astreamer_gzip.c

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/*-------------------------------------------------------------------------
 *
 * astreamer_gzip.c
 *
 * Archive streamers that deal with data compressed using gzip.
 * astreamer_gzip_writer applies gzip compression to the input data
 * and writes the result to a file. astreamer_gzip_decompressor assumes
 * that the input stream is compressed using gzip and decompresses it.
 *
 * Note that the code in this file is asymmetric with what we do for
 * other compression types: for lz4 and zstd, there is a compressor and
 * a decompressor, rather than a writer and a decompressor. The approach
 * taken here is less flexible, because a writer can only write to a file,
 * while a compressor can write to a subsequent astreamer which is free
 * to do whatever it likes. The reason it's like this is because this
 * code was adapted from old, less-modular pg_basebackup code that used
 * the same APIs that astreamer_gzip_writer now uses, and it didn't seem
 * necessary to change anything at the time.
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *        src/fe_utils/astreamer_gzip.c
 *-------------------------------------------------------------------------
 */
 
#include "postgres_fe.h"
 
#include <unistd.h>
 
#ifdef HAVE_LIBZ
#include <zlib.h>
#endif
 
#include "common/logging.h"
#include "fe_utils/astreamer.h"
 
#ifdef HAVE_LIBZ
typedef struct astreamer_gzip_writer
{
    astreamer   base;
    char       *pathname;
    gzFile      gzfile;
} astreamer_gzip_writer;
 
typedef struct astreamer_gzip_decompressor
{
    astreamer   base;
    z_stream    zstream;
    size_t      bytes_written;
} astreamer_gzip_decompressor;
 
static void astreamer_gzip_writer_content(astreamer *streamer,
                                          astreamer_member *member,
                                          const char *data, int len,
                                          astreamer_archive_context context);
static void astreamer_gzip_writer_finalize(astreamer *streamer);
static void astreamer_gzip_writer_free(astreamer *streamer);
static const char *get_gz_error(gzFile gzf);
 
static const astreamer_ops astreamer_gzip_writer_ops = {
    .content = astreamer_gzip_writer_content,
    .finalize = astreamer_gzip_writer_finalize,
    .free = astreamer_gzip_writer_free
};
 
static void astreamer_gzip_decompressor_content(astreamer *streamer,
                                                astreamer_member *member,
                                                const char *data, int len,
                                                astreamer_archive_context context);
static void astreamer_gzip_decompressor_finalize(astreamer *streamer);
static void astreamer_gzip_decompressor_free(astreamer *streamer);
static void *gzip_palloc(void *opaque, unsigned items, unsigned size);
static void gzip_pfree(void *opaque, void *address);
 
static const astreamer_ops astreamer_gzip_decompressor_ops = {
    .content = astreamer_gzip_decompressor_content,
    .finalize = astreamer_gzip_decompressor_finalize,
    .free = astreamer_gzip_decompressor_free
};
#endif
 
/*
 * Create a astreamer that just compresses data using gzip, and then writes
 * it to a file.
 *
 * The caller must specify a pathname and may specify a file. The pathname is
 * used for error-reporting purposes either way. If file is NULL, the pathname
 * also identifies the file to which the data should be written: it is opened
 * for writing and closed when done. If file is not NULL, the data is written
 * there.
 *
 * Note that zlib does not use the FILE interface, but operates directly on
 * a duplicate of the underlying fd. Hence, callers must take care if they
 * plan to write any other data to the same FILE, either before or after using
 * this.
 */
astreamer *
astreamer_gzip_writer_new(char *pathname, FILE *file,
                          pg_compress_specification *compress)
{
#ifdef HAVE_LIBZ
    astreamer_gzip_writer *streamer;
 
    streamer = palloc0(sizeof(astreamer_gzip_writer));
    *((const astreamer_ops **) &streamer->base.bbs_ops) =
        &astreamer_gzip_writer_ops;
 
    streamer->pathname = pstrdup(pathname);
 
