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Flutter API for accessing the CARP web services - authentication, file management, data points, and app-specific collections of documents.

CARP Web Service Plugin for Flutter #

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A Flutter library to access the CARP Web Service (CAWS) web API. This library is intended to be used with the carp_mobile_sensing framework, but also works on its own, if a app is to connect directly to CAWS.

For an overview of CARP and other Flutter CARP libraries, see CARP Mobile Sensing in Flutter.

Setup #

  1. You need a CARP Web Service (CAWS) host running. See the CARP Web Service GitHub repro and documentation for how to do this. If you're part of the CARP team, you can use the specified test, staging, and production servers.

  2. Add carp_services as a dependency in your pubspec.yaml file.

In order to show the "Reset Password" button in the login dialog, which will launch the "Reset Password" web page on CAWS, add the following parameters on iOS and Android. Note that the "Reset Password" button will not be shown, if the app cannot launch the URL pointing to the web page.

iOS #

Add the following LSApplicationQueriesSchemes entry in your Info.plist file:


Android #

Starting from API 30, Android requires package visibility configuration in your AndroidManifest.xml file in order to launch the "reset password" URL. A <queries> element must be added to your manifest as a child of the root element:

<!-- To enable that the "reset password" url can be launched -->
<!-- Provide required visibility configuration for API level 30 and above -->
    <action android:name="android.intent.action.VIEW" />
    <data android:scheme="https" />

Usage #

Import the needed CARP libraries.

import 'package:carp_core/carp_core.dart';
import 'package:carp_mobile_sensing/carp_mobile_sensing.dart';
import 'package:carp_webservices/carp_auth/carp_auth.dart';
import 'package:carp_webservices/carp_services/carp_services.dart';

Configuration #

The CarpService is a singleton and needs to be configured once.

  Uri get uri => Uri(
        scheme: 'https',
        host: '',
        pathSegments: [
        ], // Depends on your specific instance
CarpApp app;

app = CarpApp(
      name: "CAWS @ DTU",
      uri: uri.replace(pathSegments: [uris[bloc.deploymentMode]!]),
      authURL: uri,
      clientId: '<your personal client id from keycloak>',
      redirectURI: Uri.parse('<your-custom-redirect URL>'), // E.g. carp-studies-auth://auth
      discoveryURL: uri.replace(pathSegments: [
      studyId: studyId, // From an invitation
      studyDeploymentId: studyDeploymentId, //

// Configure the CARP Service with this app.

Note that the custom scheme for the redirect URIs has to be set up in platform configurations according to Flutter_AppAuth.

Note that you need a valid clientID and clientSecret (if you have a secret) from a CAWS instance to use it. Also note that you need the studyId and studyDeploymentId for a study deployed in your CAWS instance. On the client side (in Flutter), these can be obtained from an invitation (see below). But if you want to use the CAWS endpoints directly, you have to specify these IDs in the CarpApp configuration, as shown above.

The singleton can now be accessed via CarpService().

Authentication #

Basic authentication is using the CAWS keycloak login page, which the system opens when running:

CarpUser user = await CarpService().authenticate();

This CarpUser object contains the OAuth token in the .token (of type OAuthToken) parameter. Since the CarpUser can be serialized to JSON, the OAuth token can be stored on the phone.

To refresh the OAuth token the client (Flutter) simply calls

await CarpService().refresh()

This method returns a CarpUser, with the new access token.

A ConsentDocument can be uploaded and downloaded to and from CAWS.

try {
  ConsentDocument uploaded = await CarpService().createConsentDocument({
    'text': 'The original terms text.',
    'signature': 'Image Blob',

  ConsentDocument downloaded =
      await CarpService().getConsentDocument(;
} catch (error) {

Data Points #

A DataPointReference is used to manage DataPoint objects on a CARP Web Service, and have CRUD methods for:

  • post a data point
  • batch upload multiple data points
  • get a data point
  • delete data points
// Create a piece of data
final lightData = AmbientLight(
  maxLux: 12,
  meanLux: 23,
  minLux: 0.3,
  stdLux: 0.4,

// create a CARP data point
final data = DataPoint.fromData(lightData);

// post it to the CARP server, which returns the ID of the data point
int dataPointId =
    await CarpService().getDataPointReference().postDataPoint(data);

// get the data point back from the server
CARPDataPoint dataPoint =
    await CarpService().getDataPointReference().getDataPoint(dataPointId);

// batch upload a list of raw json data points in a file
final File file = File('test/batch.json');
await CarpService().getDataPointReference().batchPostDataPoint(file);

// delete the data point
await CarpService().getDataPointReference().deleteDataPoint(dataPointId);

Application-specific Collections and Documents #

CARP Web Service supports storing JSON documents in nested collections.

