在WP7和F#上异步POST失败

Question

当我在F#中执行 let! read = from.AsyncRead buf 时，它会阻塞并且直到 TCP socket 关闭才返回。为什么？如何解决这个问题？

代码：

module StreamUtil

open System.IO

/// copy from 'from' stream to 'toStream'
let (|>>) (from : Stream) (toStream : Stream) =
  let buf = Array.zeroCreate<byte> 1024
  let rec doBlock () =
    async {
      let! read = from.AsyncRead buf
      if read <= 0 then
        toStream.Flush()
        return ()
      else
        do! toStream.AsyncWrite(buf, 0, read)
        return! doBlock () }
  doBlock ()

这段代码调用了它：

use fs = new FileStream(targPath, FileMode.CreateNew, FileAccess.ReadWrite)
do! req.InputStream |>> fs

使用以下代码从Windows Phone 7.1模拟器请求HTTP：

public void Send()
{
    var b = new UriBuilder(_imageService.BaseUrl) {Path = "/images"};

    var req = WebRequest.CreateHttp(b.Uri);
    req.ContentType = "image/jpeg";
    req.Method = "POST";
    var imgLen = SelectedImage.ImageStream.Length;
    req.Headers[HttpRequestHeader.ContentLength] = imgLen.ToString(CultureInfo.InvariantCulture);
    req.Accept = "application/json";
    req.BeginGetRequestStream(RequestReady, new ReqState(req, imgLen));
}

void RequestReady(IAsyncResult ar)
{
    var state = (ReqState)ar.AsyncState;
    var req = state.Request;

    var reqStream = req.EndGetRequestStream(ar);

    SmartDispatcher.BeginInvoke(() =>
        {
            using (var sw = new StreamWriter(reqStream))
            using (var br = new BinaryReader(SelectedVoucher.ImageStream))
            {
                var readBytes = br.ReadBytes(state.ImgLen);

                // tried both 2
                sw.Write(readBytes);
                //sw.Write(Convert.ToBase64String(readBytes));
                sw.Flush();
                sw.Close();
            }
            req.BeginGetResponse(ResponseReady, req);
        });
}

// WHY IS IT YOU ARE NOT CALLED???
void ResponseReady(IAsyncResult ar)
{
    try
    {
        var request = (HttpWebRequest)ar.AsyncState;
        var response = request.EndGetResponse(ar);

        SmartDispatcher.BeginInvoke(() =>
            {
                var rdr = new StreamReader(response.GetResponseStream());
                var msg = rdr.ReadToEnd();

                var imageLocation = response.Headers["Location"];

                Debug.WriteLine(msg);
                Debug.WriteLine(imageLocation);
            });
    }
    catch (WebException ex)
    {
        Debug.WriteLine(ex.ToString());
    }
    catch (Exception ex)
    {
        Debug.WriteLine(ex.ToString());
    }
}

不成功。 ResponseReady 回调函数永远不会被触发。

与此同时，这段代码工作得非常好：

open System
open System.Net.Http // WebAPI nuget

let sync aw = Async.RunSynchronously aw

let postC<'a> (c : HttpClient) (r : Uri) (cont : HttpContent) =
  let response = sync <| Async.AwaitTask( c.PostAsync(r, cont) )
  let struc:'a = sync <| deserialize<'a> response
  response, struc

let withContent<'a> (fVerb : (HttpClient -> Uri -> HttpContent -> _ * 'a))=
  let c = new HttpClient()
  fVerb c

[<Test>]
let ``POST /images 201 + Location header`` () =
  let post = withContent<MyImage> postC
  let bytes = IO.File.ReadAllBytes("sample.jpg")
  let hash = SHA1.Create().ComputeHash(bytes) |> Convert.ToBase64String
  let pic = new ByteArrayContent(bytes)
  pic.Headers.Add("Content-Type", "image/jpeg")
  pic.Headers.Add("X-SHA1-Hash", hash)
  let resp, ri = (resource "/images", pic) ||> post

  resp.StatusCode =? Code.Created
  ri.sha1 =? hash
  mustHaveHeaders resp

我无法让Fiddler2在WP7上工作。

编辑：欢迎来到牦牛。我自己已经转移到更美好的领域了 ;)

- Henrik

---

如果 from.AsyncRead 阻塞，那意味着远程服务器没有发送任何字节。 - qehgt

我已经解决了流无法正确关闭的问题，但是在接收端仍然只能得到大小为40字节的文件，在WP上很多阻塞操作都会抛出NotSupportedException而不是不可用，所以调试非常痛苦。我会在找到完整解决方案后发布。 - Henrik

如果你正试图让 Fiddler 与移动设备配合使用，这篇文章可能对你有用：http://www.diaryofaninja.com/blog/2010/11/09/using-fiddler-to-sniff-mobile-device-application-traffic - Alpha

当您从TCP套接字请求无限数量的字节时，这不是预期行为吗？ - jyoung

这可能是一个愚蠢的额外问题，但在SmartDispatcher上是否应该有一个"EndInvoke"。我意识到它是一个匿名方法，但如果在异步操作中没有调用end，很多时候（我发现）它会一直锁定直到调用为止。 - iMortalitySX

Answer 1

在发送和使用BufferStream输入输出之前，您应该将字节放入其中。

- Jeff Bootsholz