pg_recvlogical.c

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/*-------------------------------------------------------------------------
 *
 * pg_recvlogical.c - receive data from a logical decoding slot in a streaming
 *                    fashion and write it to a local file.
 *
 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *        src/bin/pg_basebackup/pg_recvlogical.c
 *-------------------------------------------------------------------------
 */

#include "postgres_fe.h"

#include <dirent.h>
#include <sys/stat.h>
#include <unistd.h>
#ifdef HAVE_SYS_SELECT_H
#include <sys/select.h>
#endif

/* local includes */
#include "streamutil.h"

#include "access/xlog_internal.h"
#include "common/fe_memutils.h"
#include "getopt_long.h"
#include "libpq-fe.h"
#include "libpq/pqsignal.h"
#include "pqexpbuffer.h"


/* Time to sleep between reconnection attempts */
#define RECONNECT_SLEEP_TIME 5

/* Global Options */
static char *outfile = NULL;
static int  verbose = 0;
static int  noloop = 0;
static int  standby_message_timeout = 10 * 1000;    /* 10 sec = default */
static int  fsync_interval = 10 * 1000; /* 10 sec = default */
static XLogRecPtr startpos = InvalidXLogRecPtr;
static XLogRecPtr endpos = InvalidXLogRecPtr;
static bool do_create_slot = false;
static bool slot_exists_ok = false;
static bool do_start_slot = false;
static bool do_drop_slot = false;
static char *replication_slot = NULL;

/* filled pairwise with option, value. value may be NULL */
static char **options;
static size_t noptions = 0;
static const char *plugin = "test_decoding";

/* Global State */
static int  outfd = -1;
static volatile sig_atomic_t time_to_abort = false;
static volatile sig_atomic_t output_reopen = false;
static bool output_isfile;
static TimestampTz output_last_fsync = -1;
static bool output_needs_fsync = false;
static XLogRecPtr output_written_lsn = InvalidXLogRecPtr;
static XLogRecPtr output_fsync_lsn = InvalidXLogRecPtr;

static void usage(void);
static void StreamLogicalLog(void);
static void disconnect_and_exit(int code);
static bool flushAndSendFeedback(PGconn *conn, TimestampTz *now);
static void prepareToTerminate(PGconn *conn, XLogRecPtr endpos,
                   bool keepalive, XLogRecPtr lsn);

static void
usage(void)
{
    printf(_("%s controls PostgreSQL logical decoding streams.\n\n"),
           progname);
    printf(_("Usage:\n"));
    printf(_("  %s [OPTION]...\n"), progname);
    printf(_("\nAction to be performed:\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(_("      --start            start streaming in a replication slot (for the slot's name see --slot)\n"));
    printf(_("\nOptions:\n"));
    printf(_("  -E, --endpos=LSN       exit after receiving the specified LSN\n"));
    printf(_("  -f, --file=FILE        receive log into this file, - for stdout\n"));
    printf(_("  -F  --fsync-interval=SECS\n"
             "                         time between fsyncs to the output file (default: %d)\n"), (fsync_interval / 1000));
    printf(_("      --if-not-exists    do not error if slot already exists when creating a slot\n"));
    printf(_("  -I, --startpos=LSN     where in an existing slot should the streaming start\n"));
    printf(_("  -n, --no-loop          do not loop on connection lost\n"));
    printf(_("  -o, --option=NAME[=VALUE]\n"
             "                         pass option NAME with optional value VALUE to the\n"
             "                         output plugin\n"));
    printf(_("  -P, --plugin=PLUGIN    use output plugin PLUGIN (default: %s)\n"), plugin);
    printf(_("  -s, --status-interval=SECS\n"
             "                         time between status packets sent to server (default: %d)\n"), (standby_message_timeout / 1000));
    printf(_("  -S, --slot=SLOTNAME    name of the logical replication slot\n"));
    printf(_("  -v, --verbose          output verbose messages\n"));
    printf(_("  -V, --version          output version information, then exit\n"));
    printf(_("  -?, --help             show this help, then exit\n"));
    printf(_("\nConnection options:\n"));
    printf(_("  -d, --dbname=DBNAME    database to connect to\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(_("\nReport bugs to <pgsql-bugs@postgresql.org>.\n"));
}

