dumputils.c

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/*-------------------------------------------------------------------------
 *
 * Utility routines for SQL dumping
 *
 * Basically this is stuff that is useful in both pg_dump and pg_dumpall.
 *
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/bin/pg_dump/dumputils.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres_fe.h"
 
#include <ctype.h>
 
#include "dumputils.h"
#include "fe_utils/string_utils.h"
 
 
static bool parseAclItem(const char *item, const char *type,
                         const char *name, const char *subname, int remoteVersion,
                         PQExpBuffer grantee, PQExpBuffer grantor,
                         PQExpBuffer privs, PQExpBuffer privswgo);
static char *dequoteAclUserName(PQExpBuffer output, char *input);
static void AddAcl(PQExpBuffer aclbuf, const char *keyword,
                   const char *subname);
 
 
/*
 * Build GRANT/REVOKE command(s) for an object.
 *
 *  name: the object name, in the form to use in the commands (already quoted)
 *  subname: the sub-object name, if any (already quoted); NULL if none
 *  nspname: the namespace the object is in (NULL if none); not pre-quoted
 *  type: the object type (as seen in GRANT command: must be one of
 *      TABLE, SEQUENCE, FUNCTION, PROCEDURE, LANGUAGE, SCHEMA, DATABASE, TABLESPACE,
 *      FOREIGN DATA WRAPPER, SERVER, PARAMETER or LARGE OBJECT)
 *  acls: the ACL string fetched from the database
 *  baseacls: the initial ACL string for this object
 *  owner: username of object owner (will be passed through fmtId); can be
 *      NULL or empty string to indicate "no owner known"
 *  prefix: string to prefix to each generated command; typically empty
 *  remoteVersion: version of database
 *
 * Returns true if okay, false if could not parse the acl string.
 * The resulting commands (if any) are appended to the contents of 'sql'.
 *
 * baseacls is typically the result of acldefault() for the object's type
 * and owner.  However, if there is a pg_init_privs entry for the object,
 * it should instead be the initprivs ACLs.  When acls is itself a
 * pg_init_privs entry, baseacls is what to dump that relative to; then
 * it can be either an acldefault() value or an empty ACL "{}".
 *
 * Note: when processing a default ACL, prefix is "ALTER DEFAULT PRIVILEGES "
 * or something similar, and name is an empty string.
 *
 * Note: beware of passing a fmtId() result directly as 'name' or 'subname',
 * since this routine uses fmtId() internally.
 */
bool
buildACLCommands(const char *name, const char *subname, const char *nspname,
                 const char *type, const char *acls, const char *baseacls,
                 const char *owner, const char *prefix, int remoteVersion,
                 PQExpBuffer sql)
{
    bool        ok = true;
    char      **aclitems = NULL;
    char      **baseitems = NULL;
    char      **grantitems = NULL;
    char      **revokeitems = NULL;
    int         naclitems = 0;
    int         nbaseitems = 0;
    int         ngrantitems = 0;
    int         nrevokeitems = 0;
    int         i;
    PQExpBuffer grantee,
                grantor,
                privs,
                privswgo;
    PQExpBuffer firstsql,
                secondsql;
 
    /*
     * If the acl was NULL (initial default state), we need do nothing.  Note
     * that this is distinguishable from all-privileges-revoked, which will
     * look like an empty array ("{}").
     */
    if (acls == NULL || *acls == '\0')
        return true;            /* object has default permissions */
 
    /* treat empty-string owner same as NULL */
    if (owner && *owner == '\0')
        owner = NULL;
 
    /* Parse the acls array */
    if (!parsePGArray(acls, &aclitems, &naclitems))
    {
        free(aclitems);
        return false;
    }
 
    /* Parse the baseacls too */
    if (!parsePGArray(baseacls, &baseitems, &nbaseitems))
    {
        free(aclitems);
        free(baseitems);
        return false;
    }
 
