agent produces two times more data than it is set in zeroextenderlength

[AlexeyKasatkin]

zeroextenderlength argument description states that "Length of zero bytes extender array that will be added to the agent's payload in case its size is less than MTU value. Is used to reveal problems with network packets fragmentation."
It is really transmitted as a text string (serialized JSON) that looks as follows:
"[0 0 0 0 0 0 0 ...]". So that each zero byte is converted into "0" and space (x20). This results in two times more extra data added into the real packet.
So, let's change production of extra payload in order to keep its byte length close to zeroextenderlength value.