C＃異步ApiController過早關閉OutputStream

Question

今天的問題是，當使用WebApi 2和基於異步ApiController的Get方法時，它返回文件的內容。當我將Get方法更改爲同步時，它工作得很好，但只要我將其轉換回異步，它就會過早關閉流。 （提琴手報告連接已中止）工作同步代碼：

public void Get(int id) 
    { 
     try 
     { 
      FileInfo fileInfo = logic.GetFileInfoSync(id); 
      HttpResponse response = HttpContext.Current.Response; 
      response.Clear(); 
      response.ClearContent(); 
      response.Buffer = true; 
      response.AddHeader("Content-Disposition", "attachment; filename=\"" + fileInfo.Node.Name + fileInfo.Ext + "\""); 
      response.AddHeader("Content-Length", fileInfo.SizeInBytes.ToString()); 
      response.ContentType = "application/octet-stream"; 
      logic.GetDownloadStreamSync(id, response.OutputStream); 
      response.StatusCode = (int)HttpStatusCode.OK; 
      //HttpContext.Current.ApplicationInstance.CompleteRequest(); 
      response.End(); 
     } 
     catch(Exception ex) 
     { 
      Console.WriteLine(ex.ToString()); 
     } 
    } 

而且GetDownloadStreamSync如下：

public async Task GetDownloadStream(string fileIdentifier, Stream streamToCopyTo) 
{ 
    string filePath = Path.Combine(fileIdentifierFolder, fileIdentifier); 
    using (FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.None, BufferSize, false)) 
    { 
     fs.CopyTo(streamToCopyTo); 
    } 
} 

--------異步代碼----- -----

的異步版本是完全一樣的，除了：

public async Task Get(int id) 
{ 
    FileInfo fileInfo = await logic.GetFileInfoSync(id); // database opp 
      HttpResponse response = HttpContext.Current.Response; 
      response.Clear(); 
      response.ClearContent(); 
      response.Buffer = true; 
      response.AddHeader("Content-Disposition", "attachment; filename=\"" + fileInfo.Node.Name + fileInfo.Ext + "\""); 
      response.AddHeader("Content-Length", fileInfo.SizeInBytes.ToString()); 
      response.ContentType = "application/octet-stream"; 
      await logic.GetDownloadStreamSync(id, response.OutputStream); 
          //database opp + file I/O 
      response.StatusCode = (int)HttpStatusCode.OK; 
      //HttpContext.Current.ApplicationInstance.CompleteRequest(); 
      response.End(); 
} 

隨着異步執行GetDo的wnloadStream如下：（streamToCopyTo從response.OutputStream OutputStream的）

public async Task GetDownloadStream(string fileIdentifier, Stream streamToCopyTo) 
{ 
    using (FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.None, BufferSize, true)) 
    { 
     await fs.CopyToAsync(streamToCopyTo); 
    } 
} 

我們正試圖從正面擁抱異步/ AWAIT模式回來，所以希望有人意識到爲什麼會失敗？我也嘗試不調用Response.End（），Response.Flush（）和HttpContext.Current.ApplicationInstance.CompleteRequest（）。另外，爲了迴應下面的問題/評論，我在響應中放置了一個斷點.End（）的結果是它沒有被GetDownloadStream方法命中。也許OutputStream不是異步的？任何想法都歡迎！ 謝謝

**************************最終解決方案**************** ***********

非常感謝大家的評論，尤其是對@Noseratio對FileOptions.DeleteOnClose的建議。

[HttpGet] 
public async Task<HttpResponseMessage> Get(long id) 
{ 
     HttpResponseMessage result = new HttpResponseMessage(HttpStatusCode.OK); 
     Node node = await logic.GetFileInfoForNodeAsync(id); 

     result.Content = new StreamContent(await logic.GetDownloadStreamAsync(id)); 
     result.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream"); 
     result.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment") 
     { 
      FileName = node.Name + node.FileInfo.Extension 
     }; 
     result.Content.Headers.ContentLength = node.FileInfo.SizeInBytes; 
     return result 
} 

隨着GetDownloadStreamAsync看起來像這樣：

FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.None, BufferSize, FileOptions.DeleteOnClose | FileOptions.Asynchronous); 

我離開了，我也被解密上飛文件流，這不工作，所以對於那些有興趣...

FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.None, BufferSize, FileOptions.DeleteOnClose | FileOptions.Asynchronous); 
RijndaelManaged rm = new RijndaelManaged(); 
return new CryptoStream(fs, GetDecryptor(rm, password), CryptoStreamMode.Read); 

Answer 1

它會採取有一個完整的攝製情況回答您的具體問題，但我不認爲你需要async/await在這裏所有。我也認爲應儘可能避免直接使用HttpContext.Current.Response，尤其是在異步WebAPI控制器方法中。

在這種特殊情況下，你可以使用HttpResponseMessage：

[HttpGet] 
public HttpResponseMessage Get(int id) 
{ 
    HttpResponseMessage result = new HttpResponseMessage(HttpStatusCode.OK); 
    FileInfo fileInfo = logic.GetFileInfoSync(id); 

    FileStream fs = new FileStream(
     filePath, FileMode.Open, FileAccess.Read, FileShare.None, BufferSize, false); 

    result.Content = new StreamContent(fs); 
    result.Content.Headers.ContentType = 
     new MediaTypeHeaderValue("application/octet-stream"); 
    result.Content.Headers.ContentDisposition = 
     new ContentDispositionHeaderValue("attachment") 
     { 
      FileName = fileInfo.Node.Name + fileInfo.Ext 
     }; 
    result.Content.Headers.ContentLength = fileInfo.SizeInBytes; 

    return result; 
} 

這裏沒有明確的不同步，因此該方法不async。然而，如果你仍然需要引入一些await，方法想是這樣的：

[HttpGet] 
public async Task<HttpResponseMessage> Get(int id) 
{ 
    HttpResponseMessage result = new HttpResponseMessage(HttpStatusCode.OK); 
    // ... 
    await fs.CopyToAsync(streamToCopyTo) 
    // ... 
    return result; 
} 

Answer 2

問題的根源實際在於使用Response.End()。當你運行Async時，它將在流文件內容完成之前執行Response.End()。這在使用Sync版本時沒有看到，因爲Response.End()在完成流式傳輸文件內容之後纔會被調用。

Response.End()是一個特別糟糕的方式來說你正在處理，因爲它拋出一個TreadAbortException。相反，你應該使用HttpContext.Current.ApplicationInstance.CompleteRequest()

請參見本文的詳細信息Response.End, Response.Close, and How Customer Feedback Helps Us Improve MSDN Documentation