fix(client): Use Stream instead of TrySteam for client calls

[alce]

Motivation

Currently, client methods take TryStreams as inputs when it's not really necessary. This change makes client calls a bit simpler and potentially helps simplify a solution for #34.

Solution

This PR is a POC that changes input stream bounds from Stream<Item = Result<Message, Status>> to Stream<Item = Message>. As is, client and servers work fine but interop tests need to be adjusted for this PR to be complete.

[alce]

Updating interop was actually very easy. This is ready for review.

[olix0r]

Currently, client methods take TryStreams as inputs when it's not really necessary.

Can you expand on that? Why isn't it necessary? How does a client get notified of a stream failure (with its status/error message)?

[alce]

Hi @olix0r, maybe the title is misleading.

All this PR does is remove the need to wrap outgoing messages in Results for client and bi-directional streams, responses do not change.

So instead of this:

client.method(stream::iter(vec![Ok(1), Ok(2), Ok(3)])).await?;

we can write this

client.method(stream::iter(vec![1, 2, 3])).await?

It is totally possible that I'm missing something but I don't understand the semantics of potentially sending an Err(Status) message as part of a streaming request. If you sneak in an Err(Status...) somewhere in the stream, the server just returns an Unknown error. I don't know what else it could do other than maybe echo the error back.

If the server tries to read all messages in the stream before returning a response, we don't even know how many messages, (or which ones) it managed to process.

[olix0r]

Ah! I see: this is for request streams and not response streams. That makes sense, then.

[LucioFranco]

I think we might want to update this function to not take a result? https://github.com/hyperium/tonic/blob/master/tonic/src/codec/encode.rs#L32

[alce]

I did update that one https://github.com/hyperium/tonic/pull/61/files#diff-3bc46617ab2d94a39c2f4f488aa3e803

[LucioFranco]

@alce I must be tired I totally missed that! 😅

[LucioFranco]

Thanks for doing this <3