Not Omitting the XML Declaration

Why doesn't a message start with an XML declaration?

The XML declaration is a processing instruction at the beginning of an XML document that gives information about the format and logical structure of the document. You've probably seen the most commonly used XML declaration on many documents.

 <?xml version="1.0" encoding="UTF-8" ?>

Both the version and the encoding in this example declaration are the default values. XML documents aren't required to start with a declaration because default values are assumed. Processors that are sensitive to the size of the produced document omit the declaration to avoid transmitting redundant information. The text encoder is an example of an XML processor that can recognize when the default values are being used and omit the declaration to save space.

In some cases you want the XML declaration even when it's unnecessary because the receiver is expecting the document to start with a particular sequence of characters. Since the optimization in the text encoder isn't the result of a configuration setting, some amount of manual work is required to produce messages that contain unnecessary processing instructions. You can recreate this effect using a custom message encoder that is even simpler than the sample custom text encoder. You don't need to support a custom content type or to do any special processing when reading a message. You do need the shell for a message encoder and message encoder factory plus the logic in WriteMessage to insert the processing instruction. The sample writes the processing instruction using XmlWriterSettings although you can choose any method you wish.

Next time: Flowing Additional Identity Information

Comments

• Anonymous
  January 15, 2008
  Service operations have a declarative attribute for automatically placing the operation within a transaction.