Garmin: Fix MLR retransmission request numbers

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/DeviceCoordinator.java

@@ -821,7 +821,8 @@ public interface DeviceCoordinator {
     int[] getSupportedDeviceSpecificAuthenticationSettings();
 
     /**
-     * Returns device specific debug settings. This section is only shown in debug builds.
+     * Returns device specific debug settings. This section is only shown in debug builds, and all behavior-altering
+     * preferences should be gate-kept by the BuildConfig.DEBUG flag.
      */
     int[] getSupportedDebugSettings(final GBDevice device);
 

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/garmin/GarminCoordinator.java

@@ -8,6 +8,8 @@ import android.app.Activity;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 
+import org.apache.commons.lang3.ArrayUtils;
+
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
@@ -228,6 +230,14 @@ public abstract class GarminCoordinator extends AbstractBLEDeviceCoordinator {
         return new int[]{R.xml.devicesettings_garmin_experimental};
     }
 
+    @Override
+    public int[] getSupportedDebugSettings(final GBDevice device) {
+        return ArrayUtils.add(
+                super.getSupportedDebugSettings(device),
+                R.xml.devicesettings_debug_drop_packets
+        );
+    }
+
     @Override
     public DeviceSpecificSettings getDeviceSpecificSettings(final GBDevice device) {
         final DeviceSpecificSettings deviceSpecificSettings = new DeviceSpecificSettings();

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/devices/garmin/communicator/v2/CommunicatorV2.java

@@ -21,7 +21,9 @@ import java.util.HashMap;
 import java.util.Map;
 import java.util.Objects;
 import java.util.UUID;
+import java.util.concurrent.ThreadLocalRandom;
 
+import nodomain.freeyourgadget.gadgetbridge.BuildConfig;
 import nodomain.freeyourgadget.gadgetbridge.GBApplication;
 import nodomain.freeyourgadget.gadgetbridge.database.DBHandler;
 import nodomain.freeyourgadget.gadgetbridge.database.DBHelper;
@@ -161,6 +163,18 @@ public class CommunicatorV2 implements ICommunicator {
             final int handle = ((value[0] & MlrCommunicator.HANDLE_MASK) >> 4) | MlrCommunicator.MLR_FLAG_MASK;
             final MlrCommunicator mlrComm = mlrCommunicators.get(handle);
             if (mlrComm != null) {
+                if (BuildConfig.DEBUG) {
+                    final int packetPercentageIn = mSupport.getDevicePrefs().getInt("pref_debug_drop_packet_percentage_in", 0);
+                    if (packetPercentageIn > 0 && ThreadLocalRandom.current().nextInt(100) < packetPercentageIn) {
+                        LOG.warn(
+                                "Simulating dropped inbound packet handle={}, dataLen={}",
+                                handle,
+                                value.length
+                        );
+                        return true;
+                    }
+                }
+
                 mlrComm.onPacketReceived(value);
                 return true;
             }
@@ -639,9 +653,18 @@ public class CommunicatorV2 implements ICommunicator {
     }
 
     private MlrCommunicator createMlrCommunicator(final int handle, final ServiceCallback callback) {
-        final MlrCommunicator.MessageSender messageSender = (taskName, packet) -> mSupport.createTransactionBuilder(taskName)
-                .write(characteristicSend, packet)
-                .queue();
+        final MlrCommunicator.MessageSender messageSender = (taskName, packet) -> {
+            if (BuildConfig.DEBUG) {
+                final int packetPercentageOut = mSupport.getDevicePrefs().getInt("pref_debug_drop_packet_percentage_out", 0);
+                if (packetPercentageOut > 0 && ThreadLocalRandom.current().nextInt(100) < packetPercentageOut) {
+                    LOG.warn("Simulating dropped outbound packet for {} ({})", taskName, GB.hexdump(packet));
+                    return;
+                }
+            }
+            mSupport.createTransactionBuilder(taskName)
+                    .write(characteristicSend, packet)
+                    .queue();
+        };
 
         return new MlrCommunicator(handle, maxWriteSize, messageSender, callback::onMessage);
     }

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/devices/garmin/communicator/v2/MlrCommunicator.java

@@ -81,12 +81,12 @@ public class MlrCommunicator {
             int position = 0;
             while (remainingBytes > 0) {
                 final byte[] fragment = Arrays.copyOfRange(message, position, position + Math.min(remainingBytes, maxPacketSize - 2));
-                fragmentQueue.add(new Fragment(taskName, i++, fragment));
+                fragmentQueue.add(new Fragment(taskName, i++, fragment, 0));
                 position += fragment.length;
                 remainingBytes -= fragment.length;
             }
         } else {
-            fragmentQueue.add(new Fragment(taskName, 0, message));
+            fragmentQueue.add(new Fragment(taskName, 0, message, 0));
         }
 
         runProtocol();
@@ -219,9 +219,11 @@ public class MlrCommunicator {
         // Send next fragment if available
         final Fragment fragment = fragmentQueue.poll();
         if (fragment != null) {
+            // Update the fragment with the current reqNum before storing it
+            final Fragment fragmentWithReqNum = new Fragment(fragment.taskName, fragment.num, fragment.data, nextRcvSeq);
             final byte[] packet = createPacket(nextRcvSeq, nextSendSeq, fragment.data);
             messageSender.sendPacket(fragment.taskName + " (" + fragment.num + ")", packet);
-            sentFragments[nextSendSeq] = fragment;
+            sentFragments[nextSendSeq] = fragmentWithReqNum;
 
             nextSendSeq = (nextSendSeq + 1) % (MAX_SEQ_NUM + 1);
 
@@ -278,7 +280,8 @@ public class MlrCommunicator {
                 LOG.error("Attempting to re-send null fragment at index {}", i);
                 continue;
             }
-            final byte[] packet = createPacket(nextRcvSeq, i, fragment.data);
+            // Use the original reqNum that was stored when the fragment was first sent
+            final byte[] packet = createPacket(fragment.reqNum, i, fragment.data);
             messageSender.sendPacket("retransmission " + fragment.taskName + " (" + fragment.num + ")", packet);
         }
 
@@ -307,6 +310,6 @@ public class MlrCommunicator {
         void onDataReceived(final byte[] data);
     }
 
-    private record Fragment(String taskName, int num, byte[] data) {
+    private record Fragment(String taskName, int num, byte[] data, int reqNum) {
     }
 }

app/src/main/res/xml/devicesettings_debug_drop_packets.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.preference.PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto">
+    <SeekBarPreference
+        android:defaultValue="0"
+        android:icon="@drawable/ic_file_upload"
+        android:key="pref_debug_drop_packet_percentage_out"
+        android:max="100"
+        android:summary="Probability of failing to send a packet"
+        android:title="Simulate packet loss - outbound"
+        app:showSeekBarValue="true" />
+    <SeekBarPreference
+        android:defaultValue="0"
+        android:icon="@drawable/ic_download"
+        android:key="pref_debug_drop_packet_percentage_in"
+        android:max="100"
+        android:summary="Probability of failing to receive a packet"
+        android:title="Simulate packet loss - inbound"
+        app:showSeekBarValue="true" />
+</androidx.preference.PreferenceScreen>