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Getting a token from an external web API is returning system.threading.tasks

I'm successfully getting a token back from my GetAccessToken() and GetAccessTokenAsync methods, but the token isn't retrieved until after the main method of GetCourses, which won't work because that's the method that collects the data I need to show on my cshtml page. I've tried pulling apart this controller and creating a Globals class that will house just the URIs, apiKey, and token, but then I read that's bad practice for MVC so I ditched that effort. It was getting called after the GetCourses method anyway, so it was dead end too.
I'm newer to MVC and come from a WebForms background where I was used to being able to throw this kind of code in my PageInit, but am struggling to figure out how to pull this off in MVC. Can someone help me figure out what I am doing wrong or if I need to go about this a different way?
public ActionResult GetCourses()
{
TempData["EthosURI"] = "redacted";
TempData["Token"] = GetAccessToken().ToString();
IEnumerable<Course> courses = null;
using (var client = new HttpClient())
{
client.BaseAddress = new Uri((string)TempData["EthosURI"]);
client.DefaultRequestHeaders.Add("Authorization", "Bearer {" + (string)TempData["Token"] + "}");
client.DefaultRequestHeaders.Add("Accept", "application/json");
//HTTP GET
var responseTask = client.GetAsync("courses");
responseTask.Wait();
var result = responseTask.Result;
if (result.IsSuccessStatusCode)
{
var readTask = result.Content.ReadAsAsync<IList<Course>>();
readTask.Wait();
courses = readTask.Result;
}
else //web api sent error response
{
//log response status here..
courses = Enumerable.Empty<Course>();
ModelState.AddModelError(string.Empty, "Server error. Please contact administrator.");
}
}
return View(courses);
}
public static async Task<string> GetAccessToken()
{
var token = await GetAccessTokenAsync("redactedUrl", "redactedAPIKey");
return token;
}
public static async Task<string> GetAccessTokenAsync(string ethosURI, string apiKey)
{
using (var client = new HttpClient())
{
client.BaseAddress = new Uri(ethosURI);
client.DefaultRequestHeaders.Accept.Clear();
HttpRequestMessage request = new HttpRequestMessage
{
Method = HttpMethod.Post,
RequestUri = new Uri(ethosURI)
};
request.Headers.Clear();
request.Headers.Add("Authorization", $"Bearer {apiKey}");
request.Headers.Add("Accept", "application/json");
request.Headers.CacheControl = new CacheControlHeaderValue() { NoCache = true };
var response = await client.SendAsync(request);
response.EnsureSuccessStatusCode();
return await response.Content.ReadAsStringAsync();
}
}

The (non-blocking) way in C# to wait for a task to complete is to use the await keyword. And for a method to use the await keyword, it has to be marked async. By using await, you not only wait for the task to complete, but also the current thread is not blocked. Wrapping an asynchronous operation in another method would not make it synchronous. In other words, the asynchronous nature propagates up the call hierarchy and the caller has to await. So, the GetAccessToken() still has to be awaited. A controller action can be marked asynchronous as well, so you probably want:
public async Task<ActionResult> GetCourses()
{
TempData["EthosURI"] = "redacted";
TempData["Token"] = (await GetAccessToken()).ToString(); // note the additional parentheses
....
Note the additional parantheses above before calling ToString(). However, since GetAccessToken() already returns a string, you don't need the redundant ToString() call:
TempData["Token"] = await GetAccessToken();
Now, you can also change this:
var readTask = result.Content.ReadAsAsync<IList<Course>>();
readTask.Wait();
courses = readTask.Result;
to just:
courses = await result.Content.ReadAsAsync<IList<Course>>();
Microsoft has quite good documentation on asynchronous programming and I would recommend checking it out.

That's not how async works in C#. You need either to make GetCourses() async AND await for GetAccessToken(), or use dirty hack GetAccessToken().GetAwaiter().GetResult() but it may become not safe in certain circumstances.

