Develop Reference

C# Console App exits abruptly when calling async methods in Debug

It happens on Console and Windows Service apps, haven't tested on Windows Forms or WPF. When stepping thru the code whenever it hits an async call with await, the debug session exits abruptly, can't go further. As a workaround I'm using Task.Run() but changing all the async calls to use Task.Run() syntax during debug, and put it back to "await" syntax for deployment is a hassle.
Here in this method below, the following line is the issue during Debug, it works as expected when deployed.
var response = await httpClient.SendAsync(request);
Work around while debugging is to change the above line to this:
//var response = await httpClient.SendAsync(request);
var task = Task.Run(() => httpClient.SendAsync(request));
task.Wait();
var response = task.Result;
Code:
private static async Task<string> SendRequest()
{
string result = "";
string url = "http://localhost:5119/WeatherForecast";
var URL = new Uri(url);
var method = new HttpMethod("GET");
using (var request = new HttpRequestMessage(method, URL))
{
var response = await httpClient.SendAsync(request);
//var task = Task.Run(() => httpClient.SendAsync(request));
//task.Wait();
//var response = task.Result;
result = await response.Content.ReadAsStringAsync();
}
return result;
}

Async method calling async method and awaiting another method (http client)

I have some problem with async method.
public async void MakePost()
{
var cookieArray = GetCookies().Result;
(...)
}
async public Task<string[]> GetCookies()
{
(...)
var response = await httpClient.SendAsync(request);
string cookieTempSession = response.Headers.ToString();
(...)
return cookieArray;
}
Nothing happening after var response = await httpClient.SendAsync(request); I put breakpoint in next line string cookieTempSession = response.Headers.ToString(); but it never reach it. I tried to "try catch" but also nothing happend. When I merge this two methods into one it works perfect but it's not so pretty. I just wondering what happened there.

Since the first method is async, you should use await instead of Result:
var cookieArray = await GetCookies();
If you are not programming front end, add ConfigureAwait(false) (why?) to the call, like this:
var cookieArray = await GetCookies().ConfigureAwait(false);
...
var response = await httpClient.SendAsync(request).ConfigureAwait(false);

Deadlock on .Result from Web UI

I was reading the following topic http://blog.stephencleary.com/2012/07/dont-block-on-async-code.html
and decided to write a common utility method in my library to do a GET on remote url via HTTPClient
public static async Task<T> GetAsync<T>(HttpGetObject getObject)
{
string baseUrl = getObject.BaseUrl;
string actionUrl = getObject.ActionRelativeUrl;
string acceptType = getObject.AcceptType;
using (var client = new HttpClient())
{
client.BaseAddress = new Uri(baseUrl);
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue(acceptType));
AddCustomHeadersToHttpClient(client, getObject);
// HTTP GET
HttpResponseMessage httpResponseMessage = await client.GetAsync(actionUrl).ConfigureAwait(false);
if (httpResponseMessage.IsSuccessStatusCode)
{
T response = await httpResponseMessage.Content.ReadAsAsync<T>().ConfigureAwait(false);
return response;
}
else
{
string message = httpResponseMessage.Content.ReadAsStringAsync().Result;
throw new Exception(message);
}
}
return default(T);
}
I know the "await httpResponseMessage.Content.ReadAsAsync().ConfigureAwait(false)" will prevent the deadlock in the above code
First:
My query is for "string message = httpResponseMessage.Content.ReadAsStringAsync().Result" line, will .Result can cause deadlock or not in that line?
Second:
If I call that code from UI like this:
public static object DoGet()
{
// Build getObject
var task = Utility.GetAsync(getObject);
task.Wait();
var response = task.Result;
return response;
}
Will that cause a deadlock?
Please note that I know to avoid all the mess with async-await, all the methods from UI to DAL must be async-await but I am not in position at this moment to change all that structure, my goal at this moment is to call HttpClient library and do a few GET operations.
So my questions is that will the above code can cause a deadlock?
Third:
Is task.Wait(); even needed in the above code?

In the general case, you should assume that yes, calling .Result or .Wait() on anything awaitable is dangerous and can deadlock (unless you are the library issuing the task, and you understand the full context). It is possible that it will work OK in some specific cases, but you should not rely on that behaviour, even if it works today.

How can I get JSON data from Google API and store it in a variable?

