Create and display back-to-back trips

Back-to-back trips are exclusive, independent trips that occur one right after the other, where the driver commits to picking up the next consumer before completing the current trip.

The main difference between a back-to-back trip and a single-destination trip, is that in with a back-to-back trip, the trip operator could assign a trip to a vehicle that has already been assigned trips.

This tutorial walks you through the process of creating a back-to-back trip. It also shows how you can then integrate that trip with your consumer-application so that your customers can visualize the trip progress from their phones. You do this integration using the Consumer SDK.

Prerequisites

To complete this tutorial, be sure to complete the following:

1. Set up the Fleet Engine. For more information, see Fleet Engine: Initial setup.

2. Integrate your app with the Driver SDK. For more information, see Initializing the Driver SDK for Android, and Integration Guide for the Driver SDK for iOS.

3. Integrate your consumer-facing app with the Consumer SDK. For more information, see Getting Started with the Consumer SDK for Android, and Getting Started with the Consumer SDK for iOS.

4. Set up authorization tokens. For more information about authorization tokens, see Creating a JSON Web Token for authorization in the Getting Started with Fleet Engine guide, and Authentication and authorization in the Consumer SDK documentation for Fleet Engine.

Step 1. Create a vehicle in Fleet Engine

Vehicles are objects that represent the vehicles in your fleet. You must create them in Fleet Engine in order to be able to track them in the consumer app.

You can create a vehicle using either of the following two approaches:

gRPC

Call the CreateVehicle() method with the CreateVehicleRequest request message. You must have Fleet Engine Super User privileges to call CreateVehicle().

REST

Call https://fleetengine.googleapis.com/v1/providers.vehicles.create.

Caveats

The following caveats apply when you create a vehicle.

• Be sure to set the initial vehicle state to OFFLINE. This ensures that Fleet Engine can discover your vehicle for trip matching.

• The vehicle's provider_id must be the same as the project ID of the Google Cloud Project that contains the Service Accounts used for calling Fleet Engine. While multiple service accounts can access the Fleet Engine for the same rideshare provider, Fleet Engine doesn't currently support service accounts from different Google Cloud Projects accessing the same vehicles.

• The response returned from CreateVehicle() contains the Vehicle instance. The instance is deleted after seven days if it has not been updated using UpdateVehicle(). You should call GetVehicle() before calling CreateVehicle() just to confirm that the vehicle doesn't already exist. If GetVehicle() returns a NOT_FOUND error, then you should proceed with calling CreateVehicle(). For more information, see Vehicles and their lifecycle.

Example

The following provider code sample demonstrates how to create a vehicle in the Fleet Engine.

static final String PROJECT_ID = "my-rideshare-co-gcp-project";

VehicleServiceBlockingStub vehicleService = VehicleService.newBlockingStub(channel);

String parent = "providers/" + PROJECT_ID;

Vehicle vehicle = Vehicle.newBuilder()
    .setVehicleState(VehicleState.OFFLINE)  // Initial state
    .addSupportedTripTypes(TripType.EXCLUSIVE)
    .setMaximumCapacity(4)
    .setVehicleType(VehicleType.newBuilder().setCategory(VehicleType.Category.AUTO))
    .build();

CreateVehicleRequest createVehicleRequest = CreateVehicleRequest.newBuilder()
    .setParent(parent)
    .setVehicleId("8241890")  // Vehicle ID assigned by solution provider.
    .setVehicle(vehicle)      // Initial state.
    .build();

// The Vehicle is created in the OFFLINE state, and no initial position is
// provided.  When the driver app calls the rideshare provider, the state can be
// set to ONLINE, and the driver app updates the vehicle location.
try {
  Vehicle createdVehicle = vehicleService.createVehicle(createVehicleRequest);
} catch (StatusRuntimeException e) {
  Status s = e.getStatus();
  switch (s.getCode()) {
    case ALREADY_EXISTS:
      break;
    case PERMISSION_DENIED:
      break;
  }
  return;
}

To create a Vehicle that supports back-to-back trips, you must set the backToBackEnabled field in the Vehicle object passed to CreateVehicleRequest as true.