/*
 * Send a Standby Status Update message to server.
 */
static bool
sendFeedback(PGconn *conn, TimestampTz now, bool force, bool replyRequested)
{
    static XLogRecPtr last_written_lsn = InvalidXLogRecPtr;
    static XLogRecPtr last_fsync_lsn = InvalidXLogRecPtr;

    char        replybuf[1 + 8 + 8 + 8 + 8 + 1];
    int         len = 0;

    /*
     * we normally don't want to send superfluous feedbacks, but if it's
     * because of a timeout we need to, otherwise wal_sender_timeout will kill
     * us.
     */
    if (!force &&
        last_written_lsn == output_written_lsn &&
        last_fsync_lsn != output_fsync_lsn)
        return true;

    if (verbose)
        fprintf(stderr,
                _("%s: confirming write up to %X/%X, flush to %X/%X (slot %s)\n"),
                progname,
                (uint32) (output_written_lsn >> 32), (uint32) output_written_lsn,
                (uint32) (output_fsync_lsn >> 32), (uint32) output_fsync_lsn,
                replication_slot);

    replybuf[len] = 'r';
    len += 1;
    fe_sendint64(output_written_lsn, &replybuf[len]);   /* write */
    len += 8;
    fe_sendint64(output_fsync_lsn, &replybuf[len]); /* flush */
    len += 8;
    fe_sendint64(InvalidXLogRecPtr, &replybuf[len]);    /* apply */
    len += 8;
    fe_sendint64(now, &replybuf[len]);  /* sendTime */
    len += 8;
    replybuf[len] = replyRequested ? 1 : 0; /* replyRequested */
    len += 1;

    startpos = output_written_lsn;
    last_written_lsn = output_written_lsn;
    last_fsync_lsn = output_fsync_lsn;

    if (PQputCopyData(conn, replybuf, len) <= 0 || PQflush(conn))
    {
        fprintf(stderr, _("%s: could not send feedback packet: %s"),
                progname, PQerrorMessage(conn));
        return false;
    }

    return true;
}

static void
disconnect_and_exit(int code)
{
    if (conn != NULL)
        PQfinish(conn);

    exit(code);
}

static bool
OutputFsync(TimestampTz now)
{
    output_last_fsync = now;

    output_fsync_lsn = output_written_lsn;

    if (fsync_interval <= 0)
        return true;

    if (!output_needs_fsync)
        return true;

    output_needs_fsync = false;

    /* can only fsync if it's a regular file */
    if (!output_isfile)
        return true;

    if (fsync(outfd) != 0)
    {
        fprintf(stderr,
                _("%s: could not fsync log file \"%s\": %s\n"),
                progname, outfile, strerror(errno));
        return false;
    }

    return true;
}

/*
 * Start the log streaming
 */
static void
StreamLogicalLog(void)
{
    PGresult   *res;
    char       *copybuf = NULL;
    TimestampTz last_status = -1;
    int         i;
    PQExpBuffer query;

    output_written_lsn = InvalidXLogRecPtr;
    output_fsync_lsn = InvalidXLogRecPtr;

    query = createPQExpBuffer();

    /*
     * Connect in replication mode to the server
     */
    if (!conn)
        conn = GetConnection();
    if (!conn)
        /* Error message already written in GetConnection() */
        return;

    /*
     * Start the replication
     */
    if (verbose)
        fprintf(stderr,
                _("%s: starting log streaming at %X/%X (slot %s)\n"),
                progname, (uint32) (startpos >> 32), (uint32) startpos,
                replication_slot);

    /* Initiate the replication stream at specified location */
    appendPQExpBuffer(query, "START_REPLICATION SLOT \"%s\" LOGICAL %X/%X",
                      replication_slot, (uint32) (startpos >> 32), (uint32) startpos);

    /* print options if there are any */
    if (noptions)
        appendPQExpBufferStr(query, " (");

    for (i = 0; i < noptions; i++)
    {
        /* separator */
        if (i > 0)
            appendPQExpBufferStr(query, ", ");

        /* write option name */
        appendPQExpBuffer(query, "\"%s\"", options[(i * 2)]);

