pg_receivewal.c

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/*-------------------------------------------------------------------------
 *
 * pg_receivewal.c - receive streaming WAL data and write it
 *                    to a local file.
 *
 * Author: Magnus Hagander <magnus@hagander.net>
 *
 * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *        src/bin/pg_basebackup/pg_receivewal.c
 *-------------------------------------------------------------------------
 */
 
#include "postgres_fe.h"
 
#include <dirent.h>
#include <limits.h>
#include <signal.h>
#include <sys/stat.h>
#include <unistd.h>
 
#ifdef USE_LZ4
#include <lz4frame.h>
#endif
#ifdef HAVE_LIBZ
#include <zlib.h>
#endif
 
#include "access/xlog_internal.h"
#include "common/file_perm.h"
#include "common/logging.h"
#include "fe_utils/option_utils.h"
#include "getopt_long.h"
#include "libpq-fe.h"
#include "receivelog.h"
#include "streamutil.h"
 
/* Time to sleep between reconnection attempts */
#define RECONNECT_SLEEP_TIME 5
 
/* Global options */
static char *basedir = NULL;
static int  verbose = 0;
static int  compresslevel = 0;
static int  noloop = 0;
static int  standby_message_timeout = 10 * 1000;    /* 10 sec = default */
static volatile sig_atomic_t time_to_stop = false;
static bool do_create_slot = false;
static bool slot_exists_ok = false;
static bool do_drop_slot = false;
static bool do_sync = true;
static bool synchronous = false;
static char *replication_slot = NULL;
static pg_compress_algorithm compression_algorithm = PG_COMPRESSION_NONE;
static XLogRecPtr endpos = InvalidXLogRecPtr;
 
 
static void usage(void);
static DIR *get_destination_dir(char *dest_folder);
static void close_destination_dir(DIR *dest_dir, char *dest_folder);
static XLogRecPtr FindStreamingStart(uint32 *tli);
static void StreamLog(void);
static bool stop_streaming(XLogRecPtr xlogpos, uint32 timeline,
                           bool segment_finished);
 
static void
disconnect_atexit(void)
{
    if (conn != NULL)
        PQfinish(conn);
}
 
static void
usage(void)
{
    printf(_("%s receives PostgreSQL streaming write-ahead logs.\n\n"),
           progname);
    printf(_("Usage:\n"));
    printf(_("  %s [OPTION]...\n"), progname);
    printf(_("\nOptions:\n"));
    printf(_("  -D, --directory=DIR    receive write-ahead log files into this directory\n"));
    printf(_("  -E, --endpos=LSN       exit after receiving the specified LSN\n"));
    printf(_("      --if-not-exists    do not error if slot already exists when creating a slot\n"));
    printf(_("  -n, --no-loop          do not loop on connection lost\n"));
    printf(_("      --no-sync          do not wait for changes to be written safely to disk\n"));
    printf(_("  -s, --status-interval=SECS\n"
             "                         time between status packets sent to server (default: %d)\n"), (standby_message_timeout / 1000));
    printf(_("  -S, --slot=SLOTNAME    replication slot to use\n"));
    printf(_("      --synchronous      flush write-ahead log immediately after writing\n"));
    printf(_("  -v, --verbose          output verbose messages\n"));
    printf(_("  -V, --version          output version information, then exit\n"));
    printf(_("  -Z, --compress=METHOD[:DETAIL]\n"
             "                         compress as specified\n"));
    printf(_("  -?, --help             show this help, then exit\n"));
    printf(_("\nConnection options:\n"));
    printf(_("  -d, --dbname=CONNSTR   connection string\n"));
    printf(_("  -h, --host=HOSTNAME    database server host or socket directory\n"));
    printf(_("  -p, --port=PORT        database server port number\n"));
    printf(_("  -U, --username=NAME    connect as specified database user\n"));
    printf(_("  -w, --no-password      never prompt for password\n"));
    printf(_("  -W, --password         force password prompt (should happen automatically)\n"));
    printf(_("\nOptional actions:\n"));
    printf(_("      --create-slot      create a new replication slot (for the slot's name see --slot)\n"));
    printf(_("      --drop-slot        drop the replication slot (for the slot's name see --slot)\n"));
    printf(_("\nReport bugs to <%s>.\n"), PACKAGE_BUGREPORT);
    printf(_("%s home page: <%s>\n"), PACKAGE_NAME, PACKAGE_URL);
}
 
