Generate default deterministic offer

src/commonMain/kotlin/fr/acinq/lightning/NodeParams.kt

@@ -1,9 +1,7 @@
 package fr.acinq.lightning
 
 import co.touchlab.kermit.Logger
-import fr.acinq.bitcoin.Chain
-import fr.acinq.bitcoin.PublicKey
-import fr.acinq.bitcoin.Satoshi
+import fr.acinq.bitcoin.*
 import fr.acinq.lightning.Lightning.nodeFee
 import fr.acinq.lightning.blockchain.fee.FeerateTolerance
 import fr.acinq.lightning.blockchain.fee.OnChainFeeConf
@@ -14,6 +12,9 @@ import fr.acinq.lightning.payment.LiquidityPolicy
 import fr.acinq.lightning.utils.msat
 import fr.acinq.lightning.utils.sat
 import fr.acinq.lightning.utils.toMilliSatoshi
+import fr.acinq.lightning.wire.OfferTypes
+import io.ktor.utils.io.charsets.*
+import io.ktor.utils.io.core.*
 import kotlinx.coroutines.flow.MutableSharedFlow
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.SharedFlow
@@ -228,4 +229,21 @@ data class NodeParams(
         minFinalCltvExpiryDelta = Bolt11Invoice.DEFAULT_MIN_FINAL_EXPIRY_DELTA,
         bolt12invoiceExpiry = 60.seconds
     )
+
+    /**
+     * We generate a default, deterministic Bolt 12 offer based on the node's seed and its trampoline node.
+     * This offer will stay valid after restoring the seed on a different device.
+     * We also return the path_id included in this offer, which should be used to route onion messages.
+     */
+    fun defaultOffer(trampolineNode: NodeUri): Pair<ByteVector32, OfferTypes.Offer> {
+        // We generate a deterministic path_id based on:
+        //  - a custom tag indicating that this is used in the Bolt 12 context
+        //  - our trampoline node, which is used as an introduction node for the offer's blinded path
+        //  - our private key, which ensures that nobody else can generate the same path_id
+        val pathId = Crypto.sha256("bolt 12 default offer".toByteArray(Charsets.UTF_8) + trampolineNode.id.value.toByteArray() + nodePrivateKey.value.toByteArray()).byteVector32()
+        // We don't use our currently activated features, otherwise the offer would change when we add support for new features.
+        // If we add a new feature that we would like to use by default, we will need to explicitly create a new offer.
+        val offer = OfferTypes.Offer.createBlindedOffer(amount = null, description = null, this, trampolineNode, Features.empty, pathId)
+        return Pair(pathId, offer)
+    }
 }

src/commonMain/kotlin/fr/acinq/lightning/payment/Bolt12Invoice.kt

@@ -37,7 +37,7 @@ data class Bolt12Invoice(val records: TlvStream<InvoiceTlv>) : PaymentRequest()
     override val amount: MilliSatoshi? = records.get<InvoiceAmount>()?.amount
     val nodeId: PublicKey = records.get<InvoiceNodeId>()!!.nodeId
     override val paymentHash: ByteVector32 = records.get<InvoicePaymentHash>()!!.hash
-    val description: String = invoiceRequest.offer.description
+    val description: String? = invoiceRequest.offer.description
     val createdAtSeconds: Long = records.get<InvoiceCreatedAt>()!!.timestampSeconds
     val relativeExpirySeconds: Long = records.get<InvoiceRelativeExpiry>()?.seconds ?: DEFAULT_EXPIRY_SECONDS
 

src/commonMain/kotlin/fr/acinq/lightning/wire/OfferTypes.kt

@@ -714,15 +714,15 @@ object OfferTypes {
         } else {
             null // TODO: add exchange rates
         }
-        val description: String = records.get<OfferDescription>()!!.description
+        val description: String? = records.get<OfferDescription>()?.description
         val features: Features = records.get<OfferFeatures>()?.features ?: Features.empty
         val expirySeconds: Long? = records.get<OfferAbsoluteExpiry>()?.absoluteExpirySeconds
         private val paths: List<ContactInfo.BlindedPath>? = records.get<OfferPaths>()?.paths
         val issuer: String? = records.get<OfferIssuer>()?.issuer
         val quantityMax: Long? = records.get<OfferQuantityMax>()?.max?.let { if (it == 0L) Long.MAX_VALUE else it }
-        val nodeId: PublicKey = records.get<OfferNodeId>()!!.publicKey
-
-        val contactInfos: List<ContactInfo> = paths ?: listOf(ContactInfo.RecipientNodeId(nodeId))
+        val nodeId: PublicKey? = records.get<OfferNodeId>()?.publicKey
+        // A valid offer must contain a blinded path or a nodeId.
+        val contactInfos: List<ContactInfo> = paths ?: listOf(ContactInfo.RecipientNodeId(nodeId!!))
 
