extension.c

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/*-------------------------------------------------------------------------
 *
 * extension.c
 *    Commands to manipulate extensions
 *
 * Extensions in PostgreSQL allow management of collections of SQL objects.
 *
 * All we need internally to manage an extension is an OID so that the
 * dependent objects can be associated with it.  An extension is created by
 * populating the pg_extension catalog from a "control" file.
 * The extension control file is parsed with the same parser we use for
 * postgresql.conf.  An extension also has an installation script file,
 * containing SQL commands to create the extension's objects.
 *
 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/commands/extension.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <dirent.h>
#include <limits.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <unistd.h>

#include "access/genam.h"
#include "access/htup_details.h"
#include "access/relation.h"
#include "access/sysattr.h"
#include "access/table.h"
#include "access/xact.h"
#include "catalog/catalog.h"
#include "catalog/dependency.h"
#include "catalog/indexing.h"
#include "catalog/namespace.h"
#include "catalog/objectaccess.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_depend.h"
#include "catalog/pg_extension.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_type.h"
#include "commands/alter.h"
#include "commands/comment.h"
#include "commands/defrem.h"
#include "commands/extension.h"
#include "commands/schemacmds.h"
#include "funcapi.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "storage/fd.h"
#include "tcop/utility.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/rel.h"
#include "utils/snapmgr.h"
#include "utils/varlena.h"


/* Globally visible state variables */
bool        creating_extension = false;
Oid         CurrentExtensionObject = InvalidOid;

/*
 * Internal data structure to hold the results of parsing a control file
 */
typedef struct ExtensionControlFile
{
    char       *name;           /* name of the extension */
    char       *directory;      /* directory for script files */
    char       *default_version;    /* default install target version, if any */
    char       *module_pathname;    /* string to substitute for
                                     * MODULE_PATHNAME */
    char       *comment;        /* comment, if any */
    char       *schema;         /* target schema (allowed if !relocatable) */
    bool        relocatable;    /* is ALTER EXTENSION SET SCHEMA supported? */
    bool        superuser;      /* must be superuser to install? */
    int         encoding;       /* encoding of the script file, or -1 */
    List       *requires;       /* names of prerequisite extensions */
} ExtensionControlFile;

/*
 * Internal data structure for update path information
 */
typedef struct ExtensionVersionInfo
{
    char       *name;           /* name of the starting version */
    List       *reachable;      /* List of ExtensionVersionInfo's */
    bool        installable;    /* does this version have an install script? */
    /* working state for Dijkstra's algorithm: */
    bool        distance_known; /* is distance from start known yet? */
    int         distance;       /* current worst-case distance estimate */
    struct ExtensionVersionInfo *previous;  /* current best predecessor */
} ExtensionVersionInfo;

/* Local functions */
static List *find_update_path(List *evi_list,
                              ExtensionVersionInfo *evi_start,
                              ExtensionVersionInfo *evi_target,
                              bool reject_indirect,
                              bool reinitialize);
static Oid  get_required_extension(char *reqExtensionName,
                                   char *extensionName,
                                   char *origSchemaName,
                                   bool cascade,
                                   List *parents,
                                   bool is_create);
static void get_available_versions_for_extension(ExtensionControlFile *pcontrol,
                                                 Tuplestorestate *tupstore,
                                                 TupleDesc tupdesc);
static Datum convert_requires_to_datum(List *requires);
static void ApplyExtensionUpdates(Oid extensionOid,
                                  ExtensionControlFile *pcontrol,
                                  const char *initialVersion,
                                  List *updateVersions,
                                  char *origSchemaName,
                                  bool cascade,
                                  bool is_create);
static char *read_whole_file(const char *filename, int *length);


/*
 * get_extension_oid - given an extension name, look up the OID
 *
 * If missing_ok is false, throw an error if extension name not found.  If
 * true, just return InvalidOid.
 */
Oid
get_extension_oid(const char *extname, bool missing_ok)
{
    Oid         result;
    Relation    rel;
    SysScanDesc scandesc;
    HeapTuple   tuple;
    ScanKeyData entry[1];

    rel = table_open(ExtensionRelationId, AccessShareLock);

    ScanKeyInit(&entry[0],
                Anum_pg_extension_extname,
                BTEqualStrategyNumber, F_NAMEEQ,
                CStringGetDatum(extname));

    scandesc = systable_beginscan(rel, ExtensionNameIndexId, true,
                                  NULL, 1, entry);

    tuple = systable_getnext(scandesc);

    /* We assume that there can be at most one matching tuple */
    if (HeapTupleIsValid(tuple))
        result = ((Form_pg_extension) GETSTRUCT(tuple))->oid;
    else
        result = InvalidOid;

    systable_endscan(scandesc);

    table_close(rel, AccessShareLock);

    if (!OidIsValid(result) && !missing_ok)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("extension \"%s\" does not exist",
                        extname)));

    return result;
}

/*
 * get_extension_name - given an extension OID, look up the name
 *
 * Returns a palloc'd string, or NULL if no such extension.
 */
char *
get_extension_name(Oid ext_oid)
{
    char       *result;
    Relation    rel;
    SysScanDesc scandesc;
    HeapTuple   tuple;
    ScanKeyData entry[1];

    rel = table_open(ExtensionRelationId, AccessShareLock);

    ScanKeyInit(&entry[0],
                Anum_pg_extension_oid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(ext_oid));

    scandesc = systable_beginscan(rel, ExtensionOidIndexId, true,
                                  NULL, 1, entry);

    tuple = systable_getnext(scandesc);

    /* We assume that there can be at most one matching tuple */
    if (HeapTupleIsValid(tuple))
        result = pstrdup(NameStr(((Form_pg_extension) GETSTRUCT(tuple))->extname));
    else
        result = NULL;

    systable_endscan(scandesc);

    table_close(rel, AccessShareLock);

    return result;
}

/*
 * get_extension_schema - given an extension OID, fetch its extnamespace
 *
 * Returns InvalidOid if no such extension.
 */
static Oid
get_extension_schema(Oid ext_oid)
{
    Oid         result;
    Relation    rel;
    SysScanDesc scandesc;
    HeapTuple   tuple;
    ScanKeyData entry[1];

    rel = table_open(ExtensionRelationId, AccessShareLock);

    ScanKeyInit(&entry[0],
                Anum_pg_extension_oid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(ext_oid));

    scandesc = systable_beginscan(rel, ExtensionOidIndexId, true,
                                  NULL, 1, entry);

    tuple = systable_getnext(scandesc);

    /* We assume that there can be at most one matching tuple */
    if (HeapTupleIsValid(tuple))
        result = ((Form_pg_extension) GETSTRUCT(tuple))->extnamespace;
    else
        result = InvalidOid;

    systable_endscan(scandesc);

    table_close(rel, AccessShareLock);

    return result;
}

/*
 * Utility functions to check validity of extension and version names
 */
static void
check_valid_extension_name(const char *extensionname)
{
    int         namelen = strlen(extensionname);

    /*
     * Disallow empty names (the parser rejects empty identifiers anyway, but
     * let's check).
     */
    if (namelen == 0)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid extension name: \"%s\"", extensionname),
                 errdetail("Extension names must not be empty.")));

    /*
     * No double dashes, since that would make script filenames ambiguous.
     */
    if (strstr(extensionname, "--"))
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid extension name: \"%s\"", extensionname),
                 errdetail("Extension names must not contain \"--\".")));

    /*
     * No leading or trailing dash either.  (We could probably allow this, but
     * it would require much care in filename parsing and would make filenames
     * visually if not formally ambiguous.  Since there's no real-world use
     * case, let's just forbid it.)
     */
    if (extensionname[0] == '-' || extensionname[namelen - 1] == '-')
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid extension name: \"%s\"", extensionname),
                 errdetail("Extension names must not begin or end with \"-\".")));

    /*
     * No directory separators either (this is sufficient to prevent ".."
     * style attacks).
     */
    if (first_dir_separator(extensionname) != NULL)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid extension name: \"%s\"", extensionname),
                 errdetail("Extension names must not contain directory separator characters.")));
}

static void
check_valid_version_name(const char *versionname)
{
    int         namelen = strlen(versionname);

    /*
     * Disallow empty names (we could possibly allow this, but there seems
     * little point).
     */
    if (namelen == 0)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid extension version name: \"%s\"", versionname),
                 errdetail("Version names must not be empty.")));

    /*
     * No double dashes, since that would make script filenames ambiguous.
     */
    if (strstr(versionname, "--"))
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid extension version name: \"%s\"", versionname),
                 errdetail("Version names must not contain \"--\".")));

    /*
     * No leading or trailing dash either.
     */
    if (versionname[0] == '-' || versionname[namelen - 1] == '-')
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid extension version name: \"%s\"", versionname),
                 errdetail("Version names must not begin or end with \"-\".")));

    /*
     * No directory separators either (this is sufficient to prevent ".."
     * style attacks).
     */
    if (first_dir_separator(versionname) != NULL)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid extension version name: \"%s\"", versionname),
                 errdetail("Version names must not contain directory separator characters.")));
}

/*
 * Utility functions to handle extension-related path names
 */
static bool
is_extension_control_filename(const char *filename)
{
    const char *extension = strrchr(filename, '.');

    return (extension != NULL) && (strcmp(extension, ".control") == 0);
}

static bool
is_extension_script_filename(const char *filename)
{
    const char *extension = strrchr(filename, '.');

    return (extension != NULL) && (strcmp(extension, ".sql") == 0);
}

static char *
get_extension_control_directory(void)
{
    char        sharepath[MAXPGPATH];
    char       *result;

    get_share_path(my_exec_path, sharepath);
    result = (char *) palloc(MAXPGPATH);
    snprintf(result, MAXPGPATH, "%s/extension", sharepath);

    return result;
}

static char *
get_extension_control_filename(const char *extname)
{
    char        sharepath[MAXPGPATH];
    char       *result;

    get_share_path(my_exec_path, sharepath);
    result = (char *) palloc(MAXPGPATH);
    snprintf(result, MAXPGPATH, "%s/extension/%s.control",
             sharepath, extname);

    return result;
}

static char *
get_extension_script_directory(ExtensionControlFile *control)
{
    char        sharepath[MAXPGPATH];
    char       *result;

    /*
     * The directory parameter can be omitted, absolute, or relative to the
     * installation's share directory.
     */
    if (!control->directory)
        return get_extension_control_directory();

    if (is_absolute_path(control->directory))
        return pstrdup(control->directory);

    get_share_path(my_exec_path, sharepath);
    result = (char *) palloc(MAXPGPATH);
    snprintf(result, MAXPGPATH, "%s/%s", sharepath, control->directory);

    return result;
}

static char *
get_extension_aux_control_filename(ExtensionControlFile *control,
                                   const char *version)
{
    char       *result;
    char       *scriptdir;

    scriptdir = get_extension_script_directory(control);

    result = (char *) palloc(MAXPGPATH);
    snprintf(result, MAXPGPATH, "%s/%s--%s.control",
             scriptdir, control->name, version);

    pfree(scriptdir);

    return result;
}

static char *
get_extension_script_filename(ExtensionControlFile *control,
                              const char *from_version, const char *version)
{
    char       *result;
    char       *scriptdir;

    scriptdir = get_extension_script_directory(control);

    result = (char *) palloc(MAXPGPATH);
    if (from_version)
        snprintf(result, MAXPGPATH, "%s/%s--%s--%s.sql",
                 scriptdir, control->name, from_version, version);
    else
        snprintf(result, MAXPGPATH, "%s/%s--%s.sql",
                 scriptdir, control->name, version);

    pfree(scriptdir);

    return result;
}


/*
 * Parse contents of primary or auxiliary control file, and fill in
 * fields of *control.  We parse primary file if version == NULL,
 * else the optional auxiliary file for that version.
 *
 * Control files are supposed to be very short, half a dozen lines,
 * so we don't worry about memory allocation risks here.  Also we don't
 * worry about what encoding it's in; all values are expected to be ASCII.
 */
static void
parse_extension_control_file(ExtensionControlFile *control,
                             const char *version)
{
    char       *filename;
    FILE       *file;
    ConfigVariable *item,
               *head = NULL,
               *tail = NULL;