HttpResponseMessage to string

I am calling a method of which returns Task, in the calling method I need to read the response in form of string.
Here's the code that I have put:
static public async Task<HttpResponseMessage> Validate(string baseUri,HttpContent content) {
HttpResponseMessage response = new HttpResponseMessage();
response = await client.PostAsync(baseUri,content);
return response;
}
public string test(){
string postJson = "{Login = \"user\", Password = \"pwd\"}";
HttpContent stringContent = new StringContent(postJson,
UnicodeEncoding.UTF8, "application/json");
HttpResponseMessage result=Validate(Uri,stringContent);
var json = result.Content.ReadAsStringAsync().Result;
}
I expect string but this error is thrown:
Cannot implicitly convert type
'System.Threading.Tasks.Task<System.Net.Http.HttpResponseMessage>' to
'System.Net.Http.HttpResponseMessage'

Your problem is at:
HttpResponseMessage result=Validate(Uri,stringContent);
Validate is returning a task, not a HttpResponseMessage.
Change that to:
var result = Validate(Uri,stringContent).Result;
Just to clean up the code a bit and avoid using Result if you can afford to change it like:
static public async Task<HttpResponseMessage> Validate(string baseUri, HttpContent content)
{
return await client.PostAsync(baseUri,content);
}
public async Task<string> test()
{
var postJson = "{Login = \"user\", Password = \"pwd\"}";
var stringContent = new StringContent(postJson, UnicodeEncoding.UTF8, "application/json");
var result = await Validate(Uri,stringContent);
return await result.Content.ReadAsStringAsync();
}
Be consistent with your coding style. As to why calling .Result is bad, as people are pointing out in the comments, check this blog.

Method Validate returns the task and is asynchronous. Basically you can call this method in two different ways:
1) await the result of Validate in another async method, like this...
public async Task<string> test() {
string postJson = "{Login = \"user\", Password = \"pwd\"}";
HttpContent stringContent = new StringContent(postJson,
UnicodeEncoding.UTF8, "application/json");
HttpResponseMessage result = await Validate(Uri,stringContent);
var json = result.Content.ReadAsStringAsync().Result;
}
2) block current execution while waiting for this resul, like this...
public string test() {
string postJson = "{Login = \"user\", Password = \"pwd\"}";
HttpContent stringContent = new StringContent(postJson,
UnicodeEncoding.UTF8, "application/json");
HttpResponseMessage result = Validate(Uri,stringContent).Result;
var json = result.Content.ReadAsStringAsync().Result;
}
Choose the 1st way by default unless you really have an urge to block the calling thread.
Note that when using 2nd solution in WinForms, WPF or ASP.NET apps you will probably have a deadlock. modifying Validate method like this should solve the problem:
response = await client.PostAsync(baseUri,content).ConfigureAwait(false);

Just for readability change the method name from Validate(..) to ValidateAsync(..). Just to make clear that this method returns a task and you have to await it.
You're missing an await when calling your Validate method. If you do not want or can make the caller async then use the method GetAwaiter().GetResult() and you'll get what you want.
Replace ReadAsStringAsync().Result with ReadAsStringAsync().GetAwaiter().GetResult()
Like others wrote in comments calling .Result is bad because it could cause locks. The same applies in general to GetAwaiter().GetResult() but calling them is preferred over calling Result. The best option is to use await/async.
When you want to know whats the difference between GetAwaiter().GetResult() vs calling Result you can read this:
Is Task.Result the same as .GetAwaiter.GetResult()?

You can easily write:
var json = result.Content.ReadAsStringAsync().GetAwaiter().GetResult();

Async function call issue

I am working on a Windows Phone application. While invoking the below function, after executing this line:
HttpResponseMessage response = await client.GetAsync(connection1).ConfigureAwait(false);
it skips the rest of the code and control goes to the parent function and execute the rest of the code there and come back to this function again. How to fix this problem?
public async void vehicleValidation()
{
//isValidVehicle = true;
var client = new System.Net.Http.HttpClient();
//string connection = "http://mymlcp.co.in/mlcpapp/get_slot.php?vehiclenumber=KL07BQ973";
string connection1 = string.Format("http://mymlcp.co.in/mlcpapp/?tag=GetIsValidUser&employeeId={0}&name={1}",txtVeh.Text,"abc");
HttpResponseMessage response = await client.GetAsync(connection1).ConfigureAwait(false);
//var response = await client.GetAsync(connection1);
// HttpResponseMessage response = client.GetAsync(connection1).Result;
var cont = await response.Content.ReadAsStringAsync();
var floorObj = Newtonsoft.Json.Linq.JObject.Parse(cont);
//var resp = await (new MLCPClient()).GetIsValidUser(txtVeh.Text, "xyz");
if (String.IsNullOrEmpty(floorObj["error"].ToString()) || floorObj["error"].ToString().Equals("true"))
{
isValidVehicle = false;
}
else
{
isValidVehicle = true;
}
}

