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// Copyright (C) 2023 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*!
\example ftpclient
\title SCXML FTP Client
\ingroup examples-qtscxml
\brief Implements a simple FTP client using a state machine.
\e {FTP Client} 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.
\l{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.
The state machine has the following states:
\image ftpclient-statechart.png
\list
\li \e I as the initial state.
\li \e B for sending commands.
\li \e S for success.
\li \e F for failure.
\li \e W for waiting for a reply.
\li \e P for supplying a password upon server request.
\endlist
The state machine is specified in the \e simpleftp.scxml file and compiled
into the \c 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
\c FtpControlChannel class and a \c FtpDataChannel class that handle TCP
sockets and servers and convert line endings.
\include examples-run.qdocinc
\section1 Compiling the State Machine
We link against the Qt SCXML module by adding the following line to the
project build files.
With qmake, we add the following to \e ftpclient.pro
\quotefromfile ftpclient/ftpclient.pro
\skipto QT
\printline scxml
We then specify the state machine to compile:
\skipto STATECHARTS
\printline scxml
With CMake, we add the following to \e CMakeLists.txt
\quotefromfile ftpclient/CMakeLists.txt
\skipto find_package
\printline Scxml
\skipto target_link_libraries
\printuntil )
We then specify the state machine to compile:
\skipto qt6_add_statecharts
\printuntil )
The Qt SCXML Compiler, \c qscxmlc, is run automatically to generate
\e simpleftp.h and \e simpleftp.cpp, and to add them appropriately to
the project as headers and sources.
\section1 Instantiating the State Machine
We instantiate the generated \c FtpClient class, as well as the
\c FtpDataChannel and \c FtpControlChannel classes in the \e main.cpp file:
\quotefromfile ftpclient/main.cpp
\skipto #include
\printuntil simpleftp
\dots
\skipto int main
\printuntil {
\dots
\skipto QCoreApplication
\printuntil FtpControlChannel
\dots
\section1 Communicating with an FTP Server
We print all data retrieved from the server on the console:
\skipto QObject::connect(&dataChannel
\printuntil }
We translate server replies into state machine events:
\skipto QObject::connect(&controlChannel
\printuntil }
We translate commands from the state machine into FTP control messages:
\skipto ftpClient.connectToEvent(
\printuntil }
We send commands to log into the FTP server as an anonymous user, to
announce a port for the data connection, and to retrieve a file:
\skipto QList
\printuntil });
We specify that the FTP client should send the next command when entering
the \e B state:
\skipto ftpClient.connectToState("B"
\printuntil }));
We specify that the FTP client should send an empty string as a password if
the server asks for one:
\skipto ftpClient.connectToState("P"
\printuntil }
Finally, we connect to the FTP server specified as the first argument of
the method and retrieve the file specified as the second argument:
\skipto controlChannel.connectToServer(server)
\printuntil }
For example, the following invocation prints the specified file from the
specified server: \c {ftpclient <server> <file>}.
*/
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