 
/*
 * Check if the filename looks like a WAL file, letting caller know if this
 * WAL segment is partial and/or compressed.
 */
static bool
is_xlogfilename(const char *filename, bool *ispartial,
                pg_compress_algorithm *wal_compression_algorithm)
{
    size_t      fname_len = strlen(filename);
    size_t      xlog_pattern_len = strspn(filename, "0123456789ABCDEF");
 
    /* File does not look like a WAL file */
    if (xlog_pattern_len != XLOG_FNAME_LEN)
        return false;
 
    /* File looks like a completed uncompressed WAL file */
    if (fname_len == XLOG_FNAME_LEN)
    {
        *ispartial = false;
        *wal_compression_algorithm = PG_COMPRESSION_NONE;
        return true;
    }
 
    /* File looks like a completed gzip-compressed WAL file */
    if (fname_len == XLOG_FNAME_LEN + strlen(".gz") &&
        strcmp(filename + XLOG_FNAME_LEN, ".gz") == 0)
    {
        *ispartial = false;
        *wal_compression_algorithm = PG_COMPRESSION_GZIP;
        return true;
    }
 
    /* File looks like a completed LZ4-compressed WAL file */
    if (fname_len == XLOG_FNAME_LEN + strlen(".lz4") &&
        strcmp(filename + XLOG_FNAME_LEN, ".lz4") == 0)
    {
        *ispartial = false;
        *wal_compression_algorithm = PG_COMPRESSION_LZ4;
        return true;
    }
 
    /* File looks like a partial uncompressed WAL file */
    if (fname_len == XLOG_FNAME_LEN + strlen(".partial") &&
        strcmp(filename + XLOG_FNAME_LEN, ".partial") == 0)
    {
        *ispartial = true;
        *wal_compression_algorithm = PG_COMPRESSION_NONE;
        return true;
    }
 
    /* File looks like a partial gzip-compressed WAL file */
    if (fname_len == XLOG_FNAME_LEN + strlen(".gz.partial") &&
        strcmp(filename + XLOG_FNAME_LEN, ".gz.partial") == 0)
    {
        *ispartial = true;
        *wal_compression_algorithm = PG_COMPRESSION_GZIP;
        return true;
    }
 
    /* File looks like a partial LZ4-compressed WAL file */
    if (fname_len == XLOG_FNAME_LEN + strlen(".lz4.partial") &&
        strcmp(filename + XLOG_FNAME_LEN, ".lz4.partial") == 0)
    {
        *ispartial = true;
        *wal_compression_algorithm = PG_COMPRESSION_LZ4;
        return true;
    }
 
    /* File does not look like something we know */
    return false;
}
 
static bool
stop_streaming(XLogRecPtr xlogpos, uint32 timeline, bool segment_finished)
{
    static uint32 prevtimeline = 0;
    static XLogRecPtr prevpos = InvalidXLogRecPtr;
 
    /* we assume that we get called once at the end of each segment */
    if (verbose && segment_finished)
        pg_log_info("finished segment at %X/%X (timeline %u)",
                    LSN_FORMAT_ARGS(xlogpos),
                    timeline);
 
    if (!XLogRecPtrIsInvalid(endpos) && endpos < xlogpos)
    {
        if (verbose)
            pg_log_info("stopped log streaming at %X/%X (timeline %u)",
                        LSN_FORMAT_ARGS(xlogpos),
                        timeline);
        time_to_stop = true;
        return true;
    }
 
    /*
     * Note that we report the previous, not current, position here. After a
     * timeline switch, xlogpos points to the beginning of the segment because
     * that's where we always begin streaming. Reporting the end of previous
     * timeline isn't totally accurate, because the next timeline can begin
     * slightly before the end of the WAL that we received on the previous
     * timeline, but it's close enough for reporting purposes.
     */
    if (verbose && prevtimeline != 0 && prevtimeline != timeline)
        pg_log_info("switched to timeline %u at %X/%X",
                    timeline,
                    LSN_FORMAT_ARGS(prevpos));
 
    prevtimeline = timeline;
    prevpos = xlogpos;
 
    if (time_to_stop)
    {
        if (verbose)
            pg_log_info("received interrupt signal, exiting");
        return true;
    }
    return false;
}
 
