coap #

The Constrained Application Protocol is a RESTful web transfer protocol for resource-constrained networks and nodes. The CoAP library is an implementation in Dart providing a CoAP client, the code was initially a port from the C# .NET project CoAP.NET.

Features #

• CoAP over UDP RFC 7252
• Observe resources RFC 7641
• Block-wise transfers RFC 7959
• FETCH, PATCH, and iPATCH methods RFC 8132
• Extended Token Length RFC 8974
• Multicast over UDP (not DTLS)
• Experimental: CoAP over DTLS, using FFI and the dtls2 package for binding to OpenSSL
• Experimental: Request proxying

Roadmap #

• CoAP over TCP/TLS RFC 8323

Example #

FutureOr<void> main() async {
  final conf = CoapConfig();
  final baseUri = Uri(scheme: 'coap', host: 'coap.me', port: conf.defaultPort);
  final client = CoapClient(baseUri, conf);

  try {
    final response =
        await client.get('multi-format', accept: CoapMediaType.textPlain);
    print('/multi-format response payload: ${response.payloadString}');
  } on Exception catch (e) {
    print('CoAP encountered an exception: $e');
  }

  client.close();
}

For more detailed examples, see examples.

Setup #

• Add the dependencies in your pubspec.yaml:

dependencies:
  coap: ^4.2.1

devDependencies:
  build_runner: ^2.1.11

• Create a .yaml file containing your CoAP's configurations:
  • The file name must be separated by _ and must start with coap_config
    • Example: coap_config_all. This will generate a file called CoapConfigAll that you will use in your code.
    • Example: coap_config_debug. This will generate a file called CoapConfigDebug that you will use in your code.
    • This file must contain at least the protocol version. This is a valid configuration file with all possible properties: example/config/coap_config.yaml.
• Run the command that will generate the configuration class:
  • Run dart pub run build_runner build in your Dart project
  • Run flutter pub run build_runner build in your Flutter project After running the command above the configuration class will be generated next to the .yaml configuration file.

Considerations #

Binaries for DTLS #

If you are planning to use DTLS with OpenSSL, note that not all platforms support OpenSSL natively (iOS and Windows for example), in which case you need to ship the required binaries with your app. Also see the dtls2 package's README for more information.

Connectivity #

If connectivity is lost, the CoAP client will continuously try to re-initalize the socket. The library relies heavily on futures however, which might not survive in Flutter when the app runs in the background or when the display of the device is turned off. In this case, you might need to extend the WidgetsBindingObserver class and re-initialize the CoapClient in didChangeAppLifecycleState on AppLifecycleState.resumed.