edc-ws

Event Driven Communications (EDC) w/ WebSockets

EDC-WS Server/Clients

Is a server-clinet pakage that uses websockets to enable EDC.

Examples:

• Guessing Game Example
• Chat Room Example

What is The Event Driven Communications (EDC) Protocol?

Is a JSON based communications protocol that allows for the communication of events while enabling the sharing of common data between a chain of events.

The concept that one event is the cause of a new event is a first class citizen in the EDC protocol. This allows for the logical grouping of events based on the cause-effect chain by tie together UUIDs. In additions, a chain of events logically share data that is common to each event in the chain. This allows the detail of the events to live seperate from the shared chain data.

• See Event Driven Communications

Note: Acknowledge has a few nuances and controls if the sendEvent() resolves instantly or waits for a reply. If "acknowledge": true then the promise will reslove after a valid reply, or reject after a timeout | Error Event See this for more on Acknowledge

              Event Chain
|-----------------------------------------|
|             shared data                 |
|    |event-1|-->|event-2|-->|event-3|    |
|        |                                |
|        |-->|event-N|                    |
|-----------------------------------------|

Examples

Server initialization

import Edc, { Event } from 'edc-ws'
 
const server = new Edc.Server(port)
 
server.onEvent('event-type', async (cause, ws, reply, send, that) => {
    const event = new Event('other-event').inherit(cause)
 
    reply(event)
})
 
server.onAck = async (cause, ws, reply, send, that) => {
    // Handle events.type = "acknowledgement"
}
server.onError = async (cause, ws, reply, send, that) => {
    // Handle events.type = "error"
}

Send an Event (Server)

const cause = new Event('event-type', {
    acknowledge: true, // Note** that this is 'true'
    details: {
        test: 'prop',
        count: 23
    },
    shared: {
        id: 'shared id',
        step: 3
    }
})
 
try {
    const event = await server.sendEvent(connection, cause)
} catch (e) {
    console.log(err.message)
    if (e instanceof AckedErrorEvent) {
       console.log(`Failed Event Id:  ${e.trigger}`)
    } else if (e instanceof TimeoutError) {
        console.log(`Event timedout after  ${e.timeout}ms`)
    } else {
        // Handler other
    }
}

Note: if the cause Event was set to "acknowledge": false then no AckedErrorEvent or TimeoutError could be thrown.

Client initilization

import Edc, { Event } from 'edc-ws'
 
const client = new Edc.Client('ws://websocket.server.com')
 
client.onEvent('event-type', sync (cause, reply) => {
    const event = new Event('event-type').inherit(cause)
 
    reply(event)
})
 
client.onAck = async (cause, reply) => {
    // Handle events.type = "acknowledgement"
}
client.onError = async (cause, reply) => {
    // Handle events.type = "error"
}

Send an Event (Client)

const cause = new Event('event-type', {
    acknowledge: true, // Note** that this is 'true'
    details: {
        test: 'prop',
        count: 23
    },
    shared: {
        id: 'shared id',
        step: 3
    }
})
 
try {
    const event = await client.sendEvent(cause)
} catch (e) {
    console.log(err.message)
    if (e instanceof AckedErrorEvent) {
       console.log(`Failed Event Id:  ${e.trigger}`)
    } else if (e instanceof TimeoutError) {
        console.log(`Event timedout after  ${e.timeout}ms`)
    } else {
        // Handler other
    }
}

Note: if the cause Event was set to "acknowledge": false then no AckedErrorEvent or TimeoutError could be thrown.

Create a new Event() from a cause: Event

const cause = new Event('event-type', {
    acknowledge: true,
    details: {
        test: 'prop',
        count: 23
    },
    shared: {
        id: 'shared id',
        step: 3
    }
})
 
const event = new Event('event-type-2').inherit(cause)
 
// event.trigger === cause.id
// event.shared === cause.shared 
 

To match any event use '*' as the event type in the onEvent() function

// This will match any event. But the server|client will first try to match the event to a named one.
server.onEvent('*', async (cause, ws, reply, send, that) => {
    const event = new Event('other-event').inherit(cause)
 
    reply(event)
})

Table of Contents

• Event Driven Communications (EDC) w/ WebSockets
  • EDC-WS Server/Clients
  • What is The Event Driven Communications (EDC) Protocol?
  • Examples
  • Table of Contents
  • Event Driven Communications (EDC) Components
    • Event
    • Acknowledgement Event
    • Error Event
      • Error Event Details
    • Fields
      • edc
      • type
      • id
      • trigger
      • acknowledge
        • Request
        • Responses
      • details
      • shared
      • failed
  • Acknowledge and Flow
    • TimeoutError
    • AckedErrorEvent
    • Multiple Synchronous Events
  • Generic Events
    • Event<T, K>
    • ErrorEvent
  • Registering Routes
    • Further Organize

