variable.c

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/*-------------------------------------------------------------------------
 *
 * variable.c
 *      Routines for handling specialized SET variables.
 *
 *
 * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/commands/variable.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include <ctype.h>
 
#include "access/htup_details.h"
#include "access/parallel.h"
#include "access/xact.h"
#include "access/xlog.h"
#include "access/xlogprefetcher.h"
#include "catalog/pg_authid.h"
#include "common/string.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "postmaster/postmaster.h"
#include "postmaster/syslogger.h"
#include "storage/bufmgr.h"
#include "utils/acl.h"
#include "utils/backend_status.h"
#include "utils/datetime.h"
#include "utils/fmgrprotos.h"
#include "utils/guc_hooks.h"
#include "utils/snapmgr.h"
#include "utils/syscache.h"
#include "utils/timestamp.h"
#include "utils/tzparser.h"
#include "utils/varlena.h"
 
/*
 * DATESTYLE
 */
 
/*
 * check_datestyle: GUC check_hook for datestyle
 */
bool
check_datestyle(char **newval, void **extra, GucSource source)
{
    int         newDateStyle = DateStyle;
    int         newDateOrder = DateOrder;
    bool        have_style = false;
    bool        have_order = false;
    bool        ok = true;
    char       *rawstring;
    int        *myextra;
    char       *result;
    List       *elemlist;
    ListCell   *l;
 
    /* Need a modifiable copy of string */
    rawstring = pstrdup(*newval);
 
    /* Parse string into list of identifiers */
    if (!SplitIdentifierString(rawstring, ',', &elemlist))
    {
        /* syntax error in list */
        GUC_check_errdetail("List syntax is invalid.");
        pfree(rawstring);
        list_free(elemlist);
        return false;
    }
 
    foreach(l, elemlist)
    {
        char       *tok = (char *) lfirst(l);
 
        /* Ugh. Somebody ought to write a table driven version -- mjl */
 
        if (pg_strcasecmp(tok, "ISO") == 0)
        {
            if (have_style && newDateStyle != USE_ISO_DATES)
                ok = false;     /* conflicting styles */
            newDateStyle = USE_ISO_DATES;
            have_style = true;
        }
        else if (pg_strcasecmp(tok, "SQL") == 0)
        {
            if (have_style && newDateStyle != USE_SQL_DATES)
                ok = false;     /* conflicting styles */
            newDateStyle = USE_SQL_DATES;
            have_style = true;
        }
        else if (pg_strncasecmp(tok, "POSTGRES", 8) == 0)
        {
            if (have_style && newDateStyle != USE_POSTGRES_DATES)
                ok = false;     /* conflicting styles */
            newDateStyle = USE_POSTGRES_DATES;
            have_style = true;
        }
        else if (pg_strcasecmp(tok, "GERMAN") == 0)
        {
            if (have_style && newDateStyle != USE_GERMAN_DATES)
                ok = false;     /* conflicting styles */
            newDateStyle = USE_GERMAN_DATES;
            have_style = true;
            /* GERMAN also sets DMY, unless explicitly overridden */
            if (!have_order)
                newDateOrder = DATEORDER_DMY;
        }
        else if (pg_strcasecmp(tok, "YMD") == 0)
        {
            if (have_order && newDateOrder != DATEORDER_YMD)
                ok = false;     /* conflicting orders */
            newDateOrder = DATEORDER_YMD;
            have_order = true;
        }
        else if (pg_strcasecmp(tok, "DMY") == 0 ||
                 pg_strncasecmp(tok, "EURO", 4) == 0)
        {
            if (have_order && newDateOrder != DATEORDER_DMY)
                ok = false;     /* conflicting orders */
            newDateOrder = DATEORDER_DMY;
            have_order = true;
        }
        else if (pg_strcasecmp(tok, "MDY") == 0 ||
                 pg_strcasecmp(tok, "US") == 0 ||
                 pg_strncasecmp(tok, "NONEURO", 7) == 0)
        {
            if (have_order && newDateOrder != DATEORDER_MDY)
                ok = false;     /* conflicting orders */
            newDateOrder = DATEORDER_MDY;
            have_order = true;
        }
        else if (pg_strcasecmp(tok, "DEFAULT") == 0)
        {
            /*
             * Easiest way to get the current DEFAULT state is to fetch the
             * DEFAULT string from guc.c and recursively parse it.
             *
             * We can't simply "return check_datestyle(...)" because we need
             * to handle constructs like "DEFAULT, ISO".
             */
            char       *subval;
            void       *subextra = NULL;
 