 
/*
 * Get destination directory.
 */
static DIR *
get_destination_dir(char *dest_folder)
{
    DIR        *dir;
 
    Assert(dest_folder != NULL);
    dir = opendir(dest_folder);
    if (dir == NULL)
        pg_fatal("could not open directory \"%s\": %m", dest_folder);
 
    return dir;
}
 
 
/*
 * Close existing directory.
 */
static void
close_destination_dir(DIR *dest_dir, char *dest_folder)
{
    Assert(dest_dir != NULL && dest_folder != NULL);
    if (closedir(dest_dir))
        pg_fatal("could not close directory \"%s\": %m", dest_folder);
}
 
 
/*
 * Determine starting location for streaming, based on any existing xlog
 * segments in the directory. We start at the end of the last one that is
 * complete (size matches wal segment size), on the timeline with highest ID.
 *
 * If there are no WAL files in the directory, returns InvalidXLogRecPtr.
 */
static XLogRecPtr
FindStreamingStart(uint32 *tli)
{
    DIR        *dir;
    struct dirent *dirent;
    XLogSegNo   high_segno = 0;
    uint32      high_tli = 0;
    bool        high_ispartial = false;
 
    dir = get_destination_dir(basedir);
 
    while (errno = 0, (dirent = readdir(dir)) != NULL)
    {
        uint32      tli;
        XLogSegNo   segno;
        pg_compress_algorithm wal_compression_algorithm;
        bool        ispartial;
 
        if (!is_xlogfilename(dirent->d_name,
                             &ispartial, &wal_compression_algorithm))
            continue;
 
        /*
         * Looks like an xlog file. Parse its position.
         */
        XLogFromFileName(dirent->d_name, &tli, &segno, WalSegSz);
 
        /*
         * Check that the segment has the right size, if it's supposed to be
         * completed.  For non-compressed segments just check the on-disk size
         * and see if it matches a completed segment.  For gzip-compressed
         * segments, look at the last 4 bytes of the compressed file, which is
         * where the uncompressed size is located for files with a size lower
         * than 4GB, and then compare it to the size of a completed segment.
         * The 4 last bytes correspond to the ISIZE member according to
         * http://www.zlib.org/rfc-gzip.html.
         *
         * For LZ4-compressed segments, uncompress the file in a throw-away
         * buffer keeping track of the uncompressed size, then compare it to
         * the size of a completed segment.  Per its protocol, LZ4 does not
         * store the uncompressed size of an object by default.  contentSize
         * is one possible way to do that, but we need to rely on a method
         * where WAL segments could have been compressed by a different source
         * than pg_receivewal, like an archive_command with lz4.
         */
        if (!ispartial && wal_compression_algorithm == PG_COMPRESSION_NONE)
        {
            struct stat statbuf;
            char        fullpath[MAXPGPATH * 2];
 
            snprintf(fullpath, sizeof(fullpath), "%s/%s", basedir, dirent->d_name);
            if (stat(fullpath, &statbuf) != 0)
                pg_fatal("could not stat file \"%s\": %m", fullpath);
 
            if (statbuf.st_size != WalSegSz)
            {
                pg_log_warning("segment file \"%s\" has incorrect size %lld, skipping",
                               dirent->d_name, (long long int) statbuf.st_size);
                continue;
            }
        }
        else if (!ispartial && wal_compression_algorithm == PG_COMPRESSION_GZIP)
        {
            int         fd;
            char        buf[4];
            int         bytes_out;
            char        fullpath[MAXPGPATH * 2];
            int         r;
 
            snprintf(fullpath, sizeof(fullpath), "%s/%s", basedir, dirent->d_name);
 
            fd = open(fullpath, O_RDONLY | PG_BINARY, 0);
            if (fd < 0)
                pg_fatal("could not open compressed file \"%s\": %m",
                         fullpath);
            if (lseek(fd, (off_t) (-4), SEEK_END) < 0)
                pg_fatal("could not seek in compressed file \"%s\": %m",
                         fullpath);
            r = read(fd, (char *) buf, sizeof(buf));
            if (r != sizeof(buf))
            {
                if (r < 0)
                    pg_fatal("could not read compressed file \"%s\": %m",
                             fullpath);
                else
                    pg_fatal("could not read compressed file \"%s\": read %d of %zu",
                             fullpath, r, sizeof(buf));
            }
 