    /*
     * Locate the file to read.  Auxiliary files are optional.
     */
    if (version)
        filename = get_extension_aux_control_filename(control, version);
    else
        filename = get_extension_control_filename(control->name);

    if ((file = AllocateFile(filename, "r")) == NULL)
    {
        if (version && errno == ENOENT)
        {
            /* no auxiliary file for this version */
            pfree(filename);
            return;
        }
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not open extension control file \"%s\": %m",
                        filename)));
    }

    /*
     * Parse the file content, using GUC's file parsing code.  We need not
     * check the return value since any errors will be thrown at ERROR level.
     */
    (void) ParseConfigFp(file, filename, 0, ERROR, &head, &tail);

    FreeFile(file);

    /*
     * Convert the ConfigVariable list into ExtensionControlFile entries.
     */
    for (item = head; item != NULL; item = item->next)
    {
        if (strcmp(item->name, "directory") == 0)
        {
            if (version)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("parameter \"%s\" cannot be set in a secondary extension control file",
                                item->name)));

            control->directory = pstrdup(item->value);
        }
        else if (strcmp(item->name, "default_version") == 0)
        {
            if (version)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("parameter \"%s\" cannot be set in a secondary extension control file",
                                item->name)));

            control->default_version = pstrdup(item->value);
        }
        else if (strcmp(item->name, "module_pathname") == 0)
        {
            control->module_pathname = pstrdup(item->value);
        }
        else if (strcmp(item->name, "comment") == 0)
        {
            control->comment = pstrdup(item->value);
        }
        else if (strcmp(item->name, "schema") == 0)
        {
            control->schema = pstrdup(item->value);
        }
        else if (strcmp(item->name, "relocatable") == 0)
        {
            if (!parse_bool(item->value, &control->relocatable))
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("parameter \"%s\" requires a Boolean value",
                                item->name)));
        }
        else if (strcmp(item->name, "superuser") == 0)
        {
            if (!parse_bool(item->value, &control->superuser))
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("parameter \"%s\" requires a Boolean value",
                                item->name)));
        }
        else if (strcmp(item->name, "encoding") == 0)
        {
            control->encoding = pg_valid_server_encoding(item->value);
            if (control->encoding < 0)
                ereport(ERROR,
                        (errcode(ERRCODE_UNDEFINED_OBJECT),
                         errmsg("\"%s\" is not a valid encoding name",
                                item->value)));
        }
        else if (strcmp(item->name, "requires") == 0)
        {
            /* Need a modifiable copy of string */
            char       *rawnames = pstrdup(item->value);

            /* Parse string into list of identifiers */
            if (!SplitIdentifierString(rawnames, ',', &control->requires))
            {
                /* syntax error in name list */
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("parameter \"%s\" must be a list of extension names",
                                item->name)));
            }
        }
        else
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("unrecognized parameter \"%s\" in file \"%s\"",
                            item->name, filename)));
    }

    FreeConfigVariables(head);

    if (control->relocatable && control->schema != NULL)
        ereport(ERROR,
                (errcode(ERRCODE_SYNTAX_ERROR),
                 errmsg("parameter \"schema\" cannot be specified when \"relocatable\" is true")));

    pfree(filename);
}

/*
 * Read the primary control file for the specified extension.
 */
static ExtensionControlFile *
read_extension_control_file(const char *extname)
{
    ExtensionControlFile *control;

    /*
     * Set up default values.  Pointer fields are initially null.
     */
    control = (ExtensionControlFile *) palloc0(sizeof(ExtensionControlFile));
    control->name = pstrdup(extname);
    control->relocatable = false;
    control->superuser = true;
    control->encoding = -1;

    /*
     * Parse the primary control file.
     */
    parse_extension_control_file(control, NULL);

    return control;
}

/*
 * Read the auxiliary control file for the specified extension and version.
 *
 * Returns a new modified ExtensionControlFile struct; the original struct
 * (reflecting just the primary control file) is not modified.
 */
static ExtensionControlFile *
read_extension_aux_control_file(const ExtensionControlFile *pcontrol,
                                const char *version)
{
    ExtensionControlFile *acontrol;

    /*
     * Flat-copy the struct.  Pointer fields share values with original.
     */
    acontrol = (ExtensionControlFile *) palloc(sizeof(ExtensionControlFile));
    memcpy(acontrol, pcontrol, sizeof(ExtensionControlFile));

    /*
     * Parse the auxiliary control file, overwriting struct fields
     */
    parse_extension_control_file(acontrol, version);

    return acontrol;
}

/*
 * Read an SQL script file into a string, and convert to database encoding
 */
static char *
read_extension_script_file(const ExtensionControlFile *control,
                           const char *filename)
{
    int         src_encoding;
    char       *src_str;
    char       *dest_str;
    int         len;

    src_str = read_whole_file(filename, &len);

    /* use database encoding if not given */
    if (control->encoding < 0)
        src_encoding = GetDatabaseEncoding();
    else
        src_encoding = control->encoding;

    /* make sure that source string is valid in the expected encoding */
    pg_verify_mbstr_len(src_encoding, src_str, len, false);

    /*
     * Convert the encoding to the database encoding. read_whole_file
     * null-terminated the string, so if no conversion happens the string is
     * valid as is.
     */
    dest_str = pg_any_to_server(src_str, len, src_encoding);

    return dest_str;
}

/*
 * Execute given SQL string.
 *
 * Note: it's tempting to just use SPI to execute the string, but that does
 * not work very well.  The really serious problem is that SPI will parse,
 * analyze, and plan the whole string before executing any of it; of course
 * this fails if there are any plannable statements referring to objects
 * created earlier in the script.  A lesser annoyance is that SPI insists
 * on printing the whole string as errcontext in case of any error, and that
 * could be very long.
 */
static void
execute_sql_string(const char *sql)
{
    List       *raw_parsetree_list;
    DestReceiver *dest;
    ListCell   *lc1;

    /*
     * Parse the SQL string into a list of raw parse trees.
     */
    raw_parsetree_list = pg_parse_query(sql);

    /* All output from SELECTs goes to the bit bucket */
    dest = CreateDestReceiver(DestNone);

    /*
     * Do parse analysis, rule rewrite, planning, and execution for each raw
     * parsetree.  We must fully execute each query before beginning parse
     * analysis on the next one, since there may be interdependencies.
     */
    foreach(lc1, raw_parsetree_list)
    {
        RawStmt    *parsetree = lfirst_node(RawStmt, lc1);
        MemoryContext per_parsetree_context,
                    oldcontext;
        List       *stmt_list;
        ListCell   *lc2;

        /*
         * We do the work for each parsetree in a short-lived context, to
         * limit the memory used when there are many commands in the string.
         */
        per_parsetree_context =
            AllocSetContextCreate(CurrentMemoryContext,
                                  "execute_sql_string per-statement context",
                                  ALLOCSET_DEFAULT_SIZES);
        oldcontext = MemoryContextSwitchTo(per_parsetree_context);

        /* Be sure parser can see any DDL done so far */
        CommandCounterIncrement();

        stmt_list = pg_analyze_and_rewrite(parsetree,
                                           sql,
                                           NULL,
                                           0,
                                           NULL);
        stmt_list = pg_plan_queries(stmt_list, CURSOR_OPT_PARALLEL_OK, NULL);

        foreach(lc2, stmt_list)
        {
            PlannedStmt *stmt = lfirst_node(PlannedStmt, lc2);

            CommandCounterIncrement();

            PushActiveSnapshot(GetTransactionSnapshot());

            if (stmt->utilityStmt == NULL)
            {
                QueryDesc  *qdesc;

                qdesc = CreateQueryDesc(stmt,
                                        sql,
                                        GetActiveSnapshot(), NULL,
                                        dest, NULL, NULL, 0);

                ExecutorStart(qdesc, 0);
                ExecutorRun(qdesc, ForwardScanDirection, 0, true);
                ExecutorFinish(qdesc);
                ExecutorEnd(qdesc);

                FreeQueryDesc(qdesc);
            }
            else
            {
                if (IsA(stmt->utilityStmt, TransactionStmt))
                    ereport(ERROR,
                            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                             errmsg("transaction control statements are not allowed within an extension script")));

                ProcessUtility(stmt,
                               sql,
                               PROCESS_UTILITY_QUERY,
                               NULL,
                               NULL,
                               dest,
                               NULL);
            }

            PopActiveSnapshot();
        }

        /* Clean up per-parsetree context. */
        MemoryContextSwitchTo(oldcontext);
        MemoryContextDelete(per_parsetree_context);
    }

    /* Be sure to advance the command counter after the last script command */
    CommandCounterIncrement();
}

/*
 * Execute the appropriate script file for installing or updating the extension
 *
 * If from_version isn't NULL, it's an update
 */
static void
execute_extension_script(Oid extensionOid, ExtensionControlFile *control,
                         const char *from_version,
                         const char *version,
                         List *requiredSchemas,
                         const char *schemaName, Oid schemaOid)
{
    char       *filename;
    int         save_nestlevel;
    StringInfoData pathbuf;
    ListCell   *lc;

    /*
     * Enforce superuser-ness if appropriate.  We postpone this check until
     * here so that the flag is correctly associated with the right script(s)
     * if it's set in secondary control files.
     */
    if (control->superuser && !superuser())
    {
        if (from_version == NULL)
            ereport(ERROR,
                    (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                     errmsg("permission denied to create extension \"%s\"",
                            control->name),
                     errhint("Must be superuser to create this extension.")));
        else
            ereport(ERROR,
                    (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                     errmsg("permission denied to update extension \"%s\"",
                            control->name),
                     errhint("Must be superuser to update this extension.")));
    }

    filename = get_extension_script_filename(control, from_version, version);

    /*
     * Force client_min_messages and log_min_messages to be at least WARNING,
     * so that we won't spam the user with useless NOTICE messages from common
     * script actions like creating shell types.
     *
     * We use the equivalent of a function SET option to allow the setting to
     * persist for exactly the duration of the script execution.  guc.c also
     * takes care of undoing the setting on error.
     */
    save_nestlevel = NewGUCNestLevel();

    if (client_min_messages < WARNING)
        (void) set_config_option("client_min_messages", "warning",
                                 PGC_USERSET, PGC_S_SESSION,
                                 GUC_ACTION_SAVE, true, 0, false);
    if (log_min_messages < WARNING)
        (void) set_config_option("log_min_messages", "warning",
                                 PGC_SUSET, PGC_S_SESSION,
                                 GUC_ACTION_SAVE, true, 0, false);

    /*
     * Set up the search path to contain the target schema, then the schemas
     * of any prerequisite extensions, and nothing else.  In particular this
     * makes the target schema be the default creation target namespace.
     *
     * Note: it might look tempting to use PushOverrideSearchPath for this,
     * but we cannot do that.  We have to actually set the search_path GUC in
     * case the extension script examines or changes it.  In any case, the
     * GUC_ACTION_SAVE method is just as convenient.
     */
    initStringInfo(&pathbuf);
    appendStringInfoString(&pathbuf, quote_identifier(schemaName));
    foreach(lc, requiredSchemas)
    {
        Oid         reqschema = lfirst_oid(lc);
        char       *reqname = get_namespace_name(reqschema);

        if (reqname)
            appendStringInfo(&pathbuf, ", %s", quote_identifier(reqname));
    }

    (void) set_config_option("search_path", pathbuf.data,
                             PGC_USERSET, PGC_S_SESSION,
                             GUC_ACTION_SAVE, true, 0, false);

    /*
     * Set creating_extension and related variables so that
     * recordDependencyOnCurrentExtension and other functions do the right
     * things.  On failure, ensure we reset these variables.
     */
    creating_extension = true;
    CurrentExtensionObject = extensionOid;
    PG_TRY();
    {
        char       *c_sql = read_extension_script_file(control, filename);
        Datum       t_sql;