        /* write option value if specified */
        if (options[(i * 2) + 1] != NULL)
            appendPQExpBuffer(query, " '%s'", options[(i * 2) + 1]);
    }

    if (noptions)
        appendPQExpBufferChar(query, ')');

    res = PQexec(conn, query->data);
    if (PQresultStatus(res) != PGRES_COPY_BOTH)
    {
        fprintf(stderr, _("%s: could not send replication command \"%s\": %s"),
                progname, query->data, PQresultErrorMessage(res));
        PQclear(res);
        goto error;
    }
    PQclear(res);
    resetPQExpBuffer(query);

    if (verbose)
        fprintf(stderr,
                _("%s: streaming initiated\n"),
                progname);

    while (!time_to_abort)
    {
        int         r;
        int         bytes_left;
        int         bytes_written;
        TimestampTz now;
        int         hdr_len;
        XLogRecPtr  cur_record_lsn = InvalidXLogRecPtr;

        if (copybuf != NULL)
        {
            PQfreemem(copybuf);
            copybuf = NULL;
        }

        /*
         * Potentially send a status message to the master
         */
        now = feGetCurrentTimestamp();

        if (outfd != -1 &&
            feTimestampDifferenceExceeds(output_last_fsync, now,
                                         fsync_interval))
        {
            if (!OutputFsync(now))
                goto error;
        }

        if (standby_message_timeout > 0 &&
            feTimestampDifferenceExceeds(last_status, now,
                                         standby_message_timeout))
        {
            /* Time to send feedback! */
            if (!sendFeedback(conn, now, true, false))
                goto error;

            last_status = now;
        }

        /* got SIGHUP, close output file */
        if (outfd != -1 && output_reopen && strcmp(outfile, "-") != 0)
        {
            now = feGetCurrentTimestamp();
            if (!OutputFsync(now))
                goto error;
            close(outfd);
            outfd = -1;
        }
        output_reopen = false;

        /* open the output file, if not open yet */
        if (outfd == -1)
        {
            struct stat statbuf;

            if (strcmp(outfile, "-") == 0)
                outfd = fileno(stdout);
            else
                outfd = open(outfile, O_CREAT | O_APPEND | O_WRONLY | PG_BINARY,
                             S_IRUSR | S_IWUSR);
            if (outfd == -1)
            {
                fprintf(stderr,
                        _("%s: could not open log file \"%s\": %s\n"),
                        progname, outfile, strerror(errno));
                goto error;
            }

            if (fstat(outfd, &statbuf) != 0)
                fprintf(stderr,
                        _("%s: could not stat file \"%s\": %s\n"),
                        progname, outfile, strerror(errno));

            output_isfile = S_ISREG(statbuf.st_mode) && !isatty(outfd);
        }

        r = PQgetCopyData(conn, &copybuf, 1);
        if (r == 0)
        {
            /*
             * In async mode, and no data available. We block on reading but
             * not more than the specified timeout, so that we can send a
             * response back to the client.
             */
            fd_set      input_mask;
            TimestampTz message_target = 0;
            TimestampTz fsync_target = 0;
            struct timeval timeout;
            struct timeval *timeoutptr = NULL;

            if (PQsocket(conn) < 0)
            {
                fprintf(stderr,
                        _("%s: invalid socket: %s"),
                        progname, PQerrorMessage(conn));
                goto error;
            }

            FD_ZERO(&input_mask);
            FD_SET(PQsocket(conn), &input_mask);

            /* Compute when we need to wakeup to send a keepalive message. */
            if (standby_message_timeout)
                message_target = last_status + (standby_message_timeout - 1) *
                    ((int64) 1000);

            /* Compute when we need to wakeup to fsync the output file. */
            if (fsync_interval > 0 && output_needs_fsync)
                fsync_target = output_last_fsync + (fsync_interval - 1) *
                    ((int64) 1000);