You should never have async void unless you are writing a event handler, you need to make your function return a Task and then await the function in your parent function.
Read "Async/Await - Best Practices in Asynchronous Programming" for a introduction on the best practices like never doing async void and making your code "async all the way"

How to collect the returned value of an awaited method in a variable in another method

So I am trying to grab the source code from a url and here is my code:
public async Task<string> grabPageHtml(Uri pageUrl)
{
var request = WebRequest.Create(pageUrl) as HttpWebRequest;
request.Method = "GET";
WebResponse responseObject = await Task<WebResponse>.Factory.FromAsync(
request.BeginGetResponse,
request.EndGetResponse, request);
var responseStream = responseObject.GetResponseStream();
var sr = new StreamReader(responseStream);
received = sr.ReadToEndAsync().Result;
return received;
}
The code works correctly and returns the sourcecode. The problem is assigning "received" to a string variable in another method.
Tried this:
string pageHtml = grabPageHtml(pageUrl)
but pageHtml outputs System.Threading.Tasks.Task'1[System.String] to the console instead of the source code.

pageHtml outputs System.Threading.Tasks.Task1[System.String]` to the
console instead of the source code.
That's because your method returns a Task<string>, not a string. You need to extract that string result somehow. It should be:
public async Task FooAsync()
{
string pageHtml = await GrabPageHtmlAsync(pageUrl);
Console.WriteLine(pageHtml);
}
As a side note, don't block on async code. Using Task.Result may lead to deadlocks. Also, using HttpClient would make your code a bit cleaner, removing the need to call FromAsync:
public Task<string> GrabPageHtmlAsync(Uri pageUrl)
{
var httpClient = new HttpClient();
return httpClient.GetStringAsync(pageUrl);
}

Async await pattern help. Am I doing it right?

I have a "api" e.g. repository pattern, I wrote to return xml from the web and then hydrate it to classes.
It seems to hang on the result of the GetXmlAsync(url) method.
public async Task<string> GetXmlAsync(string url)
{
string xml = string.Empty;
HttpMessageHandler handler = new HttpClientHandler();
HttpClient httpClient = new HttpClient(handler);
Uri uri = new Uri(url, UriKind.Absolute);
HttpResponseMessage response = await httpClient.GetAsync(uri);
xml = await response.Content.ReadAsStringAsync();
return xml;
}
But when I use the same code in a unit test, it works.
In the app, I call it like so:
public async Task<IEnumerable<Post>> GetRecentAsync(int page)
{
string url = this.urls.GetRecent(page);
string xml = string.Empty;
var xmlTask = this.loader.GetXmlAsync(url);
xml = xmlTask.Result; // Hangs right here.
var results = this.modelLoader.XmlToPost(xml);
if (results.Count() < 1)
{
this.LastError = XmlLoadError;
}
return results.AsEnumerable();
}
[TestMethod]
public async Task Integration_HttpLoader_GetXmlAsync_GetRecent_Xml_ShouldNotBeNullOrEmpty()
{
int page = 1;
string xml = string.Empty;
IUrl url = this.GetUrlHelper();
ILoader loader = this.GetIntegrationLoader(false);
xml = await loader.GetXmlAsync(url.GetRecent(page));
Assert.IsTrue(!string.IsNullOrEmpty(xml));
}

In your app, you are not preceding the call to this.loader.GetXmlAsync(url) with await You hit this line, fire an async task on another thread then immediately proceed to the next line without having ever gotten the response. It works in your unit test because you correctly use the await keyword.

You are causing a deadlock by synchronously blocking on the result of the task.
Follow these best practices:
Do not block on async code (make it async all the way down).
e.g., var xml = await this.loader.GetXmlAsync(url); in GetRecentAsync.
Use ConfigureAwait(false) in your "library" async methods if they can continue on a thread pool thread.
e.g., var response = await httpClient.GetAsync(uri).ConfigureAwait(false); and xml = await response.Content.ReadAsStringAsync().ConfigureAwait(false); in GetXmlAsync.