compress_io.c

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/*-------------------------------------------------------------------------
 *
 * compress_io.c
 *   Routines for archivers to write an uncompressed or compressed data
 *   stream.
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * This file includes two APIs for dealing with compressed data. The first
 * provides more flexibility, using callbacks to read/write data from the
 * underlying stream. The second API is a wrapper around fopen and
 * friends, providing an interface similar to those, but abstracts away
 * the possible compression. The second API is aimed for the resulting
 * files to be easily manipulated with an external compression utility
 * program.
 *
 * Compressor API
 * --------------
 *
 *  The interface for writing to an archive consists of three functions:
 *  AllocateCompressor, writeData, and EndCompressor. First you call
 *  AllocateCompressor, then write all the data by calling writeData as many
 *  times as needed, and finally EndCompressor. writeData will call the
 *  WriteFunc that was provided to AllocateCompressor for each chunk of
 *  compressed data.
 *
 *  The interface for reading an archive consists of the same three functions:
 *  AllocateCompressor, readData, and EndCompressor. First you call
 *  AllocateCompressor, then read all the data by calling readData to read the
 *  whole compressed stream which repeatedly calls the given ReadFunc. ReadFunc
 *  returns the compressed data one chunk at a time. Then readData decompresses
 *  it and passes the decompressed data to ahwrite(), until ReadFunc returns 0
 *  to signal EOF. The interface is the same for compressed and uncompressed
 *  streams.
 *
 * Compressed stream API
 * ----------------------
 *
 *  The compressed stream API is providing a set of function pointers for
 *  opening, reading, writing, and finally closing files. The implemented
 *  function pointers are documented in the corresponding header file and are
 *  common for all streams. It allows the caller to use the same functions for
 *  both compressed and uncompressed streams.
 *
 *  The interface consists of three functions, InitCompressFileHandle,
 *  InitDiscoverCompressFileHandle, and EndCompressFileHandle. If the
 *  compression is known, then start by calling InitCompressFileHandle,
 *  otherwise discover it by using InitDiscoverCompressFileHandle. Then call
 *  the function pointers as required for the read/write operations. Finally
 *  call EndCompressFileHandle to end the stream.
 *
 *  InitDiscoverCompressFileHandle tries to infer the compression by the
 *  filename suffix. If the suffix is not yet known then it tries to simply
 *  open the file and if it fails, it tries to open the same file with the .gz
 *  suffix, and then again with the .lz4 suffix.
 *
 * IDENTIFICATION
 *     src/bin/pg_dump/compress_io.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres_fe.h"
 
#include <sys/stat.h>
#include <unistd.h>
 
#include "compress_gzip.h"
#include "compress_io.h"
#include "compress_lz4.h"
#include "compress_none.h"
#include "pg_backup_utils.h"
 
/*----------------------
 * Generic functions
 *----------------------
 */
 
/*
 * Checks whether a compression algorithm is supported.
 *
 * On success returns NULL, otherwise returns a malloc'ed string which can be
 * used by the caller in an error message.
 */
char *
supports_compression(const pg_compress_specification compression_spec)
{
    const pg_compress_algorithm algorithm = compression_spec.algorithm;
    bool                        supported = false;
 
    if (algorithm == PG_COMPRESSION_NONE)
        supported = true;
#ifdef HAVE_LIBZ
    if (algorithm == PG_COMPRESSION_GZIP)
        supported = true;
#endif
#ifdef USE_LZ4
    if (algorithm == PG_COMPRESSION_LZ4)
        supported = true;
#endif
 
    if (!supported)
        return psprintf("this build does not support compression with %s",
                        get_compress_algorithm_name(algorithm));
 
    return NULL;
}
 
/*----------------------
 * Compressor API
 *----------------------
 */
 
/*
 * Allocate a new compressor.
 */
CompressorState *
AllocateCompressor(const pg_compress_specification compression_spec,
                   ReadFunc readF, WriteFunc writeF)
{
    CompressorState *cs;
 
    cs = (CompressorState *) pg_malloc0(sizeof(CompressorState));
    cs->readF = readF;
    cs->writeF = writeF;
 
    if (compression_spec.algorithm == PG_COMPRESSION_NONE)
        InitCompressorNone(cs, compression_spec);
    else if (compression_spec.algorithm == PG_COMPRESSION_GZIP)
        InitCompressorGzip(cs, compression_spec);
    else if (compression_spec.algorithm == PG_COMPRESSION_LZ4)
        InitCompressorLZ4(cs, compression_spec);
 
    return cs;
}
 
/*
 * Terminate compression library context and flush its buffers.
 */
void
EndCompressor(ArchiveHandle *AH, CompressorState *cs)
{
    cs->end(AH, cs);
    pg_free(cs);
}
 
