Add support for user-defined I/O conversion casts.

[PostgreSQL.git] / src / backend / utils / mb / mbutils.c

/*
 * This file contains public functions for conversion between
 * client encoding and server internal encoding.
 * (currently mule internal code (mic) is used)
 * Tatsuo Ishii
 *
 * $PostgreSQL$
 */
#include "postgres.h"

#include "access/xact.h"
#include "catalog/namespace.h"
#include "mb/pg_wchar.h"
#include "utils/builtins.h"
#include "utils/memutils.h"
#include "utils/pg_locale.h"
#include "utils/syscache.h"

/*
 * When converting strings between different encodings, we assume that space
 * for converted result is 4-to-1 growth in the worst case. The rate for
 * currently supported encoding pairs are within 3 (SJIS JIS X0201 half width
 * kanna -> UTF8 is the worst case).  So "4" should be enough for the moment.
 *
 * Note that this is not the same as the maximum character width in any
 * particular encoding.
 */
#define MAX_CONVERSION_GROWTH  4

/*
 * We handle for actual FE and BE encoding setting encoding-identificator
 * and encoding-name too. It prevent searching and conversion from encoding
 * to encoding name in getdatabaseencoding() and other routines.
 */
static pg_enc2name *ClientEncoding = &pg_enc2name_tbl[PG_SQL_ASCII];
static pg_enc2name *DatabaseEncoding = &pg_enc2name_tbl[PG_SQL_ASCII];

/*
 * Caches for conversion function info. These values are allocated in
 * MbProcContext. That context is a child of TopMemoryContext,
 * which allows these values to survive across transactions. See
 * SetClientEncoding() for more details.
 */
static MemoryContext MbProcContext = NULL;
static FmgrInfo *ToServerConvProc = NULL;
static FmgrInfo *ToClientConvProc = NULL;

/*
 * During backend startup we can't set client encoding because we (a)
 * can't look up the conversion functions, and (b) may not know the database
 * encoding yet either.  So SetClientEncoding() just accepts anything and
 * remembers it for InitializeClientEncoding() to apply later.
 */
static bool backend_startup_complete = false;
static int      pending_client_encoding = PG_SQL_ASCII;


/* Internal functions */
static char *perform_default_encoding_conversion(const char *src,
                                                                        int len, bool is_client_to_server);
static int      cliplen(const char *str, int len, int limit);


/*
 * Set the client encoding and save fmgrinfo for the conversion
 * function if necessary.  Returns 0 if okay, -1 if not (bad encoding
 * or can't support conversion)
 */
int
SetClientEncoding(int encoding, bool doit)
{
        int                     current_server_encoding;
        Oid                     to_server_proc,
                                to_client_proc;
        FmgrInfo   *to_server;
        FmgrInfo   *to_client;
        MemoryContext oldcontext;

        if (!PG_VALID_FE_ENCODING(encoding))
                return -1;

        /* Can't do anything during startup, per notes above */
        if (!backend_startup_complete)
        {
                if (doit)
                        pending_client_encoding = encoding;
                return 0;
        }

        current_server_encoding = GetDatabaseEncoding();

        /*
         * Check for cases that require no conversion function.
         */
        if (current_server_encoding == encoding ||
                current_server_encoding == PG_SQL_ASCII ||
                encoding == PG_SQL_ASCII)
        {
                if (doit)
                {
                        ClientEncoding = &pg_enc2name_tbl[encoding];
                        ToServerConvProc = NULL;
                        ToClientConvProc = NULL;
                        if (MbProcContext)
                                MemoryContextReset(MbProcContext);
                }
                return 0;
        }

        /*
         * If we're not inside a transaction then we can't do catalog lookups, so
         * fail.  After backend startup, this could only happen if we are
         * re-reading postgresql.conf due to SIGHUP --- so basically this just
         * constrains the ability to change client_encoding on the fly from
         * postgresql.conf.  Which would probably be a stupid thing to do anyway.
         */
        if (!IsTransactionState())
                return -1;