            close(fd);
            bytes_out = (buf[3] << 24) | (buf[2] << 16) |
                (buf[1] << 8) | buf[0];
 
            if (bytes_out != WalSegSz)
            {
                pg_log_warning("compressed segment file \"%s\" has incorrect uncompressed size %d, skipping",
                               dirent->d_name, bytes_out);
                continue;
            }
        }
        else if (!ispartial && wal_compression_algorithm == PG_COMPRESSION_LZ4)
        {
#ifdef USE_LZ4
#define LZ4_CHUNK_SZ    64 * 1024   /* 64kB as maximum chunk size read */
            int         fd;
            ssize_t     r;
            size_t      uncompressed_size = 0;
            char        fullpath[MAXPGPATH * 2];
            char       *outbuf;
            char       *readbuf;
            LZ4F_decompressionContext_t ctx = NULL;
            LZ4F_decompressOptions_t dec_opt;
            LZ4F_errorCode_t status;
 
            memset(&dec_opt, 0, sizeof(dec_opt));
            snprintf(fullpath, sizeof(fullpath), "%s/%s", basedir, dirent->d_name);
 
            fd = open(fullpath, O_RDONLY | PG_BINARY, 0);
            if (fd < 0)
                pg_fatal("could not open file \"%s\": %m", fullpath);
 
            status = LZ4F_createDecompressionContext(&ctx, LZ4F_VERSION);
            if (LZ4F_isError(status))
                pg_fatal("could not create LZ4 decompression context: %s",
                         LZ4F_getErrorName(status));
 
            outbuf = pg_malloc0(LZ4_CHUNK_SZ);
            readbuf = pg_malloc0(LZ4_CHUNK_SZ);
            do
            {
                char       *readp;
                char       *readend;
 
                r = read(fd, readbuf, LZ4_CHUNK_SZ);
                if (r < 0)
                    pg_fatal("could not read file \"%s\": %m", fullpath);
 
                /* Done reading the file */
                if (r == 0)
                    break;
 
                /* Process one chunk */
                readp = readbuf;
                readend = readbuf + r;
                while (readp < readend)
                {
                    size_t      out_size = LZ4_CHUNK_SZ;
                    size_t      read_size = readend - readp;
 
                    memset(outbuf, 0, LZ4_CHUNK_SZ);
                    status = LZ4F_decompress(ctx, outbuf, &out_size,
                                             readp, &read_size, &dec_opt);
                    if (LZ4F_isError(status))
                        pg_fatal("could not decompress file \"%s\": %s",
                                 fullpath,
                                 LZ4F_getErrorName(status));
 
                    readp += read_size;
                    uncompressed_size += out_size;
                }
 
                /*
                 * No need to continue reading the file when the
                 * uncompressed_size exceeds WalSegSz, even if there are still
                 * data left to read. However, if uncompressed_size is equal
                 * to WalSegSz, it should verify that there is no more data to
                 * read.
                 */
            } while (uncompressed_size <= WalSegSz && r > 0);
 
            close(fd);
            pg_free(outbuf);
            pg_free(readbuf);
 
            status = LZ4F_freeDecompressionContext(ctx);
            if (LZ4F_isError(status))
                pg_fatal("could not free LZ4 decompression context: %s",
                         LZ4F_getErrorName(status));
 
            if (uncompressed_size != WalSegSz)
            {
                pg_log_warning("compressed segment file \"%s\" has incorrect uncompressed size %zu, skipping",
                               dirent->d_name, uncompressed_size);
                continue;
            }
#else
            pg_log_error("cannot check file \"%s\": compression with %s not supported by this build",
                         dirent->d_name, "LZ4");
            exit(1);
#endif
        }
 
        /* Looks like a valid segment. Remember that we saw it. */
        if ((segno > high_segno) ||
            (segno == high_segno && tli > high_tli) ||
            (segno == high_segno && tli == high_tli && high_ispartial && !ispartial))
        {
            high_segno = segno;
            high_tli = tli;
            high_ispartial = ispartial;
        }
    }
 
    if (errno)
        pg_fatal("could not read directory \"%s\": %m", basedir);
 
    close_destination_dir(dir, basedir);
 
    if (high_segno > 0)
    {
        XLogRecPtr  high_ptr;
 
