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This repository iopa is an API-first, Internet of Things (IoT) fabric It is the official implementation of the Internet Open 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.all('/device/lightswitch', function(context, next) {
  if ((context.get("iopa.Method) = 'ON')) this.lightswitch.turnon

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 Typescript, Node.js javascript (including V12.0+), browser-side javascript, edge cloud function javascript, C#, Swift, Objective-C, Rust and Golang. The reference implementation is written in Typescript.

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 Typescript.

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.). "Promises are returned for use with the ES6+ async/await functionality.

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

IOPA 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 when used with the iopa-edge-nodejs package.

Static Typings Design Time Experience

The version 4.0 upgrade of the iopa reference implementation added in ~2022 allows static type checking within IDEs such as Visual Studio Code of both "server.Capabilities" and the context record.

Use app.capability('urn:io.iopa:my.great.capability') and app.setCapability('urn:io.iopa:my.great.capability', this) to get and set capabilities on strongly typed App objects.

use context.headers.get('iopa.StatusCode'), context.response.headers.set('iopa.StatusCode', 'awseast-205020-55'), context.capability('urn:io.iopa:my.great.capability') to get field, set a field, and get a capability respectively.

Contribute to @iopa/types with globally used reference capabilities and field definitions (kept in a separate repository so that the core iopa package stays relatively stable)

Use of square brackets (e.g., context["iopa.StatusCode"]) and reference constants (e.g., IOPA.StatusCode) is now deprecated due to the inability to check valid values at design time. The get, set, capability, and setCapability are automatically limited to correct values through Typescript definitions.

For People, Animals, Devices and Things

iopa powers nodekit, 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 humans, devices and things.

NPM Package Contents

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

  • 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)
  • IOPA constants for commonly used properties (now deprecated as static type languages such as Typescript are preferred)

This package is intended for use in browser workers, cloud functions, embedded mobile runtimes, and deno or 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 middlewareclass parameter determines which behavior is being chained into the pipeline.

  • If the middleware given to use is a constructor that takes one argument, then it will be invoked with as a new instance with the app provided as the only parmaeter to the constructor. The class MAY also contain an invoke instance function that is invoked for each subsequent context record.

  • 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.

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


yarn add iopa

Basic Example

import { App, Factory } as Iopa = from 'iopa'

var app = new App()
app.use(async (context, next) => {'HELLO WORLD' + context.toString())
  return next()

var demo =

var context = new 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


  • appFunc = (Promise) function(context)
  • app.use = (app)function(middleware)
  • middleware = (Promise) function(context, next) with next=appFunc
  • = (appFunc) function(context) // builds middleware
  • context = IOPA context dictionary

API Reference Specification



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