            subval = guc_strdup(LOG, GetConfigOptionResetString("datestyle"));
            if (!subval)
            {
                ok = false;
                break;
            }
            if (!check_datestyle(&subval, &subextra, source))
            {
                guc_free(subval);
                ok = false;
                break;
            }
            myextra = (int *) subextra;
            if (!have_style)
                newDateStyle = myextra[0];
            if (!have_order)
                newDateOrder = myextra[1];
            guc_free(subval);
            guc_free(subextra);
        }
        else
        {
            GUC_check_errdetail("Unrecognized key word: \"%s\".", tok);
            pfree(rawstring);
            list_free(elemlist);
            return false;
        }
    }
 
    pfree(rawstring);
    list_free(elemlist);
 
    if (!ok)
    {
        GUC_check_errdetail("Conflicting \"datestyle\" specifications.");
        return false;
    }
 
    /*
     * Prepare the canonical string to return.  GUC wants it guc_malloc'd.
     */
    result = (char *) guc_malloc(LOG, 32);
    if (!result)
        return false;
 
    switch (newDateStyle)
    {
        case USE_ISO_DATES:
            strcpy(result, "ISO");
            break;
        case USE_SQL_DATES:
            strcpy(result, "SQL");
            break;
        case USE_GERMAN_DATES:
            strcpy(result, "German");
            break;
        default:
            strcpy(result, "Postgres");
            break;
    }
    switch (newDateOrder)
    {
        case DATEORDER_YMD:
            strcat(result, ", YMD");
            break;
        case DATEORDER_DMY:
            strcat(result, ", DMY");
            break;
        default:
            strcat(result, ", MDY");
            break;
    }
 
    guc_free(*newval);
    *newval = result;
 
    /*
     * Set up the "extra" struct actually used by assign_datestyle.
     */
    myextra = (int *) guc_malloc(LOG, 2 * sizeof(int));
    if (!myextra)
        return false;
    myextra[0] = newDateStyle;
    myextra[1] = newDateOrder;
    *extra = (void *) myextra;
 
    return true;
}
 
/*
 * assign_datestyle: GUC assign_hook for datestyle
 */
void
assign_datestyle(const char *newval, void *extra)
{
    int        *myextra = (int *) extra;
 
    DateStyle = myextra[0];
    DateOrder = myextra[1];
}
 
 
/*
 * TIMEZONE
 */
 
/*
 * check_timezone: GUC check_hook for timezone
 */
bool
check_timezone(char **newval, void **extra, GucSource source)
{
    pg_tz      *new_tz;
    long        gmtoffset;
    char       *endptr;
    double      hours;
 
    if (pg_strncasecmp(*newval, "interval", 8) == 0)
    {
        /*
         * Support INTERVAL 'foo'.  This is for SQL spec compliance, not
         * because it has any actual real-world usefulness.
         */
        const char *valueptr = *newval;
        char       *val;
        Interval   *interval;
 
        valueptr += 8;
        while (isspace((unsigned char) *valueptr))
            valueptr++;
        if (*valueptr++ != '\'')
            return false;
        val = pstrdup(valueptr);
        /* Check and remove trailing quote */
        endptr = strchr(val, '\'');
        if (!endptr || endptr[1] != '\0')
        {
            pfree(val);
            return false;
        }
        *endptr = '\0';
 
        /*
         * Try to parse it.  XXX an invalid interval format will result in
         * ereport(ERROR), which is not desirable for GUC.  We did what we
         * could to guard against this in flatten_set_variable_args, but a
         * string coming in from postgresql.conf might contain anything.
         */
        interval = DatumGetIntervalP(DirectFunctionCall3(interval_in,
                                                         CStringGetDatum(val),
                                                         ObjectIdGetDatum(InvalidOid),
                                                         Int32GetDatum(-1)));
 
        pfree(val);
        if (interval->month != 0)
        {
            GUC_check_errdetail("Cannot specify months in time zone interval.");
            pfree(interval);
            return false;
        }
        if (interval->day != 0)
        {
            GUC_check_errdetail("Cannot specify days in time zone interval.");
            pfree(interval);
            return false;
        }
 