         fun encode(): String {
             val data = tlvSerializer.write(records)
@@ -737,65 +737,70 @@ object OfferTypes {
             val hrp = "lno"
 
             /**
-             * @param amount      amount if it can be determined at offer creation time.
-             * @param description description of the offer.
-             * @param nodeId      the nodeId to use for this offer, which should be different from our public nodeId if we're hiding behind a blinded route.
-             * @param features    invoice features.
-             * @param chain       chain on which the offer is valid.
+             * Create an offer without using a blinded path to hide our nodeId.
+             *
+             * @param amount amount if it can be determined at offer creation time.
+             * @param description description of the offer (may be null if [amount] is also null).
+             * @param nodeId the nodeId to use for this offer.
+             * @param features invoice features.
+             * @param chain chain on which the offer is valid.
              */
-            internal fun createInternal(
+            internal fun createNonBlindedOffer(
                 amount: MilliSatoshi?,
-                description: String,
+                description: String?,
                 nodeId: PublicKey,
                 features: Features,
                 chain: BlockHash,
                 additionalTlvs: Set<OfferTlv> = setOf(),
                 customTlvs: Set<GenericTlv> = setOf()
             ): Offer {
+                if (description == null) require(amount == null) { "an offer description must be provided if the amount isn't null" }
                 val tlvs: Set<OfferTlv> = setOfNotNull(
                     if (chain != Block.LivenetGenesisBlock.hash) OfferChains(listOf(chain)) else null,
                     amount?.let { OfferAmount(it) },
-                    OfferDescription(description),
+                    description?.let { OfferDescription(it) },
                     if (features != Features.empty) OfferFeatures(features) else null,
-                    OfferNodeId(nodeId) // TODO: If the spec allows it, removes `OfferNodeId` when we already set `OfferPaths`.
-                ) + additionalTlvs
-                return Offer(TlvStream(tlvs, customTlvs))
+                    OfferNodeId(nodeId)
+                )
+                return Offer(TlvStream(tlvs + additionalTlvs, customTlvs))
             }
 
             /**
              * Create an offer using a single-hop blinded path going through our trampoline node.
              *
              * @param amount amount if it can be determined at offer creation time.
-             * @param description description of the offer.
+             * @param description description of the offer (may be null if [amount] is also null).
              * @param nodeParams our node parameters.
              * @param trampolineNode our trampoline node.
+             * @param features features that should be advertised in the offer.
              * @param pathId pathId on which we will listen for invoice requests.
              */
             fun createBlindedOffer(
                 amount: MilliSatoshi?,
-                description: String,
+                description: String?,
                 nodeParams: NodeParams,
                 trampolineNode: NodeUri,
+                features: Features,
                 pathId: ByteVector32,
                 additionalTlvs: Set<OfferTlv> = setOf(),
                 customTlvs: Set<GenericTlv> = setOf()
             ): Offer {
+                if (description == null) require(amount == null) { "an offer description must be provided if the amount isn't null" }
                 val path = OnionMessages.buildRoute(PrivateKey(pathId), listOf(OnionMessages.IntermediateNode(trampolineNode.id, ShortChannelId.peerId(nodeParams.nodeId))), OnionMessages.Destination.Recipient(nodeParams.nodeId, pathId))
-                val offerNodeId = path.blindedNodeIds.last()
-                return createInternal(
-                    amount,
-                    description,
-                    offerNodeId,
-                    nodeParams.features.bolt12Features(),
-                    nodeParams.chainHash,
-                    additionalTlvs + OfferPaths(listOf(ContactInfo.BlindedPath(path))),
-                    customTlvs
+                val tlvs: Set<OfferTlv> = setOfNotNull(
+                    if (nodeParams.chainHash != Block.LivenetGenesisBlock.hash) OfferChains(listOf(nodeParams.chainHash)) else null,
+                    amount?.let { OfferAmount(it) },
+                    description?.let { OfferDescription(it) },
+                    if (features.bolt12Features() != Features.empty) OfferFeatures(features.bolt12Features()) else null,
+                    // Note that we don't include an offer_node_id since we're using a blinded path.
+                    OfferPaths(listOf(ContactInfo.BlindedPath(path))),
                 )
+                return Offer(TlvStream(tlvs + additionalTlvs, customTlvs))
             }
 
