@fanoutio/serve-grip

js-serve-grip

GRIP library for Node.js, provided as connect-compatible middleware.

Therefore, this library is usable with frameworks such as the following:

• connect
• Express
• Next.js
• Koa *experimental support

Supported GRIP servers include:

• Pushpin
• Fastly Fanout

This library also supports legacy services hosted by Fanout Cloud.

Authors: Katsuyuki Omuro [e-mail], Konstantin Bokarius [e-mail]

Introduction

GRIP is a protocol that enables a web service to delegate realtime push behavior to a proxy component, using HTTP and headers.

@fanoutio/serve-grip is a server middleware that works with frameworks such as Express and Next.js. It:

• gives a simple and straightforward way to configure these frameworks against your GRIP proxy
• parses the Grip-Sig header in any requests to detect if they came through a Grip proxy
• provides your route handler with tools to handle such requests, such as:
  • access to information about whether the current request is proxied or is signed
  • methods you can call to issue any instructions to the GRIP proxy
• provides access to the the publisher object, enabling your application to publish messages through the GRIP publisher.

Additionally, serve-grip also handles WebSocket-Over-HTTP processing so that WebSocket connections managed by the GRIP proxy can be controlled by your route handlers.

Installation

Install the library.

npm install @fanoutio/serve-grip

Installation in Connect / Express

Import the ServeGrip class and instantiate the middleware. Then install it before your routes.

Example:

import express from 'express';
import { ServeGrip } from '@fanoutio/serve-grip';

const app = express();

const serveGrip = new ServeGrip(/* config */);
app.use( serveGrip ); 

app.use( '/path', (res, req) => {

    if (req.grip.isProxied) {
        const gripInstruct = res.grip.startInstruct();
        gripInstruct.addChannel('test');
        gripInstruct.setHoldStream();
        res.end('[stream open]\n');
    }

});

app.listen(3000);

Installation in Koa (experimental)

Import the ServeGrip class and instantiate it. The Koa middleware is available as the .koa property on the object. Install it before your routes.

Example:

import Koa from 'koa';
import Router from '@koa/router';
import { ServeGrip } from '@fanoutio/serve-grip';

const app = new Koa();

const serveGrip = new ServeGrip(/* config */);
app.use( serveGrip.koa );

const router = new Router();

router.use( '/path', ctx => {

    if (ctx.req.grip.isProxied) {
        const gripInstruct = res.grip.startInstruct();
        gripInstruct.addChannel('test');
        gripInstruct.setHoldStream();
        ctx.body = '[stream open]\n';
    }

});

app.use(router.routes())
    .use(router.allowedMethods());

app.listen(3000);

Installation in Next.js

You may use this library to add GRIP functionality to your Next.js API Routes.

Import the ServeGrip class and instantiate the middleware, and then run it in your handler before your application logic by calling the async function serveGrip.run().

Example: /lib/grip.js:

import { ServeGrip } from '@fanoutio/serve-grip';
export const serveGrip = new ServeGrip(/* config */);

/pages/api/path.js:

import { serveGrip } from '/lib/grip';

export default async(req, res) => {
    // Run the middleware
    if (!(await serveGrip.run(req, res))) {
        // If serveGrip.run() has returned false, it means the middleware has already
        // sent and ended the response, usually due to an error.  
        return;
    }

    if (req.grip.isProxied) {
        const gripInstruct = res.grip.startInstruct();
        gripInstruct.addChannel('test');
        gripInstruct.setHoldStream();
        res.end('[stream open]\n');
    }

}

Note: In Next.js, you must specifically call the middleware from each of your applicable API routes. This is because in Next.js, your API routes will typically run on a serverless platform, and objects will be recycled after each request. You are advised to construct a singleton instance of the middleware in a shared location and reference it from your API routes.

Configuration

@fanoutio/serve-grip exports a constructor function, ServeGrip. This constructor takes a configuration object that can be used to configure the instance, such as the GRIP proxies to use for publishing or whether incoming requests should require a GRIP proxy.

The following is an example of configuration against Pushpin running on localhost:

import { ServeGrip } from '@fanoutio/serve-grip';
const serveGrip = new ServeGrip({
    grip: {
        control_uri: 'https://localhost:5561/',   // Control URI for Pushpin publisher
        control_iss: '<issuer>',                  // (opt.) iss needed for publishing, if required by Pushpin
        key: '<publish-key>',                     // (opt.) key needed for publishing, if required by Pushpin
    },
    isGripProxyRequired: true,
});

The following is an example of configuration against Fastly Fanout:

import { ServeGrip } from '@fanoutio/serve-grip';
const serveGrip = new ServeGrip({
    grip: {
        control_uri: 'https://api.fastly.com/service/<service-id>/',   // Control URI
        key: '<fastly-api-token>',             // Authorization key for publishing (Fastly API Token)
        verify_iss: 'fastly:<service-id>',     // Fastly issuer used for validating Grip-Sig
        verify_key: '<verify-key>',            // Fastly public key used for validating Grip-Sig
    },
    isGripProxyRequired: true,
});

Often the configuration is done using a GRIP_URL (and if needed, GRIP_VERIFY_KEY), allowing for configuration using simple strings. This allows for configuration from environment variables:

