Payload:
32bit unsigned sequence number
32bit 'pair' count (how many key/value sequences follow)
32bit unsigned key length followed by that many bytes for the key
32bit unsigned value length followed by that many bytes for the value
repeat key/value 'count' times.
https://github.com/elastic/logstash-forwarder/blob/master/PROTOCOL.md
Is the 'pair' count signed or unsigned?