[BUGFIX] [FRONTEND] Correct chat logprobs (#5029)

Co-authored-by: Breno Faria <breno.faria@intrafind.com>

tests/async_engine/test_openapi_server_ray.py

@@ -94,8 +94,10 @@ async def test_single_chat_session(server, client: openai.AsyncOpenAI):
         chat_completion.choices) == 1
     assert chat_completion.choices[0].message is not None
     assert chat_completion.choices[0].logprobs is not None
-    assert chat_completion.choices[0].logprobs.top_logprobs is not None
+    assert chat_completion.choices[0].logprobs.content[
-    assert len(chat_completion.choices[0].logprobs.top_logprobs[0]) == 5
+        0].top_logprobs is not None
+    assert len(
+        chat_completion.choices[0].logprobs.content[0].top_logprobs) == 5
     message = chat_completion.choices[0].message
     assert message.content is not None and len(message.content) >= 10
     assert message.role == "assistant"

tests/entrypoints/test_openai_server.py

@@ -184,6 +184,26 @@ async def test_single_completion(server, client: openai.AsyncOpenAI,
         completion.choices[0].text) >= 5
 
 
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    # first test base model, then test loras
+    "model_name",
+    [MODEL_NAME, "zephyr-lora", "zephyr-lora2"],
+)
+async def test_no_logprobs(server, client: openai.AsyncOpenAI,
+                           model_name: str):
+    # test using token IDs
+    completion = await client.completions.create(
+        model=MODEL_NAME,
+        prompt=[0, 0, 0, 0, 0],
+        max_tokens=5,
+        temperature=0.0,
+        logprobs=None,
+    )
+    choice = completion.choices[0]
+    assert choice.logprobs is None
+
+
 @pytest.mark.asyncio
 @pytest.mark.parametrize(
     # first test base model, then test loras
@@ -203,7 +223,72 @@ async def test_zero_logprobs(server, client: openai.AsyncOpenAI,
     choice = completion.choices[0]
     assert choice.logprobs is not None
     assert choice.logprobs.token_logprobs is not None
-    assert choice.logprobs.top_logprobs is None
+    assert choice.logprobs.top_logprobs is not None
+    assert len(choice.logprobs.top_logprobs[0]) <= 1
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    "model_name",
+    [MODEL_NAME, "zephyr-lora"],
+)
+async def test_some_logprobs(server, client: openai.AsyncOpenAI,
+                             model_name: str):
+    # test using token IDs
+    completion = await client.completions.create(
+        model=MODEL_NAME,
+        prompt=[0, 0, 0, 0, 0],
+        max_tokens=5,
+        temperature=0.0,
+        logprobs=5,
+    )
+    choice = completion.choices[0]
+    assert choice.logprobs is not None
+    assert choice.logprobs.token_logprobs is not None
+    assert choice.logprobs.top_logprobs is not None
+    assert len(choice.logprobs.top_logprobs[0]) <= 6
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    "model_name",
+    [MODEL_NAME, "zephyr-lora"],
+)
+async def test_too_many_completion_logprobs(server, client: openai.AsyncOpenAI,
+                                            model_name: str):
+
+    with pytest.raises(
+        (openai.BadRequestError, openai.APIError)):  # test using token IDs
+        await client.completions.create(
+            model=MODEL_NAME,
+            prompt=[0, 0, 0, 0, 0],
+            max_tokens=5,
+            temperature=0.0,
+            logprobs=6,
+        )
+        ...
+    with pytest.raises(
+        (openai.BadRequestError, openai.APIError)):  # test using token IDs
+        stream = await client.completions.create(
+            model=MODEL_NAME,
+            prompt=[0, 0, 0, 0, 0],
+            max_tokens=5,
+            temperature=0.0,
+            logprobs=6,
+            stream=True,
+        )
+        async for chunk in stream:
+            ...
+
+    # the server should still work afterwards
+    completion = await client.completions.create(
+        model=model_name,
+        prompt=[0, 0, 0, 0, 0],
+        max_tokens=5,
+        temperature=0.0,
+    )
+    completion = completion.choices[0].text
+    assert completion is not None and len(completion) >= 0
 
