Tool parser regex timeout handling (#18960)

Signed-off-by: Will Eaton <weaton@redhat.com>

tests/entrypoints/openai/tool_parsers/test_llama4_pythonic_tool_parser.py

 # SPDX-License-Identifier: Apache-2.0
 
-from unittest.mock import MagicMock
+from unittest.mock import MagicMock, patch
 
 import pytest
 
@@ -191,3 +191,27 @@ def test_streaming_tool_call_with_large_steps():
     assert reconstructor.tool_calls[0].function == SIMPLE_FUNCTION_CALL
     assert reconstructor.tool_calls[1].function == PARAMETERLESS_FUNCTION_CALL
     assert reconstructor.tool_calls[2].function == EMPTY_LIST_FUNCTION_CALL
+
+
+@pytest.mark.parametrize("streaming", [False])
+def test_regex_timeout_handling(streaming: bool):
+    """test regex timeout is handled gracefully"""
+    mock_tokenizer = MagicMock()
+    tool_parser: ToolParser = ToolParserManager.get_tool_parser(
+        "llama4_pythonic")(mock_tokenizer)
+
+    fake_problematic_input = "hello world[A(A=" + "\t)A(A=,\t" * 2
+
+    # create a mock regex that raises TimeoutError
+    mock_regex = MagicMock()
+    mock_regex.match.side_effect = TimeoutError("Regex timeout")
+
+    with patch.object(tool_parser, 'TOOL_CALL_REGEX', mock_regex):
+        content, tool_calls = run_tool_extraction(tool_parser,
+                                                  fake_problematic_input,
+                                                  streaming=streaming)
+
+        # should treat as regular text when regex times out
+        assert content == fake_problematic_input
+        assert len(tool_calls) == 0
+        mock_regex.match.assert_called_once()

tests/entrypoints/openai/tool_parsers/test_pythonic_tool_parser.py

 # SPDX-License-Identifier: Apache-2.0
 
-from unittest.mock import MagicMock
+from unittest.mock import MagicMock, patch
 
 import pytest
 
@@ -159,3 +159,27 @@ def test_streaming_tool_call_with_large_steps():
     assert reconstructor.tool_calls[0].function == SIMPLE_FUNCTION_CALL
     assert reconstructor.tool_calls[1].function == PARAMETERLESS_FUNCTION_CALL
     assert reconstructor.tool_calls[2].function == EMPTY_LIST_FUNCTION_CALL
+
+
+@pytest.mark.parametrize("streaming", [False])
+def test_regex_timeout_handling(streaming: bool):
+    """test regex timeout is handled gracefully"""
+    mock_tokenizer = MagicMock()
+    tool_parser: ToolParser = ToolParserManager.get_tool_parser(
+        "llama4_pythonic")(mock_tokenizer)
+
+    fake_problematic_input = "hello world[A(A=" + "\t)A(A=,\t" * 2
+
+    # create a mock regex that raises TimeoutError
+    mock_regex = MagicMock()
+    mock_regex.match.side_effect = TimeoutError("Regex timeout")
+
+    with patch.object(tool_parser, 'TOOL_CALL_REGEX', mock_regex):
+        content, tool_calls = run_tool_extraction(tool_parser,
+                                                  fake_problematic_input,
+                                                  streaming=streaming)
+
+        # should treat as regular text when regex times out
+        assert content == fake_problematic_input
+        assert len(tool_calls) == 0
+        mock_regex.match.assert_called_once()

vllm/entrypoints/openai/tool_parsers/llama4_pythonic_tool_parser.py

@@ -7,6 +7,7 @@ from typing import Any, Union
 import regex as re
 from transformers import PreTrainedTokenizerBase
 
+import vllm.envs as envs
 from vllm.entrypoints.openai.protocol import (ChatCompletionRequest,
                                               DeltaFunctionCall, DeltaMessage,
                                               DeltaToolCall,
@@ -64,7 +65,19 @@ class Llama4PythonicToolParser(ToolParser):
         if model_output.startswith("<|python_start|>"):
             model_output = model_output[len("<|python_start|>"):]
             model_output = model_output.replace("<|python_end|>", "")
-        if not (self.TOOL_CALL_REGEX.match(model_output)):
+
+        is_tool_call_pattern = False
+        try:
+            is_tool_call_pattern = self.TOOL_CALL_REGEX.match(
+                model_output,
+                timeout=envs.VLLM_TOOL_PARSE_REGEX_TIMEOUT_SECONDS) is not None
+        except TimeoutError:
+            logger.warning(
+                "Regex timeout occurred when matching tool call pattern.")
+            logger.debug("Regex timeout occurred when matching user input: %s",
+                         model_output)
+
+        if not is_tool_call_pattern:
             return ExtractedToolCallInformation(tools_called=False,
                                                 tool_calls=[],
                                                 content=model_output)

vllm/entrypoints/openai/tool_parsers/pythonic_tool_parser.py

@@ -8,6 +8,7 @@ from typing import Any, Union
 import regex as re
 from transformers import PreTrainedTokenizerBase
 
+import vllm.envs as envs
 from vllm.entrypoints.openai.protocol import (ChatCompletionRequest,
                                               DeltaFunctionCall, DeltaMessage,
                                               DeltaToolCall,
@@ -61,8 +62,18 @@ class PythonicToolParser(ToolParser):
         """
         Extract the tool calls from a complete model response.
         """
-
-        if not (self.TOOL_CALL_REGEX.match(model_output)):
+        is_tool_call_pattern = False
+        try:
+            is_tool_call_pattern = self.TOOL_CALL_REGEX.match(
+                model_output,
+                timeout=envs.VLLM_TOOL_PARSE_REGEX_TIMEOUT_SECONDS) is not None
+        except TimeoutError:
+            logger.warning(
+                "Regex timeout occurred when matching tool call pattern.")
+            logger.debug("Regex timeout occurred when matching user input: %s",
+                         model_output)
+
+        if not is_tool_call_pattern:
             return ExtractedToolCallInformation(tools_called=False,
                                                 tool_calls=[],
                                                 content=model_output)

vllm/envs.py

@@ -119,6 +119,7 @@ if TYPE_CHECKING:
     VLLM_NIXL_SIDE_CHANNEL_PORT: int = 5557
     VLLM_ALL2ALL_BACKEND: str = "naive"
     VLLM_MAX_TOKENS_PER_EXPERT_FP4_MOE: int = 163840
+    VLLM_TOOL_PARSE_REGEX_TIMEOUT_SECONDS: int = 1
 
 
 def get_default_cache_root():
@@ -828,6 +829,10 @@ environment_variables: dict[str, Callable[[], Any]] = {
     # This is used to prevent the kernel from running out of memory.
     "VLLM_MAX_TOKENS_PER_EXPERT_FP4_MOE":
     lambda: int(os.getenv("VLLM_MAX_TOKENS_PER_EXPERT_FP4_MOE", "163840")),
+
+    # Regex timeout for use by the vLLM tool parsing plugins.
+    "VLLM_TOOL_PARSE_REGEX_TIMEOUT_SECONDS":
+    lambda: int(os.getenv("VLLM_TOOL_PARSE_REGEX_TIMEOUT_SECONDS", "1")),
 }
 
 # --8<-- [end:env-vars-definition]