common.c

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/*
 * psql - the PostgreSQL interactive terminal
 *
 * Copyright (c) 2000-2021, PostgreSQL Global Development Group
 *
 * src/bin/psql/common.c
 */
#include "postgres_fe.h"

#include <ctype.h>
#include <limits.h>
#include <math.h>
#include <signal.h>
#ifndef WIN32
#include <unistd.h>             /* for write() */
#else
#include <io.h>                 /* for _write() */
#include <win32.h>
#endif

#include "command.h"
#include "common.h"
#include "common/logging.h"
#include "copy.h"
#include "crosstabview.h"
#include "fe_utils/cancel.h"
#include "fe_utils/mbprint.h"
#include "fe_utils/string_utils.h"
#include "portability/instr_time.h"
#include "settings.h"

static bool DescribeQuery(const char *query, double *elapsed_msec);
static bool ExecQueryUsingCursor(const char *query, double *elapsed_msec);
static bool command_no_begin(const char *query);
static bool is_select_command(const char *query);


/*
 * openQueryOutputFile --- attempt to open a query output file
 *
 * fname == NULL selects stdout, else an initial '|' selects a pipe,
 * else plain file.
 *
 * Returns output file pointer into *fout, and is-a-pipe flag into *is_pipe.
 * Caller is responsible for adjusting SIGPIPE state if it's a pipe.
 *
 * On error, reports suitable error message and returns false.
 */
bool
openQueryOutputFile(const char *fname, FILE **fout, bool *is_pipe)
{
    if (!fname || fname[0] == '\0')
    {
        *fout = stdout;
        *is_pipe = false;
    }
    else if (*fname == '|')
    {
        *fout = popen(fname + 1, "w");
        *is_pipe = true;
    }
    else
    {
        *fout = fopen(fname, "w");
        *is_pipe = false;
    }

    if (*fout == NULL)
    {
        pg_log_error("%s: %m", fname);
        return false;
    }

    return true;
}

/*
 * setQFout
 * -- handler for -o command line option and \o command
 *
 * On success, updates pset with the new output file and returns true.
 * On failure, returns false without changing pset state.
 */
bool
setQFout(const char *fname)
{
    FILE       *fout;
    bool        is_pipe;

    /* First make sure we can open the new output file/pipe */
    if (!openQueryOutputFile(fname, &fout, &is_pipe))
        return false;

    /* Close old file/pipe */
    if (pset.queryFout && pset.queryFout != stdout && pset.queryFout != stderr)
    {
        if (pset.queryFoutPipe)
            pclose(pset.queryFout);
        else
            fclose(pset.queryFout);
    }

    pset.queryFout = fout;
    pset.queryFoutPipe = is_pipe;

    /* Adjust SIGPIPE handling appropriately: ignore signal if is_pipe */
    set_sigpipe_trap_state(is_pipe);
    restore_sigpipe_trap();

    return true;
}


/*
 * Variable-fetching callback for flex lexer
 *
 * If the specified variable exists, return its value as a string (malloc'd
 * and expected to be freed by the caller); else return NULL.
 *
 * If "quote" isn't PQUOTE_PLAIN, then return the value suitably quoted and
 * escaped for the specified quoting requirement.  (Failure in escaping
 * should lead to printing an error and returning NULL.)
 *
 * "passthrough" is the pointer previously given to psql_scan_set_passthrough.
 * In psql, passthrough points to a ConditionalStack, which we check to
 * determine whether variable expansion is allowed.
 */
char *
psql_get_variable(const char *varname, PsqlScanQuoteType quote,
                  void *passthrough)
{
    char       *result = NULL;
    const char *value;

    /* In an inactive \if branch, suppress all variable substitutions */
    if (passthrough && !conditional_active((ConditionalStack) passthrough))
        return NULL;

    value = GetVariable(pset.vars, varname);
    if (!value)
        return NULL;

    switch (quote)
    {
        case PQUOTE_PLAIN:
            result = pg_strdup(value);
            break;
        case PQUOTE_SQL_LITERAL:
        case PQUOTE_SQL_IDENT:
            {
                /*
                 * For these cases, we use libpq's quoting functions, which
                 * assume the string is in the connection's client encoding.
                 */
                char       *escaped_value;

                if (!pset.db)
                {
                    pg_log_error("cannot escape without active connection");
                    return NULL;
                }

                if (quote == PQUOTE_SQL_LITERAL)
                    escaped_value =
                        PQescapeLiteral(pset.db, value, strlen(value));
                else
                    escaped_value =
                        PQescapeIdentifier(pset.db, value, strlen(value));

                if (escaped_value == NULL)
                {
                    const char *error = PQerrorMessage(pset.db);

                    pg_log_info("%s", error);
                    return NULL;
                }

                /*
                 * Rather than complicate the lexer's API with a notion of
                 * which free() routine to use, just pay the price of an extra
                 * strdup().
                 */
                result = pg_strdup(escaped_value);
                PQfreemem(escaped_value);
                break;
            }
        case PQUOTE_SHELL_ARG:
            {
                /*
                 * For this we use appendShellStringNoError, which is
                 * encoding-agnostic, which is fine since the shell probably
                 * is too.  In any case, the only special character is "'",
                 * which is not known to appear in valid multibyte characters.
                 */
                PQExpBufferData buf;

                initPQExpBuffer(&buf);
                if (!appendShellStringNoError(&buf, value))
                {
                    pg_log_error("shell command argument contains a newline or carriage return: \"%s\"",
                                 value);
                    free(buf.data);
                    return NULL;
                }
                result = buf.data;
                break;
            }

            /* No default: we want a compiler warning for missing cases */
    }

    return result;
}


/*
 * for backend Notice messages (INFO, WARNING, etc)
 */
void
NoticeProcessor(void *arg, const char *message)
{
    (void) arg;                 /* not used */
    pg_log_info("%s", message);
}



/*
 * Code to support query cancellation
 *
 * Before we start a query, we enable the SIGINT signal catcher to send a
 * cancel request to the backend.
 *
 * SIGINT is supposed to abort all long-running psql operations, not only
 * database queries.  In most places, this is accomplished by checking
 * cancel_pressed during long-running loops.  However, that won't work when
 * blocked on user input (in readline() or fgets()).  In those places, we
 * set sigint_interrupt_enabled true while blocked, instructing the signal
 * catcher to longjmp through sigint_interrupt_jmp.  We assume readline and
 * fgets are coded to handle possible interruption.
 *
 * On Windows, currently this does not work, so control-C is less useful
 * there.
 */
volatile bool sigint_interrupt_enabled = false;

sigjmp_buf  sigint_interrupt_jmp;

static void
psql_cancel_callback(void)
{
#ifndef WIN32
    /* if we are waiting for input, longjmp out of it */
    if (sigint_interrupt_enabled)
    {
        sigint_interrupt_enabled = false;
        siglongjmp(sigint_interrupt_jmp, 1);
    }
#endif

    /* else, set cancel flag to stop any long-running loops */
    cancel_pressed = true;
}

void
psql_setup_cancel_handler(void)
{
    setup_cancel_handler(psql_cancel_callback);
}


/* ConnectionUp
 *
 * Returns whether our backend connection is still there.
 */
static bool
ConnectionUp(void)
{
    return PQstatus(pset.db) != CONNECTION_BAD;
}



/* CheckConnection
 *
 * Verify that we still have a good connection to the backend, and if not,
 * see if it can be restored.
 *
 * Returns true if either the connection was still there, or it could be
 * restored successfully; false otherwise.  If, however, there was no
 * connection and the session is non-interactive, this will exit the program
 * with a code of EXIT_BADCONN.
 */
static bool
CheckConnection(void)
{
    bool        OK;

