feat: Add Refund wrapper for FFI bindings

Implement Refund struct in uniffi_types to provide a wrapper around LDK's Refund for cross-language bindings.

Modified payment handling in bolt12.rs to:
- Support both native and FFI-compatible types via type aliasing
- Implement conditional compilation for transparent FFI support
- Update payment functions to handle wrapped types

Added testing to verify that properties are preserved when wrapping/unwrapping between native and FFI types.

Author: alexanderwiederin

bindings/ldk_node.udl

@@ -752,6 +752,21 @@ interface Offer {
     OfferAmount? amount();
 };
 
+interface Refund {
+	[Throws=NodeError, Name=from_str]
+	constructor([ByRef] string refund_str);
+	string description();
+	u64? absolute_expiry_seconds();
+	boolean is_expired();
+	string? issuer();
+	sequence<u8> payer_metadata();
+	Network? chain();
+	u64 amount_msats();
+	u64? quantity();
+	PublicKey payer_signing_pubkey();
+	string? payer_note();
+};
+
 [Custom]
 typedef string Txid;
 
@@ -770,9 +785,6 @@ typedef string NodeId;
 [Custom]
 typedef string Address;
 
-[Custom]
-typedef string Refund;
-
 [Custom]
 typedef string Bolt12Invoice;
 

src/payment/bolt12.rs

@@ -19,7 +19,7 @@ use lightning::ln::channelmanager::{PaymentId, Retry};
 use lightning::offers::invoice::Bolt12Invoice;
 use lightning::offers::offer::{Amount, Offer as LdkOffer, Quantity};
 use lightning::offers::parse::Bolt12SemanticError;
-use lightning::offers::refund::Refund;
+use lightning::offers::refund::Refund as LdkRefund;
 use lightning::util::string::UntrustedString;
 
 use rand::RngCore;
@@ -50,6 +50,30 @@ pub fn maybe_wrap_offer(offer: LdkOffer) -> Offer {
 pub fn maybe_wrap_offer(offer: LdkOffer) -> Offer {
 	Arc::new(offer.into())
 }
+
+#[cfg(not(feature = "uniffi"))]
+type Refund = LdkRefund;
+#[cfg(feature = "uniffi")]
+type Refund = Arc<crate::uniffi_types::Refund>;
+
+#[cfg(not(feature = "uniffi"))]
+pub fn maybe_convert_refund(refund: &Refund) -> &LdkRefund {
+	refund
+}
+#[cfg(feature = "uniffi")]
+pub fn maybe_convert_refund(refund: &Refund) -> &LdkRefund {
+	&refund.inner
+}
+
+#[cfg(not(feature = "uniffi"))]
+pub fn maybe_wrap_refund(refund: Refund) -> LdkRefund {
+	refund
+}
+#[cfg(feature = "uniffi")]
+pub fn maybe_wrap_refund(refund: LdkRefund) -> Refund {
+	Arc::new(refund.into())
+}
+
 /// A payment handler allowing to create and pay [BOLT 12] offers and refunds.
 ///
 /// Should be retrieved by calling [`Node::bolt12_payment`].
@@ -350,7 +374,10 @@ impl Bolt12Payment {
 	///
 	/// The returned [`Bolt12Invoice`] is for informational purposes only (i.e., isn't needed to
 	/// retrieve the refund).
+	///
+	/// [`Refund`]: lightning::offers::refund::Refund
 	pub fn request_refund_payment(&self, refund: &Refund) -> Result<Bolt12Invoice, Error> {
+		let refund = maybe_convert_refund(refund);
 		let invoice = self.channel_manager.request_refund_payment(refund).map_err(|e| {
 			log_error!(self.logger, "Failed to request refund payment: {:?}", e);
 			Error::InvoiceRequestCreationFailed
@@ -382,6 +409,8 @@ impl Bolt12Payment {
 	}
 
 	/// Returns a [`Refund`] object that can be used to offer a refund payment of the amount given.
+	///
+	/// [`Refund`]: lightning::offers::refund::Refund
 	pub fn initiate_refund(
 		&self, amount_msat: u64, expiry_secs: u32, quantity: Option<u64>,
 		payer_note: Option<String>,
@@ -443,6 +472,6 @@ impl Bolt12Payment {
 
 		self.payment_store.insert(payment)?;
 
-		Ok(refund)
+		Ok(maybe_wrap_refund(refund))
 	}
 }

src/uniffi_types.rs

@@ -27,7 +27,6 @@ pub use lightning::events::{ClosureReason, PaymentFailureReason};
 pub use lightning::ln::types::ChannelId;
 pub use lightning::offers::invoice::Bolt12Invoice;
 pub use lightning::offers::offer::OfferId;
-pub use lightning::offers::refund::Refund;
 pub use lightning::routing::gossip::{NodeAlias, NodeId, RoutingFees};
 pub use lightning::util::string::UntrustedString;
 