    /*
     * Compare the actual ACL with the base ACL, extracting the privileges
     * that need to be granted (i.e., are in the actual ACL but not the base
     * ACL) and the ones that need to be revoked (the reverse).  We use plain
     * string comparisons to check for matches.  In principle that could be
     * fooled by extraneous issues such as whitespace, but since all these
     * strings are the work of aclitemout(), it should be OK in practice.
     * Besides, a false mismatch will just cause the output to be a little
     * more verbose than it really needed to be.
     */
    grantitems = (char **) pg_malloc(naclitems * sizeof(char *));
    for (i = 0; i < naclitems; i++)
    {
        bool        found = false;
 
        for (int j = 0; j < nbaseitems; j++)
        {
            if (strcmp(aclitems[i], baseitems[j]) == 0)
            {
                found = true;
                break;
            }
        }
        if (!found)
            grantitems[ngrantitems++] = aclitems[i];
    }
    revokeitems = (char **) pg_malloc(nbaseitems * sizeof(char *));
    for (i = 0; i < nbaseitems; i++)
    {
        bool        found = false;
 
        for (int j = 0; j < naclitems; j++)
        {
            if (strcmp(baseitems[i], aclitems[j]) == 0)
            {
                found = true;
                break;
            }
        }
        if (!found)
            revokeitems[nrevokeitems++] = baseitems[i];
    }
 
    /* Prepare working buffers */
    grantee = createPQExpBuffer();
    grantor = createPQExpBuffer();
    privs = createPQExpBuffer();
    privswgo = createPQExpBuffer();
 
    /*
     * At the end, these two will be pasted together to form the result.
     */
    firstsql = createPQExpBuffer();
    secondsql = createPQExpBuffer();
 
    /*
     * Build REVOKE statements for ACLs listed in revokeitems[].
     */
    for (i = 0; i < nrevokeitems; i++)
    {
        if (!parseAclItem(revokeitems[i],
                          type, name, subname, remoteVersion,
                          grantee, grantor, privs, NULL))
        {
            ok = false;
            break;
        }
 
        if (privs->len > 0)
        {
            appendPQExpBuffer(firstsql, "%sREVOKE %s ON %s ",
                              prefix, privs->data, type);
            if (nspname && *nspname)
                appendPQExpBuffer(firstsql, "%s.", fmtId(nspname));
            if (name && *name)
                appendPQExpBuffer(firstsql, "%s ", name);
            appendPQExpBufferStr(firstsql, "FROM ");
            if (grantee->len == 0)
                appendPQExpBufferStr(firstsql, "PUBLIC;\n");
            else
                appendPQExpBuffer(firstsql, "%s;\n",
                                  fmtId(grantee->data));
        }
    }
 
    /*
     * At this point we have issued REVOKE statements for all initial and
     * default privileges that are no longer present on the object, so we are
     * almost ready to GRANT the privileges listed in grantitems[].
     *
     * We still need some hacking though to cover the case where new default
     * public privileges are added in new versions: the REVOKE ALL will revoke
     * them, leading to behavior different from what the old version had,
     * which is generally not what's wanted.  So add back default privs if the
     * source database is too old to have had that particular priv.  (As of
     * right now, no such cases exist in supported versions.)
     */
 
    /*
     * Scan individual ACL items to be granted.
     *
     * The order in which privileges appear in the ACL string (the order they
     * have been GRANT'd in, which the backend maintains) must be preserved to
     * ensure that GRANTs WITH GRANT OPTION and subsequent GRANTs based on
     * those are dumped in the correct order.  However, some old server
     * versions will show grants to PUBLIC before the owner's own grants; for
     * consistency's sake, force the owner's grants to be output first.
     */
    for (i = 0; i < ngrantitems; i++)
    {
        if (parseAclItem(grantitems[i], type, name, subname, remoteVersion,
                         grantee, grantor, privs, privswgo))
        {
            /*
             * If the grantor isn't the owner, we'll need to use SET SESSION
             * AUTHORIZATION to become the grantor.  Issue the SET/RESET only
             * if there's something useful to do.
             */
            if (privs->len > 0 || privswgo->len > 0)
            {
                PQExpBuffer thissql;
 
                /* Set owner as grantor if that's not explicit in the ACL */
                if (grantor->len == 0 && owner)
                    printfPQExpBuffer(grantor, "%s", owner);
 
