Why after adding a header to HttpClientRequestMessage CancellationToken.IsCancellationRequested changes to true - httpclient

Question

I use custom HttpClientHandler to authorize test if it is not authorized.
Windows Store Unit Test App project type is used
using Microsoft.WindowsAzure.MobileServices;
using Newtonsoft.Json.Linq;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Windows.Security.Credentials;
using Windows.UI.Popups;
using XperiAndri.Efficiency.Common.Http.Handlers;
namespace XperiAndri.Efficiency.Common.Tests.Online
{
public class AuthenticationHandler : DelegatingHandler
{
private const string user = "";
private const string password = "";
private const string MobileServiceAuthenticationTokenHeader = "X-ZUMO-AUTH";
private readonly PasswordVault vault = new PasswordVault();
public IMobileServiceClient Client { get; set; }
protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
HttpResponseMessage response = await base.SendAsync(request, cancellationToken);
if (response.StatusCode == HttpStatusCode.Unauthorized)
{
var headers = request.Headers;
PasswordCredential credential = FindCredential();
if (credential != null)
{
Client.CurrentUser = new MobileServiceUser(user) { MobileServiceAuthenticationToken = credential.Password };
headers.Remove(MobileServiceAuthenticationTokenHeader);
credential.RetrievePassword();
headers.Add(MobileServiceAuthenticationTokenHeader, credential.Password);
response = await base.SendAsync(request, cancellationToken);
}
if (response.StatusCode == HttpStatusCode.Unauthorized)
{
JObject content = new JObject { { "user", user }, { "password", password } };
var result = await Client.InvokeApiAsync("UnitTestLogin", content, HttpMethod.Post, null);
string token = result["token"].Value<string>();
if (Client.CurrentUser != null)
Client.CurrentUser.MobileServiceAuthenticationToken = token;
else
Client.CurrentUser = new MobileServiceUser(user) { MobileServiceAuthenticationToken = token };
headers.Remove(MobileServiceAuthenticationTokenHeader);
headers.Add(MobileServiceAuthenticationTokenHeader, token); // After execution of this line cancellationToken.IsCancellationRequested changes to true
// try again!
response = await base.SendAsync(request, cancellationToken);
if (response.StatusCode != HttpStatusCode.Unauthorized)
{
if (credential != null)
credential.Password = token;
else
{
credential = new PasswordCredential(Client.ApplicationUri.ToString(), user, token);
vault.Add(credential);
}
}
}
}
return response;
}
private PasswordCredential FindCredential()
{
try
{
return vault.FindAllByResource(Client.ApplicationUri.ToString()).FirstOrDefault();
}
catch
{
return null;
}
}
}
}
Look at the comment at the line
headers.Add(MobileServiceAuthenticationTokenHeader, token);
the second time it is executed.
Can somebody explain why does it happened? Why request becomes cancelled?

Answer 1

You're trying to add header to request after actually receiving response (since you already awaited SendAsync) which logically is not possible and causes cancellation of original request.