f dry up payment method matching

Author: dunxen

lightning/src/ln/inbound_payment.rs

@@ -269,8 +269,9 @@ pub(super) fn verify<L: Deref>(payment_hash: PaymentHash, payment_data: &msgs::F
 
 	// Make sure to check the HMAC before doing the other checks below, to mitigate timing attacks.
 	let mut payment_preimage = None;
+
 	match payment_type_res {
-		Ok(Method::UserPaymentHash) => {
+		Ok(Method::UserPaymentHash) | Ok(Method::UserPaymentHashCustomFinalCltv) => {
 			let mut hmac = HmacEngine::<Sha256>::new(&keys.user_pmt_hash_key);
 			hmac.input(&metadata_bytes[..]);
 			hmac.input(&payment_hash.0);
@@ -279,7 +280,7 @@ pub(super) fn verify<L: Deref>(payment_hash: PaymentHash, payment_data: &msgs::F
 				return Err(())
 			}
 		},
-		Ok(Method::LdkPaymentHash) => {
+		Ok(Method::LdkPaymentHash) | Ok(Method::LdkPaymentHashCustomFinalCltv) => {
 			match derive_ldk_payment_preimage(payment_hash, &iv_bytes, &metadata_bytes, keys) {
 				Ok(preimage) => payment_preimage = Some(preimage),
 				Err(bad_preimage_bytes) => {
@@ -288,40 +289,23 @@ pub(super) fn verify<L: Deref>(payment_hash: PaymentHash, payment_data: &msgs::F
 				}
 			}
 		},
-		Ok(Method::UserPaymentHashCustomFinalCltv) => {
-			let mut hmac = HmacEngine::<Sha256>::new(&keys.user_pmt_hash_key);
-			hmac.input(&metadata_bytes[..]);
-			hmac.input(&payment_hash.0);
-			if !fixed_time_eq(&iv_bytes, &Hmac::from_engine(hmac).into_inner().split_at_mut(IV_LEN).0) {
-				log_trace!(logger, "Failing HTLC with user-generated payment_hash {}: unexpected payment_secret", log_bytes!(payment_hash.0));
-				return Err(())
-			}
+		Err(unknown_bits) => {
+			log_trace!(logger, "Failing HTLC with payment hash {} due to unknown payment type {}", log_bytes!(payment_hash.0), unknown_bits);
+			return Err(());
+		}
+	}
 
+	// Match again to check for custom `min_final_cltv_expiry_delta`.
+	match payment_type_res {
+		Ok(Method::UserPaymentHashCustomFinalCltv) | Ok(Method::LdkPaymentHashCustomFinalCltv) => {
 			min_final_cltv_expiry_delta = Some(min_final_cltv_expiry_delta_from_metadata(metadata_bytes));
 			// Zero out bits reserved for first 4 bits of `min_final_cltv_expiry_delta`, leaving one bit
 			// which is the most significant bit of `min_amt_msat`.
 			amt_msat_bytes[0] &= 0b0000_0001;
 			// Zero out bits reserved for the last 8 bits of `min_final_cltv_expiry_delta`.
 			expiry_bytes[0] &= 0;
-		},
-		Ok(Method::LdkPaymentHashCustomFinalCltv) => {
-			match derive_ldk_payment_preimage(payment_hash, &iv_bytes, &metadata_bytes, keys) {
-				Ok(preimage) => payment_preimage = Some(preimage),
-				Err(bad_preimage_bytes) => {
-					log_trace!(logger, "Failing HTLC with payment_hash {} due to mismatching preimage {}", log_bytes!(payment_hash.0), log_bytes!(bad_preimage_bytes));
-					return Err(())
-				}
-			}
-			min_final_cltv_expiry_delta = Some(min_final_cltv_expiry_delta_from_metadata(metadata_bytes));
-			// Zero out bits reserved for first 4 bits of `min_final_cltv_expiry_delta`.
-			amt_msat_bytes[0] &= 0b1110_0001;
-			// Zero out bits reserved for the last 8 bits of `min_final_cltv_expiry_delta`.
-			expiry_bytes[0] &= 0;
-		},
-		Err(unknown_bits) => {
-			log_trace!(logger, "Failing HTLC with payment hash {} due to unknown payment type {}", log_bytes!(payment_hash.0), unknown_bits);
-			return Err(());
 		}
+		_ => {}
 	}
 
 	let min_amt_msat: u64 = u64::from_be_bytes(amt_msat_bytes.into());