             fun validate(records: TlvStream<OfferTlv>): Either<InvalidTlvPayload, Offer> {
-                if (records.get<OfferDescription>() == null) return Left(MissingRequiredTlv(10L))
-                if (records.get<OfferNodeId>() == null) return Left(MissingRequiredTlv(22L))
+                if (records.get<OfferDescription>() == null && records.get<OfferAmount>() != null) return Left(MissingRequiredTlv(10))
+                if (records.get<OfferNodeId>() == null && records.get<OfferPaths>() == null) return Left(MissingRequiredTlv(22))
                 if (records.unknown.any { it.tag >= 80 }) return Left(ForbiddenTlv(records.unknown.find { it.tag >= 80 }!!.tag))
                 return Right(Offer(records))
             }

src/commonTest/kotlin/fr/acinq/lightning/payment/Bolt12InvoiceTestsCommon.kt

@@ -84,7 +84,7 @@ class Bolt12InvoiceTestsCommon : LightningTestSuite() {
         val nodeKey = randomKey()
         val payerKey = randomKey()
         val chain = BlockHash(randomBytes32())
-        val offer = Offer.createInternal(10000.msat, "test offer", nodeKey.publicKey(), Features.empty, chain)
+        val offer = Offer.createNonBlindedOffer(10000.msat, "test offer", nodeKey.publicKey(), Features.empty, chain)
         val request = InvoiceRequest(offer, 11000.msat, 1, Features.empty, payerKey, chain)
         val invoice = Bolt12Invoice(
             request,
@@ -121,7 +121,7 @@ class Bolt12InvoiceTestsCommon : LightningTestSuite() {
         val nodeKey = randomKey()
         val payerKey = randomKey()
         val chain = BlockHash(randomBytes32())
-        val offer = Offer.createInternal(10000.msat, "test offer", nodeKey.publicKey(), Features.empty, chain)
+        val offer = Offer.createNonBlindedOffer(10000.msat, "test offer", nodeKey.publicKey(), Features.empty, chain)
         val basicRequest = InvoiceRequest(offer, 11000.msat, 1, Features.empty, payerKey, chain)
         val requestWithUnknownTlv = basicRequest.copy(records = TlvStream(basicRequest.records.records, setOf(GenericTlv(87, ByteVector.fromHex("0404")))))
         val invoice = Bolt12Invoice(
@@ -143,7 +143,7 @@ class Bolt12InvoiceTestsCommon : LightningTestSuite() {
         val nodeKey = randomKey()
         val payerKey = randomKey()
         val chain = BlockHash(randomBytes32())
-        val offer = Offer.createInternal(10000.msat, "test offer", nodeKey.publicKey(), Features.empty, chain)
+        val offer = Offer.createNonBlindedOffer(10000.msat, "test offer", nodeKey.publicKey(), Features.empty, chain)
         val request = InvoiceRequest(offer, 11000.msat, 1, Features.empty, payerKey, chain)
         val invoice = Bolt12Invoice(
             request,
@@ -189,7 +189,7 @@ class Bolt12InvoiceTestsCommon : LightningTestSuite() {
         val nodeKey = randomKey()
         val payerKey = randomKey()
         val chain = BlockHash(randomBytes32())
-        val offer = Offer.createInternal(15000.msat, "test offer", nodeKey.publicKey(), Features.empty, chain)
+        val offer = Offer.createNonBlindedOffer(15000.msat, "test offer", nodeKey.publicKey(), Features.empty, chain)
         val request = InvoiceRequest(offer, 15000.msat, 1, Features.empty, payerKey, chain)
         assertTrue(request.quantity_opt == null) // when paying for a single item, the quantity field must not be present
         val invoice = Bolt12Invoice(
@@ -271,7 +271,7 @@ class Bolt12InvoiceTestsCommon : LightningTestSuite() {
         val nodeKey = randomKey()
