Backported CORE-2122: Translation of large text BLOB between UNICODE_…

…FSS (UTF8) and other charsets.

src/jrd/filters.cpp

@@ -909,7 +909,7 @@ ISC_STATUS filter_transliterate_text(USHORT action, BlobControl* control)
 		/* Always keep a minimal count of bytes in the input buffer, 
 		 * to prevent the case of truncated characters.
 		 */
-		if (length < 3)
+		if (length < 4)
 			can_use_more = true;
 	}
 
@@ -920,13 +920,14 @@ ISC_STATUS filter_transliterate_text(USHORT action, BlobControl* control)
       (We don't want to blindly keep topping off this buffer if we
        already have more than we can use) */
 
-	if (!length || can_use_more
-		&& (aux->ctlaux_source_blob_status == isc_segment))
+	USHORT bytes_read_from_source = 0;
+
+	if (!length || can_use_more)
+//		&& (aux->ctlaux_source_blob_status == isc_segment))
 	{
 		// Get a segment, or partial segment, from the source
 		// into the temporary buffer
 
-		USHORT bytes_read_from_source = 0;
 		status = caller(isc_blob_filter_get_segment,
 						control,
 						(USHORT) MIN((aux->ctlaux_buffer1_len - length), control->ctl_buffer_length),
@@ -960,10 +961,17 @@ ISC_STATUS filter_transliterate_text(USHORT action, BlobControl* control)
 		return isc_transliteration_failed;
 	}
 
-	if (err_position < length) {
-		/* Bad input *might* be due to input buffer truncation in the middle
-		   of a character, so shuffle bytes, add some more data, and try again.
-		   If we already tried that then it's really some bad input */
+	if (err_position == 0 && bytes_read_from_source != 0 && length != 0 && length < 4) {
+		// We don't have sufficient bytes to always transliterate a character.
+		// A bad input on the first character is unrecoverable, so we cache
+		// the bytes for the next read.
+		result_length = 0;
+	}
+	else if (err_position < length)
+	{
+		// Bad input *might* be due to input buffer truncation in the middle
+		// of a character, so shuffle bytes, add some more data, and try again.
+		// If we already tried that then it's really some bad input.
 
 		if (err_position == 0)
 			return isc_transliteration_failed;