        /*
         * Look up the conversion functions.
         */
        to_server_proc = FindDefaultConversionProc(encoding,
                                                                                           current_server_encoding);
        if (!OidIsValid(to_server_proc))
                return -1;
        to_client_proc = FindDefaultConversionProc(current_server_encoding,
                                                                                           encoding);
        if (!OidIsValid(to_client_proc))
                return -1;

        /*
         * Done if not wanting to actually apply setting.
         */
        if (!doit)
                return 0;

        /* Before loading the new fmgr info, remove the old info, if any */
        ToServerConvProc = NULL;
        ToClientConvProc = NULL;
        if (MbProcContext != NULL)
        {
                MemoryContextReset(MbProcContext);
        }
        else
        {
                /*
                 * This is the first time through, so create the context. Make it a
                 * child of TopMemoryContext so that these values survive across
                 * transactions.
                 */
                MbProcContext = AllocSetContextCreate(TopMemoryContext,
                                                                                          "MbProcContext",
                                                                                          ALLOCSET_SMALL_MINSIZE,
                                                                                          ALLOCSET_SMALL_INITSIZE,
                                                                                          ALLOCSET_SMALL_MAXSIZE);
        }

        /* Load the fmgr info into MbProcContext */
        oldcontext = MemoryContextSwitchTo(MbProcContext);
        to_server = palloc(sizeof(FmgrInfo));
        to_client = palloc(sizeof(FmgrInfo));
        fmgr_info(to_server_proc, to_server);
        fmgr_info(to_client_proc, to_client);
        MemoryContextSwitchTo(oldcontext);

        ClientEncoding = &pg_enc2name_tbl[encoding];
        ToServerConvProc = to_server;
        ToClientConvProc = to_client;

        return 0;
}

/*
 * Initialize client encoding if necessary.
 *              called from InitPostgres() once during backend starting up.
 */
void
InitializeClientEncoding(void)
{
        Assert(!backend_startup_complete);
        backend_startup_complete = true;

        if (SetClientEncoding(pending_client_encoding, true) < 0)
        {
                /*
                 * Oops, the requested conversion is not available. We couldn't fail
                 * before, but we can now.
                 */
                ereport(FATAL,
                                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                 errmsg("conversion between %s and %s is not supported",
                                                pg_enc2name_tbl[pending_client_encoding].name,
                                                GetDatabaseEncodingName())));
        }
}

/*
 * returns the current client encoding */
int
pg_get_client_encoding(void)
{
        Assert(ClientEncoding);
        return ClientEncoding->encoding;
}

/*
 * returns the current client encoding name
 */
const char *
pg_get_client_encoding_name(void)
{
        Assert(ClientEncoding);
        return ClientEncoding->name;
}

/*
 * Apply encoding conversion on src and return it. The encoding
 * conversion function is chosen from the pg_conversion system catalog
 * marked as "default". If it is not found in the schema search path,
 * it's taken from pg_catalog schema. If it even is not in the schema,
 * warn and return src.
 *
 * In the case of no conversion, src is returned.
 *
 * Note: we try to avoid raising error, since that could get us into
 * infinite recursion when this function is invoked during error message
 * sending.  It should be OK to raise error for overlength strings though,
 * since the recursion will come with a shorter message.
 */
unsigned char *
pg_do_encoding_conversion(unsigned char *src, int len,
                                                  int src_encoding, int dest_encoding)
{
        unsigned char *result;
        Oid                     proc;

        if (!IsTransactionState())
                return src;

        if (src_encoding == dest_encoding)
                return src;

        if (src_encoding == PG_SQL_ASCII || dest_encoding == PG_SQL_ASCII)
                return src;

        if (len <= 0)
                return src;

        proc = FindDefaultConversionProc(src_encoding, dest_encoding);
        if (!OidIsValid(proc))
        {
                ereport(LOG,
                                (errcode(ERRCODE_UNDEFINED_FUNCTION),
                                 errmsg("default conversion function for encoding \"%s\" to \"%s\" does not exist",
                                                pg_encoding_to_char(src_encoding),
                                                pg_encoding_to_char(dest_encoding))));
                return src;
        }

