Add custom offers

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

@@ -248,6 +248,6 @@ data class NodeParams(
         val blindingSecret = PrivateKey(Crypto.sha256("bolt 12 default offer".toByteArray(Charsets.UTF_8).byteVector() + trampolineNodeId.value + nodePrivateKey.value).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.
-        return OfferTypes.Offer.createBlindedOffer(amount = null, description = null, this, trampolineNodeId, Features.empty, blindingSecret)
+        return OfferTypes.Offer.createBlindedOffer(amount = null, description = null, this, trampolineNodeId, Features.empty, blindingSecret, pathId = null)
     }
 }

src/commonMain/kotlin/fr/acinq/lightning/io/Peer.kt

@@ -705,6 +705,17 @@ class Peer(
         return incomingPaymentHandler.createInvoice(paymentPreimage, amount, description, extraHops, expirySeconds)
     }
 
+    /** Creates a custom offer and register it with the `offerManager`.
+     *  @param secret A random private key for creating the blinded path of the offer. Must be unique to this offer.
+     *  The offer returned is deterministic, if you need to persist you just need to save the parameters used to create it.
+     */
+    fun createOffer(secret: PrivateKey, amount: MilliSatoshi?, description: String?): OfferTypes.Offer {
+        val pathId = secret.value
+        val (offer, _) = OfferTypes.Offer.createBlindedOffer(amount, description, nodeParams, remoteNodeId, Features.empty, secret, pathId)
+        offerManager.registerOffer(offer, pathId)
+        return offer
+    }
+
     // The (node_id, fcm_token) tuple only needs to be registered once.
     // And after that, only if the tuple changes (e.g. different fcm_token).
     fun registerFcmToken(token: String?) {

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

@@ -779,6 +779,7 @@ object OfferTypes {
              * @param trampolineNodeId our trampoline node.
              * @param features features that should be advertised in the offer.
              * @param blindingSecret session key used for the blinded path included in the offer.
+             * @param pathId path id for this offer's blinded path.
              */
             fun createBlindedOffer(
                 amount: MilliSatoshi?,
@@ -787,11 +788,12 @@ object OfferTypes {
                 trampolineNodeId: PublicKey,
                 features: Features,
                 blindingSecret: PrivateKey,
+                pathId: ByteVector32?,
                 additionalTlvs: Set<OfferTlv> = setOf(),
                 customTlvs: Set<GenericTlv> = setOf()
             ): Pair<Offer, PrivateKey> {
                 if (description == null) require(amount == null) { "an offer description must be provided if the amount isn't null" }
-                val blindedRouteDetails = OnionMessages.buildRouteToRecipient(blindingSecret, listOf(OnionMessages.IntermediateNode(EncodedNodeId.WithPublicKey.Plain(trampolineNodeId))), OnionMessages.Destination.Recipient(EncodedNodeId.WithPublicKey.Wallet(nodeParams.nodeId), null))
+                val blindedRouteDetails = OnionMessages.buildRouteToRecipient(blindingSecret, listOf(OnionMessages.IntermediateNode(EncodedNodeId.WithPublicKey.Plain(trampolineNodeId))), OnionMessages.Destination.Recipient(EncodedNodeId.WithPublicKey.Wallet(nodeParams.nodeId), pathId))
                 val tlvs: Set<OfferTlv> = setOfNotNull(
                     if (nodeParams.chainHash != Block.LivenetGenesisBlock.hash) OfferChains(listOf(nodeParams.chainHash)) else null,
                     amount?.let { OfferAmount(it) },

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

@@ -4,6 +4,7 @@ import fr.acinq.bitcoin.ByteVector
 import fr.acinq.bitcoin.PrivateKey
 import fr.acinq.bitcoin.utils.Either
 import fr.acinq.lightning.*
+import fr.acinq.lightning.Lightning.randomBytes32
 import fr.acinq.lightning.Lightning.randomKey
 import fr.acinq.lightning.crypto.RouteBlinding
 import fr.acinq.lightning.crypto.sphinx.DecryptedPacket
@@ -51,15 +52,17 @@ class OfferManagerTestsCommon : LightningTestSuite() {
 
     private fun createOffer(offerManager: OfferManager, amount: MilliSatoshi? = null): OfferTypes.Offer {
         val blindingSecret = randomKey()
+        val pathId = randomBytes32()
         val (offer, _) = OfferTypes.Offer.createBlindedOffer(
             amount,
             "Blockaccino",
             offerManager.nodeParams,
             offerManager.walletParams.trampolineNode.id,
             offerManager.nodeParams.features,
             blindingSecret,
+            pathId,
         )
-        offerManager.registerOffer(offer, null)
+        offerManager.registerOffer(offer, pathId)
         return offer
     }