Handle case where blobstore_key is not set on droplet

When downloading a droplet, if the blobstore key is not set, you would
previously get a BlobNotFound error. This can make it hard to
distinguish this case from the other cases where BlobNotFound errors are
raised. We want to make it clearer when, e.g. staging does not complete
and our droplet does not have a blobstore key.

Co-authored-by: Renee Chu <rchu@pivotal.io>
Co-authored-by: Merric De Launey <mdelauney@pivotal.io>
Co-authored-by: Reid Mitchell <rmitchell@pivotal.io>

Author: 3 people

app/controllers/runtime/helpers/blob_dispatcher.rb

@@ -6,10 +6,12 @@ def initialize(blobstore:, controller:)
     end
 
     def send_or_redirect(guid:)
+      logger.error('No guid for BlobNotFound')
       raise CloudController::Errors::BlobNotFound unless guid
 
       blob = @blobstore.blob(guid)
 
+      logger.error('No blob object for BlobNotFound')
       raise CloudController::Errors::BlobNotFound unless blob
 
       send_or_redirect_blob(blob)

app/controllers/v3/droplets_controller.rb

@@ -161,6 +161,10 @@ def download
   private
 
   def send_droplet_blob(droplet)
+    if droplet.blobstore_key.nil?
+      resource_not_found_with_message!('Blobstore key not present on droplet. This may be due to a failed build.')
+    end
+
     droplet_blobstore = CloudController::DependencyLocator.instance.droplet_blobstore
     BlobDispatcher.new(blobstore: droplet_blobstore, controller: self).send_or_redirect(guid: droplet.blobstore_key)
   rescue CloudController::Errors::BlobNotFound

spec/request/droplets_spec.rb

@@ -405,6 +405,21 @@
       end
     end
 
+    context 'when the droplet cannot be retrieved from the blobstore' do
+      before do
+        droplet_model.update(
+          state: VCAP::CloudController::DropletModel::STAGED_STATE,
+          droplet_hash: nil
+        )
+      end
+
+      it 'returns an error with a helpful message' do
+        get "/v3/droplets/#{droplet_model.guid}/download", nil, developer_headers
+        expect(last_response).to have_status_code(404)
+        expect(last_response).to have_error_message('Blobstore key not present on droplet. This may be due to a failed build.')
+      end
+    end
+
     context 'when the droplet cannot be found' do
       it 'returns 404 for the droplet' do
         get '/v3/droplets/some-bogus-guid/download', nil, developer_headers