src/backend/utils/mb/mbutils.c

/*
 * This file contains public functions for conversion between
 * client encoding and server (database) encoding.
 *
 * Tatsuo Ishii
 *
 * $PostgreSQL: pgsql/src/backend/utils/mb/mbutils.c,v 1.59 2006/10/04 00:30:02 momjian Exp $
 */
#include "postgres.h"

#include "access/xact.h"
#include "catalog/catquery.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, 
									int custom_client_encoding, 
									FmgrInfo *custom_encoding_proc);
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 startup.
 */
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.
 *
 * If conversion occurs, a palloc'd null-terminated string is returned.
 * In the case of no conversion, src is returned.
 *
 * CAUTION: although the presence of a length argument means that callers
 * can pass non-null-terminated strings, care is required because the same
 * string will be passed back if no conversion occurs.	Such callers *must*
 * check whether result == src and handle that case differently.
 *
 * 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.
	 */
	/* XXX: would have been function_exists() */
	if (!(caql_getcount(
					NULL,
					cql("SELECT COUNT(*) FROM pg_proc "
						" WHERE oid = :1 ",
						ObjectIdGetDatum(proc))) > 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((char *)src),
					 CStringGetDatum((char *)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);

	/*
	 * 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 string using encoding_name.
 *
 * TEXT convert2(TEXT string, NAME src_encoding_name, NAME dest_encoding_name)
 */
Datum
pg_convert2(PG_FUNCTION_ARGS)
{
	text	   *string = PG_GETARG_TEXT_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;
	text	   *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 null terminated */
	len = VARSIZE(string) - VARHDRSZ;
	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 text data type structure. we cannot use textin() here, since
	 * textin assumes that input string encoding is same as database encoding.
	 */
	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_TEXT_P(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, -1, NULL);
}

/*
 * 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, -1, NULL);
}

/*
 *	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.
 *
 *  NOTE: this function was slightly updated to allow passing in a source
 *  encoding that is not necessarily ClientEncoding->encoding for client-to-
 *  server conversion. Default value is -1, which means: use ClientEncoding.
 *  See pg_custom_client_to_server for information.
 */
static char *
perform_default_encoding_conversion(const char *src, int len, bool is_client_to_server, 
									int custom_client_encoding, 
									FmgrInfo *custom_encoding_proc)
{
	char	   *result;
	int			src_encoding,
				dest_encoding;
	FmgrInfo   *flinfo;

	if (is_client_to_server)
	{
		if(custom_client_encoding == -1)
		{
			/* this is the normal path of execution */
			src_encoding = ClientEncoding->encoding;
			dest_encoding = DatabaseEncoding->encoding;
			flinfo = ToServerConvProc;			
		}
		else
		{
			/* this is the custom path of execution, for external tbl encodings */
			src_encoding = custom_client_encoding;
			dest_encoding = DatabaseEncoding->encoding;
			flinfo = custom_encoding_proc;
		}
	}
	else
	{
		if(custom_client_encoding == -1)
		{
			/* this is the normal path of execution */
			src_encoding = DatabaseEncoding->encoding;
			dest_encoding = ClientEncoding->encoding;
			flinfo = ToClientConvProc;			
		}
		else
		{
			/* this is the custom path of execution, for external tbl encodings */
			src_encoding = DatabaseEncoding->encoding;
			dest_encoding = custom_client_encoding;
			flinfo = custom_encoding_proc;
		}
	}

	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((char *) 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 */
	{
		Assert(!lc_ctype_is_c());
		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 */
	{
		/* mbstowcs requires ending '\0' */
		char	   *str = pnstrdup(from, fromlen);

		Assert(!lc_ctype_is_c());
		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

/*
 * pg_custom_client_to_server
 *
 * convert client encoding to server encoding, but use the passed in encodings
 * instead of the global client and server encoding variables. 
 *
 * This routine is basically a slightly modified version of pg_client_to_server.
 * Instead of creating this routine a better way may have been to just call
 * pg_do_encoding_conversion(), which takes in the necessary arguments, however
 * it does not do several necessary checks that pg_client_to_server() does, and
 * altering it to have those check may break other parts of the system. Therefore
 * until there's a better idea we resort to duplicating some code.
 *
 * The reason for creating this routine is to let external tables do data
 * conversion reliably. Since each external table has an encoding attached to
 * it we'd like to just convert from that encoding to the server encoding without
 * altering the global client_encoding variable for this local database.
 */
char *
pg_custom_to_server(const char *s, int len, int src_encoding, void *cep)
{
	FmgrInfo *custom_encoding_proc = (FmgrInfo *)cep;

	Assert(DatabaseEncoding);
	Assert(ClientEncoding);
	
	if (len <= 0)
		return (char *) s;
	
	if (src_encoding == DatabaseEncoding->encoding ||
		src_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(src_encoding))
			(void) pg_verify_mbstr(src_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, src_encoding, custom_encoding_proc);
}

