Protocol
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.
header
| code | oc | tkl |
|---|---|---|
| 8 | 8 | 16 (network order) |
- tkl = token length in bytes
- oc = number of options present
- code = CoAP specified
token (optional)
| token |
|---|
| bytes |
options (repeating)
| number | length | value | … |
|---|---|---|---|
| 16 (network order) | 16 (network order) | bytes | … |
- number = CoAP specified
- value = CoAP specified
Some options must be present depending on the type of message.
GET request
- uri_path
- uri_host
- content_format
GET request (observe)
- uri_path
- uri_host
- content_format
- observe (contains string ‘data’ or ‘’ or ‘audit’)
- max_age
GET response
- content_format
GET response (observe)
- content_format
- public_key (number 2048, contains key)
POST request
- uri_path
- uri_host
- content_format
POST response
DELETE request
- uri_path
- uri_host
- content_format
DELETE response
message payload (optional)
| payload |
|---|
| bytes |