Using UIDL Function to Mark the Email has been downloaded/read in C++/CLI/CLR

In previous section, I introduced how to use event handler. In this section, I will introduce how to use UIDL function to mark the email has been downloaded in C++/CLI/CLR.

Introduction

If you want to leave a copy of email on the server, you should not call Delete method. However, there is a problem, how can you know if the email has already been downloaded? If there is a way to identify the downloaded email, you can avoid downloading the duplicated email from your POP3/IMAP4 server.

Note

Remarks: All of examples in this section are based on first section: A simple C++/CLI/CLR project. To compile and run the following example codes successfully, please click here to learn how to create the test project and add reference to your project.

[C++/CLI/CLR Example - IMAP4 Solution]

Every email has a unique identifier (UIDL) on IMAP4 server. It is a 32bit integer and it is always unique in your email account life time. So we can use the integer as file name to identify if the email has been downloaded. In order to run it correctly, please change email server, user, password, folder, file name values.

#include "stdafx.h"

using namespace System;
using namespace System::IO;
using namespace EAGetMail; //add EAGetMail namespace

int main(array<System::String ^> ^args)
{
    // Create a folder named "inbox" under current directory
    // to save the email retrieved.
    String ^curpath = Directory::GetCurrentDirectory();
    String ^mailbox = String::Format("{0}\\inbox", curpath);

    // If the folder is not existed, create it.
    if (!Directory::Exists(mailbox))
    {
        Directory::CreateDirectory(mailbox);
    }

    MailServer ^oServer = gcnew MailServer("imap4.emailarchitect.net",
        "test@emailarchitect.net", "testpassword", ServerProtocol::Imap4 );
    MailClient ^oClient = gcnew MailClient("TryIt");

    // Set IMAP4 server port
    oServer->Port = 143;

    // If your IMAP4 server requires SSL connection,
    // Please add the following codes:
    // oServer->SSLConnection = true;
    // oServer->Port = 993;

    try
    {
        oClient->Connect(oServer);
        array<MailInfo^> ^infos = oClient->GetMailInfos();
        for (int i = 0; i < infos->Length; i++)
        {
            MailInfo ^info = infos[i];
            Console::WriteLine("Index: {0}; Size: {1}; UIDL: {2}",
                info->Index, info->Size, info->UIDL);

            // Using IMAP UIDL as the file name.
            String ^fileName = String::Format("{0}\\{1}.eml",
                mailbox, info->UIDL );

            if( File::Exists( fileName ))
            {
            // This email has been downloaded,  do not download it again.
                continue;
            }

            // Receive email from IMAP4 server
            Mail ^oMail = oClient->GetMail(info);

            Console::WriteLine("From: {0}", oMail->From->ToString());
            Console::WriteLine("Subject: {0}\r\n", oMail->Subject);

            // Save email to local disk
            oMail->SaveAs(fileName, true);

            // Do not delete email from server.

        }

        // Quit and purge emails marked as deleted from IMAP server.
        oClient->Quit();
    }
    catch (Exception ^ep)
    {
        Console::WriteLine(ep->Message);
    }

    return 0;
}

POP3/IMAP4/Exchange Web Service/WebDAV Solution

There is a little bit different in POP3 server. The UIDL is only unique in the email life time. That means if the email was deleted from the server, other email can use the old unique identifier. Another problem is: UIDL in POP3 server can be any number or characters, so we cannot use UIDL as the file name, because UIDL may contain invalid characters for file name.

UIDL is also unique in Exchange Web Service/WebDAV, but the UIDL is string but not integer. UIDL in Exchange server may contain invalid characters for file name, so we cannot use UIDL as the file name either.

To solve this problem, we have to store the UIDL to a txt file and synchronize it with server every time.

Please have a look at the following example code. It works with both POP3/IMAP4/Exchange Web Service/WebDAV protocol.