                /* Make sure owner's own grants are output before others */
                if (owner &&
                    strcmp(grantee->data, owner) == 0 &&
                    strcmp(grantor->data, owner) == 0)
                    thissql = firstsql;
                else
                    thissql = secondsql;
 
                if (grantor->len > 0
                    && (!owner || strcmp(owner, grantor->data) != 0))
                    appendPQExpBuffer(thissql, "SET SESSION AUTHORIZATION %s;\n",
                                      fmtId(grantor->data));
 
                if (privs->len > 0)
                {
                    appendPQExpBuffer(thissql, "%sGRANT %s ON %s ",
                                      prefix, privs->data, type);
                    if (nspname && *nspname)
                        appendPQExpBuffer(thissql, "%s.", fmtId(nspname));
                    if (name && *name)
                        appendPQExpBuffer(thissql, "%s ", name);
                    appendPQExpBufferStr(thissql, "TO ");
                    if (grantee->len == 0)
                        appendPQExpBufferStr(thissql, "PUBLIC;\n");
                    else
                        appendPQExpBuffer(thissql, "%s;\n", fmtId(grantee->data));
                }
                if (privswgo->len > 0)
                {
                    appendPQExpBuffer(thissql, "%sGRANT %s ON %s ",
                                      prefix, privswgo->data, type);
                    if (nspname && *nspname)
                        appendPQExpBuffer(thissql, "%s.", fmtId(nspname));
                    if (name && *name)
                        appendPQExpBuffer(thissql, "%s ", name);
                    appendPQExpBufferStr(thissql, "TO ");
                    if (grantee->len == 0)
                        appendPQExpBufferStr(thissql, "PUBLIC");
                    else
                        appendPQExpBufferStr(thissql, fmtId(grantee->data));
                    appendPQExpBufferStr(thissql, " WITH GRANT OPTION;\n");
                }
 
                if (grantor->len > 0
                    && (!owner || strcmp(owner, grantor->data) != 0))
                    appendPQExpBufferStr(thissql, "RESET SESSION AUTHORIZATION;\n");
            }
        }
        else
        {
            /* parseAclItem failed, give up */
            ok = false;
            break;
        }
    }
 
    destroyPQExpBuffer(grantee);
    destroyPQExpBuffer(grantor);
    destroyPQExpBuffer(privs);
    destroyPQExpBuffer(privswgo);
 
    appendPQExpBuffer(sql, "%s%s", firstsql->data, secondsql->data);
    destroyPQExpBuffer(firstsql);
    destroyPQExpBuffer(secondsql);
 
    free(aclitems);
    free(baseitems);
    free(grantitems);
    free(revokeitems);
 
    return ok;
}
 
/*
 * Build ALTER DEFAULT PRIVILEGES command(s) for a single pg_default_acl entry.
 *
 *  type: the object type (TABLES, FUNCTIONS, etc)
 *  nspname: schema name, or NULL for global default privileges
 *  acls: the ACL string fetched from the database
 *  acldefault: the appropriate default ACL for the object type and owner
 *  owner: username of privileges owner (will be passed through fmtId)
 *  remoteVersion: version of database
 *
 * Returns true if okay, false if could not parse the acl string.
 * The resulting commands (if any) are appended to the contents of 'sql'.
 */
bool
buildDefaultACLCommands(const char *type, const char *nspname,
                        const char *acls, const char *acldefault,
                        const char *owner,
                        int remoteVersion,
                        PQExpBuffer sql)
{
    PQExpBuffer prefix;
 
    prefix = createPQExpBuffer();
 
    /*
     * We incorporate the target role directly into the command, rather than
     * playing around with SET ROLE or anything like that.  This is so that a
     * permissions error leads to nothing happening, rather than changing
     * default privileges for the wrong user.
     */
    appendPQExpBuffer(prefix, "ALTER DEFAULT PRIVILEGES FOR ROLE %s ",
                      fmtId(owner));
    if (nspname)
        appendPQExpBuffer(prefix, "IN SCHEMA %s ", fmtId(nspname));
 