            /* Now compute when to wakeup. */
            if (message_target > 0 || fsync_target > 0)
            {
                TimestampTz targettime;
                long        secs;
                int         usecs;

                targettime = message_target;

                if (fsync_target > 0 && fsync_target < targettime)
                    targettime = fsync_target;

                feTimestampDifference(now,
                                      targettime,
                                      &secs,
                                      &usecs);
                if (secs <= 0)
                    timeout.tv_sec = 1; /* Always sleep at least 1 sec */
                else
                    timeout.tv_sec = secs;
                timeout.tv_usec = usecs;
                timeoutptr = &timeout;
            }

            r = select(PQsocket(conn) + 1, &input_mask, NULL, NULL, timeoutptr);
            if (r == 0 || (r < 0 && errno == EINTR))
            {
                /*
                 * Got a timeout or signal. Continue the loop and either
                 * deliver a status packet to the server or just go back into
                 * blocking.
                 */
                continue;
            }
            else if (r < 0)
            {
                fprintf(stderr, _("%s: select() failed: %s\n"),
                        progname, strerror(errno));
                goto error;
            }

            /* Else there is actually data on the socket */
            if (PQconsumeInput(conn) == 0)
            {
                fprintf(stderr,
                        _("%s: could not receive data from WAL stream: %s"),
                        progname, PQerrorMessage(conn));
                goto error;
            }
            continue;
        }

        /* End of copy stream */
        if (r == -1)
            break;

        /* Failure while reading the copy stream */
        if (r == -2)
        {
            fprintf(stderr, _("%s: could not read COPY data: %s"),
                    progname, PQerrorMessage(conn));
            goto error;
        }

        /* Check the message type. */
        if (copybuf[0] == 'k')
        {
            int         pos;
            bool        replyRequested;
            XLogRecPtr  walEnd;
            bool        endposReached = false;

            /*
             * Parse the keepalive message, enclosed in the CopyData message.
             * We just check if the server requested a reply, and ignore the
             * rest.
             */
            pos = 1;            /* skip msgtype 'k' */
            walEnd = fe_recvint64(&copybuf[pos]);
            output_written_lsn = Max(walEnd, output_written_lsn);

            pos += 8;           /* read walEnd */

            pos += 8;           /* skip sendTime */

            if (r < pos + 1)
            {
                fprintf(stderr, _("%s: streaming header too small: %d\n"),
                        progname, r);
                goto error;
            }
            replyRequested = copybuf[pos];

            if (endpos != InvalidXLogRecPtr && walEnd >= endpos)
            {
                /*
                 * If there's nothing to read on the socket until a keepalive
                 * we know that the server has nothing to send us; and if
                 * walEnd has passed endpos, we know nothing else can have
                 * committed before endpos.  So we can bail out now.
                 */
                endposReached = true;
            }

            /* Send a reply, if necessary */
            if (replyRequested || endposReached)
            {
                if (!flushAndSendFeedback(conn, &now))
                    goto error;
                last_status = now;
            }

            if (endposReached)
            {
                prepareToTerminate(conn, endpos, true, InvalidXLogRecPtr);
                time_to_abort = true;
                break;
            }

            continue;
        }
        else if (copybuf[0] != 'w')
        {
            fprintf(stderr, _("%s: unrecognized streaming header: \"%c\"\n"),
                    progname, copybuf[0]);
            goto error;
        }

        /*
         * Read the header of the XLogData message, enclosed in the CopyData
         * message. We only need the WAL location field (dataStart), the rest
         * of the header is ignored.
         */
        hdr_len = 1;            /* msgtype 'w' */
        hdr_len += 8;           /* dataStart */
        hdr_len += 8;           /* walEnd */
        hdr_len += 8;           /* sendTime */
        if (r < hdr_len + 1)
        {
            fprintf(stderr, _("%s: streaming header too small: %d\n"),
                    progname, r);
            goto error;
        }

        /* Extract WAL location for this block */
        cur_record_lsn = fe_recvint64(&copybuf[1]);

        if (endpos != InvalidXLogRecPtr && cur_record_lsn > endpos)
        {
            /*
             * We've read past our endpoint, so prepare to go away being
             * cautious about what happens to our output data.
             */
            if (!flushAndSendFeedback(conn, &now))
                goto error;
            prepareToTerminate(conn, endpos, false, cur_record_lsn);
            time_to_abort = true;
            break;
        }

        output_written_lsn = Max(cur_record_lsn, output_written_lsn);

        bytes_left = r - hdr_len;
        bytes_written = 0;

