Asp.net Core 2.0 RequestSizeLimit特性不生效，文件超30MB返回404

Hey there! Let's dig into this file upload issue you're hitting. That 404 error when uploading files over 30MB is tricky because it often hides the real problem—usually a combination of server-side limits that aren't fully configured. Here's how to tackle each possible culprit step by step:

1. Configure ASP.NET Core's Form Request Limits #

First, make sure your app is set to accept larger multipart form requests (since file uploads use multipart/form-data).

• In your Startup.cs ConfigureServices method, add this to adjust form options:

  services.Configure<FormOptions>(options =>
  {
      // Set to 100MB (adjust the value as needed)
      options.MultipartBodyLengthLimit = 104857600;
      options.ValueLengthLimit = 104857600;
  });
  

• Apply a size limit directly to your upload action using attributes:

  [HttpPost("upload")]
  [RequestSizeLimit(104857600)] // Enforce 100MB limit
  // Or use [DisableRequestSizeLimit] for no upper bound (not recommended for production)
  public async Task<IActionResult> Upload(IFormFile file)
  {
      // Your upload logic here
  }
  

2. Adjust Kestrel Server Limits #

ASP.NET Core 2.0 uses Kestrel as the default web server, and it has a default 30MB request body limit—this is almost certainly why you're hitting that exact threshold!

Update your Program.cs to increase this limit:

public static IWebHost BuildWebHost(string[] args) =>
    WebHost.CreateDefaultBuilder(args)
        .UseStartup<Startup>()
        .UseKestrel(options =>
        {
            // Set max request body size to 100MB
            options.Limits.MaxRequestBodySize = 104857600;
        })
        .Build();

3. If Deployed to IIS: Adjust IIS-Specific Limits #

If you're running your app on IIS, there are two more settings to tweak in your web.config:

a. Request Filtering Limit #

Add this under <system.webServer> to allow larger content lengths:

<system.webServer>
  <security>
    <requestFiltering>
      <!-- 100MB in bytes -->
      <requestLimits maxAllowedContentLength="104857600" />
    </requestFiltering>
  </security>
</system.webServer>

b. ASP.NET Core Module Timeout #

Large uploads can take longer—prevent timeouts by adding requestTimeout to the <aspNetCore> node:

<aspNetCore processPath="dotnet" arguments=".\YourApp.dll" stdoutLogEnabled="false" stdoutLogFile=".\logs\stdout" requestTimeout="00:02:00" />

4. Validate Your Ajax Upload Code #

Double-check that your Ajax request isn't adding unintended limits, and is properly formatted for file uploads:

function uploadMedia(isPhoto) {
    var formData = new FormData();
    var fileInput = document.getElementById('yourFileInputId');
    if (fileInput.files.length > 0) {
        formData.append('file', fileInput.files[0]);
    }

    $.ajax({
        url: '/api/media/upload', // Match your controller route
        type: 'POST',
        data: formData,
        processData: false, // Critical: don't process the form data
        contentType: false, // Critical: let the browser set the correct content type
        timeout: 120000, // 2 minutes to match IIS request timeout
        success: function(response) {
            console.log('Upload successful:', response);
        },
        error: function(xhr, status, error) {
            console.error('Upload failed:', xhr.status, error);
            // Check xhr.responseText for detailed error messages
        }
    });
}

Make sure you're not setting any custom maxFileSize parameters in your JS that might block larger files before they reach the server.

5. Check Logs for the Real Error #

That 404 might be a red herring—sometimes servers return 404 when they actually reject a request for being too large. Enable logging to see the true issue:

• In Startup.cs, add logging to capture request errors:

  public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
  {
      loggerFactory.AddConsole(LogLevel.Debug);
      loggerFactory.AddDebug();
  
      if (env.IsDevelopment())
      {
          app.UseDeveloperExceptionPage();
      }
      else
      {
          app.UseExceptionHandler("/Home/Error");
      }
  
      // Rest of your middleware configuration
  }
  

• Check the logs for messages like Request body too large—this will confirm which limit is still blocking your uploads.

Final Tip #

Restart your app and server after making these changes—config updates often require a restart to take effect.

内容的提问来源于stack exchange，提问作者Slade