pwa-server

An HTTP server for Node designed to serve Progressive Web Apps in production.

Usage

As a binary

$ npm install pwa-server
$ npx pwa-server --root .

Usage: pwa-server [options]

An HTTP server for Node designed to serve Progressive Web Apps in production

Options:
  -v, --version            Print the installed version.
  --host <host>            Listen on this hostname. (default: "127.0.0.1")
  --port <port>            Listen on this port; 0 for random. (default: 8080)
  --root <root>            Serve files relative to this directory. (default: ".")
  --config <file>          JS/JSON configuration file.
  --cache-control <value>  The Cache-Control header to send for all requests except the entrypoint. (default: "max-age=60")
  --entrypoint <file>      The main entrypoint to your PWA for all routes. (default: "index.html")
  -h, --help               Display this usage info

As a library

$ npm install --save pwa-server

const pwa = require('pwa-server');
const express = require('express');

const app = express();

app.get('/*', pwa.makeMiddleware(config));

app.listen(8080);

Library API

makeMiddleware(config={})

Creates an Express middleware to handle a desired route as a Progressive Web App.

expects:

• config: the configuration of the middleware:
  • config.root: Path to the root of the project on the filesystem. This can be an absolute path, or a path relative to the current working directory. Defaults to the current working directory of the process.
  • config.entrypoint: The path relative to root of the entrypoint file that will be served. Usually this is index.html.
    Default: index.html
  • config.cacheControl: The Cache-Control header to send for all requests except the entrypoint.
    Default: max-age=60
  • config.forwardErrors: If true, when a 404 or other HTTP error occurs, the Express next function will be called with the error, so that it can be handled by downstream error handling middleware. If false (or if there was no next function because Express is not being used), a minimal text/plain error will be returned..
    Default: false
  • config.helmet: Config options to pass downstream to Helmet
    Default: { contentSecurityPolicy: false }.

Entrypoint

In Progressive Web Apps, the entrypoint is a small HTML file that acts as the application bootstrap.

pwa-server will serve the entrypoint from /, and from any path that does not have a file extension and is not an existing file. By default it is index.html, or you can specify another name with the entrypoint configuration file setting.

Note that because the entrypoint is served from many URLs, and varies by user-agent, cache hits for the entrypoint will be minimal, so it should be kept as small as possible.

Service Workers

Scope header

pwa-server sets the Service-Worker-Allowed header to / for any request with the Service-Worker header. This allows a service worker served from a subdirectory to be registered with a scope outside of that directory, e.g. register('service-worker.js', { scope: '/' }).

404 handling

pwa-server automatically serves a tiny self-unregistering service worker for any request with the Service-Worker header that would otherwise have had a 404 Not Found response.

This can be useful when the location of a service worker has changed, as it will prevent clients from getting stuck with an old service worker indefinitely.

This problem arises because when a service worker updates, a 404 is treated as a failed update. It does not cause the service worker to be unregistered. See w3c/ServiceWorker#204 for more discussion of this problem.

Caching

By default, pwa-server sets the Cache-Control header to max-age=60 (1 minute), except for the entrypoint and service worker which gets max-age=0. ETag headers are also sent, so resources that have not changed on the server can be re-validated efficiently.

To change this default for non-entrypoint resources, set the cacheControl property in your configuration file, or the --cache-control command-line flag, to the desired Cache-Control header value. You may want to set --cache-control=no-cache during development.

For more advanced caching behavior, use pwa-server as a library with Express and register a middleware that sets the Cache-Control header before registering the pwa-server middleware. If pwa-server sees that the Cache-Control header has already been set, it will not modify it. For example, to set year-long caching for images:

app.get('/images/*', (req, res, next) => {
    res.setHeader('Cache-Control', 'public, max-age=31536000');
    next();
});

app.get('/*', pwa('.', config));

Choosing the right cache headers for your application can be complex. See Caching best practices & max-age gotchas for one starting point.

HTTP Errors

By default, if a 404 Not Found or other HTTP server error occurs, pwa-server will serve a minimal text/plain response. To serve custom errors, use pwa-server as a library with Express, set forwardErrors: true in your configuration object, and register an error-handling middleware after registering the pwa-server handler:

app.get('/*', pwa.makeMiddleware({
    forwardErrors: true
}));

app.use((error, req, res, next) => {
    if (error.status === 404) {
        res.status(404).sendFile('my-custom-404.html', { root: rootDir });
    } else {
        next();
    }
});