conversioncmds.c

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/*-------------------------------------------------------------------------
 *
 * conversioncmds.c
 *    conversion creation command support code
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/commands/conversioncmds.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "catalog/pg_conversion.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_type.h"
#include "commands/conversioncmds.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "parser/parse_func.h"
#include "utils/acl.h"
#include "utils/lsyscache.h"
 
/*
 * CREATE CONVERSION
 */
ObjectAddress
CreateConversionCommand(CreateConversionStmt *stmt)
{
    Oid         namespaceId;
    char       *conversion_name;
    AclResult   aclresult;
    int         from_encoding;
    int         to_encoding;
    Oid         funcoid;
    const char *from_encoding_name = stmt->for_encoding_name;
    const char *to_encoding_name = stmt->to_encoding_name;
    List       *func_name = stmt->func_name;
    static const Oid funcargs[] = {INT4OID, INT4OID, CSTRINGOID, INTERNALOID, INT4OID, BOOLOID};
    char        result[1];
    Datum       funcresult;
 
    /* Convert list of names to a name and namespace */
    namespaceId = QualifiedNameGetCreationNamespace(stmt->conversion_name,
                                                    &conversion_name);
 
    /* Check we have creation rights in target namespace */
    aclresult = object_aclcheck(NamespaceRelationId, namespaceId, GetUserId(), ACL_CREATE);
    if (aclresult != ACLCHECK_OK)
        aclcheck_error(aclresult, OBJECT_SCHEMA,
                       get_namespace_name(namespaceId));
 
    /* Check the encoding names */
    from_encoding = pg_char_to_encoding(from_encoding_name);
    if (from_encoding < 0)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("source encoding \"%s\" does not exist",
                        from_encoding_name)));
 
    to_encoding = pg_char_to_encoding(to_encoding_name);
    if (to_encoding < 0)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("destination encoding \"%s\" does not exist",
                        to_encoding_name)));
 
    /*
     * We consider conversions to or from SQL_ASCII to be meaningless.  (If
     * you wish to change this, note that pg_do_encoding_conversion() and its
     * sister functions have hard-wired fast paths for any conversion in which
     * the source or target encoding is SQL_ASCII, so that an encoding
     * conversion function declared for such a case will never be used.)
     */
    if (from_encoding == PG_SQL_ASCII || to_encoding == PG_SQL_ASCII)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                 errmsg("encoding conversion to or from \"SQL_ASCII\" is not supported")));
 
    /*
     * Check the existence of the conversion function. Function name could be
     * a qualified name.
     */
    funcoid = LookupFuncName(func_name, sizeof(funcargs) / sizeof(Oid),
                             funcargs, false);
 
    /* Check it returns int4, else it's probably the wrong function */
    if (get_func_rettype(funcoid) != INT4OID)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                 errmsg("encoding conversion function %s must return type %s",
                        NameListToString(func_name), "integer")));
 
    /* Check we have EXECUTE rights for the function */
    aclresult = object_aclcheck(ProcedureRelationId, funcoid, GetUserId(), ACL_EXECUTE);
    if (aclresult != ACLCHECK_OK)
        aclcheck_error(aclresult, OBJECT_FUNCTION,
                       NameListToString(func_name));
 
    /*
     * Check that the conversion function is suitable for the requested source
     * and target encodings. We do that by calling the function with an empty
     * string; the conversion function should throw an error if it can't
     * perform the requested conversion.
     */
    funcresult = OidFunctionCall6(funcoid,
                                  Int32GetDatum(from_encoding),
                                  Int32GetDatum(to_encoding),
                                  CStringGetDatum(""),
                                  CStringGetDatum(result),
                                  Int32GetDatum(0),
                                  BoolGetDatum(false));
 
    /*
     * The function should return 0 for empty input. Might as well check that,
     * too.
     */
    if (DatumGetInt32(funcresult) != 0)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                 errmsg("encoding conversion function %s returned incorrect result for empty input",
                        NameListToString(func_name))));
 
    /*
     * All seem ok, go ahead (possible failure would be a duplicate conversion
     * name)
     */
    return ConversionCreate(conversion_name, namespaceId, GetUserId(),
                            from_encoding, to_encoding, funcoid, stmt->def);
}