Merge #562: Expose more getters in Wallet and other useful descriptor traits

1b90148 Update changelog (Alekos Filini)
86abd86 [descriptor] Expose utilities to deal with derived descriptors (Alekos Filini)
0d9c2f7 [export] Use the new getters on `Wallet` to generate export JSONs (Alekos Filini)
63d5bce [wallet] Add more getters (Alekos Filini)

Pull request description:

  <!-- You can erase any parts of this template not applicable to your Pull Request. -->

  ### Description

  Expose more getters and internal utilities for people who need to work with descriptors.

  A good example of how this can be leveraged is in the second commit, which refactors the wallet export functionality to use the new public APIs rather than using members on `Wallet` directly.

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

  #### New Features:

  * [ ] I've added tests for the new feature
  * [x] I've added docs for the new feature
  * [x] I've updated `CHANGELOG.md`

ACKs for top commit:
  notmandatory:
    ACK 8cd0550

Tree-SHA512: 3e8833670ebc56316fce01fc572fcc9391d602ef85f0cde8edcb446295570a9012e18f6ba8af0984153e4688f66f7eea6803ef610ceb395867e464e05c01c137

Author: notmandatory

CHANGELOG.md

@@ -7,6 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 - Add `sqlite-bundled` feature for deployments that need a bundled version of sqlite, ie. for mobile platforms.
+- Added `Wallet::get_signers()`, `Wallet::descriptor_checksum()` and `Wallet::get_address_validators()`, exposed the `AsDerived` trait.
 
 ## [v0.17.0] - [v0.16.1]
 

src/descriptor/derived.rs

@@ -10,6 +10,41 @@
 // licenses.
 
 //! Derived descriptor keys
+//!
+//! The [`DerivedDescriptorKey`] type is a wrapper over the standard [`DescriptorPublicKey`] which
+//! guarantees that all the extended keys have a fixed derivation path, i.e. all the wildcards have
+//! been replaced by actual derivation indexes.
+//!
+//! The [`AsDerived`] trait provides a quick way to derive descriptors to obtain a
+//! `Descriptor<DerivedDescriptorKey>` type. This, in turn, can be used to derive public
+//! keys for arbitrary derivation indexes.
+//!
+//! Combining this with [`Wallet::get_signers`], secret keys can also be derived.
+//!
+//! # Example
+//!
+//! ```
+//! # use std::str::FromStr;
+//! # use bitcoin::secp256k1::Secp256k1;
+//! use bdk::descriptor::{AsDerived, DescriptorPublicKey};
+//! use bdk::miniscript::{ToPublicKey, TranslatePk, MiniscriptKey};
+//!
+//! let secp = Secp256k1::gen_new();
+//!
+//! let key = DescriptorPublicKey::from_str("[aa600a45/84'/0'/0']tpubDCbDXFKoLTQp44wQuC12JgSn5g9CWGjZdpBHeTqyypZ4VvgYjTJmK9CkyR5bFvG9f4PutvwmvpYCLkFx2rpx25hiMs4sUgxJveW8ZzSAVAc/0/*")?;
+//! let (descriptor, _, _) = bdk::descriptor!(wpkh(key))?;
+//!
+//! // derived: wpkh([aa600a45/84'/0'/0']tpubDCbDXFKoLTQp44wQuC12JgSn5g9CWGjZdpBHeTqyypZ4VvgYjTJmK9CkyR5bFvG9f4PutvwmvpYCLkFx2rpx25hiMs4sUgxJveW8ZzSAVAc/0/42)#3ladd0t2
+//! let derived = descriptor.as_derived(42, &secp);
+//! println!("derived: {}", derived);
+//!
+//! // with_pks: wpkh(02373ecb54c5e83bd7e0d40adf78b65efaf12fafb13571f0261fc90364eee22e1e)#p4jjgvll
+//! let with_pks = derived.translate_pk_infallible(|pk| pk.to_public_key(), |pkh| pkh.to_public_key().to_pubkeyhash());
+//! println!("with_pks: {}", with_pks);
+//! # Ok::<(), Box<dyn std::error::Error>>(())
+//! ```
+//!
+//! [`Wallet::get_signers`]: crate::wallet::Wallet::get_signers
 
 use std::cmp::Ordering;
 use std::fmt;
@@ -19,10 +54,7 @@ use std::ops::Deref;
 use bitcoin::hashes::hash160;
 use bitcoin::PublicKey;
 
