multi: update internals to support updating max htlc

In this commit, we update the router and link to support users
updating the max HTLC policy for their channels. By updating these internal
systems before updating the RPC server and lncli, we protect users from
being shown an option that doesn't actually work.

routing/localchans/manager_test.go

@@ -18,8 +18,12 @@ import (
 // TestManager tests that the local channel manager properly propagates fee
 // updates to gossiper and links.
 func TestManager(t *testing.T) {
-	chanPoint := wire.OutPoint{Hash: chainhash.Hash{1}, Index: 2}
-	chanCap := btcutil.Amount(1000)
+	var (
+		chanPoint        = wire.OutPoint{Hash: chainhash.Hash{1}, Index: 2}
+		chanCap          = btcutil.Amount(1000)
+		maxPendingAmount = lnwire.MilliSatoshi(999000)
+		minHTLC          = lnwire.MilliSatoshi(2000)
+	)
 
 	newPolicy := routing.ChannelPolicy{
 		FeeSchema: routing.FeeSchema{
@@ -27,6 +31,12 @@ func TestManager(t *testing.T) {
 			FeeRate: 200,
 		},
 		TimeLockDelta: 80,
+		MaxHTLC:       5000,
+	}
+
+	currentPolicy := channeldb.ChannelEdgePolicy{
+		MinHTLC:      minHTLC,
+		MessageFlags: lnwire.ChanUpdateOptionMaxHtlc,
 	}
 
 	updateForwardingPolicies := func(
@@ -46,7 +56,7 @@ func TestManager(t *testing.T) {
 		if uint32(policy.FeeRate) != newPolicy.FeeRate {
 			t.Fatal("unexpected base fee")
 		}
-		if policy.MaxHTLC != lnwire.NewMSatFromSatoshis(chanCap) {
+		if policy.MaxHTLC != newPolicy.MaxHTLC {
 			t.Fatal("unexpected max htlc")
 		}
 	}
@@ -71,7 +81,7 @@ func TestManager(t *testing.T) {
 		if uint32(policy.FeeProportionalMillionths) != newPolicy.FeeRate {
 			t.Fatal("unexpected base fee")
 		}
-		if policy.MaxHTLC != lnwire.NewMSatFromSatoshis(chanCap) {
+		if policy.MaxHTLC != newPolicy.MaxHTLC {
 			t.Fatal("unexpected max htlc")
 		}
 
@@ -86,14 +96,30 @@ func TestManager(t *testing.T) {
 				Capacity:     chanCap,
 				ChannelPoint: chanPoint,
 			},
-			&channeldb.ChannelEdgePolicy{},
+			&currentPolicy,
 		)
 	}
 
+	fetchChannel := func(chanPoint wire.OutPoint) (*channeldb.OpenChannel,
+		error) {
+
+		constraints := channeldb.ChannelConstraints{
+			MaxPendingAmount: maxPendingAmount,
+			MinHTLC:          minHTLC,
+		}
+
+		return &channeldb.OpenChannel{
+			LocalChanCfg: channeldb.ChannelConfig{
+				ChannelConstraints: constraints,
+			},
+		}, nil
+	}
+
 	manager := Manager{
 		UpdateForwardingPolicies:  updateForwardingPolicies,
 		PropagateChanPolicyUpdate: propagateChanPolicyUpdate,
 		ForAllOutgoingChannels:    forAllOutgoingChannels,
+		FetchChannel:              fetchChannel,
 	}
 
 	// Test updating a specific channels.
@@ -108,4 +134,15 @@ func TestManager(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
+
+	// If no max htlc is specified, the max htlc value should be kept
+	// unchanged.
+	currentPolicy.MaxHTLC = newPolicy.MaxHTLC
+	noMaxHtlcPolicy := newPolicy
+	noMaxHtlcPolicy.MaxHTLC = 0
+
+	err = manager.UpdatePolicy(noMaxHtlcPolicy)
+	if err != nil {
+		t.Fatal(err)
+	}
 }