POP3 Email Client with full MIME Support (.NET 2.0)

// POP3 Email Client
// =================
//
// copyright by Peter Huber, Singapore, 2006
// this code is provided as is, bugs are probable, free for any use at own risk, no 
// responsibility accepted. All rights, title and interest in and to the accompanying content retained.  :-)
//
// based on Standard for ARPA Internet Text Messages, http://rfc.net/rfc822.html
// based on MIME Standard,  Internet Message Bodies, http://rfc.net/rfc2045.html
// based on MIME Standard, Media Types, http://rfc.net/rfc2046.html
using System;
using System.Collections.Generic;
using System.IO;
using System.Net.Mail;
using System.Net.Mime;
using System.Text;


namespace Pop3 {
  /// <summary>
  /// Stores all MIME decoded information of a received email. One email might consist of
  /// several MIME entities, which have a very similar structure to an email. A RxMailMessage
  /// can be a top most level email or a MIME entity the emails contains.
  /// 
  /// According to various RFCs, MIME entities can contain other MIME entities 
  /// recursively. However, they usually need to be mapped to alternative views and 
  /// attachments, which are non recursive.
  ///
  /// RxMailMessage inherits from System.Net.MailMessage, but provides additional receiving related information 
  /// </summary>
  public class RxMailMessage: MailMessage {
    /// <summary>
    /// To whom the email was delivered to
    /// </summary>
    public MailAddress DeliveredTo;
    /// <summary>
    /// To whom the email was
    /// </summary>
    public MailAddress ReturnPath;
    /// <summary>
    /// 
    /// </summary>
    public DateTime DeliveryDate;
    /// <summary>
    /// Date when the email was received
    /// </summary>
    public string MessageId;
    /// <summary>
    /// probably '1,0'
    /// </summary>
    public string MimeVersion;
    /// <summary>
    /// It may be desirable to allow one body to make reference to another. Accordingly, 
    /// bodies may be labelled using the "Content-ID" header field.    
    /// </summary>
    public string ContentId;
    /// <summary>
    /// some descriptive information for body
    /// </summary>
    public string ContentDescription;
    /// <summary>
    /// ContentDisposition contains normally redundant information also stored in the 
    /// ContentType. Since ContentType is more detailed, it is enough to analyze ContentType
    /// 
    /// something like:
    /// inline
    /// inline; filename="image001.gif
    /// attachment; filename="image001.jpg"
    /// </summary>
    public ContentDisposition ContentDisposition;
    /// <summary>
    /// something like "7bit" / "8bit" / "binary" / "quoted-printable" / "base64"
    /// </summary>
    public string TransferType;
    /// <summary>
    /// similar as TransferType, but .NET supports only "7bit" / "quoted-printable"
    /// / "base64" here, "bit8" is marked as "bit7" (i.e. no transfer encoding needed), 
    /// "binary" is illegal in SMTP
    /// </summary>
    public TransferEncoding ContentTransferEncoding;
    /// <summary>
    /// The Content-Type field is used to specify the nature of the data in the body of a
    /// MIME entity, by giving media type and subtype identifiers, and by providing 
    /// auxiliary information that may be required for certain media types. Examples:
    /// text/plain;
    /// text/plain; charset=ISO-8859-1
    /// text/plain; charset=us-ascii
    /// text/plain; charset=utf-8
    /// text/html;
    /// text/html; charset=ISO-8859-1
    /// image/gif; name=image004.gif
    /// image/jpeg; name="image005.jpg"
    /// message/delivery-status
    /// message/rfc822
    /// multipart/alternative; boundary="----=_Part_4088_29304219.1115463798628"
    /// multipart/related; 	boundary="----=_Part_2067_9241611.1139322711488"
    /// multipart/mixed; 	boundary="----=_Part_3431_12384933.1139387792352"
    /// multipart/report; report-type=delivery-status; boundary="k04G6HJ9025016.1136391237/carbon.singnet.com.sg"
    /// </summary>
    public ContentType ContentType;
    /// <summary>
    /// .NET framework combines MediaType (text) with subtype (plain) in one property, but
    /// often one or the other is needed alone. MediaMainType in this example would be 'text'.
    /// </summary>
    public string MediaMainType;
    /// <summary>
    /// .NET framework combines MediaType (text) with subtype (plain) in one property, but
    /// often one or the other is needed alone. MediaSubType in this example would be 'plain'.
    /// </summary>
    public string MediaSubType;
    /// <summary>
    /// RxMessage can be used for any MIME entity, as a normal message body, an attachement or an alternative view. ContentStream
    /// provides the actual content of that MIME entity. It's mainly used internally and later mapped to the corresponding 
    /// .NET types.
    /// </summary>
    public Stream ContentStream;
    /// <summary>
    /// A MIME entity can contain several MIME entities. A MIME entity has the same structure
    /// like an email. 
    /// </summary>
    public List<RxMailMessage> Entities;
    /// <summary>
    /// This entity might be part of a parent entity
    /// </summary>
    public RxMailMessage Parent;
    /// <summary>
    /// The top most MIME entity this MIME entity belongs to (grand grand grand .... parent)
    /// </summary>
    public RxMailMessage TopParent;
    /// <summary>
    /// The complete entity in raw content. Since this might take up quiet some space, the raw content gets only stored if the
    /// Pop3MimeClient.isGetRawEmail is set.
    /// </summary>
    public string RawContent;
    /// <summary>
    /// Headerlines not interpretable by Pop3ClientEmail
    /// <example></example>
    /// </summary>
    public List<string> UnknowHeaderlines; //


