feat: add HWISigner, moved from bdk_hwi

- adds a new `signer.rs` that contains the previous implementation of
  `HWISigner`, which implements `bdk_wallet::signer::{SignerCommon,
TransactionSigner}` traits.
- expose the new `signer::HWISigner` as public.
- updates the crate documentation.
- TODO: re-add test that relies on `bdk_wallet::tests::common::get_funded_wallet`
  helper methods.

Cargo.toml

@@ -11,10 +11,11 @@ readme = "README.md"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+bdk_wallet = { version = "1.0.0-beta.1" }
 bitcoin = { version = "0.32", features = ["serde", "base64"] }
+pyo3 = { version = "0.21.2", features = ["auto-initialize"] }
 serde = { version = "^1.0", features = ["derive"] }
 serde_json = { version = "^1.0" }
-pyo3 = { version = "0.21.2", features = ["auto-initialize"] }
 
 miniscript = { version = "12.0", features = ["serde"], optional = true }
 

src/lib.rs

@@ -1,6 +1,9 @@
-//! Rust wrapper for the [Bitcoin Hardware Wallet Interface](https://github.com/bitcoin-core/HWI/).
+//! This crate is contains both:
+//! - [`HWIClient`]: A Rust wrapper for the [Bitcoin Hardware Wallet Interface](https://github.com/bitcoin-core/HWI/).
+//! - [`HWISigner`]: An implementation of a [`TransactionSigner`] to be used with hardware wallets, that relies on [`HWIClient`].
 //!
-//! # Example - display address with path
+//! # HWIClient Example:
+//! ## Display address with path
 //! ```no_run
 //! use bitcoin::bip32::{ChildNumber, DerivationPath};
 //! use hwi::error::Error;
@@ -25,18 +28,54 @@
 //!     Ok(())
 //! }
 //! ```
+//!
+//! # HWISigner Example:
+//! ## Add custom HWI signer to [`bdk_wallet`]
+//! ```no_run
+//! # use bdk_wallet::bitcoin::Network;
+//! # use bdk_wallet::descriptor::Descriptor;
+//! # use bdk_wallet::signer::SignerOrdering;
+//! # use hwi::{HWIClient, HWISigner};
+//! # use bdk_wallet::{KeychainKind, SignOptions, Wallet};
+//! # use std::sync::Arc;
+//! # use std::str::FromStr;
+//! #
+//! # fn main() -> Result<(), Box<dyn std::error::Error>> {
+//! let mut devices = HWIClient::enumerate()?;
+//! if devices.is_empty() {
+//!     panic!("No devices found!");
+//! }
+//! let first_device = devices.remove(0)?;
+//! let custom_signer = HWISigner::from_device(&first_device, Network::Testnet.into())?;
+//!
+//! # let mut wallet = Wallet::create("", "").network(Network::Testnet).create_wallet_no_persist()?;
+//! #
+//! // Adding the hardware signer to the BDK wallet
+//! wallet.add_signer(
+//!     KeychainKind::External,
+//!     SignerOrdering(200),
+//!     Arc::new(custom_signer),
+//! );
+//!
+//! # Ok(())
+//! # }
+//! ```
+//!
+//! [`TransactionSigner`]: bdk_wallet::signer::TransactionSigner
 
 #[cfg(test)]
 #[macro_use]
 extern crate serial_test;
 extern crate core;
 
 pub use interface::HWIClient;
+pub use signer::HWISigner;
 
 #[cfg(feature = "doctest")]
 pub mod doctest;
 pub mod error;
 pub mod interface;
+pub mod signer;
 pub mod types;
 
 #[cfg(test)]

src/signer.rs

@@ -0,0 +1,55 @@
+use bdk_wallet::bitcoin::bip32::Fingerprint;
+use bdk_wallet::bitcoin::secp256k1::{All, Secp256k1};
+use bdk_wallet::bitcoin::Psbt;
+
+use crate::error::Error;
+use crate::types::{HWIChain, HWIDevice};
+use crate::HWIClient;
+
+use bdk_wallet::signer::{SignerCommon, SignerError, SignerId, TransactionSigner};
+
+#[derive(Debug)]
+/// Custom signer for Hardware Wallets
+///
+/// This ignores `sign_options` and leaves the decisions up to the hardware wallet.
+pub struct HWISigner {
+    fingerprint: Fingerprint,
+    client: HWIClient,
+}
+
+impl HWISigner {
+    /// Create an instance from the specified device and chain
+    pub fn from_device(device: &HWIDevice, chain: HWIChain) -> Result<HWISigner, Error> {
+        let client = HWIClient::get_client(device, false, chain)?;
+        Ok(HWISigner {
+            fingerprint: device.fingerprint,
+            client,
+        })
+    }
+}
+
+impl SignerCommon for HWISigner {
+    fn id(&self, _secp: &Secp256k1<All>) -> SignerId {
+        SignerId::Fingerprint(self.fingerprint)
+    }
+}
+
+impl TransactionSigner for HWISigner {
+    fn sign_transaction(
+        &self,
+        psbt: &mut Psbt,
+        _sign_options: &bdk_wallet::SignOptions,
+        _secp: &Secp256k1<All>,
+    ) -> Result<(), SignerError> {
+        psbt.combine(
+            self.client
+                .sign_tx(psbt)
+                .map_err(|e| {
+                    SignerError::External(format!("While signing with hardware wallet: {}", e))
+                })?
+                .psbt,
+        )
+        .expect("Failed to combine HW signed psbt with passed PSBT");
+        Ok(())
+    }
+}