在ASP.NET Core 3.1中上传和下载大文件? [英] Uploading and Downloading large files in ASP.NET Core 3.1?

问题描述

我正在使用干净的体系结构来开发ASP.NET Core 3.1 API项目，并且具有以下类库(层):

I am working on an ASP.NET Core 3.1 API project using clean architecture and I have the following classlibs (tiers):

• 基础架构(安全性和上载助手等...)
• 持久性(DA层)
• 域(域模型)
• 应用程序(用例-业务逻辑)
• API(API项目作为我的启动项目)

我希望能够将大文件上传到服务器(例如文件大小为2Gb或更大)，然后下载它们，并希望这样做而不会造成将来的内存问题溢出等等.

I want to be able to upload large files to server (like 2Gb of file size or even more) and download them after that and want to do it without having future problems with memory overflowing and everything.

任何帮助将不胜感激.

推荐答案

如果文件很大，请不要在代码中使用byte[]或MemoryStream.仅当您下载/上传文件时，才对流进行操作.

If you have files that large, never use byte[] or MemoryStream in your code. Only operate on streams if you download/upload files.

您有两种选择:

• 如果您同时控制客户端和服务器，请考虑使用 tus 之类的方法. .NET有客户端和服务器实现.这可能是最简单，最可靠的选择.
• 如果使用HttpClient上传大文件，只需使用StreamContent类发送它们.同样，不要使用MemoryStream作为源，而是使用其他类似FileStream的源.
• 如果使用HttpClient下载大文件，则指定HttpCompletionOptions(例如var response = await httpClient.SendAsync(httpRequest, HttpCompletionOption.ResponseHeadersRead))非常重要.否则，HttpClient会将整个响应缓冲在内存中.然后，您可以通过var stream = response.Content.ReadAsStreamAsync()将响应文件作为流处理.

• If you control both client and server, consider using something like tus. There are both client- and server-implementations for .NET. This would probably the easiest and most robust option.
• If you upload large files with the HttpClient, simply use the StreamContent class to send them. Again, don't use a MemoryStream as source, but something else like a FileStream.
• If you download large files with the HttpClient, it is important to specify the HttpCompletionOptions, for example var response = await httpClient.SendAsync(httpRequest, HttpCompletionOption.ResponseHeadersRead). Otherwise, the HttpClient would buffer the entire response in memory. You can then process the response file as a stream via var stream = response.Content.ReadAsStreamAsync().

ASP.NET Core特定建议:

ASP.NET Core specific advice:

• 如果要通过HTTP POST接收文件，则需要增加请求大小限制:[RequestSizeLimit(10L * 1024L * 1024L * 1024L)]和[RequestFormLimits(MultipartBodyLengthLimit = 10L * 1024L * 1024L * 1024L)].另外，您需要禁用表单值绑定，否则整个请求将被缓冲到内存中.

• If you want to receive files via HTTP POST, you need to increase the request size limit: [RequestSizeLimit(10L * 1024L * 1024L * 1024L)] and [RequestFormLimits(MultipartBodyLengthLimit = 10L * 1024L * 1024L * 1024L)]. In addition, you need to disable the form value binding, otherwise the whole request will be buffered into memory:

   [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method)]
   public class DisableFormValueModelBindingAttribute : Attribute, IResourceFilter
   {
       public void OnResourceExecuting(ResourceExecutingContext context)
       {
           var factories = context.ValueProviderFactories;
           factories.RemoveType<FormValueProviderFactory>();
           factories.RemoveType<FormFileValueProviderFactory>();
           factories.RemoveType<JQueryFormValueProviderFactory>();
       }

       public void OnResourceExecuted(ResourceExecutedContext context)
       {
       }
   }

• 要从控制器返回文件，只需通过File方法将其返回即可，该方法接受流:return File(stream, mimeType, fileName);
• To return a file from a controller, simple return it via the File method, which accepts a stream: return File(stream, mimeType, fileName);

示例控制器将如下所示(请参见 https://docs.microsoft.com/zh-cn/aspnet/core/mvc/models/file-uploads?view=aspnetcore-3.1 (针对缺少的帮助程序类):

A sample controller would look like this (see https://docs.microsoft.com/en-us/aspnet/core/mvc/models/file-uploads?view=aspnetcore-3.1 for the missing helper classes):

private const MaxFileSize = 10L * 1024L * 1024L * 1024L; // 10GB, adjust to your need

[DisableFormValueModelBinding]
[RequestSizeLimit(MaxFileSize)]
[RequestFormLimits(MultipartBodyLengthLimit = MaxFileSize)]
public async Task ReceiveFile()
{
    if (!MultipartRequestHelper.IsMultipartContentType(Request.ContentType))
        throw new BadRequestException("Not a multipart request");

    var boundary = MultipartRequestHelper.GetBoundary(MediaTypeHeaderValue.Parse(Request.ContentType));
    var reader = new MultipartReader(boundary, Request.Body);

    // note: this is for a single file, you could also process multiple files
    var section = await reader.ReadNextSectionAsync();

    if (section == null)
        throw new BadRequestException("No sections in multipart defined");

    if (!ContentDispositionHeaderValue.TryParse(section.ContentDisposition, out var contentDisposition))
        throw new BadRequestException("No content disposition in multipart defined");

    var fileName = contentDisposition.FileNameStar.ToString();
    if (string.IsNullOrEmpty(fileName))
    {
        fileName = contentDisposition.FileName.ToString();
    }

    if (string.IsNullOrEmpty(fileName))
        throw new BadRequestException("No filename defined.");

    using var fileStream = section.Body;
    await SendFileSomewhere(fileStream);
}

// This should probably not be inside the controller class
private async Task SendFileSomewhere(Stream stream)
{
    using var request = new HttpRequestMessage()
    {
        Method = HttpMethod.Post,
        RequestUri = new Uri("YOUR_DESTINATION_URI"),
        Content = new StreamContent(stream),
    };
    using var response = await _httpClient.SendAsync(request);
    // TODO check response status etc.
}

在此示例中，我们将整个文件流式传输到另一个服务.在某些情况下，最好将文件临时保存到磁盘上.

In this example, we stream the entire file to another service. In some cases, it would be better to save the file temporarily to the disk.

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