        /* We use various functions that want to operate on text datums */
        t_sql = CStringGetTextDatum(c_sql);

        /*
         * Reduce any lines beginning with "\echo" to empty.  This allows
         * scripts to contain messages telling people not to run them via
         * psql, which has been found to be necessary due to old habits.
         */
        t_sql = DirectFunctionCall4Coll(textregexreplace,
                                        C_COLLATION_OID,
                                        t_sql,
                                        CStringGetTextDatum("^\\\\echo.*$"),
                                        CStringGetTextDatum(""),
                                        CStringGetTextDatum("ng"));

        /*
         * If it's not relocatable, substitute the target schema name for
         * occurrences of @extschema@.
         *
         * For a relocatable extension, we needn't do this.  There cannot be
         * any need for @extschema@, else it wouldn't be relocatable.
         */
        if (!control->relocatable)
        {
            const char *qSchemaName = quote_identifier(schemaName);

            t_sql = DirectFunctionCall3Coll(replace_text,
                                            C_COLLATION_OID,
                                            t_sql,
                                            CStringGetTextDatum("@extschema@"),
                                            CStringGetTextDatum(qSchemaName));
        }

        /*
         * If module_pathname was set in the control file, substitute its
         * value for occurrences of MODULE_PATHNAME.
         */
        if (control->module_pathname)
        {
            t_sql = DirectFunctionCall3Coll(replace_text,
                                            C_COLLATION_OID,
                                            t_sql,
                                            CStringGetTextDatum("MODULE_PATHNAME"),
                                            CStringGetTextDatum(control->module_pathname));
        }

        /* And now back to C string */
        c_sql = text_to_cstring(DatumGetTextPP(t_sql));

        execute_sql_string(c_sql);
    }
    PG_FINALLY();
    {
        creating_extension = false;
        CurrentExtensionObject = InvalidOid;
    }
    PG_END_TRY();

    /*
     * Restore the GUC variables we set above.
     */
    AtEOXact_GUC(true, save_nestlevel);
}

/*
 * Find or create an ExtensionVersionInfo for the specified version name
 *
 * Currently, we just use a List of the ExtensionVersionInfo's.  Searching
 * for them therefore uses about O(N^2) time when there are N versions of
 * the extension.  We could change the data structure to a hash table if
 * this ever becomes a bottleneck.
 */
static ExtensionVersionInfo *
get_ext_ver_info(const char *versionname, List **evi_list)
{
    ExtensionVersionInfo *evi;
    ListCell   *lc;

    foreach(lc, *evi_list)
    {
        evi = (ExtensionVersionInfo *) lfirst(lc);
        if (strcmp(evi->name, versionname) == 0)
            return evi;
    }

    evi = (ExtensionVersionInfo *) palloc(sizeof(ExtensionVersionInfo));
    evi->name = pstrdup(versionname);
    evi->reachable = NIL;
    evi->installable = false;
    /* initialize for later application of Dijkstra's algorithm */
    evi->distance_known = false;
    evi->distance = INT_MAX;
    evi->previous = NULL;

    *evi_list = lappend(*evi_list, evi);

    return evi;
}

/*
 * Locate the nearest unprocessed ExtensionVersionInfo
 *
 * This part of the algorithm is also about O(N^2).  A priority queue would
 * make it much faster, but for now there's no need.
 */
static ExtensionVersionInfo *
get_nearest_unprocessed_vertex(List *evi_list)
{
    ExtensionVersionInfo *evi = NULL;
    ListCell   *lc;

    foreach(lc, evi_list)
    {
        ExtensionVersionInfo *evi2 = (ExtensionVersionInfo *) lfirst(lc);

        /* only vertices whose distance is still uncertain are candidates */
        if (evi2->distance_known)
            continue;
        /* remember the closest such vertex */
        if (evi == NULL ||
            evi->distance > evi2->distance)
            evi = evi2;
    }

    return evi;
}

/*
 * Obtain information about the set of update scripts available for the
 * specified extension.  The result is a List of ExtensionVersionInfo
 * structs, each with a subsidiary list of the ExtensionVersionInfos for
 * the versions that can be reached in one step from that version.
 */
static List *
get_ext_ver_list(ExtensionControlFile *control)
{
    List       *evi_list = NIL;
    int         extnamelen = strlen(control->name);
    char       *location;
    DIR        *dir;
    struct dirent *de;

    location = get_extension_script_directory(control);
    dir = AllocateDir(location);
    while ((de = ReadDir(dir, location)) != NULL)
    {
        char       *vername;
        char       *vername2;
        ExtensionVersionInfo *evi;
        ExtensionVersionInfo *evi2;

        /* must be a .sql file ... */
        if (!is_extension_script_filename(de->d_name))
            continue;

        /* ... matching extension name followed by separator */
        if (strncmp(de->d_name, control->name, extnamelen) != 0 ||
            de->d_name[extnamelen] != '-' ||
            de->d_name[extnamelen + 1] != '-')
            continue;

        /* extract version name(s) from 'extname--something.sql' filename */
        vername = pstrdup(de->d_name + extnamelen + 2);
        *strrchr(vername, '.') = '\0';
        vername2 = strstr(vername, "--");
        if (!vername2)
        {
            /* It's an install, not update, script; record its version name */
            evi = get_ext_ver_info(vername, &evi_list);
            evi->installable = true;
            continue;
        }
        *vername2 = '\0';       /* terminate first version */
        vername2 += 2;          /* and point to second */

        /* if there's a third --, it's bogus, ignore it */
        if (strstr(vername2, "--"))
            continue;

        /* Create ExtensionVersionInfos and link them together */
        evi = get_ext_ver_info(vername, &evi_list);
        evi2 = get_ext_ver_info(vername2, &evi_list);
        evi->reachable = lappend(evi->reachable, evi2);
    }
    FreeDir(dir);

    return evi_list;
}

/*
 * Given an initial and final version name, identify the sequence of update
 * scripts that have to be applied to perform that update.
 *
 * Result is a List of names of versions to transition through (the initial
 * version is *not* included).
 */
static List *
identify_update_path(ExtensionControlFile *control,
                     const char *oldVersion, const char *newVersion)
{
    List       *result;
    List       *evi_list;
    ExtensionVersionInfo *evi_start;
    ExtensionVersionInfo *evi_target;

    /* Extract the version update graph from the script directory */
    evi_list = get_ext_ver_list(control);

    /* Initialize start and end vertices */
    evi_start = get_ext_ver_info(oldVersion, &evi_list);
    evi_target = get_ext_ver_info(newVersion, &evi_list);

    /* Find shortest path */
    result = find_update_path(evi_list, evi_start, evi_target, false, false);

    if (result == NIL)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("extension \"%s\" has no update path from version \"%s\" to version \"%s\"",
                        control->name, oldVersion, newVersion)));

    return result;
}

/*
 * Apply Dijkstra's algorithm to find the shortest path from evi_start to
 * evi_target.
 *
 * If reject_indirect is true, ignore paths that go through installable
 * versions.  This saves work when the caller will consider starting from
 * all installable versions anyway.
 *
 * If reinitialize is false, assume the ExtensionVersionInfo list has not
 * been used for this before, and the initialization done by get_ext_ver_info
 * is still good.  Otherwise, reinitialize all transient fields used here.
 *
 * Result is a List of names of versions to transition through (the initial
 * version is *not* included).  Returns NIL if no such path.
 */
static List *
find_update_path(List *evi_list,
                 ExtensionVersionInfo *evi_start,
                 ExtensionVersionInfo *evi_target,
                 bool reject_indirect,
                 bool reinitialize)
{
    List       *result;
    ExtensionVersionInfo *evi;
    ListCell   *lc;

    /* Caller error if start == target */
    Assert(evi_start != evi_target);
    /* Caller error if reject_indirect and target is installable */
    Assert(!(reject_indirect && evi_target->installable));

    if (reinitialize)
    {
        foreach(lc, evi_list)
        {
            evi = (ExtensionVersionInfo *) lfirst(lc);
            evi->distance_known = false;
            evi->distance = INT_MAX;
            evi->previous = NULL;
        }
    }

    evi_start->distance = 0;

    while ((evi = get_nearest_unprocessed_vertex(evi_list)) != NULL)
    {
        if (evi->distance == INT_MAX)
            break;              /* all remaining vertices are unreachable */
        evi->distance_known = true;
        if (evi == evi_target)
            break;              /* found shortest path to target */
        foreach(lc, evi->reachable)
        {
            ExtensionVersionInfo *evi2 = (ExtensionVersionInfo *) lfirst(lc);
            int         newdist;

            /* if reject_indirect, treat installable versions as unreachable */
            if (reject_indirect && evi2->installable)
                continue;
            newdist = evi->distance + 1;
            if (newdist < evi2->distance)
            {
                evi2->distance = newdist;
                evi2->previous = evi;
            }
            else if (newdist == evi2->distance &&
                     evi2->previous != NULL &&
                     strcmp(evi->name, evi2->previous->name) < 0)
            {
                /*
                 * Break ties in favor of the version name that comes first
                 * according to strcmp().  This behavior is undocumented and
                 * users shouldn't rely on it.  We do it just to ensure that
                 * if there is a tie, the update path that is chosen does not
                 * depend on random factors like the order in which directory
                 * entries get visited.
                 */
                evi2->previous = evi;
            }
        }
    }

    /* Return NIL if target is not reachable from start */
    if (!evi_target->distance_known)
        return NIL;

    /* Build and return list of version names representing the update path */
    result = NIL;
    for (evi = evi_target; evi != evi_start; evi = evi->previous)
        result = lcons(evi->name, result);

    return result;
}

/*
 * Given a target version that is not directly installable, find the
 * best installation sequence starting from a directly-installable version.
 *
 * evi_list: previously-collected version update graph
 * evi_target: member of that list that we want to reach
 *
 * Returns the best starting-point version, or NULL if there is none.
 * On success, *best_path is set to the path from the start point.
 *
 * If there's more than one possible start point, prefer shorter update paths,
 * and break any ties arbitrarily on the basis of strcmp'ing the starting
 * versions' names.
 */
static ExtensionVersionInfo *
find_install_path(List *evi_list, ExtensionVersionInfo *evi_target,
                  List **best_path)
{
    ExtensionVersionInfo *evi_start = NULL;
    ListCell   *lc;

    *best_path = NIL;

    /*
     * We don't expect to be called for an installable target, but if we are,
     * the answer is easy: just start from there, with an empty update path.
     */
    if (evi_target->installable)
        return evi_target;

    /* Consider all installable versions as start points */
    foreach(lc, evi_list)
    {
        ExtensionVersionInfo *evi1 = (ExtensionVersionInfo *) lfirst(lc);
        List       *path;

        if (!evi1->installable)
            continue;

        /*
         * Find shortest path from evi1 to evi_target; but no need to consider
         * paths going through other installable versions.
         */
        path = find_update_path(evi_list, evi1, evi_target, true, true);
        if (path == NIL)
            continue;

        /* Remember best path */
        if (evi_start == NULL ||
            list_length(path) < list_length(*best_path) ||
            (list_length(path) == list_length(*best_path) &&
             strcmp(evi_start->name, evi1->name) < 0))
        {
            evi_start = evi1;
            *best_path = path;
        }
    }

    return evi_start;
}

/*
 * CREATE EXTENSION worker
 *
 * When CASCADE is specified, CreateExtensionInternal() recurses if required
 * extensions need to be installed.  To sanely handle cyclic dependencies,
 * the "parents" list contains a list of names of extensions already being
 * installed, allowing us to error out if we recurse to one of those.
 */
static ObjectAddress
CreateExtensionInternal(char *extensionName,
                        char *schemaName,
                        const char *versionName,
                        const char *oldVersionName,
                        bool cascade,
                        List *parents,
                        bool is_create)
{
    char       *origSchemaName = schemaName;
    Oid         schemaOid = InvalidOid;
    Oid         extowner = GetUserId();
    ExtensionControlFile *pcontrol;
    ExtensionControlFile *control;
    List       *updateVersions;
    List       *requiredExtensions;
    List       *requiredSchemas;
    Oid         extensionOid;
    ObjectAddress address;
    ListCell   *lc;

