This is the C++/Qt implementation of the message bus program. The principles of the message bus are described in the main message bus article. Do read that article first.
Here I have used Qt’s abstractions for socket, so sorry, no down-and-dirty socket()/bind()/accept() code.
The source code
This source is split in two files, since Qt wants a header file to scan; putting the class declarations in the .cc file does not work. And anyway, it is good style, and more readable, to put declarations is a separate header file.
The Qt project file
# -*- mode: Makefile; coding: us-ascii-unix -*- QT += core QT += widgets QT += network HEADERS += redgreenblue.h SOURCES += redgreenblue.cc
Header file
// -*- coding: us-ascii-unix -*-
# pragma once
# include <qobject.h>
# include <qwidget.h>
class QTcpServer;
class QTcpSocket;
class QTextStream;
class QPushButton;
class Server : public QObject {
Q_OBJECT
public:
Server(int port, QObject *parent = 0);
~Server();
void accept_connection();
private:
QTcpServer *_tcp_server = 0;
};
class Worker : public QObject {
Q_OBJECT
public:
Worker(QTcpSocket *s, Server *parent = 0);
~Worker();
void write_current_colour();
private:
void _read_from_client();
QTcpSocket *_tcp_socket = 0;
};
class Client : public QObject {
public:
Client(int port);
void send_message(char const *buf);
static Client *instance;
private:
void _data_arrived();
void _connection_closed();
QTcpSocket *_tcp_socket = 0;
};
class Gui : public QWidget {
Q_OBJECT
public:
Gui(QWidget *parent = 0);
void on_incoming_message(char const *message);
static Gui *instance;
private:
QPushButton *btn(char const *text, int id, Gui *parent);
void on_clicked();
QPushButton *red = 0;
QPushButton *green = 0;
QPushButton *blue = 0;
};
Source file
// -*- coding: us-ascii-unix -*-
# include <redgreenblue.h>
# include <qapplication.h> //-- QApplication
# include <qtcpserver.h> //-- QTcpServer
# include <qtcpsocket.h> //-- QTcpSocket
# include <qhostaddress.h> //-- QHostAddress
# include <qevent.h> //-- QEvent
# include <qlabel.h> //-- QLabel
# include <qlayout.h> //-- QLayout
# include <qpushbutton.h> //-- QPushButton
# include <qbuttongroup.h> //-- QButtonGroup
# include <qtextstream.h> //-- QTextSTream
# include <qpalette.h> //-- QPalette
# include <qcolor.h> //-- QColor
# include <set>
# include <assert.h>
# include <stdlib.h>
enum { RED = 1001, GREEN, BLUE };
class Server;
class Worker;
static struct {
std::set<Worker *> clients;
int current_colour = RED;
} s;
//----------------------------------------------------------------------------------------
Server::Server(int port, QObject *parent)
: QObject(parent),
_tcp_server(new QTcpServer(this))
{
if (_tcp_server->listen(QHostAddress::Any, port))
assert(connect(_tcp_server, &QTcpServer::newConnection, this, &Server::accept_connection));
}
Server::~Server() { }
void Server::accept_connection()
{
printf("Incoming connection\n");
while (QTcpSocket *s = _tcp_server->nextPendingConnection()) {
printf("Adding a pending connection\n");
(new Worker(s, this))->write_current_colour();
}
}
//----------------------------------------------------------------------------------------
Worker::Worker(QTcpSocket *tcp_socket, Server *parent)
: QObject(parent),
_tcp_socket(tcp_socket)
{
s.clients.insert(this);
assert(connect(_tcp_socket, &QTcpSocket::readyRead, this, &Worker ::_read_from_client));
assert(connect(_tcp_socket, &QTcpSocket::disconnected, this, &Worker ::deleteLater ));
