Prune route hints and blinded paths in trampoline onion (#686)

When using trampoline, the route hints or blinded paths may not all fit inside the onion. If that's the case, we prune some of them until it fits.

src/commonMain/kotlin/fr/acinq/lightning/crypto/sphinx/Sphinx.kt

@@ -214,7 +214,7 @@ object Sphinx {
             is Either.Right -> packet.value.payload.size()
         }
 
-        require(payload.size <= packetLength - MacLength) { "packet payload cannot exceed ${packetLength - MacLength} bytes" }
+        require(payload.size <= packetLength - MacLength) { "packet payload cannot exceed ${packetLength - MacLength} bytes, is ${payload.size} bytes" }
 
         val (currentMac, currentPayload) = when (packet) {
             // Packet construction starts with an empty mac and random payload.

src/commonMain/kotlin/fr/acinq/lightning/payment/OutgoingPaymentPacket.kt

@@ -18,6 +18,7 @@ import fr.acinq.lightning.router.Hop
 import fr.acinq.lightning.router.NodeHop
 import fr.acinq.lightning.utils.UUID
 import fr.acinq.lightning.wire.FailureMessage
+import fr.acinq.lightning.wire.OnionPaymentPayloadTlv
 import fr.acinq.lightning.wire.OnionRoutingPacket
 import fr.acinq.lightning.wire.PaymentOnion
 
@@ -72,7 +73,7 @@ object OutgoingPaymentPacket {
         // NB: the final payload will never reach the recipient, since the next-to-last trampoline hop will convert that to a legacy payment
         // We use the smallest final payload possible, otherwise we may overflow the trampoline onion size.
         val dummyFinalPayload = PaymentOnion.FinalPayload.Standard.createSinglePartPayload(finalPayload.amount, finalPayload.expiry, finalPayload.paymentSecret, null)
-        val (firstAmount, firstExpiry, payloads) = hops.drop(1).reversed().fold(Triple(finalPayload.amount, finalPayload.expiry, listOf<PaymentOnion.PerHopPayload>(dummyFinalPayload))) { triple, hop ->
+        val (firstAmount, firstExpiry, initialPayloads) = hops.drop(1).reversed().fold(Triple(finalPayload.amount, finalPayload.expiry, listOf<PaymentOnion.PerHopPayload>(dummyFinalPayload))) { triple, hop ->
             val (amount, expiry, payloads) = triple
             val payload = when (payloads.size) {
                 // The next-to-last trampoline hop must include invoice data to indicate the conversion to a legacy payment.
@@ -81,8 +82,20 @@ object OutgoingPaymentPacket {
             }
             Triple(amount + hop.fee(amount), expiry + hop.cltvExpiryDelta, listOf(payload) + payloads)
         }
+        var payloads = initialPayloads
         val nodes = hops.map { it.nextNodeId }
-        val onion = buildOnion(nodes, payloads, invoice.paymentHash, payloadLength = null)
+        var onion = buildOnion(nodes, payloads, invoice.paymentHash, payloadLength = null)
+        // Ensure that this onion can fit inside the outer 1300 bytes onion. The outer onion fields need ~150 bytes and we add some safety margin.
+        while (onion.packet.payload.size() > 1000) {
+            payloads = payloads.map { payload -> when (payload) {
+                is PaymentOnion.RelayToNonTrampolinePayload -> payload.copy(records = payload.records.copy(records = payload.records.records.map { when (it) {
+                    is OnionPaymentPayloadTlv.InvoiceRoutingInfo -> OnionPaymentPayloadTlv.InvoiceRoutingInfo(it.extraHops.dropLast(1))
+                    else -> it
+                } }.toSet()))
+                else -> payload
+            } }
+            onion = buildOnion(nodes, payloads, invoice.paymentHash, payloadLength = null)
+        }
         return Triple(firstAmount, firstExpiry, onion)
     }
 
@@ -97,8 +110,16 @@ object OutgoingPaymentPacket {
      * @param finalExpiry cltv expiry that should be received by the final recipient.
      */
     fun buildTrampolineToNonTrampolinePacket(invoice: Bolt12Invoice, hop: NodeHop, finalAmount: MilliSatoshi, finalExpiry: CltvExpiry): Triple<MilliSatoshi, CltvExpiry, PacketAndSecrets> {
-        val payload = PaymentOnion.RelayToBlindedPayload.create(finalAmount, finalExpiry, invoice)
-        val onion = buildOnion(listOf(hop.nodeId), listOf(payload), invoice.paymentHash, payloadLength = null)
+        var payload = PaymentOnion.RelayToBlindedPayload.create(finalAmount, finalExpiry, invoice)
+        var onion = buildOnion(listOf(hop.nodeId), listOf(payload), invoice.paymentHash, payloadLength = null)
+        // Ensure that this onion can fit inside the outer 1300 bytes onion. The outer onion fields need ~150 bytes and we add some safety margin.
+        while (onion.packet.payload.size() > 1000) {
+            payload = payload.copy(records = payload.records.copy(records = payload.records.records.map { when (it) {
+                is OnionPaymentPayloadTlv.OutgoingBlindedPaths -> OnionPaymentPayloadTlv.OutgoingBlindedPaths(it.paths.dropLast(1))
+                else -> it
+            } }.toSet()))
+            onion = buildOnion(listOf(hop.nodeId), listOf(payload), invoice.paymentHash, payloadLength = null)
+        }
         return Triple(finalAmount + hop.fee(finalAmount), finalExpiry + hop.cltvExpiryDelta, onion)
     }
 

src/commonTest/kotlin/fr/acinq/lightning/payment/PaymentPacketTestsCommon.kt

@@ -12,6 +12,7 @@ import fr.acinq.lightning.channel.states.Channel
 import fr.acinq.lightning.crypto.RouteBlinding
 import fr.acinq.lightning.crypto.sphinx.Sphinx
 import fr.acinq.lightning.crypto.sphinx.Sphinx.hash
+import fr.acinq.lightning.payment.OutgoingPaymentHandler.PaymentAttempt
 import fr.acinq.lightning.router.ChannelHop
 import fr.acinq.lightning.router.NodeHop
 import fr.acinq.lightning.tests.utils.LightningTestSuite
@@ -657,5 +658,14 @@ class PaymentPacketTestsCommon : LightningTestSuite() {
         val failure = IncomingPaymentPacket.decrypt(UpdateAddHtlc(randomBytes32(), 4, amountE, paymentHash, expiryE, onionE.packet), privE)
         assertEquals(Either.Left(FinalIncorrectCltvExpiry(invalidExpiry)), failure)
     }
+
+    @Test
+    fun `relay to blinded with many large blinded routes`() {
+        val invoice = Bolt12Invoice.fromString("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").get()
+        val (trampolineAmount, trampolineExpiry, trampolineOnion) = OutgoingPaymentPacket.buildTrampolineToNonTrampolinePacket(invoice, NodeHop(randomKey().publicKey(), randomKey().publicKey(), CltvExpiryDelta(444), 0.msat), finalAmount, finalExpiry)
+        val trampolinePayload = PaymentAttempt.TrampolinePayload(trampolineAmount, trampolineExpiry, randomBytes32(), trampolineOnion.packet)
+        val channelHops: List<ChannelHop> = listOf(ChannelHop(randomKey().publicKey(), randomKey().publicKey(), defaultChannelUpdate))
+        OutgoingPaymentPacket.buildCommand(UUID.randomUUID(), randomBytes32(), channelHops, trampolinePayload.createFinalPayload(finalAmount))
+    }
 }