Develop Reference

HttpClient GetAsync not working as expected

When testing my web API with Postman my API get executes fine!
When it comes to running the code with HttpClient in my client application the code executes without error but without the expected result on the server.
What could be happening?
From my client application:
private string GetResponseFromURI(Uri u)
{
var response = "";
HttpResponseMessage result;
using (var client = new HttpClient())
{
Task task = Task.Run(async () =>
{
result = await client.GetAsync(u);
if (result.IsSuccessStatusCode)
{
response = await result.Content.ReadAsStringAsync();
}
});
task.Wait();
}
return response;
}
Here is the API controller:
[Route("api/[controller]")]
public class CartsController : Controller
{
private readonly ICartRepository _cartRepo;
public CartsController(ICartRepository cartRepo)
{
_cartRepo = cartRepo;
}
[HttpGet]
public string GetTodays()
{
return _cartRepo.GetTodaysCarts();
}
[HttpGet]
[Route("Add")]
public string GetIncrement()
{
var cart = new CountedCarts();
_cartRepo.Add(cart);
return _cartRepo.GetTodaysCarts();
}
[HttpGet]
[Route("Remove")]
public string GetDecrement()
{
_cartRepo.RemoveLast();
return _cartRepo.GetTodaysCarts();
}
}
Note these API calls work as expected when called from Postman.

You shouldn't use await with client.GetAsync, It's managed by .Net platform, because you can only send one request at the time.
just use it like this
var response = client.GetAsync("URL").Result; // Blocking call!
if (response.IsSuccessStatusCode)
{
// Parse the response body. Blocking!
var dataObjects = response.Content.ReadAsAsync<object>().Result;
}
else
{
var result = $"{(int)response.StatusCode} ({response.ReasonPhrase})";
// logger.WriteEntry(result, EventLogEntryType.Error, 40);
}

You are doing fire-and-forget approach. In your case, you need to wait for the result.
For example,
static async Task<string> GetResponseFromURI(Uri u)
{
var response = "";
using (var client = new HttpClient())
{
HttpResponseMessage result = await client.GetAsync(u);
if (result.IsSuccessStatusCode)
{
response = await result.Content.ReadAsStringAsync();
}
}
return response;
}
static void Main(string[] args)
{
var t = Task.Run(() => GetResponseFromURI(new Uri("http://www.google.com")));
t.Wait();
Console.WriteLine(t.Result);
Console.ReadLine();
}

Simple sample used to get page data.
public string GetPage(string url)
{
HttpResponseMessage response = client.GetAsync(url).Result;
if (response.IsSuccessStatusCode)
{
string page = response.Content.ReadAsStringAsync().Result;
return "Successfully load page";
}
else
{
return "Invalid Page url requested";
}
}

I've had a problem with chace control when using httpclient.
HttpBaseProtocalFilter^ filter = ref new HttpBaseProtocolFilter();
filter->CacheControl->ReadBehavior = Windows::Web::Http::Filters::HttpCacheReadBehavior::MostRecent;
HttpClient^ httpClient = ref new HttpClient(filter);
I'm not really sure what the expected results are or what results your getting at all so this is really just a guessing game right now.
When I POST something using HttpClient I found adding headers by hand seemed to work more often than using default headers.
auto httpClient = ref new HttpClient();
Windows::Web::Http::Headers::HttpMediaTypeHeaderValue^ type = ref new Windows::Web::http::Headers::HttpMediaTypeHeaderValue("application/json");
content->Headers->ContentType = type;
If I don't do these 2 things I found, for me anyways, that half the time my web requests were either not actually being sent or the headers were all messed up and the other half of the time it worked perfectly.
I just read a comment where you said it would only fire once, that makes me think it is the cachecontrol. I think what happens is something (Windows?) sees 2 requests being sent that are the exact same, so to speed things up it just assumes the same answer and never actually sends the request a 2nd time

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 GetByteArrayAsync in asp.net not returning

The following code just hangs when called from an ASP.NET app:
private async Task<XPathNavigator> UspsCreateAndPostRequest(string sUrl)
{
HttpClient client = new HttpClient();
byte[] urlContents = await client.GetByteArrayAsync(sUrl);
string sResponse = System.Text.Encoding.UTF8.GetString(urlContents);
... //more code to return XPathNavigator object based on response
}
If I change to following it works fine:
private async Task<XPathNavigator> UspsCreateAndPostRequest(string sUrl)
{
HttpClient client = new HttpClient();
byte[] urlContents = null;
var task = Task.Run(async () => { urlContents = await client.GetByteArrayAsync(strUrl); });
task.Wait();
string sResponse = System.Text.Encoding.UTF8.GetString(urlContents);
... //more code to return XPathNavigator object based on response
}
Is the fact that method signature return is a Task<XPathNavigator> causing the issue? Thank you.

