loopout: add asset id and edge node

Author: sputn1ck

client.go

@@ -530,6 +530,13 @@ func (s *Client) LoopOut(globalCtx context.Context,
 
 	// Create a new swap object for this swap.
 	swapCfg := newSwapConfig(s.lndServices, s.Store, s.Server, s.assetClient)
+
+	// Verify that if we have an asset id set, we have a valid asset client
+	// to use.
+	if request.AssetId != nil && s.assetClient == nil {
+		return nil, errors.New("asset id set but no asset client provided")
+	}
+
 	initResult, err := newLoopOutSwap(
 		globalCtx, swapCfg, initiationHeight, request,
 	)

interface.go

@@ -98,6 +98,16 @@ type OutRequest struct {
 	// the configured maximum payment timeout) the total time spent may be
 	// a multiple of this value.
 	PaymentTimeout time.Duration
+
+	// AssetId is an optional asset id that can be used to specify the asset
+	// that will be used to pay for the swap. If this is set, a connection
+	// to a tapd server is required to pay for the asset.
+	AssetId []byte
+
+	// AssetEdgeNode is an optional Parameter that is required should the
+	// tapd server have multiple channels with different peers for the given
+	// asset id.
+	AssetEdgeNode []byte
 }
 
 // Out contains the full details of a loop out request. This includes things

loopd/swapclient_server.go

@@ -206,6 +206,8 @@ func (s *swapClientServer) LoopOut(ctx context.Context,
 		Label:                   in.Label,
 		Initiator:               in.Initiator,
 		PaymentTimeout:          paymentTimeout,
+		AssetId:                 in.AssetId,
+		AssetEdgeNode:           in.AssetEdgeNode,
 	}
 
 	switch {

loopdb/loopout.go

@@ -65,6 +65,13 @@ type LoopOutContract struct {
 	// PaymentTimeout is the timeout for any individual off-chain payment
 	// attempt.
 	PaymentTimeout time.Duration
+
+	// AssetId is the optional asset id that is used to pay the swap invoice.
+	AssetId []byte
+
+	// AssetEdgeNode is the optional asset edge node that is used to pay the
+	// swap invoice.
+	AssetEdgeNode []byte
 }
 
 // ChannelSet stores a set of channels.

loopout.go

@@ -206,6 +206,8 @@ func newLoopOutSwap(globalCtx context.Context, cfg *swapConfig,
 		},
 		OutgoingChanSet: chanSet,
 		PaymentTimeout:  request.PaymentTimeout,
+		AssetId:         request.AssetId,
+		AssetEdgeNode:   request.AssetEdgeNode,
 	}
 
 	swapKit := newSwapKit(