A CollectionReference is used to access collections and a DocumentReference is used to access documents. Both of these can be used to:

  • creating, updating, and deleting documents
  • accessing documents in collections
// access a document
//  - if the document id is not specified, a new document (with a new id)
//    is created
//  - if the collection ('users') don't exist, it is created
DocumentSnapshot document = await CarpService()
    .setData({'email': username, 'name': 'Administrator'});

// update the document
DocumentSnapshot updatedDocument = await CarpService()
    .updateData({'email': username, 'name': 'Super User'});

// get the document
DocumentSnapshot newDocument =
    await CarpService().collection('users').document(;

// get the document by its unique ID
newDocument = await CarpService().documentById(;

// delete the document
await CarpService().collection('users').document(;

// get all collections from a document
List<String> collections = newDocument.collections;

// get all documents in a collection.
List<DocumentSnapshot> documents =
    await CarpService().collection('users').documents;

File Management #

CARP Web Service supports storing raw binary file.

A FileStorageReference is used to manage files and have methods for:

  • uploading a file
  • downloading a file
  • getting a file object
  • getting all file objects
  • deleting a file

When uploading a file, you can add metadata as a Map<String, String>.

// first upload a file
final File uploadFile = File('test/img.jpg');
final FileUploadTask uploadTask = CarpService()
    .upload(uploadFile, {
  'content-type': 'image/jpg',
  'content-language': 'en',
  'activity': 'test'
CarpFileResponse response = await uploadTask.onComplete;
int id =;

// then get its description back from the server
final CarpFileResponse result =
    await CarpService().getFileStorageReference(id).get();

// then download the file again
// note that a local file to download is needed
final File downloadFile = File('test/img-$id.jpg');
final FileDownloadTask downloadTask =
int responseCode = await downloadTask.onComplete;

// now get references to ALL files in this study
final List<CarpFileResponse> results =
    await CarpService().getFileStorageReference(id).getAll();

// finally, delete the file
responseCode = await CarpService().getFileStorageReference(id).delete();

Deployments #

A core notion of CARP is the Deployment subsystem. This subsystem is used for accessing deployment configurations, i.e. configurations that describe how data sampling in a study should take place. The CARP Web Service have methods for:

  • getting invitations for a specific accountId, i.e. a user. Default is the user who is authenticated to the CARP Service.
  • getting a deployment reference, which then can be used to query status, register devices, and get the deployment specification.

Deployments are accessed via a DeploymentReference.

// This example uses the
//  * CarpDeploymentService
//  * CarpParticipationService
// To use these, we first must configure them and authenticate.
// However, the [configureFrom] method is a convenient way to do this
// based on an existing service, which has been configured.


// get invitations for this account (user)
List<ActiveParticipationInvitation> invitations =
    await CarpParticipationService().getActiveParticipationInvitations();

// get a deployment reference for this master device
DeploymentReference deploymentReference =

// get the status of this deployment
StudyDeploymentStatus status = await deploymentReference.getStatus();

// register a device
status = await deploymentReference.registerDevice(deviceRoleName: 'phone');

// get the master device deployment
MasterDeviceDeployment deployment = await deploymentReference.get();

// mark the deployment as a success
status = await deploymentReference.success();

There is also support for showing a modal dialog for the user to select amongst several invitations. This is done using the getStudyInvitation method, like this:

var invitation =
    await CarpParticipationService().getStudyInvitation(context);
print('Selected CARP Study Invitation: $invitation');

Streaming Data #

Collected data can be streamed back to a CARP Web Service using the Data subsystem. Note that this is a separate subsystem from the DataPoint endpoint described above. CAWS supports both types of data upload (for legacy reasons).

// Configure a [CarpDataStreamService] from an existing CAWS service.

// Create a (very simple) data batch to upload
var measurement = Measurement(
  sensorStartTime: 1642505144000000,
  data: Geolocation(
      latitude: 55.680802203873114, longitude: 12.581802212861367));
var batch = [
    dataStream: DataStreamId(
            CarpDataStreamService().app?.studyDeploymentId ?? '',
        deviceRoleName: 'smartphone',
        dataType: Geolocation.dataType),
    firstSequenceId: 0,
    measurements: [measurement],
    triggerIds: {0}),

// Get a data stream and append the batch

Features and bugs #

Please file feature requests and bug reports at the issue tracker.

License #

This software is copyright (c) Copenhagen Center for Health Technology (CACHET) at the Technical University of Denmark (DTU). This software is made available 'as-is' in a MIT license.

pub points



Flutter API for accessing the CARP web services - authentication, file management, data points, and app-specific collections of documents.

Repository (GitHub)
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API reference




carp_core, carp_mobile_sensing, carp_serializable, flutter, flutter_appauth, form_field_validator, http, http_parser, json_annotation, jwt_decoder, meta, retry, url_launcher, uuid


Packages that depend on carp_webservices