common.c

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/*
 * psql - the PostgreSQL interactive terminal
 *
 * Copyright (c) 2000-2013, PostgreSQL Global Development Group
 *
 * src/bin/psql/common.c
 */
#include "postgres_fe.h"
#include "common.h"

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

#include "portability/instr_time.h"

#include "settings.h"
#include "command.h"
#include "copy.h"
#include "mbprint.h"



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);

/*
 * setQFout
 * -- handler for -o command line option and \o command
 *
 * Tries to open file fname (or pipe if fname starts with '|')
 * and stores the file handle in pset)
 * Upon failure, sets stdout and returns false.
 */
bool
setQFout(const char *fname)
{
    bool        status = true;

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

    /* If no filename, set stdout */
    if (!fname || fname[0] == '\0')
    {
        pset.queryFout = stdout;
        pset.queryFoutPipe = false;
    }
    else if (*fname == '|')
    {
        pset.queryFout = popen(fname + 1, "w");
        pset.queryFoutPipe = true;
    }
    else
    {
        pset.queryFout = fopen(fname, "w");
        pset.queryFoutPipe = false;
    }

    if (!(pset.queryFout))
    {
        psql_error("%s: %s\n", fname, strerror(errno));
        pset.queryFout = stdout;
        pset.queryFoutPipe = false;
        status = false;
    }

    /* Direct signals */
#ifndef WIN32
    pqsignal(SIGPIPE, pset.queryFoutPipe ? SIG_IGN : SIG_DFL);
#endif

    return status;
}



/*
 * Error reporting for scripts. Errors should look like
 *   psql:filename:lineno: message
 *
 */
void
psql_error(const char *fmt,...)
{
    va_list     ap;

    fflush(stdout);
    if (pset.queryFout && pset.queryFout != stdout)
        fflush(pset.queryFout);

    if (pset.inputfile)
        fprintf(stderr, "%s:%s:" UINT64_FORMAT ": ", pset.progname, pset.inputfile, pset.lineno);
    va_start(ap, fmt);
    vfprintf(stderr, _(fmt), ap);
    va_end(ap);
}



/*
 * for backend Notice messages (INFO, WARNING, etc)
 */
void
NoticeProcessor(void *arg, const char *message)
{
    (void) arg;                 /* not used */
    psql_error("%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. Note that sending the cancel directly from
 * the signal handler is safe because PQcancel() is written to make it
 * so. We use write() to report to stderr because it's better to use simple
 * facilities in a signal handler.
 *
 * On win32, the signal canceling happens on a separate thread, because
 * that's how SetConsoleCtrlHandler works. The PQcancel function is safe
 * for this (unlike PQrequestCancel). However, a CRITICAL_SECTION is required
 * to protect the PGcancel structure against being changed while the signal
 * thread is using it.
 *
 * 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.  (XXX currently this does
 * not work on win32, so control-C is less useful there)
 */
volatile bool sigint_interrupt_enabled = false;

sigjmp_buf  sigint_interrupt_jmp;

static PGcancel *volatile cancelConn = NULL;

#ifdef WIN32
static CRITICAL_SECTION cancelConnLock;
#endif

/* Used from signal handlers, no buffering */
#define write_stderr(str)   write(fileno(stderr), str, strlen(str))


#ifndef WIN32

static void
handle_sigint(SIGNAL_ARGS)
{
    int         save_errno = errno;
    int         rc;
    char        errbuf[256];

    /* if we are waiting for input, longjmp out of it */
    if (sigint_interrupt_enabled)
    {
        sigint_interrupt_enabled = false;
        siglongjmp(sigint_interrupt_jmp, 1);
    }