 
 @pytest.mark.asyncio
@@ -233,8 +318,10 @@ async def test_single_chat_session(server, client: openai.AsyncOpenAI,
         chat_completion.choices) == 1
     assert chat_completion.choices[0].message is not None
     assert chat_completion.choices[0].logprobs is not None
-    assert chat_completion.choices[0].logprobs.top_logprobs is not None
+    assert chat_completion.choices[0].logprobs.content[
-    assert len(chat_completion.choices[0].logprobs.top_logprobs[0]) == 5
+        0].top_logprobs is not None
+    assert len(
+        chat_completion.choices[0].logprobs.content[0].top_logprobs) == 5
     message = chat_completion.choices[0].message
     assert message.content is not None and len(message.content) >= 10
     assert message.role == "assistant"
@@ -252,9 +339,13 @@ async def test_single_chat_session(server, client: openai.AsyncOpenAI,
 
 
 @pytest.mark.asyncio
-@pytest.mark.parametrize("model_name", [MODEL_NAME])
+@pytest.mark.parametrize(
-async def test_too_many_logprobs(server, client: openai.AsyncOpenAI,
+    # first test base model, then test loras
-                                 model_name: str):
+    "model_name",
+    [MODEL_NAME, "zephyr-lora", "zephyr-lora2"],
+)
+async def test_no_logprobs_chat(server, client: openai.AsyncOpenAI,
+                                model_name: str):
     messages = [{
         "role": "system",
         "content": "you are a helpful assistant"
@@ -263,13 +354,92 @@ async def test_too_many_logprobs(server, client: openai.AsyncOpenAI,
         "content": "what is 1+1?"
     }]
 
-    # Default max_logprobs is 5, so this should raise an error
+    chat_completion = await client.chat.completions.create(model=model_name,
+                                                           messages=messages,
+                                                           max_tokens=5,
+                                                           temperature=0.0,
+                                                           logprobs=False)
+
+    choice = chat_completion.choices[0]
+    assert choice.logprobs is None
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    # just test 1 lora hereafter
+    "model_name",
+    [MODEL_NAME, "zephyr-lora"],
+)
+async def test_zero_logprobs_chat(server, client: openai.AsyncOpenAI,
+                                  model_name: str):
+    messages = [{
+        "role": "system",
+        "content": "you are a helpful assistant"
+    }, {
+        "role": "user",
+        "content": "what is 1+1?"
+    }]
+
+    chat_completion = await client.chat.completions.create(model=model_name,
+                                                           messages=messages,
+                                                           max_tokens=5,
+                                                           temperature=0.0,
+                                                           logprobs=True,
+                                                           top_logprobs=0)
+
+    choice = chat_completion.choices[0]
+    assert choice.logprobs is not None
+    assert choice.logprobs.content is not None
+    assert len(choice.logprobs.content[0].top_logprobs) <= 1
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    "model_name",
+    [MODEL_NAME, "zephyr-lora"],
+)
+async def test_some_logprobs_chat(server, client: openai.AsyncOpenAI,
+                                  model_name: str):
+    messages = [{
+        "role": "system",
+        "content": "you are a helpful assistant"
+    }, {
+        "role": "user",
+        "content": "what is 1+1?"
+    }]
+
+    chat_completion = await client.chat.completions.create(model=model_name,
+                                                           messages=messages,
+                                                           max_tokens=5,
+                                                           temperature=0.0,
+                                                           logprobs=True,
+                                                           top_logprobs=5)
+
+    choice = chat_completion.choices[0]
+    assert choice.logprobs is not None
+    assert choice.logprobs.content is not None
+    assert len(choice.logprobs.content[0].top_logprobs) <= 6
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("model_name", [MODEL_NAME])
+async def test_too_many_chat_logprobs(server, client: openai.AsyncOpenAI,
+                                      model_name: str):
+    messages = [{
+        "role": "system",
+        "content": "you are a helpful assistant"
+    }, {
+        "role": "user",
+        "content": "what is 1+1?"
+    }]
+
+    # Default max_logprobs is 20, so this should raise an error
     with pytest.raises((openai.BadRequestError, openai.APIError)):
         stream = await client.chat.completions.create(model=model_name,
                                                       messages=messages,
                                                       max_tokens=10,
                                                       logprobs=True,
-                                                      top_logprobs=10,
+                                                      top_logprobs=21,
                                                       stream=True)
         async for chunk in stream:
             ...
@@ -279,25 +449,9 @@ async def test_too_many_logprobs(server, client: openai.AsyncOpenAI,
                                              messages=messages,
                                              max_tokens=10,
                                              logprobs=True,
-                                             top_logprobs=10,
+                                             top_logprobs=30,
                                              stream=False)
 