    /*
     * Read the primary control file.  Note we assume that it does not contain
     * any non-ASCII data, so there is no need to worry about encoding at this
     * point.
     */
    pcontrol = read_extension_control_file(extensionName);

    /*
     * Determine the version to install
     */
    if (versionName == NULL)
    {
        if (pcontrol->default_version)
            versionName = pcontrol->default_version;
        else
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("version to install must be specified")));
    }
    check_valid_version_name(versionName);

    /*
     * Figure out which script(s) we need to run to install the desired
     * version of the extension.  If we do not have a script that directly
     * does what is needed, we try to find a sequence of update scripts that
     * will get us there.
     */
    if (oldVersionName)
    {
        /*
         * "FROM old_version" was specified, indicating that we're trying to
         * update from some unpackaged version of the extension.  Locate a
         * series of update scripts that will do it.
         */
        check_valid_version_name(oldVersionName);

        if (strcmp(oldVersionName, versionName) == 0)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("FROM version must be different from installation target version \"%s\"",
                            versionName)));

        updateVersions = identify_update_path(pcontrol,
                                              oldVersionName,
                                              versionName);

        if (list_length(updateVersions) == 1)
        {
            /*
             * Simple case where there's just one update script to run. We
             * will not need any follow-on update steps.
             */
            Assert(strcmp((char *) linitial(updateVersions), versionName) == 0);
            updateVersions = NIL;
        }
        else
        {
            /*
             * Multi-step sequence.  We treat this as installing the version
             * that is the target of the first script, followed by successive
             * updates to the later versions.
             */
            versionName = (char *) linitial(updateVersions);
            updateVersions = list_delete_first(updateVersions);
        }
    }
    else
    {
        /*
         * No FROM, so we're installing from scratch.  If there is an install
         * script for the desired version, we only need to run that one.
         */
        char       *filename;
        struct stat fst;

        oldVersionName = NULL;

        filename = get_extension_script_filename(pcontrol, NULL, versionName);
        if (stat(filename, &fst) == 0)
        {
            /* Easy, no extra scripts */
            updateVersions = NIL;
        }
        else
        {
            /* Look for best way to install this version */
            List       *evi_list;
            ExtensionVersionInfo *evi_start;
            ExtensionVersionInfo *evi_target;

            /* Extract the version update graph from the script directory */
            evi_list = get_ext_ver_list(pcontrol);

            /* Identify the target version */
            evi_target = get_ext_ver_info(versionName, &evi_list);

            /* Identify best path to reach target */
            evi_start = find_install_path(evi_list, evi_target,
                                          &updateVersions);

            /* Fail if no path ... */
            if (evi_start == NULL)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("extension \"%s\" has no installation script nor update path for version \"%s\"",
                                pcontrol->name, versionName)));

            /* Otherwise, install best starting point and then upgrade */
            versionName = evi_start->name;
        }
    }

    /*
     * Fetch control parameters for installation target version
     */
    control = read_extension_aux_control_file(pcontrol, versionName);

    /*
     * Determine the target schema to install the extension into
     */
    if (schemaName)
    {
        /* If the user is giving us the schema name, it must exist already. */
        schemaOid = get_namespace_oid(schemaName, false);
    }

    if (control->schema != NULL)
    {
        /*
         * The extension is not relocatable and the author gave us a schema
         * for it.
         *
         * Unless CASCADE parameter was given, it's an error to give a schema
         * different from control->schema if control->schema is specified.
         */
        if (schemaName && strcmp(control->schema, schemaName) != 0 &&
            !cascade)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("extension \"%s\" must be installed in schema \"%s\"",
                            control->name,
                            control->schema)));

        /* Always use the schema from control file for current extension. */
        schemaName = control->schema;

        /* Find or create the schema in case it does not exist. */
        schemaOid = get_namespace_oid(schemaName, true);

        if (!OidIsValid(schemaOid))
        {
            CreateSchemaStmt *csstmt = makeNode(CreateSchemaStmt);

            csstmt->schemaname = schemaName;
            csstmt->authrole = NULL;    /* will be created by current user */
            csstmt->schemaElts = NIL;
            csstmt->if_not_exists = false;
            CreateSchemaCommand(csstmt, "(generated CREATE SCHEMA command)",
                                -1, -1);

            /*
             * CreateSchemaCommand includes CommandCounterIncrement, so new
             * schema is now visible.
             */
            schemaOid = get_namespace_oid(schemaName, false);
        }
    }
    else if (!OidIsValid(schemaOid))
    {
        /*
         * Neither user nor author of the extension specified schema; use the
         * current default creation namespace, which is the first explicit
         * entry in the search_path.
         */
        List       *search_path = fetch_search_path(false);

        if (search_path == NIL) /* nothing valid in search_path? */
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_SCHEMA),
                     errmsg("no schema has been selected to create in")));
        schemaOid = linitial_oid(search_path);
        schemaName = get_namespace_name(schemaOid);
        if (schemaName == NULL) /* recently-deleted namespace? */
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_SCHEMA),
                     errmsg("no schema has been selected to create in")));

        list_free(search_path);
    }

    /*
     * Make note if a temporary namespace has been accessed in this
     * transaction.
     */
    if (isTempNamespace(schemaOid))
        MyXactFlags |= XACT_FLAGS_ACCESSEDTEMPNAMESPACE;

    /*
     * We don't check creation rights on the target namespace here.  If the
     * extension script actually creates any objects there, it will fail if
     * the user doesn't have such permissions.  But there are cases such as
     * procedural languages where it's convenient to set schema = pg_catalog
     * yet we don't want to restrict the command to users with ACL_CREATE for
     * pg_catalog.
     */

    /*
     * Look up the prerequisite extensions, install them if necessary, and
     * build lists of their OIDs and the OIDs of their target schemas.
     */
    requiredExtensions = NIL;
    requiredSchemas = NIL;
    foreach(lc, control->requires)
    {
        char       *curreq = (char *) lfirst(lc);
        Oid         reqext;
        Oid         reqschema;

        reqext = get_required_extension(curreq,
                                        extensionName,
                                        origSchemaName,
                                        cascade,
                                        parents,
                                        is_create);
        reqschema = get_extension_schema(reqext);
        requiredExtensions = lappend_oid(requiredExtensions, reqext);
        requiredSchemas = lappend_oid(requiredSchemas, reqschema);
    }

    /*
     * Insert new tuple into pg_extension, and create dependency entries.
     */
    address = InsertExtensionTuple(control->name, extowner,
                                   schemaOid, control->relocatable,
                                   versionName,
                                   PointerGetDatum(NULL),
                                   PointerGetDatum(NULL),
                                   requiredExtensions);
    extensionOid = address.objectId;

    /*
     * Apply any control-file comment on extension
     */
    if (control->comment != NULL)
        CreateComments(extensionOid, ExtensionRelationId, 0, control->comment);

    /*
     * Execute the installation script file
     */
    execute_extension_script(extensionOid, control,
                             oldVersionName, versionName,
                             requiredSchemas,
                             schemaName, schemaOid);

    /*
     * If additional update scripts have to be executed, apply the updates as
     * though a series of ALTER EXTENSION UPDATE commands were given
     */
    ApplyExtensionUpdates(extensionOid, pcontrol,
                          versionName, updateVersions,
                          origSchemaName, cascade, is_create);

    return address;
}

/*
 * Get the OID of an extension listed in "requires", possibly creating it.
 */
static Oid
get_required_extension(char *reqExtensionName,
                       char *extensionName,
                       char *origSchemaName,
                       bool cascade,
                       List *parents,
                       bool is_create)
{
    Oid         reqExtensionOid;

    reqExtensionOid = get_extension_oid(reqExtensionName, true);
    if (!OidIsValid(reqExtensionOid))
    {
        if (cascade)
        {
            /* Must install it. */
            ObjectAddress addr;
            List       *cascade_parents;
            ListCell   *lc;

            /* Check extension name validity before trying to cascade. */
            check_valid_extension_name(reqExtensionName);

            /* Check for cyclic dependency between extensions. */
            foreach(lc, parents)
            {
                char       *pname = (char *) lfirst(lc);

                if (strcmp(pname, reqExtensionName) == 0)
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_RECURSION),
                             errmsg("cyclic dependency detected between extensions \"%s\" and \"%s\"",
                                    reqExtensionName, extensionName)));
            }

            ereport(NOTICE,
                    (errmsg("installing required extension \"%s\"",
                            reqExtensionName)));

            /* Add current extension to list of parents to pass down. */
            cascade_parents = lappend(list_copy(parents), extensionName);

            /*
             * Create the required extension.  We propagate the SCHEMA option
             * if any, and CASCADE, but no other options.
             */
            addr = CreateExtensionInternal(reqExtensionName,
                                           origSchemaName,
                                           NULL,
                                           NULL,
                                           cascade,
                                           cascade_parents,
                                           is_create);

            /* Get its newly-assigned OID. */
            reqExtensionOid = addr.objectId;
        }
        else
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_OBJECT),
                     errmsg("required extension \"%s\" is not installed",
                            reqExtensionName),
                     is_create ?
                     errhint("Use CREATE EXTENSION ... CASCADE to install required extensions too.") : 0));
    }

    return reqExtensionOid;
}

/*
 * CREATE EXTENSION
 */
ObjectAddress
CreateExtension(ParseState *pstate, CreateExtensionStmt *stmt)
{
    DefElem    *d_schema = NULL;
    DefElem    *d_new_version = NULL;
    DefElem    *d_old_version = NULL;
    DefElem    *d_cascade = NULL;
    char       *schemaName = NULL;
    char       *versionName = NULL;
    char       *oldVersionName = NULL;
    bool        cascade = false;
    ListCell   *lc;

    /* Check extension name validity before any filesystem access */
    check_valid_extension_name(stmt->extname);

    /*
     * Check for duplicate extension name.  The unique index on
     * pg_extension.extname would catch this anyway, and serves as a backstop
     * in case of race conditions; but this is a friendlier error message, and
     * besides we need a check to support IF NOT EXISTS.
     */
    if (get_extension_oid(stmt->extname, true) != InvalidOid)
    {
        if (stmt->if_not_exists)
        {
            ereport(NOTICE,
                    (errcode(ERRCODE_DUPLICATE_OBJECT),
                     errmsg("extension \"%s\" already exists, skipping",
                            stmt->extname)));
            return InvalidObjectAddress;
        }
        else
            ereport(ERROR,
                    (errcode(ERRCODE_DUPLICATE_OBJECT),
                     errmsg("extension \"%s\" already exists",
                            stmt->extname)));
    }

    /*
     * We use global variables to track the extension being created, so we can
     * create only one extension at the same time.
     */
    if (creating_extension)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("nested CREATE EXTENSION is not supported")));

    /* Deconstruct the statement option list */
    foreach(lc, stmt->options)
    {
        DefElem    *defel = (DefElem *) lfirst(lc);

        if (strcmp(defel->defname, "schema") == 0)
        {
            if (d_schema)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options"),
                         parser_errposition(pstate, defel->location)));
            d_schema = defel;
            schemaName = defGetString(d_schema);
        }
        else if (strcmp(defel->defname, "new_version") == 0)
        {
            if (d_new_version)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options"),
                         parser_errposition(pstate, defel->location)));
            d_new_version = defel;
            versionName = defGetString(d_new_version);
        }
        else if (strcmp(defel->defname, "old_version") == 0)
        {
            if (d_old_version)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options"),
                         parser_errposition(pstate, defel->location)));
            d_old_version = defel;
            oldVersionName = defGetString(d_old_version);
        }
        else if (strcmp(defel->defname, "cascade") == 0)
        {
            if (d_cascade)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options"),
                         parser_errposition(pstate, defel->location)));
            d_cascade = defel;
            cascade = defGetBoolean(d_cascade);
        }
        else
            elog(ERROR, "unrecognized option: %s", defel->defname);
    }

