[Platform] Add custom default max tokens (#18557)

Signed-off-by: Gabriel Marinho <gmarinho@ibm.com>

vllm/entrypoints/openai/serving_chat.py

@@ -34,6 +34,7 @@ from vllm.entrypoints.openai.serving_models import OpenAIServingModels
 from vllm.entrypoints.openai.tool_parsers import ToolParser, ToolParserManager
 from vllm.entrypoints.openai.tool_parsers.mistral_tool_parser import (
     MistralToolCall)
+from vllm.entrypoints.utils import get_max_tokens
 from vllm.logger import init_logger
 from vllm.outputs import CompletionOutput, RequestOutput
 from vllm.reasoning import ReasoningParser, ReasoningParserManager
@@ -233,15 +234,22 @@ class OpenAIServingChat(OpenAIServing):
         try:
             for i, engine_prompt in enumerate(engine_prompts):
                 sampling_params: Union[SamplingParams, BeamSearchParams]
-                default_max_tokens = self.max_model_len - len(
-                    engine_prompt["prompt_token_ids"])
+
+                if self.default_sampling_params is None:
+                    self.default_sampling_params = {}
+
+                max_tokens = get_max_tokens(
+                    max_model_len=self.max_model_len,
+                    request=request,
+                    input_length=len(engine_prompt["prompt_token_ids"]),
+                    default_sampling_params=self.default_sampling_params)
+
                 if request.use_beam_search:
                     sampling_params = request.to_beam_search_params(
-                        default_max_tokens, self.default_sampling_params)
+                        max_tokens, self.default_sampling_params)
                 else:
                     sampling_params = request.to_sampling_params(
-                        default_max_tokens,
-                        self.model_config.logits_processor_pattern,
+                        max_tokens, self.model_config.logits_processor_pattern,
                         self.default_sampling_params)
 
                 self._log_inputs(request_id,