Event Driven Communications (EDC) Components

Event

An Event is a JSON object defined as

Note: "type": "error" and "acknowledgement" are reserved for Error Event and Acknowledgement Event respectivley

{
    "edc" : string                 // Version
    "type": string,                // Event type 
    "id": string,                  // UUID for the event,
    "trigger":? string,            // UUID of the event triggering this event
    "acknowledge":? boolean,       // A reply is expected (syncronous) if true
    "details":? {},                // Details of this event
    "shared":? {}                  // Shared information from the chain of events, (modifiable),
}

Acknowledgement Event

{
    "edc": "1.0",
    "type": "acknowledgement",
    "id": "71e92430-77b6-48ad-899c-7a5fc769f328",
    "trigger": "af0f0d3e-5c48-4265-9f3e-e37a21ff84c1"
}

Error Event

{
    "edc": "1.0",
    "type": "error",
    "id": "71e92430-77b6-48ad-899c-7a5fc769f328",
    "trigger": "af0f0d3e-5c48-4265-9f3e-e37a21ff84c1",
    "details": { 
        "code": 4083, 
        "cn": "common-error",
        "message": "Simple message about error",
        "failed": "<JSON string of failing payload>"
        "data": {}
    },
    "shared": { shared data from erroring event },
    
}

Error Event Details

The "details" of the error event MUST include

• "cn" the common name of the error

• "code" the number for the error

• "message" the message to help understand the error

• "failed" the string form of the failed event

• "data" this field is allowed for any additional information about the error.

details: { 
    code: number; 
    cn: string; 
    message: string;
    failed: string;
    data: {} | null 
}

Fields

edc

The version of the EDC protocoll

    "edc": "1.0"

type

The type field represent the event type. It can be any string except "error" and "acknowldegement" which are reserved.

Examples:

    "type": "mouse-moved"

    "type": "transcripted"

    "type": "request-action"

    "type": "initiate-action"

id

The id field is a UUID and MUST be unique for all events

trigger

The trigger is set to the event that triggered the new event. new event.trigger = cause.id

The concept is meant to build a chain of events with events becoming the cuase of new events. An event is not limited to causing only a linear chain. It is possible for one cause to trigger multiple events. cause --> event1 & event2

acknowledge

If an event is sent with the "acknowledge": true flag then the recieving system MUST reply with an event, error, or acknowledgement with the trigger field set to the id of the sent event. Multiple replies of different events is allowed.

Example:

Request

A --> B
{
    "edc": "1.0",
    "type": "initiate",
    "id": "0a385c23-4b65-4d9f-8c78-6b7bf5ad0530",
    "acknowledge": true,
}

Responses

B --> A
 
Ack Event
{
    "edc": "1.0",
    "type": "acknowledgement",
    "id": "71e92430-77b6-48ad-899c-7a5fc769f328",
    "trigger": "0a385c23-4b65-4d9f-8c78-6b7bf5ad0530"
}

-- Or --

Error Event 
{
    "edc": "1.0",
    "type": "error",
    "id": "93de2206-9669-4e07-948d-329f4b722ee2",
    "trigger": "0a385c23-4b65-4d9f-8c78-6b7bf5ad0530",
    "details": {
        "cn": "common-error",
        "code": 10983,
        "message": "Common error caused my silly mistake",
        "failed": "{\"type\":\"initiate\",\"id\":\"0a385c23-4b65-4d9f-8c78-6b7bf5ad0530\",\"acknowledge\":\"true\"}",
        "data": {}
    }
}

-- Or --

Responding Event
{
    "edc": "1.0",
    "type": "next-event",
    "id": "a201b948-4282-49e8-ae92-1c146ddd538b",
    "trigger":  "0a385c23-4b65-4d9f-8c78-6b7bf5ad0530"
}

details

The details is any JSON object and would hold the details for the OCCURING event. It is not inteded to be used for shared properties that relate to the chain of events.

shared

The shared property is any JSON object. It is inteded to be used as a property that a chain of events share in common.

When an event is triggered by a cause then it SHOULD set the trigger to the cause.id and copy the cause.shared data to the new event.shared. The shared data is not immutable and can evolve.

Examples would include a connection-Id that events share incommon, a call-Id for a phone call, a survey-Id, or a start time for a chain of events.

