如何使用 ASP.NET Core 上传大文件

最新推荐文章于 2025-04-25 11:54:21 发布

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最新推荐文章于 2025-04-25 11:54:21 发布

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分类专栏： .Net Core 文章标签： asp.net 后端 .NetCore

本文链接：https://blog.youkuaiyun.com/hefeng_aspnet/article/details/144507646

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之前有一篇文章介绍如何通过 ASP.NET core 的 API 上传文件，您可以参考链接：https://blog.youkuaiyun.com/hefeng_aspnet/article/details/144507488。文章将讨论如何处理上传大文件 [体积超过 2GB]。

相比小数据，上传大数据量数据需要一些技巧。首先，.NET MVC 框架对 IIS/Kestrel 做了一些限制。默认情况下，每个请求的体积仅为 28.6MB。如果你尝试超出限制，则会返回 http 状态代码：413 [Payload 太大]。对于 IIS，我们可以修改web.config来释放限制（maxAllowedContentLength）。对于 Kestrel，我们需要同时配置MaxReqeustBodySize和MultipartBodyLengthLimi t来释放更多体积。

其次，我们可能有两种方法来处理文件上传。我们在之前的文章中演示了使用缓冲（通过IFormFile）。但对于较大的文件，我们可能无法利用缓冲，并且可能很容易耗尽我们的资源（内存/磁盘）。因此，使用流式传输（通过MultipartReader）方式来处理这种情况是合理的。

在本篇文章中，我们修改了上传 API，使用流式传输方法来处理大容量文件。我们从客户端开始，客户端将向 API 提交请求：

RequestUpload.cs

// files: suppose we have a list of file paths
   // subDirectory: the sub-directory structure under root for storing
   public async Task<HttpResponseMessage> UploadFilesAsync(List<string> files, string subDirectory)
   {
       string boundary = $"--{DateTime.Now.Ticks:x}";
using var content = new MultipartFormDataContent(boundary);
   content.Headers.Add("ContentType", $"multipart/form-data, boundary={boundary}");
       foreach (var filePath in files)
       {
           content.Add(new StringContent(subDirectory, Encoding.UTF8), "subDirectory");

           using var stream = new FileStream(filePath, FileMode.Open, FileAccess.Read);
           var fileNameHash = Path.GetFileNameWithoutExtension(filePath) + "_" + Guid.NewGuid().ToString("N") + Path.GetExtension(filePath);
           content.Add(new StreamContent(stream), "files", fileNameHash);

       }

       // IHttpClientFactory, consider using factory would be more effeicecy
       var httpClient = new HttpClient();
       using HttpRequestMessage request = new(HttpMethod.Post, new Uri("{your file API uri}")) { Content = content };
       // fire the post with the MultipartFormDataContent to File API
       var result = await httpClient.SendAsync(request);

       return result;

   }

以下是使用 multipart/form-data 携带文件内容的 http post 请求的真实示例：

POST https://localhost:5001/devwfapi/api/form/uploadattachmentsonfly
200
45.84 s

POST /devwfapi/api/form/uploadattachmentsonfly HTTP/1.1
System: xxxxxxxx
AccessToken: ALwzpK59onuqtvZVTOEsMYbUSPAB-xVGc22RqCh8z0Y8HHkKV_w3MLmKnJE_ywj_Aw==
User-Agent: PostmanRuntime/7.29.2
Accept: */*
Cache-Control: no-cache
Postman-Token: 9edc5eb6-0397-4520-a03a-13212d1b6996
Host: localhost:5001
Accept-Encoding: gzip, deflate, br
Connection: keep-alive
Content-Type: multipart/form-data; boundary=--------------------------156313382635509050530525
Content-Length: 444312365

----------------------------156313382635509050530525
Content-Disposition: form-data; name="subDirectory"
\path1\path2
----------------------------156313382635509050530525
Content-Disposition: form-data; name="files"; filename="OnScreenControl_7.58.zip"
<OnScreenControl_7.58.zip>
----------------------------156313382635509050530525
Content-Disposition: form-data; name="files"; filename="InstallDivvy.exe"
<InstallDivvy.exe>
----------------------------156313382635509050530525
Content-Disposition: form-data; name="files"; filename="PowerToysSetup-0.64.0-x64.exe"
<PowerToysSetup-0.64.0-x64.exe>
----------------------------156313382635509050530525
Content-Disposition: form-data; name="files"; filename="2022 Scrum Sharing PPT.pdf"
<2022 Scrum Sharing PPT.pdf>
----------------------------156313382635509050530525
Content-Disposition: form-data; name="files"; filename="VSCodeUserSetup-x64-1.72.2.exe"
<VSCodeUserSetup-x64-1.72.2.exe>
----------------------------156313382635509050530525--

您应该注意“ Content-Length ”部分下的结构。因为我们将不再依赖IFormFile (缓冲模型绑定)。对于MultipartReader (流式传输)，我们需要自己解析内容部分。

接下来，我们将演示如何通过 API 端使用 MultiparReader。但首先我们需要完成以下帮助类：

MultipartRequestHelper.cs

public static class MultipartRequestManager
   {
// get the boundary information, for above exmaple would be: --------------------------156313382635509050530525
       public static string GetBoundary(MediaTypeHeaderValue contentType)
       {
           var boundary = HeaderUtilities.RemoveQuotes(contentType.Boundary).Value;

           if (string.IsNullOrWhiteSpace(boundary))
           {
               throw new InvalidDataException("Missing content-type boundary.");
           }
           return boundary;
       }