@@ -58,6 +57,7 @@ use bitcoin::hashes::Hash;
 use bitcoin::secp256k1::PublicKey;
 use lightning::ln::channelmanager::PaymentId;
 use lightning::offers::offer::{Amount as LdkAmount, Offer as LdkOffer};
+use lightning::offers::refund::Refund as LdkRefund;
 use lightning::util::ser::Writeable;
 use lightning_invoice::{Bolt11Invoice as LdkBolt11Invoice, Bolt11InvoiceDescriptionRef};
 
@@ -201,15 +201,103 @@ impl From<LdkOffer> for Offer {
 	}
 }
 
-impl UniffiCustomTypeConverter for Refund {
-	type Builtin = String;
+/// A `Refund` is a request to send an [`Bolt12Invoice`] without a preceding [`Offer`].
+///
+/// Typically, after an invoice is paid, the recipient may publish a refund allowing the sender to
+/// recoup their funds. A refund may be used more generally as an "offer for money", such as with a
+/// bitcoin ATM.
+///
+/// [`Bolt12Invoice`]: crate::offers::invoice::Bolt12Invoice
+/// [`Offer`]: crate::offers::offer::Offer
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Refund {
+	pub inner: LdkRefund,
+}
 
-	fn into_custom(val: Self::Builtin) -> uniffi::Result<Self> {
-		Refund::from_str(&val).map_err(|_| Error::InvalidRefund.into())
+impl Refund {
+	pub fn from_str(refund_str: &str) -> Result<Self, Error> {
+		refund_str.parse()
 	}
 
-	fn from_custom(obj: Self) -> Self::Builtin {
-		obj.to_string()
+	/// A complete description of the purpose of the refund. Intended to be displayed to the user
+	/// but with the caveat that it has not been verified in any way.
+	pub fn description(&self) -> String {
+		self.inner.description().to_string()
+	}
+
+	/// Seconds since the Unix epoch when an invoice should no longer be sent.
+	///
+	/// If `None`, the refund does not expire.
+	pub fn absolute_expiry_seconds(&self) -> Option<u64> {
+		self.inner.absolute_expiry().map(|duration| duration.as_secs())
+	}
+
+	/// Whether the refund has expired.
+	pub fn is_expired(&self) -> bool {
+		self.inner.is_expired()
+	}
+
+	/// The issuer of the refund, possibly beginning with `user@domain` or `domain`. Intended to be
+	/// displayed to the user but with the caveat that it has not been verified in any way.
+	pub fn issuer(&self) -> Option<String> {
+		self.inner.issuer().map(|printable| printable.to_string())
+	}
+
+	/// An unpredictable series of bytes, typically containing information about the derivation of
+	/// [`payer_signing_pubkey`].
+	///
+	/// [`payer_signing_pubkey`]: Self::payer_signing_pubkey
+	pub fn payer_metadata(&self) -> Vec<u8> {
+		self.inner.payer_metadata().to_vec()
+	}
+
+	/// A chain that the refund is valid for.
+	pub fn chain(&self) -> Option<Network> {
+		Network::try_from(self.inner.chain()).ok()
+	}
+
+	/// The amount to refund in msats (i.e., the minimum lightning-payable unit for [`chain`]).
+	///
+	/// [`chain`]: Self::chain
+	pub fn amount_msats(&self) -> u64 {
+		self.inner.amount_msats()
+	}
+
+	// pub fn features(&self)
+
+	/// The quantity of an item that refund is for.
+	pub fn quantity(&self) -> Option<u64> {
+		self.inner.quantity()
+	}
+
+	/// A public node id to send to in the case where there are no [`paths`]. Otherwise, a possibly
+	/// transient pubkey.
+	///
+	/// [`paths`]: Self::paths
+	pub fn payer_signing_pubkey(&self) -> PublicKey {
+		self.inner.payer_signing_pubkey()
+	}
+
+	/// Payer provided note to include in the invoice.
+	pub fn payer_note(&self) -> Option<String> {
+		self.inner.payer_note().map(|printable| printable.to_string())
+	}
+}
+
+impl std::str::FromStr for Refund {
+	type Err = Error;
+
+	fn from_str(refund_str: &str) -> Result<Self, Self::Err> {
+		refund_str
+			.parse::<LdkRefund>()
+			.map(|refund| Refund { inner: refund })
+			.map_err(|_| Error::InvalidRefund)
+	}
+}
+
+impl From<LdkRefund> for Refund {
+	fn from(refund: LdkRefund) -> Self {
+		Refund { inner: refund }
 	}
 }
 
@@ -736,9 +824,8 @@ impl UniffiCustomTypeConverter for DateTime {
 mod tests {
 	use std::time::{SystemTime, UNIX_EPOCH};
 
-	use lightning::offers::offer::OfferBuilder;
-
 	use super::*;
+	use lightning::offers::{offer::OfferBuilder, refund::RefundBuilder};
 
 	fn create_test_invoice() -> (LdkBolt11Invoice, Bolt11Invoice) {
 		let invoice_string = "lnbc1pn8g249pp5f6ytj32ty90jhvw69enf30hwfgdhyymjewywcmfjevflg6s4z86qdqqcqzzgxqyz5vqrzjqwnvuc0u4txn35cafc7w94gxvq5p3cu9dd95f7hlrh0fvs46wpvhdfjjzh2j9f7ye5qqqqryqqqqthqqpysp5mm832athgcal3m7h35sc29j63lmgzvwc5smfjh2es65elc2ns7dq9qrsgqu2xcje2gsnjp0wn97aknyd3h58an7sjj6nhcrm40846jxphv47958c6th76whmec8ttr2wmg6sxwchvxmsc00kqrzqcga6lvsf9jtqgqy5yexa";
@@ -768,6 +855,28 @@ mod tests {
 		(ldk_offer, wrapped_offer)
 	}
 