    /* Call CreateExtensionInternal to do the real work. */
    return CreateExtensionInternal(stmt->extname,
                                   schemaName,
                                   versionName,
                                   oldVersionName,
                                   cascade,
                                   NIL,
                                   true);
}

/*
 * InsertExtensionTuple
 *
 * Insert the new pg_extension row, and create extension's dependency entries.
 * Return the OID assigned to the new row.
 *
 * This is exported for the benefit of pg_upgrade, which has to create a
 * pg_extension entry (and the extension-level dependencies) without
 * actually running the extension's script.
 *
 * extConfig and extCondition should be arrays or PointerGetDatum(NULL).
 * We declare them as plain Datum to avoid needing array.h in extension.h.
 */
ObjectAddress
InsertExtensionTuple(const char *extName, Oid extOwner,
                     Oid schemaOid, bool relocatable, const char *extVersion,
                     Datum extConfig, Datum extCondition,
                     List *requiredExtensions)
{
    Oid         extensionOid;
    Relation    rel;
    Datum       values[Natts_pg_extension];
    bool        nulls[Natts_pg_extension];
    HeapTuple   tuple;
    ObjectAddress myself;
    ObjectAddress nsp;
    ListCell   *lc;

    /*
     * Build and insert the pg_extension tuple
     */
    rel = table_open(ExtensionRelationId, RowExclusiveLock);

    memset(values, 0, sizeof(values));
    memset(nulls, 0, sizeof(nulls));

    extensionOid = GetNewOidWithIndex(rel, ExtensionOidIndexId,
                                      Anum_pg_extension_oid);
    values[Anum_pg_extension_oid - 1] = ObjectIdGetDatum(extensionOid);
    values[Anum_pg_extension_extname - 1] =
        DirectFunctionCall1(namein, CStringGetDatum(extName));
    values[Anum_pg_extension_extowner - 1] = ObjectIdGetDatum(extOwner);
    values[Anum_pg_extension_extnamespace - 1] = ObjectIdGetDatum(schemaOid);
    values[Anum_pg_extension_extrelocatable - 1] = BoolGetDatum(relocatable);
    values[Anum_pg_extension_extversion - 1] = CStringGetTextDatum(extVersion);

    if (extConfig == PointerGetDatum(NULL))
        nulls[Anum_pg_extension_extconfig - 1] = true;
    else
        values[Anum_pg_extension_extconfig - 1] = extConfig;

    if (extCondition == PointerGetDatum(NULL))
        nulls[Anum_pg_extension_extcondition - 1] = true;
    else
        values[Anum_pg_extension_extcondition - 1] = extCondition;

    tuple = heap_form_tuple(rel->rd_att, values, nulls);

    CatalogTupleInsert(rel, tuple);

    heap_freetuple(tuple);
    table_close(rel, RowExclusiveLock);

    /*
     * Record dependencies on owner, schema, and prerequisite extensions
     */
    recordDependencyOnOwner(ExtensionRelationId, extensionOid, extOwner);

    myself.classId = ExtensionRelationId;
    myself.objectId = extensionOid;
    myself.objectSubId = 0;

    nsp.classId = NamespaceRelationId;
    nsp.objectId = schemaOid;
    nsp.objectSubId = 0;

    recordDependencyOn(&myself, &nsp, DEPENDENCY_NORMAL);

    foreach(lc, requiredExtensions)
    {
        Oid         reqext = lfirst_oid(lc);
        ObjectAddress otherext;

        otherext.classId = ExtensionRelationId;
        otherext.objectId = reqext;
        otherext.objectSubId = 0;

        recordDependencyOn(&myself, &otherext, DEPENDENCY_NORMAL);
    }
    /* Post creation hook for new extension */
    InvokeObjectPostCreateHook(ExtensionRelationId, extensionOid, 0);

    return myself;
}

/*
 * Guts of extension deletion.
 *
 * All we need do here is remove the pg_extension tuple itself.  Everything
 * else is taken care of by the dependency infrastructure.
 */
void
RemoveExtensionById(Oid extId)
{
    Relation    rel;
    SysScanDesc scandesc;
    HeapTuple   tuple;
    ScanKeyData entry[1];

    /*
     * Disallow deletion of any extension that's currently open for insertion;
     * else subsequent executions of recordDependencyOnCurrentExtension()
     * could create dangling pg_depend records that refer to a no-longer-valid
     * pg_extension OID.  This is needed not so much because we think people
     * might write "DROP EXTENSION foo" in foo's own script files, as because
     * errors in dependency management in extension script files could give
     * rise to cases where an extension is dropped as a result of recursing
     * from some contained object.  Because of that, we must test for the case
     * here, not at some higher level of the DROP EXTENSION command.
     */
    if (extId == CurrentExtensionObject)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("cannot drop extension \"%s\" because it is being modified",
                        get_extension_name(extId))));

    rel = table_open(ExtensionRelationId, RowExclusiveLock);

    ScanKeyInit(&entry[0],
                Anum_pg_extension_oid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(extId));
    scandesc = systable_beginscan(rel, ExtensionOidIndexId, true,
                                  NULL, 1, entry);

    tuple = systable_getnext(scandesc);

    /* We assume that there can be at most one matching tuple */
    if (HeapTupleIsValid(tuple))
        CatalogTupleDelete(rel, &tuple->t_self);

    systable_endscan(scandesc);

    table_close(rel, RowExclusiveLock);
}

/*
 * This function lists the available extensions (one row per primary control
 * file in the control directory).  We parse each control file and report the
 * interesting fields.
 *
 * The system view pg_available_extensions provides a user interface to this
 * SRF, adding information about whether the extensions are installed in the
 * current DB.
 */
Datum
pg_available_extensions(PG_FUNCTION_ARGS)
{
    ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
    TupleDesc   tupdesc;
    Tuplestorestate *tupstore;
    MemoryContext per_query_ctx;
    MemoryContext oldcontext;
    char       *location;
    DIR        *dir;
    struct dirent *de;

    /* check to see if caller supports us returning a tuplestore */
    if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("set-valued function called in context that cannot accept a set")));
    if (!(rsinfo->allowedModes & SFRM_Materialize))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("materialize mode required, but it is not allowed in this context")));

    /* Build a tuple descriptor for our result type */
    if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
        elog(ERROR, "return type must be a row type");

    /* Build tuplestore to hold the result rows */
    per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
    oldcontext = MemoryContextSwitchTo(per_query_ctx);

    tupstore = tuplestore_begin_heap(true, false, work_mem);
    rsinfo->returnMode = SFRM_Materialize;
    rsinfo->setResult = tupstore;
    rsinfo->setDesc = tupdesc;

    MemoryContextSwitchTo(oldcontext);

    location = get_extension_control_directory();
    dir = AllocateDir(location);

    /*
     * If the control directory doesn't exist, we want to silently return an
     * empty set.  Any other error will be reported by ReadDir.
     */
    if (dir == NULL && errno == ENOENT)
    {
        /* do nothing */
    }
    else
    {
        while ((de = ReadDir(dir, location)) != NULL)
        {
            ExtensionControlFile *control;
            char       *extname;
            Datum       values[3];
            bool        nulls[3];

            if (!is_extension_control_filename(de->d_name))
                continue;

            /* extract extension name from 'name.control' filename */
            extname = pstrdup(de->d_name);
            *strrchr(extname, '.') = '\0';

            /* ignore it if it's an auxiliary control file */
            if (strstr(extname, "--"))
                continue;

            control = read_extension_control_file(extname);

            memset(values, 0, sizeof(values));
            memset(nulls, 0, sizeof(nulls));

            /* name */
            values[0] = DirectFunctionCall1(namein,
                                            CStringGetDatum(control->name));
            /* default_version */
            if (control->default_version == NULL)
                nulls[1] = true;
            else
                values[1] = CStringGetTextDatum(control->default_version);
            /* comment */
            if (control->comment == NULL)
                nulls[2] = true;
            else
                values[2] = CStringGetTextDatum(control->comment);

            tuplestore_putvalues(tupstore, tupdesc, values, nulls);
        }

        FreeDir(dir);
    }

    /* clean up and return the tuplestore */
    tuplestore_donestoring(tupstore);

    return (Datum) 0;
}

/*
 * This function lists the available extension versions (one row per
 * extension installation script).  For each version, we parse the related
 * control file(s) and report the interesting fields.
 *
 * The system view pg_available_extension_versions provides a user interface
 * to this SRF, adding information about which versions are installed in the
 * current DB.
 */
Datum
pg_available_extension_versions(PG_FUNCTION_ARGS)
{
    ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
    TupleDesc   tupdesc;
    Tuplestorestate *tupstore;
    MemoryContext per_query_ctx;
    MemoryContext oldcontext;
    char       *location;
    DIR        *dir;
    struct dirent *de;

    /* check to see if caller supports us returning a tuplestore */
    if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("set-valued function called in context that cannot accept a set")));
    if (!(rsinfo->allowedModes & SFRM_Materialize))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("materialize mode required, but it is not allowed in this context")));

    /* Build a tuple descriptor for our result type */
    if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
        elog(ERROR, "return type must be a row type");

    /* Build tuplestore to hold the result rows */
    per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
    oldcontext = MemoryContextSwitchTo(per_query_ctx);

    tupstore = tuplestore_begin_heap(true, false, work_mem);
    rsinfo->returnMode = SFRM_Materialize;
    rsinfo->setResult = tupstore;
    rsinfo->setDesc = tupdesc;

    MemoryContextSwitchTo(oldcontext);

    location = get_extension_control_directory();
    dir = AllocateDir(location);

    /*
     * If the control directory doesn't exist, we want to silently return an
     * empty set.  Any other error will be reported by ReadDir.
     */
    if (dir == NULL && errno == ENOENT)
    {
        /* do nothing */
    }
    else
    {
        while ((de = ReadDir(dir, location)) != NULL)
        {
            ExtensionControlFile *control;
            char       *extname;

            if (!is_extension_control_filename(de->d_name))
                continue;

            /* extract extension name from 'name.control' filename */
            extname = pstrdup(de->d_name);
            *strrchr(extname, '.') = '\0';

            /* ignore it if it's an auxiliary control file */
            if (strstr(extname, "--"))
                continue;

            /* read the control file */
            control = read_extension_control_file(extname);

            /* scan extension's script directory for install scripts */
            get_available_versions_for_extension(control, tupstore, tupdesc);
        }

        FreeDir(dir);
    }

    /* clean up and return the tuplestore */
    tuplestore_donestoring(tupstore);

    return (Datum) 0;
}

/*
 * Inner loop for pg_available_extension_versions:
 *      read versions of one extension, add rows to tupstore
 */
static void
get_available_versions_for_extension(ExtensionControlFile *pcontrol,
                                     Tuplestorestate *tupstore,
                                     TupleDesc tupdesc)
{
    List       *evi_list;
    ListCell   *lc;

    /* Extract the version update graph from the script directory */
    evi_list = get_ext_ver_list(pcontrol);

    /* For each installable version ... */
    foreach(lc, evi_list)
    {
        ExtensionVersionInfo *evi = (ExtensionVersionInfo *) lfirst(lc);
        ExtensionControlFile *control;
        Datum       values[7];
        bool        nulls[7];
        ListCell   *lc2;

        if (!evi->installable)
            continue;

        /*
         * Fetch parameters for specific version (pcontrol is not changed)
         */
        control = read_extension_aux_control_file(pcontrol, evi->name);

        memset(values, 0, sizeof(values));
        memset(nulls, 0, sizeof(nulls));

        /* name */
        values[0] = DirectFunctionCall1(namein,
                                        CStringGetDatum(control->name));
        /* version */
        values[1] = CStringGetTextDatum(evi->name);
        /* superuser */
        values[2] = BoolGetDatum(control->superuser);
        /* relocatable */
        values[3] = BoolGetDatum(control->relocatable);
        /* schema */
        if (control->schema == NULL)
            nulls[4] = true;
        else
            values[4] = DirectFunctionCall1(namein,
                                            CStringGetDatum(control->schema));
        /* requires */
        if (control->requires == NIL)
            nulls[5] = true;
        else
            values[5] = convert_requires_to_datum(control->requires);
        /* comment */
        if (control->comment == NULL)
            nulls[6] = true;
        else
            values[6] = CStringGetTextDatum(control->comment);

        tuplestore_putvalues(tupstore, tupdesc, values, nulls);

