support velocity SendFast

build-and-push.sh

@@ -0,0 +1,2 @@
+podman manifest create $1
+podman build --platform linux/amd64,linux/arm64 --manifest $1 -f Dockerfile_fsd .

fsd/client.go

@@ -17,6 +17,7 @@ type Client struct {
 	sendChan  chan string
 
 	lat, lon, visRange            atomic.Float64
+	closestVelocityClientDistance float64 // The closest Velocity-compatible client in meters
 
 	flightPlan         atomic.String
 	assignedBeaconCode atomic.String
@@ -32,6 +33,10 @@ type Client struct {
 	loginData
 
 	authState       vatsimAuthState
+	sendFastEnabled bool
+}
+
+type LatLon struct {
 }
 
 func newClient(ctx context.Context, conn net.Conn, scanner *bufio.Scanner, loginData loginData) (client *Client) {

fsd/handler.go

@@ -163,6 +163,17 @@ func (s *Server) handlePilotPosition(client *Client, packet []byte) {
 	client.heading.Store(int32(heading))
 
 	client.lastUpdated.Store(time.Now())
+
+	// Check if we need to update the sendfast state
+	if client.sendFastEnabled {
+		if (client.closestVelocityClientDistance / 1852.0) > 5.0 { // 5.0 nautical miles
+			sendDisableSendFastPacket(client)
+		}
+	} else {
+		if (client.closestVelocityClientDistance / 1852.0) < 5.0 { // 5.0 nautical miles
+			sendEnableSendFastPacket(client)
+		}
+	}
 }
 
 // handleFastPilotPosition handles logic for fast `^`, stopped `#ST`, and slow `#SL` pilot position updates

fsd/postoffice.go

@@ -85,15 +85,27 @@ func (p *postOffice) updatePosition(client *Client, newCenter [2]float64, newVis
 	return
 }
 
-// search calls `callback` for every other Client within geographical range of the provided Client
+// search calls `callback` for every other Client within geographical range of the provided Client.
+//
+// It automatically resets and populates the Client.nearbyClients and Client.closestVelocityClientDistance values
 func (p *postOffice) search(client *Client, callback func(recipient *Client) bool) {
 	clientMin, clientMax := calculateBoundingBox(client.latLon(), client.visRange.Load())
 
+	client.closestVelocityClientDistance = math.MaxFloat64
+
 	p.treeLock.RLock()
 	p.tree.Search(clientMin, clientMax, func(foundMin [2]float64, foundMax [2]float64, foundClient *Client) bool {
 		if foundClient == client {
 			return true // Ignore self
 		}
+
+		if foundClient.protoRevision == 101 {
+			dist := distance(client.lat.Load(), client.lon.Load(), foundClient.lat.Load(), foundClient.lon.Load())
+			if dist < client.closestVelocityClientDistance {
+				client.closestVelocityClientDistance = dist
+			}
+		}
+		
 		return callback(foundClient)
 	})
 	p.treeLock.RUnlock()

fsd/util.go

@@ -391,3 +391,30 @@ func pitchBankHeading(packed uint32) (pitch float64, bank float64, heading float
 func strPtr(str string) *string {
 	return &str
 }
+
+// sendEnableSendFastPacket sends an 'enable' $SF Send Fast packet to the client
+func sendEnableSendFastPacket(client *Client) {
+	sendSendFastPacket(client, true)
+}
+
+// sendDisableSendFastPacket sends a 'disable' $SF Send Fast packet to the client
+func sendDisableSendFastPacket(client *Client) {
+	sendSendFastPacket(client, false)
+}
+
+// sendSendFastPacket sends a $SF Send Fast packet to the client
+func sendSendFastPacket(client *Client, enabled bool) {
+	builder := strings.Builder{}
+	builder.Grow(32)
+	builder.WriteString("$SFSERVER:")
+	builder.WriteString(client.callsign)
+	builder.WriteByte(':')
+	if enabled {
+		builder.WriteByte('1')
+	} else {
+		builder.WriteByte('0')
+	}
+	builder.WriteString("\r\n")
+
+	client.send(builder.String())
+}