    /*
     * There's no such thing as initprivs for a default ACL, so the base ACL
     * is always just the object-type-specific default.
     */
    if (!buildACLCommands("", NULL, NULL, type,
                          acls, acldefault, owner,
                          prefix->data, remoteVersion, sql))
    {
        destroyPQExpBuffer(prefix);
        return false;
    }
 
    destroyPQExpBuffer(prefix);
 
    return true;
}
 
/*
 * This will parse an aclitem string, having the general form
 *      username=privilegecodes/grantor
 *
 * Returns true on success, false on parse error.  On success, the components
 * of the string are returned in the PQExpBuffer parameters.
 *
 * The returned grantee string will be the dequoted username, or an empty
 * string in the case of a grant to PUBLIC.  The returned grantor is the
 * dequoted grantor name.  Privilege characters are translated to GRANT/REVOKE
 * comma-separated privileges lists.  If "privswgo" is non-NULL, the result is
 * separate lists for privileges with grant option ("privswgo") and without
 * ("privs").  Otherwise, "privs" bears every relevant privilege, ignoring the
 * grant option distinction.
 *
 * Note: for cross-version compatibility, it's important to use ALL to
 * represent the privilege sets whenever appropriate.
 */
static bool
parseAclItem(const char *item, const char *type,
             const char *name, const char *subname, int remoteVersion,
             PQExpBuffer grantee, PQExpBuffer grantor,
             PQExpBuffer privs, PQExpBuffer privswgo)
{
    char       *buf;
    bool        all_with_go = true;
    bool        all_without_go = true;
    char       *eqpos;
    char       *slpos;
    char       *pos;
 
    buf = pg_strdup(item);
 
    /* user or group name is string up to = */
    eqpos = dequoteAclUserName(grantee, buf);
    if (*eqpos != '=')
    {
        pg_free(buf);
        return false;
    }
 
    /* grantor should appear after / */
    slpos = strchr(eqpos + 1, '/');
    if (slpos)
    {
        *slpos++ = '\0';
        slpos = dequoteAclUserName(grantor, slpos);
        if (*slpos != '\0')
        {
            pg_free(buf);
            return false;
        }
    }
    else
    {
        pg_free(buf);
        return false;
    }
 
    /* privilege codes */
#define CONVERT_PRIV(code, keywd) \
do { \
    if ((pos = strchr(eqpos + 1, code))) \
    { \
        if (*(pos + 1) == '*' && privswgo != NULL) \
        { \
            AddAcl(privswgo, keywd, subname); \
            all_without_go = false; \
        } \
        else \
        { \
            AddAcl(privs, keywd, subname); \
            all_with_go = false; \
        } \
    } \
    else \
        all_with_go = all_without_go = false; \
} while (0)
 
    resetPQExpBuffer(privs);
    resetPQExpBuffer(privswgo);
 
    if (strcmp(type, "TABLE") == 0 || strcmp(type, "SEQUENCE") == 0 ||
        strcmp(type, "TABLES") == 0 || strcmp(type, "SEQUENCES") == 0)
    {
        CONVERT_PRIV('r', "SELECT");
 
        if (strcmp(type, "SEQUENCE") == 0 ||
            strcmp(type, "SEQUENCES") == 0)
            /* sequence only */
            CONVERT_PRIV('U', "USAGE");
        else
        {
            /* table only */
            CONVERT_PRIV('a', "INSERT");
            CONVERT_PRIV('x', "REFERENCES");
            /* rest are not applicable to columns */
            if (subname == NULL)
            {
                CONVERT_PRIV('d', "DELETE");
                CONVERT_PRIV('t', "TRIGGER");
                CONVERT_PRIV('D', "TRUNCATE");
                CONVERT_PRIV('m', "MAINTAIN");
            }
        }
 
        /* UPDATE */
        CONVERT_PRIV('w', "UPDATE");
    }
    else if (strcmp(type, "FUNCTION") == 0 ||
             strcmp(type, "FUNCTIONS") == 0)
        CONVERT_PRIV('X', "EXECUTE");
    else if (strcmp(type, "PROCEDURE") == 0 ||
             strcmp(type, "PROCEDURES") == 0)
        CONVERT_PRIV('X', "EXECUTE");
    else if (strcmp(type, "LANGUAGE") == 0)
        CONVERT_PRIV('U', "USAGE");
    else if (strcmp(type, "SCHEMA") == 0 ||
             strcmp(type, "SCHEMAS") == 0)
    {
        CONVERT_PRIV('C', "CREATE");
        CONVERT_PRIV('U', "USAGE");
    }
    else if (strcmp(type, "DATABASE") == 0)
    {
        CONVERT_PRIV('C', "CREATE");
        CONVERT_PRIV('c', "CONNECT");
        CONVERT_PRIV('T', "TEMPORARY");
    }
    else if (strcmp(type, "TABLESPACE") == 0)
        CONVERT_PRIV('C', "CREATE");
    else if (strcmp(type, "TYPE") == 0 ||
             strcmp(type, "TYPES") == 0)
        CONVERT_PRIV('U', "USAGE");
    else if (strcmp(type, "FOREIGN DATA WRAPPER") == 0)
        CONVERT_PRIV('U', "USAGE");
    else if (strcmp(type, "FOREIGN SERVER") == 0)
        CONVERT_PRIV('U', "USAGE");
    else if (strcmp(type, "FOREIGN TABLE") == 0)
        CONVERT_PRIV('r', "SELECT");
    else if (strcmp(type, "PARAMETER") == 0)
    {
        CONVERT_PRIV('s', "SET");
        CONVERT_PRIV('A', "ALTER SYSTEM");
    }
    else if (strcmp(type, "LARGE OBJECT") == 0)
    {
        CONVERT_PRIV('r', "SELECT");
        CONVERT_PRIV('w', "UPDATE");
    }
    else
        abort();
 
