Asynchronously using HttpWebRequest without blocking UI thread

Question

I am trying to use HttpWebRequest and HttpWebResonse asynchronously in a WinForms application without blocking my UI thread.

I saw this similar SO Question which explains how to do it. However, I am not 100% sure the accepted answer is the correct way to do it. The accepted answer is using BeginGetResponse.

According to the MSDN documentation:

The BeginGetResponse method requires some synchronous setup tasks to complete (DNS resolution, proxy detection, and TCP socket connection, for example) before this method becomes asynchronous. As a result, this method should never be called on a user interface (UI) thread because it might take some time, typically several seconds.

Can someone please provide me with the correct way to do this. Here is my C# function that I'm trying to make work "properly" without blocking my UI thread:

    private IDictionary<string, object> CreateWebRequest(string endPoint, string method, string data, bool addAuthHeader)
    {
        var req = (HttpWebRequest)WebRequest.Create(endPoint);
        req.Method = method;
        if (addAuthHeader)
        {
            req.Headers.Add(HttpRequestHeader.Authorization, "Bearer " + _accessToken.AccessToken);
        }

        if (!string.IsNullOrEmpty(data))
        {
            var utfenc = new UTF8Encoding();
            byte[] buffer = utfenc.GetBytes(data);
            req.ContentLength = buffer.Length;
            req.ContentType = "application/x-www-form-urlencoded";

            using (Stream strm = req.GetRequestStream())
            {
                strm.Write(buffer, 0, buffer.Length);
                strm.Close();
            }
        }

        HttpWebResponse response = null;
        try
        {
            response = (HttpWebResponse)req.GetResponse();
        }
        catch (WebException e)
        {
            if (_accessToken == null)
            {
                throw;
            }
            var responseError = (HttpWebResponse)e.Response;
            if (responseError.StatusCode == HttpStatusCode.Unauthorized)
            {
                var stackTrace = new StackTrace();
                var q = stackTrace.GetFrame(1).GetMethod().Name;
                RefreshAccessCode();

                req = (HttpWebRequest)WebRequest.Create(endPoint);
                req.Method = method;
                if (addAuthHeader)
                {
                    req.Headers.Add(HttpRequestHeader.Authorization, "Bearer " + _accessToken.AccessToken);
                }
                response = (HttpWebResponse)req.GetResponse();
            }
        }

        string jsonResponse = null;

        if (response != null)
            using (Stream stream = response.GetResponseStream())
            {
                if (stream != null)
                {
                    using (var reader = new StreamReader(stream))
                    {
                        jsonResponse = reader.ReadToEnd();
                    }
                }
            }

        return DeserializeResponse(jsonResponse);
    }

isn't @Isak's answer to the other SO question you linked what you're looking for? — vlad
– vlad, Commented Feb 26, 2013 at 21:14

Ray Saltrelli · Accepted Answer · 2013-02-26 21:35:51Z

3

If you're open to something besides WebRequest, I'm a fan of System.Net.WebClient. It uses System.Threading.Tasks instead of BeginGetResponse() and EndGetResonse().

public async Task<Dictionary<string, object>> CreateWebRequest(string endPoint, string method, string data, bool addAuthHeader)
{
    WebClient client = new WebClient();

    if (addAuthHeader)
    {
        client.Headers.Add(HttpRequestHeader.Authorization, "Bearer " + _accessToken.AccessToken);
    }

    byte[] buffer = null;

    if (!string.IsNullOrEmpty(data))
    {
        var utfenc = new UTF8Encoding();
        buffer = utfenc.GetBytes(data);
    }
    else
    {
        buffer = new byte[0];
    }

    return await client.UploadDataTaskAsync(endPoint, method, buffer)
        .ContinueWith((bytes) =>
            {
                string jsonResponse = null;

                using (var reader = new StreamReader(new MemoryStream(bytes)))
                {
                    jsonResponse = reader.ReadToEnd();
                }

                return DeserializeResponse(jsonResponse);
            });
    }
}

edited Feb 26, 2013 at 21:35

answered Feb 26, 2013 at 21:25

Ray Saltrelli

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1 Comment

Muhammad Abrar Over a year ago

It should be new MemoryStream(bytes.Result)

FlyingStreudel · Accepted Answer · 2013-02-26 21:11:15Z

0

To use your existing code, just add a method that is intended to execute on the UI thread, and create your web request on a separate thread. When the web request is complete you call the final method on the UI thread. So, a simple version would be:

//do some stuff that wont block the ui thread here
ThreadPool.QueueUserWorkItem((o) => 
{
    IDictionary<string, object> result = 
        CreateWebRequest("lalala", "lol", "butts", true);
    BeginInvoke(OnAsyncWebRequestComplete, result);
}, null);

private void OnAsyncWebRequestComplete(IDictionary<string, object> result)
{
    //do some stuff on the UI thread here
}

answered Feb 26, 2013 at 21:11

FlyingStreudel

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