[Feature]: Add OpenAI server prompt_logprobs support #6508 (#7453)

vllm/entrypoints/openai/serving_chat.py

@@ -83,6 +83,16 @@ class OpenAIServingChat(OpenAIServing):
         if error_check_ret is not None:
             return error_check_ret
 
+        if request.prompt_logprobs is not None:
+            if request.stream and request.prompt_logprobs > 0:
+                return self.create_error_response(
+                    "Prompt_logprobs are not available when stream is enabled")
+
+            if request.prompt_logprobs < 0:
+                return self.create_error_response(
+                    f"Prompt_logprobs set to invalid "
+                    f"negative value: {request.prompt_logprobs}")
+
         try:
             (
                 lora_request,
@@ -506,6 +516,7 @@ class OpenAIServingChat(OpenAIServing):
             model=model_name,
             choices=choices,
             usage=usage,
+            prompt_logprobs=final_res.prompt_logprobs,
         )
 
         return response