Handling a "400 Bad Request"

In my notes I have a URL which creates a “400 Bad Request” error and displays the following…

Bad Request
Your browser sent a request that this server could not understand.

1.) What exactly does that error mean?

2.) Should I have specific error-handling in my code to account for this?

3.) Any security holes I need to worry about?

IMHO the easiest and best way is to deal with these types of errors is to add a line to your htaccess file. eg.

ErrorDocument 400 /custom-error-page.php

or you could send them to “home” or “search” or “sitemap” etc.

If you wanted to get fancy you can pass a $_GET variable to the page.

What exactly is a 400 error?

How common is it?

In my notes, I saw that I had created one last summer, but that seemed to be by pure accident because I added a ‘%’ at the end of some URL. (Not something a user would normally do.)

I am wondering if this is obscure enough that I just don’t worry about it?

As mentioned above, the error displayed in my browser seemed good enough, but I just wasn’t sure if this was something like a 404 error where you definitely need a page to handle it or not.

“Bad Request” means a “bad http request”

If I understand correctly, I guess the most common would be when someone typoed a wrong URL eg. if you had
but they tried going to
they might get a 400 response

See, I would think they would get a 404 error instead.

I guess 400 and 404 are “cousins”?!

Anyways… do I need another custom handler, or can I assume the default is good enough - it was for me.

(Honestly, I have never seen a 400 until this summer, so it seems rather obscure to me.)

I imagine most of the 400s are script kiddies hoping to find a vulnerability eg.
hoping to see your “outside of root” info

If you already have a custom 404 page I think sending 400s there as well would work.

The majority of HTTP status codes you probably won’t see in every-day web page serving, but there are quite a few that are used in APIs to provide more detailed responses to the client.

Thee 400 error codes is returned when you make a request to a valid URL, but with missing or malformed headers or parameters. It’s basically the server saying: “OK, you got the right URL, but you’re not making the request correctly”. Take a look at Microsoft’s Azure API docs for some examples of the conditions they return a 400 response for.

So should a person have a custom error page for each?

Currently I have one for 403 and 404, but if there are dozens of codes, then I sorta don’t want to bother right now unless it is important.

If you’re not creating an API and your site only serves web pages then I’d say you probably don’t need it - I’ve never come across one before on a normal website.

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