MimeMessage.WriteTo is not thread-safe even in different instances of MimeMessage

[ymassad]

If we have multiple MimeMessage instances, say 1000 instance. And I try to call WriteTo in parallel for these messages I will get some corrupted messages.

Here is a sample code:

        string filename = @"C:\simple.eml";

        byte[] data = File.ReadAllBytes(filename);

        ConcurrentBag<MimeMessage> messages = new ConcurrentBag<MimeMessage>();

        for(int i = 0 ; i < 1000 ; i++)
        {
            messages.Add(MimeMessage.Load(new MemoryStream(data)));
        }

        int length = data.Length;

        Parallel.For(0, 1000, (int i) =>
        {
            //lock(data)
            { 
                MemoryStream ms = new MemoryStream();

                var msg = messages.Take(1).First();

                msg.WriteTo(ms);

                var message_data = ms.ToArray();

                if (message_data.Length != length)
                {
                    //There is an error
                    int ggg = 0;
                }
            }
        });

The corrupted messages have either missing or extra mime headers.

If I uncomment the lock statement, everything works fine.

Please note that in the example, each thread/task is working with a different instance of MimeMessage

The simple.eml file is a very simple email file with no attachments. I have tried different files, and the problem happened for all of them.

It seems to me that there might be some shared state for different instances of MimeMessage

[ymassad]

Instead of

                var msg = messages.Take(1).First();

It makes more sense to use

                MimeMessage msg;

                messages.TryTake(out msg);

This, however, does not fix the problem.

[jstedfast]

This will fix it:

var options = FormatOptions.Default.Clone ();
var msg = messages.Take(1).First();

msg.WriteTo(options, ms);

[ymassad]

Thanks.

I tried passing FormatOptions.Default.Clone() to the WriteTo method and the problem is solved.

I see that you have made some changes to the code base. I did not get this new code, but the issue is solved. Do you think there is a chance I will have any problems using the code base I currently have and just passing FormatOptions.Default.Clone() to the WriteTo method?

[jstedfast]

Yes, you should be fine.

[ymassad]

Thanks