#undef CONVERT_PRIV
 
    if (all_with_go)
    {
        resetPQExpBuffer(privs);
        printfPQExpBuffer(privswgo, "ALL");
        if (subname)
            appendPQExpBuffer(privswgo, "(%s)", subname);
    }
    else if (all_without_go)
    {
        resetPQExpBuffer(privswgo);
        printfPQExpBuffer(privs, "ALL");
        if (subname)
            appendPQExpBuffer(privs, "(%s)", subname);
    }
 
    pg_free(buf);
 
    return true;
}
 
/*
 * Transfer the role name at *input into the output buffer, adding
 * quoting according to the same rules as putid() in backend's acl.c.
 */
void
quoteAclUserName(PQExpBuffer output, const char *input)
{
    const char *src;
    bool        safe = true;
 
    for (src = input; *src; src++)
    {
        /* This test had better match what putid() does */
        if (!isalnum((unsigned char) *src) && *src != '_')
        {
            safe = false;
            break;
        }
    }
    if (!safe)
        appendPQExpBufferChar(output, '"');
    for (src = input; *src; src++)
    {
        /* A double quote character in a username is encoded as "" */
        if (*src == '"')
            appendPQExpBufferChar(output, '"');
        appendPQExpBufferChar(output, *src);
    }
    if (!safe)
        appendPQExpBufferChar(output, '"');
}
 
/*
 * Transfer a user or group name starting at *input into the output buffer,
 * dequoting if needed.  Returns a pointer to just past the input name.
 * The name is taken to end at an unquoted '=' or end of string.
 * Note: unlike quoteAclUserName(), this first clears the output buffer.
 */
static char *
dequoteAclUserName(PQExpBuffer output, char *input)
{
    resetPQExpBuffer(output);
 
    while (*input && *input != '=')
    {
        /*
         * If user name isn't quoted, then just add it to the output buffer
         */
        if (*input != '"')
            appendPQExpBufferChar(output, *input++);
        else
        {
            /* Otherwise, it's a quoted username */
            input++;
            /* Loop until we come across an unescaped quote */
            while (!(*input == '"' && *(input + 1) != '"'))
            {
                if (*input == '\0')
                    return input;   /* really a syntax error... */
 
                /*
                 * Quoting convention is to escape " as "".  Keep this code in
                 * sync with putid() in backend's acl.c.
                 */
                if (*input == '"' && *(input + 1) == '"')
                    input++;
                appendPQExpBufferChar(output, *input++);
            }
            input++;
        }
    }
    return input;
}
 
/*
 * Append a privilege keyword to a keyword list, inserting comma if needed.
 */
static void
AddAcl(PQExpBuffer aclbuf, const char *keyword, const char *subname)
{
    if (aclbuf->len > 0)
        appendPQExpBufferChar(aclbuf, ',');
    appendPQExpBufferStr(aclbuf, keyword);
    if (subname)
        appendPQExpBuffer(aclbuf, "(%s)", subname);
}
 
 
/*
 * buildShSecLabelQuery
 *
 * Build a query to retrieve security labels for a shared object.
 * The object is identified by its OID plus the name of the catalog
 * it can be found in (e.g., "pg_database" for database names).
 * The query is appended to "sql".  (We don't execute it here so as to
 * keep this file free of assumptions about how to deal with SQL errors.)
 */
void
buildShSecLabelQuery(const char *catalog_name, Oid objectId,
                     PQExpBuffer sql)
{
    appendPQExpBuffer(sql,
                      "SELECT provider, label FROM pg_catalog.pg_shseclabel "
                      "WHERE classoid = 'pg_catalog.%s'::pg_catalog.regclass "
                      "AND objoid = '%u'", catalog_name, objectId);
}
 