+	fn create_test_refund() -> (LdkRefund, Refund) {
+		let payer_key = bitcoin::secp256k1::PublicKey::from_str(
+			"02eec7245d6b7d2ccb30380bfbe2a3648cd7a942653f5aa340edcea1f283686619",
+		)
+		.unwrap();
+
+		let expiry =
+			(SystemTime::now() + Duration::from_secs(3600)).duration_since(UNIX_EPOCH).unwrap();
+
+		let builder = RefundBuilder::new("Test refund".to_string().into(), payer_key, 100_000)
+			.unwrap()
+			.description("Test refund description".to_string())
+			.absolute_expiry(expiry)
+			.quantity(3)
+			.issuer("test_issuer".to_string());
+
+		let ldk_refund = builder.build().unwrap();
+		let wrapped_refund = Refund::from(ldk_refund.clone());
+
+		(ldk_refund, wrapped_refund)
+	}
+
 	#[test]
 	fn test_invoice_description_conversion() {
 		let hash = "09d08d4865e8af9266f6cc7c0ae23a1d6bf868207cf8f7c5979b9f6ed850dfb0".to_string();
@@ -930,4 +1039,81 @@ mod tests {
 		assert_eq!(ldk_offer.is_expired(), wrapped_offer.is_expired());
 		assert_eq!(ldk_offer.id(), wrapped_offer.id());
 	}
+
+	#[test]
+	fn test_refund_roundtrip() {
+		let (ldk_refund, _) = create_test_refund();
+
+		let refund_str = ldk_refund.to_string();
+
+		let parsed_refund = Refund::from_str(&refund_str);
+		assert!(parsed_refund.is_ok(), "Failed to parse refund from string!");
+
+		let invalid_result = Refund::from_str("invalid_refund_string");
+		assert!(invalid_result.is_err());
+		assert!(matches!(invalid_result.err().unwrap(), Error::InvalidRefund));
+	}
+
+	#[test]
+	fn test_refund_properties() {
+		let (ldk_refund, wrapped_refund) = create_test_refund();
+
+		assert_eq!(ldk_refund.description().to_string(), wrapped_refund.description());
+		assert_eq!(ldk_refund.amount_msats(), wrapped_refund.amount_msats());
+		assert_eq!(ldk_refund.is_expired(), wrapped_refund.is_expired());
+
+		match (ldk_refund.absolute_expiry(), wrapped_refund.absolute_expiry_seconds()) {
+			(Some(ldk_expiry), Some(wrapped_expiry)) => {
+				assert_eq!(ldk_expiry.as_secs(), wrapped_expiry);
+			},
+			(None, None) => {
+				// Both fields are missing which is expected behaviour when converting
+			},
+			(Some(_), None) => {
+				panic!("LDK refund had an expiry but wrapped refund did not!");
+			},
+			(None, Some(_)) => {
+				panic!("Wrapped refund had an expiry but LDK refund did not!");
+			},
+		}
+
+		match (ldk_refund.quantity(), wrapped_refund.quantity()) {
+			(Some(ldk_expiry), Some(wrapped_expiry)) => {
+				assert_eq!(ldk_expiry, wrapped_expiry);
+			},
+			(None, None) => {
+				// Both fields are missing which is expected behaviour when converting
+			},
+			(Some(_), None) => {
+				panic!("LDK refund had an quantity but wrapped refund did not!");
+			},
+			(None, Some(_)) => {
+				panic!("Wrapped refund had an quantity but LDK refund did not!");
+			},
+		}
+
+		match (ldk_refund.issuer(), wrapped_refund.issuer()) {
+			(Some(ldk_issuer), Some(wrapped_issuer)) => {
+				assert_eq!(ldk_issuer.to_string(), wrapped_issuer);
+			},
+			(None, None) => {
+				// Both fields are missing which is expected behaviour when converting
+			},
+			(Some(_), None) => {
+				panic!("LDK refund had an issuer but wrapped refund did not!");
+			},
+			(None, Some(_)) => {
+				panic!("Wrapped refund had an issuer but LDK refund did not!");
+			},
+		}
+
+		assert_eq!(ldk_refund.payer_metadata().to_vec(), wrapped_refund.payer_metadata());
+		assert_eq!(ldk_refund.payer_signing_pubkey(), wrapped_refund.payer_signing_pubkey());
+
+		if let Ok(network) = Network::try_from(ldk_refund.chain()) {
+			assert_eq!(wrapped_refund.chain(), Some(network));
+		}
+
+		assert_eq!(ldk_refund.payer_note().map(|p| p.to_string()), wrapped_refund.payer_note());
+	}
 }