feat: expose derived_address helper on Descriptor

bdk-ffi/src/descriptor.rs

@@ -1,5 +1,7 @@
+use crate::bitcoin::Address;
 use crate::bitcoin::DescriptorId;
 use crate::bitcoin::DescriptorType;
+use crate::bitcoin::Script;
 use crate::error::DescriptorError;
 use crate::error::MiniscriptError;
 use crate::keys::DescriptorPublicKey;
@@ -12,6 +14,7 @@ use bdk_wallet::chain::DescriptorExt;
 use bdk_wallet::descriptor::{ExtendedDescriptor, IntoWalletDescriptor};
 use bdk_wallet::keys::DescriptorPublicKey as BdkDescriptorPublicKey;
 use bdk_wallet::keys::{DescriptorSecretKey as BdkDescriptorSecretKey, KeyMap};
+use bdk_wallet::miniscript::descriptor::ConversionError;
 use bdk_wallet::template::{
     Bip44, Bip44Public, Bip49, Bip49Public, Bip84, Bip84Public, Bip86, Bip86Public,
     DescriptorTemplate,
@@ -355,6 +358,35 @@ impl Descriptor {
     pub fn desc_type(&self) -> DescriptorType {
         self.extended_descriptor.desc_type()
     }
+
+    pub fn derived_address(
+        &self,
+        index: u32,
+        network: Network,
+    ) -> Result<Arc<Address>, DescriptorError> {
+        if self.extended_descriptor.is_multipath() {
+            return Err(DescriptorError::MultiPath);
+        }
+
+        let secp = Secp256k1::verification_only();
+        let derived_descriptor = self
+            .extended_descriptor
+            .at_derivation_index(index)
+            .and_then(|desc| desc.derived_descriptor(&secp))
+            .map_err(|error| match error {
+                ConversionError::HardenedChild => DescriptorError::HardenedDerivationXpub,
+                ConversionError::MultiKey => DescriptorError::MultiPath,
+            })?;
+        let script_pubkey = derived_descriptor.script_pubkey();
+        let address =
+            Address::from_script(Arc::new(Script(script_pubkey)), network).map_err(|error| {
+                DescriptorError::Miniscript {
+                    error_message: error.to_string(),
+                }
+            })?;
+
+        Ok(Arc::new(address))
+    }
 }
 
 impl Display for Descriptor {

bdk-ffi/src/tests/descriptor.rs

@@ -3,6 +3,7 @@ use crate::descriptor::Descriptor;
 use crate::error::DescriptorError;
 use crate::keys::{DerivationPath, DescriptorSecretKey, Mnemonic};
 use assert_matches::assert_matches;
+use bdk_wallet::bitcoin::secp256k1::Secp256k1;
 use bdk_wallet::KeychainKind;
 
 fn get_descriptor_secret_key() -> DescriptorSecretKey {
@@ -161,3 +162,42 @@ fn test_max_weight_to_satisfy() {
     // Verify the method works and returns a positive weight
     assert!(weight > 0, "Weight must be positive");
 }
+
+#[test]
+fn test_descriptor_derived_address() {
+    let descriptor = Descriptor::new_bip84(
+        &get_descriptor_secret_key(),
+        KeychainKind::External,
+        Network::Testnet,
+    );
+
+    let derived = descriptor
+        .derived_address(0, Network::Testnet)
+        .expect("derive address");
+
+    let secp = Secp256k1::verification_only();
+    let expected_descriptor = descriptor
+        .extended_descriptor
+        .derived_descriptor(&secp, 0)
+        .expect("derive descriptor");
+    let expected_address = bdk_wallet::bitcoin::Address::from_script(
+        &expected_descriptor.script_pubkey(),
+        Network::Testnet,
+    )
+    .expect("address from script");
+
+    assert_eq!(derived.to_string(), expected_address.to_string());
+}
+
+#[test]
+fn test_descriptor_derived_address_multipath_error() {
+    let descriptor = Descriptor::new(
+        "wpkh([9a6a2580/84'/1'/0']tpubDDnGNapGEY6AZAdQbfRJgMg9fvz8pUBrLwvyvUqEgcUfgzM6zc2eVK4vY9x9L5FJWdX8WumXuLEDV5zDZnTfbn87vLe9XceCFwTu9so9Kks/<0;1>/*)".to_string(),
+        Network::Testnet,
+    )
+    .expect("multipath descriptor parses");
+
+    let error = descriptor.derived_address(0, Network::Testnet).unwrap_err();
+
+    assert_matches!(error, DescriptorError::MultiPath);
+}