Real-time image processing for your express application.

Description

express-sharp adds real-time image processing routes to your express application. Images are processed with sharp, a fast Node.js module for resizing images.

                      express-sharp
    Express app         endpoint          image path    transformation                
┌─────────────────┐┌────────────────┐┌──────────────────┐ ┌────────┐
https://example.com/path/to/my-scaler/images/my-image.jpg?w=100&h=50

Original images are loaded via an image adapter. Currently this includes HTTP and file system adapters.

Highlights

• Fast resizing of images (see sharp Performance)
• Supports multiple backends, from which the original images are downloaded
• Supports multiple caching backends
• Image URLs can be signed to prevent attacks

Table of contents

• Install
• Express server integration
  • Server configuration
  • Image Adapters
    • File System
    • HTTP
    • Amazon S3
    • Custom
  • Caching
  • URL signing
  • Debug logging
• Client integration
• License

Install

$ yarn add express-sharp

See sharp installation for additional installation instructions.

Express server integration

Example app.js (See also example/app.ts in this project):

import express from 'express'
import { expressSharp, FsAdapter, HttpAdapter } from 'express-sharp'

const app = express()

// Fetch original images via HTTP
app.use(
  '/some-http-endpoint',
  expressSharp({
    imageAdapter: new HttpAdapter({
      prefixUrl: 'http://example.com/images',
    }),
  })
)

// Alternative: Load original images from disk
app.use(
  '/fs-endpoint',
  expressSharp({
    imageAdapter: new FsAdapter(path.join(__dirname, 'images')),
  })
)

app.listen(3000)

Render /images/image.jpg with 400x400 pixels:

curl http://my-server/express-sharp-endpoint/images/image.jpg?w=400&h=400

Same as above, but with 80% quality, webp image type and with progressive enabled:

curl http://my-server/express-sharp-endpoint/images/image.jpg?w=400&h=400&f=webp&q=80&p

Server configuration

import { expressSharp } from 'express-sharp'

app.use('/some-http-endpoint', expressSharp(options))

Supported options:

Name	Description	Default
autoUseWebp	Specifies whether images should automatically be rendered in webp format when supported by the browser.	true
cache	If specified, the keyv cache configured here is used to cache the retrieval of the original images and the transformations.	-
cors	Any valid CORS configuration option	-
imageAdapter	Configures the image adapter to be used (see below). Must be specified.	-
secret	If specified, express-sharp will validate the incoming request to verify that a valid signature has been provided. The secret is used to compute this signature.	-

Image Adapters

express-sharp contains the following standard image adapters.

File System

With this adapter original images are loaded from the hard disk.

import { FsAdapter } from 'express-sharp'

const adapter = new FsAdapter('/path/to/images')

HTTP

Loads original images via HTTP. To use this adapter, the peer dependency got must be installed:

$ yarn add got

import { HttpAdapter } from 'express-sharp'

const adapter = new HttpAdapter({
  prefixUrl: 'http://localhost:3000/images',
})

The constructor can be passed any got options.

Amazon S3

Loads images from Amazon S3. To use this adapter, the peer dependency aws-sdk must be installed:

$ yarn add aws-sdk

import { S3Adapter } from 'express-sharp'

const bucketName = 'my-bucketname'
const adapter = new S3Adapter(bucketname)

The AWS SDK expects the environment variables AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY to be set.

Custom

If you needed your own adapters can be used. An "image adapter" is a class that implements the ImageAdapter interface:

import { ImageAdapter } from 'express-sharp'

class MyAdapter implements ImageAdapter {
  async fetch(id: string): Promise<Buffer | undefined> {
    if (imageDoesNotExist(id)) {
      return undefined
    }

    return Buffer.from('my image blob')
  }
}

Caching

The fetching of the original images and the transformations can be cached. To enable this feature, the cache option must be passed to the expressSharp middleware. Any keyv cache stores can be passed.

In-memory cache example:

const cache = new Keyv({ namespace: 'express-sharp' })

app.use(
  '/my-endpoint',
  expressSharp({
    cache,
    imageAdapter: ...
  })
)

Redis example:

const cache = new Keyv('redis://', { namespace: 'express-sharp' }

app.use(
  '/my-endpoint',
  expressSharp({
    cache,
    imageAdapter: ...
  })
)

URL signing

By setting the environment variable EXPRESS_SHARP_SIGNED_URL_SECRET or by specifying the secret option when calling the express-sharp middleware, signed URLs are activated. This reduces the attack surface on the server, since the caller cannot produce an unlimited number of URLs that cause load on the server.

In order to compute the signature, the supplied client should be used:

import { createClient } from 'express-sharp'

const endpoint = 'https://example.com/my-express-sharp-endpoint'
const secret = 'test'
const client = createClient(endpoint, secret)

const imageUrl = client.url('/foo.png', { width: 500 })

// https://example.com/my-express-sharp-endpoint/foo.png?w=500&s=Of3ty8QY-NDhCsIrgIHvPvbokkDcxV8KtaYUB4NFRd8

Debug logging

This project uses debug. To display debug messages from express-sharp, the DEBUG environment variable must be exported so that it contains the value express-sharp*. Example:

$ export DEBUG='my-app:*,express-sharp*'

Client integration

express-sharp comes with a client that can be used to generate URLs for images.

import { createClient } from 'express-sharp'

const client = createClient('http://my-base-host', 'optional secret')

const originalImageUrl = '/foo.png'
const options = { width: 500 }
const fooUrl = client.url(originalImageUrl, options)

Currently the following transformations can be applied to images:

Client option name	Query param name	Description
quality	q	Quality is a number between 1 and 100 (see sharp docs).
width	w
height	h
format	f	Output image format. Valid values: every valid sharp output format string, i.e. jpeg, gif, webp or raw.
progressive	p	Only available for jpeg and png formats. Enable progressive scan by passing true.
crop	c	Setting crop to true enables the sharp cropping feature. Note: Both width and height params are neccessary for crop to work. Default is false.
trim	t	Setting trim to true enables the sharp trim feature.
gravity	g	When the crop option is activated you can specify the gravity of the cropping. Possible attributes of the optional gravity are north, northeast, east, southeast, south, southwest, west, northwest, center and centre. Default is center.

License

express-sharp is distributed under the MIT license. See LICENSE for details.