URL shortener

Web application that takes a URL as an input and generates a “short-url” for it (similar to bitly.com). Output URL should be short, readable and able to be easily copy-pasted by users.

Constraints:

URL parameters should be considered part of the URL uniqueness test.
A generated short URL should expire if not accessed for 14 or more days
Persist data in data store
Handle error cases

live app

Running application should be available on http://shuri.ajur.pl/

Please note it's running on free heroku plan, so performance and actual db size is heavily limited. Direct url to heroku in case of dns issues with custom domain: https://ajur-url-shortener.herokuapp.com/

spec

web page

Minimalistic, single page, responsive application, with one input for entering url, and submit button labeled Shorten.

Shortening done asynchronously. Input blocked until got response.

Successfully shortened URL replaces shortened url, possibly auto-selected. Shorten button changes to Copy button, allowing coping shortened URL to user's clipboard.

Errors are displayed as stylized text under input.

Any input modification changes Copy button back to Shorten and removes all error messages.

shortening

Original URL is validated for syntax, but it's not verified for existing endpoint.

Shortened URL is short (lets assume 5 characters), unique and readable (only lowercase letters). URL query parameters are considered in uniqueness test.

Passing already shortened URL results with an error.

Shortening URL that is already shortened, and not yet expired, should return same result.

redirecting

Shortened URL can be accessed withing 14 days from last access.

Request to shortened URL should redirect browser to location addressed with original URL.

Request to non existing URL return page not found error.

architecture

SPA

Single static HTML page
Vanilla JS, targeting only modern browsers (to avoid babel)
No front-end framework, to be ok with KISS and YAGNI principles
Minimalistic CSS
JS and CSS inlined? - No, but could be good idea, as well as minification

server

Newest Node.js with Express

Routes:

GET / serve index.html

uses ajax/fetch for async submit

POST / shorten url

validate URL
store new url in DB
send 200 on success, with response json {url: "original", short: "shortened"}
send 400 on validation failed

GET /:id attempt redirecting

get url from DB, if exists
send 301 with target location and simply html body when found
send 404 when url not found

db

Simple key-value store with shortened id as key, and original URL as value.

Every value has 14 day expire time.

Each access resets expiration time back to 14 days.

Expired entries should be removed permanently.

Considering 5 length key of lowercase chars, we get almost 12 million distinct keys, that gives us (according to https://zelark.github.io/nano-id-cc/ ) around 8 minutes to hit 1% chance of duplicate, with 1/s generated keys. For this example, it should be enough, but some not-perfect way of handling duplicates would be to generate n+1 length key for each n length key that is duplicated.

ajur/url-shortener