Add Bolt12Invoice wrapper for FFI bindings

Implement Bolt12Invoice struct in ffi/types.rs to provide a wrapper around LDK's Bolt12Invoice 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

@@ -774,6 +774,31 @@ interface Refund {
 	string? payer_note();
 };
 
+interface Bolt12Invoice {
+	[Throws=NodeError, Name=from_str]
+	constructor([ByRef] string invoice_str);
+	PaymentHash payment_hash();
+	u64 amount_msats();
+	OfferAmount? amount();
+	PublicKey signing_pubkey();
+	u64 created_at();
+	u64? absolute_expiry_seconds();
+	u64 relative_expiry();
+	boolean is_expired();
+	string? description();
+	string? issuer();
+	string? payer_note();
+	sequence<u8>? metadata();
+	u64? quantity();
+	sequence<u8> signable_hash();
+	PublicKey payer_signing_pubkey();
+	PublicKey? issuer_signing_pubkey();
+	sequence<u8> chain();
+	sequence<sequence<u8>>? offer_chains();
+	sequence<Address> fallback_addresses();
+	sequence<u8> encode();
+};
+
 [Custom]
 typedef string Txid;
 
@@ -792,9 +817,6 @@ typedef string NodeId;
 [Custom]
 typedef string Address;
 
-[Custom]
-typedef string Bolt12Invoice;
-
 [Custom]
 typedef string OfferId;
 

src/ffi/conversions.rs

@@ -1,13 +1,16 @@
 mod uniffi_impl {
 	use std::sync::Arc;
 
-	use lightning::offers::{offer::Offer as LdkOffer, refund::Refund as LdkRefund};
+	use lightning::offers::{
+		invoice::Bolt12Invoice as LdkBolt12Invoice, offer::Offer as LdkOffer,
+		refund::Refund as LdkRefund,
+	};
 	use lightning_invoice::{
 		Bolt11Invoice as LdkBolt11Invoice, Bolt11InvoiceDescription as LdkBolt11InvoiceDescription,
 	};
 
 	use crate::error::Error;
-	use crate::ffi::{Bolt11Invoice, Bolt11InvoiceDescription, Offer, Refund};
+	use crate::ffi::{Bolt11Invoice, Bolt11InvoiceDescription, Bolt12Invoice, Offer, Refund};
 
 	pub trait UniffiType {
 		type LdkType;
@@ -79,6 +82,20 @@ mod uniffi_impl {
 		}
 	}
 
+	impl UniffiType for Arc<Bolt12Invoice> {
+		type LdkType = LdkBolt12Invoice;
+
+		fn from_ldk(ldk_value: Self::LdkType) -> Self {
+			Arc::new(Bolt12Invoice { inner: ldk_value })
+		}
+	}
+
+	impl UniffiConversionType for Arc<Bolt12Invoice> {
+		fn as_ldk(&self) -> Self::LdkType {
+			self.inner.clone()
+		}
+	}
+
 	pub fn maybe_convert<T: UniffiConversionType>(value: &T) -> T::LdkType {
 		value.as_ldk()
 	}