docs/lib/redirects

Redirects

Docs redirects are complex! Some reasons why:

• Docs URLs have changed many times over the years, whether because docs team members have renamed individual articles or made global changes (e.g., moving all /articles to /github).
• Redirects can be hardcoded in frontmatter or generated via code in this directory (or both!).
• Live docs and archived docs require different redirect handling because they may have differently formatted URLs (e.g., legacy /enterprise/2.17 vs. modern /enterprise-server@2.22).

Read on for more about how redirects work under the hood.

Precompiled redirects

Precompiled redirects account for the majority of the docs site's redirect handling.

When lib/warm-server.js runs on server start, it creates all pages in the site by instantiating the Page class for each content file, then passes the pages to lib/redirects/precompile.js to create redirects. The precompile script runs lib/redirects/permalinks.js, which:

1. Includes all legacy redirects from static/developerjson
2. Loops over each page's frontmatter redirect_from entries and creates an array of legacy paths for each one (using the same handling as for permalinks).
3. Any other exceptions from the static/redirect-exceptions.txt file

The results comprise the page.redirects object, whose keys are always only the path without language. Sometimes it contains the specific plan/version (e.g. /enterprise-server@3.0/v3/integrations to enterprise-server@3.0/developers/apps) and sometimes it's just the plain path (e.g. /articles/viewing-your-repositorys-workflows to /actions/monitoring-and-troubleshooting-workflows)

All of the above are merged into a global redirects object. This object gets added to req.context via middleware/context.js and is made accessible on every request.

In the handle-redirects.js middleware, the language part of the URL is removed, looked up, and if matched to something, redirects with language put back in. Demonstrated with pseudo code:

var fullPath = '/ja/foo'
var newPath = redirects['/foo']
if (newPath) {
  redirect('/ja' + newPath)
}

Archived Enterprise redirects

Archived Enterprise redirects account for a much smaller percentage of redirects on the docs site.

Some background on archival: a snapshot of the HTML files for each deprecated Enterprise Server version is archived in a separate repo and proxied to docs.github.com via middleware/archived-enterprise-versions.js.

Starting with Enterprise Server 2.18, we updated the archival process to start preserving frontmatter and permalink redirects. But these redirects for 2.13 to 2.17 are not recoverable.

As a workaround for these lost redirects, we have two files in lib/redirects/static:

• archived-redirects-from-213-to-217.json

  This file contains keys equal to old routes and values equal to new routes (aka snapshots of permalinks at the time) for versions 2.13 to 2.17. (The old routes were generated via lib/redirects/get-old-paths-from-permalink.js.)

• archived-frontmatter-valid-urls.json

  This file is an object of VALID_URL to VALID_REDIRECT_SOURCES. E.g. "/enterprise/2.13/foo": ["/enterprise/2.13/bar", "/enterprise/2.13/buzz"] It was originally based on a previous file called archived-frontmatter-fallbacks.json which had a record of each possible redirect candidate that we should bother redirecting too. Now, this new file has been created by accurately comparing it to the actual content inside the github/help-docs-archived-enterprise-versions repo for the version range of 2.13 to 2.17. So every key in archived-frontmatter-valid-urls.json corresponds to a file that would work.

Here's how the middleware/archived-enterprise-versions.js fallback works: if someone tries to access an article that was updated via a now-lost frontmatter redirect (for example, an article at the path /en/enterprise/2.15/user/articles/viewing-contributions-on-your-profile-page), the middleware will first look for a redirect in archived-redirects-from-213-to-217.json. If it does not find one, it will look for it in archived-frontmatter-valid-urls.json that contains the requested path. If it finds it, it will redirect to it to because that file knows exactly which URLs are valid in help-docs-archived-enterprise-versions.

Tests

Redirect tests are mainly found in tests/routing/*, with some additional tests in tests/rendering/server.js.

The tests/fixtures/* directory includes developer-redirects.json, graphql-redirects.json, and rest-redirects.json.