Add converter files exists checking

app/main.py

@@ -1,27 +1,40 @@
-import uuid
 import asyncio
 import os
+import uuid
 
-from fastapi import FastAPI, APIRouter, File, UploadFile, Form, HTTPException, BackgroundTasks, status
+from fastapi import (
+    FastAPI,
+    APIRouter,
+    File,
+    UploadFile,
+    Form,
+    HTTPException,
+    BackgroundTasks,
+    status,
+)
 from fastapi.responses import FileResponse
+
 from starlette.background import BackgroundTask
 
 import aiofiles
+import aiofiles.ospath
 
 
-router = APIRouter(
-    tags=["converter"]
-)
+router = APIRouter(tags=["converter"])
 
 
 @router.post("/")
-async def convert(background_tasks: BackgroundTasks, file: UploadFile = File({}), format: str = Form({})):
+async def convert(
+    background_tasks: BackgroundTasks,
+    file: UploadFile = File({}),
+    format: str = Form({}),
+):
     temp_uuid = uuid.uuid1()
 
-    temp_filename = str(temp_uuid) + '.fb2'
-    converted_temp_filename = str(temp_uuid) + '.' + format
+    temp_filename = str(temp_uuid) + ".fb2"
+    converted_temp_filename = str(temp_uuid) + "." + format
 
-    async with aiofiles.open(temp_filename, 'wb') as f:
+    async with aiofiles.open(temp_filename, "wb") as f:
         content = await file.read()
 
         if isinstance(content, str):
@@ -30,21 +43,27 @@ async def convert(background_tasks: BackgroundTasks, file: UploadFile = File({})
         await f.write(content)
 
     proc = await asyncio.create_subprocess_exec(
-        './bin/fb2c', 'convert', '--to', format, temp_filename,
+        "./bin/fb2c",
+        "convert",
+        "--to",
+        format,
+        temp_filename,
         stdout=asyncio.subprocess.PIPE,
-        stderr=asyncio.subprocess.PIPE
+        stderr=asyncio.subprocess.PIPE,
     )
 
-    await proc.communicate()
+    _, stderr = await proc.communicate()
 
     background_tasks.add_task(os.remove, temp_filename)
 
-    if proc.returncode != 0:
-        return HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail="Can't convert!")
+    if proc.returncode != 0 or len(stderr) != 0:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST, detail="Can't convert!"
+        )
 
     return FileResponse(
         converted_temp_filename,
-        background=BackgroundTask(lambda: os.remove(converted_temp_filename))
+        background=BackgroundTask(lambda: os.remove(converted_temp_filename)),
     )