    // Constructors
    // ------------
    /// <summary>
    /// default constructor
    /// </summary>
    public RxMailMessage() {
      //for the moment, we assume to be at the top
      //should this entity become a child, TopParent will be overwritten
      TopParent = this; 
      Entities = new List<RxMailMessage>();
      UnknowHeaderlines = new List<string>();
    }


    /// <summary>
    /// Set all content type related fields
    /// </summary>
    public void SetContentTypeFields(string contentTypeString){
      contentTypeString = contentTypeString.Trim();
      //set content type
      if (contentTypeString ==null || contentTypeString.Length<1) {
        ContentType = new ContentType("text/plain; charset=us-ascii");
      } else {
        ContentType = new ContentType(contentTypeString);
      }

      //set encoding (character set)
      if (ContentType.CharSet==null) {
        BodyEncoding = Encoding.ASCII;
      }else{
        try {
          BodyEncoding = Encoding.GetEncoding(ContentType.CharSet);
        } catch {
          BodyEncoding = Encoding.ASCII;
        }
      }

      //set media main and sub type
      if (ContentType.MediaType==null || ContentType.MediaType.Length<1){
        //no mediatype found
        ContentType.MediaType = "text/plain";
      }else{
        string mediaTypeString = ContentType.MediaType.Trim().ToLowerInvariant();
        int slashPosition = ContentType.MediaType.IndexOf("/");
        if (slashPosition<1){
          //only main media type found
          MediaMainType = mediaTypeString;
          System.Diagnostics.Debugger.Break(); //didn't have a sample email to test this
          if (MediaMainType=="text"){
            MediaSubType = "plain";
          }else{
            MediaSubType = "";
          }
        }else{
          //also submedia found
          MediaMainType = mediaTypeString.Substring(0, slashPosition);
          if (mediaTypeString.Length>slashPosition){
            MediaSubType = mediaTypeString.Substring(slashPosition+1);
          }else{
            if (MediaMainType=="text"){
              MediaSubType = "plain";
            }else{
              MediaSubType = "";
              System.Diagnostics.Debugger.Break(); //didn't have a sample email to test this
            }
          }
        }
      }

      IsBodyHtml = MediaSubType=="html";
    }


    /// <summary>
    /// Creates an empty child MIME entity from the parent MIME entity.
    /// 
    /// An email can consist of several MIME entities. A entity has the same structure
    /// like an email, that is header and body. The child inherits few properties 
    /// from the parent as default value.
    /// </summary>
    public RxMailMessage CreateChildEntity() {
      RxMailMessage child = new RxMailMessage();
      child.Parent = this;
      child.TopParent = this.TopParent;
      child.ContentTransferEncoding = this.ContentTransferEncoding;
      return child;
    }


    private StringBuilder mailStructure;

    private void AppendLine(string format, object arg){
      if (arg!=null) {
        string argString = arg.ToString();
        if (argString.Length>0) {
          mailStructure.AppendLine(string.Format(format, argString));
        }
      }
    }


    private void decodeEntity(RxMailMessage entity) {
      AppendLine("From  : {0}", entity.From);
      AppendLine("Sender: {0}", entity.Sender);
      AppendLine("To    : {0}", entity.To);
      AppendLine("CC    : {0}", entity.CC);
      AppendLine("ReplyT: {0}", entity.ReplyTo);
      AppendLine("Sub   : {0}", entity.Subject);
      AppendLine("S-Enco: {0}", entity.SubjectEncoding);
      if (entity.DeliveryDate>DateTime.MinValue) {
        AppendLine("Date  : {0}", entity.DeliveryDate);
      }
      if (entity.Priority!=MailPriority.Normal) {
        AppendLine("Priori: {0}", entity.Priority);
      }
      if (entity.Body.Length>0) {
        AppendLine("Body  : {0} byte(s)", entity.Body.Length);
        AppendLine("B-Enco: {0}", entity.BodyEncoding);
      } else {
        if (entity.BodyEncoding!= Encoding.ASCII) {
          AppendLine("B-Enco: {0}", entity.BodyEncoding);
        }
      }
      AppendLine("T-Type: {0}", entity.TransferType);
      AppendLine("C-Type: {0}", entity.ContentType);
      AppendLine("C-Desc: {0}", entity.ContentDescription);
      AppendLine("C-Disp: {0}", entity.ContentDisposition);
      AppendLine("C-Id  : {0}", entity.ContentId);
      AppendLine("M-ID  : {0}", entity.MessageId);
      AppendLine("Mime  : Version {0}", entity.MimeVersion);
      if (entity.ContentStream!=null) {
        AppendLine("Stream: Length {0}", entity.ContentStream.Length);
      }

      //decode all shild MIME entities
      foreach (RxMailMessage child in entity.Entities) {
        mailStructure.AppendLine("------------------------------------");
        decodeEntity(child);
      }

      if (entity.ContentType!=null && entity.ContentType.MediaType!=null && entity.ContentType.MediaType.StartsWith("multipart")) {
        AppendLine("End {0}", entity.ContentType.ToString());
      }
    }


    /// <summary>
    /// Convert structure of message into a string
    /// </summary>
    /// <returns></returns>
    public string MailStructure() {
      mailStructure = new StringBuilder(1000);
      decodeEntity(this);
      mailStructure.AppendLine("====================================");
      return mailStructure.ToString();
    }
  }

}