xamarin 上的 HttpClient PostAsync 什么也不做

Question

I have a piece of code

var formContent =
    new FormUrlEncodedContent(new[]
    {
        new KeyValuePair<string, string>("grant_type", "password"),
        new KeyValuePair<string, string>("username", _userName),
        new KeyValuePair<string, string>("password", _password)
    });

var response = await InternalClient.PostAsync("/Token", formContent).ConfigureAwait(false);

It works fine when i use it in my desktop app, but this very same piece fails on Xamarin.Android. I can access my web site from emulators browser, so it's not the case of not having the connection between these two. Even more interesting part - GetAsync works absolutely fine. PostAsync always fails with TaskCancelledException because of timeout. All the PostAsync calls do not hit the server at all.
My activity where this is executed:

var isAuthSuccess = _mainClient.Authenticate();

isAuthSuccess.ContinueWith(task =>
{
    RunOnUiThread(() =>
    {
        if (isAuthSuccess.Result)
        {
            ReleaseEventHandlers();

            var nav = ServiceLocator.Current.GetInstance<INavigationService>();
            nav.NavigateTo("MainChatWindow", _mainClient);
        }

        button.Enabled = true;
    });
});

And the Authenticate method:

public async Task<bool> Authenticate()
{
    var getTokenOperation = new AsyncNetworkOperation<string>(GetTokenOperation);
    var token = await getTokenOperation.Execute().ConfigureAwait(false);

    if (getTokenOperation.IsCriticalFailure)
    {
        SetCriticalFailure(getTokenOperation.FailureReason);
    }

    if (getTokenOperation.IsFailure == false)
    {
        InternalClient.DefaultRequestHeaders.Add("Authorization", "Bearer " + token);
        return true;
    }

    else
    {
        AuthenticationFailEncounteredEvent("Authentication fail encountered: " + getTokenOperation.FailureReason);
        return false;
    }
}

Get token operation:

private async Task<string> GetTokenOperation()
{
    var formContent =
            new FormUrlEncodedContent(new[]
            {
                new KeyValuePair<string, string>("grant_type", "password"),
                new KeyValuePair<string, string>("username", _userName),
                new KeyValuePair<string, string>("password", _password)
            });

    var response = await InternalClient.PostAsync("/Token", formContent).ConfigureAwait(false);
    response.EnsureSuccessStatusCodeVerbose();

    var responseJson = await response.Content.ReadAsStringAsync();

    var jObject = JObject.Parse(responseJson);
    var token = jObject.GetValue("access_token").ToString();

    return token;
}

And the wrapper - AsyncNetworkOperation

public class AsyncNetworkOperation<T>
{
    public bool IsFailure { get; set; }

    public bool IsCriticalFailure { get; set; }

    public string FailureReason { get; set; }

    public bool IsRepeatable { get; set; }

    public int RepeatsCount { get; set; }

    public Func<Task<T>> Method { get; set; }

    public AsyncNetworkOperation(Func<Task<T>> method, int repeatsCount)
    {
        Method = method;
        IsRepeatable = true;
        RepeatsCount = repeatsCount;
    }

    public AsyncNetworkOperation(Func<Task<T>> method)
    {
        Method = method;
    }

    public async Task<T> Execute()
    {
        try
        {
            return await Method().ConfigureAwait(false);
        }

        ...exception handling logics
    }
}

Calling PostAsync right in the activity behaves the same - waits for quite a long time and then fails with TaskCancelledException because of timeout.

Answer 1

For all the struggling with the same issue - this is related to SSL (self signed cert in my case). If you are trying to connect to your server via HTTPS - try using plain HTTP first, my app can work with HTTP fine while HTTPS hangs to death.

Answer 2

I have had other problems with PostAsync() also and it is also not as customizable as SendAsync() in terms of editing the headers and things like that. I would recommend SendAsync() :

HttpRequestMessage  request = new HttpRequestMessage(HttpMethod.Post, "/Token") { Content = formContent };
HttpResponseMessage message = await InternalClient.SendAsync(request, HttpCompletionOption.ResponseContentRead).ConfigureAwait(false);