        /*
         * XXX we should avoid throwing errors in OidFunctionCall. Otherwise we
         * are going into infinite loop!  So we have to make sure that the
         * function exists before calling OidFunctionCall.
         */
        if (!SearchSysCacheExists(PROCOID,
                                                          ObjectIdGetDatum(proc),
                                                          0, 0, 0))
        {
                elog(LOG, "cache lookup failed for function %u", proc);
                return src;
        }

        /*
         * Allocate space for conversion result, being wary of integer overflow
         */
        if ((Size) len >= (MaxAllocSize / (Size) MAX_CONVERSION_GROWTH))
                ereport(ERROR,
                                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                                 errmsg("out of memory"),
                 errdetail("String of %d bytes is too long for encoding conversion.",
                                   len)));

        result = palloc(len * MAX_CONVERSION_GROWTH + 1);

        OidFunctionCall5(proc,
                                         Int32GetDatum(src_encoding),
                                         Int32GetDatum(dest_encoding),
                                         CStringGetDatum(src),
                                         CStringGetDatum(result),
                                         Int32GetDatum(len));
        return result;
}

/*
 * Convert string using encoding_name. The source
 * encoding is the DB encoding.
 *
 * BYTEA convert_to(TEXT string, NAME encoding_name) */
Datum
pg_convert_to(PG_FUNCTION_ARGS)
{
        Datum           string = PG_GETARG_DATUM(0);
        Datum           dest_encoding_name = PG_GETARG_DATUM(1);
        Datum           src_encoding_name = DirectFunctionCall1(namein,
                                                                        CStringGetDatum(DatabaseEncoding->name));
        Datum           result;

        /*
         * pg_convert expects a bytea as its first argument. We're passing it a
         * text argument here, relying on the fact that they are both in fact
         * varlena types, and thus structurally identical.
         */
        result = DirectFunctionCall3(pg_convert, string,
                                                                 src_encoding_name, dest_encoding_name);

        PG_RETURN_DATUM(result);
}

/*
 * Convert string using encoding_name. The destination
 * encoding is the DB encoding.
 *
 * TEXT convert_from(BYTEA string, NAME encoding_name) */
Datum
pg_convert_from(PG_FUNCTION_ARGS)
{
        Datum           string = PG_GETARG_DATUM(0);
        Datum           src_encoding_name = PG_GETARG_DATUM(1);
        Datum           dest_encoding_name = DirectFunctionCall1(namein,
                                                                        CStringGetDatum(DatabaseEncoding->name));
        Datum           result;

        result = DirectFunctionCall3(pg_convert, string,
                                                                 src_encoding_name, dest_encoding_name);

        /*
         * pg_convert returns a bytea, which we in turn return as text, relying on
         * the fact that they are both in fact varlena types, and thus
         * structurally identical. Although not all bytea values are valid text,
         * in this case it will be because we've told pg_convert to return one
         * that is valid as text in the current database encoding.
         */
        PG_RETURN_DATUM(result);
}

/*
 * Convert string using encoding_names.
 *
 * BYTEA convert(BYTEA string, NAME src_encoding_name, NAME dest_encoding_name)
 */
Datum
pg_convert(PG_FUNCTION_ARGS)
{
        bytea      *string = PG_GETARG_BYTEA_P(0);
        char       *src_encoding_name = NameStr(*PG_GETARG_NAME(1));
        int                     src_encoding = pg_char_to_encoding(src_encoding_name);
        char       *dest_encoding_name = NameStr(*PG_GETARG_NAME(2));
        int                     dest_encoding = pg_char_to_encoding(dest_encoding_name);
        unsigned char *result;
        bytea      *retval;
        unsigned char *str;
        int                     len;

        if (src_encoding < 0)
                ereport(ERROR,
                                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                                 errmsg("invalid source encoding name \"%s\"",
                                                src_encoding_name)));
        if (dest_encoding < 0)
                ereport(ERROR,
                                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                                 errmsg("invalid destination encoding name \"%s\"",
                                                dest_encoding_name)));

