Customize Feed Parsing

By default, Feedcanon uses Feedsmith to parse feeds. You can use any feed parser by providing a custom parser that implements the adapter interface.

Interface

The parser option must implement ParserAdapter<T>:

type ParserAdapter<T> = {
  parse: (body: string) => MaybePromise<T | undefined>
  getSelfUrl: (parsed: T) => string | undefined
  getSignature: (parsed: T, url: string) => string
}

parse

Parse the feed body and return your feed type, or undefined if parsing fails. Both sync and async parsers are supported:

parse: (body: string) => MaybePromise<Feed | undefined>

getSelfUrl

Extract the self URL from the parsed feed. This is typically the atom:link rel="self" or similar declaration:

getSelfUrl: (feed: Feed) => string | undefined

getSignature

Return a string representing the feed's identity. Two feeds are treated as the same when their signatures are equal. Used to compare feeds when exact body matching fails:

getSignature: (feed: Feed, url: string) => string

The url argument is the URL the feed was fetched from. The default parser uses it to neutralize the feed's own URLs, so two copies that differ only in protocol, www or trailing slash still match. A custom parser can ignore it.

Build the signature from fields that stay the same between requests:

• Feed title and description
• Item GUIDs or URLs
• Item timestamps

Leave out fields that change with every request or with the URL the feed was fetched from, such as the build date or the self URL.

Examples

rss-parser

import { findCanonical } from 'feedcanon'
import Parser from 'rss-parser'

const rssParser = new Parser()

const url = await findCanonical('https://example.com/feed', {
  parser: {
    parse: (body) => rssParser.parseString(body).catch(() => undefined),
    getSelfUrl: (feed) => feed.feedUrl,
    getSignature: (feed) => {
      return JSON.stringify({
        title: feed.title,
        items: feed.items?.map((item) => item.guid),
      })
    },
  },
})