         val payerKey = randomKey()
         val chain = BlockHash(randomBytes32())
-        val offer = Offer.createInternal(5000.msat, "test offer", nodeKey.publicKey(), Features.empty, chain)
+        val offer = Offer.createNonBlindedOffer(5000.msat, "test offer", nodeKey.publicKey(), Features.empty, chain)
         val request = InvoiceRequest(offer, 5000.msat, 1, Features.empty, payerKey, chain)
         val invoice = Bolt12Invoice(
             request,
@@ -307,7 +307,6 @@ class Bolt12InvoiceTestsCommon : LightningTestSuite() {
         val nodeKey = randomKey()
         val tlvs = setOf(
             InvoiceRequestMetadata(ByteVector.fromHex("012345")),
-            OfferDescription("minimal invoice"),
             OfferNodeId(nodeKey.publicKey()),
             InvoiceRequestPayerId(randomKey().publicKey()),
             InvoicePaths(listOf(createPaymentBlindedRoute(randomKey().publicKey()).route)),
@@ -408,7 +407,7 @@ class Bolt12InvoiceTestsCommon : LightningTestSuite() {
         val payerKey = PrivateKey.fromHex("d817e8896c67d0bcabfdb93da7eb7fc698c829a181f994dd0ad866a8eda745e8")
         assertEquals(payerKey.publicKey(), PublicKey.fromHex("031ef4439f638914de79220483dda32dfb7a431e799a5ce5a7643fbd70b2118e4e"))
         val preimage = ByteVector32.fromValidHex("317d1fd8fec5f3ea23044983c2ba2a8043395b2a0790a815c9b12719aa5f1516")
-        val offer = Offer.createInternal(null, "minimal tip", nodeKey.publicKey(), Features.empty, Block.LivenetGenesisBlock.hash)
+        val offer = Offer.createNonBlindedOffer(null, "minimal tip", nodeKey.publicKey(), Features.empty, Block.LivenetGenesisBlock.hash)
         val encodedOffer = "lno1pg9k66twd9kkzmpqw35hq93pqf8l2vtlq5w87m4vqfnvtn82adk9wadfgratnp2wg7l7ha4u0gzqw"
         assertEquals(offer.toString(), encodedOffer)
         assertEquals(Offer.decode(encodedOffer).get(), offer)
@@ -446,7 +445,7 @@ class Bolt12InvoiceTestsCommon : LightningTestSuite() {
         val payerKey = PrivateKey.fromHex("0e00a9ef505292f90a0e8a7aa99d31750e885c42a3ef8866dd2bf97919aa3891")
         assertEquals(payerKey.publicKey(), PublicKey.fromHex("033e94f2afd568d128f02ece844ad4a0a1ddf2a4e3a08beb2dba11b3f1134b0517"))
         val preimage = ByteVector32.fromValidHex("09ad5e952ec39d45461ebdeceac206fb45574ae9054b5a454dd02c65f5ba1b7c")
-        val offer = Offer.createInternal(456000000.msat, "minimal offer", nodeKey.publicKey(), Features.empty, Block.LivenetGenesisBlock.hash)
+        val offer = Offer.createNonBlindedOffer(456000000.msat, "minimal offer", nodeKey.publicKey(), Features.empty, Block.LivenetGenesisBlock.hash)
         val encodedOffer = "lno1pqzpktszqq9q6mtfde5k6ctvyphkven9wgtzzq7y3tyhuz0newawkdds924x6pet2aexssdrf5je2g2het9xpgw275"
         assertEquals(offer.toString(), encodedOffer)
         assertEquals(Offer.decode(encodedOffer).get(), offer)

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

@@ -389,7 +389,7 @@ class PaymentPacketTestsCommon : LightningTestSuite() {
     @Test
     fun `build a trampoline payment to blinded paths`() {
         val features = Features(Feature.BasicMultiPartPayment to FeatureSupport.Optional)
-        val offer = OfferTypes.Offer.createInternal(finalAmount, "test offer", e, features, Block.LivenetGenesisBlock.hash)
+        val offer = OfferTypes.Offer.createNonBlindedOffer(finalAmount, "test offer", e, features, Block.LivenetGenesisBlock.hash)
         // E uses a 1-hop blinded path from its LSP.
         val (invoice, blindedRoute) = run {
             val payerKey = randomKey()