        /* make sure that source string is valid and null terminated */
        len = VARSIZE(string) - VARHDRSZ;
        pg_verify_mbstr(src_encoding, VARDATA(string), len, false);
        str = palloc(len + 1);
        memcpy(str, VARDATA(string), len);
        *(str + len) = '\0';

        result = pg_do_encoding_conversion(str, len, src_encoding, dest_encoding);
        if (result == NULL)
                elog(ERROR, "encoding conversion failed");

        /*
         * build bytea data type structure.
         */
        len = strlen((char *) result) + VARHDRSZ;
        retval = palloc(len);
        SET_VARSIZE(retval, len);
        memcpy(VARDATA(retval), result, len - VARHDRSZ);

        if (result != str)
                pfree(result);
        pfree(str);

        /* free memory if allocated by the toaster */
        PG_FREE_IF_COPY(string, 0);

        PG_RETURN_BYTEA_P(retval);
}

/*
 * get the length of the string considered as text in the specified
 * encoding. Raises an error if the data is not valid in that
 * encoding.
 *
 * INT4 length (BYTEA string, NAME src_encoding_name)
 */
Datum
length_in_encoding(PG_FUNCTION_ARGS)
{
        bytea      *string = PG_GETARG_BYTEA_P(0);
        char       *src_encoding_name = NameStr(*PG_GETARG_NAME(1));
        int                     src_encoding = pg_char_to_encoding(src_encoding_name);
        int                     len = VARSIZE(string) - VARHDRSZ;
        int                     retval;

        if (src_encoding < 0)
                ereport(ERROR,
                                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                                 errmsg("invalid encoding name \"%s\"",
                                                src_encoding_name)));

        retval = pg_verify_mbstr_len(src_encoding, VARDATA(string), len, false);
        PG_RETURN_INT32(retval);

}

/*
 * convert client encoding to server encoding.
 */
char *
pg_client_to_server(const char *s, int len)
{
        Assert(DatabaseEncoding);
        Assert(ClientEncoding);

        if (len <= 0)
                return (char *) s;

        if (ClientEncoding->encoding == DatabaseEncoding->encoding ||
                ClientEncoding->encoding == PG_SQL_ASCII)
        {
                /*
                 * No conversion is needed, but we must still validate the data.
                 */
                (void) pg_verify_mbstr(DatabaseEncoding->encoding, s, len, false);
                return (char *) s;
        }

        if (DatabaseEncoding->encoding == PG_SQL_ASCII)
        {
                /*
                 * No conversion is possible, but we must still validate the data,
                 * because the client-side code might have done string escaping using
                 * the selected client_encoding.  If the client encoding is ASCII-safe
                 * then we just do a straight validation under that encoding.  For an
                 * ASCII-unsafe encoding we have a problem: we dare not pass such data
                 * to the parser but we have no way to convert it.      We compromise by
                 * rejecting the data if it contains any non-ASCII characters.
                 */
                if (PG_VALID_BE_ENCODING(ClientEncoding->encoding))
                        (void) pg_verify_mbstr(ClientEncoding->encoding, s, len, false);
                else
                {
                        int                     i;