        /* Here we change from SQL to Unix sign convention */
        gmtoffset = -(interval->time / USECS_PER_SEC);
        new_tz = pg_tzset_offset(gmtoffset);
 
        pfree(interval);
    }
    else
    {
        /*
         * Try it as a numeric number of hours (possibly fractional).
         */
        hours = strtod(*newval, &endptr);
        if (endptr != *newval && *endptr == '\0')
        {
            /* Here we change from SQL to Unix sign convention */
            gmtoffset = -hours * SECS_PER_HOUR;
            new_tz = pg_tzset_offset(gmtoffset);
        }
        else
        {
            /*
             * Otherwise assume it is a timezone name, and try to load it.
             */
            new_tz = pg_tzset(*newval);
 
            if (!new_tz)
            {
                /* Doesn't seem to be any great value in errdetail here */
                return false;
            }
 
            if (!pg_tz_acceptable(new_tz))
            {
                GUC_check_errmsg("time zone \"%s\" appears to use leap seconds",
                                 *newval);
                GUC_check_errdetail("PostgreSQL does not support leap seconds.");
                return false;
            }
        }
    }
 
    /* Test for failure in pg_tzset_offset, which we assume is out-of-range */
    if (!new_tz)
    {
        GUC_check_errdetail("UTC timezone offset is out of range.");
        return false;
    }
 
    /*
     * Pass back data for assign_timezone to use
     */
    *extra = guc_malloc(LOG, sizeof(pg_tz *));
    if (!*extra)
        return false;
    *((pg_tz **) *extra) = new_tz;
 
    return true;
}
 
/*
 * assign_timezone: GUC assign_hook for timezone
 */
void
assign_timezone(const char *newval, void *extra)
{
    session_timezone = *((pg_tz **) extra);
}
 
/*
 * show_timezone: GUC show_hook for timezone
 */
const char *
show_timezone(void)
{
    const char *tzn;
 
    /* Always show the zone's canonical name */
    tzn = pg_get_timezone_name(session_timezone);
 
    if (tzn != NULL)
        return tzn;
 
    return "unknown";
}
 
 
/*
 * LOG_TIMEZONE
 *
 * For log_timezone, we don't support the interval-based methods of setting a
 * zone, which are only there for SQL spec compliance not because they're
 * actually useful.
 */
 
/*
 * check_log_timezone: GUC check_hook for log_timezone
 */
bool
check_log_timezone(char **newval, void **extra, GucSource source)
{
    pg_tz      *new_tz;
 
    /*
     * Assume it is a timezone name, and try to load it.
     */
    new_tz = pg_tzset(*newval);
 
    if (!new_tz)
    {
        /* Doesn't seem to be any great value in errdetail here */
        return false;
    }
 
    if (!pg_tz_acceptable(new_tz))
    {
        GUC_check_errmsg("time zone \"%s\" appears to use leap seconds",
                         *newval);
        GUC_check_errdetail("PostgreSQL does not support leap seconds.");
        return false;
    }
 
    /*
     * Pass back data for assign_log_timezone to use
     */
    *extra = guc_malloc(LOG, sizeof(pg_tz *));
    if (!*extra)
        return false;
    *((pg_tz **) *extra) = new_tz;
 
    return true;
}
 
/*
 * assign_log_timezone: GUC assign_hook for log_timezone
 */
void
assign_log_timezone(const char *newval, void *extra)
{
    log_timezone = *((pg_tz **) extra);
}
 
/*
 * show_log_timezone: GUC show_hook for log_timezone
 */
const char *
show_log_timezone(void)
{
    const char *tzn;
 
    /* Always show the zone's canonical name */
    tzn = pg_get_timezone_name(log_timezone);
 
    if (tzn != NULL)
        return tzn;
 
    return "unknown";
}
 
 
/*
 * TIMEZONE_ABBREVIATIONS
 */
 
/*
 * GUC check_hook for assign_timezone_abbreviations
 */
bool
check_timezone_abbreviations(char **newval, void **extra, GucSource source)
{
    /*
     * The boot_val for timezone_abbreviations is NULL.  When we see that we
     * just do nothing.  If the value isn't overridden from the config file
     * then pg_timezone_abbrev_initialize() will eventually replace it with
     * "Default".  This hack has two purposes: to avoid wasting cycles loading
     * values that might soon be overridden from the config file, and to avoid
     * trying to read the timezone abbrev files during InitializeGUCOptions().
     * The latter doesn't work in an EXEC_BACKEND subprocess because
     * my_exec_path hasn't been set yet and so we can't locate PGSHAREDIR.
     */
    if (*newval == NULL)
    {
        Assert(source == PGC_S_DEFAULT);
        return true;
    }
 