        /* signal that a fsync is needed */
        output_needs_fsync = true;

        while (bytes_left)
        {
            int         ret;

            ret = write(outfd,
                        copybuf + hdr_len + bytes_written,
                        bytes_left);

            if (ret < 0)
            {
                fprintf(stderr,
                        _("%s: could not write %u bytes to log file \"%s\": %s\n"),
                        progname, bytes_left, outfile,
                        strerror(errno));
                goto error;
            }

            /* Write was successful, advance our position */
            bytes_written += ret;
            bytes_left -= ret;
        }

        if (write(outfd, "\n", 1) != 1)
        {
            fprintf(stderr,
                    _("%s: could not write %u bytes to log file \"%s\": %s\n"),
                    progname, 1, outfile,
                    strerror(errno));
            goto error;
        }

        if (endpos != InvalidXLogRecPtr && cur_record_lsn == endpos)
        {
            /* endpos was exactly the record we just processed, we're done */
            if (!flushAndSendFeedback(conn, &now))
                goto error;
            prepareToTerminate(conn, endpos, false, cur_record_lsn);
            time_to_abort = true;
            break;
        }
    }

    res = PQgetResult(conn);
    if (PQresultStatus(res) == PGRES_COPY_OUT)
    {
        /*
         * We're doing a client-initiated clean exit and have sent CopyDone to
         * the server. We've already sent replay confirmation and fsync'd so
         * we can just clean up the connection now.
         */
        goto error;
    }
    else if (PQresultStatus(res) != PGRES_COMMAND_OK)
    {
        fprintf(stderr,
                _("%s: unexpected termination of replication stream: %s"),
                progname, PQresultErrorMessage(res));
        goto error;
    }
    PQclear(res);

    if (outfd != -1 && strcmp(outfile, "-") != 0)
    {
        TimestampTz t = feGetCurrentTimestamp();

        /* no need to jump to error on failure here, we're finishing anyway */
        OutputFsync(t);

        if (close(outfd) != 0)
            fprintf(stderr, _("%s: could not close file \"%s\": %s\n"),
                    progname, outfile, strerror(errno));
    }
    outfd = -1;
error:
    if (copybuf != NULL)
    {
        PQfreemem(copybuf);
        copybuf = NULL;
    }
    destroyPQExpBuffer(query);
    PQfinish(conn);
    conn = NULL;
}

/*
 * Unfortunately we can't do sensible signal handling on windows...
 */
#ifndef WIN32

/*
 * When sigint is called, just tell the system to exit at the next possible
 * moment.
 */
static void
sigint_handler(int signum)
{
    time_to_abort = true;
}

/*
 * Trigger the output file to be reopened.
 */
static void
sighup_handler(int signum)
{
    output_reopen = true;
}
#endif


int
main(int argc, char **argv)
{
    static struct option long_options[] = {
/* general options */
        {"file", required_argument, NULL, 'f'},
        {"fsync-interval", required_argument, NULL, 'F'},
        {"no-loop", no_argument, NULL, 'n'},
        {"verbose", no_argument, NULL, 'v'},
        {"version", no_argument, NULL, 'V'},
        {"help", no_argument, NULL, '?'},
/* connection options */
        {"dbname", required_argument, NULL, 'd'},
        {"host", required_argument, NULL, 'h'},
        {"port", required_argument, NULL, 'p'},
        {"username", required_argument, NULL, 'U'},
        {"no-password", no_argument, NULL, 'w'},
        {"password", no_argument, NULL, 'W'},
/* replication options */
        {"startpos", required_argument, NULL, 'I'},
        {"endpos", required_argument, NULL, 'E'},
        {"option", required_argument, NULL, 'o'},
        {"plugin", required_argument, NULL, 'P'},
        {"status-interval", required_argument, NULL, 's'},
        {"slot", required_argument, NULL, 'S'},
/* action */
        {"create-slot", no_argument, NULL, 1},
        {"start", no_argument, NULL, 2},
        {"drop-slot", no_argument, NULL, 3},
        {"if-not-exists", no_argument, NULL, 4},
        {NULL, 0, NULL, 0}
    };
    int         c;
    int         option_index;
    uint32      hi,
                lo;
    char       *db_name;

