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#include "server.h"

#include <algorithm>

namespace {

QString peer_info(const QHostAddress &address, quint16 port)
{
    const static QString info = QStringLiteral("(%1:%2)");
    return info.arg(address.toString()).arg(port);
}

QString connection_info(QSharedPointer<QDtls> connection)
{
    QString info(DtlsServer::tr("Session cipher: "));
    info += connection->sessionCipher().name();

    info += DtlsServer::tr("; session protocol: ");
    switch (connection->sessionProtocol()) {
    case QSsl::DtlsV1_0:
        info += DtlsServer::tr("DTLS 1.0.");
        break;
    case QSsl::DtlsV1_2:
        info += DtlsServer::tr("DTLS 1.2.");
        break;
    case QSsl::DtlsV1_2OrLater:
        info += DtlsServer::tr("DTLS 1.2 or later.");
        break;
    default:
        info += DtlsServer::tr("Unknown protocol.");
    }

    return info;
}

} // unnamed namespace

DtlsServer::DtlsServer()
{
    connect(&serverSocket, &QAbstractSocket::readyRead, this, &DtlsServer::readyRead);

    serverConfiguration = QSslConfiguration::defaultDtlsConfiguration();
    serverConfiguration.setPreSharedKeyIdentityHint("Qt DTLS example server");
    serverConfiguration.setPeerVerifyMode(QSslSocket::VerifyNone);
}

DtlsServer::~DtlsServer()
{
    shutdown();
}

bool DtlsServer::listen(const QHostAddress &address, quint16 port)
{
    if (address != serverSocket.localAddress() || port != serverSocket.localPort()) {
        shutdown();
        listening = serverSocket.bind(address, port);
        if (!listening)
            emit errorMessage(serverSocket.errorString());
    } else {
        listening = true;
    }

    return listening;
}

bool DtlsServer::isListening() const
{
    return listening;
}

void DtlsServer::close()
{
    listening = false;
}

void DtlsServer::readyRead()
{
    const qint64 bytesToRead = serverSocket.pendingDatagramSize();
    if (bytesToRead <= 0) {
        emit warningMessage(tr("A spurious read notification"));
        return;
    }

    QByteArray dgram(bytesToRead, Qt::Uninitialized);
    QHostAddress peerAddress;
    quint16 peerPort = 0;
    const qint64 bytesRead = serverSocket.readDatagram(dgram.data(), dgram.size(),
                                                       &peerAddress, &peerPort);
    if (bytesRead <= 0) {
        emit warningMessage(tr("Failed to read a datagram: ") + serverSocket.errorString());
        return;
    }

    dgram.resize(bytesRead);
    if (peerAddress.isNull() || !peerPort) {
        emit warningMessage(tr("Failed to extract peer info (address, port)"));
        return;
    }

    const auto client = std::find_if(knownClients.begin(), knownClients.end(),
                                     [&](const DtlsConnection &connection){
        return connection->peerAddress() == peerAddress
               && connection->peerPort() == peerPort;
    });

    if (client == knownClients.end())
        return handleNewConnection(peerAddress, peerPort, dgram);

    if ((*client)->isConnectionEncrypted()) {
        decryptDatagram(*client, dgram);
        if ((*client)->dtlsError() == QDtlsError::RemoteClosedConnectionError)
            knownClients.erase(client);
        return;
    }

    doHandshake(*client, dgram);
}

void DtlsServer::pskRequired(QSslPreSharedKeyAuthenticator *auth)
{
    Q_ASSERT(auth);

    emit infoMessage(tr("PSK callback, received a client's identity: '%1'")
                     .arg(QString::fromLatin1(auth->identity())));
    auth->setPreSharedKey(QByteArrayLiteral("\x1a\x2b\x3c\x4d\x5e\x6f"));
}

void DtlsServer::handleNewConnection(const QHostAddress &peerAddress,
                                     quint16 peerPort, const QByteArray &clientHello)
{
    if (!listening)
        return;

    const QString peerInfo = peer_info(peerAddress, peerPort);
    if (cookieSender.verifyClient(&serverSocket, clientHello, peerAddress, peerPort)) {
        emit infoMessage(peerInfo + tr(": verified, starting a handshake"));
        DtlsConnection newConnection(new QDtls(QSslSocket::SslServerMode));
        newConnection->setDtlsConfiguration(serverConfiguration);
        newConnection->setPeer(peerAddress, peerPort);
        newConnection->connect(newConnection.data(), &QDtls::pskRequired,
                               this, &DtlsServer::pskRequired);
        knownClients.push_back(newConnection);
        doHandshake(newConnection, clientHello);
    } else if (cookieSender.dtlsError() != QDtlsError::NoError) {
        emit errorMessage(tr("DTLS error: ") + cookieSender.dtlsErrorString());
    } else {
        emit infoMessage(peerInfo + tr(": not verified yet"));
    }
}

void DtlsServer::doHandshake(DtlsConnection newConnection, const QByteArray &clientHello)
{
    const bool result = newConnection->doHandshake(&serverSocket, clientHello);
    if (!result) {
        emit errorMessage(newConnection->dtlsErrorString());
        return;
    }

    const QString peerInfo = peer_info(newConnection->peerAddress(),
                                       newConnection->peerPort());
    switch (newConnection->handshakeState()) {
    case QDtls::HandshakeInProgress:
        emit infoMessage(peerInfo + tr(": handshake is in progress ..."));
        break;
    case QDtls::HandshakeComplete:
        emit infoMessage(tr("Connection with %1 encrypted. %2")
                         .arg(peerInfo, connection_info(newConnection)));
        break;
    default:
        Q_UNREACHABLE();
    }
}

void DtlsServer::decryptDatagram(DtlsConnection connection, const QByteArray &clientMessage)
{
    Q_ASSERT(connection->isConnectionEncrypted());

    const QString peerInfo = peer_info(connection->peerAddress(), connection->peerPort());
    const QByteArray dgram = connection->decryptDatagram(&serverSocket, clientMessage);
    if (dgram.size()) {
        emit datagramReceived(peerInfo, clientMessage, dgram);
        connection->writeDatagramEncrypted(&serverSocket, tr("to %1: ACK").arg(peerInfo).toLatin1());
    } else if (connection->dtlsError() == QDtlsError::NoError) {
        emit warningMessage(peerInfo + ": " + tr("0 byte dgram, could be a re-connect attempt?"));
    } else {
        emit errorMessage(peerInfo + ": " + connection->dtlsErrorString());
    }
}

void DtlsServer::shutdown()
{
    for (DtlsConnection &connection : knownClients)
        connection->shutdown(&serverSocket);

    knownClients.clear();
    serverSocket.close();
}