-pub use miniscript::{
-    descriptor::KeyMap, descriptor::Wildcard, Descriptor, DescriptorPublicKey, Legacy, Miniscript,
-    ScriptContext, Segwitv0,
-};
+use miniscript::{descriptor::Wildcard, Descriptor, DescriptorPublicKey};
 use miniscript::{MiniscriptKey, ToPublicKey, TranslatePk};
 
 use crate::wallet::utils::SecpCtx;
@@ -119,14 +151,19 @@ impl<'s> ToPublicKey for DerivedDescriptorKey<'s> {
     }
 }
 
-pub(crate) trait AsDerived {
-    // Derive a descriptor and transform all of its keys to `DerivedDescriptorKey`
+/// Utilities to derive descriptors
+///
+/// Check out the [module level] documentation for more.
+///
+/// [module level]: crate::descriptor::derived
+pub trait AsDerived {
+    /// Derive a descriptor and transform all of its keys to `DerivedDescriptorKey`
     fn as_derived<'s>(&self, index: u32, secp: &'s SecpCtx)
         -> Descriptor<DerivedDescriptorKey<'s>>;
 
-    // Transform the keys into `DerivedDescriptorKey`.
-    //
-    // Panics if the descriptor is not "fixed", i.e. if it's derivable
+    /// Transform the keys into `DerivedDescriptorKey`.
+    ///
+    /// Panics if the descriptor is not "fixed", i.e. if it's derivable
     fn as_derived_fixed<'s>(&self, secp: &'s SecpCtx) -> Descriptor<DerivedDescriptorKey<'s>>;
 }
 

src/descriptor/mod.rs

@@ -21,25 +21,25 @@ use bitcoin::util::bip32::{ChildNumber, DerivationPath, ExtendedPubKey, Fingerpr
 use bitcoin::util::psbt;
 use bitcoin::{Network, PublicKey, Script, TxOut};
 
-use miniscript::descriptor::{
-    DescriptorPublicKey, DescriptorType, DescriptorXKey, InnerXKey, Wildcard,
+use miniscript::descriptor::{DescriptorType, InnerXKey};
+pub use miniscript::{
+    descriptor::DescriptorXKey, descriptor::KeyMap, descriptor::Wildcard, Descriptor,
+    DescriptorPublicKey, Legacy, Miniscript, ScriptContext, Segwitv0,
 };
-pub use miniscript::{descriptor::KeyMap, Descriptor, Legacy, Miniscript, ScriptContext, Segwitv0};
 use miniscript::{DescriptorTrait, ForEachKey, TranslatePk};
 
 use crate::descriptor::policy::BuildSatisfaction;
 
 pub mod checksum;
-pub(crate) mod derived;
+pub mod derived;
 #[doc(hidden)]
 pub mod dsl;
 pub mod error;
 pub mod policy;
 pub mod template;
 
 pub use self::checksum::get_checksum;
-use self::derived::AsDerived;
-pub use self::derived::DerivedDescriptorKey;
+pub use self::derived::{AsDerived, DerivedDescriptorKey};
 pub use self::error::Error as DescriptorError;
 pub use self::policy::Policy;
 use self::template::DescriptorTemplateOut;

src/wallet/export.rs

@@ -64,9 +64,10 @@ use std::str::FromStr;
 use serde::{Deserialize, Serialize};
 
 use miniscript::descriptor::{ShInner, WshInner};
-use miniscript::{Descriptor, DescriptorPublicKey, ScriptContext, Terminal};
+use miniscript::{Descriptor, ScriptContext, Terminal};
 
 use crate::database::BatchDatabase;
+use crate::types::KeychainKind;
 use crate::wallet::Wallet;
 
 /// Structure that contains the export of a wallet
@@ -117,8 +118,12 @@ impl WalletExport {
         include_blockheight: bool,
     ) -> Result<Self, &'static str> {
         let descriptor = wallet
-            .descriptor
-            .to_string_with_secret(&wallet.signers.as_key_map(wallet.secp_ctx()));
+            .get_descriptor_for_keychain(KeychainKind::External)
+            .to_string_with_secret(
+                &wallet
+                    .get_signers(KeychainKind::External)
+                    .as_key_map(wallet.secp_ctx()),
+            );
         let descriptor = remove_checksum(descriptor);
         Self::is_compatible_with_core(&descriptor)?;
 
