View on GitHub




Both POST and GET messages are exchanged over a ZeroMQ Request-Reply socket using a CoAP-like message format. A message contains a header followed by an optional token, any message options then an optional payload. For example, a POST message must contain a header, options and a payload, whereas a GET message will not contain a payload. An acknowledgement may consist only of a header but can also consist of a header, options, and payload.

An OBSERVE message is slightly more complex and involves an initial Request-Reply exchange to setup communication over a Router-Dealer socket. This allows multiple clients to connect to the server and receive updates posted to an observed path. An OBSERVE message is implemented as a special type of GET message with an observe option set. The server replies to the GET with a UUID in the payload which is used to identify the client over the Router-Dealer communication.

message structure

All values are in bits unless specified and all values are unsigned.

code oc tkl
8 8 16 (network order)

token (optional)


options (repeating)

number length value
16 (network order) 16 (network order) bytes

Some options must be present depending on the type of message.

GET request

GET request (observe)

GET response

GET response (observe)

POST request

POST response

DELETE request

DELETE response

message payload (optional)