    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_recvlogical (PostgreSQL) " PG_VERSION);
            exit(0);
        }
    }

    while ((c = getopt_long(argc, argv, "E:f:F:nvd:h:p:U:wWI:o:P:s:S:",
                            long_options, &option_index)) != -1)
    {
        switch (c)
        {
/* general options */
            case 'f':
                outfile = pg_strdup(optarg);
                break;
            case 'F':
                fsync_interval = atoi(optarg) * 1000;
                if (fsync_interval < 0)
                {
                    fprintf(stderr, _("%s: invalid fsync interval \"%s\"\n"),
                            progname, optarg);
                    exit(1);
                }
                break;
            case 'n':
                noloop = 1;
                break;
            case 'v':
                verbose++;
                break;
/* connection options */
            case 'd':
                dbname = pg_strdup(optarg);
                break;
            case 'h':
                dbhost = pg_strdup(optarg);
                break;
            case 'p':
                if (atoi(optarg) <= 0)
                {
                    fprintf(stderr, _("%s: invalid port number \"%s\"\n"),
                            progname, optarg);
                    exit(1);
                }
                dbport = pg_strdup(optarg);
                break;
            case 'U':
                dbuser = pg_strdup(optarg);
                break;
            case 'w':
                dbgetpassword = -1;
                break;
            case 'W':
                dbgetpassword = 1;
                break;
/* replication options */
            case 'I':
                if (sscanf(optarg, "%X/%X", &hi, &lo) != 2)
                {
                    fprintf(stderr,
                            _("%s: could not parse start position \"%s\"\n"),
                            progname, optarg);
                    exit(1);
                }
                startpos = ((uint64) hi) << 32 | lo;
                break;
            case 'E':
                if (sscanf(optarg, "%X/%X", &hi, &lo) != 2)
                {
                    fprintf(stderr,
                            _("%s: could not parse end position \"%s\"\n"),
                            progname, optarg);
                    exit(1);
                }
                endpos = ((uint64) hi) << 32 | lo;
                break;
            case 'o':
                {
                    char       *data = pg_strdup(optarg);
                    char       *val = strchr(data, '=');

                    if (val != NULL)
                    {
                        /* remove =; separate data from val */
                        *val = '\0';
                        val++;
                    }

                    noptions += 1;
                    options = pg_realloc(options, sizeof(char *) * noptions * 2);

                    options[(noptions - 1) * 2] = data;
                    options[(noptions - 1) * 2 + 1] = val;
                }

                break;
            case 'P':
                plugin = pg_strdup(optarg);
                break;
            case 's':
                standby_message_timeout = atoi(optarg) * 1000;
                if (standby_message_timeout < 0)
                {
                    fprintf(stderr, _("%s: invalid status interval \"%s\"\n"),
                            progname, optarg);
                    exit(1);
                }
                break;
            case 'S':
                replication_slot = pg_strdup(optarg);
                break;
/* action */
            case 1:
                do_create_slot = true;
                break;
            case 2:
                do_start_slot = true;
                break;
            case 3:
                do_drop_slot = true;
                break;
            case 4:
                slot_exists_ok = true;
                break;

            default:

                /*
                 * getopt_long already emitted a complaint
                 */
                fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                        progname);
                exit(1);
        }
    }

    /*
     * Any non-option arguments?
     */
    if (optind < argc)
    {
        fprintf(stderr,
                _("%s: too many command-line arguments (first is \"%s\")\n"),
                progname, argv[optind]);
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

    /*
     * Required arguments
     */
    if (replication_slot == NULL)
    {
        fprintf(stderr, _("%s: no slot specified\n"), progname);
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

    if (do_start_slot && outfile == NULL)
    {
        fprintf(stderr, _("%s: no target file specified\n"), progname);
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

    if (!do_drop_slot && dbname == NULL)
    {
        fprintf(stderr, _("%s: no database specified\n"), progname);
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

    if (!do_drop_slot && !do_create_slot && !do_start_slot)
    {
        fprintf(stderr, _("%s: at least one action needs to be specified\n"), progname);
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

    if (do_drop_slot && (do_create_slot || do_start_slot))
    {
        fprintf(stderr, _("%s: cannot use --create-slot or --start together with --drop-slot\n"), progname);
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

    if (startpos != InvalidXLogRecPtr && (do_create_slot || do_drop_slot))
    {
        fprintf(stderr, _("%s: cannot use --create-slot or --drop-slot together with --startpos\n"), progname);
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

    if (endpos != InvalidXLogRecPtr && !do_start_slot)
    {
        fprintf(stderr,
                _("%s: --endpos may only be specified with --start\n"),
                progname);
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

