Qt SCXML FTP 客戶端範例

使用狀態機實現簡單 FTP 客戶端。

FTP 客戶端 uses Qt SCXML to implement a FTP client that can communicate with a FTP service by sending FTP control messages translated from state machine events and by translating server replies into state machine events. The data received from the FTP server is printed on the console.

RFC 959 specifies state charts for the command handling of the FTP client. They can be easily translated into SCXML to benefit from SCXML nested states. Connections between the client and server and data transfer are implemented by using C++. In addition, Qt signals and slots are used.

狀態機擁有以下狀態：

I 作為初始狀態。
B for sending commands.
S for success.
F 對於故障。
W for waiting for a reply.
P for supplying a password upon server request.

The state machine is specified in the simpleftp.scxml file and compiled into the FtpClient class that implements the logic of the FTP protocol. It reacts to user input and to replies from the control channel by changing states and sending external events. In addition, we implement a FtpControlChannel class and a FtpDataChannel class that handle TCP sockets and servers and convert line endings.

運行範例

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編譯狀態機

We link against the Qt SCXML module by adding the following line to the .pro 文件：

QT = core scxml network

接著，指定要編譯的狀態機：

STATECHARTS += simpleftp.scxml

Qt SCXML 編譯器 qscxmlc , is run automatically to generate ftpclient.h and ftpclient.cpp , and to add them to the HEADERS and SOURCES variables for compilation.

實例化狀態機

We instantiate the generated FtpClient class, as well as the FtpDataChannel and FtpControlChannel 類在 main.cpp 文件：

#include "ftpcontrolchannel.h"
#include "ftpdatachannel.h"
    ...
int main(int argc, char *argv[])
{
    ...
    QCoreApplication app(argc, argv);
    FtpClient ftpClient;
    FtpDataChannel dataChannel;
    FtpControlChannel controlChannel;
    ...

與 FTP 服務器通信

We print all data retrieved from the server on the console:

    QObject::connect(&dataChannel, &FtpDataChannel::dataReceived,
                     [](const QByteArray &data) {
        std::cout << data.constData();
    });

We translate server replies into state machine events:

    QObject::connect(&controlChannel, &FtpControlChannel::reply, &ftpClient,
                     [&ftpClient](int code, const QString &parameters) {
        ftpClient.submitEvent(QString("reply.%1xx")
                              .arg(code / 100), parameters);
    });

We translate commands from the state machine into FTP control messages:

    ftpClient.connectToEvent("submit.cmd", &controlChannel,
                             [&controlChannel](const QScxmlEvent &event) {
        controlChannel.command(event.name().mid(11).toUtf8(),
                               event.data().toMap()["params"].toByteArray());
    });

We send commands to log into the FTP server as an anonymous user, to announce a port for the data connection, and to retrive a file:

    QList<Command> commands({
        {"cmd.USER", "anonymous"},// login
        {"cmd.PORT", ""},         // announce port for data connection,
                                  // args added below.
        {"cmd.RETR", file}        // retrieve a file
    });

We specify that the FTP client should send the next command when entering the B state:

    ftpClient.connectToState("B", QScxmlStateMachine::onEntry([&]() {
        if (commands.isEmpty()) {
            app.quit();
            return;
        }
        Command command = commands.takeFirst();
        qDebug() << "Posting command" << command.cmd << command.args;
        ftpClient.submitEvent(command.cmd, command.args);
    }));

We specify that the FTP client should send an empty string as a password if the server asks for one:

    ftpClient.connectToState("P", QScxmlStateMachine::onEntry([&ftpClient]() {
        qDebug() << "Sending password";
        ftpClient.submitEvent("cmd.PASS", QString());
    }));

Finally, we connect to the FTP server specified as the first argument of the method and retrieve the file specified as the second argument:

    controlChannel.connectToServer(server);
    QObject::connect(&controlChannel, &FtpControlChannel::opened,
                     [&](const QHostAddress &address, int) {
        dataChannel.listen(address);
        commands[1].args = dataChannel.portspec();
        ftpClient.start();
    });

For example, the following invocation prints the specified file from the specified server: ftpclient <server> <file> .

範例工程 @ code.qt.io