现在的问题是,当使用 WebApi 2 和基于 Async ApiController 的 Get 方法时,它会返回文件的内容。当我将 Get 方法更改为同步时,它工作得很好,但一旦我将其转换回异步,它就会过早地关闭流。 (Fiddler 报告连接已中止)工作的同步代码是:
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());
}
}
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);
}
}
--------异步代码------------
异步版本完全相同,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();
}
使用 GetDownloadStream 的异步实现如下:(streamToCopyTo 是来自 response.OutputStream 的 OutputStream)
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);
}
}
我们正在尝试从头到尾采用异步/等待模式,所以希望有人知道为什么会失败?我也试过不调用 Response.End()、Response.Flush() 和 HttpContext.Current.ApplicationInstance.CompleteRequest()。此外,为了回应下面的问题/评论,我在 response.End() 上放置了一个断点,结果是它没有被命中到 GetDownloadStream 方法已经完成。也许 OutputStream 不是异步的?欢迎任何想法! 谢谢
************************** 最终解决方案 ******************* ********
非常感谢所有发表评论的人,尤其是@Noseratio 对 FileOptions.DeleteOnClose 的建议。
[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
}
GetDownloadStreamAsync 看起来像这样:
FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.None, BufferSize, FileOptions.DeleteOnClose | FileOptions.Asynchronous);
我忽略了我也在动态解密文件流,这确实有效,所以对于那些感兴趣的人......
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);
最佳答案
需要一个完整的重现案例才能回答您的确切问题,但我认为您根本不需要 async/await
。我还认为您应该尽可能避免直接使用 HttpContext.Current.Response
,尤其是在异步 WebAPI Controller 方法中。
在这种特殊情况下,您可以使用 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;
}
这里没有明确的异步,所以方法不是async
。但是,如果您仍然需要引入一些 await
,方法将如下所示:
[HttpGet]
public async Task<HttpResponseMessage> Get(int id)
{
HttpResponseMessage result = new HttpResponseMessage(HttpStatusCode.OK);
// ...
await fs.CopyToAsync(streamToCopyTo)
// ...
return result;
}
关于C# Async ApiController 过早关闭 OutputStream,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/28439254/