[Frontend] Added support for HermesToolParser for models without special tokens (#16890)

Signed-off-by: minpeter <kali2005611@gmail.com>

tests/entrypoints/openai/tool_parsers/test_hermes_tool_parser.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import json
+
+import pytest
+
+from ....utils import RemoteOpenAIServer
+
+MODEL_NAME = "meta-llama/Llama-3.2-1B-Instruct"
+LORA_MODEL = "minpeter/LoRA-Llama-3.2-1B-tool-vllm-ci"
+
+SERVER_ARGS = [
+    "--enforce-eager",
+    "--enable-auto-tool-choice",
+    "--tool-call-parser",
+    "hermes",
+    "--enable-lora",
+    "--lora-modules",
+    f"{LORA_MODEL}={LORA_MODEL}",
+]
+
+TOOLS = [{
+    "type": "function",
+    "function": {
+        "name": "get_current_weather",
+        "description": "Get the current weather in a given location",
+        "parameters": {
+            "type": "object",
+            "properties": {
+                "location": {
+                    "type": "string",
+                    "description":
+                    "The city and state, e.g. San Francisco, CA",
+                },
+                "unit": {
+                    "type": "string",
+                    "enum": ["celsius", "fahrenheit"]
+                },
+            },
+            "required": ["location"],
+        },
+    },
+}]
+
+MESSAGES = [{"role": "user", "content": "What's the weather like in Boston?"}]
+
+
+@pytest.mark.asyncio
+async def test_non_streaming_tool_call():
+    """Test tool call in non-streaming mode."""
+    with RemoteOpenAIServer(MODEL_NAME, SERVER_ARGS) as server:
+        client = server.get_async_client()
+
+        response = await client.chat.completions.create(
+            model=LORA_MODEL,
+            messages=MESSAGES,
+            tools=TOOLS,
+            tool_choice="auto",
+            temperature=0.0,
+        )
+
+        assert response.choices
+        choice = response.choices[0]
+        message = choice.message
+
+        assert choice.finish_reason == "tool_calls"
+        assert message.tool_calls is not None
+
+        tool_call = message.tool_calls[0]
+        assert tool_call.type == "function"
+        assert tool_call.function.name == "get_current_weather"
+
+        arguments = json.loads(tool_call.function.arguments)
+        assert "location" in arguments
+        assert "Boston" in arguments["location"]
+        print("\n[Non-Streaming Test Passed]")
+        print(f"Tool Call: {tool_call.function.name}")
+        print(f"Arguments: {arguments}")
+
+
+@pytest.mark.asyncio
+async def test_streaming_tool_call():
+    """Test tool call in streaming mode."""
+    with RemoteOpenAIServer(MODEL_NAME, SERVER_ARGS) as server:
+        client = server.get_async_client()
+
+        stream = await client.chat.completions.create(
+            model=LORA_MODEL,
+            messages=MESSAGES,
+            tools=TOOLS,
+            tool_choice="auto",
+            temperature=0.0,
+            stream=True,
+        )
+
+        tool_call_chunks = {}
+        async for chunk in stream:
+            if not chunk.choices:
+                continue
+
+            delta = chunk.choices[0].delta
+            if not delta or not delta.tool_calls:
+                continue
+
+            for tool_chunk in delta.tool_calls:
+                index = tool_chunk.index
+                if index not in tool_call_chunks:
+                    tool_call_chunks[index] = {"name": "", "arguments": ""}
+
+                if tool_chunk.function.name:
+                    tool_call_chunks[index]["name"] += tool_chunk.function.name
+                if tool_chunk.function.arguments:
+                    tool_call_chunks[index][
+                        "arguments"] += tool_chunk.function.arguments
+
+        assert len(tool_call_chunks) == 1
+        reconstructed_tool_call = tool_call_chunks[0]
+
+        assert reconstructed_tool_call["name"] == "get_current_weather"
+
+        arguments = json.loads(reconstructed_tool_call["arguments"])
+        assert "location" in arguments
+        assert "Boston" in arguments["location"]
+        print("\n[Streaming Test Passed]")
+        print(f"Reconstructed Tool Call: {reconstructed_tool_call['name']}")
+        print(f"Reconstructed Arguments: {arguments}")