@@ -142,12 +147,24 @@ impl WalletExport {
             blockheight,
         };
 
-        let desc_to_string = |d: &Descriptor<DescriptorPublicKey>| {
-            let descriptor =
-                d.to_string_with_secret(&wallet.change_signers.as_key_map(wallet.secp_ctx()));
-            remove_checksum(descriptor)
+        let change_descriptor = match wallet
+            .public_descriptor(KeychainKind::Internal)
+            .map_err(|_| "Invalid change descriptor")?
+            .is_some()
+        {
+            false => None,
+            true => {
+                let descriptor = wallet
+                    .get_descriptor_for_keychain(KeychainKind::Internal)
+                    .to_string_with_secret(
+                        &wallet
+                            .get_signers(KeychainKind::Internal)
+                            .as_key_map(wallet.secp_ctx()),
+                    );
+                Some(remove_checksum(descriptor))
+            }
         };
-        if export.change_descriptor() != wallet.change_descriptor.as_ref().map(desc_to_string) {
+        if export.change_descriptor() != change_descriptor {
             return Err("Incompatible change descriptor");
         }
 

src/wallet/mod.rs

@@ -468,13 +468,41 @@ where
         signers.add_external(signer.id(&self.secp), ordering, signer);
     }
 
+    /// Get the signers
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// # use bdk::{Wallet, KeychainKind};
+    /// # use bdk::bitcoin::Network;
+    /// # use bdk::database::MemoryDatabase;
+    /// let wallet = Wallet::new("wpkh(tprv8ZgxMBicQKsPe73PBRSmNbTfbcsZnwWhz5eVmhHpi31HW29Z7mc9B4cWGRQzopNUzZUT391DeDJxL2PefNunWyLgqCKRMDkU1s2s8bAfoSk/84'/0'/0'/0/*)", None, Network::Testnet, MemoryDatabase::new())?;
+    /// for secret_key in wallet.get_signers(KeychainKind::External).signers().iter().filter_map(|s| s.descriptor_secret_key()) {
+    ///     // secret_key: tprv8ZgxMBicQKsPe73PBRSmNbTfbcsZnwWhz5eVmhHpi31HW29Z7mc9B4cWGRQzopNUzZUT391DeDJxL2PefNunWyLgqCKRMDkU1s2s8bAfoSk/84'/0'/0'/0/*
+    ///     println!("secret_key: {}", secret_key);
+    /// }
+    ///
+    /// Ok::<(), Box<dyn std::error::Error>>(())
+    /// ```
+    pub fn get_signers(&self, keychain: KeychainKind) -> Arc<SignersContainer> {
+        match keychain {
+            KeychainKind::External => Arc::clone(&self.signers),
+            KeychainKind::Internal => Arc::clone(&self.change_signers),
+        }
+    }
+
     /// Add an address validator
     ///
     /// See [the `address_validator` module](address_validator) for an example.
     pub fn add_address_validator(&mut self, validator: Arc<dyn AddressValidator>) {
         self.address_validators.push(validator);
     }
 
+    /// Get the address validators
+    pub fn get_address_validators(&self) -> &[Arc<dyn AddressValidator>] {
+        &self.address_validators
+    }
+
     /// Start building a transaction.
     ///
     /// This returns a blank [`TxBuilder`] from which you can specify the parameters for the transaction.
@@ -1568,6 +1596,18 @@ where
 
         Ok(())
     }
+
+    /// Return the checksum of the public descriptor associated to `keychain`
+    ///
+    /// Internally calls [`Self::get_descriptor_for_keychain`] to fetch the right descriptor
+    pub fn descriptor_checksum(&self, keychain: KeychainKind) -> String {
+        self.get_descriptor_for_keychain(keychain)
+            .to_string()
+            .splitn(2, '#')
+            .next()
+            .unwrap()
+            .to_string()
+    }
 }
 
 /// Return a fake wallet that appears to be funded for testing.