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

    /* and send QueryCancel if we are processing a database query */
    if (cancelConn != NULL)
    {
        if (PQcancel(cancelConn, errbuf, sizeof(errbuf)))
        {
            rc = write_stderr("Cancel request sent\n");
            (void) rc;          /* ignore errors, nothing we can do here */
        }
        else
        {
            rc = write_stderr("Could not send cancel request: ");
            (void) rc;          /* ignore errors, nothing we can do here */
            rc = write_stderr(errbuf);
            (void) rc;          /* ignore errors, nothing we can do here */
        }
    }

    errno = save_errno;         /* just in case the write changed it */
}

void
setup_cancel_handler(void)
{
    pqsignal(SIGINT, handle_sigint);
}
#else                           /* WIN32 */

static BOOL WINAPI
consoleHandler(DWORD dwCtrlType)
{
    char        errbuf[256];

    if (dwCtrlType == CTRL_C_EVENT ||
        dwCtrlType == CTRL_BREAK_EVENT)
    {
        /*
         * Can't longjmp here, because we are in wrong thread :-(
         */

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

        /* and send QueryCancel if we are processing a database query */
        EnterCriticalSection(&cancelConnLock);
        if (cancelConn != NULL)
        {
            if (PQcancel(cancelConn, errbuf, sizeof(errbuf)))
                write_stderr("Cancel request sent\n");
            else
            {
                write_stderr("Could not send cancel request: ");
                write_stderr(errbuf);
            }
        }
        LeaveCriticalSection(&cancelConnLock);

        return TRUE;
    }
    else
        /* Return FALSE for any signals not being handled */
        return FALSE;
}

void
setup_cancel_handler(void)
{
    InitializeCriticalSection(&cancelConnLock);

    SetConsoleCtrlHandler(consoleHandler, TRUE);
}
#endif   /* WIN32 */


/* 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)
        {
            psql_error("connection to server was lost\n");
            exit(EXIT_BADCONN);
        }

        psql_error("The connection to the server was lost. Attempting reset: ");
        PQreset(pset.db);
        OK = ConnectionUp();
        if (!OK)
        {
            psql_error("Failed.\n");
            PQfinish(pset.db);
            pset.db = NULL;
            ResetCancelConn();
            UnsyncVariables();
        }
        else
            psql_error("Succeeded.\n");
    }

    return OK;
}



/*
 * SetCancelConn
 *
 * Set cancelConn to point to the current database connection.
 */
void
SetCancelConn(void)
{
    PGcancel   *oldCancelConn;

#ifdef WIN32
    EnterCriticalSection(&cancelConnLock);
#endif

    /* Free the old one if we have one */
    oldCancelConn = cancelConn;
    /* be sure handle_sigint doesn't use pointer while freeing */
    cancelConn = NULL;

    if (oldCancelConn != NULL)
        PQfreeCancel(oldCancelConn);

    cancelConn = PQgetCancel(pset.db);

#ifdef WIN32
    LeaveCriticalSection(&cancelConnLock);
#endif
}


/*
 * ResetCancelConn
 *
 * Free the current cancel connection, if any, and set to NULL.
 */
void
ResetCancelConn(void)
{
    PGcancel   *oldCancelConn;

#ifdef WIN32
    EnterCriticalSection(&cancelConnLock);
#endif

    oldCancelConn = cancelConn;
    /* be sure handle_sigint doesn't use pointer while freeing */
    cancelConn = NULL;

    if (oldCancelConn != NULL)
        PQfreeCancel(oldCancelConn);

#ifdef WIN32
    LeaveCriticalSection(&cancelConnLock);
#endif
}


/*
 * 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;
                psql_error("unexpected PQresultStatus: %d\n",
                           PQresultStatus(result));
                break;
        }

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

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

        CheckConnection();
    }

    return OK;
}



/*
 * PSQLexec
 *
 * This is the way to send "backdoor" queries (those not directly entered
 * by the user). It is subject to -E but not -e.
 *
 * In autocommit-off mode, a new transaction block is started if start_xact
 * is true; nothing special is done when start_xact is false.  Typically,
 * start_xact = false is used for SELECTs and explicit BEGIN/COMMIT commands.
 *
 * 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, bool start_xact)
{
    PGresult   *res;

    if (!pset.db)
    {
        psql_error("You are currently not connected to a database.\n");
        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();

    if (start_xact &&
        !pset.autocommit &&
        PQtransactionStatus(pset.db) == PQTRANS_IDLE)
    {
        res = PQexec(pset.db, "BEGIN");
        if (PQresultStatus(res) != PGRES_COMMAND_OK)
        {
            psql_error("%s", PQerrorMessage(pset.db));
            PQclear(res);
            ResetCancelConn();
            return NULL;
        }
        PQclear(res);
    }

    res = PQexec(pset.db, query);

