RFC: Total refactor to support sync & async clients

[stevenroose]

This is a reboot of https://github.com/rust-bitcoin/rust-bitcoincore-rpc/pull/212.

So this turned into an insane amount of changes that I've been working on on and off for the last several years.

The current state of things is

• primarily: in need for feedback and review, but more specifically
• near ready, SyncClient and AsyncClient API seems good to go
• supports all methods in current master
• locally passed tests for all bitcoind version we support (and 22.0 as well)
• example how to use with hyper (latest)
• currently based on an MR branch of jsonrpc and pending on 1 or 2 MRs for rust-bitcoin

Some highlights of the changes:

• Instead of having one RpcApi trait, we have a requests module that is meant for internal use that builds Request objects that is fully ready to be sent to the server, with serializable type wrappers for all arguments. The intent here is to reduce re-allocation for argument serialization and focus is made to reduce allocations as much as possible. This has the side effect that sometimes we have things like &'r &'r str in internal APIs, but the external API is clean.
• Two new traits: SyncClient and AsyncClient that provide the actual RPC methods, but internally call the methods inside the request module to reduce code duplication.
• Many argument types have been generalized, so you can easily pass &Transaction, &Vec<u8> or &str as arguments for txs f.e.. Same for blocks, addresses, PSBTs and sighash types.
• Quite some refactor of intergration test to make it more ergonomic when many tests fail :)

As for review, I realize the changes are massive and I believe it makes more sense to first review the new code as is, looking at requests.rs, sync_client.rs, async_client.rs and maybe client.rs. And only then review changes to maybe integration_test/src/main.rs to check if nothing accidentally got removed.

By way of not forgetting, I keep a todo.md file inside the branch so that I don't lose them, current items are:

• Generic optional arguments are quite inergonomic because the [None] variant requires a generic argument: F.e. Option::<&bitcoin::EcdsaSighashType>::None. This counts for all Option<impl SomeTrait> in arguments, I think for now that's only SighashParam and AddressParam. (Sighash type is more often used optionally, maybe we can make our own type for that and not need generics?)

• Fix logging

[Kixunil]

Perhaps it'd make sense to upgrade to bitcoin 0.30 first and hen do this PR? Also I just remembered setting version to 1.0.0 is literally wrong because this crate has an unstable dependency in public API: bitcoin.

[Kixunil]

• Many argument types have been generalized, so you can easily pass &Transaction, &Vec<u8> or &str as arguments for txs f.e.. Same for blocks, addresses, PSBTs and sighash types.

Also this looks like a footgun unless it's explicit. (didn't check)

[stevenroose]

Perhaps it'd make sense to upgrade to bitcoin 0.30 first and hen do this PR?

That already happened in master.

Also I just remembered setting version to 1.0.0 is literally wrong because this crate has an unstable dependency in public API: bitcoin.

What do you mean with an unstable dependency? The 0.x in just a convention.. rust-miniscript has major versions and relies on _hashes and secp that have not.. But anyway the version is just a placeholder now, but I wouldn't mind bumping to 1.0.0 either way, this crate will have breaking changes quite often anyway so whether we could 0.x.0 or x.0.0 doesn't make much difference.

[stevenroose]

• Many argument types have been generalized, so you can easily pass &Transaction, &Vec<u8> or &str as arguments for txs f.e.. Same for blocks, addresses, PSBTs and sighash types.

Also this looks like a footgun unless it's explicit. (didn't check)

It's so that you can pass in hex txs as well. Same for string addresses, etc. You can argue that people should be encouraged to use strong types, and that's what the default return values are, but it's just more efficient to pass in strings, especially if you have methods that allow you to get strings too.

[Kixunil]

Yes, it's a convention that is so common that it's probably best to consider it a rule. 0.x means unstable API - frequent changes, 1+.x means stable API - infrequent changes. It's a shame miniscript got this wrong. Anyway we're trying to push for stabilizing bitcoin or its parts and there's a good chance we could stabilize parts needed here somewhat sooner. But don't expect anything less than a year.

I understand why Vec<u8> (should be &[u8], I guess) or &str are accepted. I just think it should be explicit. Something like RawBytes(b) and HexStr(s).

[tcharding]

Have you considered just having a single Client and using maybe_async to add the async/await stuff?

[tcharding]

I had a read and it looks good to me.

[Kixunil]

@tcharding that one uses feature flags to switch between sync and async which is a horrible approach. NACK from me.

[tcharding]

Not disagreeing just wanting to understand; why is a feature flag approach bad? I can't come up with an example usecase that one would want both an async client and a sync client.

[stevenroose]

@tcharding that one uses feature flags to switch between sync and async which is a horrible approach. NACK from me.

Yeah same opinion.

[stevenroose]

Not disagreeing just wanting to understand; why is a feature flag approach bad? I can't come up with an example usecase that one would want both an async client and a sync client.

Just off the top of my head, not 100% sure this scenario makes sense. But basically it's trivial to turn an async client into a sync one, so a library that somehow doesn't want to support async code (tokio..) could take a sync client as an input and a larger project using async can still pass a sync client (wrapped async one) into that lib. In the feature approach, the sync-only lib wouldn't even compile, or would not be able to compile in the same project as any other lib that uses async-only.

[stevenroose]

Thanks for the review! I'm really wanting to get this out of my head, so I'd like to either get this out as a 1.0.0-rc0 and invite others to help improve from there, or maybe fork into another lib. Or just drop it alltogether.

[tcharding]

Don't you have to push https://github.com/apoelstra/rust-jsonrpc/pull/56 through first? I'm happy to review that if/when in comes off WIP or is it ready to go (excluding rebase on master). To rebase you'll need to add SyncTransport impl for MnreqHttpTransport.

[stevenroose]

I'm seeing them two as a change together though, the jsonrpc change is only useful in function of this MR, if no one wants this or if this will never land there is no point in making the jsonrpc changes.

[tcharding]

The LDK folk want to see async in rust-json so I do not think you'll get any pushback against the changes there being merged. The reason for the quietness is, in my opinion, not negative just neither I nor Andrew care much and no one else seems to review/watch/comment on rust-jsonrpc. If you get the two PRs ready, I'll review them. The LDK folk have been hounding us so this is actually quite useful work. JSONRPC is just not that exciting to me.

[apoelstra]

Agreed, I'd love to have async support in rust-jsonprc and here, but I don't ever use async and I have enough borrowck issues without introducing implicit state machines and Pins everywhere. So I'm not going to write (or review) any code since I never use async.

[tcharding]

Perhaps some of the LDK folk will review it? CC @TheBlueMatt to see if anyone in his crew is psyched enough for this to do reviews.