Switch encoding preference from client controlled to server

[anuraaga]

Fixes #319

Currently, the preference of encoding is based on the client's accept-encoding. This unfortunately leaves connect-web generally unable to use modern compression schemes because the header is set by the browser, which always starts with gzip (i.e. Accept-Encoding: gzip, deflate, br, zstd). It also differs in behavior from common servers like Envoy, nginx, Apache, which all use the order of encodings configured on the server for preference instead of the accept-encoding, for equal quality values.

This PR proposes to align behavior with those servers, by making the order configured on the server the encoding preference, not client. If server is configured as [zstd, br, gzip], a browser would finally be able to use br or zstd.

Compatibility note - I was hoping the Go, Python, Node all behaved the same with only supporting gzip by default. But I found Node supports gzip and br by default

https://github.com/connectrpc/connect-es/blob/main/packages/connect-express/src/express-connect-middleware.ts#L69

This means, this spec change will actually be a breaking change there, since a connect-node (not connect-web) client configured to send br, gzip and a default server will switch from br to gzip. I was hoping we'd be able to get through this without breaking change worries, so this definitely makes me less convinced by the proposal. At the same time, since I suspect using both connect-node and connect-web is a common pattern, connect-node stands to benefit the most from this change to improve compression from the browser. Curious to hear thoughts on that.

connect-go defaults to only gzip, though it also technically accepts compressions as an ordered list of Option. They're currently merged into an unordered map, but if making it actually ordered, it may also be considered a breaking change in behavior, though with the gzip-only default I think the impact is lower there.

Anyways, let me know any thoughts. Thanks!

[vercel]

@anuraaga is attempting to deploy a commit to the connectrpc Team on Vercel.

A member of the Team first needs to authorize it.

[codefromthecrypt]

could it be helpful or appropriate to add an example of both sides configuration and which wins? This might underscore the conflict that led to this PR

[anuraaga]

Sounds good, added some. If they seem too noisy, can cut down or remove them anyways, works either way for me

[codefromthecrypt]

thanks!

[anuraaga]

Thanks @thezachdrake @timostamm for the discussion on #319. Wondering if we can continue here, to hopefully make a change here, or decide not to if it seems like too much. Happy to hear any thoughts.