在.NET中序列化MailMessage对象的优雅方法

Question

I'm currently looking at serializing a MailMessage object in C# and although there are a couple of variations of an example on the net, they serialize to binary which kind of misses the point IMO.

My approach is that I'd like to serialize a MailMessage to an RFC2822 eml string and the code below is what I've come up with.

    public string SerializeEmail(MailMessageArgs e)
    {
        string rfc822eml = "";
        Guid g = Guid.NewGuid();
        lock (g.ToString())
        {
            System.IO.DirectoryInfo di = new System.IO.DirectoryInfo(@"C:\tmpspool");
            di.CreateSubdirectory(g.ToString());
            string spoolDir = @"C:\tmpspool\" + g.ToString();
            SmtpClient Client = new SmtpClient("localhost");
            Client.DeliveryMethod = SmtpDeliveryMethod.SpecifiedPickupDirectory;
            Client.PickupDirectoryLocation = spoolDir;
            Client.Send(e.mailObj);
            var files = from file in Directory.EnumerateFiles(spoolDir)
                       select file;
            string serializedEml = files.First();
            rfc822eml = File.ReadAllText(serializedEml);
            File.Delete(serializedEml);
            Directory.Delete(spoolDir);
        }

        return rfc822eml;
    }

It's pretty nasty but it does work. Ideally though, I'd create a new SMTPClient and add in a Serialize function which would return the rfc822 string automatically without it ever hitting the file system.

As I don't seem to be able to trace into the SMTPClient.Send function with Visual Studio, this "ideal" way of doing things is a tad tricky.

I've already sorted out the deserialization of the RFC message by adding in some small changes to Peter Huber's POP3MimeClient and POP3MailClient classes so I can deserialize a file on the HDD or a string back into a MailMessage.

The thing that's nagging at me is that I really should be able to serialize the MailMessaage using a stream and writing the stream to a string -or- file of my choice instead of going around the houses to create GUID based folders as the code above does and reading the content of the file back into a string...

Any pointers as to how I could make this more elegant will be much appreciated.

Thanks.

Answer 1

This will be a hack. Don't forget, MS can change it in the next versions of .Net.

(With the help of ILSpy) you can write an extension method like below

public static class MailExtensions
{
    public static string ToEml(this MailMessage mail)
    {
        var stream = new MemoryStream();
        var mailWriterType = mail.GetType().Assembly.GetType("System.Net.Mail.MailWriter");
        var mailWriter = Activator.CreateInstance(
                            type: mailWriterType,
                            bindingAttr: BindingFlags.Instance | BindingFlags.NonPublic,
                            binder: null,
                            args: new object[] { stream },
                            culture: null,
                            activationAttributes: null);

        mail.GetType().InvokeMember(
                            name: "Send",
                            invokeAttr: BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.InvokeMethod,
                            binder: null,
                            target: mail,
                            args: new object[] { mailWriter, true, true });


        return Encoding.UTF8.GetString(stream.ToArray());
    }
}

and use as

string eml = mailMessage.ToEml();

Answer 2

I finally managed to deserialize the MailMessage after a lot of work:

To get it right, I created a dll which will be used in both the client application and the webservice. This needs to be the same for the deserialization to work :)

I picked the dll serialization classes here: https://bitbucket.org/burningice/compositec1contrib.email/src/0bba07df532c8134717cfb40757f4cb22f002b1d/Email/Serialization/?at=default

Many thanks for sharing!

Once compiled and added my new dll to the projects, the send and receive worked.

So I convert the MailMessage this way : string serializedMessage = SerializeAsBase64(mail); and in the Webservice, I reconstruct it this way : MailMessage Mm = DeserializeFromBase64(serializedMessage);

I hope this helps...