#ifndef WIN32
    pqsignal(SIGINT, sigint_handler);
    pqsignal(SIGHUP, sighup_handler);
#endif

    /*
     * Obtain a connection to server. This is not really necessary but it
     * helps to get more precise error messages about authentication, required
     * GUC parameters and such.
     */
    conn = GetConnection();
    if (!conn)
        /* Error message already written in GetConnection() */
        exit(1);

    /*
     * Run IDENTIFY_SYSTEM to make sure we connected using a database specific
     * replication connection.
     */
    if (!RunIdentifySystem(conn, NULL, NULL, NULL, &db_name))
        disconnect_and_exit(1);

    if (db_name == NULL)
    {
        fprintf(stderr,
                _("%s: could not establish database-specific replication connection\n"),
                progname);
        disconnect_and_exit(1);
    }

    /* Drop a replication slot. */
    if (do_drop_slot)
    {
        if (verbose)
            fprintf(stderr,
                    _("%s: dropping replication slot \"%s\"\n"),
                    progname, replication_slot);

        if (!DropReplicationSlot(conn, replication_slot))
            disconnect_and_exit(1);
    }

    /* Create a replication slot. */
    if (do_create_slot)
    {
        if (verbose)
            fprintf(stderr,
                    _("%s: creating replication slot \"%s\"\n"),
                    progname, replication_slot);

        if (!CreateReplicationSlot(conn, replication_slot, plugin,
                                   false, slot_exists_ok))
            disconnect_and_exit(1);
        startpos = InvalidXLogRecPtr;
    }

    if (!do_start_slot)
        disconnect_and_exit(0);

    /* Stream loop */
    while (true)
    {
        StreamLogicalLog();
        if (time_to_abort)
        {
            /*
             * We've been Ctrl-C'ed or reached an exit limit condition. That's
             * not an error, so exit without an errorcode.
             */
            disconnect_and_exit(0);
        }
        else if (noloop)
        {
            fprintf(stderr, _("%s: disconnected\n"), progname);
            exit(1);
        }
        else
        {
            fprintf(stderr,
            /* translator: check source for value for %d */
                    _("%s: disconnected; waiting %d seconds to try again\n"),
                    progname, RECONNECT_SLEEP_TIME);
            pg_usleep(RECONNECT_SLEEP_TIME * 1000000);
        }
    }
}

/*
 * Fsync our output data, and send a feedback message to the server.  Returns
 * true if successful, false otherwise.
 *
 * If successful, *now is updated to the current timestamp just before sending
 * feedback.
 */
static bool
flushAndSendFeedback(PGconn *conn, TimestampTz *now)
{
    /* flush data to disk, so that we send a recent flush pointer */
    if (!OutputFsync(*now))
        return false;
    *now = feGetCurrentTimestamp();
    if (!sendFeedback(conn, *now, true, false))
        return false;

    return true;
}

/*
 * Try to inform the server about of upcoming demise, but don't wait around or
 * retry on failure.
 */
static void
prepareToTerminate(PGconn *conn, XLogRecPtr endpos, bool keepalive, XLogRecPtr lsn)
{
    (void) PQputCopyEnd(conn, NULL);
    (void) PQflush(conn);

    if (verbose)
    {
        if (keepalive)
            fprintf(stderr, "%s: endpos %X/%X reached by keepalive\n",
                    progname,
                    (uint32) (endpos >> 32), (uint32) endpos);
        else
            fprintf(stderr, "%s: endpos %X/%X reached by record at %X/%X\n",
                    progname, (uint32) (endpos >> 32), (uint32) (endpos),
                    (uint32) (lsn >> 32), (uint32) lsn);

    }
}