Troubleshooting File Upload Error: 413 Request Body Too Large in .NET Core

Troubleshooting File Upload Error: 413 Request Body Too Large in .NET Core

When working with file uploads in .NET Core, you might encounter the 413 "Request Body Too Large" error even if the maxAllowedContentLength value in your web.config file is correctly set. This issue can be perplexing, especially when all configurations seem to be in place. In this blog, we will explore a common cause of this error related to the ASPNETCORE_TEMP environment variable and how to resolve it.

Understanding the Issue

The 413 error indicates that the request body size exceeds the server's configured limit. Typically, this is controlled by the maxAllowedContentLength setting in the web.config file. However, if the ASPNETCORE_TEMP environment variable is incorrectly set, it can lead to this error despite having the correct maxAllowedContentLength value.

Scenario

Let's consider a scenario where the maxAllowedContentLength in the web.config file is set to 50 MB, but the application still throws a 413 error for files larger than 10 MB. Upon investigation, it is found that the ASPNETCORE_TEMP environment variable is incorrectly configured in the launchSettings.json file.

Steps to Resolve the Issue

1. Verify maxAllowedContentLength in web.config: Ensure that the maxAllowedContentLength value in your web.config file is correctly set according to your requirements. For example:

   <system.webServer>

       <security>

           <requestFiltering>

               <requestLimits maxAllowedContentLength="52428800" />

           </requestFiltering>

       </security>

   </system.webServer>

1. Check ASPNETCORE_TEMP Environment Variable: The ASPNETCORE_TEMP environment variable specifies the location where ASP.NET Core stores temporary files, such as those used for buffering large request bodies. If this variable is incorrectly set, it can cause the 413 error.
2. Update launchSettings.json: Ensure that the ASPNETCORE_TEMP environment variable is correctly configured in the launchSettings.json file. Here is an example of how to set it:

   {

       "profiles": {

           "IIS Express": {

               "commandName": "IISExpress",

               "launchBrowser": true,

               "environmentVariables": {

                   "ASPNETCORE_ENVIRONMENT": "Development",

                   "ASPNETCORE_TEMP": "C:\\Temp\\ASPNETCORE"

               }

           },

           "YourProjectName": {

               "commandName": "Project",

               "dotnetRunMessages": true,

               "launchBrowser": true,

               "applicationUrl": "https://localhost:5001;http://localhost:5000",

               "environmentVariables": {

                   "ASPNETCORE_ENVIRONMENT": "Development",

                   "ASPNETCORE_TEMP": "C:\\Temp\\ASPNETCORE"

               }

           }

       }

   }

1. Verify the Temporary Directory: Ensure that the directory specified in the ASPNETCORE_TEMP environment variable exists and has the necessary permissions for the application to write temporary files.

Example Case

In a recent support case, the maxAllowedContentLength was set to 50 MB in the web.config file, but the application was still throwing a 413 error for files larger than 10 MB. Upon checking, it was found that the ASPNETCORE_TEMP environment variable was set to an incorrect path in the launchSettings.json file. Correcting the path resolved the issue.

Conclusion

By ensuring that the ASPNETCORE_TEMP environment variable is correctly set and the maxAllowedContentLength value in the web.config file is appropriate, you can resolve the 413 "Request Body Too Large" error in your .NET Core application. Proper configuration of these settings ensures smooth handling of large file uploads without encountering size-related errors.

If you have any further questions or need additional assistance, feel free to reach out!