QF-2711 Fine tune error handling in the files API endpoint (#684)

* Rebasing on main
* dropping libqfieldsync changes
* Update docker-app/qfieldcloud/core/exceptions.py

Co-authored-by: Ivan Ivanov <[email protected]>

* renamed exception
* improved clarity around ensuring the existence of bucket resource
* new test
* doctrings; assertions
* cleanup
* removed argument
* leftover

Co-authored-by: Ivan Ivanov <[email protected]>

docker-app/qfieldcloud/core/utils.py

@@ -109,13 +109,22 @@ def get_s3_session() -> boto3.Session:
 
 
 def get_s3_bucket() -> mypy_boto3_s3.service_resource.Bucket:
-    """Get a new S3 Bucket instance using Django settings"""
+    """
+    Get a new S3 Bucket instance using Django settings.
+    """
 
-    session = get_s3_session()
+    bucket_name = settings.STORAGE_BUCKET_NAME
+
+    assert bucket_name, "Expected `bucket_name` to be non-empty string!"
 
-    # Get the bucket objects
+    session = get_s3_session()
     s3 = session.resource("s3", endpoint_url=settings.STORAGE_ENDPOINT_URL)
-    return s3.Bucket(settings.STORAGE_BUCKET_NAME)
+
+    # Ensure the bucket exists
+    s3.meta.client.head_bucket(Bucket=bucket_name)
+
+    # Get the bucket resource
+    return s3.Bucket(bucket_name)
 
 
 def get_s3_client() -> mypy_boto3_s3.Client:

docker-app/qfieldcloud/core/views/files_views.py

@@ -18,8 +18,9 @@
     purge_old_file_versions,
 )
 from rest_framework import permissions, status, views
-from rest_framework.exceptions import NotFound, server_error
+from rest_framework.exceptions import NotFound
 from rest_framework.parsers import MultiPartParser
+from rest_framework.request import Request
 from rest_framework.response import Response
 
 logger = logging.getLogger(__name__)
@@ -42,23 +43,13 @@ class ListFilesView(views.APIView):
 
     permission_classes = [permissions.IsAuthenticated, ListFilesViewPermissions]
 
-    def get(self, request, projectid):
+    def get(self, request: Request, projectid: str) -> Response:
         try:
             project = Project.objects.get(id=projectid)
-            bucket = utils.get_s3_bucket()
-            if not bucket.creation_date:
-                # Let DRF return 500 when bucket does not exist, since it needed but
-                # not what the client tried to get
-                return server_error(
-                    request=request,
-                    reason=f"Unable to fetch needed resource for {projectid}",
-                )
         except ObjectDoesNotExist:
-            # map failure to get from db into failure to GET from API
             raise NotFound(detail=projectid)
-        except Exception as unknown_reason:
-            return server_error(request=request, reason=str(unknown_reason))
 
+        bucket = utils.get_s3_bucket()
         prefix = f"projects/{projectid}/files/"
 
         files = {}