Quick Secure CoAP Client

采用 Qt Quick 用户界面保护 CoAP 客户端并使用它。

Quick Secure CoAP Client demonstrates how to create a secure CoAP client and use it in a Qt Quick application.

注意： Qt CoAP does not provide a QML API in its current version. However, you can make the C++ classes of the module available to QML as it is shown in the example.

运行范例

要运行范例从 Qt Creator ，打开 Welcome 模式，然后选择范例从 Examples 。更多信息，拜访构建和运行范例 .

To run the example application, you first need to set up a secure CoAP server. You can run the example with any secure CoAP server supporting one of the pre-shared key (PSK) or certificate authentication modes. For more information about setting up a secure CoAP server, see 设置安全 CoAP 服务器 .

Exposing C++ Classes to QML

In this example, you need to expose the QCoapClient 类和 QtCoap namespace to QML. To achieve this, create a custom wrapper class and use the special registration macros .

创建 QmlCoapSecureClient class as a wrapper around QCoapClient . This class also holds the selected security mode and security configuration parameters. Use the Q_INVOKABLE macro to expose several methods to QML. Also use the QML_NAMED_ELEMENT macro to register the class in QML as CoapSecureClient .

class QmlCoapSecureClient : public QObject
{
    Q_OBJECT
    QML_NAMED_ELEMENT(CoapSecureClient)
public:
    QmlCoapSecureClient(QObject *parent = nullptr);
    ~QmlCoapSecureClient() override;
    Q_INVOKABLE void setSecurityMode(QtCoap::SecurityMode mode);
    Q_INVOKABLE void sendGetRequest(const QString &host, const QString &path, int port);
    Q_INVOKABLE void setSecurityConfiguration(const QString &preSharedKey, const QString &identity);
    Q_INVOKABLE void setSecurityConfiguration(const QString &localCertificatePath,
                                              const QString &caCertificatePath,
                                              const QString &privateKeyPath);
    Q_INVOKABLE void disconnect();
Q_SIGNALS:
    void finished(const QString &result);
private:
    QCoapClient *m_coapClient;
    QCoapSecurityConfiguration m_configuration;
    QtCoap::SecurityMode m_securityMode;
};

After that, register the QtCoap namespace, so that you can use the enums provided there:

namespace QCoapForeignNamespace
{
    Q_NAMESPACE
    QML_FOREIGN_NAMESPACE(QtCoap)
    QML_NAMED_ELEMENT(QtCoap)
}

Adjusting Build Files

To make the custom types available from QML, update the build system files accordingly.

CMake

For a CMake-based build, add the following to the CMakeLists.txt :

qt_add_qml_module(quicksecureclient
    URI CoapSecureClientModule
    SOURCES
        qmlcoapsecureclient.cpp qmlcoapsecureclient.h
    QML_FILES
        FilePicker.qml
        Main.qml
)

qmake

For a qmake build, modify the quicksecureclient.pro file in the following way:

CONFIG += qmltypes
QML_IMPORT_NAME = CoapSecureClientModule
QML_IMPORT_MAJOR_VERSION = 1
    ...
qml_resources.files = \
    qmldir \
    FilePicker.qml \
    Main.qml
qml_resources.prefix = /qt/qml/CoapSecureClientModule
RESOURCES += qml_resources

Using New QML Types

Now, when the C++ classes are properly exposed to QML, you can use the new types.

Creating the Client

CoapSecureClient is instantiated from the Main.qml file. It handles the QmlCoapSecureClient::finished() signal and updates the UI accordingly:

CoapSecureClient {
    id: client
    onFinished: (result) => {
        outputView.text = result;
        statusLabel.text = "";
        disconnectButton.enabled = true;
    }
}

The instance of QCoapClient is created when the user selects or changes the security mode in the UI. The QmlCoapSecureClient::setSecurityMode() method is invoked from the QML code, when one of the security modes is selected:

ButtonGroup {
    id: securityModeGroup
    onClicked: {
        if ((securityModeGroup.checkedButton as RadioButton) === preSharedMode)
            client.setSecurityMode(QtCoap.SecurityMode.PreSharedKey);
        else
            client.setSecurityMode(QtCoap.SecurityMode.Certificate);
    }
}