        /*
         * Move the starting pointer to the start of the next segment, if the
         * highest one we saw was completed. Otherwise start streaming from
         * the beginning of the .partial segment.
         */
        if (!high_ispartial)
            high_segno++;
 
        XLogSegNoOffsetToRecPtr(high_segno, 0, WalSegSz, high_ptr);
 
        *tli = high_tli;
        return high_ptr;
    }
    else
        return InvalidXLogRecPtr;
}
 
/*
 * Start the log streaming
 */
static void
StreamLog(void)
{
    XLogRecPtr  serverpos;
    TimeLineID  servertli;
    StreamCtl   stream = {0};
    char       *sysidentifier;
 
    /*
     * Connect in replication mode to the server
     */
    if (conn == NULL)
        conn = GetConnection();
    if (!conn)
        /* Error message already written in GetConnection() */
        return;
 
    if (!CheckServerVersionForStreaming(conn))
    {
        /*
         * Error message already written in CheckServerVersionForStreaming().
         * There's no hope of recovering from a version mismatch, so don't
         * retry.
         */
        exit(1);
    }
 
    /*
     * Identify server, obtaining start LSN position and current timeline ID
     * at the same time, necessary if not valid data can be found in the
     * existing output directory.
     */
    if (!RunIdentifySystem(conn, &sysidentifier, &servertli, &serverpos, NULL))
        exit(1);
 
    /*
     * Figure out where to start streaming.  First scan the local directory.
     */
    stream.startpos = FindStreamingStart(&stream.timeline);
    if (stream.startpos == InvalidXLogRecPtr)
    {
        /*
         * Try to get the starting point from the slot if any.  This is
         * supported in PostgreSQL 15 and newer.
         */
        if (replication_slot != NULL &&
            PQserverVersion(conn) >= 150000)
        {
            if (!GetSlotInformation(conn, replication_slot, &stream.startpos,
                                    &stream.timeline))
            {
                /* Error is logged by GetSlotInformation() */
                return;
            }
        }
 
        /*
         * If it the starting point is still not known, use the current WAL
         * flush value as last resort.
         */
        if (stream.startpos == InvalidXLogRecPtr)
        {
            stream.startpos = serverpos;
            stream.timeline = servertli;
        }
    }
 
    Assert(stream.startpos != InvalidXLogRecPtr &&
           stream.timeline != 0);
 
    /*
     * Always start streaming at the beginning of a segment
     */
    stream.startpos -= XLogSegmentOffset(stream.startpos, WalSegSz);
 
    /*
     * Start the replication
     */
    if (verbose)
        pg_log_info("starting log streaming at %X/%X (timeline %u)",
                    LSN_FORMAT_ARGS(stream.startpos),
                    stream.timeline);
 
    stream.stream_stop = stop_streaming;
    stream.stop_socket = PGINVALID_SOCKET;
    stream.standby_message_timeout = standby_message_timeout;
    stream.synchronous = synchronous;
    stream.do_sync = do_sync;
    stream.mark_done = false;
    stream.walmethod = CreateWalDirectoryMethod(basedir,
                                                compression_algorithm,
                                                compresslevel,
                                                stream.do_sync);
    stream.partial_suffix = ".partial";
    stream.replication_slot = replication_slot;
    stream.sysidentifier = sysidentifier;
 
    ReceiveXlogStream(conn, &stream);
 
    if (!stream.walmethod->ops->finish(stream.walmethod))
    {
        pg_log_info("could not finish writing WAL files: %m");
        return;
    }
 
    PQfinish(conn);
    conn = NULL;
 
    stream.walmethod->ops->free(stream.walmethod);
}
 
/*
 * When SIGINT/SIGTERM are caught, just tell the system to exit at the next
 * possible moment.
 */
#ifndef WIN32
 
