Tonic: Expose hyper BDP config

[pranjalssh]

Feature Request

Is it possible to support grpc retry configs and grpc channel args? These are quite frequently used in production.

My requests on a single tonic channel seem to fail at high concurrency(10s of thousands) and without these, it is painful to handle these correctly and optimally.

[LucioFranco]

We support some of these but this mostly relies on hyper. @seanmonstar might be interested in hearing what other options you'd like.

[seanmonstar]

I believe retries could be added into tonic using tower::retry.

We'd need to be more specific about "channel args" to know what is desired.

[pranjalssh]

Among the ones not currently implemented in Tonic, our production code uses
GRPC_ARG_HTTP2_BDP_PROBE
GRPC_ARG_HTTP2_MAX_PINGS_WITHOUT_DATA
GRPC_ARG_HTTP2_MIN_RECV_PING_INTERVAL_WITHOUT_DATA_MS
GRPC_ARG_HTTP2_MIN_SENT_PING_INTERVAL_WITHOUT_DATA_MS

I think grpcio provides support for a fairly common list of grpc args
https://docs.rs/grpcio/0.5.3/grpcio/struct.ChannelBuilder.html

Retry configs are the big one though.

[seanmonstar]

So hyper, the underlying HTTP library used in Tonic, has support for http2_adaptive_window, which uses BDP pings. Tonic could add a builder option to enable it. Tonic already has exposed some of the keep alive properties as well.