Populate response fields when decoding a BOLT12 invoice

Following review feedback: the BOLT12 path previously only validated
the invoice and reported `kind`, returning no other data. It now
extracts the fields that map onto `DecodeInvoiceResponse` -- signing
pubkey, payment hash, amount, creation time, relative expiry,
description, fallback address, invoice features, and expiry status.

BOLT11-only fields (`payment_secret`, `route_hints`, `currency`, etc.)
remain empty for BOLT12 invoices.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: vincenzopalazzo

ldk-server-grpc/src/api.rs

@@ -1122,7 +1122,8 @@ pub struct DecodeInvoiceRequest {
 	pub invoice: ::prost::alloc::string::String,
 }
 /// The response for the `DecodeInvoice` RPC. On failure, a gRPC error status is returned.
-/// For a BOLT12 invoice only `kind` is populated; all other fields apply to BOLT11 invoices.
+/// `kind` indicates which invoice type was decoded; fields that do not apply to that type
+/// are left empty (e.g. `payment_secret` and `route_hints` are BOLT11-only).
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 #[cfg_attr(feature = "serde", serde(rename_all = "snake_case"))]
 #[cfg_attr(feature = "serde", serde(default))]

ldk-server-grpc/src/proto/api.proto

@@ -803,7 +803,8 @@ message DecodeInvoiceRequest {
 }
 
 // The response for the `DecodeInvoice` RPC. On failure, a gRPC error status is returned.
-// For a BOLT12 invoice only `kind` is populated; all other fields apply to BOLT11 invoices.
+// `kind` indicates which invoice type was decoded; fields that do not apply to that type
+// are left empty (e.g. `payment_secret` and `route_hints` are BOLT11-only).
 message DecodeInvoiceResponse {
   // The hex-encoded public key of the destination node.
   string destination = 1;

ldk-server/src/api/decode_invoice.rs

@@ -13,7 +13,7 @@ use std::sync::Arc;
 use hex::prelude::*;
 use ldk_node::lightning::offers::invoice::Bolt12Invoice;
 use ldk_node::lightning_invoice::Bolt11Invoice;
-use ldk_node::lightning_types::features::Bolt11InvoiceFeatures;
+use ldk_node::lightning_types::features::{Bolt11InvoiceFeatures, Bolt12InvoiceFeatures};
 use ldk_server_grpc::api::{DecodeInvoiceRequest, DecodeInvoiceResponse};
 use ldk_server_grpc::types::{Bolt11HopHint, Bolt11RouteHint};
 
@@ -47,11 +47,29 @@ fn decode_invoice(invoice: &str) -> Result<DecodeInvoiceResponse, LdkServerError
 ///
 /// Unlike offers and BOLT11 invoices, a BOLT12 invoice has no human-readable string
 /// encoding — it is exchanged as raw bytes — so the input is expected to be hex-encoded.
-/// Only the `kind` field is populated for a BOLT12 invoice.
+/// Fields that do not apply to BOLT12 invoices (e.g. `payment_secret`, `route_hints`) are
+/// left at their default empty values.
 fn decode_bolt12_invoice(invoice: &str) -> Option<DecodeInvoiceResponse> {
 	let bytes = Vec::<u8>::from_hex(invoice).ok()?;
-	Bolt12Invoice::try_from(bytes).ok()?;
-	Some(DecodeInvoiceResponse { kind: INVOICE_KIND_BOLT12.to_string(), ..Default::default() })
+	let invoice = Bolt12Invoice::try_from(bytes).ok()?;
+
+	let features = decode_features(invoice.invoice_features().le_flags(), |bytes| {
+		Bolt12InvoiceFeatures::from_le_bytes(bytes).to_string()
+	});
+
+	Some(DecodeInvoiceResponse {
+		destination: invoice.signing_pubkey().to_string(),
+		payment_hash: invoice.payment_hash().0.to_lower_hex_string(),
+		amount_msat: Some(invoice.amount_msats()),
+		timestamp: invoice.created_at().as_secs(),
+		expiry: invoice.relative_expiry().as_secs(),
+		description: invoice.description().map(|d| d.to_string()),
+		fallback_address: invoice.fallbacks().into_iter().next().map(|a| a.to_string()),
+		features,
+		is_expired: invoice.is_expired(),
+		kind: INVOICE_KIND_BOLT12.to_string(),
+		..Default::default()
+	})
 }
 
 fn decode_bolt11_invoice(invoice: &Bolt11Invoice) -> DecodeInvoiceResponse {
@@ -152,11 +170,18 @@ mod tests {
 		PublicKey::from_secret_key(&secp, &SecretKey::from_slice(&[byte; 32]).unwrap())
 	}
 
+	/// The keypair the sample BOLT12 invoice is signed with; its public key is the
+	/// invoice's `signing_pubkey`.
+	fn signing_keypair() -> Keypair {
+		let secp = Secp256k1::new();
+		Keypair::from_secret_key(&secp, &SecretKey::from_slice(&[43; 32]).unwrap())
+	}
+
 	/// Builds a signed BOLT12 invoice and returns it hex-encoded, matching how a BOLT12
 	/// invoice would be supplied to `DecodeInvoice`.
 	fn sample_bolt12_invoice_hex() -> String {
 		let secp = Secp256k1::new();
-		let keys = Keypair::from_secret_key(&secp, &SecretKey::from_slice(&[43; 32]).unwrap());
+		let keys = signing_keypair();
 
 		let payment_paths = vec![BlindedPaymentPath::from_blinded_path_and_payinfo(
 			pubkey(40),
@@ -203,8 +228,11 @@ mod tests {
 	}
 
 	#[test]
-	fn decodes_bolt12_invoice_with_bolt12_kind() {
+	fn decodes_bolt12_invoice_and_populates_fields() {
 		let response = decode_invoice(&sample_bolt12_invoice_hex()).unwrap();
 		assert_eq!(response.kind, INVOICE_KIND_BOLT12);
+		assert_eq!(response.destination, signing_keypair().public_key().to_string());
+		assert_eq!(response.payment_hash, "2a".repeat(32));
+		assert_eq!(response.amount_msat, Some(1_000));
 	}
 }