Vehicle vehicle = Vehicle.newBuilder()
    .setVehicleState(VehicleState.OFFLINE)
    .addSupportedTripTypes(TripType.EXCLUSIVE)
    .setMaximumCapacity(4)
    .setVehicleType(VehicleType.newBuilder().setCategory(VehicleType.Category.AUTO))
    .setBackToBackEnabled(true) // Set as 'true' so vehicle can be assigned back-to-back trips.
    .build();

Step 2. Enable location tracking

Location tracking refers to tracking the vehicle's location during the trip, where the driver app sends telemetry to the Fleet Engine, which contains the vehicles current location. This constantly updated stream of position information is used to convey the vehicle's progress along the trip's route. When you enable location tracking, the driver app starts sending this telemetry, at a default frequency of once every five seconds.

You enable location tracking for Android and iOS as follows:

• Call the Driver SDK for Android method enableLocationTracking().

• Set the Driver SDK for iOS boolean property locationTrackingEnabled to true.

Example

The following code example demonstrates how to enable location tracking.

RidesharingVehicleReporter vehicleReporter = ...;

vehicleReporter.enableLocationTracking();

val vehicleReporter = ...

vehicleReporter.enableLocationTracking()

vehicleReporter.locationTrackingEnabled = true

_vehicleReporter.locationTrackingEnabled = YES;

Step 3. Set the vehicle's state to online

You bring a vehicle into service (that is, to make it available for use) by setting its state to online, but you cannot do this until after you have enabled location tracking.

You set the vehicle's state to online for Android and iOS as follows:

• Call the Driver SDK for Android method setVehicleState(VehicleState.ONLINE).

• Call the Driver SDK for iOS method vehicleReporter.update(.online).

Example

The following code example demonstrates how to set the vehicle's state to ONLINE.

vehicleReporter.setVehicleState(VehicleState.ONLINE);

vehicleReporter.setVehicleState(VehicleState.ONLINE)

vehicleReporter.update(.online)

[_vehicleReporter updateVehicleState:GMTDVehicleStateOnline];

Step 4. Create a trip in Fleet Engine

In order to create a back-to-back trip, you create a Trip object just like you would for a single-destination trip.

A trip is an object that represents a journey, which is a collection geocoordinate points, including origin, waypoints, and dropoff points. You must create one Trip object for each trip request so that the request can be matched to a vehicle and then tracked.

• Create a trip by calling the CreateTrip() method with the CreateTripRequest request message.

Supply required attributes

To create a back-to-back trip, you must supply the following fields:

parent

A string that includes the provider ID. This must be the same as the project ID of the Google Cloud Project that contains the Service Accounts used for calling Fleet Engine

trip_id

A string that you create, that uniquely identifies this trip.

trip

Trip object to create.

The following fields must be set in the Trip object passed to CreateTripRequest:

trip_type

TripType.EXCLUSIVE

pickup_point

The trip's point of origin.

dropoff_point

The trip's dropoff point. This field is not required at trip creation and can be set later by calling UpdateTrip.

Example

The following backend integration sample demonstrates how to create a trip and assign it to a vehicle.

// A vehicle with ID 'my-vehicle' is already created and it is assigned to a trip with ID 'current-trip'.

static final String PROJECT_ID = "my-rideshare-co-gcp-project";
static final String VEHICLE_ID =" my-vehicle";
static final String TRIP_ID = "back-to-back-trip");

TripServiceBlockingStub tripService = TripService.newBlockingStub(channel);

String parent = "providers/" + PROJECT_ID;

Trip trip = Trip.newBuilder()
    .setTripType(TripType.EXCLUSIVE)
    .setPickupPoint(
        TerminalLocation.newBuilder().setPoint(
            LatLng.newBuilder()
                .setLatitude(-6.195139).setLongitude(106.820826)))
    .setDropoffPoint(
        TerminalLocation.newBuilder().setPoint(
            LatLng.newBuilder()
                .setLatitude(-6.1275).setLongitude(106.6537)))
    .setVehicleId(VEHICLE_ID)
    .build();

// Create trip request
CreateTripRequest createTripRequest = CreateTripRequest.newBuilder()
    .setParent(parent)
    .setTripId(TRIP_ID)
    .setTrip(trip)
    .build();

// Error handling.
try {
  // Fleet Engine automatically assigns a 'waypoints' list to the trip containing
  // the vehicle's current trip waypoints.
  Trip createdTrip =
      tripService.createTrip(createTripRequest);
} catch (StatusRuntimeException e) {
  Status s = e.getStatus();
  switch (s.getCode()) {
    case ALREADY_EXISTS:
      break;
    case PERMISSION_DENIED:
      break;
  }
  return;
}

Step 5. Update the trip with the vehicle ID and waypoints

You must configure the trip with a vehicle ID so that Fleet Engine can track the vehicle along its route. For back-to-back, a trip is assigned to a vehicle even if it has already been assigned one.