    /* OK, load the file and produce a guc_malloc'd TimeZoneAbbrevTable */
    *extra = load_tzoffsets(*newval);
 
    /* tzparser.c returns NULL on failure, reporting via GUC_check_errmsg */
    if (!*extra)
        return false;
 
    return true;
}
 
/*
 * GUC assign_hook for assign_timezone_abbreviations
 */
void
assign_timezone_abbreviations(const char *newval, void *extra)
{
    /* Do nothing for the boot_val default of NULL */
    if (!extra)
        return;
 
    InstallTimeZoneAbbrevs((TimeZoneAbbrevTable *) extra);
}
 
 
/*
 * SET TRANSACTION READ ONLY and SET TRANSACTION READ WRITE
 *
 * We allow idempotent changes (r/w -> r/w and r/o -> r/o) at any time, and
 * we also always allow changes from read-write to read-only.  However,
 * read-only may be changed to read-write only when in a top-level transaction
 * that has not yet taken an initial snapshot.  Can't do it in a hot standby,
 * either.
 *
 * If we are not in a transaction at all, just allow the change; it means
 * nothing since XactReadOnly will be reset by the next StartTransaction().
 * The IsTransactionState() test protects us against trying to check
 * RecoveryInProgress() in contexts where shared memory is not accessible.
 * (Similarly, if we're restoring state in a parallel worker, just allow
 * the change.)
 */
bool
check_transaction_read_only(bool *newval, void **extra, GucSource source)
{
    if (*newval == false && XactReadOnly && IsTransactionState() && !InitializingParallelWorker)
    {
        /* Can't go to r/w mode inside a r/o transaction */
        if (IsSubTransaction())
        {
            GUC_check_errcode(ERRCODE_ACTIVE_SQL_TRANSACTION);
            GUC_check_errmsg("cannot set transaction read-write mode inside a read-only transaction");
            return false;
        }
        /* Top level transaction can't change to r/w after first snapshot. */
        if (FirstSnapshotSet)
        {
            GUC_check_errcode(ERRCODE_ACTIVE_SQL_TRANSACTION);
            GUC_check_errmsg("transaction read-write mode must be set before any query");
            return false;
        }
        /* Can't go to r/w mode while recovery is still active */
        if (RecoveryInProgress())
        {
            GUC_check_errcode(ERRCODE_FEATURE_NOT_SUPPORTED);
            GUC_check_errmsg("cannot set transaction read-write mode during recovery");
            return false;
        }
    }
 
    return true;
}
 
/*
 * SET TRANSACTION ISOLATION LEVEL
 *
 * We allow idempotent changes at any time, but otherwise this can only be
 * changed in a toplevel transaction that has not yet taken a snapshot.
 *
 * As in check_transaction_read_only, allow it if not inside a transaction,
 * or if restoring state in a parallel worker.
 */
bool
check_transaction_isolation(int *newval, void **extra, GucSource source)
{
    int         newXactIsoLevel = *newval;
 
    if (newXactIsoLevel != XactIsoLevel &&
        IsTransactionState() && !InitializingParallelWorker)
    {
        if (FirstSnapshotSet)
        {
            GUC_check_errcode(ERRCODE_ACTIVE_SQL_TRANSACTION);
            GUC_check_errmsg("SET TRANSACTION ISOLATION LEVEL must be called before any query");
            return false;
        }
        /* We ignore a subtransaction setting it to the existing value. */
        if (IsSubTransaction())
        {
            GUC_check_errcode(ERRCODE_ACTIVE_SQL_TRANSACTION);
            GUC_check_errmsg("SET TRANSACTION ISOLATION LEVEL must not be called in a subtransaction");
            return false;
        }
        /* Can't go to serializable mode while recovery is still active */
        if (newXactIsoLevel == XACT_SERIALIZABLE && RecoveryInProgress())
        {
            GUC_check_errcode(ERRCODE_FEATURE_NOT_SUPPORTED);
            GUC_check_errmsg("cannot use serializable mode in a hot standby");
            GUC_check_errhint("You can use REPEATABLE READ instead.");
            return false;
        }
    }
 
