Refactor OfferManager tests

We add a helper function to decrypt the `pathId` included in the
invoice's blinded path.

Author: t-bast

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

@@ -63,6 +63,15 @@ class OfferManagerTestsCommon : LightningTestSuite() {
         return offer
     }
 
+    private fun decryptPathId(invoice: Bolt12Invoice, trampolineKey: PrivateKey): OfferPaymentMetadata.V1 {
+        val blindedRoute = invoice.blindedPaths.first().route.route
+        assertEquals(2, blindedRoute.encryptedPayloads.size)
+        val (_, nextBlinding) = RouteBlinding.decryptPayload(trampolineKey, blindedRoute.blindingKey, blindedRoute.encryptedPayloads.first()).right!!
+        val (lastPayload, _) = RouteBlinding.decryptPayload(TestConstants.Alice.nodeParams.nodePrivateKey, nextBlinding, blindedRoute.encryptedPayloads.last()).right!!
+        val pathId = RouteBlindingEncryptedData.read(lastPayload.toByteArray()).right!!.pathId!!
+        return OfferPaymentMetadata.fromPathId(TestConstants.Alice.nodeParams.nodeId, pathId) as OfferPaymentMetadata.V1
+    }
+
     @Test
     fun `pay offer through the same trampoline node`() = runSuspendTest {
         // Alice and Bob use the same trampoline node.
@@ -276,17 +285,8 @@ class OfferManagerTestsCommon : LightningTestSuite() {
         assertEquals(OfferInvoiceReceived(payOffer, payInvoice.invoice), bobOfferManager.eventsFlow.first())
         assertEquals(payOffer, payInvoice.payOffer)
 
-        val blindedRoute = payInvoice.invoice.blindedPaths.first().route.route
-        val (firstPayload, secondBlinding) = RouteBlinding.decryptPayload(aliceTrampolineKey, blindedRoute.blindingKey, blindedRoute.encryptedPayloads.first()).right!!
-        var blinding = secondBlinding
-        var lastPayload = firstPayload
-        for (encryptedPayload in blindedRoute.encryptedPayloads.drop(1)) {
-            val (payload, nextBlinding) = RouteBlinding.decryptPayload(TestConstants.Alice.nodeParams.nodePrivateKey, blinding, encryptedPayload).right!!
-            blinding = nextBlinding
-            lastPayload = payload
-        }
-        val pathId = RouteBlindingEncryptedData.read(lastPayload.toByteArray()).right!!.pathId!!
-        val metadata = OfferPaymentMetadata.fromPathId(TestConstants.Alice.nodeParams.nodeId, pathId) as OfferPaymentMetadata.V1
+        // The payer note is correctly included in the payment metadata.
+        val metadata = decryptPathId(payInvoice.invoice, aliceTrampolineKey)
         assertEquals(payerNote, metadata.payerNote)
     }
 
@@ -314,18 +314,10 @@ class OfferManagerTestsCommon : LightningTestSuite() {
         assertEquals(OfferInvoiceReceived(payOffer, payInvoice.invoice), bobOfferManager.eventsFlow.first())
         assertEquals(payOffer, payInvoice.payOffer)
 
-        val blindedRoute = payInvoice.invoice.blindedPaths.first().route.route
-        val (firstPayload, secondBlinding) = RouteBlinding.decryptPayload(aliceTrampolineKey, blindedRoute.blindingKey, blindedRoute.encryptedPayloads.first()).right!!
-        var blinding = secondBlinding
-        var lastPayload = firstPayload
-        for (encryptedPayload in blindedRoute.encryptedPayloads.drop(1)) {
-            val (payload, nextBlinding) = RouteBlinding.decryptPayload(TestConstants.Alice.nodeParams.nodePrivateKey, blinding, encryptedPayload).right!!
-            blinding = nextBlinding
-            lastPayload = payload
-        }
-        val pathId = RouteBlindingEncryptedData.read(lastPayload.toByteArray()).right!!.pathId!!
-        val metadata = OfferPaymentMetadata.fromPathId(TestConstants.Alice.nodeParams.nodeId, pathId) as OfferPaymentMetadata.V1
+        // The payer note is truncated in the payment metadata.
+        val metadata = decryptPathId(payInvoice.invoice, aliceTrampolineKey)
         assertEquals(64, metadata.payerNote!!.length)
         assertEquals(payerNote.take(63), metadata.payerNote!!.take(63))
     }
+
 }