packet

Packet encoding/decoding without writing specialized code, uses struct field tag to help with processing:

• length for length of the field, expecting a number with following specifiers
  • b for bits
  • B for bytes
• lengthfor indicate the length for the attribute can be return from the object, which needs to provide the LengthFor interface
• lengthtotal indicate the attribute value is for the whole message stucture

When an interface{} field is encounted, Unmarshal will check to see if the struct satisfies the InstanceFor interface, and call the InstanceFor(fieldname string) function to get a instance object for the field.

see fixture, and unittest for example.