.NET 8 中 使用 IFormFile 上传大文件报错解决方案

前言：

项目中使用 IFormFile写了一个上传文件的api，测试小文件时正常，当上传大文件（几十兆）时如下报错：
使用默认的http启动，如下提示

使用IIS启动，如下报错
Error: Request Entity Too Large

原因：

.NET官方出于安全考虑，对body的大小做了限制，超出了限制就会form转化失败，导致我们Reuest.Form为空，最终抛出异常，解决办法也很简单，根据你的启动方式，主要分为三个方面

1. IIS content length limit

The default request limit (maxAllowedContentLength) is 30,000,000 bytes, which is approximately 28.6MB. Customize the limit in the web.config file:

<system.webServer>
  <security>
    <requestFiltering>
      <!-- Handle requests up to 1 GB -->
      <requestLimits maxAllowedContentLength="1073741824" />
    </requestFiltering>
  </security>
</system.webServer>

Note: Without this application running on IIS would not work.

2. ASP.NET Core Request length limit:

For application running on IIS:

 builder.Services.Configure<IISServerOptions>(options =>
 {
      options.MaxRequestBodySize = int.MaxValue;
 });

For application running on Kestrel:

builder.Services.Configure<KestrelServerOptions>(options =>
{
     options.Limits.MaxRequestBodySize = int.MaxValue; // if don't set default value is: 30 MB
});

3. Form's MultipartBodyLengthLimit

builder.Services.Configure<FormOptions>(x =>
{
     x.ValueLengthLimit = int.MaxValue;
     x.MultipartBodyLengthLimit = int.MaxValue; // if don't set default value is: 128 MB
     x.MultipartHeadersLengthLimit = int.MaxValue;
});