url-unshort

This library expands urls provided by url shortening services (see full list).

Why should I use it?

It has been argued that “shorteners are bad for the ecosystem as a whole”. In particular, if you're running a forum or a blog, such services might cause trouble for your users:

• such links load slower than usual (shortening services require an extra DNS and HTTP request)
• it adds another point of failure (should this service go down, the links will die; 301works tries to solve this, but it's better to avoid the issue in the first place)
• users don't see where the link points to (tinyurl previews don't really solve this)
• it can be used for user activity tracking
• certain shortening services are displaying ads before redirect
• shortening services can be malicious or be hacked so they could redirect to a completely different place next month

Also, short links are used to bypass the spam filters. So if you're implementing a domain black list for your blog comments, you might want to check where all those short links actually point to.

Installation

$ npm install url-unshort

Basic usage

const uu = require('url-unshort')()

try {
  const url = await uu.expand('http://goo.gl/HwUfwd')

  if (url) console.log('Original url is: ${url}')
  else console.log('This url can\'t be expanded')

} catch (err) {
  console.log(err);
}

Retrying errors

Temporary network errors are retried automatically once (options.request.retry=1 by default).

You may choose to retry some errors after an extended period of time using code like this:

const uu = require('url-unshort')()
const { isErrorFatal } = require('url-unshort')
let tries = 0

while (true) {
  try {
    tries++
    const url = await uu.expand('http://goo.gl/HwUfwd')

    // If url is expanded, it returns string (expanded url);
    // "undefined" is returned if service is unknown
    if (url) console.log(`Original url is: ${url}`)
    else console.log("This url can't be expanded")
    break

  } catch (err) {
    // use isErrorFatal function to check if url can be retried or not
    if (isErrorFatal(err)) {
      // this url can't be expanded (e.g. 404 error)
      console.log(`Unshort error (fatal): ${err}`)
      break
    }

    // Temporary error, trying again in 10 minutes
    // (5xx errors, ECONNRESET, etc.)
    console.log(`Unshort error (retrying): ${err}`)
    if (tries >= 3) {
      console.log(`Too many errors, aborting`)
      break
    }
    await new Promise(resolve => setTimeout(resolve, 10 * 60 * 1000))
  }
}

API

Creating an instance

When you create an instance, you can pass an options object to fine-tune unshortener behavior.

const uu = require('url-unshort')({
  nesting: 3,
  cache: {
    get: async key => {},
    set: async (key, value) => {}
  }
});

Available options are:

• nesting (Number, default: 3) - stop resolving urls when nesting amount of redirects is reached.

  It happens if one shortening service refers to a link belonging to another shortening service which in turn points to yet another one and so on.

  If this limit is reached, expand() will return an error.

• cache (Object) - set a custom cache implementation (e.g. if you wish to store urls in Redis).

  You need to specify 2 promise-based functions, set(key, value) & get(key).

• request (Object) - default options for got in .request() method. Can be used to set custom User-Agent and other headers.

uu.expand(url) -> Promise

Expand an URL supplied. If we don't know how to expand it, returns null.

const uu = require('url-unshort')();

try {
  const url = await uu.expand('http://goo.gl/HwUfwd')

  if (url) console.log('Original url is: ${url}')
  // no shortening service or an unknown one is used
  else console.log('This url can\'t be expanded')

} catch (err) {
  console.log(err)
}

uu.add(domain [, options])

Add a new url shortening service (domain name or an array of them) to the white list of domains we know how to expand.

uu.add([ 'tinyurl.com', 'bit.ly' ])

The default behavior will be to follow the URL with a HEAD request and check the status code. If it's 3xx, return the Location header. You can override this behavior by supplying your own function in options.

Options:

• aliases (Array) - Optional. List of alternate domaine names, if exist.
• match (String|RegExp) - Optional. Custom regexp to use for URL match. For example, if you need to match wildcard prefixes or country-specific suffixes. If used with validate, then regexp may be not precise, only to filter out noise. If match not passed, then exact value auto-generated from domain & aliases.
• validate (Function) - Optional. Does exact URL check, when complex logic required and regexp is not enouth (when match is only preliminary). See ./lib/providers/* for example.
• fetch (Function) - Optional. Specifies custom function to retrieve expanded url, see ./lib/providers/* for examples. If not set - default method used (it checks 30X redirect codes & <meta http-equiv="refresh" content='...'> in HTML).
• link_selector (String) - Optional. Some sites may return HTML pages instead of 302 redirects. This option allows use jquery-like selector to extract <a href="..."> value.

Example:

const uu = require('url-unshort')()

uu.add('notlong.com', {
  match: '^(https?:)//[a-zA-Z0-9_-]+[.]notlong[.]com/'
})

uu.add('tw.gs', {
  link_selector: '#lurllink > a'
})

uu.remove(domain)

(String|Array|Undefined). Opposite to .add(). Remove selected domains from instance config. If no params passed - remove everything.

Security considerations

Only http and https protocols are allowed in the output. Browsers technically support redirects to other protocols (like ftp or magnet), but most url shortening services limit redirects to http and https anyway. In case service redirects to an unknown protocol, expand() will return an error.

expand() function returns url from the url shortening as is without any escaping or even ensuring that the url is valid. If you want to guarantee a valid url as an output, you're encouraged to re-encode it like this:

var URL = require('url');

url = await uu.expand('http://goo.gl/HwUfwd')

if (url) url = URL.format(URL.parse(url, null, true))

console.log(url));

License

MIT