WebAPI StreamContent与PushStreamContent
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)
{
}
回答：
关于这两种方法的内存使用情况，对于StreamContent和PushStreamContent，Web
API不会缓冲响应。以下代码快照来自WebHostBufferPolicySelector。源代码
。
/// <summary> /// Determines whether the host should buffer the <see cref="HttpResponseMessage"/> entity body.
/// </summary>
/// <param name="response">The <see cref="HttpResponseMessage"/>response for which to determine
/// whether host output buffering should be used for the response entity body.</param>
/// <returns><c>true</c> if buffering should be used; otherwise a streamed response should be used.</returns>
public virtual bool UseBufferedOutputStream(HttpResponseMessage response)
{
if (response == null)
{
throw Error.ArgumentNull("response");
}
// Any HttpContent that knows its length is presumably already buffered internally.
HttpContent content = response.Content;
if (content != null)
{
long? contentLength = content.Headers.ContentLength;
if (contentLength.HasValue && contentLength.Value >= 0)
{
return false;
}
// Content length is null or -1 (meaning not known).
// Buffer any HttpContent except StreamContent and PushStreamContent
return !(content is StreamContent || content is PushStreamContent);
}
return false;
}
另外，PushStreamContent适用于需要将数据“推”到流中的场景，当StreamContent从流中“拉”数据时。因此，对于当前的文件下载情况，使用StreamContent应该可以。
以下示例：
// Here when the response is being written out the data is pulled from the file to the destination(network) streamresponse.Content = new StreamContent(File.OpenRead(filePath));
// Here we create a push stream content so that we can use XDocument.Save to push data to the destination(network) stream
XDocument xDoc = XDocument.Load("Sample.xml", LoadOptions.None);
PushStreamContent xDocContent = new PushStreamContent(
(stream, content, context) =>
{
// After save we close the stream to signal that we are done writing.
xDoc.Save(stream);
stream.Close();
},
"application/xml");
以上是 WebAPI StreamContent与PushStreamContent 的全部内容， 来源链接： utcz.com/qa/424237.html