        /*
         * Find all non-directly-installable versions that would be installed
         * starting from this version, and report them, inheriting the
         * parameters that aren't changed in updates from this version.
         */
        foreach(lc2, evi_list)
        {
            ExtensionVersionInfo *evi2 = (ExtensionVersionInfo *) lfirst(lc2);
            List       *best_path;

            if (evi2->installable)
                continue;
            if (find_install_path(evi_list, evi2, &best_path) == evi)
            {
                /*
                 * Fetch parameters for this version (pcontrol is not changed)
                 */
                control = read_extension_aux_control_file(pcontrol, evi2->name);

                /* name stays the same */
                /* version */
                values[1] = CStringGetTextDatum(evi2->name);
                /* superuser */
                values[2] = BoolGetDatum(control->superuser);
                /* relocatable */
                values[3] = BoolGetDatum(control->relocatable);
                /* schema stays the same */
                /* requires */
                if (control->requires == NIL)
                    nulls[5] = true;
                else
                {
                    values[5] = convert_requires_to_datum(control->requires);
                    nulls[5] = false;
                }
                /* comment stays the same */

                tuplestore_putvalues(tupstore, tupdesc, values, nulls);
            }
        }
    }
}

/*
 * Convert a list of extension names to a name[] Datum
 */
static Datum
convert_requires_to_datum(List *requires)
{
    Datum      *datums;
    int         ndatums;
    ArrayType  *a;
    ListCell   *lc;

    ndatums = list_length(requires);
    datums = (Datum *) palloc(ndatums * sizeof(Datum));
    ndatums = 0;
    foreach(lc, requires)
    {
        char       *curreq = (char *) lfirst(lc);

        datums[ndatums++] =
            DirectFunctionCall1(namein, CStringGetDatum(curreq));
    }
    a = construct_array(datums, ndatums,
                        NAMEOID,
                        NAMEDATALEN, false, 'c');
    return PointerGetDatum(a);
}

/*
 * This function reports the version update paths that exist for the
 * specified extension.
 */
Datum
pg_extension_update_paths(PG_FUNCTION_ARGS)
{
    Name        extname = PG_GETARG_NAME(0);
    ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
    TupleDesc   tupdesc;
    Tuplestorestate *tupstore;
    MemoryContext per_query_ctx;
    MemoryContext oldcontext;
    List       *evi_list;
    ExtensionControlFile *control;
    ListCell   *lc1;

    /* Check extension name validity before any filesystem access */
    check_valid_extension_name(NameStr(*extname));

    /* check to see if caller supports us returning a tuplestore */
    if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("set-valued function called in context that cannot accept a set")));
    if (!(rsinfo->allowedModes & SFRM_Materialize))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("materialize mode required, but it is not allowed in this context")));

    /* Build a tuple descriptor for our result type */
    if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
        elog(ERROR, "return type must be a row type");

    /* Build tuplestore to hold the result rows */
    per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
    oldcontext = MemoryContextSwitchTo(per_query_ctx);

    tupstore = tuplestore_begin_heap(true, false, work_mem);
    rsinfo->returnMode = SFRM_Materialize;
    rsinfo->setResult = tupstore;
    rsinfo->setDesc = tupdesc;

    MemoryContextSwitchTo(oldcontext);

    /* Read the extension's control file */
    control = read_extension_control_file(NameStr(*extname));

    /* Extract the version update graph from the script directory */
    evi_list = get_ext_ver_list(control);

    /* Iterate over all pairs of versions */
    foreach(lc1, evi_list)
    {
        ExtensionVersionInfo *evi1 = (ExtensionVersionInfo *) lfirst(lc1);
        ListCell   *lc2;

        foreach(lc2, evi_list)
        {
            ExtensionVersionInfo *evi2 = (ExtensionVersionInfo *) lfirst(lc2);
            List       *path;
            Datum       values[3];
            bool        nulls[3];

            if (evi1 == evi2)
                continue;

            /* Find shortest path from evi1 to evi2 */
            path = find_update_path(evi_list, evi1, evi2, false, true);

            /* Emit result row */
            memset(values, 0, sizeof(values));
            memset(nulls, 0, sizeof(nulls));

            /* source */
            values[0] = CStringGetTextDatum(evi1->name);
            /* target */
            values[1] = CStringGetTextDatum(evi2->name);
            /* path */
            if (path == NIL)
                nulls[2] = true;
            else
            {
                StringInfoData pathbuf;
                ListCell   *lcv;

                initStringInfo(&pathbuf);
                /* The path doesn't include start vertex, but show it */
                appendStringInfoString(&pathbuf, evi1->name);
                foreach(lcv, path)
                {
                    char       *versionName = (char *) lfirst(lcv);

                    appendStringInfoString(&pathbuf, "--");
                    appendStringInfoString(&pathbuf, versionName);
                }
                values[2] = CStringGetTextDatum(pathbuf.data);
                pfree(pathbuf.data);
            }

            tuplestore_putvalues(tupstore, tupdesc, values, nulls);
        }
    }

    /* clean up and return the tuplestore */
    tuplestore_donestoring(tupstore);

    return (Datum) 0;
}

/*
 * pg_extension_config_dump
 *
 * Record information about a configuration table that belongs to an
 * extension being created, but whose contents should be dumped in whole
 * or in part during pg_dump.
 */
Datum
pg_extension_config_dump(PG_FUNCTION_ARGS)
{
    Oid         tableoid = PG_GETARG_OID(0);
    text       *wherecond = PG_GETARG_TEXT_PP(1);
    char       *tablename;
    Relation    extRel;
    ScanKeyData key[1];
    SysScanDesc extScan;
    HeapTuple   extTup;
    Datum       arrayDatum;
    Datum       elementDatum;
    int         arrayLength;
    int         arrayIndex;
    bool        isnull;
    Datum       repl_val[Natts_pg_extension];
    bool        repl_null[Natts_pg_extension];
    bool        repl_repl[Natts_pg_extension];
    ArrayType  *a;

    /*
     * We only allow this to be called from an extension's SQL script. We
     * shouldn't need any permissions check beyond that.
     */
    if (!creating_extension)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("%s can only be called from an SQL script executed by CREATE EXTENSION",
                        "pg_extension_config_dump()")));

    /*
     * Check that the table exists and is a member of the extension being
     * created.  This ensures that we don't need to register an additional
     * dependency to protect the extconfig entry.
     */
    tablename = get_rel_name(tableoid);
    if (tablename == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_TABLE),
                 errmsg("OID %u does not refer to a table", tableoid)));
    if (getExtensionOfObject(RelationRelationId, tableoid) !=
        CurrentExtensionObject)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("table \"%s\" is not a member of the extension being created",
                        tablename)));

    /*
     * Add the table OID and WHERE condition to the extension's extconfig and
     * extcondition arrays.
     *
     * If the table is already in extconfig, treat this as an update of the
     * WHERE condition.
     */

    /* Find the pg_extension tuple */
    extRel = table_open(ExtensionRelationId, RowExclusiveLock);

    ScanKeyInit(&key[0],
                Anum_pg_extension_oid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(CurrentExtensionObject));

    extScan = systable_beginscan(extRel, ExtensionOidIndexId, true,
                                 NULL, 1, key);

    extTup = systable_getnext(extScan);

    if (!HeapTupleIsValid(extTup))  /* should not happen */
        elog(ERROR, "could not find tuple for extension %u",
             CurrentExtensionObject);

    memset(repl_val, 0, sizeof(repl_val));
    memset(repl_null, false, sizeof(repl_null));
    memset(repl_repl, false, sizeof(repl_repl));

    /* Build or modify the extconfig value */
    elementDatum = ObjectIdGetDatum(tableoid);

    arrayDatum = heap_getattr(extTup, Anum_pg_extension_extconfig,
                              RelationGetDescr(extRel), &isnull);
    if (isnull)
    {
        /* Previously empty extconfig, so build 1-element array */
        arrayLength = 0;
        arrayIndex = 1;

        a = construct_array(&elementDatum, 1,
                            OIDOID,
                            sizeof(Oid), true, 'i');
    }
    else
    {
        /* Modify or extend existing extconfig array */
        Oid        *arrayData;
        int         i;

        a = DatumGetArrayTypeP(arrayDatum);

        arrayLength = ARR_DIMS(a)[0];
        if (ARR_NDIM(a) != 1 ||
            ARR_LBOUND(a)[0] != 1 ||
            arrayLength < 0 ||
            ARR_HASNULL(a) ||
            ARR_ELEMTYPE(a) != OIDOID)
            elog(ERROR, "extconfig is not a 1-D Oid array");
        arrayData = (Oid *) ARR_DATA_PTR(a);

        arrayIndex = arrayLength + 1;   /* set up to add after end */

        for (i = 0; i < arrayLength; i++)
        {
            if (arrayData[i] == tableoid)
            {
                arrayIndex = i + 1; /* replace this element instead */
                break;
            }
        }

        a = array_set(a, 1, &arrayIndex,
                      elementDatum,
                      false,
                      -1 /* varlena array */ ,
                      sizeof(Oid) /* OID's typlen */ ,
                      true /* OID's typbyval */ ,
                      'i' /* OID's typalign */ );
    }
    repl_val[Anum_pg_extension_extconfig - 1] = PointerGetDatum(a);
    repl_repl[Anum_pg_extension_extconfig - 1] = true;

    /* Build or modify the extcondition value */
    elementDatum = PointerGetDatum(wherecond);

    arrayDatum = heap_getattr(extTup, Anum_pg_extension_extcondition,
                              RelationGetDescr(extRel), &isnull);
    if (isnull)
    {
        if (arrayLength != 0)
            elog(ERROR, "extconfig and extcondition arrays do not match");

        a = construct_array(&elementDatum, 1,
                            TEXTOID,
                            -1, false, 'i');
    }
    else
    {
        a = DatumGetArrayTypeP(arrayDatum);

        if (ARR_NDIM(a) != 1 ||
            ARR_LBOUND(a)[0] != 1 ||
            ARR_HASNULL(a) ||
            ARR_ELEMTYPE(a) != TEXTOID)
            elog(ERROR, "extcondition is not a 1-D text array");
        if (ARR_DIMS(a)[0] != arrayLength)
            elog(ERROR, "extconfig and extcondition arrays do not match");

        /* Add or replace at same index as in extconfig */
        a = array_set(a, 1, &arrayIndex,
                      elementDatum,
                      false,
                      -1 /* varlena array */ ,
                      -1 /* TEXT's typlen */ ,
                      false /* TEXT's typbyval */ ,
                      'i' /* TEXT's typalign */ );
    }
    repl_val[Anum_pg_extension_extcondition - 1] = PointerGetDatum(a);
    repl_repl[Anum_pg_extension_extcondition - 1] = true;

    extTup = heap_modify_tuple(extTup, RelationGetDescr(extRel),
                               repl_val, repl_null, repl_repl);

    CatalogTupleUpdate(extRel, &extTup->t_self, extTup);

    systable_endscan(extScan);

    table_close(extRel, RowExclusiveLock);

    PG_RETURN_VOID();
}

/*
 * extension_config_remove
 *
 * Remove the specified table OID from extension's extconfig, if present.
 * This is not currently exposed as a function, but it could be;
 * for now, we just invoke it from ALTER EXTENSION DROP.
 */
static void
extension_config_remove(Oid extensionoid, Oid tableoid)
{
    Relation    extRel;
    ScanKeyData key[1];
    SysScanDesc extScan;
    HeapTuple   extTup;
    Datum       arrayDatum;
    int         arrayLength;
    int         arrayIndex;
    bool        isnull;
    Datum       repl_val[Natts_pg_extension];
    bool        repl_null[Natts_pg_extension];
    bool        repl_repl[Natts_pg_extension];
    ArrayType  *a;

