26 Nov 2015

768 is the Magic Number

When reconstrucing a binary MSMQ message from a backup I was first tempted to just set the Body property on the message directly. This doesn’t quite work however as the Body property is serialised with whatever formatter you’re using when the message is sent.

var mq = new MessageQueue(@".\Private%\test");
var messageBody = File.ReadAllBytes("...");

var message = new Message();
message.Body = messageBody;

mq.Send(message); // double-encodes the body :-(

There is a way around this serialisation though. MSDN has this to say:

The contents of the Body property are serialized when the message is sent, using the Formatter property you specify. The serialized contents are found in the BodyStream property. You can also set the BodyStream property directly, for example, to send a file as the data content of a message.

Sounds just like what we want! Just setting the BodyStream property to a MemoryStream with our bytes in gets us started. The only problem is that tools peeking at the message don’t know what format it is in. This is where the magic number 768 makes it’s show. By setting the BodyType to this magic number tools will know the body is serlialised with a BinaryMessageFormatter:

var message = new Message();
message.BodyStream = new MemoryStream(messageBody);
message.BodyType = 768; // Binary formatted .NET object

Now you can send the message and recipients won’t know the differnece from the origional backup.