Async POST fails on WP7 and F#

When I do let! read = from.AsyncRead buf in F#, it blocks and doesn't return until the TCP socket is dead. Why? And how do I fix it?

Its code:

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 ()

It's being called from this code:

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

and requested over HTTP with this code from Windows Phone 7.1 emulator:

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());
	}
}

Unsuccessfully. The ResponseReady callback is never reached.

Meanwhile, this code works excellent:

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

I couldn't get Fiddler2 working with WP7.

EDIT: Welcome to a yak. I've moved onto greener pastures myself ;)

YOu should put the bytes into the before sending and using BufferStream INput output