我正在实施一个MVC4 + WebAPI版本的BluImp jQuery File
Upload，在我初次尝试时都可以很好地工作，但是Im试图确保在下载非常大的文件（〜2GB）的同时充分利用内存。

我已阅读Filip
Woj在PushStreamContent上的文章，并尽我所能实现了这一点（删除异步部分-
也许这是问题所在？）。当我运行测试并观看TaskManager时，我并没有看到明智的内存使用差异，而是试图了解响应处理方式之间的差异。

这是我的StreamContent版本：

private HttpResponseMessage DownloadContentNonChunked()
{
    var filename = HttpContext.Current.Request["f"];
    var filePath = _storageRoot + filename;
    if (File.Exists(filePath))
    {
        HttpResponseMessage response = new HttpResponseMessage(HttpStatusCode.OK);
        response.Content = new StreamContent(new FileStream(filePath, FileMode.Open, FileAccess.Read));
        response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
        response.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
        {
            FileName = filename
        };
        return response;
    }
    return ControllerContext.Request.CreateErrorResponse(HttpStatusCode.NotFound, "");
}

这是我的PushStreamContent版本：

public class FileDownloadStream
{
    private readonly string _filename;

    public FileDownloadStream(string filePath)
    {
        _filename = filePath;
    }

    public void WriteToStream(Stream outputStream, HttpContent content, TransportContext context)
    {
        try
        {
            var buffer = new byte[4096];

            using (var video = File.Open(_filename, FileMode.Open, FileAccess.Read))
            {
                var length = (int)video.Length;
                var bytesRead = 1;

                while (length > 0 && bytesRead > 0)
                {
                    bytesRead = video.Read(buffer, 0, Math.Min(length, buffer.Length));
                    outputStream.Write(buffer, 0, bytesRead);
                    length -= bytesRead;
                }
            }
        }
        catch (HttpException ex)
        {
            return;
        }
        finally
        {
            outputStream.Close();
        }
    }
}

private HttpResponseMessage DownloadContentChunked()
{
    var filename = HttpContext.Current.Request["f"];
    var filePath = _storageRoot + filename;
    if (File.Exists(filePath))
    {
        var fileDownload = new FileDownloadStream(filePath);
        var response = Request.CreateResponse();
        response.Content = new PushStreamContent(fileDownload.WriteToStream, new MediaTypeHeaderValue("application/octet-stream"));
        response.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
        {
            FileName = filename
        };
        return response;
    }
    return ControllerContext.Request.CreateErrorResponse(HttpStatusCode.NotFound, "");
}

我的问题是为什么两种方法的内存使用量没有太大差异？另外，我已经下载了适用于StreamContent类型的PDB，并且可以看到对缓冲区大小的引用等（请参见下文），因此我想确切地知道PushStreamContent在StreamContent之上和之外正在做什么。我已经检查了MSDN上的Type信息，但本文对解释的解释有点小！

namespace System.Net.Http
{
  /// <summary>
  /// Provides HTTP content based on a stream.
  /// </summary>
  [__DynamicallyInvokable]
  public class StreamContent : HttpContent
  {
    private Stream content;
    private int bufferSize;
    private bool contentConsumed;
    private long start;
    private const int defaultBufferSize = 4096;

    /// <summary>
    /// Creates a new instance of the <see cref="T:System.Net.Http.StreamContent"/> class.
    /// </summary>
    /// <param name="content">The content used to initialize the <see cref="T:System.Net.Http.StreamContent"/>.</param>
    [__DynamicallyInvokable]
    [TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")]
    public StreamContent(Stream content)
      : this(content, 4096)
    {
    }