[Bugfix] Suppress HarmonyError Unexpected token while expecting start token 200006 (#59254)

Signed-off-by: Yifan Zong <yzong@redhat.com>

tests/parser/test_harmony.py

@@ -872,6 +872,15 @@ class TestProcessChunk:
             ("final", "Two"),
         ]
 
+    def test_malformed_token_does_not_raise(self, harmony_parser):
+        malformed = encode_output(
+            "<|channel|>analysis<|message|>think<|end|><|return|>"
+            "<|start|>assistant<|channel|>final<|message|>answer<|return|>"
+        )
+
+        result = harmony_parser.process_chunk(malformed)
+        assert "".join(s.delta for s in result.segments if s.delta) == "thinkanswer"
+
 
 class TestCountReasoningTokens:
     def test_matches_process_chunk(self, harmony_parser, gpt_oss_tokenizer):

vllm/parser/harmony.py

@@ -335,7 +335,10 @@ class HarmonyParser(DelegatingParser):
         segments: list[Segment] = []
         reasoning_token_count = 0
         for token_id in token_ids:
-            self._harmony_parser.process(token_id)
+            try:
+                self._harmony_parser.process(token_id)
+            except HarmonyError:
+                continue
             channel = self._harmony_parser.current_channel
             recipient = self._normalize_recipient(
                 self._harmony_parser.current_recipient
@@ -376,7 +379,10 @@ class HarmonyParser(DelegatingParser):
         parser = get_streamable_parser_for_assistant()
         count = 0
         for token_id in token_ids:
-            parser.process(token_id)
+            try:
+                parser.process(token_id)
+            except HarmonyError:
+                continue
             recipient = self._normalize_recipient(parser.current_recipient)
             if self._is_reasoning_token(token_id, parser.current_channel, recipient):
                 count += 1