Somewhere higher up the call stack there is a .Wait() being performed on the task that is returned from UspsCreateAndPostRequest.
Because you wrapped the call inside a Task.Run you lost the execution context, that is why it works. Doing
private async Task<XPathNavigator> UspsCreateAndPostRequest(string sUrl)
{
HttpClient client = new HttpClient();
byte[] urlContents = await client.GetByteArrayAsync(sUrl).ConfigureAwait(false);
string sResponse = System.Text.Encoding.UTF8.GetString(urlContents);
... //more code to return XPathNavigator object based on response
}
would achieve the same goal with less resources (but it would be even better to fix the wait higher up on the chain).

.NET HttpClient hangs when using await keyword?

After considering this interesting answer HttpClient.GetAsync(...) never returns..., I still have a situation where my HttpClient is not returning when I use await (sample code below). In addition. I use this helper routine from both asp.net MVC5 Controllers (UI-driven) and the WebApi. What can I do to:
Use await instead of the (dreaded) .Result and still have this function return?
Reuse this same routine from both MVC Controllers and WebApi?
Apparently, I should replace the .Result with .ConfigureAwait(false) but this seems to contradict with the fact that "Task4" in the post cited above works fine with an await httpClient.GetAsync. Or do I need separate routines for Controller and WebApi cases?
public static async Task<IEnumerable<TcMarketUserFullV1>> TcSearchMultiUsersAsync(string elasticQuery)
{
if (string.IsNullOrEmpty(elasticQuery)) return null;
IEnumerable<TcMarketUserFullV1> res = null;
using (var hclient = new HttpClient())
{
hclient.BaseAddress = new Uri("https://addr.servicex.com");
hclient.DefaultRequestHeaders.Accept.Clear();
hclient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
hclient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer",
CloudConfigurationManager.GetSetting("jwt-bearer-token"));
// Why does this never return when await is used?
HttpResponseMessage response = hclient.GetAsync("api/v2/users?q=" + elasticQuery + "&search_engine=v2").Result;
if (response.IsSuccessStatusCode)
{
var content = await response.Content.ReadAsStringAsync();
res = JsonConvert.DeserializeObject<TcMarketUserFullV1[]>(content).AsEnumerable();
}
else{log.Warn("...");}
}
return res;
}
UPDATE: My call chain, which starts with a Telerik Kendo Mvc.Grid DataBinding call is as follows:
[HttpPost]
public async Task<ActionResult> TopLicenseGrid_Read([DataSourceRequest]DataSourceRequest request)
{
var res = await GetLicenseInfo();
return Json(res.ToDataSourceResult(request)); // Kendo.Mvc.Extensions.DataSourceRequest
}
Then:
private async Task<IEnumerable<CsoPortalLicenseInfoModel>> GetLicenseInfo()
{
...
// Never returns
var qry = #"app_metadata.tc_app_user.country:""DE""";
return await TcSearchMultiUsersAsync(qry);
}
Then, the routine shown in full above but now WITHOUT the .Result:
public static async Task<IEnumerable<TcMarketUserFullV1>> TcSearchMultiUsersAsync(string elasticQuery)
{
if (string.IsNullOrEmpty(elasticQuery)) return null;
IEnumerable<TcMarketUserFullV1> res = null;
using (var hclient = new HttpClient())
{
hclient.BaseAddress = new Uri("https://addr.servicex.com");
hclient.DefaultRequestHeaders.Accept.Clear();
hclient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
hclient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer",
CloudConfigurationManager.GetSetting("jwt-bearer-token"));
// This now returns fine
HttpResponseMessage response = hclient.GetAsync("api/v2/users?search_engine=v2&q=" + elasticQuery");
if (response.IsSuccessStatusCode)
{
// This returns my results fine too
var content = await response.Content.ReadAsStringAsync();
// The following line never returns results. When debugging, everything flows perfectly until I reach the following line, which never
// returns and the debugger returns me immediately to the top level HttpPost with a result of null.
res = JsonConvert.DeserializeObject<TcMarketUserFullV1[]>(content).AsEnumerable();
}
else{log.Warn("...");}
}
return res;
}

You need to await everything. It's not enough that you await on one of them, you need to await on all of them:
This:
HttpResponseMessage response = hclient.GetAsync(
"api/v2/users?q=" + elasticQuery + "&search_engine=v2").Result;
Should be:
HttpResponseMessage response = await hclient.GetAsync(
"api/v2/users?q=" + elasticQuery + "&search_engine=v2");
It is enough to have one blocking call to .Result in order to deadlock. You need "async all the way".

