Harden handling of Nextcloud errors

A status of 500+ in ocs.meta indicates that something went so wrong,
that we shouldn't rely on the ocs.data being filled with what we usually
expect to be there.

modules/storages/app/common/storages/adapters/providers/nextcloud/base.rb

@@ -78,6 +78,17 @@ module Storages
               Failure(error.with(payload: "No origin user ID or user token found. Cannot execute query without user context."))
             end
           end
+
+          # Validates the OCS Meta Statuscode for fatal errors (i.e. unexpected server-side errors). Client-side errors,
+          # such as a 404 File Not Found do not cause an error.
+          # @return [Dry::Result]
+          def fail_on_ocs_error(json, error)
+            if json.dig(:ocs, :meta, :statuscode) < 500
+              Success(json)
+            else
+              Failure(error.with(code: :error))
+            end
+          end
         end
       end
     end

modules/storages/app/common/storages/adapters/providers/nextcloud/queries/file_info_query.rb

@@ -55,7 +55,7 @@ module Storages
 
               case response
               in { status: 200..299 }
-                Success(response.json(symbolize_keys: true))
+                fail_on_ocs_error(response.json(symbolize_keys: true), error)
               in { status: 404 }
                 Failure(error.with(code: :not_found))
               in { status: 401 }

modules/storages/app/common/storages/adapters/providers/nextcloud/queries/files_info_query.rb

@@ -57,7 +57,7 @@ module Storages
 
               case response
               in { status: 200..299 }
-                verify_successful_response(response.json(symbolize_keys: true), error)
+                fail_on_ocs_error(response.json(symbolize_keys: true), error)
               in { status: 404 }
                 Failure(error.with(code: :not_found))
               in { status: 401 }
@@ -67,14 +67,6 @@ module Storages
               end
             end
 
-            def verify_successful_response(json, error)
-              if json.dig(:ocs, :meta, :status) == "ok"
-                Success(json)
-              else
-                Failure(error.with(code: :error))
-              end
-            end
-
             def create_storage_file_infos(parsed_json)
               parsed_json.dig(:ocs, :data)&.map do |(key, value)|
                 if value[:statuscode] == 200

spec/support/storage_server_helpers.rb

@@ -141,6 +141,7 @@ module StorageServerHelpers
     folder1_xml_response = build(:webdav_data_folder)
     folder1_fileinfo_response = {
       ocs: {
+        meta: { statuscode: 100 },
         data: {
           status: "OK",
           statuscode: 200,