/*
 * emitShSecLabels
 *
 * Construct SECURITY LABEL commands using the data retrieved by the query
 * generated by buildShSecLabelQuery, and append them to "buffer".
 * Here, the target object is identified by its type name (e.g. "DATABASE")
 * and its name (not pre-quoted).
 */
void
emitShSecLabels(PGconn *conn, PGresult *res, PQExpBuffer buffer,
                const char *objtype, const char *objname)
{
    int         i;
 
    for (i = 0; i < PQntuples(res); i++)
    {
        char       *provider = PQgetvalue(res, i, 0);
        char       *label = PQgetvalue(res, i, 1);
 
        /* must use fmtId result before calling it again */
        appendPQExpBuffer(buffer,
                          "SECURITY LABEL FOR %s ON %s",
                          fmtId(provider), objtype);
        appendPQExpBuffer(buffer,
                          " %s IS ",
                          fmtId(objname));
        appendStringLiteralConn(buffer, label, conn);
        appendPQExpBufferStr(buffer, ";\n");
    }
}
 
 
/*
 * Detect whether the given GUC variable is of GUC_LIST_QUOTE type.
 *
 * It'd be better if we could inquire this directly from the backend; but even
 * if there were a function for that, it could only tell us about variables
 * currently known to guc.c, so that it'd be unsafe for extensions to declare
 * GUC_LIST_QUOTE variables anyway.  Lacking a solution for that, it doesn't
 * seem worth the work to do more than have this list, which must be kept in
 * sync with the variables actually marked GUC_LIST_QUOTE in guc_tables.c.
 */
bool
variable_is_guc_list_quote(const char *name)
{
    if (pg_strcasecmp(name, "local_preload_libraries") == 0 ||
        pg_strcasecmp(name, "search_path") == 0 ||
        pg_strcasecmp(name, "session_preload_libraries") == 0 ||
        pg_strcasecmp(name, "shared_preload_libraries") == 0 ||
        pg_strcasecmp(name, "temp_tablespaces") == 0 ||
        pg_strcasecmp(name, "unix_socket_directories") == 0)
        return true;
    else
        return false;
}
 
/*
 * SplitGUCList --- parse a string containing identifiers or file names
 *
 * This is used to split the value of a GUC_LIST_QUOTE GUC variable, without
 * presuming whether the elements will be taken as identifiers or file names.
 * See comparable code in src/backend/utils/adt/varlena.c.
 *
 * Inputs:
 *  rawstring: the input string; must be overwritable!  On return, it's
 *             been modified to contain the separated identifiers.
 *  separator: the separator punctuation expected between identifiers
 *             (typically '.' or ',').  Whitespace may also appear around
 *             identifiers.
 * Outputs:
 *  namelist: receives a malloc'd, null-terminated array of pointers to
 *            identifiers within rawstring.  Caller should free this
 *            even on error return.
 *
 * Returns true if okay, false if there is a syntax error in the string.
 */
bool
SplitGUCList(char *rawstring, char separator,
             char ***namelist)
{
    char       *nextp = rawstring;
    bool        done = false;
    char      **nextptr;
 
    /*
     * Since we disallow empty identifiers, this is a conservative
     * overestimate of the number of pointers we could need.  Allow one for
     * list terminator.
     */
    *namelist = nextptr = (char **)
        pg_malloc((strlen(rawstring) / 2 + 2) * sizeof(char *));
    *nextptr = NULL;
 
    while (isspace((unsigned char) *nextp))
        nextp++;                /* skip leading whitespace */
 
    if (*nextp == '\0')
        return true;            /* allow empty string */
 
    /* At the top of the loop, we are at start of a new identifier. */
    do
    {
        char       *curname;
        char       *endp;
 