    /* Find the pg_extension tuple */
    extRel = table_open(ExtensionRelationId, RowExclusiveLock);

    ScanKeyInit(&key[0],
                Anum_pg_extension_oid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(extensionoid));

    extScan = systable_beginscan(extRel, ExtensionOidIndexId, true,
                                 NULL, 1, key);

    extTup = systable_getnext(extScan);

    if (!HeapTupleIsValid(extTup))  /* should not happen */
        elog(ERROR, "could not find tuple for extension %u",
             extensionoid);

    /* Search extconfig for the tableoid */
    arrayDatum = heap_getattr(extTup, Anum_pg_extension_extconfig,
                              RelationGetDescr(extRel), &isnull);
    if (isnull)
    {
        /* nothing to do */
        a = NULL;
        arrayLength = 0;
        arrayIndex = -1;
    }
    else
    {
        Oid        *arrayData;
        int         i;

        a = DatumGetArrayTypeP(arrayDatum);

        arrayLength = ARR_DIMS(a)[0];
        if (ARR_NDIM(a) != 1 ||
            ARR_LBOUND(a)[0] != 1 ||
            arrayLength < 0 ||
            ARR_HASNULL(a) ||
            ARR_ELEMTYPE(a) != OIDOID)
            elog(ERROR, "extconfig is not a 1-D Oid array");
        arrayData = (Oid *) ARR_DATA_PTR(a);

        arrayIndex = -1;        /* flag for no deletion needed */

        for (i = 0; i < arrayLength; i++)
        {
            if (arrayData[i] == tableoid)
            {
                arrayIndex = i; /* index to remove */
                break;
            }
        }
    }

    /* If tableoid is not in extconfig, nothing to do */
    if (arrayIndex < 0)
    {
        systable_endscan(extScan);
        table_close(extRel, RowExclusiveLock);
        return;
    }

    /* Modify or delete the extconfig value */
    memset(repl_val, 0, sizeof(repl_val));
    memset(repl_null, false, sizeof(repl_null));
    memset(repl_repl, false, sizeof(repl_repl));

    if (arrayLength <= 1)
    {
        /* removing only element, just set array to null */
        repl_null[Anum_pg_extension_extconfig - 1] = true;
    }
    else
    {
        /* squeeze out the target element */
        Datum      *dvalues;
        int         nelems;
        int         i;

        /* We already checked there are no nulls */
        deconstruct_array(a, OIDOID, sizeof(Oid), true, 'i',
                          &dvalues, NULL, &nelems);

        for (i = arrayIndex; i < arrayLength - 1; i++)
            dvalues[i] = dvalues[i + 1];

        a = construct_array(dvalues, arrayLength - 1,
                            OIDOID, sizeof(Oid), true, 'i');

        repl_val[Anum_pg_extension_extconfig - 1] = PointerGetDatum(a);
    }
    repl_repl[Anum_pg_extension_extconfig - 1] = true;

    /* Modify or delete the extcondition value */
    arrayDatum = heap_getattr(extTup, Anum_pg_extension_extcondition,
                              RelationGetDescr(extRel), &isnull);
    if (isnull)
    {
        elog(ERROR, "extconfig and extcondition arrays do not match");
    }
    else
    {
        a = DatumGetArrayTypeP(arrayDatum);

        if (ARR_NDIM(a) != 1 ||
            ARR_LBOUND(a)[0] != 1 ||
            ARR_HASNULL(a) ||
            ARR_ELEMTYPE(a) != TEXTOID)
            elog(ERROR, "extcondition is not a 1-D text array");
        if (ARR_DIMS(a)[0] != arrayLength)
            elog(ERROR, "extconfig and extcondition arrays do not match");
    }

    if (arrayLength <= 1)
    {
        /* removing only element, just set array to null */
        repl_null[Anum_pg_extension_extcondition - 1] = true;
    }
    else
    {
        /* squeeze out the target element */
        Datum      *dvalues;
        int         nelems;
        int         i;

        /* We already checked there are no nulls */
        deconstruct_array(a, TEXTOID, -1, false, 'i',
                          &dvalues, NULL, &nelems);

        for (i = arrayIndex; i < arrayLength - 1; i++)
            dvalues[i] = dvalues[i + 1];

        a = construct_array(dvalues, arrayLength - 1,
                            TEXTOID, -1, false, 'i');

        repl_val[Anum_pg_extension_extcondition - 1] = PointerGetDatum(a);
    }
    repl_repl[Anum_pg_extension_extcondition - 1] = true;

    extTup = heap_modify_tuple(extTup, RelationGetDescr(extRel),
                               repl_val, repl_null, repl_repl);

    CatalogTupleUpdate(extRel, &extTup->t_self, extTup);

    systable_endscan(extScan);

    table_close(extRel, RowExclusiveLock);
}

/*
 * Execute ALTER EXTENSION SET SCHEMA
 */
ObjectAddress
AlterExtensionNamespace(const char *extensionName, const char *newschema, Oid *oldschema)
{
    Oid         extensionOid;
    Oid         nspOid;
    Oid         oldNspOid = InvalidOid;
    AclResult   aclresult;
    Relation    extRel;
    ScanKeyData key[2];
    SysScanDesc extScan;
    HeapTuple   extTup;
    Form_pg_extension extForm;
    Relation    depRel;
    SysScanDesc depScan;
    HeapTuple   depTup;
    ObjectAddresses *objsMoved;
    ObjectAddress extAddr;

    extensionOid = get_extension_oid(extensionName, false);

    nspOid = LookupCreationNamespace(newschema);

    /*
     * Permission check: must own extension.  Note that we don't bother to
     * check ownership of the individual member objects ...
     */
    if (!pg_extension_ownercheck(extensionOid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_EXTENSION,
                       extensionName);

    /* Permission check: must have creation rights in target namespace */
    aclresult = pg_namespace_aclcheck(nspOid, GetUserId(), ACL_CREATE);
    if (aclresult != ACLCHECK_OK)
        aclcheck_error(aclresult, OBJECT_SCHEMA, newschema);

    /*
     * If the schema is currently a member of the extension, disallow moving
     * the extension into the schema.  That would create a dependency loop.
     */
    if (getExtensionOfObject(NamespaceRelationId, nspOid) == extensionOid)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("cannot move extension \"%s\" into schema \"%s\" "
                        "because the extension contains the schema",
                        extensionName, newschema)));

    /* Locate the pg_extension tuple */
    extRel = table_open(ExtensionRelationId, RowExclusiveLock);

    ScanKeyInit(&key[0],
                Anum_pg_extension_oid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(extensionOid));

    extScan = systable_beginscan(extRel, ExtensionOidIndexId, true,
                                 NULL, 1, key);

    extTup = systable_getnext(extScan);

    if (!HeapTupleIsValid(extTup))  /* should not happen */
        elog(ERROR, "could not find tuple for extension %u",
             extensionOid);

    /* Copy tuple so we can modify it below */
    extTup = heap_copytuple(extTup);
    extForm = (Form_pg_extension) GETSTRUCT(extTup);

    systable_endscan(extScan);

    /*
     * If the extension is already in the target schema, just silently do
     * nothing.
     */
    if (extForm->extnamespace == nspOid)
    {
        table_close(extRel, RowExclusiveLock);
        return InvalidObjectAddress;
    }

    /* Check extension is supposed to be relocatable */
    if (!extForm->extrelocatable)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("extension \"%s\" does not support SET SCHEMA",
                        NameStr(extForm->extname))));

    objsMoved = new_object_addresses();

    /*
     * Scan pg_depend to find objects that depend directly on the extension,
     * and alter each one's schema.
     */
    depRel = table_open(DependRelationId, AccessShareLock);

    ScanKeyInit(&key[0],
                Anum_pg_depend_refclassid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(ExtensionRelationId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_refobjid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(extensionOid));

    depScan = systable_beginscan(depRel, DependReferenceIndexId, true,
                                 NULL, 2, key);

    while (HeapTupleIsValid(depTup = systable_getnext(depScan)))
    {
        Form_pg_depend pg_depend = (Form_pg_depend) GETSTRUCT(depTup);
        ObjectAddress dep;
        Oid         dep_oldNspOid;

        /*
         * Ignore non-membership dependencies.  (Currently, the only other
         * case we could see here is a normal dependency from another
         * extension.)
         */
        if (pg_depend->deptype != DEPENDENCY_EXTENSION)
            continue;

        dep.classId = pg_depend->classid;
        dep.objectId = pg_depend->objid;
        dep.objectSubId = pg_depend->objsubid;

        if (dep.objectSubId != 0)   /* should not happen */
            elog(ERROR, "extension should not have a sub-object dependency");

        /* Relocate the object */
        dep_oldNspOid = AlterObjectNamespace_oid(dep.classId,
                                                 dep.objectId,
                                                 nspOid,
                                                 objsMoved);

        /*
         * Remember previous namespace of first object that has one
         */
        if (oldNspOid == InvalidOid && dep_oldNspOid != InvalidOid)
            oldNspOid = dep_oldNspOid;

        /*
         * If not all the objects had the same old namespace (ignoring any
         * that are not in namespaces), complain.
         */
        if (dep_oldNspOid != InvalidOid && dep_oldNspOid != oldNspOid)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("extension \"%s\" does not support SET SCHEMA",
                            NameStr(extForm->extname)),
                     errdetail("%s is not in the extension's schema \"%s\"",
                               getObjectDescription(&dep),
                               get_namespace_name(oldNspOid))));
    }

    /* report old schema, if caller wants it */
    if (oldschema)
        *oldschema = oldNspOid;

    systable_endscan(depScan);

    relation_close(depRel, AccessShareLock);

    /* Now adjust pg_extension.extnamespace */
    extForm->extnamespace = nspOid;

    CatalogTupleUpdate(extRel, &extTup->t_self, extTup);

    table_close(extRel, RowExclusiveLock);

    /* update dependencies to point to the new schema */
    changeDependencyFor(ExtensionRelationId, extensionOid,
                        NamespaceRelationId, oldNspOid, nspOid);

    InvokeObjectPostAlterHook(ExtensionRelationId, extensionOid, 0);

    ObjectAddressSet(extAddr, ExtensionRelationId, extensionOid);

    return extAddr;
}

/*
 * Execute ALTER EXTENSION UPDATE
 */
ObjectAddress
ExecAlterExtensionStmt(ParseState *pstate, AlterExtensionStmt *stmt)
{
    DefElem    *d_new_version = NULL;
    char       *versionName;
    char       *oldVersionName;
    ExtensionControlFile *control;
    Oid         extensionOid;
    Relation    extRel;
    ScanKeyData key[1];
    SysScanDesc extScan;
    HeapTuple   extTup;
    List       *updateVersions;
    Datum       datum;
    bool        isnull;
    ListCell   *lc;
    ObjectAddress address;

    /*
     * We use global variables to track the extension being created, so we can
     * create/update only one extension at the same time.
     */
    if (creating_extension)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("nested ALTER EXTENSION is not supported")));

    /*
     * Look up the extension --- it must already exist in pg_extension
     */
    extRel = table_open(ExtensionRelationId, AccessShareLock);

    ScanKeyInit(&key[0],
                Anum_pg_extension_extname,
                BTEqualStrategyNumber, F_NAMEEQ,
                CStringGetDatum(stmt->extname));

    extScan = systable_beginscan(extRel, ExtensionNameIndexId, true,
                                 NULL, 1, key);

    extTup = systable_getnext(extScan);

    if (!HeapTupleIsValid(extTup))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("extension \"%s\" does not exist",
                        stmt->extname)));

    extensionOid = ((Form_pg_extension) GETSTRUCT(extTup))->oid;

    /*
     * Determine the existing version we are updating from
     */
    datum = heap_getattr(extTup, Anum_pg_extension_extversion,
                         RelationGetDescr(extRel), &isnull);
    if (isnull)
        elog(ERROR, "extversion is null");
    oldVersionName = text_to_cstring(DatumGetTextPP(datum));

    systable_endscan(extScan);

    table_close(extRel, AccessShareLock);