    OK = ConnectionUp();
    if (!OK)
    {
        if (!pset.cur_cmd_interactive)
        {
            pg_log_fatal("connection to server was lost");
            exit(EXIT_BADCONN);
        }

        fprintf(stderr, _("The connection to the server was lost. Attempting reset: "));
        PQreset(pset.db);
        OK = ConnectionUp();
        if (!OK)
        {
            fprintf(stderr, _("Failed.\n"));

            /*
             * Transition to having no connection; but stash away the failed
             * connection so that we can still refer to its parameters in a
             * later \connect attempt.  Keep the state cleanup here in sync
             * with do_connect().
             */
            if (pset.dead_conn)
                PQfinish(pset.dead_conn);
            pset.dead_conn = pset.db;
            pset.db = NULL;
            ResetCancelConn();
            UnsyncVariables();
        }
        else
        {
            fprintf(stderr, _("Succeeded.\n"));

            /*
             * Re-sync, just in case anything changed.  Keep this in sync with
             * do_connect().
             */
            SyncVariables();
            connection_warnings(false); /* Must be after SyncVariables */
        }
    }

    return OK;
}




/*
 * AcceptResult
 *
 * Checks whether a result is valid, giving an error message if necessary;
 * and ensures that the connection to the backend is still up.
 *
 * Returns true for valid result, false for error state.
 */
static bool
AcceptResult(const PGresult *result)
{
    bool        OK;

    if (!result)
        OK = false;
    else
        switch (PQresultStatus(result))
        {
            case PGRES_COMMAND_OK:
            case PGRES_TUPLES_OK:
            case PGRES_EMPTY_QUERY:
            case PGRES_COPY_IN:
            case PGRES_COPY_OUT:
                /* Fine, do nothing */
                OK = true;
                break;

            case PGRES_BAD_RESPONSE:
            case PGRES_NONFATAL_ERROR:
            case PGRES_FATAL_ERROR:
                OK = false;
                break;

            default:
                OK = false;
                pg_log_error("unexpected PQresultStatus: %d",
                             PQresultStatus(result));
                break;
        }

    if (!OK)
    {
        const char *error = PQerrorMessage(pset.db);

        if (strlen(error))
            pg_log_info("%s", error);

        CheckConnection();
    }

    return OK;
}


/*
 * Set special variables from a query result
 * - ERROR: true/false, whether an error occurred on this query
 * - SQLSTATE: code of error, or "00000" if no error, or "" if unknown
 * - ROW_COUNT: how many rows were returned or affected, or "0"
 * - LAST_ERROR_SQLSTATE: same for last error
 * - LAST_ERROR_MESSAGE: message of last error
 *
 * Note: current policy is to apply this only to the results of queries
 * entered by the user, not queries generated by slash commands.
 */
static void
SetResultVariables(PGresult *results, bool success)
{
    if (success)
    {
        const char *ntuples = PQcmdTuples(results);

        SetVariable(pset.vars, "ERROR", "false");
        SetVariable(pset.vars, "SQLSTATE", "00000");
        SetVariable(pset.vars, "ROW_COUNT", *ntuples ? ntuples : "0");
    }
    else
    {
        const char *code = PQresultErrorField(results, PG_DIAG_SQLSTATE);
        const char *mesg = PQresultErrorField(results, PG_DIAG_MESSAGE_PRIMARY);

        SetVariable(pset.vars, "ERROR", "true");

        /*
         * If there is no SQLSTATE code, use an empty string.  This can happen
         * for libpq-detected errors (e.g., lost connection, ENOMEM).
         */
        if (code == NULL)
            code = "";
        SetVariable(pset.vars, "SQLSTATE", code);
        SetVariable(pset.vars, "ROW_COUNT", "0");
        SetVariable(pset.vars, "LAST_ERROR_SQLSTATE", code);
        SetVariable(pset.vars, "LAST_ERROR_MESSAGE", mesg ? mesg : "");
    }
}


/*
 * ClearOrSaveResult
 *
 * If the result represents an error, remember it for possible display by
 * \errverbose.  Otherwise, just PQclear() it.
 *
 * Note: current policy is to apply this to the results of all queries,
 * including "back door" queries, for debugging's sake.  It's OK to use
 * PQclear() directly on results known to not be error results, however.
 */
static void
ClearOrSaveResult(PGresult *result)
{
    if (result)
    {
        switch (PQresultStatus(result))
        {
            case PGRES_NONFATAL_ERROR:
            case PGRES_FATAL_ERROR:
                if (pset.last_error_result)
                    PQclear(pset.last_error_result);
                pset.last_error_result = result;
                break;

            default:
                PQclear(result);
                break;
        }
    }
}


/*
 * Print microtiming output.  Always print raw milliseconds; if the interval
 * is >= 1 second, also break it down into days/hours/minutes/seconds.
 */
static void
PrintTiming(double elapsed_msec)
{
    double      seconds;
    double      minutes;
    double      hours;
    double      days;

    if (elapsed_msec < 1000.0)
    {
        /* This is the traditional (pre-v10) output format */
        printf(_("Time: %.3f ms\n"), elapsed_msec);
        return;
    }

    /*
     * Note: we could print just seconds, in a format like %06.3f, when the
     * total is less than 1min.  But that's hard to interpret unless we tack
     * on "s" or otherwise annotate it.  Forcing the display to include
     * minutes seems like a better solution.
     */
    seconds = elapsed_msec / 1000.0;
    minutes = floor(seconds / 60.0);
    seconds -= 60.0 * minutes;
    if (minutes < 60.0)
    {
        printf(_("Time: %.3f ms (%02d:%06.3f)\n"),
               elapsed_msec, (int) minutes, seconds);
        return;
    }

    hours = floor(minutes / 60.0);
    minutes -= 60.0 * hours;
    if (hours < 24.0)
    {
        printf(_("Time: %.3f ms (%02d:%02d:%06.3f)\n"),
               elapsed_msec, (int) hours, (int) minutes, seconds);
        return;
    }

    days = floor(hours / 24.0);
    hours -= 24.0 * days;
    printf(_("Time: %.3f ms (%.0f d %02d:%02d:%06.3f)\n"),
           elapsed_msec, days, (int) hours, (int) minutes, seconds);
}


/*
 * PSQLexec
 *
 * This is the way to send "backdoor" queries (those not directly entered
 * by the user). It is subject to -E but not -e.
 *
 * Caller is responsible for handling the ensuing processing if a COPY
 * command is sent.
 *
 * Note: we don't bother to check PQclientEncoding; it is assumed that no
 * caller uses this path to issue "SET CLIENT_ENCODING".
 */
PGresult *
PSQLexec(const char *query)
{
    PGresult   *res;

    if (!pset.db)
    {
        pg_log_error("You are currently not connected to a database.");
        return NULL;
    }

    if (pset.echo_hidden != PSQL_ECHO_HIDDEN_OFF)
    {
        printf(_("********* QUERY **********\n"
                 "%s\n"
                 "**************************\n\n"), query);
        fflush(stdout);
        if (pset.logfile)
        {
            fprintf(pset.logfile,
                    _("********* QUERY **********\n"
                      "%s\n"
                      "**************************\n\n"), query);
            fflush(pset.logfile);
        }

        if (pset.echo_hidden == PSQL_ECHO_HIDDEN_NOEXEC)
            return NULL;
    }

    SetCancelConn(pset.db);

    res = PQexec(pset.db, query);