    return true;
}
 
/*
 * SET TRANSACTION [NOT] DEFERRABLE
 */
 
bool
check_transaction_deferrable(bool *newval, void **extra, GucSource source)
{
    /* Just accept the value when restoring state in a parallel worker */
    if (InitializingParallelWorker)
        return true;
 
    if (IsSubTransaction())
    {
        GUC_check_errcode(ERRCODE_ACTIVE_SQL_TRANSACTION);
        GUC_check_errmsg("SET TRANSACTION [NOT] DEFERRABLE cannot be called within a subtransaction");
        return false;
    }
    if (FirstSnapshotSet)
    {
        GUC_check_errcode(ERRCODE_ACTIVE_SQL_TRANSACTION);
        GUC_check_errmsg("SET TRANSACTION [NOT] DEFERRABLE must be called before any query");
        return false;
    }
 
    return true;
}
 
/*
 * Random number seed
 *
 * We can't roll back the random sequence on error, and we don't want
 * config file reloads to affect it, so we only want interactive SET SEED
 * commands to set it.  We use the "extra" storage to ensure that rollbacks
 * don't try to do the operation again.
 */
 
bool
check_random_seed(double *newval, void **extra, GucSource source)
{
    *extra = guc_malloc(LOG, sizeof(int));
    if (!*extra)
        return false;
    /* Arm the assign only if source of value is an interactive SET */
    *((int *) *extra) = (source >= PGC_S_INTERACTIVE);
 
    return true;
}
 
void
assign_random_seed(double newval, void *extra)
{
    /* We'll do this at most once for any setting of the GUC variable */
    if (*((int *) extra))
        DirectFunctionCall1(setseed, Float8GetDatum(newval));
    *((int *) extra) = 0;
}
 
const char *
show_random_seed(void)
{
    return "unavailable";
}
 
 
/*
 * SET CLIENT_ENCODING
 */
 
bool
check_client_encoding(char **newval, void **extra, GucSource source)
{
    int         encoding;
    const char *canonical_name;
 
    /* Look up the encoding by name */
    encoding = pg_valid_client_encoding(*newval);
    if (encoding < 0)
        return false;
 
    /* Get the canonical name (no aliases, uniform case) */
    canonical_name = pg_encoding_to_char(encoding);
 
    /*
     * Parallel workers send data to the leader, not the client.  They always
     * send data using the database encoding; therefore, we should never
     * actually change the client encoding in a parallel worker.  However,
     * during parallel worker startup, we want to accept the leader's
     * client_encoding setting so that anyone who looks at the value in the
     * worker sees the same value that they would see in the leader.  A change
     * other than during startup, for example due to a SET clause attached to
     * a function definition, should be rejected, as there is nothing we can
     * do inside the worker to make it take effect.
     */
    if (IsParallelWorker() && !InitializingParallelWorker)
    {
        GUC_check_errcode(ERRCODE_INVALID_TRANSACTION_STATE);
        GUC_check_errdetail("Cannot change \"client_encoding\" during a parallel operation.");
        return false;
    }
 
    /*
     * If we are not within a transaction then PrepareClientEncoding will not
     * be able to look up the necessary conversion procs.  If we are still
     * starting up, it will return "OK" anyway, and InitializeClientEncoding
     * will fix things once initialization is far enough along.  After
     * startup, we'll fail.  This would only happen if someone tries to change
     * client_encoding in postgresql.conf and then SIGHUP existing sessions.
     * It seems like a bad idea for client_encoding to change that way anyhow,
     * so we don't go out of our way to support it.
     *
     * In a parallel worker, we might as well skip PrepareClientEncoding since
     * we're not going to use its results.
     *
     * Note: in the postmaster, or any other process that never calls
     * InitializeClientEncoding, PrepareClientEncoding will always succeed,
     * and so will SetClientEncoding; but they won't do anything, which is OK.
     */
    if (!IsParallelWorker() &&
        PrepareClientEncoding(encoding) < 0)
    {
        if (IsTransactionState())
        {
            /* Must be a genuine no-such-conversion problem */
            GUC_check_errcode(ERRCODE_FEATURE_NOT_SUPPORTED);
            GUC_check_errdetail("Conversion between %s and %s is not supported.",
                                canonical_name,
                                GetDatabaseEncodingName());
        }
        else
        {
            /* Provide a useful complaint */
            GUC_check_errdetail("Cannot change \"client_encoding\" now.");
        }
        return false;
    }
 