Implementing a synchronous method with calling the <asyncmethod>.Result

I have this async method:
public async Task<RES> PostAsync<RES>(string url, string content) where RES : new()
{
using (var client = new HttpClient())
{
HttpResponseMessage message = await client.PostAsync(url, new StringContent(content, Encoding.UTF8, "application/json"));
var readAsStringAsync = await message.Content.ReadAsStringAsync();
return await readAsStringAsync.FromJsonAsync<RES>(mySerializerSettings);
}
}
Where FromJsonAsync is implemented as an extension method:
public async static Task<T> FromJsonAsync<T>(this string data, JsonSerializerSettings settings) where T : new()
{
return (T)(await JsonConvert.DeserializeObjectAsync<T>(data, settings));
}
Now I want to add a regular synchronous Post method and I thought the implementation would be:
public RES Post<RES>(string url, string content) where RES : new()
{
return PostAsync<RES>(url, content).Result;
}
But this doesn't really work. I see that the request is sent via a Http sniffer and I get a response back, but I get stuck when debugging and can't continue.
BTW, this does work (with Result instead of await):
public RES Post<RES>(string url, string content) where RES : new()
{
using (var client = new HttpClient())
{
HttpResponseMessage message = client.PostAsync(url, new StringContent(content, Encoding.UTF8, "application/json")).Result;
var readAsStringAsync = message.Content.ReadAsStringAsync().Result;
return readAsStringAsync.FromJson<RES>(mySerializerSettings);
}
}
Where FromJson is implemented as an extension method:
public static T FromJson<T>(this string data, JsonSerializerSettings settings) where T : new()
{
return (T)JsonConvert.DeserializeObject<T>(data, settings);
}
The application is a web backend (WebApi).
What am I doing wrong?

You probably have a deadlock on your hands.
Asp.net uses a SynchronizationContext to post continuations back to the request context. If the context is blocked (like it is in your case on PostAsync<RES>(url, content).Result) then the continuation can't be executed and so the async method can't complete and you have a deadlock.
You can avoid it by using ConfigureAwait(false):
public async Task<RES> PostAsync<RES>(string url, string content) where RES : new()
{
using (var client = new HttpClient())
{
HttpResponseMessage message = await client.PostAsync(url, new StringContent(content, Encoding.UTF8, "application/json"));
var readAsStringAsync = await message.Content.ReadAsStringAsync().ConfigureAwait(false);
return await readAsStringAsync.FromJsonAsync<RES>(mySerializerSettings).ConfigureAwait(false);
}
}
But it's better to just avoid blocking synchronously on async code to begin with and having two different versions for sync and async.

Although possible, I wouldn't use the answer provided by #i3arnon. Generally, you shouldn't block on async code. Although ConfigureAwait(false) does work, it can lead to confusion in your code-base where other developers may also end up blocking using .Result, without using ConfigureAwait or understanding the implications of that.
Instead, expose synchronous methods which are really synchronous:
public RES Post<RES>(string url, string content) where RES : new()
{
using (var client = new WebClient())
{
client.Headers[HttpRequestHeader.ContentType] = "application/json";
var result = client.UploadString(url, content);
return JsonConvert.DeserializeObject<RES>(result, jsonSerializerSettings);
}
}

It seems you have a non-async function and you want to start a task that will call PostAsync and wait for this task to finish and return the result of the Task. Is this your problem?
To start a Task, use Task.Run( () => ...);
To wait for the Task use Task.Wait(...);
To see if the task stopped because of an exception: Task.IsFaulted
The result of the task is in Task.Result
Your code could be:
public async Task<RES> PostAsync<RES>(string url, string content) where RES : new()
{
// start the task that will call PostAsync:
var postTask = Task.Run( () => PostAsync(url, content));
// while this task is running you can do other things
// once you need the result: wait for the task to finish:
postTask.Wait();
// If needed check Task.IsFaulted / Task.IsCanceled etc. to check for errors
// the returned value is in Task.Result:
return postTask.Result;
}