    if (file == NULL)
    {
        streamer->gzfile = gzopen(pathname, "wb");
        if (streamer->gzfile == NULL)
            pg_fatal("could not create compressed file \"%s\": %m",
                     pathname);
    }
    else
    {
        /*
         * We must dup the file handle so that gzclose doesn't break the
         * caller's FILE.  See comment for astreamer_gzip_writer_finalize.
         */
        int         fd = dup(fileno(file));
 
        if (fd < 0)
            pg_fatal("could not duplicate stdout: %m");
 
        streamer->gzfile = gzdopen(fd, "wb");
        if (streamer->gzfile == NULL)
            pg_fatal("could not open output file: %m");
    }
 
    if (gzsetparams(streamer->gzfile, compress->level, Z_DEFAULT_STRATEGY) != Z_OK)
        pg_fatal("could not set compression level %d: %s",
                 compress->level, get_gz_error(streamer->gzfile));
 
    return &streamer->base;
#else
    pg_fatal("this build does not support compression with %s", "gzip");
    return NULL;                /* keep compiler quiet */
#endif
}
 
#ifdef HAVE_LIBZ
/*
 * Write archive content to gzip file.
 */
static void
astreamer_gzip_writer_content(astreamer *streamer,
                              astreamer_member *member, const char *data,
                              int len, astreamer_archive_context context)
{
    astreamer_gzip_writer *mystreamer;
 
    mystreamer = (astreamer_gzip_writer *) streamer;
 
    if (len == 0)
        return;
 
    errno = 0;
    if (gzwrite(mystreamer->gzfile, data, len) != len)
    {
        /* if write didn't set errno, assume problem is no disk space */
        if (errno == 0)
            errno = ENOSPC;
        pg_fatal("could not write to compressed file \"%s\": %s",
                 mystreamer->pathname, get_gz_error(mystreamer->gzfile));
    }
}
 
/*
 * End-of-archive processing when writing to a gzip file consists of just
 * calling gzclose.
 *
 * It makes no difference whether we opened the file or the caller did it,
 * because libz provides no way of avoiding a close on the underlying file
 * handle. Notice, however, that astreamer_gzip_writer_new() uses dup() to
 * work around this issue, so that the behavior from the caller's viewpoint
 * is the same as for astreamer_plain_writer.
 */
static void
astreamer_gzip_writer_finalize(astreamer *streamer)
{
    astreamer_gzip_writer *mystreamer;
 
    mystreamer = (astreamer_gzip_writer *) streamer;
 
    errno = 0;                  /* in case gzclose() doesn't set it */
    if (gzclose(mystreamer->gzfile) != 0)
        pg_fatal("could not close compressed file \"%s\": %m",
                 mystreamer->pathname);
 
    mystreamer->gzfile = NULL;
}
 
/*
 * Free memory associated with this astreamer.
 */
static void
astreamer_gzip_writer_free(astreamer *streamer)
{
    astreamer_gzip_writer *mystreamer;
 
    mystreamer = (astreamer_gzip_writer *) streamer;
 
    Assert(mystreamer->base.bbs_next == NULL);
    Assert(mystreamer->gzfile == NULL);
 
    pfree(mystreamer->pathname);
    pfree(mystreamer);
}
 
/*
 * Helper function for libz error reporting.
 */
static const char *
get_gz_error(gzFile gzf)
{
    int         errnum;
    const char *errmsg;
 
    errmsg = gzerror(gzf, &errnum);
    if (errnum == Z_ERRNO)
        return strerror(errno);
    else
        return errmsg;
}
#endif
 
/*
 * Create a new base backup streamer that performs decompression of gzip
 * compressed blocks.
 */
astreamer *
astreamer_gzip_decompressor_new(astreamer *next)
{
#ifdef HAVE_LIBZ
    astreamer_gzip_decompressor *streamer;
    z_stream   *zs;
 
    Assert(next != NULL);
 
    streamer = palloc0(sizeof(astreamer_gzip_decompressor));
    *((const astreamer_ops **) &streamer->base.bbs_ops) =
        &astreamer_gzip_decompressor_ops;
 
    streamer->base.bbs_next = next;
    initStringInfo(&streamer->base.bbs_buffer);
 
    /* Initialize internal stream state for decompression */
    zs = &streamer->zstream;
    zs->zalloc = gzip_palloc;
    zs->zfree = gzip_pfree;
    zs->next_out = (uint8 *) streamer->base.bbs_buffer.data;
    zs->avail_out = streamer->base.bbs_buffer.maxlen;
 
