From f21ac743c2ef423cb4ce11ae3974e3c0436eaea5 Mon Sep 17 00:00:00 2001
From: Matthew <ramsden@hey.com>
Date: Tue, 25 Nov 2025 13:28:41 -0600
Subject: [PATCH] feat: expose `derived_address` helper on `Descriptor`

---
 bdk-ffi/src/descriptor.rs       | 29 ++++++++++++++++++++++++++
 bdk-ffi/src/tests/descriptor.rs | 36 +++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)

diff --git a/bdk-ffi/src/descriptor.rs b/bdk-ffi/src/descriptor.rs
index c07de859..e52769d7 100644
--- a/bdk-ffi/src/descriptor.rs
+++ b/bdk-ffi/src/descriptor.rs
@@ -1,3 +1,4 @@
+use crate::bitcoin::Address;
 use crate::bitcoin::DescriptorId;
 use crate::bitcoin::DescriptorType;
 use crate::error::DescriptorError;
@@ -12,6 +13,7 @@ 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 +357,33 @@ impl Descriptor {
     pub fn desc_type(&self) -> DescriptorType {
         self.extended_descriptor.desc_type()
     }
+
+    pub fn derive_address(
+        &self,
+        index: u32,
+        network: Network,
+    ) -> Result<Arc<Address>, DescriptorError> {
+        if self.extended_descriptor.is_multipath() {
+            return Err(DescriptorError::MultiPath);
+        }
+
+        let derived_descriptor = self
+            .extended_descriptor
+            .at_derivation_index(index)
+            .map_err(|error| match error {
+                ConversionError::HardenedChild => DescriptorError::HardenedDerivationXpub,
+                ConversionError::MultiKey => DescriptorError::MultiPath,
+            })?;
+
+        let address = derived_descriptor
+            .address(network)
+            .map_err(|error| DescriptorError::Miniscript {
+                error_message: error.to_string(),
+            })?
+            .into();
+
+        Ok(Arc::new(address))
+    }
 }
 
 impl Display for Descriptor {
diff --git a/bdk-ffi/src/tests/descriptor.rs b/bdk-ffi/src/tests/descriptor.rs
index fed07b89..c6dcb432 100644
--- a/bdk-ffi/src/tests/descriptor.rs
+++ b/bdk-ffi/src/tests/descriptor.rs
@@ -161,3 +161,39 @@ 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_derive_address() {
+    let descriptor = Descriptor::new_bip84(
+        &get_descriptor_secret_key(),
+        KeychainKind::External,
+        Network::Testnet,
+    );
+
+    let derived = descriptor
+        .derive_address(0, Network::Testnet)
+        .expect("derive address");
+
+    let expected_descriptor = descriptor
+        .extended_descriptor
+        .at_derivation_index(0)
+        .expect("derive descriptor");
+    let expected_address = expected_descriptor
+        .address(Network::Testnet)
+        .expect("address from descriptor");
+
+    assert_eq!(derived.to_string(), expected_address.to_string());
+}
+
+#[test]
+fn test_descriptor_derive_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.derive_address(0, Network::Testnet).unwrap_err();
+
+    assert_matches!(error, DescriptorError::MultiPath);
+}