At present the Chrome UI Catalog Viewer can only access screenshots on Google Storage. Chrome developers should also be able to view screenshots generated by local test runs.

The reason for this is that the screenshot description file is read and processed in the back end of the viewer, and all other file access in the viewer is via the back end. The back end, as an App Engine application, runs on a server,so cannot access the user's computer or any files on it.

We have considered three solutions:
- There is an alternative back end (pylib/local_server.py) within the UI Catalog's workspace, and the make file contains a build step for packaging this as an executable using PyInstaller. The problem is, however, how we distribute this to Chrome Developers. Doing so officially requires a separate deployment process from that used for Chrome Infra web apps.
- We could move all file access to the front end (which would make the back end trivial). I have not investigated this in detail, and I am not sure what the difficulties would be, although there are significant restrictions on what file access is possible from a web app.
- We could upload the test results to Google Storage. It would be quite easy to write a script that would upload the local test results to a Google Storage bucket, and then run the viewer using this bucket. The problem is that Google Storage buckets have to be associated with a Google Cloud project, so users would need a Google Storage project available.