Customize URL Rewrites

Rewrites transform known URLs before any other processing. They're useful for:

• Consolidating domain aliases to a single canonical domain
• Transforming platform-specific URL patterns
• Handling URL redirects at the domain level

Interface

Each rewrite has two methods:

type Rewrite = {
  match: (url: URL) => boolean
  rewrite: (url: URL) => URL
}

match

Return true if this rewrite should process the URL:

match: (url) => url.hostname === 'feeds.example.com'

rewrite

Transform the URL and return it. The URL object is mutable:

rewrite: (url) => {
  url.hostname = 'canonical.example.com'
  return url
}

Built-in

WARNING

No URL rewrites are enabled by default. To use built-in rewrites, you must explicitly pass them via the rewrites option.

FeedBurner

Transforms various FeedBurner domain aliases. Since FeedBurner URL structure is well-known, the rewrite also normalizes URLs (strips query params, trailing slashes, etc.):

From	To
https://feedproxy.google.com/example?format=xml	https://feeds.feedburner.com/example
https://feeds2.feedburner.com/example/	https://feeds.feedburner.com/example

Blogger / Blogspot

Transforms Blogger and Blogspot URLs to canonical form. Since Blogger/Blogspot URL structure is well-known, the rewrite also normalizes URLs:

From	To
https://example.blogspot.co.uk/feeds/posts/default	https://example.blogspot.com/feeds/posts/default
https://example.blogspot.de/atom.xml	https://example.blogspot.com/feeds/posts/default
http://blogger.com/feeds/123/posts/default	https://www.blogger.com/feeds/123/posts/default

Transformations applied:

• Country-specific TLDs (.blogspot.co.uk, .blogspot.de) → .blogspot.com
• Legacy paths (/atom.xml, /rss.xml) → /feeds/posts/default
• HTTP → HTTPS
• blogger.com → www.blogger.com
• Strips tracking params (redirect, alt=atom, v, pagination params)

Examples

Using Built-in Rewrites

import { findCanonical, feedburnerRewrite, bloggerRewrite } from 'feedcanon'

const url = await findCanonical('https://feedproxy.google.com/example', {
  rewrites: [feedburnerRewrite, bloggerRewrite],
})

Custom Domain Alias

import { findCanonical, feedburnerRewrite } from 'feedcanon'

const url = await findCanonical('https://old.example.com/feed', {
  rewrites: [
    feedburnerRewrite,
    {
      match: (url) => url.hostname === 'old.example.com',
      rewrite: (url) => {
        url.hostname = 'new.example.com'
        return url
      },
    },
  ],
})