WASM-compatible networking layer for the Light Client

[thanethomson]

Requires #953

At present, we only have one implementation of the Io trait in the Light Client, which makes use of the tendermint-rpc to fetch light blocks (over HTTP/WebSocket).

To be able to support a full WASM build of the Light Client, we need to implement a fetch API-compatible version of the Io trait.

What's the definition of "done" for this issue?

When we can compile the tendermint-light-client crate to WASM and make use of its full API (including networking) from JavaScript.

[celsobonutti]

Hey @thanethomson, I'd like to work on that. I was previous working on adding wasm support for tendermint-rpc (as it was specified in the previous issue). Was there any reason behind moving the implementation from the rpc to the Io trait?

[thanethomson]

Hey @thanethomson, I'd like to work on that. I was previous working on adding wasm support for tendermint-rpc (as it was specified in the previous issue). Was there any reason behind moving the implementation from the rpc to the Io trait?

Cool! Yes the main reason was that:

1. We're going to probably end up renaming that Io trait to something like LightBlockFetcher, since its primary purpose is not general I/O but is very specifically to provide LightBlocks.
2. As a result, we don't need the entire RPC to be able to build to WASM - we only need something WASM-compatible that's going to fetch and deserialize light blocks.

I'd be interested, however, to know if you feel like you'd want a more general-purpose Tendermint RPC client that compiles to WASM? I know that CosmJS provides a TypeScript implementation: https://github.com/cosmos/cosmjs/tree/main/packages/tendermint-rpc

[celsobonutti]

Nice, that makes a lot of sense!

I'd be interested, however, to know if you feel like you'd want a more general-purpose Tendermint RPC client that compiles to WASM?

Not at all, we'll only need the Light Client to compile to WASM, so I started working on the RPC compilation.
I'll start working on WASM Io, then. Thanks for your attention!