WCF messageheader vs messagebodymember?

Question

I do not understand when I should put the [MessageHeader] instead of the [MessageBodyMember]?

I have read that it's used to conform some protocol like Soap, but still, what does it change at the end?

Answer 1

SOAP is a protocol in which each message (request or response) is made up of two parts: the Header and the Body, inside an Envelope:

<s:Envelope xmlns:s='the namespace for the soap version'>
  <s:Header>
    <!-- SOAP headers will come here -->
  </s:Header>
  <s:Body>
    <!-- SOAP body members will come here -->
  </s:Body>
</s:Envelope>

You normally wouldn't use [MessageContract] (and MessageHeader or MessageBodyMember) in WCF services, only if you really need to interop with some 3rd party which expects the data in a certain format.

Answer 2

I think when I want to put something independent of message content, I will put it in the message header. And if you want another party to read something from your message, it should be put in the header, because sometimes you may allow someone to read the message header not message body as it contains confidential contents.