@sliit-foss/express-http-context

A rework of the express-http-context package to use the new async_hooks API

Built as the existing package does not work alongside the Bun runtime

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Get and set request-scoped context anywhere. This is just an unopinionated, idiomatic ExpressJS implementation of AsyncLocalStorage. It's a great place to store user state, claims from a JWT, request/correlation IDs, and any other request-scoped data. Context is preserved even over async/await.

How to use it

Install: bun install --save @sliit-foss/express-http-context

Use the middleware immediately before the first middleware that needs to have access to the context. You won't have access to the context in any middleware "used" before this one.

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.

1const express = require("express");
2const httpContext = require("@sliit-foss/express-http-context");
3
4const app = express();
5// Use any third party middleware that does not need access to the context here, e.g.
6// app.use(some3rdParty.middleware);
7app.use(httpContext.middleware);
8// all code from here on has access to the same context for each request

Set values based on the incoming request:

1// Example authorization middleware
2app.use((req, res, next) => {
3  userService.getUser(req.get("Authorization"), (err, result) => {
4    if (err) {
5      next(err);
6    } else {
7      httpContext.set("user", result.user);
8      next();
9    }
10  });
11});

Get them from code that doesn't have access to the express req object:

1const httpContext = require("@sliit-foss/express-http-context");
2
3// Somewhere deep in the Todo Service
4function createTodoItem(title, content, callback) {
5  const user = httpContext.get("user");
6  db.insert({ title, content, userId: user.id }, callback);
7}

You can access the store directly as follows

1const store = require("@sliit-foss/express-http-context").store;

Troubleshooting

For users of Node below version 14

1. Unfortunatly, this package does not work with any version of Node below 14. This is due to the fact that the AsyncLocalStorage API was introduced in Node 14. If you are using Node below version 14, you can use the original express-http-context package but as of writing this, it will not work with Bun.