    ResetCancelConn();

    if (!AcceptResult(res))
    {
        ClearOrSaveResult(res);
        res = NULL;
    }

    return res;
}


/*
 * PSQLexecWatch
 *
 * This function is used for \watch command to send the query to
 * the server and print out the results.
 *
 * Returns 1 if the query executed successfully, 0 if it cannot be repeated,
 * e.g., because of the interrupt, -1 on error.
 */
int
PSQLexecWatch(const char *query, const printQueryOpt *opt, FILE *printQueryFout)
{
    PGresult   *res;
    double      elapsed_msec = 0;
    instr_time  before;
    instr_time  after;
    FILE       *fout;

    if (!pset.db)
    {
        pg_log_error("You are currently not connected to a database.");
        return 0;
    }

    SetCancelConn(pset.db);

    if (pset.timing)
        INSTR_TIME_SET_CURRENT(before);

    res = PQexec(pset.db, query);

    ResetCancelConn();

    if (!AcceptResult(res))
    {
        ClearOrSaveResult(res);
        return 0;
    }

    if (pset.timing)
    {
        INSTR_TIME_SET_CURRENT(after);
        INSTR_TIME_SUBTRACT(after, before);
        elapsed_msec = INSTR_TIME_GET_MILLISEC(after);
    }

    /*
     * If SIGINT is sent while the query is processing, the interrupt will be
     * consumed.  The user's intention, though, is to cancel the entire watch
     * process, so detect a sent cancellation request and exit in this case.
     */
    if (cancel_pressed)
    {
        PQclear(res);
        return 0;
    }

    fout = printQueryFout ? printQueryFout : pset.queryFout;

    switch (PQresultStatus(res))
    {
        case PGRES_TUPLES_OK:
            printQuery(res, opt, fout, false, pset.logfile);
            break;

        case PGRES_COMMAND_OK:
            fprintf(fout, "%s\n%s\n\n", opt->title, PQcmdStatus(res));
            break;

        case PGRES_EMPTY_QUERY:
            pg_log_error("\\watch cannot be used with an empty query");
            PQclear(res);
            return -1;

        case PGRES_COPY_OUT:
        case PGRES_COPY_IN:
        case PGRES_COPY_BOTH:
            pg_log_error("\\watch cannot be used with COPY");
            PQclear(res);
            return -1;

        default:
            pg_log_error("unexpected result status for \\watch");
            PQclear(res);
            return -1;
    }

    PQclear(res);

    fflush(fout);

    /* Possible microtiming output */
    if (pset.timing)
        PrintTiming(elapsed_msec);

    return 1;
}


/*
 * PrintNotifications: check for asynchronous notifications, and print them out
 */
static void
PrintNotifications(void)
{
    PGnotify   *notify;

    PQconsumeInput(pset.db);
    while ((notify = PQnotifies(pset.db)) != NULL)
    {
        /* for backward compatibility, only show payload if nonempty */
        if (notify->extra[0])
            fprintf(pset.queryFout, _("Asynchronous notification \"%s\" with payload \"%s\" received from server process with PID %d.\n"),
                    notify->relname, notify->extra, notify->be_pid);
        else
            fprintf(pset.queryFout, _("Asynchronous notification \"%s\" received from server process with PID %d.\n"),
                    notify->relname, notify->be_pid);
        fflush(pset.queryFout);
        PQfreemem(notify);
        PQconsumeInput(pset.db);
    }
}


/*
 * PrintQueryTuples: assuming query result is OK, print its tuples
 *
 * Returns true if successful, false otherwise.
 */
static bool
PrintQueryTuples(const PGresult *results)
{
    bool        result = true;

    /* write output to \g argument, if any */
    if (pset.gfname)
    {
        FILE       *fout;
        bool        is_pipe;

        if (!openQueryOutputFile(pset.gfname, &fout, &is_pipe))
            return false;
        if (is_pipe)
            disable_sigpipe_trap();

        printQuery(results, &pset.popt, fout, false, pset.logfile);
        if (ferror(fout))
        {
            pg_log_error("could not print result table: %m");
            result = false;
        }

        if (is_pipe)
        {
            pclose(fout);
            restore_sigpipe_trap();
        }
        else
            fclose(fout);
    }
    else
    {
        printQuery(results, &pset.popt, pset.queryFout, false, pset.logfile);
        if (ferror(pset.queryFout))
        {
            pg_log_error("could not print result table: %m");
            result = false;
        }
    }

    return result;
}


/*
 * StoreQueryTuple: assuming query result is OK, save data into variables
 *
 * Returns true if successful, false otherwise.
 */
static bool
StoreQueryTuple(const PGresult *result)
{
    bool        success = true;

    if (PQntuples(result) < 1)
    {
        pg_log_error("no rows returned for \\gset");
        success = false;
    }
    else if (PQntuples(result) > 1)
    {
        pg_log_error("more than one row returned for \\gset");
        success = false;
    }
    else
    {
        int         i;

        for (i = 0; i < PQnfields(result); i++)
        {
            char       *colname = PQfname(result, i);
            char       *varname;
            char       *value;

            /* concatenate prefix and column name */
            varname = psprintf("%s%s", pset.gset_prefix, colname);

            if (VariableHasHook(pset.vars, varname))
            {
                pg_log_warning("attempt to \\gset into specially treated variable \"%s\" ignored",
                               varname);
                continue;
            }

            if (!PQgetisnull(result, 0, i))
                value = PQgetvalue(result, 0, i);
            else
            {
                /* for NULL value, unset rather than set the variable */
                value = NULL;
            }

            if (!SetVariable(pset.vars, varname, value))
            {
                free(varname);
                success = false;
                break;
            }

            free(varname);
        }
    }

    return success;
}


/*
 * ExecQueryTuples: assuming query result is OK, execute each query
 * result field as a SQL statement
 *
 * Returns true if successful, false otherwise.
 */
static bool
ExecQueryTuples(const PGresult *result)
{
    bool        success = true;
    int         nrows = PQntuples(result);
    int         ncolumns = PQnfields(result);
    int         r,
                c;

    /*
     * We must turn off gexec_flag to avoid infinite recursion.  Note that
     * this allows ExecQueryUsingCursor to be applied to the individual query
     * results.  SendQuery prevents it from being applied when fetching the
     * queries-to-execute, because it can't handle recursion either.
     */
    pset.gexec_flag = false;

    for (r = 0; r < nrows; r++)
    {
        for (c = 0; c < ncolumns; c++)
        {
            if (!PQgetisnull(result, r, c))
            {
                const char *query = PQgetvalue(result, r, c);

                /* Abandon execution if cancel_pressed */
                if (cancel_pressed)
                    goto loop_exit;

                /*
                 * ECHO_ALL mode should echo these queries, but SendQuery
                 * assumes that MainLoop did that, so we have to do it here.
                 */
                if (pset.echo == PSQL_ECHO_ALL && !pset.singlestep)
                {
                    puts(query);
                    fflush(stdout);
                }

                if (!SendQuery(query))
                {
                    /* Error - abandon execution if ON_ERROR_STOP */
                    success = false;
                    if (pset.on_error_stop)
                        goto loop_exit;
                }
            }
        }
    }

loop_exit:

    /*
     * Restore state.  We know gexec_flag was on, else we'd not be here. (We
     * also know it'll get turned off at end of command, but that's not ours
     * to do here.)
     */
    pset.gexec_flag = true;

