rfq: make BuyOrder.Peer field an Option type

Currently, the `BuyOrder.Peer` field must be specified, but in the
future, the negotiator should be able to select the optimal peer
automatically. This commit updates the interface to support this future
functionality by making `BuyOrder.Peer` an Option type. Note that this
field was already a pointer.

rfq/manager.go

@@ -702,7 +702,10 @@ type BuyOrder struct {
 
 	// Peer is the peer that the buy order is intended for. This field is
 	// optional.
-	Peer *route.Vertex
+	//
+	// TODO(ffranr): Currently, this field must be specified. In the future,
+	//  the negotiator should be able to determine the optimal peer.
+	Peer fn.Option[route.Vertex]
 }
 
 // UpsertAssetBuyOrder upserts an asset buy order for management.
@@ -711,7 +714,7 @@ func (m *Manager) UpsertAssetBuyOrder(order BuyOrder) error {
 	//
 	// TODO(ffranr): Add support for peerless buy orders. The negotiator
 	//  should be able to determine the optimal peer.
-	if order.Peer == nil {
+	if order.Peer.IsNone() {
 		return fmt.Errorf("buy order peer must be specified")
 	}
 

rfq/negotiator.go

@@ -159,6 +159,15 @@ func (n *Negotiator) HandleOutgoingBuyOrder(buyOrder BuyOrder) error {
 	go func() {
 		defer n.Wg.Done()
 
+		// Unwrap the peer from the buy order. For now, we can assume
+		// that the peer is always specified.
+		peer, err := buyOrder.Peer.UnwrapOrErr(
+			fmt.Errorf("buy order peer must be specified"),
+		)
+		if err != nil {
+			n.cfg.ErrChan <- err
+		}
+
 		// We calculate a proposed bid price for our peer's
 		// consideration. If a price oracle is not specified we will
 		// skip this step.
@@ -169,7 +178,7 @@ func (n *Negotiator) HandleOutgoingBuyOrder(buyOrder BuyOrder) error {
 
 			// Query the price oracle for a bid price.
 			assetRate, err := n.queryBidFromPriceOracle(
-				*buyOrder.Peer, buyOrder.AssetSpecifier,
+				peer, buyOrder.AssetSpecifier,
 				fn.Some(buyOrder.AssetMaxAmt),
 				fn.None[lnwire.MilliSatoshi](),
 				fn.None[rfqmsg.AssetRate](),
@@ -186,8 +195,9 @@ func (n *Negotiator) HandleOutgoingBuyOrder(buyOrder BuyOrder) error {
 			assetRateHint = fn.Some[rfqmsg.AssetRate](*assetRate)
 		}
 
+		// Construct a new buy request to send to the peer.
 		request, err := rfqmsg.NewBuyRequest(
-			*buyOrder.Peer, buyOrder.AssetSpecifier,
+			peer, buyOrder.AssetSpecifier,
 			buyOrder.AssetMaxAmt, assetRateHint,
 		)
 		if err != nil {

rpcserver.go

@@ -6315,7 +6315,7 @@ func unmarshalAssetBuyOrder(
 		AssetSpecifier: assetSpecifier,
 		AssetMaxAmt:    req.AssetMaxAmt,
 		Expiry:         req.Expiry,
-		Peer:           peer,
+		Peer:           fn.MaybeSome(peer),
 	}, nil
 }
 
@@ -6335,12 +6335,13 @@ func (r *rpcServer) AddAssetBuyOrder(_ context.Context,
 		return nil, fmt.Errorf("error unmarshalling buy order: %w", err)
 	}
 
-	var peer string
-	if buyOrder.Peer != nil {
-		peer = buyOrder.Peer.String()
-	}
+	peerStr := fn.MapOptionZ(
+		buyOrder.Peer, func(peerVertex route.Vertex) string {
+			return peerVertex.String()
+		},
+	)
 	rpcsLog.Debugf("[AddAssetBuyOrder]: upserting buy order "+
-		"(dest_peer=%s)", peer)
+		"(dest_peer=%s)", peerStr)
 
 	// Register an event listener before actually inserting the order, so we
 	// definitely don't miss any responses.
@@ -6382,7 +6383,7 @@ func (r *rpcServer) AddAssetBuyOrder(_ context.Context,
 
 		case <-timeout:
 			return nil, fmt.Errorf("timeout waiting for response "+
-				"from peer %x", buyOrder.Peer[:])
+				"(peer=%s)", peerStr)
 		}
 	}
 }