Add flow control

README.md

@@ -51,7 +51,7 @@ From a "make money routing" perspective, theoretically, these most distant nodes
 
 **Passively manage channel liquidity**
 
-Set channel fees based on the channel's current liquidity. The idea here is to encourage passive channel re-balancing through fees. If a channel has a too much local liquidity (high), fees are lowered in order to encourage relatively more outbound transactions. Visa versa for a channel with too little local liquidity (low). 
+Set channel fees based on the channel's current liquidity. The idea here is to encourage passive channel rebalancing through fees. If a channel has a too much local liquidity (high), fees are lowered in order to encourage relatively more outbound transactions. Visa versa for a channel with too little local liquidity (low). 
 
 The global `-liquidity-thresholds` flag determines how channels are grouped into liquidity buckets, while the `-liquidity-fees` flag determines the fee settings applied to those groups. For example, if thresholds are set to `80,20` and fees set to `5,50,500`, then channels with over 80% local liquidity will have a 5 PPM fee, channels between 80% and 20% local liquidity will have a 50 PPM fee, and channels with less than 20% liquidity will have a 500 PPM fee.
 
@@ -61,6 +61,8 @@ The `-liquidity-thresholds`, `-liquidity-fees`, and `-liquidity-stickiness` are
 
 `fees` follows the [zero-base-fee movement](http://www.rene-pickhardt.de/). I am honestly not sure if this is financially sound, but I appreciate the simpler mental model of only thinking in ppm.
 
+`fees` also automatically applies some [flow control](https://blog.bitmex.com/the-power-of-htlc_maximum_msat-as-a-control-valve-for-better-flow-control-improved-reliability-and-lower-expected-payment-failure-rates-on-the-lightning-network/) to channels in order to encourage more rebalancing.
+
 ## rebalance
 
 **Actively manage channel liquidity**

lightning/lightning.go

@@ -14,6 +14,14 @@ func (s Satoshi) BTC() float64 {
 	return float64(s) / 100000000
 }
 
+// BTC value of Satoshi.
+func (s Satoshi) Millis() MilliSatoshi {
+	return MilliSatoshi(s * 1000)
+}
+
+// MilliSatoshi unit of bitcoin.
+type MilliSatoshi int64
+
 // FeePPM is the channel fee in part per million.
 type FeePPM float64
 

lightning/lnd.go

@@ -234,7 +234,7 @@ func (l LndClient) ListChannels(ctx context.Context) (Channels, error) {
 }
 
 // SetFees for channel with rate in ppm.
-func (l LndClient) SetFees(ctx context.Context, channelID ChannelID, fee FeePPM) error {
+func (l LndClient) SetFees(ctx context.Context, channelID ChannelID, fee FeePPM, maxHTLC MilliSatoshi) error {
 	ce, err := l.c.GetChanInfo(ctx, uint64(channelID))
 	if err != nil {
 		return err
@@ -250,6 +250,7 @@ func (l LndClient) SetFees(ctx context.Context, channelID ChannelID, fee FeePPM)
 		BaseFeeMsat:   0,
 		FeeRate:       fee.Rate(),
 		TimeLockDelta: 80,
+		MaxHtlcMsat:   uint64(maxHTLC),
 	}
 	return l.c.UpdateChanPolicy(ctx, req, outpoint)
 }

raiju.go

@@ -29,7 +29,7 @@ type lightninger interface {
 	GetChannel(ctx context.Context, channelID lightning.ChannelID) (lightning.Channel, error)
 	ListChannels(ctx context.Context) (lightning.Channels, error)
 	SendPayment(ctx context.Context, invoice lightning.Invoice, outChannelID lightning.ChannelID, lastHopPubKey lightning.PubKey, maxFee lightning.FeePPM) (lightning.Satoshi, error)
-	SetFees(ctx context.Context, channelID lightning.ChannelID, fee lightning.FeePPM) error
+	SetFees(ctx context.Context, channelID lightning.ChannelID, fee lightning.FeePPM, maxHTLC lightning.MilliSatoshi) error
 	SubscribeChannelUpdates(ctx context.Context) (<-chan lightning.Channels, <-chan error, error)
 }
 
@@ -308,8 +308,10 @@ func (r Raiju) setFees(ctx context.Context, channels lightning.Channels) (map[li
 	// update channel fees based on liquidity, but only change if necessary
 	for _, c := range channels {
 		fee := r.f.Fee(c)
+		// flow control, broadcast to the network the max payment size to forward through this channel.
+		maxPayment := c.LocalBalance.Millis() / 2
 		if c.LocalFee != fee && !c.Private {
-			err := r.l.SetFees(ctx, c.ChannelID, fee)
+			err := r.l.SetFees(ctx, c.ChannelID, fee, maxPayment)
 			if err != nil {
 				return map[lightning.ChannelID]lightning.FeePPM{}, err
 			}