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readme.md

rehype-github-image

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rehype plugin to enhance images.

Contents

What is this?

This plugin enhances images by dropping them if they are invalid, creating links around them, and optionally passing images through an image proxy.

An image proxy requires a dedicated server, which could become costly if you have tons of user content, but it prevents leaking the readers information to external servers, and it solves CORS errors.

This plugin is part of a monorepo rehype-github. See its readme for more info.

When should I use this?

You can use this plugin when you want to match how github.com works or when you want to build similar pipelines that have user content. You should likely use this in combination with an image proxy, such as camomile (Node.js) or go-camo (Go).

Install

This package is ESM only. In Node.js (version 16+), install with npm:

npm install rehype-github-image

In Deno with esm.sh:

import rehypeGithubImage from 'https://esm.sh/rehype-github-image@1'

In browsers with esm.sh:

<script type="module">
  import rehypeGithubImage from 'https://esm.sh/rehype-github-image@1?bundle'
</script>

Use

Say our module example.js looks as follows:

import rehypeGithubImage from 'rehype-github-image'
import rehypeParse from 'rehype-parse'
import rehypeStringify from 'rehype-stringify'
import {unified} from 'unified'

const file = await unified()
  .use(rehypeParse, {fragment: true})
  .use(rehypeGithubImage)
  .use(rehypeStringify)
  .process('<img src="https://example.com/index.png">')

console.log(String(file))

…now running node example.js yields:

<p><a target="_blank" rel="noopener noreferrer" href="https://example.com/index.png"><img src="https://example.com/index.png" style="max-width: 100%;"></a></p>

API

This package exports the identifier camo. The default export is rehypeGithubImage.

camo(path, secret)

Create a toProxyUrl for a camo server.

See for example:

Parameters
  • path (string, required) — where the camo server runs (such as https://camo.githubusercontent.com)
  • secret (string, required) — shared secret with your camo server (such as myVerySecretSecret)
Returns

Function to create a URL to a proxy from an external URL (ToProxyUrl).

rehypeGithubImage(options?)

Plugin to enhance images.

Parameters
  • options (Options, optional) — configuration

Options

Configuration (TypeScript type).

Fields
  • toProxyUrl (ToProxyUrl, optional) — change external URLs to go through an image proxy
  • internal (Array<string> or string, optional) — hostname or hostnames to not mark as external; URLs to these hostnames will not be passed through the image proxy
  • rel (Array<string> or string, default: ['noopener', 'noreferrer']) — relationship(s) of your site to external content, used in rel on as wrapping the images; no rel field is set on URLs that go to your image proxy
  • targetBlank (boolean, default: true) — whether to open images in a new window
Notes

These options are safe by default, but you should change them. You should likely include 'nofollow' and 'ugc' in rel. If you have targetBlank: true (default), make sure to include 'noopener' and 'noreferrer' (default).

👉 Note: to summarize, with targetBlank: false, use rel: ['nofollow', 'ugc']. With targetBlank: true (default), use rel: ['nofollow', 'noopener', 'noreferrer', 'ugc'].

ToProxyUrl

Create a URL to a proxy from an external URL (TypeScript type).

Parameters
  • url (string) — URL to hash
Returns

URL to proxy (Promise<string> or string).

Bugs

There are no bugs with how GitHub does this, but they drop the target and use ['nofollow', 'ugc'] in the rel.

Authoring

There are no additional recommendations on how to author links in markdown.

HTML

The markup that github.com uses for invalid URLs is:

<img src="" alt="" style="max-width: 100%;">

For valid URLs, they keep the value in src:

<img src="../image.jpg" alt="" style="max-width: 100%;">

If the image is not in an a element, they add one:

<a target="_blank" rel="noopener noreferrer" href="image.jpg"><img src="image.jpg" alt="alt" style="max-width: 100%;"></a>

If the image goes to some domain, that isn’t http://github.com (or https:), they pass the image through a camo image proxy:

<a target="_blank" href="https://camo.githubusercontent.com/559e4923433749bd3cd9c1e4ddb7317442c7ca8e836e2a843189d13e264c9ff2/68747470733a2f2f6578616d706c652e636f6d"><img src="https://camo.githubusercontent.com/559e4923433749bd3cd9c1e4ddb7317442c7ca8e836e2a843189d13e264c9ff2/68747470733a2f2f6578616d706c652e636f6d" data-canonical-src="https://example.com" style="max-width: 100%;"></a>

These urls have the following format:

<base>/<digest>/<hex>

…where hex is the hex encoded original URL, digest is the hex encoded HMAC digest generated with a shared secret key and the original URL, and base is the path where camo is running (such as https://camo.githubusercontent.com).

CSS

No CSS is needed.

Syntax

No syntax is applicable.

Types

This package is fully typed with TypeScript. It exports the additional type Options and ToProxyUrl.

Compatibility

Projects maintained by the unified collective are compatible with all maintained versions of Node.js. As of now, that is Node.js 16+. Our projects sometimes work with older versions, but this is not guaranteed.

This plugin works with rehype-parse version 3+, rehype-stringify version 3+, rehype version 5+, and unified version 6+.

Security

This package is safe.

Related

Contribute

See contributing.md in rehypejs/.github for ways to get started. See support.md for ways to get help.

This project has a code of conduct. By interacting with this repository, organization, or community you agree to abide by its terms.

Notice

This project is not affiliated with GitHub.

License

MIT © Titus Wormer