Inapproproate way of sending locations is used

[fynngodau]

The Signal app currently uses the following method of sharing a user's location, after the user has selected a location on the in-app map.

1. Load Google Map.
2. Wait for Google Map to finish loading.
3. Take snapshot of Google Map.
4. Remove Google Map and replace it with its snapshot.
5. Once the user hits send, send this snapshot as an image.

This is implemented in the following snippet:

Signal-Android/app/src/main/java/org/thoughtcrime/securesms/components/location/SignalMapView.java

Lines 77 to 99 in 6eaebd1

	public static ListenableFuture<Bitmap> snapshot(final LatLng place, @NonNull final MapView mapView) {
	final SettableFuture<Bitmap> future = new SettableFuture<>();
	mapView.onCreate(null);
	mapView.onStart();
	mapView.onResume();
	mapView.setVisibility(View.VISIBLE);
	mapView.getMapAsync(googleMap -> {
	googleMap.moveCamera(CameraUpdateFactory.newLatLngZoom(place, 13));
	googleMap.addMarker(new MarkerOptions().position(place));
	googleMap.setBuildingsEnabled(true);
	googleMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
	googleMap.getUiSettings().setAllGesturesEnabled(false);
	googleMap.setOnMapLoadedCallback(() -> googleMap.snapshot(bitmap -> {
	future.set(bitmap);
	mapView.setVisibility(View.GONE);
	mapView.onPause();
	mapView.onStop();
	mapView.onDestroy();
	}));
	});

The two issues are:

• 1.-4. is an inappropriate way of generating a snapshot. It is better to use a lite mode map instead, because this implements exactly what is needed (non-interactive snapshot of a map).
  • An instance in which the current implementation is inappropriate is when onMapLoaded and onSnapshotReady have not yet been called, but the activity hosting the map is destroyed. In this case, the activity's onDestroy method must call the map's onDestroy method (which is not implemented). Lite mode maps do not expect lifecycle methods to be called, except for onCreate.
  • In fact, Signal originally forgot to call a few of the lifecycle methods. See Call all lifecycle methods on snapshot mapView #13008.
  • Additional info: this is also related to Unable to share location on Android #12723 (comment), because microG does not implement GoogleMap.OnMapLoadedCallback correctly (Implement GoogleMap.OnMapLoadedCallback correctly microg/GmsCore#1960).
• ⁠5. is in violation of the contract of the snapshot API, and by extension likely also of the terms of usage of the Google Maps API.

  Note: Images of the map must not be transmitted to your servers, or otherwise used outside of the application. If you need to send a map to another application or user, send data that allows them to reconstruct the map for the new user instead of a snapshot.

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