From ab215e26df9eae26883f678d7979ea905aa0f5ab Mon Sep 17 00:00:00 2001
From: benthecarman <benthecarman@live.com>
Date: Sat, 11 Jun 2022 09:36:19 -0500
Subject: [PATCH] Set recovery id properly for buildLnInvoiceSignature (#4379)

---
 .../core/protocol/ln/LnInvoiceUnitTest.scala       | 14 +++++++++++++-
 .../org/bitcoins/core/protocol/ln/LnInvoice.scala  |  5 ++++-
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/core-test/src/test/scala/org/bitcoins/core/protocol/ln/LnInvoiceUnitTest.scala b/core-test/src/test/scala/org/bitcoins/core/protocol/ln/LnInvoiceUnitTest.scala
index ca2fb146be..a0a24600e7 100644
--- a/core-test/src/test/scala/org/bitcoins/core/protocol/ln/LnInvoiceUnitTest.scala
+++ b/core-test/src/test/scala/org/bitcoins/core/protocol/ln/LnInvoiceUnitTest.scala
@@ -5,6 +5,7 @@ import org.bitcoins.core.protocol.ln.LnParams.{
   LnBitcoinMainNet,
   LnBitcoinTestNet
 }
+import org.bitcoins.core.protocol.ln.LnTag.{DescriptionTag, PaymentHashTag}
 import org.bitcoins.core.protocol.ln.channel.ShortChannelId
 import org.bitcoins.core.protocol.ln.currency.{
   MicroBitcoins,
@@ -22,7 +23,7 @@ import org.bitcoins.core.util.Bech32
 import org.bitcoins.crypto._
 import org.bitcoins.testkitcore.gen.ln.LnInvoiceGen
 import org.bitcoins.testkitcore.util.BitcoinSUnitTest
-import scodec.bits.ByteVector
+import scodec.bits._
 
 class LnInvoiceUnitTest extends BitcoinSUnitTest {
   behavior of "LnInvoice"
@@ -565,4 +566,15 @@ class LnInvoiceUnitTest extends BitcoinSUnitTest {
       "lntbs42949672960n1p3qavpxpp59mdvu0tw0mzf2kl96ddfcm0597nuxwp42tzsehrn66jrmlg7nu8sdqqcqzpgxqyz5vqsp5y70pg45suf546mses9cp54fk4uke2rmppk9dy4926prhe5v54g4s9qyyssqmtpasu8map7hegdxfzmgusuqnkrssy6m34wcup3lmu0mae3xtht5d49204a3wm9wpklalx49g33cer5gqfractwt79vrc8p7wlpsdlqp296km0"
     assert(LnInvoice.fromStringT(str).isSuccess)
   }
+
+  it must "build an invoice with a recoverable pub key" in {
+    val priv = ECPrivateKey.fromBytes(
+      hex"deeb3f23a850090b9033e3400584923a281d3c7d914a6d1587369abe2071d8c5")
+    val hrp = LnHumanReadablePart.fromLnParams(LnParams.LnBitcoinRegTest)
+    val tags = LnTaggedFields(
+      Vector(PaymentHashTag(Sha256Digest.empty), DescriptionTag("test")))
+    val invoice = LnInvoice.build(hrp, tags, priv)
+
+    assert(invoice.nodeId == NodeId(priv.publicKey))
+  }
 }
diff --git a/core/src/main/scala/org/bitcoins/core/protocol/ln/LnInvoice.scala b/core/src/main/scala/org/bitcoins/core/protocol/ln/LnInvoice.scala
index f9e7a5b98d..c36e7703af 100644
--- a/core/src/main/scala/org/bitcoins/core/protocol/ln/LnInvoice.scala
+++ b/core/src/main/scala/org/bitcoins/core/protocol/ln/LnInvoice.scala
@@ -275,7 +275,10 @@ object LnInvoice extends StringFactory[LnInvoice] {
     val sigHash = buildSigHashData(hrp, timestamp, lnTags)
     val sig = privateKey.sign(sigHash)
 
-    LnInvoiceSignature(recoverId = UInt8.zero, signature = sig)
+    val (pub1, _) = CryptoUtil.recoverPublicKey(sig, sigHash.bytes)
+    val recoveryId = if (privateKey.publicKey == pub1) UInt8.zero else UInt8.one
+
+    LnInvoiceSignature(recoverId = recoveryId, signature = sig)
   }
 
   /** The easiest way to create a [[org.bitcoins.core.protocol.ln.LnInvoice LnInvoice]]