linux: do not randomize order of returned discovered services/chars

Previously the list of services and characteristics wasn't sorted, and
because of the way Go maps work they were in fact randomized.
This commit fixes the sorting for services and characteristics, which
both suffered from the same lack of sorting.

This fixes #135.

Author: aykevl

gattc_linux.go

@@ -5,9 +5,11 @@ package bluetooth
 
 import (
 	"errors"
+	"sort"
 	"strings"
 	"time"
 
+	"github.com/godbus/dbus/v5"
 	"github.com/muka/go-bluetooth/bluez"
 	"github.com/muka/go-bluetooth/bluez/profile/gatt"
 )
@@ -70,15 +72,20 @@ func (d *Device) DiscoverServices(uuids []UUID) ([]DeviceService, error) {
 	if err != nil {
 		return nil, err
 	}
+	objects := make([]string, 0, len(list))
 	for objectPath := range list {
-		if !strings.HasPrefix(string(objectPath), string(d.device.Path())+"/service") {
+		objects = append(objects, string(objectPath))
+	}
+	sort.Strings(objects)
+	for _, objectPath := range objects {
+		if !strings.HasPrefix(objectPath, string(d.device.Path())+"/service") {
 			continue
 		}
-		suffix := string(objectPath)[len(d.device.Path()+"/"):]
+		suffix := objectPath[len(d.device.Path()+"/"):]
 		if len(strings.Split(suffix, "/")) != 1 {
 			continue
 		}
-		service, err := gatt.NewGattService1(objectPath)
+		service, err := gatt.NewGattService1(dbus.ObjectPath(objectPath))
 		if err != nil {
 			return nil, err
 		}
@@ -160,15 +167,20 @@ func (s *DeviceService) DiscoverCharacteristics(uuids []UUID) ([]DeviceCharacter
 	if err != nil {
 		return nil, err
 	}
+	objects := make([]string, 0, len(list))
 	for objectPath := range list {
-		if !strings.HasPrefix(string(objectPath), string(s.service.Path())+"/char") {
+		objects = append(objects, string(objectPath))
+	}
+	sort.Strings(objects)
+	for _, objectPath := range objects {
+		if !strings.HasPrefix(objectPath, string(s.service.Path())+"/char") {
 			continue
 		}
-		suffix := string(objectPath)[len(s.service.Path()+"/"):]
+		suffix := objectPath[len(s.service.Path()+"/"):]
 		if len(strings.Split(suffix, "/")) != 1 {
 			continue
 		}
-		characteristic, err := gatt.NewGattCharacteristic1(objectPath)
+		characteristic, err := gatt.NewGattCharacteristic1(dbus.ObjectPath(objectPath))
 		if err != nil {
 			return nil, err
 		}