node-service-worker-proxy

node-service-worker-proxy

A proxy server that allows you to send HTTP requests through an instance of node-service-worker.

Why?

While most service worker demos demonstrate using the fetch event to return items in the service worker cache, it can actually construct responses manually.

So, we can use the service worker to manually construct HTTP responses just like we would with a Node server, complete with whatever templating library we choose. But the API is entirely different to that of Express or any other Node HTTP server library, which is where this proxy comes in.

What works?

Much like node-service-worker, very little right now. But it does succesfully pass requests through into the worker, and to the source if fetch() is called from inside the worker (or we'd get an infinite loop).

It does not (and will not) do things like gzip responses – you should put this behind Nginx or similar when serving to the public, and setup compression, caching etc. there.

How do I use it?

After running:

npm install node-service-worker-proxy

you can call service-worker-proxy in any NPM script. Or just manually call:

node cli.js

with these arguments:

• source: the directory or HTTP server you want to pull content from. For example:

  • ../html-build
  • https://proxy-origin.example.com

  Note: only local directory usage has been tested, but remote should work as well

• target: the address this proxy will be serving from (i.e. the URL we will send into the worker). Example: https://www.example.com.

• worker: the relative path (from source) of the JS file to load as a worker. Example: sw.js.

• scope: the scope to register the worker under. Just like navigator.serviceWorker.register in the browser this is optional, and will default to the directory the worker is in.

• maxAge: if you're using a local source there won't be any HTTP headers to forward - this argument lets you specify how long static files should be cached, by default. Accepts an integer value millisecond value, or a string parsable by ms. Examples:

  • 6000 = 6 seconds
  • 60s = 60 seconds

in the format of:

service-worker-proxy --source ../html-build --target https://www.example.com --maxAge 60s

Using in Docker

I've thrown together a quick Dockerfile that'll let you use this in Docker. You need to specify the arguments above as --build-args, as well as make sure your local source directory is in the current directory. Also, use sourcelocal instead of source (and you can only specify a local path).

Example script to assemble:

cp -r ../html-build ./build-source
docker build -t gdnmobilelab/app-proxy . --build-arg sourcelocal=./build-source --build-arg target=https://www.example.com --build-arg worker=sw.js --build-arg maxAge="60s"
rm -rf ./build-source

This could do with some improvement. But it works.

Tests

Some quick tests are available. Just run:

npm test

To see the results. Needs a lot more test coverage.