-    with pytest.raises((openai.BadRequestError, openai.APIError)):
-        stream = await client.completions.create(model=model_name,
-                                                 prompt="Test",
-                                                 max_tokens=10,
-                                                 logprobs=10,
-                                                 stream=True)
-        async for chunk in stream:
-            ...
-
-    with pytest.raises(openai.BadRequestError):
-        await client.completions.create(model=model_name,
-                                        prompt="Test",
-                                        max_tokens=10,
-                                        logprobs=10,
-                                        stream=False)
-
     # the server should still work afterwards
     chat_completion = await client.chat.completions.create(model=model_name,
                                                            messages=messages,
@@ -744,13 +898,12 @@ async def test_guided_choice_chat_logprobs(server, client: openai.AsyncOpenAI,
         top_logprobs=5,
         extra_body=dict(guided_choice=TEST_CHOICE,
                         guided_decoding_backend=guided_decoding_backend))
-    top_logprobs = chat_completion.choices[0].logprobs.top_logprobs
+    top_logprobs = chat_completion.choices[0].logprobs.content[0].top_logprobs
 
     # -9999.0 is the minimum logprob returned by OpenAI
     assert all(
-        isinstance(logprob, float) and logprob >= -9999.0
+        isinstance(token.logprob, float) and token.logprob >= -9999.0
-        for token_dict in top_logprobs
+        for token in top_logprobs)
-        for token, logprob in token_dict.items())
 
 
 @pytest.mark.asyncio

vllm/entrypoints/openai/protocol.py

@@ -250,6 +250,19 @@ class ChatCompletionRequest(OpenAIBaseModel):
                 "('guided_json', 'guided_regex' or 'guided_choice').")
         return data
 
+    @model_validator(mode="before")
+    @classmethod
+    def check_logprobs(cls, data):
+        if "top_logprobs" in data and data["top_logprobs"] is not None:
+            if "logprobs" not in data or data["logprobs"] is False:
+                raise ValueError(
+                    "when using `top_logprobs`, `logprobs` must be set to true."
+                )
+            elif not 0 <= data["top_logprobs"] <= 20:
+                raise ValueError(
+                    "`top_logprobs` must be a value in the interval [0, 20].")
+        return data
+
 
 class CompletionRequest(OpenAIBaseModel):
     # Ordered by official OpenAI API documentation
@@ -396,6 +409,15 @@ class CompletionRequest(OpenAIBaseModel):
                 "('guided_json', 'guided_regex' or 'guided_choice').")
         return data
 
+    @model_validator(mode="before")
+    @classmethod
+    def check_logprobs(cls, data):
+        if "logprobs" in data and data[
+                "logprobs"] is not None and not 0 <= data["logprobs"] <= 5:
+            raise ValueError(("if passed, `logprobs` must be a value",
+                              " in the interval [0, 5]."))
+        return data
+
 
 class EmbeddingRequest(BaseModel):
     # Ordered by official OpenAI API documentation
@@ -415,7 +437,7 @@ class EmbeddingRequest(BaseModel):
         return PoolingParams(additional_data=self.additional_data)
 