#include "stdafx.h"

using namespace System;
using namespace System::Text;
using namespace System::Collections;
using namespace System::IO;
using namespace EAGetMail; //add EAGetMail namespace

public ref class MyMailClient
{
private: String ^m_uidlfile;
private: String ^m_curpath;
private: ArrayList ^m_arUidl;
// UIDL Functions
// uidl is the identifier of every email on POP3/IMAP4 server, to avoid retrieve
// the same email from server more than once, we record the email uidl retrieved every time
// if you delete the email from server every time and not to leave a copy of email on
// the server, then please remove all the function about uidl.

private: bool _FindUIDL( array<MailInfo^>^ infos, String ^uidl )
{
    int count = infos->Length;
    for( int i = 0; i < count; i++ )
    {
        if( String::Compare( infos[i]->UIDL, uidl, false ) == 0 )
            return true;
    }
    return false;
}

// Remove the local uidl which is not existed on the server.
private: void _SyncUIDL( MailServer ^oServer, array<MailInfo^>^ infos)
{
    String ^s = String::Format( "{0}#{1} ", oServer->Server, oServer->User );

    bool bcontinue = false;
    int n = 0;
    do
    {
        bcontinue = false;
        int count = m_arUidl->Count;
        for( int i = n; i < count; i++ )
        {
            String ^x = dynamic_cast<String^>( m_arUidl[i]);
            if( String::Compare( s, 0, x, 0, s->Length, true ) == 0 )
            {
                int pos = x->LastIndexOf( ' ' );
                if( pos != -1 )
                {
                    String ^uidl = x->Substring( pos + 1 );
                    if(!_FindUIDL( infos, uidl ))
                    {
                        // This uidl doesn't exist on server,
                        // so we should remove it from local uidl list.
                        bcontinue = true;
                        n = i;
                        m_arUidl->RemoveAt(i);
                        break;
                    }
                }
            }
        }
    }while( bcontinue );

}

private: bool _FindExistedUIDL( MailServer ^oServer, String ^uidl )
{
    String ^s = String::Format( "{0}#{1} {2}",
        oServer->Server->ToLower(), oServer->User->ToLower(), uidl );
    int count = m_arUidl->Count;
    for( int i = 0; i < count; i++ )
    {
        String ^x = dynamic_cast<String^>(m_arUidl[i]);
        if( String::Compare( s, x, false ) == 0 )
            return true;
    }
    return false;
}

private: void _AddUIDL( MailServer ^oServer, String ^uidl )
{
    String ^s = String::Format( "{0}#{1} {2}",
        oServer->Server->ToLower(), oServer->User->ToLower(), uidl );
    m_arUidl->Add( s );
}

private: void _UpdateUIDL()
{
    StringBuilder ^s = gcnew StringBuilder();
    int count = m_arUidl->Count;
    for( int i = 0; i < count; i++ )
    {
        s->Append( dynamic_cast<String^>(m_arUidl[i]));
        s->Append( "\r\n" );
    }

    String ^file = String::Format( "{0}\\{1}", m_curpath, m_uidlfile );

    FileStream ^fs  = nullptr;
    try
    {
        fs = gcnew FileStream( file, FileMode::Create, FileAccess::Write, FileShare::None );
        array<unsigned char>^ data = System::Text::Encoding::Default->GetBytes( s->ToString());
        fs->Write( data, 0, data->Length );
        fs->Close();
    }
    catch(Exception ^ep )
    {
        if( fs != nullptr )
            fs->Close();

        throw ep;
    }

}

private: void _LoadUIDL( )
{
    m_arUidl->Clear();
    String ^file = String::Format( "{0}\\{1}", m_curpath, m_uidlfile );
    StreamReader ^read = nullptr;
    try
    {
        read = File::OpenText( file );
        while( true )
        {
            String ^strim = "\r\n \t";
            String ^line = read->ReadLine()->Trim( strim->ToCharArray());
            m_arUidl->Add( line );
        }
    }
    catch(Exception ^ep )
    {}

    if( read != nullptr )
        read->Close();
}

public: void ReceiveEmail(MailServer ^oServer, bool bLeaveCopy )
{
    m_arUidl = gcnew ArrayList();
    m_uidlfile = "uidl.txt";
    MailClient ^oClient = gcnew MailClient("TryIt");
    m_curpath = Directory::GetCurrentDirectory();
    try
    {
    // uidl is the identifier of every email on POP3/IMAP4 server, to
    // avoid retrieve the same email from server more than once,
    // we record the email uidl retrieved every time if you delete the
    // email from server every time and not to leave a copy of email on
    // the server, then please remove all the function about uidl.
        _LoadUIDL();

