adaptive

adaptive

Simple adaptive image server based on smartcrop.js

Image: https://www.flickr.com/photos/endogamia/5682480447/ by N. Feans

Usage

Adaptive exposes a single function that creates an Express app:

var adaptive = require('adaptive');
 
var opts = {
  secret: 'mysecret',
  cache: '/tmp/adaptive'
};
 
adaptive(opts).listen(3000);

The generated images will be stored in the filesystem. If you don't specify a cache directory, adaptive will store the files in the system's temp directory.

REST API

You can request images using the following URL pattern:

http://localhost:3000/<auth-key>/<width>x<height>/<src-url>

The following URL will generate a 200x200 crop from the example image shown above: http://localhost:3000/unsafe/200x200/https://farm6.staticflickr.com/5189/…

Compression Settings

You can parametrize the JPEG compression by adding :<quality> where quality is a value from 0 to 100, optionally followed by a p to create a progressive JPEG.

Examples:

• http://localhost:3000/unsafe/200x200:75/<src-url> 75% quality
• http://localhost:3000/unsafe/200x200:p/<src-url> progressive, default quality
• http://localhost:3000/unsafe/200x200:75p/<src-url> 75% quality, progressive

Security

In order to prevent DoS attacks adaptive allows you to specify shared secret that is used to generate a hash-based message authentication code.

The web server that serves a page which contains adaptive images generates an auth key for the options and src-url.

When end-users access the page and thus load the image, adaptive generates a key using the same algorithm. If both auth keys match, the request is processed.

Generating auth-keys

Adaptive uses standard HMAC with SHA1 signing.

In order to convert http://example.com/unsafe/200x200/path/to/image.jpg into a safe URL we must sign the part 200x200/path/to/image.jpg

1. Generate a signature of that part using HMAC-SHA1 with the secret.
2. Encode the signature as base64.
3. Replace + by -
4. Replace / by _
5. Replace unsafe at the beginning of the URL with the generated key

CLI

Adaptive also comes with a binary that can be used to start a HTTP server:

adaptive -p <port> -s <secret> -c <cache-dir>

Alternatively the options can be set using environment variables:

PORT=3000 SECRET=mysecret npm start

Deploying to Heroku/dokku

The easiest way to deploy adaptive to Heroku or a dokku instance is to create an empty project with nothing but a package.json:

{
  "name": "my-adaptive-images",
  "private": true,
  "version": "0.0.1",
  "dependencies": { "adaptive": "*" },
  "scripts": { "start": "adaptive" }
}

Prerequisites

Adpative uses node-canvas which in turn is based on Cairo. For system-specific installation instructions please refer to the wiki.

Dokku's Ubuntu image provides all required dependencies except for libgif. The easiest way to add it is to do this:

echo https://github.com/fgnass/buildpack-install > .buildpacks
echo https://github.com/heroku/heroku-buildpack-nodejs >> .buildpacks
echo apt-get install -y libgif-dev > .install

git add .buildpacks .install
git commit -m "add node-canvas prerequisites"

Logging

You can turn on debug output by setting the DEBUG env var to adaptive:*

The MIT License (MIT)

Copyright (c) 2014 Felix Gnass

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.