static void
sigexit_handler(SIGNAL_ARGS)
{
    time_to_stop = true;
}
#endif
 
int
main(int argc, char **argv)
{
    static struct option long_options[] = {
        {"help", no_argument, NULL, '?'},
        {"version", no_argument, NULL, 'V'},
        {"directory", required_argument, NULL, 'D'},
        {"dbname", required_argument, NULL, 'd'},
        {"endpos", required_argument, NULL, 'E'},
        {"host", required_argument, NULL, 'h'},
        {"port", required_argument, NULL, 'p'},
        {"username", required_argument, NULL, 'U'},
        {"no-loop", no_argument, NULL, 'n'},
        {"no-password", no_argument, NULL, 'w'},
        {"password", no_argument, NULL, 'W'},
        {"status-interval", required_argument, NULL, 's'},
        {"slot", required_argument, NULL, 'S'},
        {"verbose", no_argument, NULL, 'v'},
        {"compress", required_argument, NULL, 'Z'},
/* action */
        {"create-slot", no_argument, NULL, 1},
        {"drop-slot", no_argument, NULL, 2},
        {"if-not-exists", no_argument, NULL, 3},
        {"synchronous", no_argument, NULL, 4},
        {"no-sync", no_argument, NULL, 5},
        {NULL, 0, NULL, 0}
    };
 
    int         c;
    int         option_index;
    char       *db_name;
    uint32      hi,
                lo;
    pg_compress_specification compression_spec;
    char       *compression_detail = NULL;
    char       *compression_algorithm_str = "none";
    char       *error_detail = NULL;
 
    pg_logging_init(argv[0]);
    progname = get_progname(argv[0]);
    set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_basebackup"));
 
    if (argc > 1)
    {
        if (strcmp(argv[1], "--help") == 0 || strcmp(argv[1], "-?") == 0)
        {
            usage();
            exit(0);
        }
        else if (strcmp(argv[1], "-V") == 0 ||
                 strcmp(argv[1], "--version") == 0)
        {
            puts("pg_receivewal (PostgreSQL) " PG_VERSION);
            exit(0);
        }
    }
 
    while ((c = getopt_long(argc, argv, "D:d:E:h:p:U:s:S:nwWvZ:",
                            long_options, &option_index)) != -1)
    {
        switch (c)
        {
            case 'D':
                basedir = pg_strdup(optarg);
                break;
            case 'd':
                connection_string = pg_strdup(optarg);
                break;
            case 'h':
                dbhost = pg_strdup(optarg);
                break;
            case 'p':
                dbport = pg_strdup(optarg);
                break;
            case 'U':
                dbuser = pg_strdup(optarg);
                break;
            case 'w':
                dbgetpassword = -1;
                break;
            case 'W':
                dbgetpassword = 1;
                break;
            case 's':
                if (!option_parse_int(optarg, "-s/--status-interval", 0,
                                      INT_MAX / 1000,
                                      &standby_message_timeout))
                    exit(1);
                standby_message_timeout *= 1000;
                break;
            case 'S':
                replication_slot = pg_strdup(optarg);
                break;
            case 'E':
                if (sscanf(optarg, "%X/%X", &hi, &lo) != 2)
                    pg_fatal("could not parse end position \"%s\"", optarg);
                endpos = ((uint64) hi) << 32 | lo;
                break;
            case 'n':
                noloop = 1;
                break;
            case 'v':
                verbose++;
                break;
            case 'Z':
                parse_compress_options(optarg, &compression_algorithm_str,
                                       &compression_detail);
                break;
/* action */
            case 1:
                do_create_slot = true;
                break;
            case 2:
                do_drop_slot = true;
                break;
            case 3:
                slot_exists_ok = true;
                break;
            case 4:
                synchronous = true;
                break;
            case 5:
                do_sync = false;
                break;
            default:
                /* getopt_long already emitted a complaint */
                pg_log_error_hint("Try \"%s --help\" for more information.", progname);
                exit(1);
        }
    }
 
    /*
     * Any non-option arguments?
     */
    if (optind < argc)
    {
        pg_log_error("too many command-line arguments (first is \"%s\")",
                     argv[optind]);
        pg_log_error_hint("Try \"%s --help\" for more information.", progname);
        exit(1);
    }
 
    if (do_drop_slot && do_create_slot)
    {
        pg_log_error("cannot use --create-slot together with --drop-slot");
        pg_log_error_hint("Try \"%s --help\" for more information.", progname);
        exit(1);
    }
 
    if (replication_slot == NULL && (do_drop_slot || do_create_slot))
    {
        /* translator: second %s is an option name */
        pg_log_error("%s needs a slot to be specified using --slot",
                     do_drop_slot ? "--drop-slot" : "--create-slot");
        pg_log_error_hint("Try \"%s --help\" for more information.", progname);
        exit(1);
    }
 
    if (synchronous && !do_sync)
    {
        pg_log_error("cannot use --synchronous together with --no-sync");
        pg_log_error_hint("Try \"%s --help\" for more information.", progname);
        exit(1);
    }
 
