Express Context

Express middleware to get and set request-scoped context. It uses cls-hooked under the hood (forked from express-http-context). Context is preserved over async/await (in node 8+).

Usage

Installation: npm i --save @niveus/express-context

Use the middleware before the first middleware that needs access to the context. Any middleware used before this won't have access to the expressContext.

Note that some popular middlewares (such as body-parser, express-jwt) may cause context to get lost. To workaround such issues, you are advised to use any third party middleware that does NOT need the context BEFORE you use this middleware.

`` js
const express = require('express');
const expressContext = require('@niveus/express-context');

const app = express();

// Use any third-party middleware here.

app.use(expressContext.expressContextMiddleware());

// all code from here on has access to the same context for each request

`


$3

Set values for the incomming request
` js
// Example auth middleware
app.use((req, res, next) => {
try {
const token = authService.Authenticate(req.body);

expressContext.set('userToken', token);

next();
} catch(err) {
next(err);
}
})
`

$3


Get the value from the block of code that does not have access to the req object.

>⚠️ If there is no value available for the key, the default value will be undefined.

` js
const expressContext = require('@niveus/express-context');

function invalidateToken() {
const token = expressContext.get('userToken');

await userService.invalidateToken(token);

// ...
}
`

$3

To access the namespace directly, use this.
` js
const expressContext = require('@niveus/express-context');

let ns = expressContext.getNs();
`

$3

TO set multiple values at the same time, pass an object to the setMany function. The data will be set in the context using the key and value of the object.
` js
// Example middleware
app.use((req, res, next) => {
try {
const {userId, sessionId} = authService.getUserDetails(req.data);


expressContext.setMany({userId: userId, sessionId: sessionId});

} catch(err) {
next(err);
}
})
`

$3

To get multiple values from the context, pass an array containing the key name (as string) to getMany function. The function returns an array with the values of the keys in the same order as the input array.

>⚠️ If there is no value available for the key, the default value will be undefined.

` js
const expressContext = require('@niveus/express-context');

function invalidateToken() {
const [userId, sessionId] = expressContext.getMany(['userId', 'sessionId']);

await userService.invalidateToken(userId, sessionId);

// ...
}
`

Additional Options


@niveus/express-context gives the option to create custom context namespaces if required. To use custom namespace, pass the ExpressContextOptions as the last option in the functions.

` js
// ExpressContextOptions example

let expressContextOptions = { nsid: 'custom namespace id'};
`

Examples

` js
// ExpressContextOptions in the middleware.

let expressContextOptions = { nsid: 'custom namespace id'};

app.use(expressContext.expressContextMiddleware(expressContextOptions));

`

` js
// ExpressContextOptions in set, get, setMany, getMany, getNs functions

const expressContext = require('@niveus/express-context');

// ExpressContextOptions object
let expressContextOptions = { nsid: 'custom namespace id'};

// set
expressContext.set('userToken', 'value', expressContextOptions);

// get
const token = expressContext.get('userToken', expressContextOptions);

// setMany
expressContext.setMany({userId: userId, sessionId: sessionId}, expressContextOptions);


// getMany
const [userId, sessionId] = expressContext.getMany(['userId', 'sessionId'], expressContextOptions);

// getNs
let ns = expressContext.getNs(expressContextOptions);

`

Troubleshooting


To avoid weird behavior with express:
1. Make sure you require @niveus/express-context in the first row of your app. Some popular packages use async which breaks CLS.

For users of Node 10
1. Node 10.0.x - 10.3.x are not supported. V8 version 6.6 introduced a bug that breaks async_hooks during async/await. Node 10.4.x uses V8 v6.7 in which the bug is fixed. See: https://github.com/nodejs/node/issues/20274.

Credits

This code is derived from https://github.com/skonves/express-http-context`
License(MIT) https://github.com/skonves/express-http-context/blob/b141fd3fb6a408c3c4ec37fd74ab08fab41ea27f/LICENSE