Add option to completion API to truncate prompt tokens (#3144)

vllm/entrypoints/openai/protocol.py

@@ -4,7 +4,7 @@ import time
 from typing import Dict, List, Literal, Optional, Union
 
 import torch
-from pydantic import BaseModel, Field, model_validator
+from pydantic import BaseModel, Field, conint, model_validator
 
 from vllm.sampling_params import SamplingParams
 from vllm.utils import random_uuid
@@ -229,6 +229,7 @@ class CompletionRequest(BaseModel):
     min_tokens: Optional[int] = 0
     skip_special_tokens: Optional[bool] = True
     spaces_between_special_tokens: Optional[bool] = True
+    truncate_prompt_tokens: Optional[conint(ge=1)] = None
     # doc: end-completion-sampling-params
 
     # doc: begin-completion-extra-params
@@ -309,6 +310,7 @@ class CompletionRequest(BaseModel):
             include_stop_str_in_output=self.include_stop_str_in_output,
             length_penalty=self.length_penalty,
             logits_processors=logits_processors,
+            truncate_prompt_tokens=self.truncate_prompt_tokens,
         )
 
     @model_validator(mode="before")

vllm/entrypoints/openai/serving_completion.py

@@ -137,10 +137,16 @@ class OpenAIServingCompletion(OpenAIServing):
             for i, prompt in enumerate(prompts):
                 if prompt_is_tokens:
                     input_ids = self._validate_prompt_and_tokenize(
-                        request, prompt_ids=prompt)
+                        request,
+                        prompt_ids=prompt,
+                        truncate_prompt_tokens=sampling_params.
+                        truncate_prompt_tokens)
                 else:
                     input_ids = self._validate_prompt_and_tokenize(
-                        request, prompt=prompt)
+                        request,
+                        prompt=prompt,
+                        truncate_prompt_tokens=sampling_params.
+                        truncate_prompt_tokens)
 
                 generators.append(
                     self.engine.generate(prompt,

vllm/entrypoints/openai/serving_engine.py

@@ -4,6 +4,8 @@ from dataclasses import dataclass
 from http import HTTPStatus
 from typing import Dict, List, Optional, Union
 
+from pydantic import conint
+
 from vllm.engine.async_llm_engine import AsyncLLMEngine
 from vllm.entrypoints.openai.protocol import (ChatCompletionRequest,
                                               CompletionRequest, ErrorResponse,
@@ -66,7 +68,8 @@ class OpenAIServing:
         self.tokenizer = get_tokenizer(
             engine_model_config.tokenizer,
             tokenizer_mode=engine_model_config.tokenizer_mode,
-            trust_remote_code=engine_model_config.trust_remote_code)
+            trust_remote_code=engine_model_config.trust_remote_code,
+            truncation_side="left")
 
     async def show_available_models(self) -> ModelList:
         """Show available models. Right now we only have one model."""
@@ -164,15 +167,26 @@ class OpenAIServing:
             self,
             request: Union[ChatCompletionRequest, CompletionRequest],
             prompt: Optional[str] = None,
-            prompt_ids: Optional[List[int]] = None) -> List[int]:
+            prompt_ids: Optional[List[int]] = None,
+            truncate_prompt_tokens: Optional[conint(ge=1)] = None
+    ) -> List[int]:
         if not (prompt or prompt_ids):
             raise ValueError("Either prompt or prompt_ids should be provided.")
         if (prompt and prompt_ids):
             raise ValueError(
                 "Only one of prompt or prompt_ids should be provided.")
 
-        input_ids = prompt_ids if prompt_ids is not None else self.tokenizer(
+        if prompt_ids is None:
-            prompt).input_ids
+            tokenizer_kwargs = {} if truncate_prompt_tokens is None else {
+                "truncation": True,
+                "max_length": truncate_prompt_tokens,
+            }
+            input_ids = self.tokenizer(prompt, **tokenizer_kwargs).input_ids
+        elif truncate_prompt_tokens is not None:
+            input_ids = prompt_ids[-truncate_prompt_tokens:]
+        else:
+            input_ids = prompt_ids
+
         token_num = len(input_ids)
 
         if request.max_tokens is None:

vllm/sampling_params.py

@@ -5,6 +5,7 @@ from functools import cached_property
 from typing import Callable, List, Optional, Union
 
 import torch
+from pydantic import conint
 
 _SAMPLING_EPS = 1e-5
 
@@ -94,6 +95,9 @@ class SamplingParams:
             tokens in the output.  Defaults to True.
         logits_processors: List of functions that modify logits based on
             previously generated tokens.
+        truncate_prompt_tokens: If set to an integer k, will use only the last k
+            tokens from the prompt (i.e., left truncation). Defaults to None
+            (i.e., no truncation).
     """
 
     def __init__(
@@ -123,6 +127,7 @@ class SamplingParams:
         skip_special_tokens: bool = True,
         spaces_between_special_tokens: bool = True,
         logits_processors: Optional[List[LogitsProcessor]] = None,
+        truncate_prompt_tokens: Optional[conint(ge=1)] = None,
     ) -> None:
         self.n = n
         self.best_of = best_of if best_of is not None else n
@@ -160,6 +165,7 @@ class SamplingParams:
         self.spaces_between_special_tokens = spaces_between_special_tokens
         self.logits_processors = logits_processors
         self.include_stop_str_in_output = include_stop_str_in_output
+        self.truncate_prompt_tokens = truncate_prompt_tokens
         self._verify_args()
         if self.use_beam_search:
             self._verify_beam_search()
@@ -216,6 +222,10 @@ class SamplingParams:
         if self.prompt_logprobs is not None and self.prompt_logprobs < 0:
             raise ValueError(f"prompt_logprobs must be non-negative, got "
                              f"{self.prompt_logprobs}.")
+        if (self.truncate_prompt_tokens is not None
+                and self.truncate_prompt_tokens < 1):
+            raise ValueError(f"truncate_prompt_tokens must be >= 1, "
+                             f"got {self.truncate_prompt_tokens}")
         if self.stop and not self.detokenize:
             raise ValueError(
                 "stop strings are only supported when detokenize is True. "
@@ -300,4 +310,5 @@ class SamplingParams:
             f"prompt_logprobs={self.prompt_logprobs}, "
             f"skip_special_tokens={self.skip_special_tokens}, "
             "spaces_between_special_tokens="
-            f"{self.spaces_between_special_tokens})")
+            f"{self.spaces_between_special_tokens}, "
+            f"truncate_prompt_tokens={self.truncate_prompt_tokens})")