Properly Abort or Cancel PostAsync

Question

Is there a guaranteed way to cancel a post when using HttpClient? I currently have a call do PostAsync that I am attempting to cancel using a cancellationToken, but it appears that it does not actually abort/stop the operation. I still can see that the image I am uploading is posted properly.

Am I doing something wrong here or is it possible that HttpClient is not processing the cancellation token until after the upload?

var sc = new StreamContent(uploadFile.Data);
content.Add(sc, uploadFile.FieldName, uploadFile.FileName);

var request = new HttpRequestMessage
{
    RequestUri = new Uri(ApiImageUrlUpload),
    Content = content
};

request.Headers.TryAddWithoutValidation("User-Agent", _sessionManager.UserAgent);
request.Headers.TransferEncodingChunked = true;

using(cancellationToken.Register(() => httpClient.CancelPendingRequests()))
    httpResponse = await HttpClient.PostAsync(new Uri(ApiImageUrlUpload), content, cancellationToken);

Answer 1

Try this code example

public partial class LoginForm : MaterialForm
    {
        static NLog.Logger logger = LogManager.GetLogger("LoginForm");
        HttpClient client;
        HttpResponseMessage response;

        public LoginForm()
        {
            InitializeComponent();

            materialLabelErrMessage.Visible = false;
        }

        #region GUI events
        private void BntCancel_Click(object sender, EventArgs e)
        {
            CancelLogin();
            Close();
        }

        private void BtnOK_Click(object sender, EventArgs e)
        {
            Login();
        }

        private void TextBoxPassword_KeyDown(object sender, KeyEventArgs e)
        {
            if (e.KeyCode == Keys.Enter)
            {
                Login();
            }

        }

        private void TextBoxUsername_KeyDown(object sender, KeyEventArgs e)
        {
            if (e.KeyCode == Keys.Enter)
            {
                Login();
            }
        }

        #endregion

        #region Keyboard Helpers
        protected override bool ProcessDialogKey(Keys keyData)
        {
            if (Form.ModifierKeys == Keys.None && keyData == Keys.Escape)
            {
                CancelLogin();
                Close();
                return true;
            }
            return base.ProcessDialogKey(keyData);
        }
        #endregion

        async void Login()
        {
            try
            {
                pbLogin.Visible = true;
                btnOK.Enabled = false;

                materialLabelErrMessage.Text = string.Empty;
                materialLabelErrMessage.Visible = false;

                client = new HttpClient();

                var user = new User() { Username = textBoxUsername.Text.Trim(), Password = StringUtils.Crypt(textBoxPassword.Text.Trim()) };

                var url = Properties.Settings.Default.ServerBaseUrl + @"/api/account/VerifyUserNamePassword";
                response = await client.PostAsync(url, user.AsJson());

                if (response.IsSuccessStatusCode)    // Check the response StatusCode
                {
                    var serSettings = new JsonSerializerSettings() { TypeNameHandling = TypeNameHandling.All };   
                    string responseBody = await response.Content.ReadAsStringAsync();

                    var loggedUser = JsonConvert.DeserializeObject<User>(responseBody, serSettings);

                    if (loggedUser.IsLogged == false && loggedUser.UserId == Guid.Empty)
                    {
                        logger.Warn(Properties.Resources.LOGINUsernameOrPasswordWrong + " Username:" + user.Username);

                        BeginInvoke((Action)(() =>
                        {
                            materialLabelErrMessage.Text = Properties.Resources.LOGINUsernameOrPasswordWrong;
                            materialLabelErrMessage.Visible = true;
                            pbLogin.Visible = false;
                            btnOK.Enabled = true;
                        }));
                    }
                    else
                    {
                        logger.Info(Properties.Resources.LOGINPassed + " Username:" + user.Username);

                        BeginInvoke((Action)(() =>
                        {
                            materialLabelErrMessage.Text = string.Empty;
                            materialLabelErrMessage.Visible = false;

                            Program.UserInfo = loggedUser;

                            DialogResult = DialogResult.OK;
                            pbLogin.Visible = false;

                        }));
                    }
                }
                else if (response.StatusCode == HttpStatusCode.Forbidden)
                {
                    pbLogin.Visible = false;
                    btnOK.Enabled = true;

                    materialLabelErrMessage.Text = Properties.Resources.LOGINUsernameOrPasswordWrong;
                    materialLabelErrMessage.Visible = true;
                    logger.Warn(Properties.Resources.LOGINUsernameOrPasswordWrong + " Username:" + user.Username);
                }
                else
                {
                    pbLogin.Visible = false;
                    btnOK.Enabled = true;

                    materialLabelErrMessage.Text = Properties.Resources.LOGINCannotConnectToServer;
                    materialLabelErrMessage.Visible = true;

                    logger.Error("Reason: " + response.ReasonPhrase + " Message: " + response.RequestMessage + " Username:" + user.Username);
                }
            }
            catch (ObjectDisposedException ex)
            {
                logger.Error("Login has been canceled. " + ex.Message);
                pbLogin.Visible = false;
                btnOK.Enabled = true;
            }
            catch (Exception ex)
            {
                logger.Error(Properties.Resources.LOGINUsernameOrPasswordWrong + " " + ex.Message);
                pbLogin.Visible = false;
                btnOK.Enabled = true;
            }
        }

        void CancelLogin()
        {
            if (client != null)
            { 
                client.CancelPendingRequests();
                client = null;
            }
        }
    }

Answer 2

You could dispose of the request object manually which should throw an ObjectDisposedException and cancel any network activity.