Skip to content
Permalink
Branch: master
Find file Copy path
Find file Copy path
Fetching contributors…
Cannot retrieve contributors at this time
251 lines (220 sloc) 8.37 KB
name shortname status editor contributors
Extension Service Protocol
4/ESP
draft
Dmitry Sergeev <dsergeev@kaaiot.io>
Andrew Kokhanovskyi <akokhanovskyi@kaaiot.io>, Alexey Shmalko <ashmalko@kaaiot.io>

Introduction

Extension Service Protocol (ESP) is a simple, generic inter-service protocol for Kaa extension services to receive application layer data from and send to clients through the communication services. ESP helps abstracting out extension services from transport protocol stacks implemented in the communication services. On the other hand, since Kaa extension services may significantly differ in their messaging patterns or the payload structure, ESP is designed to be unaware of these specifics.

ESP is based on the targeted messaging IPC design.

Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

The following terms and definitions are used in this RFC.

  • Communication service: service that implements the transport protocol stack to communicate with Kaa clients.

  • Extension service: service that implements the application layer to exchange data with Kaa clients.

Design

Client data transfer to extension services

ClientData messages are used by communication services to transfer client-originated data to extension services. Non-affinity session messages MUST be published to a service instance-wide subject:

kaa.v1.service.<service-instance-name>.esp.ClientData

where <service-instance-name> is the instance name of the target extension service.

In case of affinity sessions, ClientData message MUST be published to the service replica-specific subject defined by the replyTo subject in the previously received message that set up the session affinity.

Implementations of communication services SHOULD set replyTo subject when sending ClientData messages according to the session affinity rules.

The NATS message payload is an Avro object with the following schema (0004-client-data.avsc):

{
    "namespace":"org.kaaproject.ipc.esp.gen.v1",
    "name":"ClientData",
    "type":"record",
    "doc":"Client-originated message from communication to extension services",
    "fields":[
        {
            "name":"correlationId",
            "type":"string",
            "doc":"Message ID primarily used to track message processing across services"
        },
        {
            "name":"timestamp",
            "type":"long",
            "doc":"Message creation UNIX timestamp in milliseconds"
        },
        {
            "name":"timeout",
            "type":"long",
            "default":0,
            "doc":"Amount of milliseconds since the timestamp until the message expires. Value of 0 is reserved to indicate no expiration."
        },
        {
            "name":"appVersionName",
            "type":"string",
            "doc":"Application version name the data is sent for"
        },
        {
            "name":"endpointId",
            "type":[
                "string",
                "null"
            ],
            "doc":"Identifier of the endpoint, on behalf of which client sent data. Null for endpoint-unaware extensions."
        },
        {
            "name":"resourcePath",
            "type":"string",
            "doc":"Resource path used for determining the message handling function and the payload format"
        },
        {
            "name":"requestId",
            "type":[
                "int",
                "null"
            ],
            "doc":"Request ID used by endpoint to match messages. Optional."
        },
        {
            "name":"payload",
            "type":"bytes",
            "doc":"Serialized message content"
        }
    ]
}

Example:

{
    "correlationId":"07d78e95-2c4d-4899-957c-b9e5a3701fbb",
    "timestamp":1490262793349,
    "timeout":3600000,
    "appVersionName":"humidity-sensor-v3",
    "endpointId":{
        "string":"7ad263ec-3347-4c7d-af89-50c67061367a"
    },
    "resourcePath":"/json",
    "requestId":{
        "int":42
    },
    "payload":"Ww0KICB7ICJodW1pZGl0eSI6IDg4IH0NCl0="
}

Extension data transfer to clients

ExtensionData messages are used by extension services to send data to clients through communication services. Non-affinity session messages MUST be published to a service instance-wide subject:

kaa.v1.service.<service-instance-name>.esp.ExtensionData

where service-instance-name is the instance name of the target communication service.

In case of affinity sessions, ExtensionData message MUST be published to the service replica-specific subject defined by the replyTo subject in the previously received message that set up the session affinity.

Extensions MAY also set replyTo subject when sending ExtensionData messages according to the session affinity rules.

The NATS message payload is an Avro object with the following schema (0004-extension-data.avsc):

{
    "namespace":"org.kaaproject.ipc.esp.gen.v1",
    "name":"ExtensionData",
    "type":"record",
    "doc":"Extension-originated messages intended for clients of ECS",
    "fields":[
        {
            "name":"correlationId",
            "type":"string",
            "doc":"Message ID primarily used to track message processing across services"
        },
        {
            "name":"timestamp",
            "type":"long",
            "doc":"Message creation UNIX timestamp in milliseconds"
        },
        {
            "name":"timeout",
            "type":"long",
            "default":0,
            "doc":"Amount of milliseconds since the timestamp until the message expires. Value of 0 is reserved to indicate no expiration."
        },
        {
            "name":"appVersionName",
            "type":[
                "string",
                "null"
            ],
            "doc":"Application version name the data is sent for. Null in case the extension does not know application version the endpoint belongs to. MUST NOT be null for endpoint-unaware extensions."
        },
        {
            "name":"extensionInstanceName",
            "type":[
                "string",
                "null"
            ],
            "doc":"Name of the extension instance that originated the message"
        },
        {
            "name":"endpointId",
            "type":[
                "string",
                "null"
            ],
            "doc":"Identifier of the endpoint, to which the data is sent. Null for endpoint-unaware extensions."
        },
        {
            "name":"resourcePath",
            "type":"string",
            "doc":"Resource path used for determining the message handling function and the payload format"
        },
        {
            "name":"requestId",
            "type":[
                "int",
                "null"
            ],
            "doc":"Request ID used by endpoint to match messages. Optional."
        },
        {
            "name":"payload",
            "type":[
                "bytes",
                "null"
            ],
            "doc":"Serialized message content"
        },
        {
            "name":"statusCode",
            "type":"int",
            "doc":"HTTP status code of the request processing"
        },
        {
            "name":"reasonPhrase",
            "type":[
                "null",
                "string"
            ],
            "default":null,
            "doc":"Human-readable status reason phrase"
        }
    ]
}

Example:

{
    "correlationId":"07d78e95-2c4d-4899-957c-b9e5a3701fbb",
    "timestamp":1490262793349,
    "timeout":3600000,
    "extensionInstanceName":"humidity-sensor-cmx-1",
    "appVersionName":"humidity-sensor-v3",
    "endpointId":{
        "string":"7ad263ec-3347-4c7d-af89-50c67061367a"
    },
    "resourcePath":"/config/json",
    "requestId":{
        "int":42
    },
    "payload":{
        "bytes":"ewogICJzYW1wbGluZyIgOiAyMDAKfQ=="
    },
    "statusCode":200,
    "reasonPhrase":"OK"
}
You can’t perform that action at this time.