WebHost + MultiServer: Allow game clients to request datapackages through the HTTP API provided by the WebHost

[colin969]

What is this fixing or adding?

Adds an optional datapackage_url to RoomInfo to allow game clients to use HTTP requests to retrieve datapackages instead of using GetDataPackage commands.

PUBLIC_URL has been added to the app config, and datapackage_url is built inside get_static_server_data() for rooms using WebHost's customserver

This should help:

• Clients to pull datapackages faster through multiple connections, and allow clients that can't reasonably support websocket compression an alternative to GetDataPackage
• The server host to have more options with load balancing + CDN usage for datapackages, or choose to block uncompressed clients from using GetDataPackage in the future

How was this tested?

For a local server, add PUBLIC_URL: http://localhost to app config

Host a room through the webhost.

Get the datapackage checksum from the RoomInfo message

Append /<checksum> to the datapackage_url in RoomInfo and confirm you can retrieve from this url in a browser

[duckboycool]

Feedback of descending importance.

[duckboycool]

This (for good reason) isn't actually the default value like the comment at the top of here says. Using it as an example would probably be better in the comment above.

(Also HOST_ADDRESS gets this wrong currently as well I guess...)

[colin969]

Fixed the value to be null, and reworded the comments around it to be more clear about how it's used.

It might be worth defaulting this to http://localhost for people doing apworld development that want to test against it? Unsure.

[duckboycool]

Worked as expected from MultiServer, from WebHost without a URL set, and with one. I think maybe the default should be to match to HOST_ADDRESS (I guess with a value like "" to distinguish from specifically opting out with null?), but I'll leave that up to other reviewers.