    /*
     * Replace the user-supplied string with the encoding's canonical name.
     * This gets rid of aliases and case-folding variations.
     *
     * XXX Although canonicalizing seems like a good idea in the abstract, it
     * breaks pre-9.1 JDBC drivers, which expect that if they send "UNICODE"
     * as the client_encoding setting then it will read back the same way. As
     * a workaround, don't replace the string if it's "UNICODE".  Remove that
     * hack when pre-9.1 JDBC drivers are no longer in use.
     */
    if (strcmp(*newval, canonical_name) != 0 &&
        strcmp(*newval, "UNICODE") != 0)
    {
        guc_free(*newval);
        *newval = guc_strdup(LOG, canonical_name);
        if (!*newval)
            return false;
    }
 
    /*
     * Save the encoding's ID in *extra, for use by assign_client_encoding.
     */
    *extra = guc_malloc(LOG, sizeof(int));
    if (!*extra)
        return false;
    *((int *) *extra) = encoding;
 
    return true;
}
 
void
assign_client_encoding(const char *newval, void *extra)
{
    int         encoding = *((int *) extra);
 
    /*
     * In a parallel worker, we never override the client encoding that was
     * set by ParallelWorkerMain().
     */
    if (IsParallelWorker())
        return;
 
    /* We do not expect an error if PrepareClientEncoding succeeded */
    if (SetClientEncoding(encoding) < 0)
        elog(LOG, "SetClientEncoding(%d) failed", encoding);
}
 
 
/*
 * SET SESSION AUTHORIZATION
 */
 
typedef struct
{
    /* This is the "extra" state for both SESSION AUTHORIZATION and ROLE */
    Oid         roleid;
    bool        is_superuser;
} role_auth_extra;
 
bool
check_session_authorization(char **newval, void **extra, GucSource source)
{
    HeapTuple   roleTup;
    Form_pg_authid roleform;
    Oid         roleid;
    bool        is_superuser;
    role_auth_extra *myextra;
 
    /* Do nothing for the boot_val default of NULL */
    if (*newval == NULL)
        return true;
 
    if (!IsTransactionState())
    {
        /*
         * Can't do catalog lookups, so fail.  The result of this is that
         * session_authorization cannot be set in postgresql.conf, which seems
         * like a good thing anyway, so we don't work hard to avoid it.
         */
        return false;
    }
 
    /*
     * When source == PGC_S_TEST, we don't throw a hard error for a
     * nonexistent user name or insufficient privileges, only a NOTICE. See
     * comments in guc.h.
     */
 
    /* Look up the username */
    roleTup = SearchSysCache1(AUTHNAME, PointerGetDatum(*newval));
    if (!HeapTupleIsValid(roleTup))
    {
        if (source == PGC_S_TEST)
        {
            ereport(NOTICE,
                    (errcode(ERRCODE_UNDEFINED_OBJECT),
                     errmsg("role \"%s\" does not exist", *newval)));
            return true;
        }
        GUC_check_errmsg("role \"%s\" does not exist", *newval);
        return false;
    }
 
    roleform = (Form_pg_authid) GETSTRUCT(roleTup);
    roleid = roleform->oid;
    is_superuser = roleform->rolsuper;
 
    ReleaseSysCache(roleTup);
 
    /*
     * Only superusers may SET SESSION AUTHORIZATION a role other than itself.
     * Note that in case of multiple SETs in a single session, the original
     * authenticated user's superuserness is what matters.
     */
    if (roleid != GetAuthenticatedUserId() &&
        !superuser_arg(GetAuthenticatedUserId()))
    {
        if (source == PGC_S_TEST)
        {
            ereport(NOTICE,
                    (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                     errmsg("permission will be denied to set session authorization \"%s\"",
                            *newval)));
            return true;
        }
        GUC_check_errcode(ERRCODE_INSUFFICIENT_PRIVILEGE);
        GUC_check_errmsg("permission denied to set session authorization \"%s\"",
                         *newval);
        return false;
    }
 
    /* Set up "extra" struct for assign_session_authorization to use */
    myextra = (role_auth_extra *) guc_malloc(LOG, sizeof(role_auth_extra));
    if (!myextra)
        return false;
    myextra->roleid = roleid;
    myextra->is_superuser = is_superuser;
    *extra = (void *) myextra;
 
    return true;
}
 
void
assign_session_authorization(const char *newval, void *extra)
{
    role_auth_extra *myextra = (role_auth_extra *) extra;
 
