Explorations for support of N keychains

[thunderbiscuit]

Just pushing here to show/discuss as I explore the potential for support of any number of descriptors for the Wallet type for maybe a 3.0.

Overview

The gist of my idea is a KeyRing (KeychainRing? KeychainSet?), which is basically a structure that holds a vector of keychains. You create a key ring with any number of descriptors (must have 1 default, can have 1 change, plus any number of others). The wallet constructors take this KeyRing as an argument, and from there the wallet methods need to be adjusted to work with the new paradigm.

The KeyRing has methods to add/check/query descriptors it holds, and is where the domain logic of ensuring only 1 descriptor is the default, that all descriptors use the same network, and any other requirements we have for basically this group of keychains lives. The wallet type then gets a new field key_ring, which it can use to query things like KeyRing::get_default_descriptor() or KeyRing::list_keychains().

pub enum KeychainKind {
    Default,
    Change,
    Other(DescriptorId),
}

pub type WalletKeychain = (KeychainKind, Descriptor<DescriptorPublicKey>);

pub struct KeyRing {
    keychains: Vec<WalletKeychain>,
}

Resulting API

The API is showcased in the wallet/examples/n_keychains.rs file.

// Create a keyring with a single, default descriptor (aka the KeychainKind::External from the 1.2.0 API)
let mut keyring = KeyRing::new(EXTERNAL_DESC, Network::Testnet4);

// Add 3 new custom descriptors
keyring.add_other_descriptor(OTHER_DESC_21);
keyring.add_other_descriptor(OTHER_DESC_31);
keyring.add_other_descriptor(OTHER_DESC_41);

let keychain_ids: Vec<DescriptorId> = keyring.list_keychain_ids();
println!("{:?}", keychain_ids);

// Create the wallet and peek addresses on each of the descriptors
let wallet: Wallet = Wallet::new(keyring).create_wallet_no_persist()?;
let address_1 = wallet.peek_address(KeychainKind::Default, 0).unwrap();
let address_2 = wallet.peek_address(KeychainKind::Other(keychain_ids[1]), 0).unwrap();
let address_3 = wallet.peek_address(KeychainKind::Other(keychain_ids[2]), 0).unwrap();
let address_4 = wallet.peek_address(KeychainKind::Other(keychain_ids[3]), 0).unwrap();

println!("Address 1 {:?} at index {:?} on keychain {:?}", address_1.address, address_1.index, address_1.keychain);
println!("Address 2 {:?} at index {:?} on keychain {:?}", address_2.address, address_2.index, address_2.keychain);
println!("Address 3 {:?} at index {:?} on keychain {:?}", address_3.address, address_3.index, address_3.keychain);
println!("Address 4 {:?} at index {:?} on keychain {:?}", address_4.address, address_4.index, address_4.keychain);

[thunderbiscuit]

Some development notes as I go along:

1. The CreateParams struct had 2 constructors: CreateParams::new and CreateParams::new_single. This simplifies the constructors because the KeyRing type handles all that stuff now.
2. One sad thing is that some of the previous infallible APIs now return Results, complexifying a little bit the call-sites (Wallet::peek_address, Wallet::reveal_next_address, Wallet::next_unused_address, Wallet:mark_used, Wallet::unmark_used).