/*----------------------
 * Compressed stream API
 *----------------------
 */
 
/*
 * Private routines
 */
static int
hasSuffix(const char *filename, const char *suffix)
{
    int         filenamelen = strlen(filename);
    int         suffixlen = strlen(suffix);
 
    if (filenamelen < suffixlen)
        return 0;
 
    return memcmp(&filename[filenamelen - suffixlen],
                  suffix,
                  suffixlen) == 0;
}
 
/* free() without changing errno; useful in several places below */
static void
free_keep_errno(void *p)
{
    int         save_errno = errno;
 
    free(p);
    errno = save_errno;
}
 
/*
 * Public interface
 */
 
/*
 * Initialize a compress file handle for the specified compression algorithm.
 */
CompressFileHandle *
InitCompressFileHandle(const pg_compress_specification compression_spec)
{
    CompressFileHandle *CFH;
 
    CFH = pg_malloc0(sizeof(CompressFileHandle));
 
    if (compression_spec.algorithm == PG_COMPRESSION_NONE)
        InitCompressFileHandleNone(CFH, compression_spec);
    else if (compression_spec.algorithm == PG_COMPRESSION_GZIP)
        InitCompressFileHandleGzip(CFH, compression_spec);
    else if (compression_spec.algorithm == PG_COMPRESSION_LZ4)
        InitCompressFileHandleLZ4(CFH, compression_spec);
 
    return CFH;
}
 
/*
 * Open a file for reading. 'path' is the file to open, and 'mode' should
 * be either "r" or "rb".
 *
 * If the file at 'path' contains the suffix of a supported compression method,
 * currently this includes ".gz" and ".lz4", then this compression will be used
 * throughout. Otherwise the compression will be inferred by iteratively trying
 * to open the file at 'path', first as is, then by appending known compression
 * suffixes. So if you pass "foo" as 'path', this will open either "foo" or
 * "foo.gz" or "foo.lz4", trying in that order.
 *
 * On failure, return NULL with an error code in errno.
 */
CompressFileHandle *
InitDiscoverCompressFileHandle(const char *path, const char *mode)
{
    CompressFileHandle *CFH = NULL;
    struct stat st;
    char       *fname;
    pg_compress_specification compression_spec = {0};
 
    compression_spec.algorithm = PG_COMPRESSION_NONE;
 
    Assert(strcmp(mode, PG_BINARY_R) == 0);
 
    fname = strdup(path);
 
    if (hasSuffix(fname, ".gz"))
        compression_spec.algorithm = PG_COMPRESSION_GZIP;
    else
    {
        bool        exists;
 
        exists = (stat(path, &st) == 0);
        /* avoid unused warning if it is not built with compression */
        if (exists)
            compression_spec.algorithm = PG_COMPRESSION_NONE;
#ifdef HAVE_LIBZ
        if (!exists)
        {
            free_keep_errno(fname);
            fname = psprintf("%s.gz", path);
            exists = (stat(fname, &st) == 0);
 
            if (exists)
                compression_spec.algorithm = PG_COMPRESSION_GZIP;
        }
#endif
#ifdef USE_LZ4
        if (!exists)
        {
            free_keep_errno(fname);
            fname = psprintf("%s.lz4", path);
            exists = (stat(fname, &st) == 0);
 
            if (exists)
                compression_spec.algorithm = PG_COMPRESSION_LZ4;
        }
#endif
    }
 
    CFH = InitCompressFileHandle(compression_spec);
    if (!CFH->open_func(fname, -1, mode, CFH))
    {
        free_keep_errno(CFH);
        CFH = NULL;
    }
    free_keep_errno(fname);
 
    return CFH;
}
 
/*
 * Close an open file handle and release its memory.
 *
 * On failure, returns false and sets errno appropriately.
 */
bool
EndCompressFileHandle(CompressFileHandle *CFH)
{
    bool        ret = false;
 
    if (CFH->private_data)
        ret = CFH->close_func(CFH);
 
    free_keep_errno(CFH);
 
    return ret;
}