gzfp, &errnum);
 
        pg_fatal("could not read from input file: %s",
                 errnum == Z_ERRNO ? strerror(errno) : errmsg);
    }
 
    return (size_t) gzret;
}
 
static void
Gzip_write(const void *ptr, size_t size, CompressFileHandle *CFH)
{
    gzFile      gzfp = (gzFile) CFH->private_data;
    int         errnum;
    const char *errmsg;
 
    if (gzwrite(gzfp, ptr, size) != size)
    {
        errmsg = gzerror(gzfp, &errnum);
        pg_fatal("could not write to file: %s",
                 errnum == Z_ERRNO ? strerror(errno) : errmsg);
    }
}
 
static int
Gzip_getc(CompressFileHandle *CFH)
{
    gzFile      gzfp = (gzFile) CFH->private_data;
    int         ret;
 
    errno = 0;
    ret = gzgetc(gzfp);
    if (ret == EOF)
    {
        if (!gzeof(gzfp))
            pg_fatal("could not read from input file: %m");
        else
            pg_fatal("could not read from input file: end of file");
    }
 
    return ret;
}
 
static char *
Gzip_gets(char *ptr, int size, CompressFileHandle *CFH)
{
    gzFile      gzfp = (gzFile) CFH->private_data;
 
    return gzgets(gzfp, ptr, size);
}
 
static bool
Gzip_close(CompressFileHandle *CFH)
{
    gzFile      gzfp = (gzFile) CFH->private_data;
 
    CFH->private_data = NULL;
 
    return gzclose(gzfp) == Z_OK;
}
 
static bool
Gzip_eof(CompressFileHandle *CFH)
{
    gzFile      gzfp = (gzFile) CFH->private_data;
 
    return gzeof(gzfp) == 1;
}
 
static const char *
Gzip_get_error(CompressFileHandle *CFH)
{
    gzFile      gzfp = (gzFile) CFH->private_data;
    const char *errmsg;
    int         errnum;
 
    errmsg = gzerror(gzfp, &errnum);
    if (errnum == Z_ERRNO)
        errmsg = strerror(errno);
 
    return errmsg;
}
 
static bool
Gzip_open(const char *path, int fd, const char *mode, CompressFileHandle *CFH)
{
    gzFile      gzfp;
    char        mode_compression[32];
 
    if (CFH->compression_spec.level != Z_DEFAULT_COMPRESSION)
    {
        /*
         * user has specified a compression level, so tell zlib to use it
         */
        snprintf(mode_compression, sizeof(mode_compression), "%s%d",
                 mode, CFH->compression_spec.level);
    }
    else
        strcpy(mode_compression, mode);
 
    if (fd >= 0)
        gzfp = gzdopen(dup(fd), mode_compression);
    else
        gzfp = gzopen(path, mode_compression);
 
    if (gzfp == NULL)
        return false;
 
    CFH->private_data = gzfp;
 
    return true;
}
 
static bool
Gzip_open_write(const char *path, const char *mode, CompressFileHandle *CFH)
{
    char       *fname;
    bool        ret;
    int         save_errno;
 
    fname = psprintf("%s.gz", path);
    ret = CFH->open_func(fname, -1, mode, CFH);
 
    save_errno = errno;
    pg_free(fname);
    errno = save_errno;
 
    return ret;
}
 
void
InitCompressFileHandleGzip(CompressFileHandle *CFH,
                           const pg_compress_specification compression_spec)
{
    CFH->open_func = Gzip_open;
    CFH->open_write_func = Gzip_open_write;
    CFH->read_func = Gzip_read;
    CFH->write_func = Gzip_write;
    CFH->gets_func = Gzip_gets;
    CFH->getc_func = Gzip_getc;
    CFH->close_func = Gzip_close;
    CFH->eof_func = Gzip_eof;
    CFH->get_error_func = Gzip_get_error;
 
    CFH->compression_spec = compression_spec;
 
    CFH->private_data = NULL;
}
#else                           /* HAVE_LIBZ */
void
InitCompressorGzip(CompressorState *cs,
                   const pg_compress_specification compression_spec)
{
    pg_fatal("this build does not support compression with %s", "gzip");
}
 
void
InitCompressFileHandleGzip(CompressFileHandle *CFH,
                           const pg_compress_specification compression_spec)
{
    pg_fatal("this build does not support compression with %s", "gzip");
}
#endif                          /* HAVE_LIBZ */