 
-class LogProbs(OpenAIBaseModel):
+class CompletionLogProbs(OpenAIBaseModel):
     text_offset: List[int] = Field(default_factory=list)
     token_logprobs: List[Optional[float]] = Field(default_factory=list)
     tokens: List[str] = Field(default_factory=list)
@@ -425,7 +447,7 @@ class LogProbs(OpenAIBaseModel):
 class CompletionResponseChoice(OpenAIBaseModel):
     index: int
     text: str
-    logprobs: Optional[LogProbs] = None
+    logprobs: Optional[CompletionLogProbs] = None
     finish_reason: Optional[str] = None
     stop_reason: Optional[Union[int, str]] = Field(
         default=None,
@@ -448,7 +470,7 @@ class CompletionResponse(OpenAIBaseModel):
 class CompletionResponseStreamChoice(OpenAIBaseModel):
     index: int
     text: str
-    logprobs: Optional[LogProbs] = None
+    logprobs: Optional[CompletionLogProbs] = None
     finish_reason: Optional[str] = None
     stop_reason: Optional[Union[int, str]] = Field(
         default=None,
@@ -488,11 +510,25 @@ class ChatMessage(OpenAIBaseModel):
     content: str
 
 
+class ChatCompletionLogProb(OpenAIBaseModel):
+    token: str
+    logprob: float = -9999.0
+    bytes: Optional[List[int]] = None
+
+
+class ChatCompletionLogProbsContent(ChatCompletionLogProb):
+    top_logprobs: List[ChatCompletionLogProb] = Field(default_factory=list)
+
+
+class ChatCompletionLogProbs(OpenAIBaseModel):
+    content: Optional[List[ChatCompletionLogProbsContent]] = None
+
+
 class ChatCompletionResponseChoice(OpenAIBaseModel):
     index: int
     message: ChatMessage
-    logprobs: Optional[LogProbs] = None
+    logprobs: Optional[ChatCompletionLogProbs] = None
-    finish_reason: Optional[str] = None
+    finish_reason: Optional[Literal["stop", "length", "tool_calls"]] = None
     stop_reason: Optional[Union[int, str]] = None
 
 
@@ -513,8 +549,8 @@ class DeltaMessage(OpenAIBaseModel):
 class ChatCompletionResponseStreamChoice(OpenAIBaseModel):
     index: int
     delta: DeltaMessage
-    logprobs: Optional[LogProbs] = None
+    logprobs: Optional[ChatCompletionLogProbs] = None
-    finish_reason: Optional[str] = None
+    finish_reason: Optional[Literal["stop", "length", "tool_calls"]] = None
     stop_reason: Optional[Union[int, str]] = None
 
 

vllm/entrypoints/openai/serving_chat.py

@@ -1,8 +1,10 @@
 import codecs
 import time
 from dataclasses import dataclass
-from typing import (AsyncGenerator, AsyncIterator, Iterable, List, Optional,
+from typing import (AsyncGenerator, AsyncIterator, Dict, Iterable, List,
-                    TypedDict, Union, cast, final)
+                    Optional)
+from typing import Sequence as GenericSequence
+from typing import TypedDict, Union, cast, final
 
 from fastapi import Request
 from openai.types.chat import ChatCompletionContentPartTextParam
@@ -10,8 +12,9 @@ from openai.types.chat import ChatCompletionContentPartTextParam
 from vllm.config import ModelConfig
 from vllm.engine.async_llm_engine import AsyncLLMEngine
 from vllm.entrypoints.openai.protocol import (
-    ChatCompletionContentPartParam, ChatCompletionMessageParam,
+    ChatCompletionContentPartParam, ChatCompletionLogProb,
-    ChatCompletionRequest, ChatCompletionResponse,
+    ChatCompletionLogProbs, ChatCompletionLogProbsContent,
+    ChatCompletionMessageParam, ChatCompletionRequest, ChatCompletionResponse,
     ChatCompletionResponseChoice, ChatCompletionResponseStreamChoice,
     ChatCompletionStreamResponse, ChatMessage, DeltaMessage, ErrorResponse,
     UsageInfo)
@@ -21,6 +24,7 @@ from vllm.logger import init_logger
 from vllm.model_executor.guided_decoding import (
     get_guided_decoding_logits_processor)
 from vllm.outputs import RequestOutput
+from vllm.sequence import Logprob
 from vllm.utils import random_uuid
 
