OCPP-J Codec

Wire Format

The OCPP-J protocol (JSON over WebSocket) uses JSON arrays with a message type ID as the first element:

Type	ID	Format	Purpose
`Call`	2	`[2, unique_id, action, payload]`	Request from client or server
`CallResult`	3	`[3, unique_id, payload]`	Successful response
`CallError`	4	`[4, unique_id, error_code, description, details]`	Error response

The unique_id correlates a CallResult or CallError back to its originating Call.

using OCPPData

The three concrete subtypes of OCPPMessage:

using InteractiveUtils: subtypes
subtypes(OCPPMessage)

3-element Vector{Any}:
 Call
 CallError
 CallResult

Convenience constructors auto-fill message_type_id:

call = Call("id-1", "Heartbeat", Dict{String,Any}())

Call(2, "id-1", "Heartbeat", Dict{String, Any}())

result = CallResult("id-1", Dict{String,Any}("status" => "Accepted"))

CallResult(3, "id-1", Dict{String, Any}("status" => "Accepted"))

error = CallError("id-1", "NotImplemented", "Not supported", Dict{String,Any}())

CallError(4, "id-1", "NotImplemented", "Not supported", Dict{String, Any}())

encode converts an OCPPMessage to a JSON string ready for WebSocket transmission:

encode(call)

"[2,\"id-1\",\"Heartbeat\",{}]"

encode(result)

"[3,\"id-1\",{\"status\":\"Accepted\"}]"

encode(error)

"[4,\"id-1\",\"NotImplemented\",\"Not supported\",{}]"

decode parses a raw JSON string back into the appropriate OCPPMessage subtype:

decoded = decode("[2,\"id-1\",\"Heartbeat\",{}]")

Call(2, "id-1", "Heartbeat", Dict{String, Any}())

decoded isa Call

true

decoded.action

"Heartbeat"

decoded.payload

Dict{String, Any}()

Decoding a CallResult:

decode("[3,\"id-1\",{\"status\":\"Accepted\"}]")

CallResult(3, "id-1", Dict{String, Any}("status" => "Accepted"))

Decoding a CallError:

decode("[4,\"id-1\",\"NotImplemented\",\"Not supported\",{}]")

CallError(4, "id-1", "NotImplemented", "Not supported", Dict{String, Any}())

msg = Call("abc-123", "BootNotification", Dict{String,Any}(
    "chargePointVendor" => "V",
    "chargePointModel" => "M",
))
wire = encode(msg)

"[2,\"abc-123\",\"BootNotification\",{\"chargePointVendor\":\"V\",\"chargePointModel\":\"M\"}]"

decoded = decode(wire)
decoded.action, decoded.payload

("BootNotification", Dict{String, Any}("chargePointVendor" => "V", "chargePointModel" => "M"))

id = generate_unique_id()
println(id)  # UUID v4 string
length(id)   # 36 characters (8-4-4-4-12 format)