Handle error when `str` passed to `/v1/audio/transcriptions` (#17909)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

vllm/entrypoints/openai/protocol.py

@@ -5,10 +5,11 @@
 import json
 import re
 import time
+from http import HTTPStatus
 from typing import Annotated, Any, ClassVar, Literal, Optional, Union
 
 import torch
-from fastapi import UploadFile
+from fastapi import HTTPException, UploadFile
 from pydantic import (BaseModel, ConfigDict, Field, TypeAdapter,
                       ValidationInfo, field_validator, model_validator)
 from typing_extensions import TypeAlias
@@ -1727,7 +1728,13 @@ class TranscriptionRequest(OpenAIBaseModel):
 
     @model_validator(mode="before")
     @classmethod
-    def validate_stream_options(cls, data):
+    def validate_transcription_request(cls, data):
+        if isinstance(data.get("file"), str):
+            raise HTTPException(
+                status_code=HTTPStatus.UNPROCESSABLE_ENTITY,
+                detail="Expected 'file' to be a file-like object, not 'str'.",
+            )
+
         stream_opts = ["stream_include_usage", "stream_continuous_usage_stats"]
         stream = data.get("stream", False)
         if any(bool(data.get(so, False)) for so in stream_opts) and not stream: