Real-time image processing for your express application.

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.

• 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

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

$ yarn add express-sharp

See sharp installation for additional installation instructions.

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

import { expressSharp } from 'express-sharp'

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

Supported options:

express-sharp contains the following standard image adapters.

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

import { FsAdapter } from 'express-sharp'

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

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.

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.

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')
  }
}

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: ...
  })
)

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

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*'

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:

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