 logger = init_logger(__name__)
@@ -283,11 +287,10 @@ class OpenAIServingChat(OpenAIServing):
                         previous_num_tokens[i]:] if output.logprobs else None
 
                     if request.logprobs:
-                        logprobs = self._create_logprobs(
+                        logprobs = self._create_chat_logprobs(
                             token_ids=delta_token_ids,
                             top_logprobs=top_logprobs,
                             num_output_top_logprobs=request.top_logprobs,
-                            initial_text_offset=len(previous_texts[i]),
                         )
                     else:
                         logprobs = None
@@ -370,7 +373,7 @@ class OpenAIServingChat(OpenAIServing):
             top_logprobs = output.logprobs
 
             if request.logprobs:
-                logprobs = self._create_logprobs(
+                logprobs = self._create_chat_logprobs(
                     token_ids=token_ids,
                     top_logprobs=top_logprobs,
                     num_output_top_logprobs=request.top_logprobs,
@@ -383,8 +386,7 @@ class OpenAIServingChat(OpenAIServing):
                 message=ChatMessage(role=role, content=output.text),
                 logprobs=logprobs,
                 finish_reason=output.finish_reason,
-                stop_reason=output.stop_reason,
+                stop_reason=output.stop_reason)
-            )
             choices.append(choice_data)
 
         if request.echo:
@@ -414,3 +416,51 @@ class OpenAIServingChat(OpenAIServing):
         )
 
         return response
+
+    def _get_top_logprobs(
+            self, logprobs: Dict[int, Logprob],
+            top_logprobs: Optional[int]) -> List[ChatCompletionLogProb]:
+        return [
+            ChatCompletionLogProb(
+                token=self._get_decoded_token(p[1], p[0]),
+                logprob=max(p[1].logprob, -9999.0),
+                bytes=list(
+                    self._get_decoded_token(p[1],
+                                            p[0]).encode("utf-8",
+                                                         errors="replace")))
+            for i, p in enumerate(logprobs.items())
+            if top_logprobs and i < top_logprobs
+        ]
+
+    def _create_chat_logprobs(
+        self,
+        token_ids: GenericSequence[int],
+        top_logprobs: GenericSequence[Optional[Dict[int, Logprob]]],
+        num_output_top_logprobs: Optional[int] = None,
+    ) -> ChatCompletionLogProbs:
+        """Create OpenAI-style logprobs."""
+
+        logprobs_content = []
+
+        for i, token_id in enumerate(token_ids):
+            step_top_logprobs = top_logprobs[i]
+            if step_top_logprobs is None:
+                logprobs_content.append(
+                    ChatCompletionLogProbsContent(
+                        token=self.tokenizer.decode(token_id),
+                        bytes=list(
+                            self.tokenizer.decode(token_id).encode(
+                                "utf-8", errors="replace"))))
+            else:
+                logprobs_content.append(
+                    ChatCompletionLogProbsContent(
+                        token=step_top_logprobs[token_id].decoded_token,
+                        logprob=max(step_top_logprobs[token_id].logprob,
+                                    -9999.0),
+                        bytes=list(
+                            step_top_logprobs[token_id].decoded_token.encode(
+                                "utf-8", errors="replace")),
+                        top_logprobs=self._get_top_logprobs(
+                            step_top_logprobs, num_output_top_logprobs)))
+
+        return ChatCompletionLogProbs(content=logprobs_content)