• You can update the trip with the vehicle ID by calling the UpdateTrip endpoint with an UpdateTripRequest. Use the update_mask field to specify that you are updating the vehicle ID.

After you assign the trip to a vehicle, Fleet Engine automatically adds the waypoints associated with the back-to-back trips to the vehicle's waypoints field. A trip's remainingWaypoints field contains a list of all of the waypoints, including those from concurrent trips, that will be visited before the trip's drop-off.

For example, consider two back-to-back trips: Trip A and Trip B. The vehicle has picked up the consumer for Trip A, and while en route to the drop-off location, the driver receives a request to pickup another consumer for the next trip (Trip B).

• Calling getVehicle() returns a list of remaining waypoints (remainingWaypoints) that contains
  A _Drop-off → B _Pickup → B _Drop-off.
• Either getTrip() or the onTripRemainingWaypointsUpdated callback for Trip A returns a list of remaining waypoints (remainingWaypoints) that contains A _Drop-off.
• Either getTrip() or the onTripRemainingWaypointsUpdated callback for Trip B returns a list of remaining waypoints (remainingWaypoints) that contains A _Drop-off → B _Pickup → and B _Drop-off.

Step 6. Listen for trip updates in the consumer app

• For Android, you can listen for data updates from a trip by obtaining a TripModel object from the TripModelManager and registering a TripModelCallback listener.

• For iOS, you can listen for data updates from a trip by obtaining a GMTCTripModel object from the GMTCTripService and registering a GMTCTripModelSubscriber subscriber.

A TripModelCallback listener and GMTCTripModelSubscriber subscriber let your app receive periodic trip progress updates on each refresh based on the auto refresh interval. Only values that change can trigger the callback. Otherwise, the callback remains silent.

The TripModelCallback.onTripUpdated() and tripModel(_:didUpdate:updatedPropertyFields:) methods are always called, regardless of any data changes.

Example 1

The following code sample demonstrates how to obtain a TripModel from TripModelManager/GMTCTripService and set a listener on it.

// Start journey sharing after a trip has been created via Fleet Engine.
TripModelManager tripModelManager = consumerApi.getTripModelManager();

// Get a TripModel object.
TripModel tripModel = tripModelManager.getTripModel(tripName);

// Register a listener on the trip.
TripModelCallback tripCallback = new TripModelCallback() {
  ...
};
tripModel.registerTripCallback(tripCallback);

// Set the refresh interval.
TripModelOptions tripModelOptions = TripModelOptions.builder()
    .setRefreshInterval(5000) // interval in milliseconds, so 5 seconds
    .build();
tripModel.setTripModelOptions(tripModelOptions);

// The trip stops auto-refreshing when all listeners are unregistered.
tripModel.unregisterTripCallback(tripCallback);

// Start journey sharing after a trip has been created via Fleet Engine.
val tripModelManager = consumerApi.getTripModelManager()

// Get a TripModel object.
val tripModel = tripModelManager.getTripModel(tripName)

// Register a listener on the trip.
val tripCallback = TripModelCallback() {
  ...
}

tripModel.registerTripCallback(tripCallback)

// Set the refresh interval.
val tripModelOptions =
  TripModelOptions.builder()
    .setRefreshInterval(5000) // interval in milliseconds, so 5 seconds
    .build()

tripModel.setTripModelOptions(tripModelOptions)

// The trip stops auto-refreshing when all listeners are unregistered.
tripModel.unregisterTripCallback(tripCallback)

let tripService = GMTCServices.shared().tripService

// Create a tripModel instance for listening for updates from the trip
// specified by the trip name.
let tripModel = tripService.tripModel(forTripName: tripName)

// Register for the trip update events.
tripModel.register(self)

// Set the refresh interval (in seconds).
tripModel.options.autoRefreshTimeInterval = 5

// Unregister for the trip update events.
tripModel.unregisterSubscriber(self)

GMTCTripService *tripService = [GMTCServices sharedServices].tripService;

// Create a tripModel instance for listening for updates from the trip
// specified by the trip name.
GMTCTripModel *tripModel = [tripService tripModelForTripName:tripName];

// Register for the trip update events.
[tripModel registerSubscriber:self];

// Set the refresh interval (in seconds).
tripModel.options.autoRefreshTimeInterval = 5;

// Unregister for the trip update events.
[tripModel unregisterSubscriber:self];

Example 2

The following code sample demonstrates how to set up a TripModelCallback listener and GMTCTripModelSubscriber subscriber.

