[Draft] Improve BLE reliability

 - Increase timeouts for BLE dialer and listener
 - Retry initial connection on non-fatal errors until context expires
 - Tweak scanning interval to reflect BLE advertisement parameters

TODO:

 - Retry connection using client MAC address instead of scanning
 - Optimize scanning interval
 - Adjust timeouts using caller context
 - Test Maximum BLE connections
 - Test vehicles with different BLE advertisement intervals

cmd/tesla-control/commands.go

@@ -655,7 +655,7 @@ var commands = map[string]*Command{
 	},
 	"session-info": &Command{
 		help:             "Retrieve session info for PUBLIC_KEY from DOMAIN",
-		requiresAuth:     true,
+		requiresAuth:     false,
 		requiresFleetAPI: false,
 		args: []Argument{
 			Argument{name: "PUBLIC_KEY", help: "file containing public key (or corresponding private key)"},

pkg/connector/ble/ble.go

@@ -6,16 +6,20 @@ import (
 	"context"
 	"crypto/sha1"
 	"fmt"
+	"strings"
 	"sync"
 	"time"
 
 	"github.com/go-ble/ble"
 	"github.com/teslamotors/vehicle-command/internal/log"
 	"github.com/teslamotors/vehicle-command/pkg/connector"
+	"github.com/teslamotors/vehicle-command/pkg/protocol"
 )
 
 const maxBLEMessageSize = 1024
 
+var ErrMaxConnectionsExceeded = protocol.NewError("the vehicle is already connected to the maximum number of BLE devices", false, false)
+
 var (
 	rxTimeout  = time.Second     // Timeout interval between receiving chunks of a mesasge
 	maxLatency = 4 * time.Second // Max allowed error when syncing vehicle clock
@@ -122,6 +126,27 @@ func (c *Connection) VIN() string {
 }
 
 func NewConnection(ctx context.Context, vin string) (*Connection, error) {
+	var lastError error
+	for {
+		conn, err := tryToConnect(ctx, vin)
+		if err == nil {
+			return conn, nil
+		}
+		if strings.Contains(err.Error(), "operation not permitted") {
+			return nil, err
+		}
+		log.Warning("BLE connection attempt failed: %s", err)
+		if err := ctx.Err(); err != nil {
+			if lastError != nil {
+				return nil, lastError
+			}
+			return nil, err
+		}
+		lastError = err
+	}
+}
+
+func tryToConnect(ctx context.Context, vin string) (*Connection, error) {
 	var err error
 	// We don't want concurrent calls to NewConnection that would defeat
 	// the point of reusing the existing BLE device. Note that this is not
@@ -145,19 +170,27 @@ func NewConnection(ctx context.Context, vin string) (*Connection, error) {
 
 	localName := fmt.Sprintf("S%02xC", digest[:8])
 	log.Debug("Searching for BLE beacon %s...", localName)
+	canConnect := false
 	filter := func(adv ble.Advertisement) bool {
-		if !adv.Connectable() || adv.LocalName() != localName {
+		ln := adv.LocalName()
+		log.Debug(" ... found '%s' (RSSI=%3d)", ln, adv.RSSI())
+		if ln != localName {
 			return false
 		}
+		canConnect = adv.Connectable()
 		return true
 	}
 
-	log.Debug("Connecting to BLE beacon...")
 	client, err := ble.Connect(ctx, filter)
 	if err != nil {
 		return nil, fmt.Errorf("failed to find BLE beacon for %s (%s): %s", vin, localName, err)
 	}
 
+	if !canConnect {
+		return nil, ErrMaxConnectionsExceeded
+	}
+
+	log.Debug("Connecting to BLE beacon %s...", client.Addr())
 	services, err := client.DiscoverServices([]ble.UUID{vehicleServiceUUID})
 	if err != nil {
 		return nil, fmt.Errorf("ble: failed to enumerate device services: %s", err)

pkg/connector/ble/device_linux.go

@@ -3,10 +3,24 @@ package ble
 import (
 	"github.com/go-ble/ble"
 	"github.com/go-ble/ble/linux"
+	"github.com/go-ble/ble/linux/hci/cmd"
+	"time"
 )
 
+const bleTimeout = 20 * time.Second
+
+// TODO: Depending on the model and state, BLE advertisements come every 20ms or every 150ms.
+
+var scanParams = cmd.LESetScanParameters{
+	LEScanType:           1,    // Active scanning
+	LEScanInterval:       0x10, // 10ms
+	LEScanWindow:         0x10, // 10ms
+	OwnAddressType:       0,    // Static
+	ScanningFilterPolicy: 2,    // Basic filtered
+}
+
 func newDevice() (ble.Device, error) {
-	device, err := linux.NewDevice()
+	device, err := linux.NewDevice(ble.OptListenerTimeout(bleTimeout), ble.OptDialerTimeout(bleTimeout), ble.OptScanParams(scanParams))
 	if err != nil {
 		return nil, err
 	}