On the C++ side, this method creates a QCoapClient and connects to its finished () 和 error () signals. The class handles both signals internally, and forwards them to the new finished() 信号。

void QmlCoapSecureClient::setSecurityMode(QtCoap::SecurityMode mode)
{
    // Create a new client, if the security mode has changed
    if (m_coapClient && mode != m_securityMode) {
        delete m_coapClient;
        m_coapClient = nullptr;
    }
    if (!m_coapClient) {
        m_coapClient = new QCoapClient(mode);
        m_securityMode = mode;
        connect(m_coapClient, &QCoapClient::finished, this,
                [this](QCoapReply *reply) {
                    if (!reply)
                        emit finished(tr("Something went wrong, received a null reply"));
                    else if (reply->errorReceived() != QtCoap::Error::Ok)
                        emit finished(errorMessage(reply->errorReceived()));
                    else
                        emit finished(reply->message().payload());
                });
        connect(m_coapClient, &QCoapClient::error, this,
                [this](QCoapReply *, QtCoap::Error errorCode) {
                    emit finished(errorMessage(errorCode));
                });
    }
}

发送请求

点击 Send Request button to set the security configuration based on the selected security mode and send a GET 请求：

Button {
    id: requestButton
    text: qsTr("Send Request")
    enabled: securityModeGroup.checkState !== Qt.Unchecked
    onClicked: {
        outputView.text = "";
        if ((securityModeGroup.checkedButton as RadioButton) === preSharedMode)
            client.setSecurityConfiguration(pskField.text, identityField.text);
        else
            client.setSecurityConfiguration(localCertificatePicker.selectedFile,
                                            caCertificatePicker.selectedFile,
                                            privateKeyPicker.selectedFile);
        client.sendGetRequest(hostComboBox.editText, resourceField.text,
                              parseInt(portField.text));
        statusLabel.text = qsTr("Sending request to %1%2...").arg(hostComboBox.editText)
                                                             .arg(resourceField.text);
    }
}

There are two overloads for the setSecurityConfiguration 方法。

The overload for the PSK mode simply sets the client identity and the pre-shared key:

void
QmlCoapSecureClient::setSecurityConfiguration(const QString &preSharedKey, const QString &identity)
{
    QCoapSecurityConfiguration configuration;
    configuration.setPreSharedKey(preSharedKey.toUtf8());
    configuration.setPreSharedKeyIdentity(identity.toUtf8());
    m_configuration = configuration;
}

And the overload for X.509 certificates reads the certificate files and the private key and sets the security configuration:

void QmlCoapSecureClient::setSecurityConfiguration(const QString &localCertificatePath,
                                                   const QString &caCertificatePath,
                                                   const QString &privateKeyPath)
{
    QCoapSecurityConfiguration configuration;
    const auto localCerts =
            QSslCertificate::fromPath(QUrl(localCertificatePath).toLocalFile(), QSsl::Pem,
                                      QSslCertificate::PatternSyntax::FixedString);
    if (localCerts.isEmpty())
        qCWarning(lcCoapClient, "The specified local certificate file is not valid.");
    else
        configuration.setLocalCertificateChain(localCerts.toVector());
    const auto caCerts = QSslCertificate::fromPath(QUrl(caCertificatePath).toLocalFile(), QSsl::Pem,
                                                   QSslCertificate::PatternSyntax::FixedString);
    if (caCerts.isEmpty())
        qCWarning(lcCoapClient, "The specified CA certificate file is not valid.");
    else
        configuration.setCaCertificates(caCerts.toVector());
    QFile privateKey(QUrl(privateKeyPath).toLocalFile());
    if (privateKey.open(QIODevice::ReadOnly)) {
        QCoapPrivateKey key(privateKey.readAll(), QSsl::Ec);
        configuration.setPrivateKey(key);
    } else {
        qCWarning(lcCoapClient) << "Unable to read the specified private key file"
                                << privateKeyPath;
    }
    m_configuration = configuration;
}

After setting the security configuration, the sendGetRequest method sets the request URL and sends a GET 请求：

void QmlCoapSecureClient::sendGetRequest(const QString &host, const QString &path, int port)
{
    if (!m_coapClient)
        return;
    m_coapClient->setSecurityConfiguration(m_configuration);
    QUrl url;
    url.setHost(host);
    url.setPath(path);
    url.setPort(port);
    m_coapClient->get(url);
}

When sending the first request, a handshake with the CoAP server is performed. After the handshake is successfully done, all the subsequent messages are encrypted, and changing the security configuration after a successful handshake won't have any effect. If you want to change it, or change the host, you need to disconnect first.

