Handle feature-less BOLT 11 invoices (#687)

We were not handling correctly feature-less invoices, which are
spec-compliant. We do reject invoices that don't have
`var_onion_optin`, but the check happens later. Instead, we currently
throw a `NullPointerException`.

The way we are checking requirements in the `init` block requires
lazy-init properties, otherwise the object initialization will fail
before any logic can happen.

Also, as per the spec, the feature tag must be skipped at serialization if
there are no features enabled.

Author: pm47

src/commonMain/kotlin/fr/acinq/lightning/payment/Bolt11Invoice.kt

@@ -21,25 +21,25 @@ data class Bolt11Invoice(
     val tags: List<TaggedField>,
     val signature: ByteVector
 ) : PaymentRequest() {
-    val chain: Chain? = prefixes.entries.firstOrNull { it.value == prefix }?.key
+    val chain: Chain? get() = prefixes.entries.firstOrNull { it.value == prefix }?.key
 
-    override val paymentHash: ByteVector32 = tags.find { it is TaggedField.PaymentHash }!!.run { (this as TaggedField.PaymentHash).hash }
+    override val paymentHash: ByteVector32 get() = tags.find { it is TaggedField.PaymentHash }!!.run { (this as TaggedField.PaymentHash).hash }
 
-    val paymentSecret: ByteVector32 = tags.find { it is TaggedField.PaymentSecret }!!.run { (this as TaggedField.PaymentSecret).secret }
+    val paymentSecret: ByteVector32 get() = tags.find { it is TaggedField.PaymentSecret }!!.run { (this as TaggedField.PaymentSecret).secret }
 
-    val paymentMetadata: ByteVector? = tags.find { it is TaggedField.PaymentMetadata }?.run { (this as TaggedField.PaymentMetadata).data }
+    val paymentMetadata: ByteVector? get() = tags.find { it is TaggedField.PaymentMetadata }?.run { (this as TaggedField.PaymentMetadata).data }
 
-    val description: String? = tags.find { it is TaggedField.Description }?.run { (this as TaggedField.Description).description }
+    val description: String? get() = tags.find { it is TaggedField.Description }?.run { (this as TaggedField.Description).description }
 
-    val descriptionHash: ByteVector32? = tags.find { it is TaggedField.DescriptionHash }?.run { (this as TaggedField.DescriptionHash).hash }
+    val descriptionHash: ByteVector32? get() = tags.find { it is TaggedField.DescriptionHash }?.run { (this as TaggedField.DescriptionHash).hash }
 
-    val expirySeconds: Long? = tags.find { it is TaggedField.Expiry }?.run { (this as TaggedField.Expiry).expirySeconds }
+    val expirySeconds: Long? get() = tags.find { it is TaggedField.Expiry }?.run { (this as TaggedField.Expiry).expirySeconds }
 
-    val minFinalExpiryDelta: CltvExpiryDelta? = tags.find { it is TaggedField.MinFinalCltvExpiry }?.run { CltvExpiryDelta((this as TaggedField.MinFinalCltvExpiry).cltvExpiry.toInt()) }
+    val minFinalExpiryDelta: CltvExpiryDelta? get() = tags.find { it is TaggedField.MinFinalCltvExpiry }?.run { CltvExpiryDelta((this as TaggedField.MinFinalCltvExpiry).cltvExpiry.toInt()) }
 
     val fallbackAddress: String? = tags.find { it is TaggedField.FallbackAddress }?.run { (this as TaggedField.FallbackAddress).toAddress(prefix) }
 
-    override val features: Features = tags.find { it is TaggedField.Features }.run { Features((this as TaggedField.Features).bits) }
+    override val features: Features get() = tags.filterIsInstance<TaggedField.Features>().firstOrNull()?.run { Features(this.bits) } ?: Features.empty
 
     val routingInfo: List<TaggedField.RoutingInfo> = tags.filterIsInstance<TaggedField.RoutingInfo>()
 
@@ -55,7 +55,7 @@ data class Bolt11Invoice(
         require(description != null || descriptionHash != null) { "there must be exactly one description tag or one description hash tag" }
     }
 
-    override fun isExpired(currentTimestampSeconds: Long): Boolean = when (expirySeconds) {
+    override fun isExpired(currentTimestampSeconds: Long): Boolean = when (val expirySeconds = expirySeconds) {
         null -> timestampSeconds + DEFAULT_EXPIRY_SECONDS <= currentTimestampSeconds
         else -> timestampSeconds + expirySeconds <= currentTimestampSeconds
     }
@@ -65,14 +65,16 @@ data class Bolt11Invoice(
     private fun rawData(): List<Int5> {
         val data5 = ArrayList<Int5>()
         data5.addAll(encodeTimestamp(timestampSeconds))
-        tags.forEach {
-            val encoded = it.encode()
-            val len = encoded.size
-            data5.add(it.tag)
-            data5.add((len / 32).toByte())
-            data5.add((len.rem(32)).toByte())
-            data5.addAll(encoded)
-        }
+        tags
+            .filterNot { it is TaggedField.Features && it.bits.isEmpty() }
+            .forEach {
+                val encoded = it.encode()
+                val len = encoded.size
+                data5.add(it.tag)
+                data5.add((len / 32).toByte())
+                data5.add((len.rem(32)).toByte())
+                data5.addAll(encoded)
+            }
         return data5
     }
 
