Check if file exists before processing

api.py

@@ -2,8 +2,6 @@
 import os
 import shutil
 import uuid
-from random import randint
-from time import sleep
 from typing import Annotated
 
 from fastapi import FastAPI, Depends, status, HTTPException, BackgroundTasks, Response
@@ -41,7 +39,18 @@ def start(
             detail={"message": "input must be a PDF file"}
         )
 
-    task.start(payload.file, background_tasks, lambda: process(payload, settings))
+    aws_client = aws.connect(settings)
+    has_file = aws_client.exists_file(
+        settings.s3_input_bucket,
+        f'{settings.s3_input_folder}{payload.file}',
+    )
+    if not has_file:
+        raise HTTPException(
+            status_code=status.HTTP_422_BAD_REQUEST,
+            detail={"message": "file does not exist"}
+        )
+
+    task.start(payload.file, background_tasks, lambda: process(payload, aws_client, settings))
     return Response(status_code=status.HTTP_204_NO_CONTENT)
 
 
@@ -84,6 +93,7 @@ def collect(
 
 def process(
         payload: StartPayload,
+        aws_client: aws.Client,
         settings: Annotated[ApiSettings, Depends(api_settings)],
 ):
     if settings.skip_processing:
@@ -98,7 +108,6 @@ def process(
     input_path = os.path.join(tmp_dir, "input.pdf")
     output_path = os.path.join(tmp_dir, "output.pdf")
 
-    aws_client = aws.connect(settings)
     aws.load_file(
         aws_client.bucket(settings.s3_input_bucket),
         f'{settings.s3_input_folder}{payload.file}',

aws/aws.py

@@ -1,6 +1,7 @@
 from dataclasses import dataclass
 
 import boto3
+from botocore.exceptions import ClientError
 from mypy_boto3_s3 import S3ServiceResource
 from mypy_boto3_s3.service_resource import Bucket
 from mypy_boto3_textract import TextractClient as Textractor
@@ -18,6 +19,16 @@ class Client:
     def bucket(self, name: str) -> Bucket:
         return self.s3.Bucket(name)
 
+    def exists_file(self, bucket_name: str, key: str) -> bool:
+        try:
+            self.s3.Object(bucket_name, key).load()
+            return True
+        except ClientError as e:
+            if e.response['Error']['Code'] == '404':
+                return False
+            else:
+                raise e
+
 
 def connect(settings: ApiSettings) -> Client:
     has_profile = is_set(settings.aws_profile)

utils/task.py

@@ -55,7 +55,7 @@ def run(file: str, target: typing.Callable[[], Result]):
         value = target()
         result = Output(ok=True, value=value)
         logging.info(f"Task for file '{file}' has been completed.")
-    except RuntimeError as e:
+    except Exception as e:
         logging.exception(f"Processing of '{file}' failed")
         result = Output(ok=False, value=e)