Relax cltv-expiry-delta requirement when selecting a channel to relay (…

…#1655)

We only need the `cltv-expiry-delta` offered to be greater than our
requirement instead of strictly equal.

Co-authored-by: t-bast <bastuc@hotmail.fr>

eclair-core/src/main/scala/fr/acinq/eclair/payment/relay/ChannelRelay.scala

@@ -259,7 +259,7 @@ class ChannelRelay private(nodeParams: NodeParams,
         RelayFailure(CMD_FAIL_HTLC(add.id, Right(ChannelDisabled(channelUpdate.messageFlags, channelUpdate.channelFlags, channelUpdate)), commit = true))
       case Some(channelUpdate) if payload.amountToForward < channelUpdate.htlcMinimumMsat =>
         RelayFailure(CMD_FAIL_HTLC(add.id, Right(AmountBelowMinimum(payload.amountToForward, channelUpdate)), commit = true))
-      case Some(channelUpdate) if r.expiryDelta != channelUpdate.cltvExpiryDelta =>
+      case Some(channelUpdate) if r.expiryDelta < channelUpdate.cltvExpiryDelta =>
         RelayFailure(CMD_FAIL_HTLC(add.id, Right(IncorrectCltvExpiry(payload.outgoingCltv, channelUpdate)), commit = true))
       case Some(channelUpdate) if r.relayFeeMsat < nodeFee(channelUpdate.feeBaseMsat, channelUpdate.feeProportionalMillionths, payload.amountToForward) =>
         RelayFailure(CMD_FAIL_HTLC(add.id, Right(FeeInsufficient(add.amountMsat, channelUpdate)), commit = true))

eclair-core/src/test/scala/fr/acinq/eclair/payment/relay/ChannelRelayerSpec.scala

@@ -198,25 +198,25 @@ class ChannelRelayerSpec extends ScalaTestWithActorTestKit(ConfigFactory.load("a
     expectFwdFail(register, r.add.channelId, CMD_FAIL_HTLC(r.add.id, Right(AmountBelowMinimum(outgoingAmount, u.channelUpdate)), commit = true))
   }
 
-  test("fail to relay an htlc-add (expiry too small)") { f =>
+  test("relay an htlc-add (expiry larger than our requirements)") { f =>
     import f._
 
-    val payload = RelayLegacyPayload(shortId1, outgoingAmount, outgoingExpiry - CltvExpiryDelta(1))
-    val r = createValidIncomingPacket(1100000 msat, CltvExpiry(400100), payload)
+    val payload = RelayLegacyPayload(shortId1, outgoingAmount, outgoingExpiry)
     val u = createLocalUpdate(shortId1)
+    val r = createValidIncomingPacket(1100000 msat, outgoingExpiry + u.channelUpdate.cltvExpiryDelta + CltvExpiryDelta(1), payload)
 
     channelRelayer ! WrappedLocalChannelUpdate(u)
     channelRelayer ! Relay(r)
 
-    expectFwdFail(register, r.add.channelId, CMD_FAIL_HTLC(r.add.id, Right(IncorrectCltvExpiry(payload.outgoingCltv, u.channelUpdate)), commit = true))
+    expectFwdAdd(register, shortId1, payload.amountToForward, payload.outgoingCltv).message
   }
 
-  test("fail to relay an htlc-add (expiry too large)") { f =>
+  test("fail to relay an htlc-add (expiry too small)") { f =>
     import f._
 
-    val payload = RelayLegacyPayload(shortId1, outgoingAmount, outgoingExpiry + CltvExpiryDelta(1))
-    val r = createValidIncomingPacket(1100000 msat, CltvExpiry(400100), payload)
+    val payload = RelayLegacyPayload(shortId1, outgoingAmount, outgoingExpiry)
     val u = createLocalUpdate(shortId1)
+    val r = createValidIncomingPacket(1100000 msat, outgoingExpiry + u.channelUpdate.cltvExpiryDelta - CltvExpiryDelta(1), payload)
 
     channelRelayer ! WrappedLocalChannelUpdate(u)
     channelRelayer ! Relay(r)
@@ -330,11 +330,18 @@ class ChannelRelayerSpec extends ScalaTestWithActorTestKit(ConfigFactory.load("a
       expectFwdAdd(register, ShortChannelId(12345), payload.amountToForward, payload.outgoingCltv).message
     }
     {
-      // invalid cltv expiry, no suitable channel found
-      val payload = RelayLegacyPayload(ShortChannelId(12345), 998900 msat, CltvExpiry(40))
+      // cltv expiry larger than our requirements
+      val payload = RelayLegacyPayload(ShortChannelId(12345), 998900 msat, CltvExpiry(50))
+      val r = createValidIncomingPacket(1000000 msat, CltvExpiry(70), payload)
+      channelRelayer ! Relay(r)
+      expectFwdAdd(register, ShortChannelId(22223), payload.amountToForward, payload.outgoingCltv).message
+    }
+    {
+      // cltv expiry too small, no suitable channel found
+      val payload = RelayLegacyPayload(ShortChannelId(12345), 998900 msat, CltvExpiry(61))
       val r = createValidIncomingPacket(1000000 msat, CltvExpiry(70), payload)
       channelRelayer ! Relay(r)
-      expectFwdFail(register, r.add.channelId, CMD_FAIL_HTLC(r.add.id, Right(IncorrectCltvExpiry(CltvExpiry(40), channelUpdates(ShortChannelId(12345)).channelUpdate)), commit = true))
+      expectFwdFail(register, r.add.channelId, CMD_FAIL_HTLC(r.add.id, Right(IncorrectCltvExpiry(CltvExpiry(61), channelUpdates(ShortChannelId(12345)).channelUpdate)), commit = true))
     }
   }