Move from slow JSON to much quicker byte transfer

app/build.gradle

@@ -28,7 +28,6 @@ android {
 }
 
 dependencies {
-    implementation 'com.google.code.gson:gson:2.8.8'
     implementation 'androidx.appcompat:appcompat:1.2.0'
     implementation 'com.google.android.material:material:1.3.0'
     implementation 'androidx.constraintlayout:constraintlayout:2.0.4'

app/src/main/java/uk/robware/vanlights/Light.java

@@ -1,12 +1,14 @@
 package uk.robware.vanlights;
 
 public class Light {
+	public byte id;
 	public String name;
 	public boolean on;
 	public float brightness = 1;
 	public int timer;
 
-	public Light(String lightName) {
+	public Light(byte id, String lightName) {
+		this.id = id;
 		name=lightName;
 	}
 }

app/src/main/java/uk/robware/vanlights/LightsService.java

@@ -12,8 +12,7 @@ import android.os.Binder;
 import android.os.Handler;
 import android.os.IBinder;
 
-import com.google.gson.Gson;
+import java.nio.ByteBuffer;
-
 import java.util.HashMap;
 import java.util.Map;
 import java.util.UUID;
@@ -21,13 +20,18 @@ import java.util.UUID;
 public class LightsService extends Service {
 	private final IBinder binder = new LightsBinder();
 	private Map<String, Light> _lights= new HashMap<>();
+	private Map<Integer, Light> _lightsById= new HashMap<>();
 	private MainActivity _mainActivity;
 
 	public LightsService(){
-		_lights.put("seating", new Light("seating"));
+		_lights.put("seating", new Light((byte) 1, "seating"));
-		_lights.put("kitchen", new Light("kitchen"));
+		_lights.put("kitchen", new Light((byte) 2, "kitchen"));
-		_lights.put("bathroom", new Light("bathroom"));
+		_lights.put("bathroom", new Light((byte) 3, "bathroom"));
-		_lights.put("awning", new Light("awning"));
+		_lights.put("awning", new Light((byte) 4, "awning"));
+
+		for (Light light : _lights.values()) {
+			_lightsById.put(Integer.valueOf(light.id), light);
+		}
 	}
 
 	public class LightsBinder extends Binder {
@@ -79,21 +83,34 @@ public class LightsService extends Service {
 		}
 	};
 
-	private void readControllerData(BluetoothGattCharacteristic characteristic) {
+	public int bytesToInt(byte[] bytes) {
-		byte[] value = characteristic.getValue();
+		ByteBuffer buffer = ByteBuffer.allocate(Integer.BYTES);
-		if (value.length == 0)
+		buffer.put(bytes);
-			return;
+		buffer.flip();//need flip
-
+		return buffer.getInt();
-		String jsonString = new String(value);
-		Gson json = new Gson();
-		Light[] lights = new Light[0];
-		lights = json.fromJson(jsonString, lights.getClass());
-		for (Light light : lights) {
-			_lights.put(light.name, light);
 	}
 
-		if (_mainActivity!=null)
+	public float bytesToFloat(byte[] bytes) {
-			_mainActivity.dataReadCallback(_lights);
+		ByteBuffer buffer = ByteBuffer.allocate(Float.BYTES);
+		buffer.put(bytes);
+		buffer.flip();//need flip
+		return buffer.getFloat();
+	}
+
+	private void readControllerData(BluetoothGattCharacteristic characteristic) {
+//		byte[] value = characteristic.getValue();
+//		if (value.length == 0)
+//			return;
+//
+//		for (int i=0; i<value.length;i+=10){
+//			Light light=_lightsById.get(Integer.valueOf(value[i]));
+//			light.on=value[i+1]==1;
+//			light.brightness=bytesToFloat(new byte[]{value[i+2],value[i+3],value[i+4],value[i+5]});
+//			light.timer=bytesToInt(new byte[]{value[i+6],value[i+7],value[i+8],value[i+9]});
+//		}
+//
+//		if (_mainActivity!=null)
+//			_mainActivity.dataReadCallback(_lights);
 	}
 
 	public void registerUI(MainActivity mainActivity){
@@ -109,10 +126,49 @@ public class LightsService extends Service {
     	_gatt.disconnect();
 	}
 
+	public byte[] intToBytes(int x) {
+		ByteBuffer buffer = ByteBuffer.allocate(Integer.BYTES);
+		buffer.putInt(x);
+		return buffer.array();
+	}
+
+	public byte[] floatToBytes(float x) {
+		ByteBuffer buffer = ByteBuffer.allocate(Float.BYTES);
+		buffer.putFloat(x);
+		return buffer.array();
+	}
+
+	private byte[] getLightDataAsBytes() {
+		byte[] data=new byte[10 * _lights.size()];
+
+		int dataIndex=0;
+		for (Light light : _lights.values()) {
+			data[dataIndex]= light.id;
+			data[dataIndex+1]= (byte) (light.on?1:0);
+
+			int brightnessByteIndex=0;
+			byte[] brightnessToBytes = intToBytes((int) (light.brightness*100));
+			for (byte brightnessByte: brightnessToBytes) {
+				data[dataIndex + 2 + brightnessByteIndex] = brightnessByte;
+				brightnessByteIndex++;
+			}
+
+			int timerByteIndex=0;
+			byte[] timerToBytes = intToBytes(light.timer);
+			for (byte timerByte: timerToBytes) {
+				data[dataIndex + 6 + timerByteIndex] = timerByte;
+				timerByteIndex++;
+			}
+
+			dataIndex+=10;
+		}
+
+		return data;
+	}
+
 	public boolean sendUpdate() {
-		Gson json=new Gson();
+		byte[] data=getLightDataAsBytes();
-		String value = json.toJson(_lights.values());
+		return write(data);
-		return write(value);
 	}
 
 	public void updateState(String name, boolean state) {
@@ -131,7 +187,7 @@ public class LightsService extends Service {
 		light.timer=totalSeconds;
 	}
 
-    private boolean write(String value){
+    private boolean write(byte[] value){
     	if (_characteristic==null || _gatt==null)
     		return false;
         _characteristic.setValue(value);