Building a URL Shortener with Redis

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Introduction

In this tutorial, we’ll build a simple URL shortener using Redis and Python. The short URL service will generate a random short code for each URL, store it in Redis, and allow users to retrieve the original URL using the short code. We’ll also implement an expiration time for each shortened URL, making it expire after a specified period.

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Environment Setup

First, install the necessary dependencies, including Upstash Redis and python-dotenv for environment variables:

pip install upstash-redis

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Database Setup

Create a Redis database using the Upstash Console or Upstash CLI, and export the UPSTASH_REDIS_REST_URL and UPSTASH_REST_TOKEN to your environment:

export UPSTASH_REDIS_REST_URL=<YOUR_URL>
export UPSTASH_REST_TOKEN=<YOUR_TOKEN>

You can also use python-dotenv to load environment variables from a .env file:

UPSTASH_REDIS_REST_URL=<YOUR_URL>
UPSTASH_REDIS_REST_TOKEN=<YOUR_TOKEN>

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Application Setup

In this example, we will build a URL shortener where each short URL will be stored in Redis with an expiration time.

Create url_shortener.py:

import string
import random
from upstash_redis import Redis
from dotenv import load_dotenv
import os

# Load environment variables
load_dotenv()

# Redis connection
redis = Redis.from_env()

# Characters to generate the short URL from
CHARS = string.ascii_letters + string.digits
BASE_URL = "https://short.url/"

# Function to generate a random string for the short URL
def generate_short_code(length=6):
    return ''.join(random.choices(CHARS, k=length))

# Function to shorten the URL with an expiration time
def shorten_url(url, expiration=3600):
    # Generate a random short code
    short_code = generate_short_code()
    # Save the short code in Redis
    redis.set(short_code, url, ex=expiration)
    return BASE_URL + short_code

# Function to get the original URL from the short URL
def get_original_url(short_code):
    return redis.get(short_code)

# Example usage
if __name__ == "__main__":
    original_url = "https://example.com/my-very-long-url"

    # Shorten the URL
    short_url = shorten_url(original_url, expiration=600)
    print(f"Shortened URL: {short_url}")

    # Get the original URL
    original_url = get_original_url(short_url.split("/")[-1])

    if original_url:
        print(f"Original URL: {original_url}")
    else:
        print("Short URL expired or not found")

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Running the Application

Simply run the Python script:

python url_shortener.py

This script will shorten a long URL, store the mapping in Redis, and print the shortened URL. It will then attempt to retrieve the original URL using the short code.

Here is an example output:

Shortened URL: https://short.url/0lSLFI
Original URL: https://example.com/my-very-long-url

To monitor your data in Redis, you can use the Upstash Console and check out the Data Browser tab.

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How to Use the URL Shortener for Web Applications

1. Extract the short code from the shortened URL (e.g., 0lSLFI).

2. Look up the original URL in Redis using that code.

3. Redirect the user to the original URL.

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Code Breakdown

1. Random Short Code Generation: The generate_short_code function creates a random string of characters (letters and digits) that will serve as the short code for the URL.

2. Storing in Redis: The shorten_url function takes the original URL and stores it in Redis using the randomly generated short code as the key. The ex parameter sets an expiration time (in seconds) for how long the shortened URL will be valid.

3. Retrieving the Original URL: The get_original_url function takes the short code and looks it up in Redis to retrieve the original URL. If the short code doesn’t exist (due to expiration or other reasons), it returns None.

4. Expiration Handling: If the short code has expired, Redis automatically removes the entry, and the script will print a message indicating that the URL has expired or cannot be found.