vllm/entrypoints/openai/serving_completion.py

@@ -1,23 +1,29 @@
 import time
 from typing import (AsyncGenerator, AsyncIterator, Callable, Dict, List,
-                    Optional, Tuple)
+                    Optional)
+from typing import Sequence as GenericSequence
+from typing import Tuple
 
 from fastapi import Request
 
 from vllm.config import ModelConfig
 from vllm.engine.async_llm_engine import AsyncLLMEngine
-from vllm.entrypoints.openai.protocol import (CompletionRequest,
+# yapf: disable
+from vllm.entrypoints.openai.protocol import (CompletionLogProbs,
+                                              CompletionRequest,
                                               CompletionResponse,
                                               CompletionResponseChoice,
                                               CompletionResponseStreamChoice,
                                               CompletionStreamResponse,
-                                              LogProbs, UsageInfo)
+                                              UsageInfo)
+# yapf: enable
 from vllm.entrypoints.openai.serving_engine import (LoRAModulePath,
                                                     OpenAIServing)
 from vllm.logger import init_logger
 from vllm.model_executor.guided_decoding import (
     get_guided_decoding_logits_processor)
 from vllm.outputs import RequestOutput
+from vllm.sequence import Logprob
 from vllm.utils import merge_async_iterators, random_uuid
 
 logger = init_logger(__name__)
@@ -25,7 +31,7 @@ logger = init_logger(__name__)
 TypeTokenIDs = List[int]
 TypeTopLogProbs = List[Optional[Dict[int, float]]]
 TypeCreateLogProbsFn = Callable[
-    [TypeTokenIDs, TypeTopLogProbs, Optional[int], int], LogProbs]
+    [TypeTokenIDs, TypeTopLogProbs, Optional[int], int], CompletionLogProbs]
 
 
 def parse_prompt_format(prompt) -> Tuple[bool, list]:
@@ -235,7 +241,7 @@ class OpenAIServingCompletion(OpenAIServing):
                             i]:] if output.logprobs else None
 
                     if request.logprobs is not None:
-                        logprobs = self._create_logprobs(
+                        logprobs = self._create_completion_logprobs(
                             token_ids=delta_token_ids,
                             top_logprobs=top_logprobs,
                             num_output_top_logprobs=request.logprobs,
@@ -317,7 +323,7 @@ class OpenAIServingCompletion(OpenAIServing):
                     assert top_logprobs is not None, (
                         "top_logprobs must be provided when logprobs "
                         "is requested")
-                    logprobs = self._create_logprobs(
+                    logprobs = self._create_completion_logprobs(
                         token_ids=token_ids,
                         top_logprobs=top_logprobs,
                         num_output_top_logprobs=request.logprobs,
@@ -351,3 +357,59 @@ class OpenAIServingCompletion(OpenAIServing):
             choices=choices,
             usage=usage,
         )
+
+    def _create_completion_logprobs(
+        self,
+        token_ids: GenericSequence[int],
+        top_logprobs: GenericSequence[Optional[Dict[int, Logprob]]],
+        num_output_top_logprobs: int,
+        initial_text_offset: int = 0,
+    ) -> CompletionLogProbs:
+        """Create logprobs for OpenAI Completion API."""
+        out_text_offset: List[int] = []
+        out_token_logprobs: List[Optional[float]] = []
+        out_tokens: List[str] = []
+        out_top_logprobs: List[Optional[Dict[str, float]]] = []
+
+        last_token_len = 0
+
+        for i, token_id in enumerate(token_ids):
+            step_top_logprobs = top_logprobs[i]
+            if step_top_logprobs is None:
+                token = self.tokenizer.decode(token_id)
+                out_tokens.append(token)
+                out_token_logprobs.append(None)
+                out_top_logprobs.append(None)
+            else:
+                token = self._get_decoded_token(step_top_logprobs[token_id],
+                                                token_id)
+                token_logprob = max(step_top_logprobs[token_id].logprob,
+                                    -9999.0)
+                out_tokens.append(token)
+                out_token_logprobs.append(token_logprob)
+
+                # makes sure to add the top num_output_top_logprobs + 1
+                # logprobs, as defined in the openai API
+                # (cf. https://github.com/openai/openai-openapi/blob/
+                # 893ba52242dbd5387a97b96444ee1c742cfce9bd/openapi.yaml#L7153)
+                out_top_logprobs.append({
+                    # Convert float("-inf") to the
+                    # JSON-serializable float that OpenAI uses
+                    self._get_decoded_token(top_lp[1], top_lp[0]):
+                    max(top_lp[1].logprob, -9999.0)
+                    for i, top_lp in enumerate(step_top_logprobs.items())
+                    if num_output_top_logprobs >= i
+                })
+
+            if len(out_text_offset) == 0:
+                out_text_offset.append(initial_text_offset)
+            else:
+                out_text_offset.append(out_text_offset[-1] + last_token_len)
+            last_token_len = len(token)
+
+        return CompletionLogProbs(
+            text_offset=out_text_offset,
+            token_logprobs=out_token_logprobs,
+            tokens=out_tokens,
+            top_logprobs=out_top_logprobs,
+        )

