在 .NET 4.5 beta 中将 System.Net.Mail.MailMessage 作为 MemoryStream

Question

So, the below code used to work in .NET 4 to get a System.Net.Mail.MailMessage object as a MemoryStream, however with the release of .NET 4.5 beta a runtime exception occurs.

Assembly assembly = typeof(SmtpClient).Assembly;
Type mailWriterType = assembly.GetType("System.Net.Mail.MailWriter");
using (MemoryStream stream = new MemoryStream())
{
    ConstructorInfo mailWriterContructor = mailWriterType.GetConstructor(BindingFlags.Instance | BindingFlags.NonPublic, null, new[] { typeof(Stream) }, null);
    object mailWriter = mailWriterContructor.Invoke(new object[] { stream });
    MethodInfo sendMethod = typeof(MailMessage).GetMethod("Send", BindingFlags.Instance | BindingFlags.NonPublic);
    sendMethod.Invoke(message, BindingFlags.Instance | BindingFlags.NonPublic, null, new[] { mailWriter, true }, null);

    .....
}

Runtime exception occurs on sendMethod.Invoke().

Answer 1

Managed to figure out how to get this working again in .NET 4.5 beta. The private API Send() method in MailMessage has changed to: internal void Send(BaseWriter writer, bool sendEnvelope, bool allowUnicode)

Please find updated code below.

Assembly assembly = typeof(SmtpClient).Assembly;
Type mailWriterType = assembly.GetType("System.Net.Mail.MailWriter");
using (MemoryStream stream = new MemoryStream())
{
    ConstructorInfo mailWriterContructor = mailWriterType.GetConstructor(BindingFlags.Instance | BindingFlags.NonPublic, null, new[] { typeof(Stream) }, null);
    object mailWriter = mailWriterContructor.Invoke(new object[] { stream });
    MethodInfo sendMethod = typeof(MailMessage).GetMethod("Send", BindingFlags.Instance | BindingFlags.NonPublic);
    sendMethod.Invoke(message, BindingFlags.Instance | BindingFlags.NonPublic, null, new[] { mailWriter, true, true }, null);

    .....
}

Answer 2

This might be usable if you don't want to go with unsupported hacks and don't mind extra performance hit.

public static class MailMessageExtensions
    {
    public static string  RawMessage(this MailMessage m)
        {
        var smtpClient = new SmtpClient { DeliveryMethod = SmtpDeliveryMethod.SpecifiedPickupDirectory };

        using (var tempDir = new TemporaryDirectory())
            {
            smtpClient.PickupDirectoryLocation = tempDir.DirectoryPath;
            smtpClient.Send( m );
            var emlFile = Directory.GetFiles( smtpClient.PickupDirectoryLocation ).FirstOrDefault();
            if ( emlFile != null )
                {
                return File.ReadAllText( emlFile );
                }
            else
                return null;
            }
        return null;
        }

    }

class TemporaryDirectory : IDisposable
    {
    public TemporaryDirectory()
        {
        DirectoryPath = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName());
        Directory.CreateDirectory( DirectoryPath );
        }

    public string DirectoryPath { get; private set; }

    public void Dispose()
        {
        if ( Directory.Exists( DirectoryPath ) )
            Directory.Delete( DirectoryPath, true );
        }
    }

Answer 3

for checking if extra boolean i use :

 If _sendMethod.GetParameters.Length = 2 Then
    _sendMethod.Invoke(Message, BindingFlags.Instance Or BindingFlags.NonPublic, Nothing, New Object() {_mailWriter, True}, Nothing)
 Else
    _sendMethod.Invoke(Message, BindingFlags.Instance Or BindingFlags.NonPublic, Nothing, New Object() {_mailWriter, True, True}, Nothing)
 End If

Answer 4

The proposed solution with the extra TRUE works beautifully.

I started to getting the error while running my project in VS2012 even though I am not using .net 4.5 but 4.0 in all my libraries.

The error only happens on the machine where you have installed VS2012, looks like VS2012 makes reference to .net 4.5 while you are debugging. When you deploy and run the application in clients running .net 4.0 everything works fine.

Thus : If you run 4.0 - do not add the extra TRUE, if you run 4.5 add it.

Answer 5

We fought with the mail message conversion for a long time. Ultimately the solution was to use MimeKit .

var memoryStream = new MemoryStream();
var mimeMessage = MimeMessage.CreateFromMailMessage(message);
mimeMessage.WriteTo(memoryStream);

If you use the methods above you will get really close and it will work in most cultures but eventually the subject encoding will defeat you.

Answer 6

For those, who are struggling with mailWriterContructor being null in .NET 5 or facing Parameter count mismatch exception, take a closer look on my solution usable for any stream. Link here