                        for (i = 0; i < len; i++)
                        {
                                if (s[i] == '\0' || IS_HIGHBIT_SET(s[i]))
                                        ereport(ERROR,
                                                        (errcode(ERRCODE_CHARACTER_NOT_IN_REPERTOIRE),
                                         errmsg("invalid byte value for encoding \"%s\": 0x%02x",
                                                        pg_enc2name_tbl[PG_SQL_ASCII].name,
                                                        (unsigned char) s[i])));
                        }
                }
                return (char *) s;
        }

        return perform_default_encoding_conversion(s, len, true);
}

/*
 * convert server encoding to client encoding.
 */
char *
pg_server_to_client(const char *s, int len)
{
        Assert(DatabaseEncoding);
        Assert(ClientEncoding);

        if (len <= 0)
                return (char *) s;

        if (ClientEncoding->encoding == DatabaseEncoding->encoding ||
                ClientEncoding->encoding == PG_SQL_ASCII ||
                DatabaseEncoding->encoding == PG_SQL_ASCII)
                return (char *) s;              /* assume data is valid */

        return perform_default_encoding_conversion(s, len, false);
}

/*
 *      Perform default encoding conversion using cached FmgrInfo. Since
 *      this function does not access database at all, it is safe to call
 *      outside transactions. Explicit setting client encoding required
 *      before calling this function. Otherwise no conversion is
 *      performed.
*/
static char *
perform_default_encoding_conversion(const char *src, int len, bool is_client_to_server)
{
        char       *result;
        int                     src_encoding,
                                dest_encoding;
        FmgrInfo   *flinfo;

        if (is_client_to_server)
        {
                src_encoding = ClientEncoding->encoding;
                dest_encoding = DatabaseEncoding->encoding;
                flinfo = ToServerConvProc;
        }
        else
        {
                src_encoding = DatabaseEncoding->encoding;
                dest_encoding = ClientEncoding->encoding;
                flinfo = ToClientConvProc;
        }

        if (flinfo == NULL)
                return (char *) src;

        /*
         * Allocate space for conversion result, being wary of integer overflow
         */
        if ((Size) len >= (MaxAllocSize / (Size) MAX_CONVERSION_GROWTH))
                ereport(ERROR,
                                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                                 errmsg("out of memory"),
                 errdetail("String of %d bytes is too long for encoding conversion.",
                                   len)));

        result = palloc(len * MAX_CONVERSION_GROWTH + 1);

        FunctionCall5(flinfo,
                                  Int32GetDatum(src_encoding),
                                  Int32GetDatum(dest_encoding),
                                  CStringGetDatum(src),
                                  CStringGetDatum(result),
                                  Int32GetDatum(len));
        return result;
}



#ifdef USE_WIDE_UPPER_LOWER

/*
 * wchar2char --- convert wide characters to multibyte format
 *
 * This has the same API as the standard wcstombs() function; in particular,
 * tolen is the maximum number of bytes to store at *to, and *from must be
 * zero-terminated.  The output will be zero-terminated iff there is room.
 */
size_t
wchar2char(char *to, const wchar_t *from, size_t tolen)
{
        size_t result;
        
        if (tolen == 0)
                return 0;

#ifdef WIN32
        /*
         * On Windows, the "Unicode" locales assume UTF16 not UTF8 encoding,
         * and for some reason mbstowcs and wcstombs won't do this for us,
         * so we use MultiByteToWideChar().
         */
        if (GetDatabaseEncoding() == PG_UTF8)
        {
                result = WideCharToMultiByte(CP_UTF8, 0, from, -1, to, tolen,
                                                                NULL, NULL);
                /* A zero return is failure */
                if (result <= 0)
                        result = -1;
                else
                {
                        Assert(result <= tolen);
                        /* Microsoft counts the zero terminator in the result */
                        result--;
                }
        }
        else
#endif   /* WIN32 */
                result = wcstombs(to, from, tolen);
        return result;
}

/*
 * char2wchar --- convert multibyte characters to wide characters
 *
 * This has almost the API of mbstowcs(), except that *from need not be
 * null-terminated; instead, the number of input bytes is specified as
 * fromlen.  Also, we ereport() rather than returning -1 for invalid
 * input encoding.      tolen is the maximum number of wchar_t's to store at *to.
 * The output will be zero-terminated iff there is room.
 */
size_t
char2wchar(wchar_t *to, size_t tolen, const char *from, size_t fromlen)
{
        size_t          result;

        if (tolen == 0)
                return 0;