    /*
     * Required arguments
     */
    if (basedir == NULL && !do_drop_slot && !do_create_slot)
    {
        pg_log_error("no target directory specified");
        pg_log_error_hint("Try \"%s --help\" for more information.", progname);
        exit(1);
    }
 
    /*
     * Compression options
     */
    if (!parse_compress_algorithm(compression_algorithm_str,
                                  &compression_algorithm))
        pg_fatal("unrecognized compression algorithm: \"%s\"",
                 compression_algorithm_str);
 
    parse_compress_specification(compression_algorithm, compression_detail,
                                 &compression_spec);
    error_detail = validate_compress_specification(&compression_spec);
    if (error_detail != NULL)
        pg_fatal("invalid compression specification: %s",
                 error_detail);
 
    /* Extract the compression level */
    compresslevel = compression_spec.level;
 
    if (compression_algorithm == PG_COMPRESSION_ZSTD)
        pg_fatal("compression with %s is not yet supported", "ZSTD");
 
    /*
     * Check existence of destination folder.
     */
    if (!do_drop_slot && !do_create_slot)
    {
        DIR        *dir = get_destination_dir(basedir);
 
        close_destination_dir(dir, basedir);
    }
 
    /*
     * Obtain a connection before doing anything.
     */
    conn = GetConnection();
    if (!conn)
        /* error message already written in GetConnection() */
        exit(1);
    atexit(disconnect_atexit);
 
    /*
     * Trap signals.  (Don't do this until after the initial password prompt,
     * if one is needed, in GetConnection.)
     */
#ifndef WIN32
    pqsignal(SIGINT, sigexit_handler);
    pqsignal(SIGTERM, sigexit_handler);
#endif
 
    /*
     * Run IDENTIFY_SYSTEM to make sure we've successfully have established a
     * replication connection and haven't connected using a database specific
     * connection.
     */
    if (!RunIdentifySystem(conn, NULL, NULL, NULL, &db_name))
        exit(1);
 
    /*
     * Check that there is a database associated with connection, none should
     * be defined in this context.
     */
    if (db_name)
        pg_fatal("replication connection using slot \"%s\" is unexpectedly database specific",
                 replication_slot);
 
    /*
     * Set umask so that directories/files are created with the same
     * permissions as directories/files in the source data directory.
     *
     * pg_mode_mask is set to owner-only by default and then updated in
     * GetConnection() where we get the mode from the server-side with
     * RetrieveDataDirCreatePerm() and then call SetDataDirectoryCreatePerm().
     */
    umask(pg_mode_mask);
 
    /*
     * Drop a replication slot.
     */
    if (do_drop_slot)
    {
        if (verbose)
            pg_log_info("dropping replication slot \"%s\"", replication_slot);
 
        if (!DropReplicationSlot(conn, replication_slot))
            exit(1);
        exit(0);
    }
 
    /* Create a replication slot */
    if (do_create_slot)
    {
        if (verbose)
            pg_log_info("creating replication slot \"%s\"", replication_slot);
 
        if (!CreateReplicationSlot(conn, replication_slot, NULL, false, true, false,
                                   slot_exists_ok, false))
            exit(1);
        exit(0);
    }
 
    /* determine remote server's xlog segment size */
    if (!RetrieveWalSegSize(conn))
        exit(1);
 
    /*
     * Don't close the connection here so that subsequent StreamLog() can
     * reuse it.
     */
 
    while (true)
    {
        StreamLog();
        if (time_to_stop)
        {
            /*
             * We've been Ctrl-C'ed or end of streaming position has been
             * willingly reached, so exit without an error code.
             */
            exit(0);
        }
        else if (noloop)
            pg_fatal("disconnected");
        else
        {
            /* translator: check source for value for %d */
            pg_log_info("disconnected; waiting %d seconds to try again",
                        RECONNECT_SLEEP_TIME);
            pg_usleep(RECONNECT_SLEEP_TIME * 1000000);
        }
    }
}