// validate if it was multipart form data
       public static bool IsMultipartContentType(string contentType)
       {
           return !string.IsNullOrEmpty(contentType)
               && contentType.IndexOf("multipart/", StringComparison.OrdinalIgnoreCase) >= 0;
       }

       public static bool HasFormDataContentDisposition(ContentDispositionHeaderValue contentDisposition)
       {
           // for exmaple, Content-Disposition: form-data; name="subdirectory";
           return contentDisposition != null
               && contentDisposition.DispositionType.Equals("form-data")
               && string.IsNullOrEmpty(contentDisposition.FileName.Value)
               && string.IsNullOrEmpty(contentDisposition.FileNameStar.Value);
       }

       public static bool HasFileContentDisposition(ContentDispositionHeaderValue contentDisposition)
       {
           // for example, Content-Disposition: form-data; name="files"; filename="OnScreenControl_7.58.zip"
// ...
           return contentDisposition != null
               && contentDisposition.DispositionType.Equals("form-data")
               && (!string.IsNullOrEmpty(contentDisposition.FileName.Value)
                   || !string.IsNullOrEmpty(contentDisposition.FileNameStar.Value));
       }
   }

// we disable automatic model binding for MVC default behavior than to the access streaming directly
   [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method)]
   public class DisableFormValueModelBindingAttribute : Attribute, IResourceFilter
   {
       public void OnResourceExecuting(ResourceExecutingContext context)
       {
           var factories = context.ValueProviderFactories;
           factories.RemoveType<FormValueProviderFactory>();
           factories.RemoveType<JQueryFormValueProviderFactory>();
       }

       public void OnResourceExecuted(ResourceExecutedContext context)
       {
       }
   }

需要提一下的是，如果您的文件API向公众开放，那么您必须更加关心可能发生的安全性和病毒威胁。

最后我们将完成文件上传功能 API：

FileController.cs

[Route("api/[controller]")]
   public class FileController : ControllerBase
   {
       [HttpPost("uploadlarge")]
       [DisableFormValueModelBinding]
       public async Task<IActionResult> UploadLargeFileAsync()
       {
           try
           {
               if (!MultipartRequestHelper.IsMultipartContentType(Request.ContentType))
               {
                   throw new FormatException("Form without multipart content.");
               }

               var subDirectory = string.Empty;
               var count = 0;
               var totalSize = 0L;
// find the boundary
               var boundary = MultipartRequestHelper.GetBoundary(MediaTypeHeaderValue.Parse(Request.ContentType));
// use boundary to iterator through the multipart section
               var reader = new MultipartReader(boundary, HttpContext.Request.Body);

               var section = await reader.ReadNextSectionAsync();
               do
               {
                   ContentDispositionHeaderValue.TryParse(section.ContentDisposition, out var contentDisposition);
                   if (!MultipartRequestHelper.HasFileContentDisposition(contentDisposition))
                   {
                       if (MultipartRequestHelper.HasFormDataContentDisposition(contentDisposition) && contentDisposition.Name == nameof(subDirectory))
                       {
                           using var streamReader = new StreamReader(section.Body, Encoding.UTF8);
// get the subdirectory first
                           subDirectory = streamReader.ReadToEnd();
                       }

                       section = await reader.ReadNextSectionAsync();
                       continue;
                   }
                   totalSize += await SaveFileAsync(section, subDirectory);

                   count++;
                   section = await reader.ReadNextSectionAsync();
               } while (section != null);

return Ok(new { Count = count, Size = SizeConverter(totalSize) });

           }
           catch (Exception exception)
           {
               return BadRequest($"Error: {exception.Message}");
           }
       }

       private async Task<long> SaveFileAsync(MultipartSection section, string subDirectory)
       {
           subDirectory ??= string.Empty;
           var target = Path.Combine("{root}", subDirectory);
           Directory.CreateDirectory(target);

var fileSection = section.AsFileSection();

           var filePath = Path.Combine(target, fileSection.FileName);
           using var stream = new FileStream(filePath, FileMode.Create, FileAccess.Write, FileShare.None, 1024);
           await fileSection.FileStream.CopyToAsync(stream);

return fileSection.FileStream.Length;
}

       private string SizeConverter(long bytes)
       {
           var fileSize = new decimal(bytes);
           var kilobyte = new decimal(1024);
           var megabyte = new decimal(1024 * 1024);
           var gigabyte = new decimal(1024 * 1024 * 1024);

           switch (fileSize)
           {
               case var _ when fileSize < kilobyte:
                   return $"Less then 1KB";
               case var _ when fileSize < megabyte:
                   return $"{Math.Round(fileSize / kilobyte, 0, MidpointRounding.AwayFromZero):##,###.##}KB";
               case var _ when fileSize < gigabyte:
                   return $"{Math.Round(fileSize / megabyte, 2, MidpointRounding.AwayFromZero):##,###.##}MB";
               case var _ when fileSize >= gigabyte:
                   return $"{Math.Round(fileSize / gigabyte, 2, MidpointRounding.AwayFromZero):##,###.##}GB";
               default:
                   return "n/a";
           }
       }
   }

我们在将子目录路径传递给 API 时做了一些小技巧。您会发现我们在内容顶部（MultipartFormDataContent 内）添加了“子目录”字符串。然后我们可以在 API 端检索第一部分。

其余部分，我们只需向我们的文件 API 发送上传请求，并在本地测试环境下比较缓冲与流式上传相同文件量。流式方法在处理较大文件方面具有优势，这一点并不令我们感到惊讶。