Updates SI to render /lookup even if reply files are missing from storage

[zenmonkeykstop]

Status

Ready for review / Work in progress

Description of Changes

Fixes #5402

Adds exception handling to cover the case when a source has replies in the db
whose corresponding files are missing from disk. Previously the /lookup path
would fail, preventing the source from viewing replies or uploading submissions.

Testing

dev environment:

• check out this branch and run make dev
• note the codename and journalist designation in the docker output for one of the sources created with 2 reply files in the docker output
• run docker ps in a separate terminal to determine the ID for the dev container
• run docker exec -it <dockerID> bash to connect to the dev container
• find and delete one of the reply files for the source identified above, under /var/lib/securedrop/store.
• open the source interface at localhost:8080 and log in with the source codename:
  • The login is successful and the /lookup page is displayed
  • One reply is displayed
  • An error message like [2020-09-15 17:49:31,400] ERROR in main: Reply file missing: 3-blameless_fumble-reply.gpg is printed in the docker output.

staging environment:

• check out this branch and run make staging
• log in to the source interface and submit a message, note the codename, then log out.
• log into the journalist interface and reply to a message
• log back into the SI and verify that the reply is visible, then logout
• log into the app staging serve, andr find and delete the reply file for the source, under /var/lib/securedrop/store.
• log into the source interface with the source codename:
  • The login is successful and the /lookup page is displayed
  • No replies are displayed.
  • An error message like Reply file missing: 3-blameless_fumble-reply.gpg is printed in the source error log on the app server.

Deployment

No special deployment requirements.

Checklist

If you made changes to the server application code:

• Linting (make lint) and tests (make test) pass in the development container

If you made non-trivial code changes:

• I have written a test plan and validated it for this PR

[kushaldas]

Testing

dev environment:

• check out this branch and run make dev
• note the codename and journalist designation in the docker output for one of the sources created with 2 reply files in the docker output
• run docker ps in a separate terminal to determine the ID for the dev container
• run docker exec -it <dockerID> bash to connect to the dev container
• find and delete one of the reply files for the source identified above, under /var/lib/securedrop/store.
• open the source interface at localhost:8080 and log in with the source codename:
  • The login is successful and the /lookup page is displayed
  • One reply is displayed
  • An error message like [2020-09-15 17:49:31,400] ERROR in main: Reply file missing: 3-blameless_fumble-reply.gpg is printed in the docker output.

staging environment:

• check out this branch and run make staging
• log in to the source interface and submit a message, note the codename, then log out.
• log into the journalist interface and reply to a message
• log back into the SI and verify that the reply is visible, then logout
• log into the app staging serve, andr find and delete the reply file for the source, under /var/lib/securedrop/store.
• log into the source interface with the source codename:
  • The login is successful and the /lookup page is displayed
  • No replies are displayed.
  • An error message like Reply file missing: 3-blameless_fumble-reply.gpg is printed in the source error log on the app server.

This is good, approved. 🦄