// Implements a callback for the trip model so your app can listen for trip
// updates from Fleet Engine.
TripModelCallback subscriber =
  new TripModelCallback() {

    @Override
    public void onTripStatusUpdated(TripInfo tripInfo, @TripStatus int status) {
      // ...
    }

    @Override
    public void onTripActiveRouteUpdated(TripInfo tripInfo, List<LatLng> route) {
      // ...
    }

    @Override
    public void onTripVehicleLocationUpdated(
        TripInfo tripInfo, @Nullable VehicleLocation vehicleLocation) {
      // ...
    }

    @Override
    public void onTripPickupLocationUpdated(
        TripInfo tripInfo, @Nullable TerminalLocation pickup) {
      // ...
    }

    @Override
    public void onTripPickupTimeUpdated(TripInfo tripInfo, @Nullable Long timestampMillis) {
      // ...
    }

    @Override
    public void onTripDropoffLocationUpdated(
        TripInfo tripInfo, @Nullable TerminalLocation dropoff) {
      // ...
    }

    @Override
    public void onTripDropoffTimeUpdated(TripInfo tripInfo, @Nullable Long timestampMillis) {
      // ...
    }

    @Override
    public void onTripETAToNextWaypointUpdated(
        TripInfo tripInfo, @Nullable Long timestampMillis) {
      // ...
    }

    @Override
    public void onTripActiveRouteRemainingDistanceUpdated(
        TripInfo tripInfo, @Nullable Integer distanceMeters) {
      // ...
    }

    @Override
    public void onTripUpdateError(TripInfo tripInfo, TripUpdateError error) {
      // ...
    }

    @Override
    public void onTripUpdated(TripInfo tripInfo) {
      // ...
    }

    @Override
    public void onTripRemainingWaypointsUpdated(
        TripInfo tripInfo, List<TripWaypoint> waypointList) {
      // ...
    }

    @Override
    public void onTripIntermediateDestinationsUpdated(
        TripInfo tripInfo, List<TerminalLocation> intermediateDestinations) {
      // ...
    }

    @Override
    public void onTripRemainingRouteDistanceUpdated(
        TripInfo tripInfo, @Nullable Integer distanceMeters) {
      // ...
    }

    @Override
    public void onTripRemainingRouteUpdated(TripInfo tripInfo, List<LatLng> route) {
      // ...
    }
  };

// Implements a callback for the trip model so your app can listen for trip
// updates from Fleet Engine.
val subscriber =
  object : TripModelCallback() {
    override fun onTripStatusUpdated(tripInfo: TripInfo, status: @TripStatus Int) {
      // ...
    }

    override fun onTripActiveRouteUpdated(tripInfo: TripInfo, route: List<LatLng>) {
      // ...
    }

    override fun onTripVehicleLocationUpdated(
      tripInfo: TripInfo,
      vehicleLocation: VehicleLocation?
    ) {
      // ...
    }

    override fun onTripPickupLocationUpdated(tripInfo: TripInfo, pickup: TerminalLocation?) {
      // ...
    }

    override fun onTripPickupTimeUpdated(tripInfo: TripInfo, timestampMillis: Long?) {
      // ...
    }

    override fun onTripDropoffLocationUpdated(tripInfo: TripInfo, dropoff: TerminalLocation?) {
      // ...
    }

    override fun onTripDropoffTimeUpdated(tripInfo: TripInfo, timestampMillis: Long?) {
      // ...
    }

    override fun onTripETAToNextWaypointUpdated(tripInfo: TripInfo, timestampMillis: Long?) {
      // ...
    }

    override fun onTripActiveRouteRemainingDistanceUpdated(
      tripInfo: TripInfo,
      distanceMeters: Int?
    ) {
      // ...
    }

    override fun onTripUpdateError(tripInfo: TripInfo, error: TripUpdateError) {
      // ...
    }

    override fun onTripUpdated(tripInfo: TripInfo) {
      // ...
    }

    override fun onTripRemainingWaypointsUpdated(
      tripInfo: TripInfo,
      waypointList: List<TripWaypoint>
    ) {
      // ...
    }

