Function pg_do_encoding_conversion_buf

src/backend/utils/mb/mbutils.c:470–495

* Convert src string to another encoding. * * This function has a different API than the other conversion functions. * The caller should've looked up the conversion function using * FindDefaultConversionProc(). Unlike the other functions, the converted * result is not palloc'd. It is written to the caller-supplied buffer * instead. * * src_encoding - encoding to convert from * dest_en

 * to strlen().
 */
int
pg_do_encoding_conversion_buf(Oid proc,
							  int src_encoding,
							  int dest_encoding,
							  unsigned char *src, int srclen,
							  unsigned char *dest, int destlen,
							  bool noError)
{
	Datum		result;

	/*
	 * If the destination buffer is not large enough to hold the result in the
	 * worst case, limit the input size passed to the conversion function.
	 */
	if ((Size) srclen >= ((destlen - 1) / (Size) MAX_CONVERSION_GROWTH))
		srclen = ((destlen - 1) / (Size) MAX_CONVERSION_GROWTH);

	result = OidFunctionCall6(proc,
							  Int32GetDatum(src_encoding),
							  Int32GetDatum(dest_encoding),
							  CStringGetDatum((char *)src),
							  CStringGetDatum((char *)dest),
							  Int32GetDatum(srclen),
							  BoolGetDatum(noError));
	return DatumGetInt32(result);
}

/*
 * Convert string to encoding encoding_name. The source