@@ -266,7 +268,7 @@ data class Bolt11Invoice(
         // converts a list of 5 bits values to a byte array
         internal fun toByteArray(int5s: List<Int5>): ByteArray {
             val allbits = int5s.flatMap { toBits(it) }
-            return allbits.windowed(8, 8, partialWindows = true){ toByte(it) }.toByteArray()
+            return allbits.windowed(8, 8, partialWindows = true) { toByte(it) }.toByteArray()
         }
     }
 

src/commonTest/kotlin/fr/acinq/lightning/payment/Bolt11InvoiceTestsCommon.kt

@@ -2,6 +2,7 @@ package fr.acinq.lightning.payment
 
 import fr.acinq.bitcoin.*
 import fr.acinq.bitcoin.utils.Either
+import fr.acinq.bitcoin.utils.Try
 import fr.acinq.lightning.*
 import fr.acinq.lightning.Lightning.randomBytes32
 import fr.acinq.lightning.Lightning.randomKey
@@ -498,10 +499,12 @@ class Bolt11InvoiceTestsCommon : LightningTestSuite() {
         assertEquals(pr1.paymentSecret, pr.paymentSecret)
 
         // An invoice without the payment secret feature should be rejected
-        assertTrue(Bolt11Invoice.read("lnbc40n1pw9qjvwpp5qq3w2ln6krepcslqszkrsfzwy49y0407hvks30ec6pu9s07jur3sdpstfshq5n9v9jzucm0d5s8vmm5v5s8qmmnwssyj3p6yqenwdencqzysxqrrss7ju0s4dwx6w8a95a9p2xc5vudl09gjl0w2n02sjrvffde632nxwh2l4w35nqepj4j5njhh4z65wyfc724yj6dn9wajvajfn5j7em6wsq2elakl").isFailure)
+        assertIs<Try.Failure<Throwable>>((Bolt11Invoice.read("lnbc40n1pw9qjvwpp5qq3w2ln6krepcslqszkrsfzwy49y0407hvks30ec6pu9s07jur3sdpstfshq5n9v9jzucm0d5s8vmm5v5s8qmmnwssyj3p6yqenwdencqzysxqrrss7ju0s4dwx6w8a95a9p2xc5vudl09gjl0w2n02sjrvffde632nxwh2l4w35nqepj4j5njhh4z65wyfc724yj6dn9wajvajfn5j7em6wsq2elakl")))
+            .let { failure -> assertContains(failure.error.message ?: "", "var_onion_optin must be supported") }
 
         // An invoice that sets the payment secret feature bit must provide a payment secret.
-        assertTrue(Bolt11Invoice.read("lnbc1230p1pwljzn3pp5qyqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqdq52dhk6efqd9h8vmmfvdjs9qypqsqylvwhf7xlpy6xpecsnpcjjuuslmzzgeyv90mh7k7vs88k2dkxgrkt75qyfjv5ckygw206re7spga5zfd4agtdvtktxh5pkjzhn9dq2cqz9upw7").isFailure)
+        assertIs<Try.Failure<Throwable>>(Bolt11Invoice.read("lnbc1230p1pwljzn3pp5qyqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqdq52dhk6efqd9h8vmmfvdjs9qypqsqylvwhf7xlpy6xpecsnpcjjuuslmzzgeyv90mh7k7vs88k2dkxgrkt75qyfjv5ckygw206re7spga5zfd4agtdvtktxh5pkjzhn9dq2cqz9upw7"))
+            .let { failure -> assertContains(failure.error.message ?: "", "there must be exactly one payment secret tag") }
 
         // Invoices must use a payment secret.
         assertFails {
@@ -517,6 +520,13 @@ class Bolt11InvoiceTestsCommon : LightningTestSuite() {
         }
     }
 
+    @Test
+    fun `decode invoice without features`() {
+        val s = "lnbc10n1pnglwsfpp5fdcjk5vudhe2jzuz0q65dkh4gfmxnn6vexlchc6ta9f25wynp2qshp59warmg27z4nkuvhs5x3vdv998jck5ue8nge2t68dtfvm27n8kvsqxqrrssnp4qf3rsvu5xdrxnv2kgkr4hvpefx257fjw8ugupnug4ls6rf2d5w6yc2rnnz0zuymgjl3p4dvyh8dr4mp969gjrnaggx50nv5ax7wy6yflyr07ek5hdevxtz9angp3jfyfz9ram8d7gw9pr0csr6fpa8rfeu7gpgesr58"
+        val failure = assertIs<Try.Failure<Throwable>>(Bolt11Invoice.read(s))
+        assertContains(failure.error.message ?: "", "var_onion_optin must be supported")
+    }
+
     @Test
     fun `invoice with descriptionHash`() {
         val descriptionHash = randomBytes32()