Rust SDK: Add passthrough openssl feature

[rib]

Grpc-rs depends on boringssl by default which can conflict with crates
that depend on openssl.

Newer versions of grpc-rs expose an "openssl" feature to optionally use
openssl instead. To make Agones' Rust SDK compatible with openssl, this
bumps the grpc-rs dependency version and adds "openssl" and
"openssl-vendored" features that simply forward to grpc-rs.

Fixes #1201

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[rib]

@googlebot I signed it!

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[markmandel]

Thanks for the PR!

Looks like there are issues with the conformance tests. Are you finding your changes are working locally?

[rib]

hmm, I had only tested that things compiled and assumed initially there would be no semantic changes for grpc-rs 0.4, but testing rust-simple here I see these errors now:

Health ping failed : Error(HealthPingConnectionFailure("failed to hold client stream for health ping"), State { next_error: None, backtrace: None })

which I don't have if I revert that change, so I guess porting to 0.4 will be more involved somehow :/

sorry for jumping the gun here.

[markmandel]

No worries at all - in theory, with gRPC, there should be no issue. But Rust gRPC apparently may have some issues.

Might be worth checking in with the rust-rs team, see if they know what's up.

[markmandel]

We recently updated gRPC, and I noted there is a 0.4.7 of grpcio, wondering if the combination will solve this problem?

Wondering if you would like to take this up again?

[rib]

Thanks for the update. I ended up using Tonic for handling gRPC and interfacing with Agones' sdk.proto interface directly. Tonic has been working well so far and has support for async/await in Rust which has been really handy; I'm also currently dependant on authentication/custom metadata support for passing in JWT tokens to my frontend and game servers (apparently grpc-rs doesn't support that yet).

I might be able to help provide a Tonic based example if that would be useful?

[markmandel]

Given we have a client layer in front of the grpc implementation, we could switch out gRPC implementations (I counted 4 of them in Rust at last Google), without breaking anything.

If there is a specific one that is clearly better than the rest, it may be worth making the switch in the official Rust client?

[markmandel]

Asking around a bit, it sounds like Tonic is the most lauded grpc implementation in Rust. It sounds like it might be worth starting a ticket on migrating our SDK to Tonic, and then doing the implementation!

[rib]

Yeah, I've been really happy with Tonic and the maintainer is really responsive on Discord which has been great too.

When it comes to defining an SDK I'd perhaps be weary of stabalising anything for Rust too soon. Quite a bit is in flux at the moment within the Rust ecosystem given that async/await only stabilised in November. Considering how useful they for network services I'd assume projects like grpc-rs will overhaul their api at some point to work in terms of async futures. Even though Tonic is one of the more mature grpc implementations, it's still only at a 0.1 version and the maintainer will be breaking the api soon as he iterates for 0.2.

For game servers interacting with the Agones sidecar then I currently tend to think it's enough to provide the sdk.proto gRPC interface. Considering how simple the interface is vs how varied game engines might be then maybe just providing a variety of examples in different languages is enough?

I suppose if you're set on having a stable Rust SDK then it might at least be best to constrain it to only work with the Tokio runtime for now (Tonic is built on Tokio and a library called Tower). Any stability should probably just be provided on a best-effort basis though, since Tonic isn't stable yet.

[markmandel]

So TL;DR:

• We should close this PR, since it's currently not working.
• At some point in the future, we should review the Rust gRPC ecosystem and decide what is best of breed and consistently maintained, and use that.

Sound good to everyone?

[markmandel]

Closing the PR! Will come back to the Rust ecosystem in a bit.

Ticket filed: #1300