vllm/entrypoints/openai/tool_parsers/hermes_tool_parser.py

@@ -52,14 +52,51 @@ class Hermes2ProToolParser(ToolParser):
             raise ValueError(
                 "The model tokenizer must be passed to the ToolParser "
                 "constructor during construction.")
-        self.tool_call_start_token_id = self.vocab.get(
-            self.tool_call_start_token)
-        self.tool_call_end_token_id = self.vocab.get(self.tool_call_end_token)
-        if (self.tool_call_start_token_id is None
-                or self.tool_call_end_token_id is None):
-            raise RuntimeError(
-                "Hermes 2 Pro Tool parser could not locate tool call start/end "
-                "tokens in the tokenizer!")
+        self.tool_call_start_token_ids = self.model_tokenizer.encode(
+            self.tool_call_start_token, add_special_tokens=False)
+        self.tool_call_end_token_ids = self.model_tokenizer.encode(
+            self.tool_call_end_token, add_special_tokens=False)
+
+        self.tool_call_start_token_array = [
+            self.model_tokenizer.decode([token_id])
+            for token_id in self.tool_call_start_token_ids
+        ]
+
+        self.tool_call_end_token_array = [
+            self.model_tokenizer.decode([token_id])
+            for token_id in self.tool_call_end_token_ids
+        ]
+
+        self.buffered_delta_text = ""
+
+    # Very simple idea: when encountering tokens like <, tool, _call, >,
+    # <, /, tool, _call, >, store them in a buffer.
+    # When the last token is encountered, empty the buffer and return it.
+    # If a token appears in an incorrect sequence while storing in the buffer,
+    # return the preceding buffer along with the token.
+    def tool_call_delta_buffer(self, delta_text: str):
+        # If the sequence of tool_call_start or tool_call_end tokens is not yet
+        # complete, fill the buffer with the token and return "".
+        if (delta_text in self.tool_call_start_token_array
+                or delta_text in self.tool_call_end_token_array):
+            # If delta_text is the last token of tool_call_start_token or
+            # tool_call_end_token, empty the buffer and return
+            # the buffered text + delta_text.
+            if (delta_text == self.tool_call_start_token_array[-1]
+                    or delta_text == self.tool_call_end_token_array[-1]):
+                buffered_text = self.buffered_delta_text
+                self.buffered_delta_text = ""
+                return buffered_text + delta_text
+            else:
+                self.buffered_delta_text = self.buffered_delta_text + delta_text
+                return ""
+        else:
+            if self.buffered_delta_text:
+                buffered_text = self.buffered_delta_text
+                self.buffered_delta_text = ""
+                return buffered_text + delta_text
+            else:
+                return delta_text
 
     def extract_tool_calls(
         self,
@@ -124,11 +161,23 @@ class Hermes2ProToolParser(ToolParser):
         delta_token_ids: Sequence[int],
         request: ChatCompletionRequest,
     ) -> Union[DeltaMessage, None]:
+        # 1. All tokens are parsed based on _text, not token_ids.
+        # 2. All incoming text data is processed by the tool_call_delta_buffer
+        #    function for buffering before being used for parsing.
+
+        delta_text = self.tool_call_delta_buffer(delta_text)
+        # If the last characters of previous_text
+        # match self.buffered_delta_text, remove only the matching part.
+        if (len(previous_text) >= len(self.buffered_delta_text)
+                and previous_text[-len(self.buffered_delta_text):]
+                == self.buffered_delta_text):
+            previous_text = previous_text[:-len(self.buffered_delta_text)]
+            current_text = previous_text + delta_text
 
         logger.debug("delta_text: %s", delta_text)
         logger.debug("delta_token_ids: %s", delta_token_ids)
         # check to see if we should be streaming a tool call - is there a
-        if self.tool_call_start_token_id not in current_token_ids:
+        if self.tool_call_start_token not in current_text:
             logger.debug("No tool call tokens found!")
             return DeltaMessage(content=delta_text)
 
@@ -136,14 +185,12 @@ class Hermes2ProToolParser(ToolParser):
 
             # figure out where we are in the parsing by counting tool call
             # start & end tags
-            prev_tool_start_count = previous_token_ids.count(
-                self.tool_call_start_token_id)
-            prev_tool_end_count = previous_token_ids.count(
-                self.tool_call_end_token_id)
-            cur_tool_start_count = current_token_ids.count(
-                self.tool_call_start_token_id)
-            cur_tool_end_count = current_token_ids.count(
-                self.tool_call_end_token_id)
+            prev_tool_start_count = previous_text.count(
+                self.tool_call_start_token)
+            prev_tool_end_count = previous_text.count(self.tool_call_end_token)
+            cur_tool_start_count = current_text.count(
+                self.tool_call_start_token)
+            cur_tool_end_count = current_text.count(self.tool_call_end_token)
             tool_call_portion = None
             text_portion = None