MIME Component Recursive Decoding for Nested Messages

MIME messages may contain nested structures where a part includes another encoded MIME entity, requiring traversal of all parts to decode embedded content.

Recursive MIME Decoding Example

A recursive function can be used to decode each entity and process its parts, including sub-MIME messages, text content, and attachments.

//C#
private void MimeDecode(string EntityHeaders, string Entity)
{
  Mime mime1 = new Mime();
  mime1.MessageHeadersString = EntityHeaders;
  mime1.Message = Entity;
  mime1.DecodeFromString();
  for (int i = 0; i <= mime1.Parts.Count - 1; i++)
  {
    // If the Content-Type is "Multipart/????", then that part is an encoded entity
    if (mime1.Parts[i].ContentType.ToLower().StartsWith("multipart"))
    {
      MimeDecode(mime1.Parts[i].Headers, mime1.Parts[i].DecodedString);
    }
    // If the part is plain text
    if (mime1.Parts[i].Filename == "" && 
        mime1.Parts[i].ContentType.ToString() == "text/plain")
    {
      // At this point we could check the ContentTypeAttr field for the charset
      // and use the charset (if set) when displaying the text.
      // For simplicity we will skip checking the charset in this example.
      Console.WriteLine("Plain text: " + mime1.Parts[i].DecodedString);
    }
    // If the part has an associated Filename, it is an attachment
    if (!mime1.Parts[i].Filename.Equals(""))
    {
      Console.WriteLine("Attachment: " + mime1.Parts[i].Filename);
    }
  }
}

//VB6
Private Function MimeDecode(EntityHeaders As String, Entity As String)
Dim mime1 As New MIME
Dim i As Integer
mime1.MessageHeadersString = EntityHeaders
mime1.Message = Entity
mime1.DecodeFromString
For i = 0 To mime1.PartCount - 1
    If (InStr(LCase(mime1.PartContentType(i)), "multipart") > 0) Then
        MimeDecode mime1.PartHeaders(i), mime1.PartDecodedString(i)
    ElseIf (mime1.PartFilename(i) = "" And mime1.PartContentType(i) = "text/plain") Then
        Debug.Print "Plain text: " & mime1.PartDecodedString(i)
    ElseIf (mime1.PartFilename(i) <> "") Then
        Debug.Print "Attachment: " & mime1.PartFilename(i)
    End If
Next i
End Function

This approach can be extended to handle additional content types and conditions, enabling flexible processing of complex MIME structures.

Note: These examples use the IPWorks Version 8 API and may require minor adjustments for earlier versions.