Add external USB GNSS and NTRIP support

project/app/build.gradle.kts

@@ -234,6 +234,9 @@ dependencies {
   implementation(libs.paho.mqttclient)
   implementation(libs.okhttp)
 
+  // External USB GNSS (u-blox F9P et al.)
+  implementation("com.github.mik3y:usb-serial-for-android:3.5.1")
+
   // Utility libraries
   implementation(libs.bundles.hilt)
   implementation(libs.square.tape2)

project/app/src/gms/java/org/owntracks/android/di/LocationProviderClientModule.kt

@@ -8,14 +8,21 @@ import dagger.hilt.android.qualifiers.ApplicationContext
 import dagger.hilt.components.SingletonComponent
 import javax.inject.Singleton
 import org.owntracks.android.gms.location.GMSLocationProviderClient
+import org.owntracks.android.location.ExternalGnssLocationProviderClient
 import org.owntracks.android.location.LocationProviderClient
+import org.owntracks.android.location.external.ExternalGnssController
 
 @InstallIn(SingletonComponent::class)
 @Module
 class LocationProviderClientModule {
   @Provides
   @Singleton
   fun getLocationProviderClient(
-      @ApplicationContext applicationContext: Context
-  ): LocationProviderClient = GMSLocationProviderClient.create(applicationContext)
+      @ApplicationContext applicationContext: Context,
+      externalGnssController: ExternalGnssController,
+  ): LocationProviderClient =
+      ExternalGnssLocationProviderClient(
+          delegate = GMSLocationProviderClient.create(applicationContext),
+          controller = externalGnssController,
+      )
 }

project/app/src/main/AndroidManifest.xml

@@ -19,6 +19,10 @@
         android:name="android.hardware.wifi"
         android:required="false" />
 
+    <uses-feature
+        android:name="android.hardware.usb.host"
+        android:required="false" />
+
     <uses-permission android:name="android.permission.INTERNET" />
     <!-- To access the network -->
     <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
@@ -243,6 +247,12 @@
                 <category android:name="android.intent.category.LAUNCHER" />
                 <category android:name="android.intent.category.DEFAULT" />
             </intent-filter>
+            <intent-filter>
+                <action android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED" />
+            </intent-filter>
+            <meta-data
+                android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED"
+                android:resource="@xml/usb_device_filter" />
             <meta-data
                 android:name="android.app.shortcuts"
                 android:resource="@xml/shortcuts" />

project/app/src/main/java/org/owntracks/android/location/ExternalGnssLocationProviderClient.kt

@@ -0,0 +1,54 @@
+package org.owntracks.android.location
+
+import android.location.Location
+import android.os.Looper
+import androidx.annotation.RequiresPermission
+import org.owntracks.android.location.external.ExternalGnssController
+
+/**
+ * [LocationProviderClient] that wraps an existing provider (AOSP or GMS) and augments it with fixes
+ * coming from an external USB GNSS receiver managed by [ExternalGnssController].
+ *
+ * All location requests are transparently forwarded to the [delegate]; in addition, every
+ * [LocationCallback] is registered with the controller so it also receives synthetic
+ * [android.location.Location] objects built from external NMEA fixes.
+ */
+class ExternalGnssLocationProviderClient(
+    private val delegate: LocationProviderClient,
+    private val controller: ExternalGnssController,
+) : LocationProviderClient() {
+
+  @RequiresPermission(
+      anyOf =
+          ["android.permission.ACCESS_FINE_LOCATION", "android.permission.ACCESS_COARSE_LOCATION"])
+  override fun singleHighAccuracyLocation(clientCallBack: LocationCallback, looper: Looper) {
+    delegate.singleHighAccuracyLocation(clientCallBack, looper)
+  }
+
+  @RequiresPermission(
+      anyOf =
+          ["android.permission.ACCESS_FINE_LOCATION", "android.permission.ACCESS_COARSE_LOCATION"])
+  override fun actuallyRequestLocationUpdates(
+      locationRequest: LocationRequest,
+      clientCallBack: LocationCallback,
+      looper: Looper
+  ) {
+    // Forward to the real provider (uses the public entry point because the "actually" method is
+    // protected on the delegate).
+    delegate.requestLocationUpdates(locationRequest, clientCallBack, looper)
+    controller.registerCallback(clientCallBack)
+  }
+
+  override fun removeLocationUpdates(clientCallBack: LocationCallback) {
+    delegate.removeLocationUpdates(clientCallBack)
+    controller.unregisterCallback(clientCallBack)
+  }
+
+  override fun flushLocations() {
+    delegate.flushLocations()
+  }
+
+  override fun getLastLocation(): Location? {
+    return controller.getLastExternalLocation() ?: delegate.getLastLocation()
+  }
+}