assert(connect(_tcp_socket, &QTcpSocket::disconnected, _tcp_socket, &QTcpSocket::deleteLater ));
}
Worker::~Worker()
{
s.clients.erase(this);
}
void Worker::write_current_colour()
{
char buf[20];
snprintf(buf, sizeof buf, "%d\n", s.current_colour);
assert(strlen(buf) == 0LLU + _tcp_socket->write(buf));
}
void Worker::_read_from_client()
{
char buf[20];
auto count = _tcp_socket->QIODevice::readLine(buf, sizeof buf);
assert(1 < count && count < 10);
for (auto it : s.clients)
assert(strlen(buf) == 0LLU + it->_tcp_socket->write(buf));
}
//-----------------------------------------------------------------------------
Client *Client::instance = 0;
Client::Client(int port)
: _tcp_socket(new QTcpSocket(this))
{
assert(0 == instance);
_tcp_socket->connectToHost("localhost", port);
printf("Connection opened\n");
if (_tcp_socket->isOpen()) {
assert(connect(_tcp_socket, &QTcpSocket::readyRead, this, &Client::_data_arrived )); //dataAvailable(int)
assert(connect(_tcp_socket, &QTcpSocket::disconnected, this, &Client::_connection_closed));
} else {
printf("******* Gui::open_connection(): Failed\n");
exit(1);
}
instance = this;
}
void Client::_data_arrived()
{
char buf[20];
auto n = _tcp_socket->QIODevice::readLine(buf, sizeof buf);
assert(1 < n && n < 10);
for (--n; n >= 0 && buf[n] <= ' '; n--)
buf[n] = 0;
Gui::instance->on_incoming_message(buf);
}
void Client::_connection_closed() { exit(0); }
void Client::send_message(char const *buf)
{
printf("Writing to server: [%s]\n", buf);
_tcp_socket->write(buf);
}
//-----------------------------------------------------------------------------
Gui *Gui::instance = 0;
static struct {
QPalette p_white;
QPalette p_red;
QPalette p_green;
QPalette p_blue;
} s_gui;
Gui::Gui(QWidget *parent)
: QWidget(parent ),
red (btn("Red", RED, this)),
green (btn("Green", GREEN, this)),
blue (btn("Blue", BLUE, this))
{
assert(0 == instance);
QBoxLayout *buttons = new QHBoxLayout();
buttons->addWidget(red );
buttons->addWidget(green);
buttons->addWidget(blue );
s_gui.p_white = red->palette();
s_gui.p_red = s_gui.p_white;
s_gui.p_green = s_gui.p_white;
s_gui.p_blue = s_gui.p_white;
s_gui.p_red .setColor(QPalette::Button, QColor(Qt::red ));
s_gui.p_green.setColor(QPalette::Button, QColor(Qt::green));
s_gui.p_blue .setColor(QPalette::Button, QColor(Qt::blue ));
this->setWindowTitle("C++ and Qt");
this->setLayout(buttons);
instance = this;
}
QPushButton *Gui::btn(char const *text, int id, Gui *parent) {
QPushButton *rval = new QPushButton(text, parent);
rval ->setMinimumSize(rval ->sizeHint());
rval ->setProperty ("id", id);
rval ->setMinimumSize(100, 30);
assert(QObject::connect(rval, &QPushButton::clicked, parent, &Gui::on_clicked));
return rval;
}
void Gui::on_clicked () {
char buf[20];
auto var = sender()->property("id");
int id = var.toInt();
snprintf(buf, sizeof buf, "%d\n", id);
Client::instance->send_message(buf);
}
void Gui::on_incoming_message(char const *message)
{
int colour = atoi(message);
red ->setPalette(RED == colour ? s_gui.p_red : s_gui.p_white); red ->update();
green->setPalette(GREEN == colour ? s_gui.p_green : s_gui.p_white); green->update();
blue ->setPalette(BLUE == colour ? s_gui.p_blue : s_gui.p_white); blue ->update();
}
int main(int argc, char **argv)
{
QApplication app(argc, argv);
Server server(4711);
Client client(4711);
Gui *f = new Gui();
f->show();
app.exec();
return 0;
}
You can reach me by email at “lars dash 7 dot sdu dot se” or by telephone +46 705 189090