Kafka Headers

[iancooper]

Our implementation of a header builder for Kafka lacked tests and had bugs around GUIDs. Adding tests revealed naive thinking about translating headers to and from Kafka.

• A Kafka header a string key and a byte[] value
• If it is a Brighter header, we can convert a type to a byte[] and back.
• If it a user defined header (the bag) we can at best convert the type to a string and byte[] and then back to a string
  • We would need to know the serialized type to convert back into the same type
  • Adding type information has implications for security if implemented (see retirement of BinaryFormatter)
  • We can in this case expect the consumer to convert back from a string to a type they know

We used unix timestamps for our own Header timestamp. There is no need to do this, and it simplifies not tol