    /* Return true if all queries were successful */
    return success;
}


/*
 * ProcessResult: utility function for use by SendQuery() only
 *
 * When our command string contained a COPY FROM STDIN or COPY TO STDOUT,
 * PQexec() has stopped at the PGresult associated with the first such
 * command.  In that event, we'll marshal data for the COPY and then cycle
 * through any subsequent PGresult objects.
 *
 * When the command string contained no such COPY command, this function
 * degenerates to an AcceptResult() call.
 *
 * Changes its argument to point to the last PGresult of the command string,
 * or NULL if that result was for a COPY TO STDOUT.  (Returning NULL prevents
 * the command status from being printed, which we want in that case so that
 * the status line doesn't get taken as part of the COPY data.)
 *
 * Returns true on complete success, false otherwise.  Possible failure modes
 * include purely client-side problems; check the transaction status for the
 * server-side opinion.
 */
static bool
ProcessResult(PGresult **results)
{
    bool        success = true;
    bool        first_cycle = true;

    for (;;)
    {
        ExecStatusType result_status;
        bool        is_copy;
        PGresult   *next_result;

        if (!AcceptResult(*results))
        {
            /*
             * Failure at this point is always a server-side failure or a
             * failure to submit the command string.  Either way, we're
             * finished with this command string.
             */
            success = false;
            break;
        }

        result_status = PQresultStatus(*results);
        switch (result_status)
        {
            case PGRES_EMPTY_QUERY:
            case PGRES_COMMAND_OK:
            case PGRES_TUPLES_OK:
                is_copy = false;
                break;

            case PGRES_COPY_OUT:
            case PGRES_COPY_IN:
                is_copy = true;
                break;

            default:
                /* AcceptResult() should have caught anything else. */
                is_copy = false;
                pg_log_error("unexpected PQresultStatus: %d", result_status);
                break;
        }

        if (is_copy)
        {
            /*
             * Marshal the COPY data.  Either subroutine will get the
             * connection out of its COPY state, then call PQresultStatus()
             * once and report any error.
             *
             * For COPY OUT, direct the output to pset.copyStream if it's set,
             * otherwise to pset.gfname if it's set, otherwise to queryFout.
             * For COPY IN, use pset.copyStream as data source if it's set,
             * otherwise cur_cmd_source.
             */
            FILE       *copystream;
            PGresult   *copy_result;

            SetCancelConn(pset.db);
            if (result_status == PGRES_COPY_OUT)
            {
                bool        need_close = false;
                bool        is_pipe = false;

                if (pset.copyStream)
                {
                    /* invoked by \copy */
                    copystream = pset.copyStream;
                }
                else if (pset.gfname)
                {
                    /* invoked by \g */
                    if (openQueryOutputFile(pset.gfname,
                                            &copystream, &is_pipe))
                    {
                        need_close = true;
                        if (is_pipe)
                            disable_sigpipe_trap();
                    }
                    else
                        copystream = NULL;  /* discard COPY data entirely */
                }
                else
                {
                    /* fall back to the generic query output stream */
                    copystream = pset.queryFout;
                }

                success = handleCopyOut(pset.db,
                                        copystream,
                                        &copy_result)
                    && success
                    && (copystream != NULL);

                /*
                 * Suppress status printing if the report would go to the same
                 * place as the COPY data just went.  Note this doesn't
                 * prevent error reporting, since handleCopyOut did that.
                 */
                if (copystream == pset.queryFout)
                {
                    PQclear(copy_result);
                    copy_result = NULL;
                }

                if (need_close)
                {
                    /* close \g argument file/pipe */
                    if (is_pipe)
                    {
                        pclose(copystream);
                        restore_sigpipe_trap();
                    }
                    else
                    {
                        fclose(copystream);
                    }
                }
            }
            else
            {
                /* COPY IN */
                copystream = pset.copyStream ? pset.copyStream : pset.cur_cmd_source;
                success = handleCopyIn(pset.db,
                                       copystream,
                                       PQbinaryTuples(*results),
                                       &copy_result) && success;
            }
            ResetCancelConn();

            /*
             * Replace the PGRES_COPY_OUT/IN result with COPY command's exit
             * status, or with NULL if we want to suppress printing anything.
             */
            PQclear(*results);
            *results = copy_result;
        }
        else if (first_cycle)
        {
            /* fast path: no COPY commands; PQexec visited all results */
            break;
        }

        /*
         * Check PQgetResult() again.  In the typical case of a single-command
         * string, it will return NULL.  Otherwise, we'll have other results
         * to process that may include other COPYs.  We keep the last result.
         */
        next_result = PQgetResult(pset.db);
        if (!next_result)
            break;

        PQclear(*results);
        *results = next_result;
        first_cycle = false;
    }

    SetResultVariables(*results, success);

    /* may need this to recover from conn loss during COPY */
    if (!first_cycle && !CheckConnection())
        return false;

    return success;
}


/*
 * PrintQueryStatus: report command status as required
 *
 * Note: Utility function for use by PrintQueryResults() only.
 */
static void
PrintQueryStatus(PGresult *results)
{
    char        buf[16];

    if (!pset.quiet)
    {
        if (pset.popt.topt.format == PRINT_HTML)
        {
            fputs("<p>", pset.queryFout);
            html_escaped_print(PQcmdStatus(results), pset.queryFout);
            fputs("</p>\n", pset.queryFout);
        }
        else
            fprintf(pset.queryFout, "%s\n", PQcmdStatus(results));
    }

    if (pset.logfile)
        fprintf(pset.logfile, "%s\n", PQcmdStatus(results));

    snprintf(buf, sizeof(buf), "%u", (unsigned int) PQoidValue(results));
    SetVariable(pset.vars, "LASTOID", buf);
}


/*
 * PrintQueryResults: print out (or store or execute) query results as required
 *
 * Note: Utility function for use by SendQuery() only.
 *
 * Returns true if the query executed successfully, false otherwise.
 */
static bool
PrintQueryResults(PGresult *results)
{
    bool        success;
    const char *cmdstatus;

    if (!results)
        return false;

    switch (PQresultStatus(results))
    {
        case PGRES_TUPLES_OK:
            /* store or execute or print the data ... */
            if (pset.gset_prefix)
                success = StoreQueryTuple(results);
            else if (pset.gexec_flag)
                success = ExecQueryTuples(results);
            else if (pset.crosstab_flag)
                success = PrintResultsInCrosstab(results);
            else
                success = PrintQueryTuples(results);
            /* if it's INSERT/UPDATE/DELETE RETURNING, also print status */
            cmdstatus = PQcmdStatus(results);
            if (strncmp(cmdstatus, "INSERT", 6) == 0 ||
                strncmp(cmdstatus, "UPDATE", 6) == 0 ||
                strncmp(cmdstatus, "DELETE", 6) == 0)
                PrintQueryStatus(results);
            break;

        case PGRES_COMMAND_OK:
            PrintQueryStatus(results);
            success = true;
            break;

        case PGRES_EMPTY_QUERY:
            success = true;
            break;

        case PGRES_COPY_OUT:
        case PGRES_COPY_IN:
            /* nothing to do here */
            success = true;
            break;

        case PGRES_BAD_RESPONSE:
        case PGRES_NONFATAL_ERROR:
        case PGRES_FATAL_ERROR:
            success = false;
            break;

        default:
            success = false;
            pg_log_error("unexpected PQresultStatus: %d",
                         PQresultStatus(results));
            break;
    }

    fflush(pset.queryFout);

    return success;
}


/*
 * SendQuery: send the query string to the backend
 * (and print out results)
 *
 * Note: This is the "front door" way to send a query. That is, use it to
 * send queries actually entered by the user. These queries will be subject to
 * single step mode.
 * To send "back door" queries (generated by slash commands, etc.) in a
 * controlled way, use PSQLexec().
 *
 * Returns true if the query executed successfully, false otherwise.
 */
bool
SendQuery(const char *query)
{
    PGresult   *results;
    PGTransactionStatusType transaction_status;
    double      elapsed_msec = 0;
    bool        OK = false;
    int         i;
    bool        on_error_rollback_savepoint = false;
    static bool on_error_rollback_warning = false;

    if (!pset.db)
    {
        pg_log_error("You are currently not connected to a database.");
        goto sendquery_cleanup;
    }

    if (pset.singlestep)
    {
        char        buf[3];

        fflush(stderr);
        printf(_("***(Single step mode: verify command)*******************************************\n"
                 "%s\n"
                 "***(press return to proceed or enter x and return to cancel)********************\n"),
               query);
        fflush(stdout);
        if (fgets(buf, sizeof(buf), stdin) != NULL)
            if (buf[0] == 'x')
                goto sendquery_cleanup;
        if (cancel_pressed)
            goto sendquery_cleanup;
    }
    else if (pset.echo == PSQL_ECHO_QUERIES)
    {
        puts(query);
        fflush(stdout);
    }

    if (pset.logfile)
    {
        fprintf(pset.logfile,
                _("********* QUERY **********\n"
                  "%s\n"
                  "**************************\n\n"), query);
        fflush(pset.logfile);
    }

