Summary:
Some WS-related code was touched in a recent PR to grist-core. This extends
those changes to the rest of the codebase so that builds work again.
Test Plan: N/A
Reviewers: dsagal
Reviewed By: dsagal
Subscribers: dsagal
Differential Revision: https://phab.getgrist.com/D4224
The motivation for supporting an alternative to WebSockets is that while all browsers supported by Grist offer native WebSocket support, some networking environments do not allow WebSocket traffic.
Engine.IO is used as the underlying implementation of HTTP long polling. The Grist client will first attempt a regular WebSocket connection, using the same protocol and endpoints as before, but fall back to long polling using Engine.IO if the WebSocket connection fails.
Include these changes:
- CORS websocket requests are now rejected as a stronger security measure. This shouldn’t affect anything in practice; but previously it could be possible to make unauthenticated websocket requests from another origin.
- GRIST_HOST variable no longer affects CORS responses (also should not affect anything in practice, as it wasn't serving a useful purpose)