        String ^mailFolder = String::Format("{0}\\inbox", m_curpath);
        if (!Directory::Exists(mailFolder))
            Directory::CreateDirectory(mailFolder);

        Console::WriteLine("Connecting server ... ");
        oClient->Connect(oServer);
        array<MailInfo^> ^infos = oClient->GetMailInfos();
        Console::WriteLine( "Total {0} email(s)", infos->Length);

        _SyncUIDL(oServer, infos);
        int count = infos->Length;

        for (int i = 0; i < count; i++)
        {
            MailInfo ^info = infos[i];
            if (_FindExistedUIDL(oServer, info->UIDL))
            {
                // This email has existed on local disk.
                continue;
            }

            Console::WriteLine("Retrieving {0}/{1}...", info->Index, count);

            Mail ^oMail = oClient->GetMail(info);
            System::DateTime d = System::DateTime::Now;
            System::Globalization::CultureInfo ^cur =
                gcnew System::Globalization::CultureInfo("en-US");
            String ^sdate = d.ToString("yyyyMMddHHmmss", cur);
            String ^fileName = String::Format("{0}\\{1}{2}{3}.eml",
                    mailFolder, sdate, d.Millisecond.ToString("d3"), i);
            oMail->SaveAs(fileName, true);

            if (bLeaveCopy)
            {
                // Add the email uidl to uidl file to avoid we retrieve it next time.
                _AddUIDL(oServer, info->UIDL);
            }
        }

        if (!bLeaveCopy)
        {
            Console::WriteLine( "Deleting ..." );
            for (int i = 0; i < count; i++)
                oClient->Delete(infos[i]);
        }

        Console::WriteLine("Completed");
        // Delete method just mark the email as deleted,
        // Quit method purge the emails from server exactly.
        oClient->Quit();

    }
    catch (Exception ^ep)
    {
        Console::WriteLine(ep->Message);
    }

    // Update the uidl list to a text file and then we can load it next time.
    _UpdateUIDL();
}

};

int main(array<System::String ^> ^args)
{
    // Create a folder named "inbox" under current directory
    // to save the email retrieved.
    String ^curpath = Directory::GetCurrentDirectory();
    String ^mailbox = String::Format("{0}\\inbox", curpath);

    // If the folder is not existed, create it.
    if (!Directory::Exists(mailbox))
    {
        Directory::CreateDirectory(mailbox);
    }

    MailServer ^oServer = gcnew MailServer("pop3.emailarchitect.net",
        "test@emailarchitect.net", "testpassword", ServerProtocol::Pop3 );
    MailClient ^oClient = gcnew MailClient("TryIt");

    // If your POP3 server requires SSL connection,
    // Please add the following codes:
    // oServer->SSLConnection = true;
    // oServer->Port = 995;

    MyMailClient ^MyClient = gcnew MyMailClient();
    MyClient->ReceiveEmail( oServer, true );

    return 0;
}

UIDLManager Object

With EAGetMail 4.0, it provides a new class named “UIDLManager”. This object provides an easy way to maintain UIDL between your server and your local client. How does it work? It stores UIDL collection to a local disk file and you can use this object to add, remove and search UIDL with this local file. Then you don’t have to handle UIDL in your code. Please click here to learn more detail.

Mark Email as Read on IMAP4/Exchange Server

With IMAP4/Exchange Web Service/WebDAV protocol, you can also mark the email as read on the server, but POP3 doesn’t support this feature. Please refer to MarkAsRead method to learn more detail.

Next Section

At next section I will introduce how to download email in background.

Appendix

Comments

If you have any comments or questions about above example codes, please click here to add your comments.