We don't automatically want to make the interface `async` based on the
used architecture, but now require the user to explicitly set the
`async-interface` feature.
Create blockchain::GetBlockHash trait
with a method to get block hash given
a block height. Then, implement this
trait for all backends (Electrum, RPC
, Esplora, CBF). Referenced in issue 603.
Add two new traits:
- `StatelessBlockchain` is used to tag `Blockchain`s that don't have any
wallet-specic state, i.e. they can be used as-is to sync multiple wallets.
- `BlockchainFactory` is a trait for objects that can build multiple
blockchains for different descriptors. It's implemented automatically
for every `Arc<T>` where `T` is a `StatelessBlockchain`. This allows a
piece of code that deals with multiple sub-wallets to just get a
`&B: BlockchainFactory` to sync all of them.
These new traits have been implemented for Electrum, Esplora and RPC
(the first two being stateless and the latter having a dedicated
`RpcBlockchainFactory` struct). It hasn't been implemented on the CBF
blockchain, because I don't think it would work in its current form
(it throws away old block filters, so it's hard to go back and rescan).
This is the first step for #549, as BIP47 needs to sync many different
descriptors internally.
It's also very useful for #486.
Although somewhat convenient to have, coupling the Wallet with
the blockchain trait causes development friction and complexity.
What if sometimes the wallet is "offline" (no access to the blockchain)
but sometimes its online?
The only thing the Wallet needs the blockchain for is to sync.
But not all applications will even use the sync method and the sync
method doesn't require the full blockchain functionality.
So we instead pass the blockchain in when we want to sync.
- To further reduce the coupling with blockchain I removed the get_height call from `new` and just use the height of the
last sync in the database.
- I split up the blockchain trait a bit into subtraits.
Make every request in batch, to save round trip times
Fetch timestamp of blockheader to populate timestamp field in transaction
Remove listunspent requests because we can compute it from our history
Instead of having two traits, `Blockchain` and `OnlineBlockchain` that need
to be implemented by the user, only the relevant one (`OnlineBlockchain`, here
renamed to `Blockchain`) will need to be implemented, since we provide a
blanket implementation for the "marker" trait (previously `Blockchain`, here
renamed to `BlockchainMarker`).
Users of the library will probably never need to implement `BlockchainMarker`
by itself, since we expose the `OfflineBlockchain` type that already does
that and should be good for any "offline" wallet. Still, it's exposed since
they might need to import it to define types with generics.
The procedural macro `#[maybe_async]` makes a method or every method of a trait
"async" whenever the target_arch is `wasm32`, and leaves them untouched on
every other platform.
The macro `maybe_await!($e:expr)` can be used to call `maybe_async` methods on
multi-platform code: it expands to `$e` on non-wasm32 platforms and to
`$e.await` on wasm32.
The macro `await_or_block!($e:expr)` can be used to contain async code as much
as possible: it expands to `tokio::runtime::Runtime::new().unwrap().block_on($e)`
on non-wasm32 platforms, and to `$e.await` on wasm32.
