inbound_payment: Add utility to get payment preimage given hash/secret

User-requested feature

lightning/src/ln/channelmanager.rs

@@ -73,12 +73,14 @@ use core::ops::Deref;
 use std::time::Instant;
 
 mod inbound_payment {
+	use alloc::string::ToString;
 	use bitcoin::hashes::{Hash, HashEngine};
 	use bitcoin::hashes::cmp::fixed_time_eq;
 	use bitcoin::hashes::hmac::{Hmac, HmacEngine};
 	use bitcoin::hashes::sha256::Hash as Sha256;
 	use chain::keysinterface::{KeyMaterial, KeysInterface, Sign};
 	use ln::{PaymentHash, PaymentPreimage, PaymentSecret};
+	use ln::channelmanager::APIError;
 	use ln::msgs;
 	use ln::msgs::MAX_VALUE_MSAT;
 	use util::chacha20::ChaCha20;
@@ -288,6 +290,23 @@ mod inbound_payment {
 		Ok(payment_preimage)
 	}
 
+	pub(super) fn get_payment_preimage(payment_hash: PaymentHash, payment_secret: PaymentSecret, keys: &ExpandedKey) -> Result<PaymentPreimage, APIError> {
+		let (iv_bytes, metadata_bytes) = decrypt_metadata(payment_secret, keys);
+
+		match Method::from_bits((metadata_bytes[0] & 0b1110_0000) >> METHOD_TYPE_OFFSET) {
+			Ok(Method::LdkPaymentHash) => {
+				derive_ldk_payment_preimage(payment_hash, &iv_bytes, &metadata_bytes, keys)
+					.map_err(|bad_preimage_bytes| APIError::APIMisuseError {
+						err: format!("Payment hash {} did not match decoded preimage {}", log_bytes!(payment_hash.0), log_bytes!(bad_preimage_bytes))
+					})
+			},
+			Ok(Method::UserPaymentHash) => Err(APIError::APIMisuseError {
+				err: "Expected payment type to be LdkPaymentHash, instead got UserPaymentHash".to_string()
+			}),
+			Err(other) => Err(APIError::APIMisuseError { err: format!("Unknown payment type: {}", other) }),
+		}
+	}
+
 	fn decrypt_metadata(payment_secret: PaymentSecret, keys: &ExpandedKey) -> ([u8; IV_LEN], [u8; METADATA_LEN]) {
 		let mut iv_bytes = [0; IV_LEN];
 		let (iv_slice, encrypted_metadata_bytes) = payment_secret.0.split_at(IV_LEN);
@@ -5097,6 +5116,14 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 		self.set_payment_hash_secret_map(payment_hash, None, min_value_msat, invoice_expiry_delta_secs)
 	}
 
+	/// Gets an LDK-generated payment preimage from a payment hash and payment secret that were
+	/// previously returned from [`create_inbound_payment`].
+	///
+	/// [`create_inbound_payment`]: Self::create_inbound_payment
+	pub fn get_payment_preimage(&self, payment_hash: PaymentHash, payment_secret: PaymentSecret) -> Result<PaymentPreimage, APIError> {
+		inbound_payment::get_payment_preimage(payment_hash, payment_secret, &self.inbound_payment_key)
+	}
+
 	#[cfg(any(test, feature = "fuzztarget", feature = "_test_utils"))]
 	pub fn get_and_clear_pending_events(&self) -> Vec<events::Event> {
 		let events = core::cell::RefCell::new(Vec::new());

lightning/src/ln/payment_tests.rs

@@ -15,9 +15,10 @@ use chain::{ChannelMonitorUpdateErr, Confirm, Listen, Watch};
 use chain::channelmonitor::{ANTI_REORG_DELAY, ChannelMonitor, LATENCY_GRACE_PERIOD_BLOCKS};
 use chain::transaction::OutPoint;
 use ln::channelmanager::{BREAKDOWN_TIMEOUT, ChannelManager, ChannelManagerReadArgs, PaymentId, PaymentSendFailure};
-use ln::features::InitFeatures;
+use ln::features::{InitFeatures, InvoiceFeatures};
 use ln::msgs;
 use ln::msgs::ChannelMessageHandler;
+use routing::router::{Payee, get_route};
 use util::events::{ClosureReason, Event, MessageSendEvent, MessageSendEventsProvider};
 use util::test_utils;
 use util::errors::APIError;
@@ -706,3 +707,34 @@ fn test_fulfill_restart_failure() {
 	// it had already considered the payment fulfilled, and now they just got free money.
 	assert!(nodes[0].node.get_and_clear_pending_events().is_empty());
 }
+
+#[test]
+fn get_ldk_payment_preimage() {
+	// Ensure that `ChannelManager::get_payment_preimage` can successfully be used to claim a payment.
+	let chanmon_cfgs = create_chanmon_cfgs(2);
+	let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
+	let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None]);
+	let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs);
+	create_announced_chan_between_nodes(&nodes, 0, 1, InitFeatures::known(), InitFeatures::known());
+
+	let amt_msat = 60_000;
+	let expiry_secs = 60 * 60;
+	let (payment_hash, payment_secret) = nodes[1].node.create_inbound_payment(Some(amt_msat), expiry_secs).unwrap();
+
+	let payee = Payee::from_node_id(nodes[1].node.get_our_node_id())
+		.with_features(InvoiceFeatures::known());
+	let scorer = test_utils::TestScorer::with_fixed_penalty(0);
+	let route = get_route(
+		&nodes[0].node.get_our_node_id(), &payee, &nodes[0].network_graph,
+		Some(&nodes[0].node.list_usable_channels().iter().collect::<Vec<_>>()),
+		amt_msat, TEST_FINAL_CLTV, nodes[0].logger, &scorer).unwrap();
+	let _payment_id = nodes[0].node.send_payment(&route, payment_hash, &Some(payment_secret)).unwrap();
+	check_added_monitors!(nodes[0], 1);
+
+	// Make sure to use `get_payment_preimage`
+	let payment_preimage = nodes[1].node.get_payment_preimage(payment_hash, payment_secret).unwrap();
+	let mut events = nodes[0].node.get_and_clear_pending_msg_events();
+	assert_eq!(events.len(), 1);
+	pass_along_path(&nodes[0], &[&nodes[1]], amt_msat, payment_hash, Some(payment_secret), events.pop().unwrap(), true, Some(payment_preimage));
+	claim_payment_along_route(&nodes[0], &[&[&nodes[1]]], false, payment_preimage);
+}