#ifdef WIN32
        /* See WIN32 "Unicode" comment above */
        if (GetDatabaseEncoding() == PG_UTF8)
        {
                /* Win32 API does not work for zero-length input */
                if (fromlen == 0)
                        result = 0;
                else
                {
                        result = MultiByteToWideChar(CP_UTF8, 0, from, fromlen, to, tolen - 1);
                        /* A zero return is failure */
                        if (result == 0)
                                result = -1;
                }

                if (result != -1)
                {
                        Assert(result < tolen);
                        /* Append trailing null wchar (MultiByteToWideChar() does not) */
                        to[result] = 0;
                }
        }
        else
#endif   /* WIN32 */
        {
                if (lc_ctype_is_c())
                {
                        /*
                         * pg_mb2wchar_with_len always adds trailing '\0', so 'to' should be
                         * allocated with sufficient space
                         */
                        result = pg_mb2wchar_with_len(from, (pg_wchar *) to, fromlen);
                }
                else
                {
                        /* mbstowcs requires ending '\0' */
                        char       *str = pnstrdup(from, fromlen);

                        result = mbstowcs(to, str, tolen);
                        pfree(str);
                }
        }

        if (result == -1)
        {
                /*
                 * Invalid multibyte character encountered.  We try to give a useful
                 * error message by letting pg_verifymbstr check the string.  But it's
                 * possible that the string is OK to us, and not OK to mbstowcs ---
                 * this suggests that the LC_CTYPE locale is different from the
                 * database encoding.  Give a generic error message if verifymbstr
                 * can't find anything wrong.
                 */
                pg_verifymbstr(from, fromlen, false);   /* might not return */
                /* but if it does ... */
                ereport(ERROR,
                                (errcode(ERRCODE_CHARACTER_NOT_IN_REPERTOIRE),
                                 errmsg("invalid multibyte character for locale"),
                                 errhint("The server's LC_CTYPE locale is probably incompatible with the database encoding.")));
        }       

        return result;
}

#endif

/* convert a multibyte string to a wchar */
int
pg_mb2wchar(const char *from, pg_wchar *to)
{
        return (*pg_wchar_table[DatabaseEncoding->encoding].mb2wchar_with_len) ((const unsigned char *) from, to, strlen(from));
}

/* convert a multibyte string to a wchar with a limited length */
int
pg_mb2wchar_with_len(const char *from, pg_wchar *to, int len)
{
        return (*pg_wchar_table[DatabaseEncoding->encoding].mb2wchar_with_len) ((const unsigned char *) from, to, len);
}

/* same, with any encoding */
int
pg_encoding_mb2wchar_with_len(int encoding,
                                                          const char *from, pg_wchar *to, int len)
{
        return (*pg_wchar_table[encoding].mb2wchar_with_len) ((const unsigned char *) from, to, len);
}

/* returns the byte length of a multibyte word */
int
pg_mblen(const char *mbstr)
{
        return ((*pg_wchar_table[DatabaseEncoding->encoding].mblen) ((const unsigned char *) mbstr));
}

/* returns the display length of a multibyte word */
int
pg_dsplen(const char *mbstr)
{
        return ((*pg_wchar_table[DatabaseEncoding->encoding].dsplen) ((const unsigned char *) mbstr));
}

/* returns the length (counted in wchars) of a multibyte string */
int
pg_mbstrlen(const char *mbstr)
{
        int                     len = 0;

        /* optimization for single byte encoding */
        if (pg_database_encoding_max_length() == 1)
                return strlen(mbstr);

        while (*mbstr)
        {
                mbstr += pg_mblen(mbstr);
                len++;
        }
        return len;
}