    SetCancelConn(pset.db);

    transaction_status = PQtransactionStatus(pset.db);

    if (transaction_status == PQTRANS_IDLE &&
        !pset.autocommit &&
        !command_no_begin(query))
    {
        results = PQexec(pset.db, "BEGIN");
        if (PQresultStatus(results) != PGRES_COMMAND_OK)
        {
            pg_log_info("%s", PQerrorMessage(pset.db));
            ClearOrSaveResult(results);
            ResetCancelConn();
            goto sendquery_cleanup;
        }
        ClearOrSaveResult(results);
        transaction_status = PQtransactionStatus(pset.db);
    }

    if (transaction_status == PQTRANS_INTRANS &&
        pset.on_error_rollback != PSQL_ERROR_ROLLBACK_OFF &&
        (pset.cur_cmd_interactive ||
         pset.on_error_rollback == PSQL_ERROR_ROLLBACK_ON))
    {
        if (on_error_rollback_warning == false && pset.sversion < 80000)
        {
            char        sverbuf[32];

            pg_log_warning("The server (version %s) does not support savepoints for ON_ERROR_ROLLBACK.",
                           formatPGVersionNumber(pset.sversion, false,
                                                 sverbuf, sizeof(sverbuf)));
            on_error_rollback_warning = true;
        }
        else
        {
            results = PQexec(pset.db, "SAVEPOINT pg_psql_temporary_savepoint");
            if (PQresultStatus(results) != PGRES_COMMAND_OK)
            {
                pg_log_info("%s", PQerrorMessage(pset.db));
                ClearOrSaveResult(results);
                ResetCancelConn();
                goto sendquery_cleanup;
            }
            ClearOrSaveResult(results);
            on_error_rollback_savepoint = true;
        }
    }

    if (pset.gdesc_flag)
    {
        /* Describe query's result columns, without executing it */
        OK = DescribeQuery(query, &elapsed_msec);
        ResetCancelConn();
        results = NULL;         /* PQclear(NULL) does nothing */
    }
    else if (pset.fetch_count <= 0 || pset.gexec_flag ||
             pset.crosstab_flag || !is_select_command(query))
    {
        /* Default fetch-it-all-and-print mode */
        instr_time  before,
                    after;

        if (pset.timing)
            INSTR_TIME_SET_CURRENT(before);

        results = PQexec(pset.db, query);

        /* these operations are included in the timing result: */
        ResetCancelConn();
        OK = ProcessResult(&results);

        if (pset.timing)
        {
            INSTR_TIME_SET_CURRENT(after);
            INSTR_TIME_SUBTRACT(after, before);
            elapsed_msec = INSTR_TIME_GET_MILLISEC(after);
        }

        /* but printing results isn't: */
        if (OK && results)
            OK = PrintQueryResults(results);
    }
    else
    {
        /* Fetch-in-segments mode */
        OK = ExecQueryUsingCursor(query, &elapsed_msec);
        ResetCancelConn();
        results = NULL;         /* PQclear(NULL) does nothing */
    }

    if (!OK && pset.echo == PSQL_ECHO_ERRORS)
        pg_log_info("STATEMENT:  %s", query);

    /* If we made a temporary savepoint, possibly release/rollback */
    if (on_error_rollback_savepoint)
    {
        const char *svptcmd = NULL;

        transaction_status = PQtransactionStatus(pset.db);

        switch (transaction_status)
        {
            case PQTRANS_INERROR:
                /* We always rollback on an error */
                svptcmd = "ROLLBACK TO pg_psql_temporary_savepoint";
                break;

            case PQTRANS_IDLE:
                /* If they are no longer in a transaction, then do nothing */
                break;

            case PQTRANS_INTRANS:

                /*
                 * Do nothing if they are messing with savepoints themselves:
                 * If the user did COMMIT AND CHAIN, RELEASE or ROLLBACK, our
                 * savepoint is gone. If they issued a SAVEPOINT, releasing
                 * ours would remove theirs.
                 */
                if (results &&
                    (strcmp(PQcmdStatus(results), "COMMIT") == 0 ||
                     strcmp(PQcmdStatus(results), "SAVEPOINT") == 0 ||
                     strcmp(PQcmdStatus(results), "RELEASE") == 0 ||
                     strcmp(PQcmdStatus(results), "ROLLBACK") == 0))
                    svptcmd = NULL;
                else
                    svptcmd = "RELEASE pg_psql_temporary_savepoint";
                break;

            case PQTRANS_ACTIVE:
            case PQTRANS_UNKNOWN:
            default:
                OK = false;
                /* PQTRANS_UNKNOWN is expected given a broken connection. */
                if (transaction_status != PQTRANS_UNKNOWN || ConnectionUp())
                    pg_log_error("unexpected transaction status (%d)",
                                 transaction_status);
                break;
        }

        if (svptcmd)
        {
            PGresult   *svptres;

            svptres = PQexec(pset.db, svptcmd);
            if (PQresultStatus(svptres) != PGRES_COMMAND_OK)
            {
                pg_log_info("%s", PQerrorMessage(pset.db));
                ClearOrSaveResult(svptres);
                OK = false;

                PQclear(results);
                ResetCancelConn();
                goto sendquery_cleanup;
            }
            PQclear(svptres);
        }
    }

    ClearOrSaveResult(results);

    /* Possible microtiming output */
    if (pset.timing)
        PrintTiming(elapsed_msec);

    /* check for events that may occur during query execution */

    if (pset.encoding != PQclientEncoding(pset.db) &&
        PQclientEncoding(pset.db) >= 0)
    {
        /* track effects of SET CLIENT_ENCODING */
        pset.encoding = PQclientEncoding(pset.db);
        pset.popt.topt.encoding = pset.encoding;
        SetVariable(pset.vars, "ENCODING",
                    pg_encoding_to_char(pset.encoding));
    }

    PrintNotifications();

    /* perform cleanup that should occur after any attempted query */

sendquery_cleanup:

    /* reset \g's output-to-filename trigger */
    if (pset.gfname)
    {
        free(pset.gfname);
        pset.gfname = NULL;
    }

    /* restore print settings if \g changed them */
    if (pset.gsavepopt)
    {
        restorePsetInfo(&pset.popt, pset.gsavepopt);
        pset.gsavepopt = NULL;
    }

    /* reset \gset trigger */
    if (pset.gset_prefix)
    {
        free(pset.gset_prefix);
        pset.gset_prefix = NULL;
    }

    /* reset \gdesc trigger */
    pset.gdesc_flag = false;

    /* reset \gexec trigger */
    pset.gexec_flag = false;

