SoB/BDKWallet: Explore on BDK signers (make it compatible for Swapcoin kind.)

[wthrajat]

Part of #142

• build create_signers fn
• build add_signers which will add an external signer to a particular keychain

[15IITian]

I'' take this up

[15IITian]

Overview

Wallet Struct

• Required Field:
  • signers: HashMap<KeychainKind, Arc<SignersContainer>>
  • This indicates that each KeychainKind (e.g., External, Internal, Coinswap) will have its own SignersContainer.

SignersContainer Creation

• Function:
  https://github.com/bitcoindevkit/bdk/blob/b4a847f801ee824336026fed29ec620be3d30f51/crates/wallet/src/wallet/signer.rs#L651

  • SignersContainer::build
  • Takes a Descriptor<DescriptorPublicKey> and its corresponding KeyMap.
  • KeyMap: BTreeMap<DescriptorPublicKey, DescriptorSecretKey>.

KeyMap Generation

• Requirement:
  • We need a KeyMap for each descriptor of a KeychainKind to create a SignersContainer.
• Function Available:
  https://github.com/rust-bitcoin/rust-miniscript/blob/9e1b3cdf7e38563f4f2e7c2832a994f4c91a5e36/src/descriptor/mod.rs#L668
  • Descriptor<DescriptorPublicKey>::parse_descriptor
  • Takes a descriptor in string format and returns the descriptor and its corresponding KeyMap.

Issue with Non-Extended Descriptors

• Extended Descriptors:
  • They can derive child keys.
  • No problem generating KeyMap in BDK.
• Non-Extended Descriptors (e.g., Coinswap):

  • These descriptors have no wildcard.

  • BDK Definitions:

  • https://github.com/bitcoindevkit/bdk/blob/b4a847f801ee824336026fed29ec620be3d30f51/crates/wallet/src/descriptor/mod.rs#L54

    • ExtendedDescriptor: Alias for extended descriptors.
    • DerivedDescriptor: Alias for descriptors without wildcards.

  • BDK Bias:

    • Focuses on ExtendedDescriptor.
    • https://github.com/bitcoindevkit/bdk/blob/b4a847f801ee824336026fed29ec620be3d30f51/crates/wallet/src/descriptor/mod.rs#L74
    • Trait IntoWalletDescriptor converts into an ExtendedDescriptor and KeyMap using parse_descriptor.
    • https://github.com/bitcoindevkit/bdk/blob/b4a847f801ee824336026fed29ec620be3d30f51/crates/wallet/src/descriptor/mod.rs#L84C8-L84C30
    • In this trait -> there is a corresponding function -> into_wallet_descriptor which does some checksum calculation from given descriptor in string format -> then pass it to parse_discriptor fun.
    • No equivalent methods & traits for DerivedDescriptor.

Conclusion

• Problem:
  • There is no way to create a DerivedDescriptor from a string using parse_descriptor in BDK.
  • This missing functionality is needed to build SignersContainer for coinswap KeychainKind.

[15IITian]

Solution

Handling ExtendedDescriptor

• No issues: These are well-handled by BDK.

Handling Non-ExtendedDescriptor (Swapcoin)

Proposed Solution:

1. Create a Function: Develop a function similar to into_wallet_descriptor.
2. Function Responsibilities:
   • Perform checksum-related checks.
   • Call parse_descriptor to obtain Descriptor<DescriptorPublicKey> and its KeyMap.

Reference:

• The implementation can be based on the BDK codebase: BDK Source Code.

Difference Between Handling ExtendedDescriptor and Non-ExtendedDescriptor

• ExtendedDescriptor:

  • Implements the Into_Wallet_Descriptor trait.

• Non-ExtendedDescriptor:

  • Does not require any traits such as Into_Wallet_Descriptor.

---

By following these steps, we can effectively manage both ExtendedDescriptor and Non-ExtendedDescriptor

[15IITian]

Create a Function: Develop a function similar to into_wallet_descriptor.
Function Responsibilities:
Perform checksum-related checks.
Call parse_descriptor to obtain Descriptor and its KeyMap.

This will also remove the need of using rpc-call to create discriptor from the string

[mojoX911]

ACK on all the approaches. Yes, we will need to build whats missing in BDK. Excited to see the product.