    override fun onTripIntermediateDestinationsUpdated(
      tripInfo: TripInfo,
      intermediateDestinations: List<TerminalLocation>
    ) {
      // ...
    }

    override fun onTripRemainingRouteDistanceUpdated(tripInfo: TripInfo, distanceMeters: Int?) {
      // ...
    }

    override fun onTripRemainingRouteUpdated(tripInfo: TripInfo, route: List<LatLng>) {
      // ...
    }
  }

class TripModelSubscriber: NSObject, GMTCTripModelSubscriber {

  func tripModel(_: GMTCTripModel, didUpdate trip: GMTSTrip?, updatedPropertyFields: GMTSTripPropertyFields) {
    // Update the UI with the new `trip` data.
    updateUI(with: trip)
    ...
  }

  func tripModel(_: GMTCTripModel, didUpdate tripStatus: GMTSTripStatus) {
    // Handle trip status did change.
  }

  func tripModel(_: GMTCTripModel, didUpdateActiveRoute activeRoute: [GMTSLatLng]?) {
    // Handle trip active route did update.
  }

  func tripModel(_: GMTCTripModel, didUpdate vehicleLocation: GMTSVehicleLocation?) {
    // Handle vehicle location did update.
  }

  func tripModel(_: GMTCTripModel, didUpdatePickupLocation pickupLocation: GMTSTerminalLocation?) {
    // Handle pickup location did update.
  }

  func tripModel(_: GMTCTripModel, didUpdateDropoffLocation dropoffLocation: GMTSTerminalLocation?) {
    // Handle drop off location did update.
  }

  func tripModel(_: GMTCTripModel, didUpdatePickupETA pickupETA: TimeInterval) {
    // Handle the pickup ETA did update.
  }

  func tripModel(_: GMTCTripModel, didUpdateDropoffETA dropoffETA: TimeInterval) {
    // Handle the drop off ETA did update.
  }

  func tripModel(_: GMTCTripModel, didUpdateRemaining remainingWaypoints: [GMTSTripWaypoint]?) {
    // Handle updates to the pickup, dropoff or intermediate destinations of the trip.
  }

  func tripModel(_: GMTCTripModel, didFailUpdateTripWithError error: Error?) {
    // Handle the error.
  }

  func tripModel(_: GMTCTripModel, didUpdateIntermediateDestinations intermediateDestinations: [GMTSTerminalLocation]?) {
    // Handle the intermediate destinations being updated.
  }

  ...
}

@interface TripModelSubscriber : NSObject <GMTCTripModelSubscriber>
@end

@implementation TripModelSubscriber

- (void)tripModel:(GMTCTripModel *)tripModel
            didUpdateTrip:(nullable GMTSTrip *)trip
    updatedPropertyFields:(GMTSTripPropertyFields)updatedPropertyFields {
  // Update the UI with the new `trip` data.
  [self updateUIWithTrip:trip];
  ...
}

- (void)tripModel:(GMTCTripModel *)tripModel didUpdateTripStatus:(enum GMTSTripStatus)tripStatus {
  // Handle trip status did change.
}

- (void)tripModel:(GMTCTripModel *)tripModel
    didUpdateActiveRoute:(nullable NSArray<GMTSLatLng *> *)activeRoute {
  // Handle trip route did update.
}

- (void)tripModel:(GMTCTripModel *)tripModel
    didUpdateVehicleLocation:(nullable GMTSVehicleLocation *)vehicleLocation {
  // Handle vehicle location did update.
}

- (void)tripModel:(GMTCTripModel *)tripModel
    didUpdatePickupLocation:(nullable GMTSTerminalLocation *)pickupLocation {
  // Handle pickup location did update.
}

- (void)tripModel:(GMTCTripModel *)tripModel
    didUpdateDropoffLocation:(nullable GMTSTerminalLocation *)dropoffLocation {
  // Handle drop off location did update.
}

- (void)tripModel:(GMTCTripModel *)tripModel didUpdatePickupETA:(NSTimeInterval)pickupETA {
  // Handle the pickup ETA did update.
}

- (void)tripModel:(GMTCTripModel *)tripModel
    didUpdateRemainingWaypoints:(nullable NSArray<GMTSTripWaypoint *> *)remainingWaypoints {
  // Handle updates to the pickup, dropoff or intermediate destinations of the trip.
}

