An Express middleware to serve up minified images retrieved from a backend.
master: 
Your environment must have imagemagick and graphicsmagick available in the $PATH.
First, instantiate the route. You must pass in two arguments: a backend function and an object of options.
The backend function is passed two arguments: the Express request object, and the Express response object. However, you can't just put an Express route here. This function is expected to return a Promise that resolves to a Buffer containing an image.
In the options, pass in any Imagemin plugins as an array called plugins.
const fetch = require('node-fetch')
const express = require('express')
const app = express()
/* ... plugin requires go here ... */
const imageminProxy = new ImageminProxy((req, res) => {
// Here's my backend function.
// This is a very basic function that always returns the same image.
return fetch('http://my.backend/folder/some-image.png')
.then(x => x.ok ? x.buffer() : Promise.reject(x))
}, {
plugins: [
imageminPngQuant({quality: '45-80', strip: true, speed: 3}),
imageminJpegOptim({max: 90}),
imageminGifsicle({colors: 256, optimizationLevel: 3, interlaced: true}),
imageminSvgo({plugins: [{removeViewBox: false}]}),
]
})
app.use('/img', imageminProxy)
app.listen()Act as a reverse proxy for some backend:
const url = require('url')
const baseUrl = 'https://some-server-with-a-folder-of-images/imgSubfolder'
const myBackendFunc = (req, res) => {
// Change the URL so that it's pointing to the other server's folder
const cleanUrl = url.parse(baseUrl + req.url)
// Clean out all the query parameters from it
cleanUrl.search = ''
return fetch(cleanUrl)
.then(x => {
if( !x.ok ) {
return Promise.reject(x)
}
// Set the content type from the backend if there is one
if( x.headers.has('content-type') ) {
res.contentType(x.headers.get('content-type'))
}
return x.buffer()
})
.catch(err => {
if( 'status' in err ) {
// A Fetch error -- send it to the client
res.status(err.status)
res.send(err.statusText)
}
return Promise.reject(err)
})
}Default: []
Specify an array containing Imagemin plugins here. These will be used to minify any applicable images.
Default: true
If this is true and the backend has not set Content-Type headers (or they are set to application/octet-stream), try to figure out what the response really is.
- If the
formatquery parameter is specified, use that as a file extension for determining a MIME type. - Otherwise, try to guess using file-type.
This is a useful option if you're not always certain what you're going to get, or for some reason the backend can't get file extensions on its own.
Default: undefined
If GraphicsMagick is not in your $PATH, you will get an error like Stream yields empty buffer when attempting to resize or convert images. You can specify a directory containing the Graphicsmagick binaries (not the binary itself) here. See imagemin-gm for more information.
Default: 404
If this is a non-false value and the backend gives an empty response, send this HTTP code.
If this is a false value, throw a EmptyResponseError instead.
EmptyResponseError can be accessed at imageminProxy.errors.EmptyResponseError for type checking if desired.
If this route receives certain query parameters, it will pass those along to Imagemin.
Currently supported parameters:
width: the width of the image as a number of pixelsheight: the height of the image as a number of pixelsgravity: when resizing the image, what side of the image should be prioritized?
See imagemin-gm for more information.
- other GM functions?
Please use the included ESlint configuration to enforce style when developing. Use yarn test --coverage to run the linter and test suite as well as coverage before commits.
To generate documentation, use yarn doc or yarn docdev.