/*
 * pg_server_to_custom
 * 
 * convert server encoding to custom encoding. the reverse of pg_custom_to_server.
 * see pg_custom_to_server, and perform_default_encoding_conversion headers for
 * more information.
 */
char *
pg_server_to_custom(const char *s, int len, int dest_encoding, void *cep)
{
	FmgrInfo *custom_encoding_proc = (FmgrInfo *)cep;
	
	Assert(DatabaseEncoding);

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

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

	return perform_default_encoding_conversion(s, len, false, dest_encoding, custom_encoding_proc);
}

/* 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 character */
int
pg_mblen(const char *mbstr)
{
	return ((*pg_wchar_table[DatabaseEncoding->encoding].mblen) ((const unsigned char *) mbstr));
}

/* returns the display length of a multibyte character */
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 character boundary.
 */
int
pg_mbcliplen(const char *mbstr, int len, int limit)
{
	return pg_encoding_mbcliplen(DatabaseEncoding->encoding, mbstr,
								 len, limit);
}

/*
 * pg_mbcliplen with specified encoding
 */
int
pg_encoding_mbcliplen(int encoding, const char *mbstr,
					  int len, int limit)
{
	mblen_converter mblen_fn;
	int			clen = 0;
	int			l;

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

	mblen_fn = pg_wchar_table[encoding].mblen;

	while (len > 0 && *mbstr)
	{
		l = (*mblen_fn) ((const unsigned char *) 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;
}

/* mbcliplen for any single-byte encoding */
static int
cliplen(const char *str, int len, int limit)
{
	int			l = 0;

	len = Min(len, limit);
	while (l < len && str[l])
		l++;
	return l;
}

#if defined(ENABLE_NLS) && defined(WIN32)
static const struct codeset_map {
	int	encoding;
	const char *codeset;
} codeset_map_array[] = {
	{PG_UTF8, "UTF-8"},
	{PG_LATIN1, "LATIN1"},
	{PG_LATIN2, "LATIN2"},
	{PG_LATIN3, "LATIN3"},
	{PG_LATIN4, "LATIN4"},
	{PG_ISO_8859_5, "ISO-8859-5"},
	{PG_ISO_8859_6, "ISO_8859-6"},
	{PG_ISO_8859_7, "ISO-8859-7"},
	{PG_ISO_8859_8, "ISO-8859-8"},
	{PG_LATIN5, "LATIN5"},
	{PG_LATIN6, "LATIN6"},
	{PG_LATIN7, "LATIN7"},
	{PG_LATIN8, "LATIN8"},
	{PG_LATIN9, "LATIN-9"},
	{PG_LATIN10, "LATIN10"},
	{PG_KOI8R, "KOI8-R"},
	{PG_WIN1250, "CP1250"},
	{PG_WIN1251, "CP1251"},
	{PG_WIN1252, "CP1252"},
	{PG_WIN1253, "CP1253"},
	{PG_WIN1254, "CP1254"},
	{PG_WIN1255, "CP1255"},
	{PG_WIN1256, "CP1256"},
	{PG_WIN1257, "CP1257"},
	{PG_WIN1258, "CP1258"},
	{PG_WIN866, "CP866"},
	{PG_WIN874, "CP874"},
	{PG_EUC_CN, "EUC-CN"},
	{PG_EUC_JP, "EUC-JP"},
	{PG_EUC_KR, "EUC-KR"},
	{PG_EUC_TW, "EUC-TW"},
	{PG_EUC_JIS_2004, "EUC-JP"}
};
#endif /* WIN32 */

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);
}

/*
 * Bind gettext to the codeset equivalent with the database encoding.
 */
void
pg_bind_textdomain_codeset(const char *domainname)
{
#if defined(ENABLE_NLS)
	int			encoding = GetDatabaseEncoding();
	int			i;

	/*
	 * gettext() uses the codeset specified by LC_CTYPE by default, so if that
	 * matches the database encoding we don't need to do anything. In CREATE
	 * DATABASE, we enforce or trust that the locale's codeset matches
	 * database encoding, except for the C locale. In C locale, we bind
	 * gettext() explicitly to the right codeset.
	 *
	 * On Windows, though, gettext() tends to get confused so we always bind
	 * it.
	 */
#ifndef WIN32
	const char *ctype = setlocale(LC_CTYPE, NULL);

	if (pg_strcasecmp(ctype, "C") != 0 && pg_strcasecmp(ctype, "POSIX") != 0)
		return;
#endif

	for (i = 0; pg_enc2gettext_tbl[i].name != NULL; i++)
	{
		if (pg_enc2gettext_tbl[i].encoding == encoding)
		{
			if (bind_textdomain_codeset(domainname,
										pg_enc2gettext_tbl[i].name) == NULL)
				elog(LOG, "bind_textdomain_codeset failed");
			break;
		}
	}
#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));
}