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This is the Qt CoAP module repository. CoAP is a protocol for IoT devices, and machine to machine communication. The full specification can be found in RFC 7252.

Supported features

Unsupported yet

How to use the library


QCoapClient* client = new QCoapClient(this);
connect(client, &QCoapClient::finished, this, &MyClass::onFinished);
client->put(QUrl("coap://coap.me/test"), QByteArray("payload"));


QCoapReply* reply = client->get(QCoapRequest("coap://coap.me/test"));
connect(reply, &QCoapReply::finished, this, &MyClass::onFinished);

The slot connected to the QCoapReply::finished(QCoapReply *) signal can use the QCoapReply object like a QIODevice object.

OBSERVE requests

Observe requests are used to receive automatic server notifications for a resource. For Observe requests specifically, you can use the QCoapReply::notified(QCoapReply *, QCoapMessage) signal to handle notifications from the CoAP server.

QCoapRequest request = QCoapRequest("coap://coap.me/obs");
QCoapReply* reply = client->observe(request);
connect(reply, &QCoapReply::notified, this, &MyClass::onNotified);

You can then stop the observation with


The notified signal will provide the QCoapReply and most recent message.

DISCOVERY requests

For machine to machine communication, CoAP Discovery requests is used to query the resources available to an endpoint, or to the complete network.

QCoapResourceDiscoveryReply *reply = client->discover("coap://coap.me/");
connect(reply, &QCoapReply::discovered, this, &MyClass::onDiscovered);

For multicast discovery use one of the groups from the QtCoap::MulticastGroup enum, instead of specifying the discovery path:

QCoapResourceDiscoveryReply *reply = client->discover(QtCoap::AllCoapNodesIPv6LinkLocal);

If no group is specified, QtCoap::AllCoapNodesIPv4 will be used by default.

The signal discovered can be triggered multiple times, and will provide the list of resources returned by the server(s).

Using security

The following example code can be used to secure CoAP communication:

QCoapClient* client = new QCoapClient(this, QtCoap::PreSharedKey);
QCoapSecurityConfiguration config;

To use X.509 certificate-based security use QtCoap::Certificate for the security mode. QtCoap::RawPublicKey mode is not supported yet.

Automated tests

Automated tests require a Californium plugtest server. Plugtest is a CoAP server used to test the main features of the CoAP protocol. The following command starts a plugtest server using Docker.

docker run --name coap-test-server -d --rm -p 5683:5683/udp aleravat/coap-test-server:latest

Automated tests require COAP_TEST_SERVER_IP environment variable to be set, containing Plugtest server IP address. This address will be used to connect to the Plugtest server on port 5683.

The IP address of the docker container can found identified by: 1. Retrieve the container id with docker ps

$ docker ps
CONTAINER ID        IMAGE                                           [...]
826073e84e7f        aleravat/coap-test-server:latest                [...]
  1. Get the IP address with docker inspect <container_id> | grep IPAddress
$ docker inspect 826073e84e7f | grep IPAddress
        "IPAddress": "",
  1. Set the environment variable in QtCreator, or in a the terminal used export COAP_TEST_SERVER_IP=""