void QmlCoapSecureClient::disconnect()
{
    if (m_coapClient)
        m_coapClient->disconnect();
}

这将中止握手并关闭打开套接字。

For the authentication using X.509 certificates, the certificate files need to be specified. The FilePicker component is used for this purpose. It combines a text field and a button for opening a file dialog when the button is pressed:

Item {
    id: filePicker
    property string dialogText
    property alias selectedFile: filePathField.text
    height: addFileButton.height
    FileDialog {
        id: fileDialog
        title: qsTr("Please Choose %1").arg(filePicker.dialogText)
        currentFolder: StandardPaths.writableLocation(StandardPaths.HomeLocation)
        fileMode: FileDialog.OpenFile
        onAccepted: filePathField.text = fileDialog.selectedFile
    }
    RowLayout {
        anchors.fill: parent
        TextField {
            id: filePathField
            placeholderText: qsTr("<%1>").arg(filePicker.dialogText)
            inputMethodHints: Qt.ImhUrlCharactersOnly
            selectByMouse: true
            Layout.fillWidth: true
        }
        Button {
            id: addFileButton
            text: qsTr("Add %1").arg(filePicker.dialogText)
            onClicked: fileDialog.open()
        }
    }
}

FilePicker is instantiated several times in the Main.qml file for creating input fields for certificates and the private key:

FilePicker {
    id: localCertificatePicker
    dialogText: qsTr("Local Certificate")
    enabled: (securityModeGroup.checkedButton as RadioButton) === certificateMode
    Layout.columnSpan: 2
    Layout.fillWidth: true
}
FilePicker {
    id: caCertificatePicker
    dialogText: qsTr("CA Certificate")
    enabled: (securityModeGroup.checkedButton as RadioButton) === certificateMode
    Layout.columnSpan: 2
    Layout.fillWidth: true
}
FilePicker {
    id: privateKeyPicker
    dialogText: qsTr("Private Key")
    enabled: (securityModeGroup.checkedButton as RadioButton) === certificateMode
    Layout.columnSpan: 2
    Layout.fillWidth: true
}

设置安全 CoAP 服务器

To run this example, you need to have a secure CoAP server supporting either PSK or Certificate modes (or both). You have the following options:

Manually build and run a secure CoAP server using, for example, libcoap , Californium , FreeCoAP , or any other CoAP library which supports DTLS.
Use the ready Docker images available at Docker Hub, which build and run the secure CoAP servers suitable for our example. The steps required for using the docker-based CoAP servers are described below.

为 PSK 模式设置服务器

The following command pulls the docker container for a secure CoAP server based on Californium plugtest (which is not secure by default) from the Docker Hub and starts it:

docker run --name coap-test-server -d --rm -p 5683:5683/udp -p 5684:5684/udp tqtc/coap-californium-test-server:3.8.0

The CoAP test server will be reachable on ports 5683 (non-secure) and 5684 (secure). For instructions on retrieving the IP address see 获取 IP 地址 .

To run the example with this server, you need to set the pre-shared key to secretPSK and the identity to Client_identity .

为证书模式设置服务器

The docker image of the secure server using authentication with X.509 certificates is based on the 时间服务器 example from the FreeCoAP library. The following command pulls the container from Docker Hub and starts it:

docker run --name coap-time-server -d --rm -p 5684:5684/udp tqtc/coap-secure-time-server:freecoap

For instructions on retrieving the IP address see 获取 IP 地址 . The CoAP test server will be reachable by the retrieved IP address on port 5684 and resource path /time .

To run the example with this server, you need to specify the certificate files required by the server. They are located in the docker container, under /root/certs directory. To copy them to a local directory, use the following command:

docker cp <container_id>:/root/certs <local_directory_path>

例如：

$ docker cp 5e46502df88f:/root/certs ~/

The instructions for getting the container ID are described below.

获取 IP 地址

To find out the IP address of a docker container, first retrieve the container ID by running the docker ps command, which will output something like:

$ docker ps
CONTAINER ID        IMAGE
5e46502df88f        tqtc/coap-californium-test-server:3.8.0

Then you can obtain the IP address with the following command:

docker inspect <container_id> | grep IPAddress

例如：

$ docker inspect 5e46502df88f | grep IPAddress
...
"IPAddress": "172.17.0.2",
...

Terminating a Docker Container

To terminate a docker container after usage, use the following command:

docker stop <container_id>

The <container_id> here is the same as retrieved by the docker ps 命令。

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