/* returns the length (counted in wchars) of a multibyte string
 * (not necessarily NULL terminated)
 */
int
pg_mbstrlen_with_len(const char *mbstr, int limit)
{
        int                     len = 0;

        /* optimization for single byte encoding */
        if (pg_database_encoding_max_length() == 1)
                return limit;

        while (limit > 0 && *mbstr)
        {
                int                     l = pg_mblen(mbstr);

                limit -= l;
                mbstr += l;
                len++;
        }
        return len;
}

/*
 * returns the byte length of a multibyte string
 * (not necessarily  NULL terminated)
 * that is no longer than limit.
 * this function does not break multibyte word boundary.
 */
int
pg_mbcliplen(const char *mbstr, int len, int limit)
{
        int                     clen = 0;
        int                     l;

        /* optimization for single byte encoding */
        if (pg_database_encoding_max_length() == 1)
                return cliplen(mbstr, len, limit);

        while (len > 0 && *mbstr)
        {
                l = pg_mblen(mbstr);
                if ((clen + l) > limit)
                        break;
                clen += l;
                if (clen == limit)
                        break;
                len -= l;
                mbstr += l;
        }
        return clen;
}

/*
 * Similar to pg_mbcliplen except the limit parameter specifies the
 * character length, not the byte length.  */
int
pg_mbcharcliplen(const char *mbstr, int len, int limit)
{
        int                     clen = 0;
        int                     nch = 0;
        int                     l;

        /* optimization for single byte encoding */
        if (pg_database_encoding_max_length() == 1)
                return cliplen(mbstr, len, limit);

        while (len > 0 && *mbstr)
        {
                l = pg_mblen(mbstr);
                nch++;
                if (nch > limit)
                        break;
                clen += l;
                len -= l;
                mbstr += l;
        }
        return clen;
}

void
SetDatabaseEncoding(int encoding)
{
        if (!PG_VALID_BE_ENCODING(encoding))
                elog(ERROR, "invalid database encoding: %d", encoding);

        DatabaseEncoding = &pg_enc2name_tbl[encoding];
        Assert(DatabaseEncoding->encoding == encoding);

        /*
         * On Windows, we allow UTF-8 database encoding to be used with any
         * locale setting, because UTF-8 requires special handling anyway.
         * But this means that gettext() might be misled about what output
         * encoding it should use, so we have to tell it explicitly.
         *
         * In future we might want to call bind_textdomain_codeset
         * unconditionally, but that requires knowing how to spell the codeset
         * name properly for all encodings on all platforms, which might be
         * problematic.
         *
         * This is presently unnecessary, but harmless, on non-Windows platforms.
         */
#ifdef ENABLE_NLS
        if (encoding == PG_UTF8)
                if (bind_textdomain_codeset("postgres", "UTF-8") == NULL)
                        elog(LOG, "bind_textdomain_codeset failed");
#endif
}

void
SetDefaultClientEncoding(void)
{
        ClientEncoding = &pg_enc2name_tbl[GetDatabaseEncoding()];
}

int
GetDatabaseEncoding(void)
{
        Assert(DatabaseEncoding);
        return DatabaseEncoding->encoding;
}

const char *
GetDatabaseEncodingName(void)
{
        Assert(DatabaseEncoding);
        return DatabaseEncoding->name;
}

Datum
getdatabaseencoding(PG_FUNCTION_ARGS)
{
        Assert(DatabaseEncoding);
        return DirectFunctionCall1(namein, CStringGetDatum(DatabaseEncoding->name));
}

Datum
pg_client_encoding(PG_FUNCTION_ARGS)
{
        Assert(ClientEncoding);
        return DirectFunctionCall1(namein, CStringGetDatum(ClientEncoding->name));
}

static int
cliplen(const char *str, int len, int limit)
{
        int                     l = 0;
        const char *s;

        for (s = str; *s; s++, l++)
        {
                if (l >= len || l >= limit)
                        return l;
        }
        return (s - str);
}