[BugFix] Fix handling of stop strings and stop token ids (#3672)

vllm/sequence.py

@@ -235,6 +235,12 @@ class Sequence:
     def lora_int_id(self) -> int:
         return self.lora_request.lora_int_id if self.lora_request else 0
 
+    def get_output_text_to_return(self, buffer_length: int):
+        # We return the full output text if the sequence is finished.
+        truncate = buffer_length and not self.is_finished()
+        return self.output_text[:-buffer_length] if truncate else (
+            self.output_text)
+
     def hash_of_block(self, logical_idx: int) -> int:
         # TODO This can produce incorrect hash when block size > prompt size