Network Chat Example

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#include <QtNetwork>

#include "client.h"
#include "connection.h"
#include "peermanager.h"

static const qint32 BroadcastInterval = 2000;
static const unsigned broadcastPort = 45000;

PeerManager::PeerManager(Client *client)
    : QObject(client)
{
    this->client = client;

    static const char *envVariables[] = {
        "USERNAME", "USER", "USERDOMAIN", "HOSTNAME", "DOMAINNAME"
    };

    for (const char *varname : envVariables) {
        username = qEnvironmentVariable(varname);
        if (!username.isNull())
            break;
    }

    if (username.isEmpty())
        username = "unknown";

    updateAddresses();
    serverPort = 0;

    broadcastSocket.bind(QHostAddress::Any, broadcastPort, QUdpSocket::ShareAddress
                         | QUdpSocket::ReuseAddressHint);
    connect(&broadcastSocket, SIGNAL(readyRead()),
            this, SLOT(readBroadcastDatagram()));

    broadcastTimer.setInterval(BroadcastInterval);
    connect(&broadcastTimer, SIGNAL(timeout()),
            this, SLOT(sendBroadcastDatagram()));
}

void PeerManager::setServerPort(int port)
{
    serverPort = port;
}

QString PeerManager::userName() const
{
    return username;
}

void PeerManager::startBroadcasting()
{
    broadcastTimer.start();
}

bool PeerManager::isLocalHostAddress(const QHostAddress &address)
{
    foreach (QHostAddress localAddress, ipAddresses) {
        if (address.isEqual(localAddress))
            return true;
    }
    return false;
}

void PeerManager::sendBroadcastDatagram()
{
    QByteArray datagram;
    {
        QCborStreamWriter writer(&datagram);
        writer.startArray(2);
        writer.append(username);
        writer.append(serverPort);
        writer.endArray();
    }

    bool validBroadcastAddresses = true;
    foreach (QHostAddress address, broadcastAddresses) {
        if (broadcastSocket.writeDatagram(datagram, address,
                                          broadcastPort) == -1)
            validBroadcastAddresses = false;
    }

    if (!validBroadcastAddresses)
        updateAddresses();
}

void PeerManager::readBroadcastDatagram()
{
    while (broadcastSocket.hasPendingDatagrams()) {
        QHostAddress senderIp;
        quint16 senderPort;
        QByteArray datagram;
        datagram.resize(broadcastSocket.pendingDatagramSize());
        if (broadcastSocket.readDatagram(datagram.data(), datagram.size(),
                                         &senderIp, &senderPort) == -1)
            continue;

        int senderServerPort;
        {
            // decode the datagram
            QCborStreamReader reader(datagram);
            if (reader.lastError() != QCborError::NoError || !reader.isArray())
                continue;
            if (!reader.isLengthKnown() || reader.length() != 2)
                continue;

            reader.enterContainer();
            if (reader.lastError() != QCborError::NoError || !reader.isString())
                continue;
            while (reader.readString().status == QCborStreamReader::Ok) {
                // we don't actually need the username right now
            }

            if (reader.lastError() != QCborError::NoError || !reader.isUnsignedInteger())
                continue;
            senderServerPort = reader.toInteger();
        }

        if (isLocalHostAddress(senderIp) && senderServerPort == serverPort)
            continue;

        if (!client->hasConnection(senderIp)) {
            Connection *connection = new Connection(this);
            emit newConnection(connection);
            connection->connectToHost(senderIp, senderServerPort);
        }
    }
}

void PeerManager::updateAddresses()
{
    broadcastAddresses.clear();
    ipAddresses.clear();
    foreach (QNetworkInterface interface, QNetworkInterface::allInterfaces()) {
        foreach (QNetworkAddressEntry entry, interface.addressEntries()) {
            QHostAddress broadcastAddress = entry.broadcast();
            if (broadcastAddress != QHostAddress::Null && entry.ip() != QHostAddress::LocalHost) {
                broadcastAddresses << broadcastAddress;
                ipAddresses << entry.ip();
            }
        }
    }
}