vllm/entrypoints/openai/serving_engine.py

@@ -11,7 +11,7 @@ from vllm.engine.async_llm_engine import AsyncLLMEngine
 from vllm.entrypoints.openai.protocol import (ChatCompletionRequest,
                                               CompletionRequest,
                                               EmbeddingRequest, ErrorResponse,
-                                              LogProbs, ModelCard, ModelList,
+                                              ModelCard, ModelList,
                                               ModelPermission)
 from vllm.logger import init_logger
 from vllm.lora.request import LoRARequest
@@ -75,51 +75,6 @@ class OpenAIServing:
         model_cards.extend(lora_cards)
         return ModelList(data=model_cards)
 
-    def _create_logprobs(
-        self,
-        token_ids: List[int],
-        top_logprobs: List[Optional[Dict[int, Logprob]]],
-        num_output_top_logprobs: Optional[int] = None,
-        initial_text_offset: int = 0,
-    ) -> LogProbs:
-        """Create OpenAI-style logprobs."""
-        logprobs = LogProbs()
-        last_token_len = 0
-        if num_output_top_logprobs:
-            logprobs.top_logprobs = []
-
-        for i, token_id in enumerate(token_ids):
-            step_top_logprobs = top_logprobs[i]
-            if step_top_logprobs is None:
-                token = self.tokenizer.decode(token_id)
-                logprobs.tokens.append(token)
-                logprobs.token_logprobs.append(None)
-                assert logprobs.top_logprobs is not None
-                logprobs.top_logprobs.append(None)
-            else:
-                token_logprob = step_top_logprobs[token_id].logprob
-                token = step_top_logprobs[token_id].decoded_token
-                logprobs.tokens.append(token)
-                token_logprob = max(token_logprob, -9999.0)
-                logprobs.token_logprobs.append(token_logprob)
-
-                if num_output_top_logprobs:
-                    assert logprobs.top_logprobs is not None
-                    logprobs.top_logprobs.append({
-                        # Convert float("-inf") to the
-                        # JSON-serializable float that OpenAI uses
-                        p.decoded_token: max(p.logprob, -9999.0)
-                        for i, p in step_top_logprobs.items()
-                    } if step_top_logprobs else None)
-
-            if len(logprobs.text_offset) == 0:
-                logprobs.text_offset.append(initial_text_offset)
-            else:
-                logprobs.text_offset.append(logprobs.text_offset[-1] +
-                                            last_token_len)
-            last_token_len = len(token)
-        return logprobs
-
     def create_error_response(
             self,
             message: str,
@@ -235,3 +190,8 @@ class OpenAIServing:
                 f"Please reduce the length of the messages or completion.", )
         else:
             return input_ids, input_text
+
+    def _get_decoded_token(self, logprob: Logprob, token_id: int) -> str:
+        if logprob.decoded_token is not None:
+            return logprob.decoded_token
+        return self.tokenizer.decode(token_id)