GRIP_URL="https://api.fastly.com/service/<service-id>/?verify-iss=fastly:<service-id>&key=<fastly-api-token>"
GRIP_VERIFY_KEY="base64:LS0tLS1CRUdJTiBQVUJMSUMgS0VZLS0tLS0KTUZrd0V3WUhLb1pJemowQ0FRWUlLb1pJemowREFRY0RRZ0FFQ0tvNUExZWJ5RmNubVZWOFNFNU9uKzhHODFKeQpCalN2Y3J4NFZMZXRXQ2p1REFtcHBUbzN4TS96ejc2M0NPVENnSGZwLzZsUGRDeVlqanFjK0dNN3N3PT0KLS0tLS1FTkQgUFVCTElDIEtFWS0tLS0t"

import { ServeGrip } from '@fanoutio/serve-grip';

const serveGrip = new ServeGrip({
    grip: process.env.GRIP_URL,
    gripVerifyKey: process.env.GRIP_VERIFY_KEY,
    isGripProxyRequired: true,
});

Available options:

Key	Value
grip	A definition of GRIP proxies used to publish messages, or a preconfigured Publisher object from @fanoutio/grip. See below for details.
gripVerifyKey	(optional) A string or Buffer that can be used to specify the verify-key component of the GRIP configuration. Applies only if - * grip is provided as a string, configuration object, or array of configuration objects * grip does not already contain a verify_key value.
gripProxyRequired	(optional) A boolean value representing whether all incoming requests should require that they be called behind a GRIP proxy. If this is true and a GRIP proxy is not detected, then a 501 Not Implemented error will be issued. Defaults to false.
prefix	(optional) A string that will be prepended to the name of channels being published to. This can be used for namespacing. Defaults to ''.

In most cases your application will construct a singleton instance of this class and use it as the middleware.

The grip parameter may be provided as any of the following:

1. An object with the following fields:

   Field	Description
   control_uri	The Control URI of the GRIP client.
   control_iss	(optional) The Control ISS, if required by the GRIP client.
   key	(optional) string or Buffer. The key to use with the Control ISS, if required by the GRIP client.
   verify_iss	(optional) The ISS to use when validating a GRIP signature.
   verify_key	(optional) string or Buffer. The key to use when validating a GRIP signature.

2. An array of such objects.

3. A GRIP URI, which is a string that encodes the above as a single string.

4. (advanced) A Publisher object that you have instantiated and configured yourself, from @fanoutio/grip.

Handling a route

After the middleware has run, your handler will receive req and res objects that have been extended with grip properties. These provide access to the following:

Key	Description
req.grip.isProxied	A boolean value indicating whether the current request has been called via a GRIP proxy.
req.grip.isSigned	A boolean value indicating whether the current request is a signed request called via a GRIP proxy.
req.grip.wsContext	If the current request has been made through WebSocket-Over-HTTP, then a WebSocketContext object for the current request. See @fanoutio/grip for details on WebSocketContext.

Key	Description
res.grip.startInstruct()	Returns an instance of GripInstruct, which can be used to issue instructions to the GRIP proxy to hold connections. See @fanoutio/grip for details on GripInstruct.

To publish messages, call serveGrip.getPublisher() to obtain a Publisher. Use it to publish messages using the endpoints and prefix specified to the ServeGrip constructor.

Key	Description
serveGrip.getPublisher()	Returns an instance of Publisher, which can be used to publish messages to the provided publishing endpoints using the provided prefix. See @fanoutio/grip for details on Publisher.

Examples

This repository contains examples to illustrate the use of serve-grip in Connect / Express and Next.js, which can be found in the examples directory. For details on each example, please read the README.md files in the corresponding directories.

Advanced

Next.js alternative invocation

As an alternative method of running serveGrip in a Next.js API route, since serveGrip is connect-compatible, you may use the process described in API Middlewares. This may be useful for example if you have multiple middlewares and you wish to call them in a uniform manner.

Example: /lib/grip.js:

import { ServeGrip } from '@fanoutio/serve-grip';
export const serveGrip = new ServeGrip(/* config */);

// Helper method to wait for a middleware to execute before continuing
// And to throw an error when an error happens in a middleware
// https://nextjs.org/docs/api-routes/api-middlewares#connectexpress-middleware-support
export function runMiddleware(req, res, fn) {
    return new Promise((resolve, reject) => {
        fn(req, res, (result) => {
            if (result instanceof Error) {
                return reject(result)
            }

            return resolve(result)
        })
    })
}

/pages/api/path.js:

import { serveGrip, runMiddleware } from '/lib/grip';

export default async(req, res) => {

    // Run the middleware
    await runMiddleware(req, res, serveGrip);

    if (req.grip.isProxied) {
        const gripInstruct = res.grip.startInstruct();
        gripInstruct.addChannel('test');
        gripInstruct.setHoldStream();
        res.end('[stream open]\n');
    }

}

Changes from express-grip

If you have used express-grip in the past, you will notice that this library no longer requires the use of pre-route and post-route middlewares. Consequently, you do not need to call next() for route handlers that complete their work. In fact, you should follow the standard practice of calling res.end() at the end of each of your route handlers.