Additional reestablish test (#1875)

This test was added to lightning-kmp where this case wasn't correctly
handled: https://github.com/ACINQ/lightning-kmp/pull/278

It is correctly handled by eclair, but an additional test doesn't hurt.

eclair-core/src/test/scala/fr/acinq/eclair/channel/states/e/OfflineStateSpec.scala

@@ -231,6 +231,53 @@ class OfflineStateSpec extends TestKitBaseClass with FixtureAnyFunSuiteLike with
     awaitCond(bob.stateName == NORMAL)
   }
 
+  test("resume htlc settlement") { f =>
+    import f._
+
+    // Successfully send a first payment.
+    val (r1, htlc1) = addHtlc(15_000_000 msat, bob, alice, bob2alice, alice2bob)
+    crossSign(bob, alice, bob2alice, alice2bob)
+    fulfillHtlc(htlc1.id, r1, alice, bob, alice2bob, bob2alice)
+    crossSign(alice, bob, alice2bob, bob2alice)
+
+    // Send a second payment and disconnect right after the fulfill was signed.
+    val (r2, htlc2) = addHtlc(25_000_000 msat, bob, alice, bob2alice, alice2bob)
+    crossSign(bob, alice, bob2alice, alice2bob)
+    fulfillHtlc(htlc2.id, r2, alice, bob, alice2bob, bob2alice)
+    val sender = TestProbe()
+    alice ! CMD_SIGN(Some(sender.ref))
+    sender.expectMsgType[RES_SUCCESS[CMD_SIGN]]
+    alice2bob.expectMsgType[CommitSig]
+    alice2bob.forward(bob)
+    val revB = bob2alice.expectMsgType[RevokeAndAck]
+    bob2alice.expectMsgType[CommitSig]
+    disconnect(alice, bob)
+
+    reconnect(alice, bob, alice2bob, bob2alice)
+    val reestablishA = alice2bob.expectMsgType[ChannelReestablish]
+    assert(reestablishA.nextLocalCommitmentNumber === 4)
+    assert(reestablishA.nextRemoteRevocationNumber === 3)
+    val reestablishB = bob2alice.expectMsgType[ChannelReestablish]
+    assert(reestablishB.nextLocalCommitmentNumber === 5)
+    assert(reestablishB.nextRemoteRevocationNumber === 3)
+
+    bob2alice.forward(alice, reestablishB)
+    // alice does not re-send messages bob already received
+    alice2bob.expectNoMessage(100 millis)
+
+    alice2bob.forward(bob, reestablishA)
+    // bob re-sends its revocation and signature, alice then completes the update
+    bob2alice.expectMsg(revB)
+    bob2alice.forward(alice)
+    bob2alice.expectMsgType[CommitSig]
+    bob2alice.forward(alice)
+    alice2bob.expectMsgType[RevokeAndAck]
+    alice2bob.forward(bob)
+
+    assert(alice.stateData.asInstanceOf[DATA_NORMAL].commitments.localCommit.index === 4)
+    assert(bob.stateData.asInstanceOf[DATA_NORMAL].commitments.localCommit.index === 4)
+  }
+
   test("discover that we have a revoked commitment") { f =>
     import f._
 
@@ -258,11 +305,11 @@ class OfflineStateSpec extends TestKitBaseClass with FixtureAnyFunSuiteLike with
     reconnect(alice, bob, alice2bob, bob2alice)
 
     // peers exchange channel_reestablish messages
-    alice2bob.expectMsgType[ChannelReestablish]
-    bob2alice.expectMsgType[ChannelReestablish]
+    val reestablishA = alice2bob.expectMsgType[ChannelReestablish]
+    val reestablishB = bob2alice.expectMsgType[ChannelReestablish]
 
     // alice then realizes it has an old state...
-    bob2alice.forward(alice)
+    bob2alice.forward(alice, reestablishB)
     // ... and ask bob to publish its current commitment
     val error = alice2bob.expectMsgType[Error]
     assert(error === Error(channelId(alice), PleasePublishYourCommitment(channelId(alice)).getMessage))
@@ -270,8 +317,9 @@ class OfflineStateSpec extends TestKitBaseClass with FixtureAnyFunSuiteLike with
     // alice now waits for bob to publish its commitment
     awaitCond(alice.stateName == WAIT_FOR_REMOTE_PUBLISH_FUTURE_COMMITMENT)
 
-    // bob is nice and publishes its commitment
-    val bobCommitTx = bob.stateData.asInstanceOf[DATA_NORMAL].commitments.localCommit.commitTxAndRemoteSig.commitTx.tx
+    // bob publishes its commitment when it detects that alice has an outdated commitment
+    alice2bob.forward(bob, reestablishA)
+    val bobCommitTx = bob2blockchain.expectMsgType[PublishRawTx].tx
     alice ! WatchFundingSpentTriggered(bobCommitTx)
 
     // alice is able to claim its main output