A simple mail client

This example shows how to use the QSocket class. The client can only be used to send mails. The interesting part is the implementation of the SMTP protocol.

Header file (smtp.h):

/****************************************************************************
** $Id: qt/smtp.h   3.3.7   edited Aug 31 2005 $
**
** Copyright (C) 1992-2005 Trolltech AS.  All rights reserved.
**
** This file is part of an example program for Qt.  This example
** program may be used, distributed and modified without limitation.
**
*****************************************************************************/

#ifndef SMTP_H
#define SMTP_H

#include <qobject.h>
#include <qstring.h>

class QSocket;
class QTextStream;
class QDns;

class Smtp : public QObject
{
    Q_OBJECT

public:
    Smtp( const QString &from, const QString &to,
          const QString &subject, const QString &body );
    ~Smtp();

signals:
    void status( const QString & );

private slots:
    void dnsLookupHelper();
    void readyRead();
    void connected();

private:
    enum State {
        Init,
        Mail,
        Rcpt,
        Data,
        Body,
        Quit,
        Close
    };

    QString message;
    QString from;
    QString rcpt;
    QSocket *socket;
    QTextStream * t;
    int state;
    QString response;
    QDns * mxLookup;
};

#endif

Implementation (smtp.cpp):

/****************************************************************************
** $Id: qt/smtp.cpp   3.3.7   edited Aug 31 2005 $
**
** Copyright (C) 1992-2005 Trolltech AS.  All rights reserved.
**
** This file is part of an example program for Qt.  This example
** program may be used, distributed and modified without limitation.
**
*****************************************************************************/

#include "smtp.h"

#include <qtextstream.h>
#include <qsocket.h>
#include <qdns.h>
#include <qtimer.h>
#include <qapplication.h>
#include <qmessagebox.h>
#include <qregexp.h>


Smtp::Smtp( const QString &from, const QString &to,
            const QString &subject,
            const QString &body )
{
    socket = new QSocket( this );
    connect ( socket, SIGNAL( readyRead() ),
              this, SLOT( readyRead() ) );
    connect ( socket, SIGNAL( connected() ),
              this, SLOT( connected() ) );

    mxLookup = new QDns( to.mid( to.find( '@' )+1 ), QDns::Mx );
    connect( mxLookup, SIGNAL(resultsReady()),
             this, SLOT(dnsLookupHelper()) );

    message = QString::fromLatin1( "From: " ) + from +
              QString::fromLatin1( "\nTo: " ) + to +
              QString::fromLatin1( "\nSubject: " ) + subject +
              QString::fromLatin1( "\n\n" ) + body + "\n";
    message.replace( QString::fromLatin1( "\n" ),
                     QString::fromLatin1( "\r\n" ) );
    message.replace( QString::fromLatin1( "\r\n.\r\n" ),
                     QString::fromLatin1( "\r\n..\r\n" ) );

    this->from = from;
    rcpt = to;

    state = Init;
}


Smtp::~Smtp()
{
    delete t;
    delete socket;
}


void Smtp::dnsLookupHelper()
{
    QValueList<QDns::MailServer> s = mxLookup->mailServers();
    if ( s.isEmpty() ) {
        if ( !mxLookup->isWorking() )
            emit status( tr( "Error in MX record lookup" ) );
        return;
    }

    emit status( tr( "Connecting to %1" ).arg( s.first().name ) );

    socket->connectToHost( s.first().name, 25 );
    t = new QTextStream( socket );
}


void Smtp::connected()
{
    emit status( tr( "Connected to %1" ).arg( socket->peerName() ) );
}

void Smtp::readyRead()
{
    // SMTP is line-oriented
    if ( !socket->canReadLine() )
        return;

    QString responseLine;
    do {
        responseLine = socket->readLine();
        response += responseLine;
    } while( socket->canReadLine() && responseLine[3] != ' ' );
    responseLine.truncate( 3 );

    if ( state == Init && responseLine[0] == '2' ) {
        // banner was okay, let's go on
        *t << "HELO there\r\n";
        state = Mail;
    } else if ( state == Mail && responseLine[0] == '2' ) {
        // HELO response was okay (well, it has to be)
        *t << "MAIL FROM: <" << from << ">\r\n";
        state = Rcpt;
    } else if ( state == Rcpt && responseLine[0] == '2' ) {
        *t << "RCPT TO: <" << rcpt << ">\r\n";
        state = Data;
    } else if ( state == Data && responseLine[0] == '2' ) {
        *t << "DATA\r\n";
        state = Body;
    } else if ( state == Body && responseLine[0] == '3' ) {
        *t << message << ".\r\n";
        state = Quit;
    } else if ( state == Quit && responseLine[0] == '2' ) {
        *t << "QUIT\r\n";
        // here, we just close.
        state = Close;
        emit status( tr( "Message sent" ) );
    } else if ( state == Close ) {
        deleteLater();
        return;
    } else {
        // something broke.
        QMessageBox::warning( qApp->activeWindow(),
                              tr( "Qt Mail Example" ),
                              tr( "Unexpected reply from SMTP server:\n\n" ) +
                              response );
        state = Close;
    }

    response = "";
}

See also Network Examples.