If you receive the ASP.NET error System.Web.HttpException: Maximum request length exceeded.” while trying to upload one or more files via HTTP, the cause is most likely a file uploading size limit that is set too low. The most accessible way to change this limit is through the web.config configuration file. Create this file if you don’t have it already, and after you open it add the following line inside the
<system.web> tags:

<system.web> tags: <httpRuntime maxRequestLength="102400" />

This will increase the file upload size through HTTP to 100MB (102400).

The System.Web.HttpException: Maximum request length exceeded error in ASP.NET often occurs during large file uploads. This error is a result of exceeding the default request size limit set in ASP.NET applications.

Understanding the Error

ASP.NET sets a default maximum request length to prevent excessively large uploads, which can strain server resources. When a file exceeds this limit, the server throws a System.Web.HttpException.

Solutions

Modifying Web.config

To resolve this, increase the maxRequestLength in the web.config file:

• Locate the web.config file in your ASP.NET project.
• Inside the <system.web> tags, add or modify the httpRuntime element:

<httpRuntime maxRequestLength="20480" />

This example sets the limit to 20 MB. Adjust the value based on your requirements.

IIS Configuration Changes

For applications hosted on IIS:

• Open IIS Manager.
• Select your website, and open the “Request Filtering” feature.
• In the “Edit Feature Settings” window, increase the “Maximum allowed content length” value.

Managing Large File Uploads

For very large files, consider:

• Implementing file chunking.
• Using third-party services or libraries designed for large file handling.

Code Examples

Example for a medium-sized file limit in web.config:

<httpRuntime maxRequestLength="40960" />

Error Handling

Handle this error by:

• Using try-catch blocks to catch the exception.
• Displaying a user-friendly error message or redirecting to an error page.

Performance and Security Considerations

• Increasing upload size can impact server performance. Monitor resource usage and adjust as needed.
• Implement security measures like file type restrictions and virus scanning on uploaded files.

Alternative Methods

Consider AJAX-based uploads for a more responsive user experience. Tools like DropzoneJS can facilitate this.

Best Practices

• Set realistic file size limits.
• Provide clear feedback to users on the allowed file sizes and types.
• Regularly review and update your upload handling strategy to ensure security and efficiency.

Conclusion

Managing file uploads in ASP.NET applications requires a balance between user needs, security, and server performance. By understanding and appropriately configuring settings, developers can efficiently handle large file uploads while maintaining a secure and robust application environment.