How to Fix HTTP Error Code 400?
The 400 Bad Request Error is an HTTP response status code that indicates that the server was unable to process the request sent by the client due to invalid syntax. As with the dozens of potential HTTP response codes, receiving a 400 Bad Request Error while accessing your own application can be both frustrating and challenging to fix. Such HTTP response codes represent the complex relationship between the client, a web application, a web server, and often multiple third-party web services, so determining the cause of a particular status code can be a difficult, even within a controlled development environment.
Throughout this article we’ll examine the 400 Bad Request Error by digging into whether the root cause is on the local client or remote server. We’ll also go over a few tips and tricks to help you diagnose and debug your own application if it’s reporting a 400 Bad Request Error for some reason. Lastly, we’ll explore a handful of the most common content management systems (CMSs) that are in use today and provide you with some insight into potential problem areas within these systems that might cause an unexpected 400 Bad Request Error, so let’s get to it!
Server- or Client-Side?
All HTTP response status codes that are in the 4xx category are considered client error responses. These types of messages contrast with errors in the 5xx category, such as the 504 Gateway Timeout Error we looked at last week, which are considered server error responses. With that in mind, the appearance of a 4xx error doesn’t necessarily mean the issue has something to do with the client, where the client is the web browser or device being used to access the application. Oftentimes, if you’re trying to diagnose an issue with your own application, you can immediately ignore most client-side code and components, such as HTML, cascading style sheets (CSS), client-side JavaScript, and so forth. This doesn’t apply solely to web sites, either. Many smart phone apps that have a modern looking user interface are actually powered by a normal web application behind the scenes; one that is simply hidden from the user.
On the other hand, since a 400 Bad Request Error indicates that the request sent by the client was invalid for one reason or another, it’s entirely possible the issue steps from the client. Your client may be trying to send a file that’s too big, the request could be malformed in some way, the request HTTP headers could be invalid, and so forth. We’ll explore some of these scenarios (and potential solutions) down below, but be aware that, even though the 400 Bad Request Error is considered a client error response, it doesn’t inherently mean we can rule out either the client nor the server as the root of the problem. In these scenarios, the server is still the network object that is producing the 400 Bad Request Error, and returning it as the HTTP response code to the client, but it could be that the client is causing the issue in some way.
Start With a Thorough Application Backup
It’s always better to be safer rather than sorry. This is particularly true when making modifications to your own website or application. As such, it is critical that you perform a full backup of your application, database, and so forth, before attempting any fixes or changes to the system. Even better, if you have the capability, create a complete copy of the application onto a secondary staging server that isn’t “live,” or isn’t otherwise active and available to the public. This will give you a clean testing ground with which to test all potential fixes to resolve the issue, without threatening the security or sanctity of your live application.
Diagnosing a 400 Bad Request Error
A 400 Bad Request Error indicates that the server (remote computer) is unable (or refuses) to process the request sent by the client (web browser), due to an issue that is perceived by the server to be a client problem. There are a wide variety of scenarios in which a 400 Bad Request Error could appear in an application, but below are some of the most likely causes:
- The client may be accidentally (or intentionally) sending
deceptive request routinginformation. Some web applications/web servers look for custom HTTP headers to process requests and verify the client isn’t attempting anything malicious. If an expected custom HTTP header is missing or invalid, a400 Bad Request Erroris a likely result. - The client may be uploading a file that is too large. Most web servers or applications have an explicit file size limit that prevents files that are too big from being uploaded and clogging up bandwidth and other resources in the server. In many cases, the server will produce a
400 Bad Request Errorwhen a file is too large (and, thus, the request cannot be completed). - The client is accessing an invalid URL. If the client is sending a request to an invalid URL — particularly one that is malformed via improper characters — this could result in a
400 Bad Request Error. - The client is using an invalid or expired local cookie. Again, this could be malicious or accidental, but it’s possible that a local cookie in the web browser is identifying you via a
session cookie. If this particular session token matches the session token from another request from a different client, the server/application may see this is a malicious act and produce a400 Bad Request Errorcode.
Comments
Post a Comment