linux: rewrite everything to use DBus directly

This is a big rewrite to use DBus calls directly instead of going
through go-bluetooth first.

This is a big change, but I believe it is an improvement. While the
go-bluetooth works for many cases, it's a layer in between that I
believe hurts more than it helps. Without it, we can just program
directly against the BlueZ D-Bus API. The end result is about 10% more
code.

With this rewrite, I fixed the following issues:

  * All MapToStruct warnings are gone, like in
    #193.
  * Advertisements can be restarted after they were stopped. Previously
    this resulted in a panic.
  * Looking at the source code of go-bluetooth, it appears that it
    includes devices from a different Bluetooth adapter than the one
    that's currently scanning. This is fixed with the rewrite.
  * Fix a bug in Adapter.AddService where it would only allow adding a
    single service. Multiple services can now be added.
    This was actually the motivating bug that led me down to rewrite the
    whole thing because I couldn't figure out where the bug was in
    go-bluetooth (it's many layers deep).
  * The `WriteEvent` callback in a characteristic now also gets the
    'offset' parameter which wasn't provided by go-bluetooth.

This rewrite also avoids go-bluetooth specific workarounds like
#74 and
#121.

I have tested all examples in the smoketest-linux Makefile target. They
all still work with this rewrite.

README.md

@@ -106,7 +106,7 @@ func must(action string, err error) {
 
 ## Linux
 
-Go Bluetooth support for Linux uses [BlueZ](http://www.bluez.org/) via the [D-Bus](https://en.wikipedia.org/wiki/D-Bus) interface thanks to the https://github.com/muka/go-bluetooth package. This should work with most distros that support BlueZ such as Ubuntu, Debian, Fedora, and Arch Linux, among others. 
+Go Bluetooth support for Linux uses [BlueZ](http://www.bluez.org/) via the [D-Bus](https://en.wikipedia.org/wiki/D-Bus) interface. This should work with most distros that support BlueZ such as Ubuntu, Debian, Fedora, and Arch Linux, among others.
 
 Linux can be used both as a BLE Central or as a BLE Peripheral.
 

adapter_linux.go

@@ -7,15 +7,20 @@ package bluetooth
 
 import (
 	"errors"
+	"fmt"
 
-	"github.com/muka/go-bluetooth/api"
-	"github.com/muka/go-bluetooth/bluez/profile/adapter"
+	"github.com/godbus/dbus/v5"
 )
 
+const defaultAdapter = "hci0"
+
 type Adapter struct {
-	adapter              *adapter.Adapter1
 	id                   string
-	cancelChan           chan struct{}
+	scanCancelChan       chan struct{}
+	bus                  *dbus.Conn
+	bluez                dbus.BusObject // object at /
+	adapter              dbus.BusObject // object at /org/bluez/hciX
+	address              string
 	defaultAdvertisement *Advertisement
 
 	connectHandler func(device Address, connected bool)
@@ -26,29 +31,38 @@ type Adapter struct {
 //
 // Make sure to call Enable() before using it to initialize the adapter.
 var DefaultAdapter = &Adapter{
+	id: defaultAdapter,
 	connectHandler: func(device Address, connected bool) {
-		return
 	},
 }
 
 // Enable configures the BLE stack. It must be called before any
 // Bluetooth-related calls (unless otherwise indicated).
 func (a *Adapter) Enable() (err error) {
-	if a.id == "" {
-		a.adapter, err = api.GetDefaultAdapter()
-		if err != nil {
-			return
+	bus, err := dbus.SystemBus()
+	if err != nil {
+		return err
+	}
+	a.bus = bus
+	a.bluez = a.bus.Object("org.bluez", dbus.ObjectPath("/"))
+	a.adapter = a.bus.Object("org.bluez", dbus.ObjectPath("/org/bluez/"+a.id))
+	addr, err := a.adapter.GetProperty("org.bluez.Adapter1.Address")
+	if err != nil {
+		if err, ok := err.(dbus.Error); ok && err.Name == "org.freedesktop.DBus.Error.UnknownObject" {
+			return fmt.Errorf("bluetooth: adapter %s does not exist", a.adapter.Path())
 		}
-		a.id, err = a.adapter.GetAdapterID()
+		return fmt.Errorf("could not activate BlueZ adapter: %w", err)
 	}
+	addr.Store(&a.address)
+
 	return nil
 }
 
 func (a *Adapter) Address() (MACAddress, error) {
-	if a.adapter == nil {
+	if a.address == "" {
 		return MACAddress{}, errors.New("adapter not enabled")
 	}
-	mac, err := ParseMAC(a.adapter.Properties.Address)
+	mac, err := ParseMAC(a.address)
 	if err != nil {
 		return MACAddress{}, err
 	}