    /* Permission check: must own extension */
    if (!pg_extension_ownercheck(extensionOid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_EXTENSION,
                       stmt->extname);

    /*
     * Read the primary control file.  Note we assume that it does not contain
     * any non-ASCII data, so there is no need to worry about encoding at this
     * point.
     */
    control = read_extension_control_file(stmt->extname);

    /*
     * Read the statement option list
     */
    foreach(lc, stmt->options)
    {
        DefElem    *defel = (DefElem *) lfirst(lc);

        if (strcmp(defel->defname, "new_version") == 0)
        {
            if (d_new_version)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options"),
                         parser_errposition(pstate, defel->location)));
            d_new_version = defel;
        }
        else
            elog(ERROR, "unrecognized option: %s", defel->defname);
    }

    /*
     * Determine the version to update to
     */
    if (d_new_version && d_new_version->arg)
        versionName = strVal(d_new_version->arg);
    else if (control->default_version)
        versionName = control->default_version;
    else
    {
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("version to install must be specified")));
        versionName = NULL;     /* keep compiler quiet */
    }
    check_valid_version_name(versionName);

    /*
     * If we're already at that version, just say so
     */
    if (strcmp(oldVersionName, versionName) == 0)
    {
        ereport(NOTICE,
                (errmsg("version \"%s\" of extension \"%s\" is already installed",
                        versionName, stmt->extname)));
        return InvalidObjectAddress;
    }

    /*
     * Identify the series of update script files we need to execute
     */
    updateVersions = identify_update_path(control,
                                          oldVersionName,
                                          versionName);

    /*
     * Update the pg_extension row and execute the update scripts, one at a
     * time
     */
    ApplyExtensionUpdates(extensionOid, control,
                          oldVersionName, updateVersions,
                          NULL, false, false);

    ObjectAddressSet(address, ExtensionRelationId, extensionOid);

    return address;
}

/*
 * Apply a series of update scripts as though individual ALTER EXTENSION
 * UPDATE commands had been given, including altering the pg_extension row
 * and dependencies each time.
 *
 * This might be more work than necessary, but it ensures that old update
 * scripts don't break if newer versions have different control parameters.
 */
static void
ApplyExtensionUpdates(Oid extensionOid,
                      ExtensionControlFile *pcontrol,
                      const char *initialVersion,
                      List *updateVersions,
                      char *origSchemaName,
                      bool cascade,
                      bool is_create)
{
    const char *oldVersionName = initialVersion;
    ListCell   *lcv;

    foreach(lcv, updateVersions)
    {
        char       *versionName = (char *) lfirst(lcv);
        ExtensionControlFile *control;
        char       *schemaName;
        Oid         schemaOid;
        List       *requiredExtensions;
        List       *requiredSchemas;
        Relation    extRel;
        ScanKeyData key[1];
        SysScanDesc extScan;
        HeapTuple   extTup;
        Form_pg_extension extForm;
        Datum       values[Natts_pg_extension];
        bool        nulls[Natts_pg_extension];
        bool        repl[Natts_pg_extension];
        ObjectAddress myself;
        ListCell   *lc;

        /*
         * Fetch parameters for specific version (pcontrol is not changed)
         */
        control = read_extension_aux_control_file(pcontrol, versionName);

        /* Find the pg_extension tuple */
        extRel = table_open(ExtensionRelationId, RowExclusiveLock);

        ScanKeyInit(&key[0],
                    Anum_pg_extension_oid,
                    BTEqualStrategyNumber, F_OIDEQ,
                    ObjectIdGetDatum(extensionOid));

        extScan = systable_beginscan(extRel, ExtensionOidIndexId, true,
                                     NULL, 1, key);

        extTup = systable_getnext(extScan);

        if (!HeapTupleIsValid(extTup))  /* should not happen */
            elog(ERROR, "could not find tuple for extension %u",
                 extensionOid);

        extForm = (Form_pg_extension) GETSTRUCT(extTup);

        /*
         * Determine the target schema (set by original install)
         */
        schemaOid = extForm->extnamespace;
        schemaName = get_namespace_name(schemaOid);

        /*
         * Modify extrelocatable and extversion in the pg_extension tuple
         */
        memset(values, 0, sizeof(values));
        memset(nulls, 0, sizeof(nulls));
        memset(repl, 0, sizeof(repl));

        values[Anum_pg_extension_extrelocatable - 1] =
            BoolGetDatum(control->relocatable);
        repl[Anum_pg_extension_extrelocatable - 1] = true;
        values[Anum_pg_extension_extversion - 1] =
            CStringGetTextDatum(versionName);
        repl[Anum_pg_extension_extversion - 1] = true;

        extTup = heap_modify_tuple(extTup, RelationGetDescr(extRel),
                                   values, nulls, repl);

        CatalogTupleUpdate(extRel, &extTup->t_self, extTup);

        systable_endscan(extScan);

        table_close(extRel, RowExclusiveLock);

        /*
         * Look up the prerequisite extensions for this version, install them
         * if necessary, and build lists of their OIDs and the OIDs of their
         * target schemas.
         */
        requiredExtensions = NIL;
        requiredSchemas = NIL;
        foreach(lc, control->requires)
        {
            char       *curreq = (char *) lfirst(lc);
            Oid         reqext;
            Oid         reqschema;

            reqext = get_required_extension(curreq,
                                            control->name,
                                            origSchemaName,
                                            cascade,
                                            NIL,
                                            is_create);
            reqschema = get_extension_schema(reqext);
            requiredExtensions = lappend_oid(requiredExtensions, reqext);
            requiredSchemas = lappend_oid(requiredSchemas, reqschema);
        }

        /*
         * Remove and recreate dependencies on prerequisite extensions
         */
        deleteDependencyRecordsForClass(ExtensionRelationId, extensionOid,
                                        ExtensionRelationId,
                                        DEPENDENCY_NORMAL);

        myself.classId = ExtensionRelationId;
        myself.objectId = extensionOid;
        myself.objectSubId = 0;

        foreach(lc, requiredExtensions)
        {
            Oid         reqext = lfirst_oid(lc);
            ObjectAddress otherext;

            otherext.classId = ExtensionRelationId;
            otherext.objectId = reqext;
            otherext.objectSubId = 0;

            recordDependencyOn(&myself, &otherext, DEPENDENCY_NORMAL);
        }

        InvokeObjectPostAlterHook(ExtensionRelationId, extensionOid, 0);

        /*
         * Finally, execute the update script file
         */
        execute_extension_script(extensionOid, control,
                                 oldVersionName, versionName,
                                 requiredSchemas,
                                 schemaName, schemaOid);

        /*
         * Update prior-version name and loop around.  Since
         * execute_sql_string did a final CommandCounterIncrement, we can
         * update the pg_extension row again.
         */
        oldVersionName = versionName;
    }
}

/*
 * Execute ALTER EXTENSION ADD/DROP
 *
 * Return value is the address of the altered extension.
 *
 * objAddr is an output argument which, if not NULL, is set to the address of
 * the added/dropped object.
 */
ObjectAddress
ExecAlterExtensionContentsStmt(AlterExtensionContentsStmt *stmt,
                               ObjectAddress *objAddr)
{
    ObjectAddress extension;
    ObjectAddress object;
    Relation    relation;
    Oid         oldExtension;

    extension.classId = ExtensionRelationId;
    extension.objectId = get_extension_oid(stmt->extname, false);
    extension.objectSubId = 0;

    /* Permission check: must own extension */
    if (!pg_extension_ownercheck(extension.objectId, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_EXTENSION,
                       stmt->extname);

    /*
     * Translate the parser representation that identifies the object into an
     * ObjectAddress.  get_object_address() will throw an error if the object
     * does not exist, and will also acquire a lock on the object to guard
     * against concurrent DROP and ALTER EXTENSION ADD/DROP operations.
     */
    object = get_object_address(stmt->objtype, stmt->object,
                                &relation, ShareUpdateExclusiveLock, false);

    Assert(object.objectSubId == 0);
    if (objAddr)
        *objAddr = object;

    /* Permission check: must own target object, too */
    check_object_ownership(GetUserId(), stmt->objtype, object,
                           stmt->object, relation);

    /*
     * Check existing extension membership.
     */
    oldExtension = getExtensionOfObject(object.classId, object.objectId);

    if (stmt->action > 0)
    {
        /*
         * ADD, so complain if object is already attached to some extension.
         */
        if (OidIsValid(oldExtension))
            ereport(ERROR,
                    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                     errmsg("%s is already a member of extension \"%s\"",
                            getObjectDescription(&object),
                            get_extension_name(oldExtension))));

        /*
         * Prevent a schema from being added to an extension if the schema
         * contains the extension.  That would create a dependency loop.
         */
        if (object.classId == NamespaceRelationId &&
            object.objectId == get_extension_schema(extension.objectId))
            ereport(ERROR,
                    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                     errmsg("cannot add schema \"%s\" to extension \"%s\" "
                            "because the schema contains the extension",
                            get_namespace_name(object.objectId),
                            stmt->extname)));

        /*
         * OK, add the dependency.
         */
        recordDependencyOn(&object, &extension, DEPENDENCY_EXTENSION);

        /*
         * Also record the initial ACL on the object, if any.
         *
         * Note that this will handle the object's ACLs, as well as any ACLs
         * on object subIds.  (In other words, when the object is a table,
         * this will record the table's ACL and the ACLs for the columns on
         * the table, if any).
         */
        recordExtObjInitPriv(object.objectId, object.classId);
    }
    else
    {
        /*
         * DROP, so complain if it's not a member.
         */
        if (oldExtension != extension.objectId)
            ereport(ERROR,
                    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                     errmsg("%s is not a member of extension \"%s\"",
                            getObjectDescription(&object),
                            stmt->extname)));

        /*
         * OK, drop the dependency.
         */
        if (deleteDependencyRecordsForClass(object.classId, object.objectId,
                                            ExtensionRelationId,
                                            DEPENDENCY_EXTENSION) != 1)
            elog(ERROR, "unexpected number of extension dependency records");

        /*
         * If it's a relation, it might have an entry in the extension's
         * extconfig array, which we must remove.
         */
        if (object.classId == RelationRelationId)
            extension_config_remove(extension.objectId, object.objectId);

        /*
         * Remove all the initial ACLs, if any.
         *
         * Note that this will remove the object's ACLs, as well as any ACLs
         * on object subIds.  (In other words, when the object is a table,
         * this will remove the table's ACL and the ACLs for the columns on
         * the table, if any).
         */
        removeExtObjInitPriv(object.objectId, object.classId);
    }

    InvokeObjectPostAlterHook(ExtensionRelationId, extension.objectId, 0);

    /*
     * If get_object_address() opened the relation for us, we close it to keep
     * the reference count correct - but we retain any locks acquired by
     * get_object_address() until commit time, to guard against concurrent
     * activity.
     */
    if (relation != NULL)
        relation_close(relation, NoLock);

    return extension;
}

/*
 * Read the whole of file into memory.
 *
 * The file contents are returned as a single palloc'd chunk. For convenience
 * of the callers, an extra \0 byte is added to the end.
 */
static char *
read_whole_file(const char *filename, int *length)
{
    char       *buf;
    FILE       *file;
    size_t      bytes_to_read;
    struct stat fst;

    if (stat(filename, &fst) < 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not stat file \"%s\": %m", filename)));

    if (fst.st_size > (MaxAllocSize - 1))
        ereport(ERROR,
                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                 errmsg("file \"%s\" is too large", filename)));
    bytes_to_read = (size_t) fst.st_size;

    if ((file = AllocateFile(filename, PG_BINARY_R)) == NULL)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not open file \"%s\" for reading: %m",
                        filename)));

    buf = (char *) palloc(bytes_to_read + 1);

    *length = fread(buf, 1, bytes_to_read, file);

    if (ferror(file))
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not read file \"%s\": %m", filename)));

    FreeFile(file);

    buf[*length] = '\0';
    return buf;
}