Log message when upload via API exceeds limit

Since Workhorse started accelerating attachments in the upload API
(https://gitlab.com/gitlab-org/gitlab/-/merge_requests/57250), the
`content_length` log in `api_json.log` no longer holds the actual bytes
used by the uploaded file. It now reports the number of bytes from the
Workhorse JSON metadata.

In order to determine which projects might be exceeding this limit, we
log a JSON warning that will make it easier to fill in the allow list
for https://gitlab.com/gitlab-org/gitlab/-/issues/325788.

changelogs/unreleased/sh-log-upload-api-exceed-size.yml

+---
+title: Log message when upload via API exceeds limit
+merge_request: 57774
+author:
+type: added

lib/api/projects.rb

@@ -67,6 +67,16 @@ module API
 
         PROJECT_ATTACHMENT_SIZE_EXEMPT
       end
+
+      # This is to help determine which projects to use in https://gitlab.com/gitlab-org/gitlab/-/issues/325788
+      def log_if_upload_exceed_max_size(user_project, file)
+        return if file.size <= user_project.max_attachment_size
+        return if exempt_from_global_attachment_size?(user_project)
+
+        if file.size > user_project.max_attachment_size
+          Gitlab::AppLogger.info({ message: "File exceeds maximum size", file_bytes: file.size, project_id: user_project.id, project_path: user_project.full_path })
+        end
+      end
     end
 
     helpers do
@@ -576,6 +586,8 @@ module API
         requires :file, types: [Rack::Multipart::UploadedFile, ::API::Validations::Types::WorkhorseFile], desc: 'The attachment file to be uploaded'
       end
       post ":id/uploads", feature_category: :not_owned do
+        log_if_upload_exceed_max_size(user_project, params[:file])
+
         service = UploadService.new(user_project, params[:file])
         service.override_max_attachment_size = project_attachment_size(user_project)
         upload = service.execute

spec/requests/api/projects_spec.rb

@@ -1519,6 +1519,8 @@ RSpec.describe API::Projects do
   end
 
   describe "POST /projects/:id/uploads" do
+    let(:file) { fixture_file_upload("spec/fixtures/dk.png", "image/png") }
+
     before do
       project
     end
@@ -1528,7 +1530,7 @@ RSpec.describe API::Projects do
         expect(instance).to receive(:override_max_attachment_size=).with(project.max_attachment_size).and_call_original
       end
 
-      post api("/projects/#{project.id}/uploads", user), params: { file: fixture_file_upload("spec/fixtures/dk.png", "image/png") }
+      post api("/projects/#{project.id}/uploads", user), params: { file: file }
 
       expect(response).to have_gitlab_http_status(:created)
       expect(json_response['alt']).to eq("dk")
@@ -1538,13 +1540,21 @@ RSpec.describe API::Projects do
       expect(json_response['full_path']).to start_with("/#{project.namespace.path}/#{project.path}/uploads")
     end
 
+    it "logs a warning if file exceeds attachment size" do
+      allow(Gitlab::CurrentSettings).to receive(:max_attachment_size).and_return(0)
+
+      expect(Gitlab::AppLogger).to receive(:info).with(hash_including(message: 'File exceeds maximum size')).and_call_original
+
+      post api("/projects/#{project.id}/uploads", user), params: { file: file }
+    end
+
     shared_examples 'capped upload attachments' do
       it "limits the upload to 1 GB" do
         expect_next_instance_of(UploadService) do |instance|
           expect(instance).to receive(:override_max_attachment_size=).with(1.gigabyte).and_call_original
         end
 
-        post api("/projects/#{project.id}/uploads", user), params: { file: fixture_file_upload("spec/fixtures/dk.png", "image/png") }
+        post api("/projects/#{project.id}/uploads", user), params: { file: file }
 
         expect(response).to have_gitlab_http_status(:created)
       end