    /* reset \crosstabview trigger */
    pset.crosstab_flag = false;
    for (i = 0; i < lengthof(pset.ctv_args); i++)
    {
        pg_free(pset.ctv_args[i]);
        pset.ctv_args[i] = NULL;
    }

    return OK;
}


/*
 * DescribeQuery: describe the result columns of a query, without executing it
 *
 * Returns true if the operation executed successfully, false otherwise.
 *
 * If pset.timing is on, total query time (exclusive of result-printing) is
 * stored into *elapsed_msec.
 */
static bool
DescribeQuery(const char *query, double *elapsed_msec)
{
    PGresult   *results;
    bool        OK;
    instr_time  before,
                after;

    *elapsed_msec = 0;

    if (pset.timing)
        INSTR_TIME_SET_CURRENT(before);

    /*
     * To parse the query but not execute it, we prepare it, using the unnamed
     * prepared statement.  This is invisible to psql users, since there's no
     * way to access the unnamed prepared statement from psql user space. The
     * next Parse or Query protocol message would overwrite the statement
     * anyway.  (So there's no great need to clear it when done, which is a
     * good thing because libpq provides no easy way to do that.)
     */
    results = PQprepare(pset.db, "", query, 0, NULL);
    if (PQresultStatus(results) != PGRES_COMMAND_OK)
    {
        pg_log_info("%s", PQerrorMessage(pset.db));
        SetResultVariables(results, false);
        ClearOrSaveResult(results);
        return false;
    }
    PQclear(results);

    results = PQdescribePrepared(pset.db, "");
    OK = AcceptResult(results) &&
        (PQresultStatus(results) == PGRES_COMMAND_OK);
    if (OK && results)
    {
        if (PQnfields(results) > 0)
        {
            PQExpBufferData buf;
            int         i;

            initPQExpBuffer(&buf);

            printfPQExpBuffer(&buf,
                              "SELECT name AS \"%s\", pg_catalog.format_type(tp, tpm) AS \"%s\"\n"
                              "FROM (VALUES ",
                              gettext_noop("Column"),
                              gettext_noop("Type"));

            for (i = 0; i < PQnfields(results); i++)
            {
                const char *name;
                char       *escname;

                if (i > 0)
                    appendPQExpBufferStr(&buf, ",");

                name = PQfname(results, i);
                escname = PQescapeLiteral(pset.db, name, strlen(name));

                if (escname == NULL)
                {
                    pg_log_info("%s", PQerrorMessage(pset.db));
                    PQclear(results);
                    termPQExpBuffer(&buf);
                    return false;
                }

                appendPQExpBuffer(&buf, "(%s, '%u'::pg_catalog.oid, %d)",
                                  escname,
                                  PQftype(results, i),
                                  PQfmod(results, i));

                PQfreemem(escname);
            }

            appendPQExpBufferStr(&buf, ") s(name, tp, tpm)");
            PQclear(results);

            results = PQexec(pset.db, buf.data);
            OK = AcceptResult(results);

            if (pset.timing)
            {
                INSTR_TIME_SET_CURRENT(after);
                INSTR_TIME_SUBTRACT(after, before);
                *elapsed_msec += INSTR_TIME_GET_MILLISEC(after);
            }

            if (OK && results)
                OK = PrintQueryResults(results);

            termPQExpBuffer(&buf);
        }
        else
            fprintf(pset.queryFout,
                    _("The command has no result, or the result has no columns.\n"));
    }

    SetResultVariables(results, OK);
    ClearOrSaveResult(results);

    return OK;
}


/*
 * ExecQueryUsingCursor: run a SELECT-like query using a cursor
 *
 * This feature allows result sets larger than RAM to be dealt with.
 *
 * Returns true if the query executed successfully, false otherwise.
 *
 * If pset.timing is on, total query time (exclusive of result-printing) is
 * stored into *elapsed_msec.
 */
static bool
ExecQueryUsingCursor(const char *query, double *elapsed_msec)
{
    bool        OK = true;
    PGresult   *results;
    PQExpBufferData buf;
    printQueryOpt my_popt = pset.popt;
    FILE       *fout;
    bool        is_pipe;
    bool        is_pager = false;
    bool        started_txn = false;
    int64       total_tuples = 0;
    int         ntuples;
    int         fetch_count;
    char        fetch_cmd[64];
    instr_time  before,
                after;
    int         flush_error;

    *elapsed_msec = 0;

    /* initialize print options for partial table output */
    my_popt.topt.start_table = true;
    my_popt.topt.stop_table = false;
    my_popt.topt.prior_records = 0;

    if (pset.timing)
        INSTR_TIME_SET_CURRENT(before);

    /* if we're not in a transaction, start one */
    if (PQtransactionStatus(pset.db) == PQTRANS_IDLE)
    {
        results = PQexec(pset.db, "BEGIN");
        OK = AcceptResult(results) &&
            (PQresultStatus(results) == PGRES_COMMAND_OK);
        ClearOrSaveResult(results);
        if (!OK)
            return false;
        started_txn = true;
    }

    /* Send DECLARE CURSOR */
    initPQExpBuffer(&buf);
    appendPQExpBuffer(&buf, "DECLARE _psql_cursor NO SCROLL CURSOR FOR\n%s",
                      query);

    results = PQexec(pset.db, buf.data);
    OK = AcceptResult(results) &&
        (PQresultStatus(results) == PGRES_COMMAND_OK);
    if (!OK)
        SetResultVariables(results, OK);
    ClearOrSaveResult(results);
    termPQExpBuffer(&buf);
    if (!OK)
        goto cleanup;

    if (pset.timing)
    {
        INSTR_TIME_SET_CURRENT(after);
        INSTR_TIME_SUBTRACT(after, before);
        *elapsed_msec += INSTR_TIME_GET_MILLISEC(after);
    }

    /*
     * In \gset mode, we force the fetch count to be 2, so that we will throw
     * the appropriate error if the query returns more than one row.
     */
    if (pset.gset_prefix)
        fetch_count = 2;
    else
        fetch_count = pset.fetch_count;

    snprintf(fetch_cmd, sizeof(fetch_cmd),
             "FETCH FORWARD %d FROM _psql_cursor",
             fetch_count);

    /* prepare to write output to \g argument, if any */
    if (pset.gfname)
    {
        if (!openQueryOutputFile(pset.gfname, &fout, &is_pipe))
        {
            OK = false;
            goto cleanup;
        }
        if (is_pipe)
            disable_sigpipe_trap();
    }
    else
    {
        fout = pset.queryFout;
        is_pipe = false;        /* doesn't matter */
    }

    /* clear any pre-existing error indication on the output stream */
    clearerr(fout);

    for (;;)
    {
        if (pset.timing)
            INSTR_TIME_SET_CURRENT(before);

        /* get fetch_count tuples at a time */
        results = PQexec(pset.db, fetch_cmd);

        if (pset.timing)
        {
            INSTR_TIME_SET_CURRENT(after);
            INSTR_TIME_SUBTRACT(after, before);
            *elapsed_msec += INSTR_TIME_GET_MILLISEC(after);
        }

        if (PQresultStatus(results) != PGRES_TUPLES_OK)
        {
            /* shut down pager before printing error message */
            if (is_pager)
            {
                ClosePager(fout);
                is_pager = false;
            }

            OK = AcceptResult(results);
            Assert(!OK);
            SetResultVariables(results, OK);
            ClearOrSaveResult(results);
            break;
        }

        if (pset.gset_prefix)
        {
            /* StoreQueryTuple will complain if not exactly one row */
            OK = StoreQueryTuple(results);
            ClearOrSaveResult(results);
            break;
        }

        /*
         * Note we do not deal with \gdesc, \gexec or \crosstabview modes here
         */

        ntuples = PQntuples(results);
        total_tuples += ntuples;

        if (ntuples < fetch_count)
        {
            /* this is the last result set, so allow footer decoration */
            my_popt.topt.stop_table = true;
        }
        else if (fout == stdout && !is_pager)
        {
            /*
             * If query requires multiple result sets, hack to ensure that
             * only one pager instance is used for the whole mess
             */
            fout = PageOutput(INT_MAX, &(my_popt.topt));
            is_pager = true;
        }

        printQuery(results, &my_popt, fout, is_pager, pset.logfile);

