Invalid FIX Message Header

[lmax-exchange]

Invalid FIX Message Header

[juddgaddie]

This is expected behaviour the FixMessageBuilder doesn't enforce order of fields. Fields are written in the order that they are appended to the builder. JavaDoc and test added.

[tom-smalls]

I have to say I disagree Fix version, body length, message type, and checksum are the only fields in fix messages that have to be in a certain position. Fix version, body length, and checksum all have their positions determined internally to the FixMessageBuilder (not by when they are appended), whilst message type is not, which provides an inconsistency with the api. Fields where order matters should all be treated the same.