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1.4.19 • Public • Published


Build Status NPM limerun



This repository iopa is an API-first, Internet of Things (IoT) fabric It is the official implementation of the Internet of Protocols Alliance (IOPA) reference pattern

Target Audience

This repository is primarily geared at application developers and device developers who want to connect their products to the Internet of Things, but don't want to be tied down to any one protocol or standard (be it hardware or software based). Further, they want to have a simple "all data flows one way" approach to developing applications or device logic, with a fabric that encourages good programming patterns and discourages anti-patterns. They don't want to reinvent the wheel and therefore want all boilerplate and common logic for implementing a server to be simple use statements:


app.mount('/device/lightswitch', function(context, next){
 if (context[IOPA.Method] = "ON")

Pattern, Standards, Fabrics and Frameworks.

IOPA is neither a protocol STANDARD nor a FRAMEWORK. Rather it is a PATTERN that defines a well-defined API (by convention not reference) between the broadest scope of Internet of Things (IoT) transport layers and application/device logic. The reference implementation is a fabric that speeds development of applications that use the pattern, but is not necessary to implement or to interoperate with any other application, or middleware micro-service -- it just provides some very handy reference classes and constants for intellisense development, and provides a robust, tested example of the most common logic required (a dispatcher called the AppBuilder class, and a factory for creating IOPA context with automatic scope tracking).

IOPA is a loose port of the OWIN specification to expand the reach to Node.js servers but is language independent. The pattern works for Node.js javascript (including V4.0+), browser-side javascript, Swift V2., Objective-C and Golang. The reference implementation is written in javascript for Node.js 5.x

Published as open-source without dependence on any implementation or platform, the IOPA specs allow applications to be developed independently of the actual server (nGinX, IIS, Node.js, Katana, node-coap, iopa-mqtt, iopa-coap, iopa-http, etc.). Because it is a well-defined pattern that uses only base language features it is not even necessary to include this repository in any microservices that rely on it. The entire pattern works using well-known string constants (published in the open-source IOPA specification). However, inclusion of this repository gives access to intellisense, constant optimization, etc.

In contrast to the IOPA specification, this repository contains an actual IOPA reference implementation for node.js Javascript.

A broad ecosystem of servers and middleware, such as routers and view engines, exist in the the [iopa-io](] and [limerun](] organizations on GitHub.

Core Principles

An IOPA middleware/application is simply a function(context, next) that we call an "AppFunc" that provides a single REST-like IOPA context for each request, where it is easy to access all the HTTP/COAP parameters (context.path, context.response.body etc.). "Tasks" (promises) are returned for full async programming without callback hell, and for full compatibility with the upcoming ES7 async/await functionality.

Middleware can be chained with app.use(middleware1).use(middleware2) etc.

With the iopa-connect package, IOPA servers can also call legacy Node HTTP middleware in the same chain with app.use( function(req,res){ ... } ).

IOPA middleware and legacy middleware can be used with a COAP server such as node-coap with app.buildCoap() and can be used directly with Node's built-in http server with app.buildHttp() when used with the iopa-connect package. It can even be used in embedded webkit applications such as

For People, Animals, Devices and Things

iopa powers, an open-source cross-platform IOPA certified user interface framework for Mac, Windows, iOS, Android, Node.js, etc. Anything that can be written as a web application or REST application can be run on a single device with no coding changes, in javascript. As such IOPA is for communicating with people, animals, devices and things.

iopa also powers limerun, a cross-platform IOPA connected IoT framework for any device that runs Node.js (including Raspberry Pi, BeagleBone, etc. ). As such iopa is for communicating things.

NPM Package Contents

This repository contains a Node Package Manager (NPM) package with helper functions for:

  • IOPA constants for commonly used properties
  • AppBuilder dispatcher for chaining middleware and applications, with automatic bridging to async-based Tasks (Promises), use of this for IopaContext instead of separate argument, and next argument for middleware chaining
  • Context factory for creating your own IOPA contexts (typically used by a server)

This package is intended for use in Node.js applications that either run on a web server that conform to the IOPA specifications (such as the embedded webserver inside or run using the iopa-coap, iopa-mqtt, and iopa-http bridges when used with those respective packages.

Middleware/Application Pipeline Creator and Dispatcher: AppBuilder


Adds a middleware node to the IOPA function pipeline. The middleware are invoked in the order they are added: the first middleware passed to app.use will be the outermost function, and the last middleware passed to Use will be the innermost.


The middleware parameter determines which behavior is being chained into the pipeline.

  • If the middleware given to use is a function that takes one argument, then it will be invoked with the next component in the chain as its parameter, and with the this context set to the IOPA context. It MUST return a promise that conforms to the Promise/A specification.

  • If the middleware given to use is a function that takes two arguments, then it will be invoked with the next component in the chain as its parameter, with a Node-based callback (function(err, result){})as its second parameter, and with the this context set to the IOPA context. This type of middleware should return void.

  • Legacy middleware can also be invoked with app.use( function(req,res){ ... } ), app.use( function(req, res, next){ ... } ) or app.use( function(err, req, res, next){ ... } ). The AppBuilder is smart enough to detect the two argument function with parameters named req and res in this case (use of different naming conventions need to be wrapped in a function(req,res){}), and assumes three and four argument functions are legacy.

returns app

The AppBuilder app itself is returned. This enables you to chain your use statements together.

build pipeline when all middleware added:

returns an IOPA AppFunc (promise) function(context) that can be inserted into any IOPA server.

Example Usage


npm install iopa

Basic Example

const iopa = require('iopa')
var app = new iopa.App();
app.use(function (context, next) {"HELLO WORLD" + context.toString());
  return Promise.resolve(null);
var demo =;
var context = (new iopa.Factory()).createContext();    // typically done within a TCP or UDP server
context.using(demo);     // the using automatically disposes of the context (returning it to a pool) when demo AppFunc is complete

Automatic Connect Bridge to Legacy Connect/Express Middleware and Node HTTP Server

var iopa = require('iopa')
  , http = require('http')
  , iopaConnect = require('iopa-connect')
var app = new iopa.App();
app.use(function(req, res) {
    response.writeHead(200, {"Content-Type": "text/html"});
    response.end("<html><head></head><body>Hello World</body>");

IOPA - HTTP Bridge Only with IOPA Promise based middleware

var iopa = require('iopa'),
    http = require('http'),
    iopaConnect = require('iopa-connect');
var app = new iopa.App();
    this.response.writeHead(200, {'Content-Type': 'text/html'});
    this.response.end("<html><head></head><body>Hello World</body>");
    return next();


  • appFunc = (Promise) function(context)
  • app.use = (app)function(middleware)
  • middleware = (Promise) function(context, next) with next=appFunc
  • OR middleware = fn(req, res, next) for compatibility with Connect/ExpressJS middleware
  • OR middleware = fn(err, req, res, next) for compatibility with Connect/ExpressJS middleware
  • = (appFunc) function(context) // builds middleware
  • app.buildHttp = (function(req, res)) function() // builds middleware for compatibility with Connect/ExpressJS hosts
  • context = IOPA context dictionary

API Reference Specification




npm i iopa

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