        ClearOrSaveResult(results);

        /* after the first result set, disallow header decoration */
        my_popt.topt.start_table = false;
        my_popt.topt.prior_records += ntuples;

        /*
         * Make sure to flush the output stream, so intermediate results are
         * visible to the client immediately.  We check the results because if
         * the pager dies/exits/etc, there's no sense throwing more data at
         * it.
         */
        flush_error = fflush(fout);

        /*
         * Check if we are at the end, if a cancel was pressed, or if there
         * were any errors either trying to flush out the results, or more
         * generally on the output stream at all.  If we hit any errors
         * writing things to the stream, we presume $PAGER has disappeared and
         * stop bothering to pull down more data.
         */
        if (ntuples < fetch_count || cancel_pressed || flush_error ||
            ferror(fout))
            break;
    }

    if (pset.gfname)
    {
        /* close \g argument file/pipe */
        if (is_pipe)
        {
            pclose(fout);
            restore_sigpipe_trap();
        }
        else
            fclose(fout);
    }
    else if (is_pager)
    {
        /* close transient pager */
        ClosePager(fout);
    }

    if (OK)
    {
        /*
         * We don't have a PGresult here, and even if we did it wouldn't have
         * the right row count, so fake SetResultVariables().  In error cases,
         * we already set the result variables above.
         */
        char        buf[32];

        SetVariable(pset.vars, "ERROR", "false");
        SetVariable(pset.vars, "SQLSTATE", "00000");
        snprintf(buf, sizeof(buf), INT64_FORMAT, total_tuples);
        SetVariable(pset.vars, "ROW_COUNT", buf);
    }

cleanup:
    if (pset.timing)
        INSTR_TIME_SET_CURRENT(before);

    /*
     * We try to close the cursor on either success or failure, but on failure
     * ignore the result (it's probably just a bleat about being in an aborted
     * transaction)
     */
    results = PQexec(pset.db, "CLOSE _psql_cursor");
    if (OK)
    {
        OK = AcceptResult(results) &&
            (PQresultStatus(results) == PGRES_COMMAND_OK);
        ClearOrSaveResult(results);
    }
    else
        PQclear(results);

    if (started_txn)
    {
        results = PQexec(pset.db, OK ? "COMMIT" : "ROLLBACK");
        OK &= AcceptResult(results) &&
            (PQresultStatus(results) == PGRES_COMMAND_OK);
        ClearOrSaveResult(results);
    }

    if (pset.timing)
    {
        INSTR_TIME_SET_CURRENT(after);
        INSTR_TIME_SUBTRACT(after, before);
        *elapsed_msec += INSTR_TIME_GET_MILLISEC(after);
    }

    return OK;
}


/*
 * Advance the given char pointer over white space and SQL comments.
 */
static const char *
skip_white_space(const char *query)
{
    int         cnestlevel = 0; /* slash-star comment nest level */

    while (*query)
    {
        int         mblen = PQmblenBounded(query, pset.encoding);

        /*
         * Note: we assume the encoding is a superset of ASCII, so that for
         * example "query[0] == '/'" is meaningful.  However, we do NOT assume
         * that the second and subsequent bytes of a multibyte character
         * couldn't look like ASCII characters; so it is critical to advance
         * by mblen, not 1, whenever we haven't exactly identified the
         * character we are skipping over.
         */
        if (isspace((unsigned char) *query))
            query += mblen;
        else if (query[0] == '/' && query[1] == '*')
        {
            cnestlevel++;
            query += 2;
        }
        else if (cnestlevel > 0 && query[0] == '*' && query[1] == '/')
        {
            cnestlevel--;
            query += 2;
        }
        else if (cnestlevel == 0 && query[0] == '-' && query[1] == '-')
        {
            query += 2;

            /*
             * We have to skip to end of line since any slash-star inside the
             * -- comment does NOT start a slash-star comment.
             */
            while (*query)
            {
                if (*query == '\n')
                {
                    query++;
                    break;
                }
                query += PQmblenBounded(query, pset.encoding);
            }
        }
        else if (cnestlevel > 0)
            query += mblen;
        else
            break;              /* found first token */
    }

    return query;
}


/*
 * Check whether a command is one of those for which we should NOT start
 * a new transaction block (ie, send a preceding BEGIN).
 *
 * These include the transaction control statements themselves, plus
 * certain statements that the backend disallows inside transaction blocks.
 */
static bool
command_no_begin(const char *query)
{
    int         wordlen;

    /*
     * First we must advance over any whitespace and comments.
     */
    query = skip_white_space(query);

    /*
     * Check word length (since "beginx" is not "begin").
     */
    wordlen = 0;
    while (isalpha((unsigned char) query[wordlen]))
        wordlen += PQmblenBounded(&query[wordlen], pset.encoding);

    /*
     * Transaction control commands.  These should include every keyword that
     * gives rise to a TransactionStmt in the backend grammar, except for the
     * savepoint-related commands.
     *
     * (We assume that START must be START TRANSACTION, since there is
     * presently no other "START foo" command.)
     */
    if (wordlen == 5 && pg_strncasecmp(query, "abort", 5) == 0)
        return true;
    if (wordlen == 5 && pg_strncasecmp(query, "begin", 5) == 0)
        return true;
    if (wordlen == 5 && pg_strncasecmp(query, "start", 5) == 0)
        return true;
    if (wordlen == 6 && pg_strncasecmp(query, "commit", 6) == 0)
        return true;
    if (wordlen == 3 && pg_strncasecmp(query, "end", 3) == 0)
        return true;
    if (wordlen == 8 && pg_strncasecmp(query, "rollback", 8) == 0)
        return true;
    if (wordlen == 7 && pg_strncasecmp(query, "prepare", 7) == 0)
    {
        /* PREPARE TRANSACTION is a TC command, PREPARE foo is not */
        query += wordlen;

        query = skip_white_space(query);

        wordlen = 0;
        while (isalpha((unsigned char) query[wordlen]))
            wordlen += PQmblenBounded(&query[wordlen], pset.encoding);

        if (wordlen == 11 && pg_strncasecmp(query, "transaction", 11) == 0)
            return true;
        return false;
    }

    /*
     * Commands not allowed within transactions.  The statements checked for
     * here should be exactly those that call PreventInTransactionBlock() in
     * the backend.
     */
    if (wordlen == 6 && pg_strncasecmp(query, "vacuum", 6) == 0)
        return true;
    if (wordlen == 7 && pg_strncasecmp(query, "cluster", 7) == 0)
    {
        /* CLUSTER with any arguments is allowed in transactions */
        query += wordlen;

        query = skip_white_space(query);

        if (isalpha((unsigned char) query[0]))
            return false;       /* has additional words */
        return true;            /* it's CLUSTER without arguments */
    }

    if (wordlen == 6 && pg_strncasecmp(query, "create", 6) == 0)
    {
        query += wordlen;

        query = skip_white_space(query);

        wordlen = 0;
        while (isalpha((unsigned char) query[wordlen]))
            wordlen += PQmblenBounded(&query[wordlen], pset.encoding);

        if (wordlen == 8 && pg_strncasecmp(query, "database", 8) == 0)
            return true;
        if (wordlen == 10 && pg_strncasecmp(query, "tablespace", 10) == 0)
            return true;

