The websocket protocol x-afb-ws-json1
=====================================

The WebSocket protocol *x-afb-ws-json1* is used to communicate between
an application and a binder. It allows access to all registered apis
of the binder.

This protocol is inspired from the protocol **OCPP - SRPC** as described for
example here:
[OCPP transport specification - SRPC over WebSocket](http://www.gir.fr/ocppjs/ocpp_srpc_spec.shtml).

The registration to the IANA is still to be done, see:
[WebSocket Protocol Registries](https://www.iana.org/assignments/websocket/websocket.xml)

This document gives a short description of the protocol *x-afb-ws-json1*.
A more formal description has to be done.


Architecture
------------

The protocol is intended to be symmetric. It allows:

 - to CALL a remote procedure that returns a result
 - to push and receive EVENT


Messages
--------

Valid messages are made of *text* frames that are all valid JSON.

Valid messages are:

Calls:
```
[ 2, ID, PROCN, ARGS ]
[ 2, ID, PROCN, ARGS, TOKEN ]
```

Replies (3: OK, 4: ERROR):
```
[ 3, ID, RESP ]
[ 3, ID, RESP, TOKEN ]
[ 4, ID, RESP ]
[ 4, ID, RESP, TOKEN ]
```

Events:
```
[ 5, EVTN, OBJ ]
```

Where:

| Field | Type   | Description
|-------|--------|------------------
| ID    | string | A string that identifies the call. A reply to that call use the ID of the CALL.
| PROCN | string | The procedure name to call of the form "api/verb"
| ARGS  | any    | Any argument to pass to the call (see afb_req_json that returns it)
| RESP  | any    | The response to the call
| TOKEN | string | The token in case of refresh
| EVTN  | string | Name of the event in the form "api/event"
| OBJ   | any    | The companion object of the event

Below, an example of exchange:

```
C->S:   [2,"156","hello/ping",null]
S->C:   [3,"156",{"response":"Some String","jtype":"afb-reply","request":{"status":"success","info":"Ping Binder Daemon tag=pingSample count=1 query=\"null\"","uuid":"ec30120c-6997-4529-9d63-c0de0cce56c0"}}]
```


Future
------

Here are the planned extensions:

 - add binary messages with cbor data
 - add calls with unstructured replies

This could be implemented by extending the current protocol or by
allowing the binder to accept either protocol including the new ones.


Javascript implementation
-------------------------

The file **AFB.js** is a javascript implementation of the protocol.

Here is that code:

```javascript
/*
 * Copyright (C) 2017-2019 "IoT.bzh"
 * Author: José Bollo <jose.bollo@iot.bzh>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
AFB = function(base, initialtoken){

if (typeof base != "object")
	base = { base: base, token: initialtoken };

var initial = {
	base: base.base || "api",
	token: base.token || initialtoken || "HELLO",
	host: base.host || window.location.host,
	url: base.url || undefined
};

var urlws = initial.url || "ws://"+initial.host+"/"+initial.base;

/*********************************************/
/****                                     ****/
/****             AFB_context             ****/
/****                                     ****/
/*********************************************/
var AFB_context;
{
	var UUID = undefined;
	var TOKEN = initial.token;

	var context = function(token, uuid) {
		this.token = token;
		this.uuid = uuid;
	}

	context.prototype = {
		get token() {return TOKEN;},
		set token(tok) {if(tok) TOKEN=tok;},
		get uuid() {return UUID;},
		set uuid(id) {if(id) UUID=id;}
	};

	AFB_context = new context();
}
/*********************************************/
/****                                     ****/
/****             AFB_websocket           ****/
/****                                     ****/
/*********************************************/
var AFB_websocket;
{
	var CALL = 2;
	var RETOK = 3;
	var RETERR = 4;
	var EVENT = 5;

	var PROTO1 = "x-afb-ws-json1";

	AFB_websocket = function(on_open, on_abort) {
		var u = urlws;
		if (AFB_context.token) {
			u = u + '?x-afb-token=' + AFB_context.token;
			if (AFB_context.uuid)
				u = u + '&x-afb-uuid=' + AFB_context.uuid;
		}
		this.ws = new WebSocket(u, [ PROTO1 ]);
		this.url = u;
		this.pendings = {};
		this.awaitens = {};
		this.counter = 0;
		this.ws.onopen = onopen.bind(this);
		this.ws.onerror = onerror.bind(this);
		this.ws.onclose = onclose.bind(this);
		this.ws.onmessage = onmessage.bind(this);
		this.onopen = on_open;
		this.onabort = on_abort;
	}

	function onerror(event) {
		var f = this.onabort;
		if (f) {
			delete this.onopen;
			delete this.onabort;
			f && f(this);
		}
		this.onerror && this.onerror(this);
	}

	function onopen(event) {
		var f = this.onopen;
		delete this.onopen;
		delete this.onabort;
		f && f(this);
	}

	function onclose(event) {
		for (var id in this.pendings) {
			try { this.pendings[id][1](); } catch (x) {/*TODO?*/}
		}
		this.pendings = {};
		this.onclose && this.onclose();
	}

	function fire(awaitens, name, data) {
		var a = awaitens[name];
		if (a)
			a.forEach(function(handler){handler(data);});
		var i = name.indexOf("/");
		if (i >= 0) {
			a = awaitens[name.substring(0,i)];
			if (a)
				a.forEach(function(handler){handler(data);});
		}
		a = awaitens["*"];
		if (a)
			a.forEach(function(handler){handler(data);});
	}

	function reply(pendings, id, ans, offset) {
		if (id in pendings) {
			var p = pendings[id];
			delete pendings[id];
			try { p[offset](ans); } catch (x) {/*TODO?*/}
		}
	}

	function onmessage(event) {
		var obj = JSON.parse(event.data);
		var code = obj[0];
		var id = obj[1];
		var ans = obj[2];
		AFB_context.token = obj[3];
		switch (code) {
		case RETOK:
			reply(this.pendings, id, ans, 0);
			break;
		case RETERR:
			reply(this.pendings, id, ans, 1);
			break;
		case EVENT:
		default:
			fire(this.awaitens, id, ans);
			break;
		}
	}

	function close() {
		this.ws.close();
		this.ws.onopen =
		this.ws.onerror =
		this.ws.onclose =
		this.ws.onmessage =
		this.onopen =
		this.onabort = function(){};
	}

	function call(method, request, callid) {
		return new Promise((function(resolve, reject){
			var id, arr;
			if (callid) {
				id = String(callid);
				if (id in this.pendings)
					throw new Error("pending callid("+id+") exists");
			} else {
				do {
					id = String(this.counter = 4095 & (this.counter + 1));
				} while (id in this.pendings);
			}
			this.pendings[id] = [ resolve, reject ];
			arr = [CALL, id, method, request ];
			if (AFB_context.token) arr.push(AFB_context.token);
			this.ws.send(JSON.stringify(arr));
		}).bind(this));
	}

	function onevent(name, handler) {
		var id = name;
		var list = this.awaitens[id] || (this.awaitens[id] = []);
		list.push(handler);
	}

	AFB_websocket.prototype = {
		close: close,
		call: call,
		onevent: onevent
	};
}
/*********************************************/
/****                                     ****/
/****                                     ****/
/****                                     ****/
/*********************************************/
return {
	context: AFB_context,
	ws: AFB_websocket
};
};
```