    /* Do nothing for the boot_val default of NULL */
    if (!myextra)
        return;
 
    SetSessionAuthorization(myextra->roleid, myextra->is_superuser);
}
 
 
/*
 * SET ROLE
 *
 * The SQL spec requires "SET ROLE NONE" to unset the role, so we hardwire
 * a translation of "none" to InvalidOid.  Otherwise this is much like
 * SET SESSION AUTHORIZATION.
 */
 
bool
check_role(char **newval, void **extra, GucSource source)
{
    HeapTuple   roleTup;
    Oid         roleid;
    bool        is_superuser;
    role_auth_extra *myextra;
    Form_pg_authid roleform;
 
    if (strcmp(*newval, "none") == 0)
    {
        /* hardwired translation */
        roleid = InvalidOid;
        is_superuser = false;
    }
    else
    {
        if (!IsTransactionState())
        {
            /*
             * Can't do catalog lookups, so fail.  The result of this is that
             * role cannot be set in postgresql.conf, which seems like a good
             * thing anyway, so we don't work hard to avoid it.
             */
            return false;
        }
 
        /*
         * When source == PGC_S_TEST, we don't throw a hard error for a
         * nonexistent user name or insufficient privileges, only a NOTICE.
         * See comments in guc.h.
         */
 
        /* Look up the username */
        roleTup = SearchSysCache1(AUTHNAME, PointerGetDatum(*newval));
        if (!HeapTupleIsValid(roleTup))
        {
            if (source == PGC_S_TEST)
            {
                ereport(NOTICE,
                        (errcode(ERRCODE_UNDEFINED_OBJECT),
                         errmsg("role \"%s\" does not exist", *newval)));
                return true;
            }
            GUC_check_errmsg("role \"%s\" does not exist", *newval);
            return false;
        }
 
        roleform = (Form_pg_authid) GETSTRUCT(roleTup);
        roleid = roleform->oid;
        is_superuser = roleform->rolsuper;
 
        ReleaseSysCache(roleTup);
 
        /*
         * Verify that session user is allowed to become this role, but skip
         * this in parallel mode, where we must blindly recreate the parallel
         * leader's state.
         */
        if (!InitializingParallelWorker &&
            !member_can_set_role(GetSessionUserId(), roleid))
        {
            if (source == PGC_S_TEST)
            {
                ereport(NOTICE,
                        (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                         errmsg("permission will be denied to set role \"%s\"",
                                *newval)));
                return true;
            }
            GUC_check_errcode(ERRCODE_INSUFFICIENT_PRIVILEGE);
            GUC_check_errmsg("permission denied to set role \"%s\"",
                             *newval);
            return false;
        }
    }
 
    /* Set up "extra" struct for assign_role to use */
    myextra = (role_auth_extra *) guc_malloc(LOG, sizeof(role_auth_extra));
    if (!myextra)
        return false;
    myextra->roleid = roleid;
    myextra->is_superuser = is_superuser;
    *extra = (void *) myextra;
 
    return true;
}
 
void
assign_role(const char *newval, void *extra)
{
    role_auth_extra *myextra = (role_auth_extra *) extra;
 
    SetCurrentRoleId(myextra->roleid, myextra->is_superuser);
}
 
const char *
show_role(void)
{
    /*
     * Check whether SET ROLE is active; if not return "none".  This is a
     * kluge to deal with the fact that SET SESSION AUTHORIZATION logically
     * resets SET ROLE to NONE, but we cannot set the GUC role variable from
     * assign_session_authorization (because we haven't got enough info to
     * call set_config_option).
     */
    if (!OidIsValid(GetCurrentRoleId()))
        return "none";
 
    /* Otherwise we can just use the GUC string */
    return role_string ? role_string : "none";
}
 
 
/*
 * PATH VARIABLES
 *
 * check_canonical_path is used for log_directory and some other GUCs where
 * all we want to do is canonicalize the represented path name.
 */
 
bool
check_canonical_path(char **newval, void **extra, GucSource source)
{
    /*
     * Since canonicalize_path never enlarges the string, we can just modify
     * newval in-place.  But watch out for NULL, which is the default value
     * for external_pid_file.
     */
    if (*newval)
        canonicalize_path(*newval);
    return true;
}
 
