About

An Uniform Resource Locator (URL) is a universal identifier for a resource.

Because the resource can be created dynamically, an URL is also logically a request.

It's the string that is understood by a browser when you put it in the address bar.

When the HTTP protocol is used as scheme, it's a identifier for a Web resource.

An URL was originally created to provide a method for finding an item such as a person's street address.

On a format level, the URL is a subset of an URI.

Syntax

scheme://[user-info@]host[:port]/path?query#fragment

where:

• scheme is the scheme and defines the access protocol that can be:
  • http or https defines the HTTP protocol (and we will make HTTP request)
  • file defines the local file system (and will make call to the local OS)
• user-info is optional and defines the credential (not used with the file scheme)
• host[:port]] defines the endpoint (not used with the file scheme)
• path is the path to the resource
• query is the query string
• fragment is the fragment that identify a part in the resource.

Shortener

An URL shortener is an application that creates a shorter URL.

Typically:

• the URL is added to a table with a numerical id
• with optionally a hash of the URL (to fasten the lookup by hash URL)
• the numerical id is used in the new shorten version

http://do.com/id

The numerical id based on the decimal system is generally converted to a greater base (ie above 10 with characters ) making it shorter. The hashid library being the most known example.

How to create an identifier

You can create unique same-length identifier via hashing

How to get the url of the actual HTML page with Javascript

See Browser URL

Canonical

See HTML - Canonical URL

Documentation / Reference

• W3C URL specification
• The W3C URL specification defines the term URL, various algorithms for dealing with URLs, and an API for constructing, parsing, and resolving URLs.
• HTML5 URL parsing