        /* CREATE [UNIQUE] INDEX CONCURRENTLY isn't allowed in xacts */
        if (wordlen == 6 && pg_strncasecmp(query, "unique", 6) == 0)
        {
            query += wordlen;

            query = skip_white_space(query);

            wordlen = 0;
            while (isalpha((unsigned char) query[wordlen]))
                wordlen += PQmblenBounded(&query[wordlen], pset.encoding);
        }

        if (wordlen == 5 && pg_strncasecmp(query, "index", 5) == 0)
        {
            query += wordlen;

            query = skip_white_space(query);

            wordlen = 0;
            while (isalpha((unsigned char) query[wordlen]))
                wordlen += PQmblenBounded(&query[wordlen], pset.encoding);

            if (wordlen == 12 && pg_strncasecmp(query, "concurrently", 12) == 0)
                return true;
        }

        return false;
    }

    if (wordlen == 5 && pg_strncasecmp(query, "alter", 5) == 0)
    {
        query += wordlen;

        query = skip_white_space(query);

        wordlen = 0;
        while (isalpha((unsigned char) query[wordlen]))
            wordlen += PQmblenBounded(&query[wordlen], pset.encoding);

        /* ALTER SYSTEM isn't allowed in xacts */
        if (wordlen == 6 && pg_strncasecmp(query, "system", 6) == 0)
            return true;

        return false;
    }

    /*
     * Note: these tests will match DROP SYSTEM and REINDEX TABLESPACE, which
     * aren't really valid commands so we don't care much. The other four
     * possible matches are correct.
     */
    if ((wordlen == 4 && pg_strncasecmp(query, "drop", 4) == 0) ||
        (wordlen == 7 && pg_strncasecmp(query, "reindex", 7) == 0))
    {
        query += wordlen;

        query = skip_white_space(query);

        wordlen = 0;
        while (isalpha((unsigned char) query[wordlen]))
            wordlen += PQmblenBounded(&query[wordlen], pset.encoding);

        if (wordlen == 8 && pg_strncasecmp(query, "database", 8) == 0)
            return true;
        if (wordlen == 6 && pg_strncasecmp(query, "system", 6) == 0)
            return true;
        if (wordlen == 10 && pg_strncasecmp(query, "tablespace", 10) == 0)
            return true;
        if (wordlen == 5 && (pg_strncasecmp(query, "index", 5) == 0 ||
                             pg_strncasecmp(query, "table", 5) == 0))
        {
            query += wordlen;
            query = skip_white_space(query);
            wordlen = 0;
            while (isalpha((unsigned char) query[wordlen]))
                wordlen += PQmblenBounded(&query[wordlen], pset.encoding);

            /*
             * REINDEX [ TABLE | INDEX ] CONCURRENTLY are not allowed in
             * xacts.
             */
            if (wordlen == 12 && pg_strncasecmp(query, "concurrently", 12) == 0)
                return true;
        }

        /* DROP INDEX CONCURRENTLY isn't allowed in xacts */
        if (wordlen == 5 && pg_strncasecmp(query, "index", 5) == 0)
        {
            query += wordlen;

            query = skip_white_space(query);

            wordlen = 0;
            while (isalpha((unsigned char) query[wordlen]))
                wordlen += PQmblenBounded(&query[wordlen], pset.encoding);

            if (wordlen == 12 && pg_strncasecmp(query, "concurrently", 12) == 0)
                return true;

            return false;
        }

        return false;
    }

    /* DISCARD ALL isn't allowed in xacts, but other variants are allowed. */
    if (wordlen == 7 && pg_strncasecmp(query, "discard", 7) == 0)
    {
        query += wordlen;

        query = skip_white_space(query);

        wordlen = 0;
        while (isalpha((unsigned char) query[wordlen]))
            wordlen += PQmblenBounded(&query[wordlen], pset.encoding);

        if (wordlen == 3 && pg_strncasecmp(query, "all", 3) == 0)
            return true;
        return false;
    }

    return false;
}


/*
 * Check whether the specified command is a SELECT (or VALUES).
 */
static bool
is_select_command(const char *query)
{
    int         wordlen;

    /*
     * First advance over any whitespace, comments and left parentheses.
     */
    for (;;)
    {
        query = skip_white_space(query);
        if (query[0] == '(')
            query++;
        else
            break;
    }

    /*
     * Check word length (since "selectx" is not "select").
     */
    wordlen = 0;
    while (isalpha((unsigned char) query[wordlen]))
        wordlen += PQmblenBounded(&query[wordlen], pset.encoding);

    if (wordlen == 6 && pg_strncasecmp(query, "select", 6) == 0)
        return true;

    if (wordlen == 6 && pg_strncasecmp(query, "values", 6) == 0)
        return true;

    return false;
}


/*
 * Test if the current user is a database superuser.
 */
bool
is_superuser(void)
{
    const char *val;

    if (!pset.db)
        return false;

    val = PQparameterStatus(pset.db, "is_superuser");

    if (val && strcmp(val, "on") == 0)
        return true;

    return false;
}


/*
 * Test if the current session uses standard string literals.
 */
bool
standard_strings(void)
{
    const char *val;

    if (!pset.db)
        return false;

    val = PQparameterStatus(pset.db, "standard_conforming_strings");

    if (val && strcmp(val, "on") == 0)
        return true;

    return false;
}


/*
 * Return the session user of the current connection.
 */
const char *
session_username(void)
{
    const char *val;

    if (!pset.db)
        return NULL;

    val = PQparameterStatus(pset.db, "session_authorization");
    if (val)
        return val;
    else
        return PQuser(pset.db);
}


/* expand_tilde
 *
 * substitute '~' with HOME or '~username' with username's home dir
 *
 */
void
expand_tilde(char **filename)
{
    if (!filename || !(*filename))
        return;

    /*
     * WIN32 doesn't use tilde expansion for file names. Also, it uses tilde
     * for short versions of long file names, though the tilde is usually
     * toward the end, not at the beginning.
     */
#ifndef WIN32

    /* try tilde expansion */
    if (**filename == '~')
    {
        char       *fn;
        char        oldp,
                   *p;
        struct passwd *pw;
        char        home[MAXPGPATH];

        fn = *filename;
        *home = '\0';

        p = fn + 1;
        while (*p != '/' && *p != '\0')
            p++;

        oldp = *p;
        *p = '\0';

        if (*(fn + 1) == '\0')
            get_home_path(home);    /* ~ or ~/ only */
        else if ((pw = getpwnam(fn + 1)) != NULL)
            strlcpy(home, pw->pw_dir, sizeof(home));    /* ~user */

        *p = oldp;
        if (strlen(home) != 0)
        {
            char       *newfn;

            newfn = psprintf("%s%s", home, p);
            free(fn);
            *filename = newfn;
        }
    }
#endif
}

/*
 * Checks if connection string starts with either of the valid URI prefix
 * designators.
 *
 * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
 *
 * XXX This is a duplicate of the eponymous libpq function.
 */
static int
uri_prefix_length(const char *connstr)
{
    /* The connection URI must start with either of the following designators: */
    static const char uri_designator[] = "postgresql://";
    static const char short_uri_designator[] = "postgres://";

    if (strncmp(connstr, uri_designator,
                sizeof(uri_designator) - 1) == 0)
        return sizeof(uri_designator) - 1;

    if (strncmp(connstr, short_uri_designator,
                sizeof(short_uri_designator) - 1) == 0)
        return sizeof(short_uri_designator) - 1;

    return 0;
}

/*
 * Recognized connection string either starts with a valid URI prefix or
 * contains a "=" in it.
 *
 * Must be consistent with parse_connection_string: anything for which this
 * returns true should at least look like it's parseable by that routine.
 *
 * XXX This is a duplicate of the eponymous libpq function.
 */
bool
recognized_connection_string(const char *connstr)
{
    return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
}