 
/*
 * MISCELLANEOUS
 */
 
/*
 * GUC check_hook for application_name
 */
bool
check_application_name(char **newval, void **extra, GucSource source)
{
    char       *clean;
    char       *ret;
 
    /* Only allow clean ASCII chars in the application name */
    clean = pg_clean_ascii(*newval, MCXT_ALLOC_NO_OOM);
    if (!clean)
        return false;
 
    ret = guc_strdup(WARNING, clean);
    if (!ret)
    {
        pfree(clean);
        return false;
    }
 
    pfree(clean);
    *newval = ret;
    return true;
}
 
/*
 * GUC assign_hook for application_name
 */
void
assign_application_name(const char *newval, void *extra)
{
    /* Update the pg_stat_activity view */
    pgstat_report_appname(newval);
}
 
/*
 * GUC check_hook for cluster_name
 */
bool
check_cluster_name(char **newval, void **extra, GucSource source)
{
    char       *clean;
    char       *ret;
 
    /* Only allow clean ASCII chars in the cluster name */
    clean = pg_clean_ascii(*newval, MCXT_ALLOC_NO_OOM);
    if (!clean)
        return false;
 
    ret = guc_strdup(WARNING, clean);
    if (!ret)
    {
        pfree(clean);
        return false;
    }
 
    pfree(clean);
    *newval = ret;
    return true;
}
 
/*
 * GUC assign_hook for maintenance_io_concurrency
 */
void
assign_maintenance_io_concurrency(int newval, void *extra)
{
#ifdef USE_PREFETCH
    /*
     * Reconfigure recovery prefetching, because a setting it depends on
     * changed.
     */
    maintenance_io_concurrency = newval;
    if (AmStartupProcess())
        XLogPrefetchReconfigure();
#endif
}
 
 
/*
 * These show hooks just exist because we want to show the values in octal.
 */
 
/*
 * GUC show_hook for data_directory_mode
 */
const char *
show_data_directory_mode(void)
{
    static char buf[12];
 
    snprintf(buf, sizeof(buf), "%04o", data_directory_mode);
    return buf;
}
 
/*
 * GUC show_hook for log_file_mode
 */
const char *
show_log_file_mode(void)
{
    static char buf[12];
 
    snprintf(buf, sizeof(buf), "%04o", Log_file_mode);
    return buf;
}
 
/*
 * GUC show_hook for unix_socket_permissions
 */
const char *
show_unix_socket_permissions(void)
{
    static char buf[12];
 
    snprintf(buf, sizeof(buf), "%04o", Unix_socket_permissions);
    return buf;
}
 
 
/*
 * These check hooks do nothing more than reject non-default settings
 * in builds that don't support them.
 */
 
bool
check_bonjour(bool *newval, void **extra, GucSource source)
{
#ifndef USE_BONJOUR
    if (*newval)
    {
        GUC_check_errmsg("Bonjour is not supported by this build");
        return false;
    }
#endif
    return true;
}
 
bool
check_default_with_oids(bool *newval, void **extra, GucSource source)
{
    if (*newval)
    {
        /* check the GUC's definition for an explanation */
        GUC_check_errcode(ERRCODE_FEATURE_NOT_SUPPORTED);
        GUC_check_errmsg("tables declared WITH OIDS are not supported");
 
        return false;
    }
 
    return true;
}
 
bool
check_effective_io_concurrency(int *newval, void **extra, GucSource source)
{
#ifndef USE_PREFETCH
    if (*newval != 0)
    {
        GUC_check_errdetail("\"%s\" must be set to 0 on platforms that lack support for issuing read-ahead advice.",
                            "effective_io_concurrency");
        return false;
    }
#endif                          /* USE_PREFETCH */
    return true;
}
 
bool
check_maintenance_io_concurrency(int *newval, void **extra, GucSource source)
{
#ifndef USE_PREFETCH
    if (*newval != 0)
    {
        GUC_check_errdetail("\"%s\" must be set to 0 on platforms that lack support for issuing read-ahead advice.",
                            "maintenance_io_concurrency");
        return false;
    }
#endif                          /* USE_PREFETCH */
    return true;
}
 
bool
check_ssl(bool *newval, void **extra, GucSource source)
{
#ifndef USE_SSL
    if (*newval)
    {
        GUC_check_errmsg("SSL is not supported by this build");
        return false;
    }
#endif
    return true;
}