    ResetCancelConn();

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

    return res;
}



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

    while ((notify = PQnotifies(pset.db)))
    {
        /* 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);
    }
}


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

    /* write output to \g argument, if any */
    if (pset.gfname)
    {
        /* keep this code in sync with ExecQueryUsingCursor */
        FILE       *queryFout_copy = pset.queryFout;
        bool        queryFoutPipe_copy = pset.queryFoutPipe;

        pset.queryFout = stdout;    /* so it doesn't get closed */

        /* open file/pipe */
        if (!setQFout(pset.gfname))
        {
            pset.queryFout = queryFout_copy;
            pset.queryFoutPipe = queryFoutPipe_copy;
            return false;
        }

        printQuery(results, &my_popt, pset.queryFout, pset.logfile);

        /* close file/pipe, restore old setting */
        setQFout(NULL);

        pset.queryFout = queryFout_copy;
        pset.queryFoutPipe = queryFoutPipe_copy;
    }
    else
        printQuery(results, &my_popt, pset.queryFout, pset.logfile);

    return true;
}


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

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

            /* concate prefix and column name */
            varname = pg_malloc(strlen(pset.gset_prefix) + strlen(colname) + 1);
            strcpy(varname, pset.gset_prefix);
            strcat(varname, colname);

            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))
            {
                psql_error("could not set variable \"%s\"\n", varname);
                free(varname);
                success = false;
                break;
            }

            free(varname);
        }
    }

    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 affected 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 FROM STDIN or COPY TO STDOUT.
 *
 * 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)
{
    PGresult   *next_result;
    bool        success = true;
    bool        first_cycle = true;

    do
    {
        ExecStatusType result_status;
        bool        is_copy;

        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;
                psql_error("unexpected PQresultStatus: %d\n", 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.
             */
            SetCancelConn();
            if (result_status == PGRES_COPY_OUT)
                success = handleCopyOut(pset.db, pset.queryFout) && success;
            else
                success = handleCopyIn(pset.db, pset.cur_cmd_source,
                                       PQbinaryTuples(*results)) && success;
            ResetCancelConn();

            /*
             * Call PQgetResult() once more.  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.
             */
            PQclear(*results);
            *results = next_result = PQgetResult(pset.db);
        }
        else if (first_cycle)
            /* fast path: no COPY commands; PQexec visited all results */
            break;
        else if ((next_result = PQgetResult(pset.db)))
        {
            /* non-COPY command(s) after a COPY: keep the last one */
            PQclear(*results);
            *results = next_result;
        }

        first_cycle = false;
    } while (next_result);

    /* 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) 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 print the data ... */
            if (pset.gset_prefix)
                success = StoreQueryTuple(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;
            psql_error("unexpected PQresultStatus: %d\n",
                       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;
    bool        on_error_rollback_savepoint = false;
    static bool on_error_rollback_warning = false;

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

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

        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;
    }
    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();

    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)
        {
            psql_error("%s", PQerrorMessage(pset.db));
            PQclear(results);
            ResetCancelConn();
            goto sendquery_cleanup;
        }
        PQclear(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)
        {
            psql_error("The server (version %d.%d) does not support savepoints for ON_ERROR_ROLLBACK.\n",
                       pset.sversion / 10000, (pset.sversion / 100) % 100);
            on_error_rollback_warning = true;
        }
        else
        {
            results = PQexec(pset.db, "SAVEPOINT pg_psql_temporary_savepoint");
            if (PQresultStatus(results) != PGRES_COMMAND_OK)
            {
                psql_error("%s", PQerrorMessage(pset.db));
                PQclear(results);
                ResetCancelConn();
                goto sendquery_cleanup;
            }
            PQclear(results);
            on_error_rollback_savepoint = true;
        }
    }

    if (pset.fetch_count <= 0 || !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 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 RELEASE or ROLLBACK, our savepoint is gone.
                 * If they issued a SAVEPOINT, releasing ours would remove
                 * theirs.
                 */
                if (results &&
                    (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())
                    psql_error("unexpected transaction status (%d)\n",
                               transaction_status);
                break;
        }

        if (svptcmd)
        {
            PGresult   *svptres;