    /*
     * Data compression was initialized using deflateInit2 to request a gzip
     * header. Similarly, we are using inflateInit2 to initialize data
     * decompression.
     *
     * Per the documentation for inflateInit2, the second argument is
     * "windowBits" and its value must be greater than or equal to the value
     * provided while compressing the data, so we are using the maximum
     * possible value for safety.
     */
    if (inflateInit2(zs, 15 + 16) != Z_OK)
        pg_fatal("could not initialize compression library");
 
    return &streamer->base;
#else
    pg_fatal("this build does not support compression with %s", "gzip");
    return NULL;                /* keep compiler quiet */
#endif
}
 
#ifdef HAVE_LIBZ
/*
 * Decompress the input data to output buffer until we run out of input
 * data. Each time the output buffer is full, pass on the decompressed data
 * to the next streamer.
 */
static void
astreamer_gzip_decompressor_content(astreamer *streamer,
                                    astreamer_member *member,
                                    const char *data, int len,
                                    astreamer_archive_context context)
{
    astreamer_gzip_decompressor *mystreamer;
    z_stream   *zs;
 
    mystreamer = (astreamer_gzip_decompressor *) streamer;
 
    zs = &mystreamer->zstream;
    zs->next_in = (const uint8 *) data;
    zs->avail_in = len;
 
    /* Process the current chunk */
    while (zs->avail_in > 0)
    {
        int         res;
 
        Assert(mystreamer->bytes_written < mystreamer->base.bbs_buffer.maxlen);
 
        zs->next_out = (uint8 *)
            mystreamer->base.bbs_buffer.data + mystreamer->bytes_written;
        zs->avail_out =
            mystreamer->base.bbs_buffer.maxlen - mystreamer->bytes_written;
 
        /*
         * This call decompresses data starting at zs->next_in and updates
         * zs->next_in * and zs->avail_in. It generates output data starting
         * at zs->next_out and updates zs->next_out and zs->avail_out
         * accordingly.
         */
        res = inflate(zs, Z_NO_FLUSH);
 
        if (res == Z_STREAM_ERROR)
            pg_log_error("could not decompress data: %s", zs->msg);
 
        mystreamer->bytes_written =
            mystreamer->base.bbs_buffer.maxlen - zs->avail_out;
 
        /* If output buffer is full then pass data to next streamer */
        if (mystreamer->bytes_written >= mystreamer->base.bbs_buffer.maxlen)
        {
            astreamer_content(mystreamer->base.bbs_next, member,
                              mystreamer->base.bbs_buffer.data,
                              mystreamer->base.bbs_buffer.maxlen, context);
            mystreamer->bytes_written = 0;
        }
    }
}
 
/*
 * End-of-stream processing.
 */
static void
astreamer_gzip_decompressor_finalize(astreamer *streamer)
{
    astreamer_gzip_decompressor *mystreamer;
 
    mystreamer = (astreamer_gzip_decompressor *) streamer;
 
    /*
     * End of the stream, if there is some pending data in output buffers then
     * we must forward it to next streamer.
     */
    astreamer_content(mystreamer->base.bbs_next, NULL,
                      mystreamer->base.bbs_buffer.data,
                      mystreamer->base.bbs_buffer.maxlen,
                      ASTREAMER_UNKNOWN);
 
    astreamer_finalize(mystreamer->base.bbs_next);
}
 
/*
 * Free memory.
 */
static void
astreamer_gzip_decompressor_free(astreamer *streamer)
{
    astreamer_free(streamer->bbs_next);
    pfree(streamer->bbs_buffer.data);
    pfree(streamer);
}
 
/*
 * Wrapper function to adjust the signature of palloc to match what libz
 * expects.
 */
static void *
gzip_palloc(void *opaque, unsigned items, unsigned size)
{
    return palloc(items * size);
}
 
/*
 * Wrapper function to adjust the signature of pfree to match what libz
 * expects.
 */
static void
gzip_pfree(void *opaque, void *address)
{
    pfree(address);
}
#endif