htlcswitch: add channel link config

Step №1 in making htlcManager (aka channelLink) testable:
Start use config which will allow as mock/stub external subsystems.

htlcswitch/interfaces.go

@@ -3,10 +3,25 @@ package htlcswitch
 import (
 	"crypto/sha256"
 
+	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/roasbeef/btcd/chaincfg/chainhash"
 	"github.com/roasbeef/btcutil"
 )
 
+// InvoiceDatabase is an interface which represents the persistent subsystem
+// which may search, lookup and settle invoices.
+type InvoiceDatabase interface {
+	// LookupInvoice attempts to look up an invoice according to it's 32
+	// byte payment hash.
+	LookupInvoice(chainhash.Hash) (*channeldb.Invoice, error)
+
+	// SettleInvoice attempts to mark an invoice corresponding to the passed
+	// payment hash as fully settled.
+	SettleInvoice(chainhash.Hash) error
+}
+
 // ChannelLink is an interface which represents the subsystem for managing
 // the incoming htlc requests, applying the changes to the channel, and also
 // propagating/forwarding it to htlc switch.
@@ -66,6 +81,10 @@ type Peer interface {
 	// ID returns the lightning network peer id.
 	ID() [sha256.Size]byte
 
+	// WipeChannel removes the passed channel from all indexes associated
+	// with the peer.
+	WipeChannel(*lnwallet.LightningChannel) error
+
 	// PubKey returns the peer public key.
 	PubKey() []byte
 

htlcswitch/link.go

@@ -17,6 +17,33 @@ import (
 	"github.com/roasbeef/btcutil"
 )
 
+// ChannelLinkConfig defines the configuration for the channel link. ALL
+// elements within the configuration MUST be non-nil for channel link to carry
+// out its duties.
+type ChannelLinkConfig struct {
+	// Switch is a subsystem which is used to forward the incoming htlc
+	// packets to other peer which should handle it.
+	Switch *Switch
+
+	// Peer is a lightning network node with which we have the channel
+	// link opened.
+	Peer Peer
+
+	// Registry is a sub-system which responsible for managing the
+	// invoices in thread-safe manner.
+	Registry InvoiceDatabase
+
+	// SettledContracts is used to notify that a channel has peacefully been
+	// closed. Once a channel has been closed the other subsystem no longer
+	// needs to watch for breach closes.
+	SettledContracts chan *wire.OutPoint
+
+	// DebugHTLC should be turned on if you want all HTLCs sent to a node
+	// with the debug htlc R-Hash are immediately settled in the next
+	// available state transition.
+	DebugHTLC bool
+}
+
 // commitmentState is the volatile+persistent state of an active channel's
 // commitment update state-machine. This struct is used by htlcManager's to
 // save meta-state required for proper functioning.
@@ -63,6 +90,10 @@ type commitmentState struct {
 	channel   *lnwallet.LightningChannel
 	chanPoint *wire.OutPoint
 	chanID    lnwire.ChannelID
+
+	// cfg is a structure which carries all dependable fields/handlers
+	// which may affect behaviour of the service.
+	cfg *ChannelLinkConfig
 }
 
 // htlcManager is the primary goroutine which drives a channel's commitment

htlcswitch/mock.go

@@ -10,6 +10,7 @@ import (
 	"github.com/go-errors/errors"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/roasbeef/btcutil"
+	"github.com/lightningnetwork/lnd/lnwallet"
 )
 
 type mockServer struct {
@@ -152,6 +153,10 @@ func (s *mockServer) Disconnect() {
 	s.t.Fatalf("server %v was disconnected", s.name)
 }
 
+func (s *mockServer) WipeChannel(*lnwallet.LightningChannel) error {
+	return nil
+}
+
 func (s *mockServer) Stop() {
 	if !atomic.CompareAndSwapInt32(&s.shutdown, 0, 1) {
 		return