From af7cfd6c8b33c44be983640e45d2a65dead979b3 Mon Sep 17 00:00:00 2001
From: Olaoluwa Osuntokun <laolu32@gmail.com>
Date: Tue, 12 Jul 2016 17:40:32 -0700
Subject: [PATCH] lnd: add basic HtlcSwitch logic for forwarding L2 payments

---
 htlcswitch.go | 51 ++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 48 insertions(+), 3 deletions(-)

diff --git a/htlcswitch.go b/htlcswitch.go
index 05fd7b6b..829db4c4 100644
--- a/htlcswitch.go
+++ b/htlcswitch.go
@@ -41,7 +41,7 @@ type link struct {
 type htlcPacket struct {
 	dest wire.ShaHash
 
-	htlc lnwire.Message
+	msg lnwire.Message
 }
 
 // HtlcSwitch is a central messaging bus for all incoming/outgoing HTLC's.
@@ -65,6 +65,8 @@ type htlcSwitch struct {
 
 	outgoingPayments chan *htlcPacket
 
+	htlcPlex chan *htlcPacket
+
 	// TODO(roasbeef): messaging chan to/from upper layer (routing - L3)
 
 	wg   sync.WaitGroup
@@ -77,6 +79,7 @@ func newHtlcSwitch() *htlcSwitch {
 		chanIndex:        make(map[wire.OutPoint]*link),
 		interfaces:       make(map[wire.ShaHash][]*link),
 		linkControl:      make(chan interface{}),
+		htlcPlex:         make(chan *htlcPacket, htlcQueueSize),
 		outgoingPayments: make(chan *htlcPacket, 20),
 	}
 }
@@ -107,6 +110,16 @@ func (h *htlcSwitch) Stop() error {
 	return nil
 }
 
+// SendHTLC queues a HTLC packet for forwarding over the designated interface.
+// In the event that the interface has insufficient capacity for the payment,
+// an error is returned. Additionally, if the interface cannot be found, an
+// alternative error is returned.
+func (h *htlcSwitch) SendHTLC(htlcPkt *htlcPacket) error {
+	// TODO(roasbeef): hook in errors
+	h.outgoingPayments <- htlcPkt
+	return nil
+}
+
 // htlcForwarder is responsible for optimally forwarding (and possibly
 // fragmenting) incoming/outgoing HTLC's amongst all active interfaces and
 // their links.
@@ -114,7 +127,37 @@ func (h *htlcSwitch) htlcForwarder() {
 out:
 	for {
 		select {
-		case <-h.outgoingPayments:
+		case htlcPkt := <-h.outgoingPayments:
+			chanInterface, ok := h.interfaces[htlcPkt.dest]
+			if !ok {
+				hswcLog.Errorf("unable to locate link %x", htlcPkt.dest[:])
+				continue
+			}
+
+			wireMsg := htlcPkt.msg.(*lnwire.HTLCAddRequest)
+			amt := btcutil.Amount(wireMsg.Amount)
+			hswcLog.Debugf("attempting to send %v to %v", amt,
+				hex.EncodeToString(htlcPkt.dest[:]))
+
+			for _, link := range chanInterface {
+				// TODO(roasbeef): implement HTLC fragmentation
+				if link.availableBandwidth >= amt {
+					hswcLog.Debugf("selected %v for payment of %v to %x",
+						link.chanPoint, amt, htlcPkt.dest[:])
+
+					wireMsg.ChannelPoint = link.chanPoint
+					link.linkChan <- wireMsg
+					// TODO(roasbeef): update link info on
+					// timeout/settle
+					link.availableBandwidth -= amt
+				}
+			}
+
+			if wireMsg.ChannelPoint == nil {
+				hswcLog.Errorf("unable to send payment, " +
+					"insufficient capacity")
+			}
+		case <-h.htlcPlex:
 		case <-h.quit:
 			break out
 		}
@@ -230,13 +273,15 @@ type registerLinkMsg struct {
 // RegisterLink requests the htlcSwitch to register a new active link. The new
 // link encapsulates an active channel.
 func (h *htlcSwitch) RegisterLink(p *peer, linkInfo *channeldb.ChannelSnapshot,
-	linkChan chan lnwire.Message) {
+	linkChan chan lnwire.Message) chan *htlcPacket {
 
 	done := make(chan struct{}, 1)
 	req := &registerLinkMsg{p, linkInfo, linkChan, done}
 	h.linkControl <- req
 
 	<-done
+
+	return h.htlcPlex
 }
 
 // unregisterLinkMsg is a message which requests the active ink be unregistered.