        if (*nextp == '"')
        {
            /* Quoted name --- collapse quote-quote pairs */
            curname = nextp + 1;
            for (;;)
            {
                endp = strchr(nextp + 1, '"');
                if (endp == NULL)
                    return false;   /* mismatched quotes */
                if (endp[1] != '"')
                    break;      /* found end of quoted name */
                /* Collapse adjacent quotes into one quote, and look again */
                memmove(endp, endp + 1, strlen(endp));
                nextp = endp;
            }
            /* endp now points at the terminating quote */
            nextp = endp + 1;
        }
        else
        {
            /* Unquoted name --- extends to separator or whitespace */
            curname = nextp;
            while (*nextp && *nextp != separator &&
                   !isspace((unsigned char) *nextp))
                nextp++;
            endp = nextp;
            if (curname == nextp)
                return false;   /* empty unquoted name not allowed */
        }
 
        while (isspace((unsigned char) *nextp))
            nextp++;            /* skip trailing whitespace */
 
        if (*nextp == separator)
        {
            nextp++;
            while (isspace((unsigned char) *nextp))
                nextp++;        /* skip leading whitespace for next */
            /* we expect another name, so done remains false */
        }
        else if (*nextp == '\0')
            done = true;
        else
            return false;       /* invalid syntax */
 
        /* Now safe to overwrite separator with a null */
        *endp = '\0';
 
        /*
         * Finished isolating current name --- add it to output array
         */
        *nextptr++ = curname;
 
        /* Loop back if we didn't reach end of string */
    } while (!done);
 
    *nextptr = NULL;
    return true;
}
 
/*
 * Helper function for dumping "ALTER DATABASE/ROLE SET ..." commands.
 *
 * Parse the contents of configitem (a "name=value" string), wrap it in
 * a complete ALTER command, and append it to buf.
 *
 * type is DATABASE or ROLE, and name is the name of the database or role.
 * If we need an "IN" clause, type2 and name2 similarly define what to put
 * there; otherwise they should be NULL.
 * conn is used only to determine string-literal quoting conventions.
 */
void
makeAlterConfigCommand(PGconn *conn, const char *configitem,
                       const char *userset,
                       const char *type, const char *name,
                       const char *type2, const char *name2,
                       PQExpBuffer buf)
{
    char       *mine;
    char       *pos;
 
    /* Parse the configitem.  If we can't find an "=", silently do nothing. */
    mine = pg_strdup(configitem);
    pos = strchr(mine, '=');
    if (pos == NULL)
    {
        pg_free(mine);
        return;
    }
    *pos++ = '\0';
 
    /* Build the command, with suitable quoting for everything. */
    appendPQExpBuffer(buf, "ALTER %s %s ", type, fmtId(name));
    if (type2 != NULL && name2 != NULL)
        appendPQExpBuffer(buf, "IN %s %s ", type2, fmtId(name2));
    appendPQExpBuffer(buf, "SET %s TO ", fmtId(mine));
 
    /*
     * Variables that are marked GUC_LIST_QUOTE were already fully quoted by
     * flatten_set_variable_args() before they were put into the setconfig
     * array.  However, because the quoting rules used there aren't exactly
     * like SQL's, we have to break the list value apart and then quote the
     * elements as string literals.  (The elements may be double-quoted as-is,
     * but we can't just feed them to the SQL parser; it would do the wrong
     * thing with elements that are zero-length or longer than NAMEDATALEN.)
     *
     * Variables that are not so marked should just be emitted as simple
     * string literals.  If the variable is not known to
     * variable_is_guc_list_quote(), we'll do that; this makes it unsafe to
     * use GUC_LIST_QUOTE for extension variables.
     */
    if (variable_is_guc_list_quote(mine))
    {
        char      **namelist;
        char      **nameptr;
 
        /* Parse string into list of identifiers */
        /* this shouldn't fail really */
        if (SplitGUCList(pos, ',', &namelist))
        {
            for (nameptr = namelist; *nameptr; nameptr++)
            {
                if (nameptr != namelist)
                    appendPQExpBufferStr(buf, ", ");
                appendStringLiteralConn(buf, *nameptr, conn);
            }
        }
        pg_free(namelist);
    }
    else
        appendStringLiteralConn(buf, pos, conn);
 
    /* Add USER SET flag if specified in the string */
    if (userset && !strcmp(userset, "t"))
        appendPQExpBufferStr(buf, " USER SET");
 
    appendPQExpBufferStr(buf, ";\n");
 
    pg_free(mine);
}