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

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

    PQclear(results);

    /* Possible microtiming output */
    if (pset.timing)
        printf(_("Time: %.3f ms\n"), 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;
    }

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

    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       *queryFout_copy = pset.queryFout;
    bool        queryFoutPipe_copy = pset.queryFoutPipe;
    bool        started_txn = false;
    bool        did_pager = false;
    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);
        PQclear(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);
    PQclear(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)
    {
        /* keep this code in sync with PrintQueryTuples */
        pset.queryFout = stdout;    /* so it doesn't get closed */

        /* open file/pipe */
        if (!setQFout(pset.gfname))
        {
            pset.queryFout = queryFout_copy;
            pset.queryFoutPipe = queryFoutPipe_copy;
            OK = false;
            goto cleanup;
        }
    }

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

    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 (did_pager)
            {
                ClosePager(pset.queryFout);
                pset.queryFout = queryFout_copy;
                pset.queryFoutPipe = queryFoutPipe_copy;
                did_pager = false;
            }

            OK = AcceptResult(results);
            Assert(!OK);
            PQclear(results);
            break;
        }

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

        ntuples = PQntuples(results);

        if (ntuples < fetch_count)
        {
            /* this is the last result set, so allow footer decoration */
            my_popt.topt.stop_table = true;
        }
        else if (pset.queryFout == stdout && !did_pager)
        {
            /*
             * If query requires multiple result sets, hack to ensure that
             * only one pager instance is used for the whole mess
             */
            pset.queryFout = PageOutput(100000, my_popt.topt.pager);
            did_pager = true;
        }

        printQuery(results, &my_popt, pset.queryFout, pset.logfile);

        PQclear(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(pset.queryFout);

        /*
         * 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(pset.queryFout))
            break;
    }

    /* close \g argument file/pipe, restore old setting */
    if (pset.gfname)
    {
        /* keep this code in sync with PrintQueryTuples */
        setQFout(NULL);

        pset.queryFout = queryFout_copy;
        pset.queryFoutPipe = queryFoutPipe_copy;
    }
    else if (did_pager)
    {
        ClosePager(pset.queryFout);
        pset.queryFout = queryFout_copy;
        pset.queryFoutPipe = queryFoutPipe_copy;
    }

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);
    }
    PQclear(results);

    if (started_txn)
    {
        results = PQexec(pset.db, OK ? "COMMIT" : "ROLLBACK");
        OK &= AcceptResult(results) &&
            (PQresultStatus(results) == PGRES_COMMAND_OK);
        PQclear(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 = PQmblen(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 += PQmblen(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 += PQmblen(&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 += PQmblen(&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 PreventTransactionChain() 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 += PQmblen(&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 += PQmblen(&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 += PQmblen(&query[wordlen], pset.encoding);

            if (wordlen == 12 && pg_strncasecmp(query, "concurrently", 12) == 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 += PQmblen(&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;
        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 += PQmblen(&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 += PQmblen(&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.
 *
 * Note: this will correctly detect superuserness only with a protocol-3.0
 * or newer backend; otherwise it will always say "false".
 */
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.
 *
 * Note: With a pre-protocol-3.0 connection this will always say "false",
 * which should be the right answer.
 */
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.
 *
 * Note: this will correctly detect the session user only with a
 * protocol-3.0 or newer backend; otherwise it will return the
 * connection user.
 */
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 = pg_malloc(strlen(home) + strlen(p) + 1);
            strcpy(newfn, home);
            strcat(newfn, p);

            free(fn);
            *filename = newfn;
        }
    }
#endif

    return;
}