Developers: David Colgan helps you escape 9-to-5 employment by building an effective freelance business you'll love to run.

One day Gregor Samsa woke to find he had been used to determine the character limit of text boxes

Takeaway: Check the length of form field inputs!

Once I was doing a livestream making a website called "Internet Flamewar" in front of a squirrely audience. The idea was to submit two things and then argue why one was better than the other in a sort of Reddit-style comments system. Vim vs Emacs. Cats vs Dogs. Stuffed lambs vs stuffed frogs. Important stuff ya know?

Despite the fact that this was a horrible idea for a website because it would quickly become a steaming cesspool of horrible comments, I also made a wee little mistake with the code. I was creating the database table for a comment, and used this Django class:

class Comment(models.Model):
    user = models.ForeignKey(User)
    body = models.TextField()
    date = models.DateField()

Can you spot the problem?

It was made clear to me when I put the site up and the viewers of my livestream descended upon it. The first rule of launching a new website is that someone is definitely going to try to break your site immediately. I looked at some of the posts people were making and then discovered a page that had a bit of a formatting problem.

Someone had decided to try pasting the entirety of Kafka's Metamorphosis into the comment box.

They just went to and copied all 121,177 characters of the book's text and shoved it right up into my database. And the database happily saved every last character.

The solution was simple: Just add a length limit to the body field.

class Comment(models.Model):
    user = models.ForeignKey(User)
    # Add max_length to the body field:
    body = models.TextField(max_length=255)
    date = models.DateField()

So please, validate the max length of your form fields. And not only in Javascript on the browser for that matter!

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