A --> B
{
    "edc": "1.0",
    "type": "survey-question",
    "id": "e680a8a0-ad3e-4f9e-991b-fa0fe752b8d1",
    "details": {
        "question": "what is your favorite programming language?"
    },
    "shared": {
        "survey": "programming-favorites",
        "step": 0
    }
}

B --> A
// Note the shared data is copied
{
    "edc": "1.0",
    "type": "survey-answer",
    "id": "09d0bc49-29be-4e2e-a347-aee23f9a815b",
    "trigger": "e680a8a0-ad3e-4f9e-991b-fa0fe752b8d1",
    "details": {
        "answer": "I love them all!"
    },
    "shared": {
        "survey": "programming-favorites",
        "step": 0
    }
}

A --> B
// Note that the shared.step was increased
{
    "edc": "1.0",
    "type": "survey-question",
    "id": "9d37afee-9b68-4d8f-ae63-2bc8f9b2d7a7",
    "trigger": "09d0bc49-29be-4e2e-a347-aee23f9a815b",
    "details": {
        "question": "Who is your favorite computer scientist?"
    },
    "shared": {
        "survey": "programming-favorites",
        "step": 1
    }
}

failed

Is only used with the "type": "error" event. It MUST be a string copy of the event that triggered the error

{
    "edc": "1.0",
    "type": "error",
    "id": "93de2206-9669-4e07-948d-329f4b722ee2",
    "trigger": "0a385c23-4b65-4d9f-8c78-6b7bf5ad0530",
    "details": {
        "cn": "common-error",
        "code": 10983,
        "message": "Common error caused my silly mistake",
        "failed": "{\"type\":\"initiate\",\"id\":\"0a385c23-4b65-4d9f-8c78-6b7bf5ad0530\",\"acknowledge\":\"true\"}",
        "data": {}
     }
}

Acknowledge and Flow

The requirement that "acknowledge": true event MUST have a reply leads to two thrown errors AckedErrorEvent and TimeoutError. In addition, "acknowledge": false events are asynchronous even if await is used. This is because the promise will resolve instantly on the sendEvent() as Promise<undefined>.

TimeoutError

The TimeoutError is thrown on "acknowledge": true if no non-error reply is recived before the after client/server timeout is reached. Since the "acknowledge": true events expects a reply and it is not possible to wait forever it is logical that there must be a timeout and that it would be a error by the system.

AckedErrorEvent

The AckedErrorEvent is throw on "acknowledge": true event if an event of type "error" is recieved in response to the sent event. The motivation for this is to allow the handling of events that were expected or NEEDED to be successful in order to continue.

Multiple Synchronous Events

Acknowledge is key in sending multiple synchronous events in which the order of recieval matters. If event A must be before event B, then event A should be sent with "acknowledge": true this would gurantee an acknowledging reply that A was recieved and that B could now be sent. This would be true for any length of synchronous dependant events. A before B, B before C, C before D, etc.... [A, B, C, D, ...]

Generic Events

Event<T, K>

The type T represents the type that details is. While the type K represents the type that the shared property is.

type T = { foo: string }
type K = { baz: string }
 
const event = new Event<T, K>('event-type', {
    details: {
        // type T
        foo: 'bar'
    },
    shared: {
        // type K
        baz: 'taz'
    }
})

ErrorEvent

The type T for the ErrorEvent represents the type of error.details.data

type T = { foo: string }
 
const error = new ErrorEvent<T>({
    cn: 'cn',
    code: 9999,
    message: 'simple message',
    failed: failedEventStr,
    data: {
        // type T
        foo: 'bar'
    }
})

Registering Routes

In the hopes of staying organized it is possible to register event-routes in seperate files. Each route file would have to export an eventType string and a handler function

The file sturcture would look something like bellow:

src/
|-- main.ts   
|----routes/   
     |-- index.ts
     |-- route-1.ts
     |-- route-2.ts
     |-- route-3.ts

index.ts

import * as route1 from './route-1'
import * as route2 from './route-2'
import * as route3 from './route-3'
 
export default [route1, route2, route3]

route-1.ts

import { ServerOnEventHandler, Event } from 'edc-ws'
 
export const eventType = 'route-1'
 
export const handler: ServerOnEventHandler = async (cause, conn, reply) => {
    const event = new Event('answer-route-1').inherit(cause)
    reply(event)
}

main.ts

import routes from './routes'
 
const server = new Edc.Server(port)
server.register(routes)

Note: register() will add all event routes that are exported in the array that is in the src/routes/index.ts

Further Organize

src/
|-- main.ts   
|-----routes/   
      |-- index.ts
      |-- route-1.ts
      |-- route-2.ts
      |-- route-3.ts
      |-----sub/
              |-- index.ts
              |-- sub-route-1.ts
              |-- sub-route-2.ts

src/routes/sub/index.ts

import * as sub1 from './route-sub-1'
import * as sub2 from './route-sub-2'
 
export default [sub1, sub2]

src/routes/index.ts

import * as route1 from './route-1'
import * as route2 from './route-2'
import sub from './sub'
 
export default [route1, route2, ...sub] // Spread Operator makes this one long array.

It is possible to go to extreme depths using this, grouping common events together.