- (void)tripModel:(GMTCTripModel *)tripModel didUpdateDropoffETA:(NSTimeInterval)dropoffETA {
  // Handle the drop off ETA did update.
}

- (void)tripModel:(GMTCTripModel *)tripModel didFailUpdateTripWithError:(nullable NSError *)error {
  // Handle the error.
}

- (void)tripModel:(GMTCTripModel *)tripModel
    didUpdateIntermediateDestinations:
        (nullable NSArray<GMTSTerminalLocation *> *)intermediateDestinations {
  // Handle the intermediate destinations being updated.
}
…
@end

You can access information for the trip any time as follows:

• Call the Consumer SDK for Android method TripModel.getTripInfo(). Calling this method doesn't force a data refresh, although data still continues to be refreshed at the refresh frequency.

• Get the Consumer SDK for iOS property GMTCTripModel.currentTrip.

Step 7. Display the journey in the consumer app

You can access the Rides and Deliveries user interface element APIs as follows:

• Get the Consumer SDK for Android ConsumerController object. For more information, see Using the user interface element APIs.

• Get the Consumer SDK for iOS GMTCMapView object. For more information, see Using the user interface element APIs.

Example

The following code example demonstrates how to start the journey sharing user interface.

JourneySharingSession session = JourneySharingSession.createInstance(tripModel);
consumerController.showSession(session);

val session = JourneySharingSession.createInstance(tripModel)
consumerController.showSession(session)

let journeySharingSession = GMTCJourneySharingSession(tripModel: tripModel)
mapView.show(journeySharingSession)

GMTCJourneySharingSession *journeySharingSession =
    [[GMTCJourneySharingSession alloc] initWithTripModel:tripModel];
[self.mapView showMapViewSession:journeySharingSession];

Example scenario

Consider a back-to-back trip in which the vehicle has already picked up the consumer for the first trip. The vehicle is en route to the drop-off point when the driver receives a request to pickup a different consumer upon completion of the current trip.

At this point in time, the consumer for the first trip sees the following.

At the same point in time, the consumer for the second trip sees the following.

By default, the Consumer SDK displays just the active leg in the route, but you have the option of displaying the remaining leg, which includes the destination.

If you want to display information about waypoints from other trips, you can access all of the waypoints relevant to a trip as follows:

• Call the Consumer SDK for Android method TripModel.getTripInfo(). Then call TripInfo.getRemainingWaypoints() to get the TripWaypoints. Each TripWaypoint object contains the trip ID, waypoint location, and waypoint type.

• Get the Consumer SDK for iOS property GMTCTripModel.currentTrip. Then get the GMTSTrip.remainingWaypoints array to access the GMTSTripWaypoints. Each GMTSTripWaypoint object contains the trip ID, waypoint location, and waypoint type.

Step 8. Manage the trip state in the Fleet Engine

You specify the state of a trip using one of the TripStatus enumeration values. When a trip's state changes (for example, changing from ENROUTE_TO_PICKUP to ARRIVED_AT_PICKUP) you must update the trip state via the Fleet Engine. Trip state always begins with a value of NEW, and ends with a value of either COMPLETE or CANCELED. For more information, see trip_status.

Example

The following backend integration sample demonstrates how to update the trip state in Fleet Engine.

static final String PROJECT_ID = "my-rideshare-co-gcp-project";
static final String TRIP_ID = "trip-8241890";

String tripName = "providers/" + PROJECT_ID + "/trips/" + TRIP_ID;

TripServiceBlockingStub tripService = TripService.newBlockingStub(channel);

// Trip settings to be updated.
Trip trip = Trip.newBuilder()
    .setTripStatus(TripStatus.ARRIVED_AT_PICKUP)
    .build();

// Trip update request
UpdateTripRequest updateTripRequest = UpdateTripRequest.newBuilder()
    .setName(tripName)
    .setTrip(trip)
    .setUpdateMask(FieldMask.newBuilder().addPaths("trip_status"))
    .build();

// Error handling.
try {
  Trip updatedTrip = tripService.updateTrip(updateTripRequest);
} catch (StatusRuntimeException e) {
  Status s = e.getStatus();
  switch (s.getCode()) {
    case NOT_FOUND:            // The trip doesn't exist.
      break;
    case FAILED_PRECONDITION:  // The given trip status is invalid.
      break;
    case PERMISSION_DENIED:
      break;
  }
  return;
}