I am trying to send an Http Get message to the Google location Api which is supposed to have Json data such as this
https://maps.googleapis.com/maps/api/geocode/json?address=Los%20Angeles,CA=AIzaSyDABt
as you noticed the response is in Json. I want to give a a Http Call to that URL and save the Json content in a variable or string. My code does not give out any errors but it is also not returning anything
public async System.Threading.Tasks.Task<ActionResult> GetRequest()
{
var client = new HttpClient();
HttpResponseMessage response = await client.GetAsync("https://maps.googleapis.com/maps/api/geocode/json?address=Los%20Angeles,CA=AIzaSyDABt");
string data = response.Content.ToString();
return data;
}
I want to send out a Get Request using HttpClient() or anything that will send out the URL request and then save that content into a string variable . Any suggestions would be appreciated, again my code gives no errors but it is not returning anything.

Use ReadAsStringAsync to get the json response...
static void Main(string[] args)
{
HttpClient client = new HttpClient();
Task.Run(async () =>
{
HttpResponseMessage response = await client.GetAsync("https://maps.googleapis.com/maps/api/geocode/json?address=Los%20Angeles,CA=AIzaSyDABt");
string responseString = await response.Content.ReadAsStringAsync();
Console.WriteLine(responseString);
});
Console.ReadLine();
}
If you use response.Content.ToString() it is actually converting the datatype of the Content to string so you will get System.Net.Http.StreamContent

Try this.
var client = new HttpClient();
HttpResponseMessage httpResponse = await client.GetAsync("https://maps.googleapis.com/maps/api/geocode/json?address=Los%20Angeles,CA=AIzaSyDABt");
string data = await httpResponse.Content.ReadAsStringAsync();

How about using the Json framework for .NET powered by Newtonsoft ?
You can try to parse your content to a string with this.

Well, your code can be simplified:
public async Task<ActionResult> GetRequest()
{
var client = new HttpClient();
return await client.GetStringAsync("https://maps.googleapis.com/maps/api/geocode/json?address=Los%20Angeles,CA=AIzaSyDABt");
}
However...
My code does not give out any errors but it is also not returning anything
This is almost certainly due to using Result or Wait further up the call stack. Blocking on asynchronous code like that causes a deadlock that I explain in full on my blog. The short version is that there is an ASP.NET request context that only permits one thread at a time; await by default will capture the current context and resume in that context; and since Wait/Result is blocking a thread in the request context, the await cannot resume executing.

Try this
public async static Task<string> Something()
{
var http = new HttpClient();
var url = "https://maps.googleapis.com/maps/api/geocode/json?address=Los%20Angeles,CA=AIzaSyDABt";
var response = await http.GetAsync(url);
if (response.IsSuccessStatusCode)
{
var result = await response.Content.ReadAsStringAsync();
result = JsonConvert.DeserializeObject<string>(result);
return result;
}
return "";
}
var result = Task.Run(() => Something()).Result;

Await in async request webapi 2 client

I am trying to understand await an async operation in asp.net MVC web api 2 client (console application). I believe I have done it wrong (due to lack of understanding await and async). It doesn't seem to run async. Here is code to understand the problem
//Main function
static void Main()
{
RunAsync().Wait();
}
//RunAsync
static async Task RunAsync()
{
using (var client = new HttpClient())
{
var apiUrl = ConfigurationManager.AppSettings["apiurl"];
client.BaseAddress = new Uri(apiUrl);
....some code to fetch data
foreach (var updateObject in updatedata)
{
HttpResponse response = await client.PostAsJsonAsync("webapimethod", updateObject);
if (response.IsSuccessStatusCode)
{
JArray content = await response.Content.ReadAsAsync<JArray>();
}
}
}
}
In the above code, foreach loop I am making request in loop as PostAsJsonAsync call and then I use ReadAsAsync to get response back but request always runs sync. not like fired and then when response arrives read the data.
It works fine but I want it to be async and not waiting on each request. How to achieve that or please explain await async in this context? Trying to read blogs and articles but I don't get how it will work.

The syntax you're probably looking for is this:
public async Task<JArray> GetContentAsync(... updateObject)
{
HttpResponse response = await client.PostAsJsonAsync("webapimethod", updateObject);
if (response.IsSuccessStatusCode)
{
return await response.Content.ReadAsAsync<JArray>();
}
}
Here your thread from the GetContentAsync() method will be put back on the threadpool while the client.PostAsJsonAsync is happening due to the await keyword.
Then you can create all the tasks in your method which calls it:
var updateData = fetchData();
var tasks = updateData.Select(d => GetContentAsync(d));
var result = (await Task.WhenAll(tasks)).ToList();
The Select will create a task for each of your result.
The await Task.WhenAll will unwrap the Task<JArray> and create a List<JArray>

You have to move foreach out of RunAsync method.
To get RunAsync in a foreach loop to work in async mode, you have to create several tasks and then call Task.WaitAll