Question

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   3.0.5   edited Oct 12 2001 $
**
** Copyright (C) 1992-2000 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   3.0.5   edited Apr 18 14:18 $
**
** Copyright (C) 1992-2000 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( QRegExp( QString::fromLatin1( "\n" ) ),
                     QString::fromLatin1( "\r\n" ) );
    message.replace( QRegExp( 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() && mxLookup->isWorking() )
        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 ) {
        delete this;
        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.