Correctly undo or undo PostAsync

Question

Is there a guaranteed way to cancel a message when using HttpClient? I currently have a PostAsync call that I am trying to cancel using cancelationToken, but it does not seem to actually interrupt / stop the operation. I still see that the image I am uploading is published correctly.

Am I doing something wrong here or is it possible that the HttpClient is not processing the cancel token before loading?

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

You can remove the request object manually, which should throw an ObjectDisposedException and discard any network activity.

Answer 2

Try this sample code.

 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; } } }