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;
}
Related
I have a PostAsync method in an internal part of my code that doesn't seem to ever return a response. However, I use it synchronously via .GetAwaiter().GetResult(). The target framework is net45.
public async Task<TResponse> PostAsync<TResponse, TRequest>(string method, TRequest body)
{
_logger.Log($"Method {method}, body {JsonConvert.SerializeObject(body)} on url {_configuration.ApiUrl}");
using (var customDelegatingHandler = new HMACDelegatingHandler(_configuration, _apiId))
{
using (var client = new HttpClient(customDelegatingHandler))
{
var response = await client.PostAsync($"{_configuration.ApiUrl}/{method}",
new StringContent(JsonConvert.SerializeObject(body), Encoding.UTF8, "application/json"));
if (response.StatusCode == HttpStatusCode.OK)
{
var content = await response.Content.ReadAsStringAsync();
return JsonConvert.DeserializeObject<TResponse>(content);
}
else
{
await Log(body, response);
}
return default;
}
}
}
What I do is call the PostAsync in another method:
public async Task<decimal> GetBalance(Request request)
{
// = new MyCustomClient...
QueryFundsResponse response = await customClient.PostAsync<Response, Request>("testAction", request);
if (response == default)
return 0.0m;
return response.Amount;
}
Then, finally at the very top of the flow, I call the GetBalance method like this:
var sw = new Stopwatch();
sw.Start();
var balance = _provider
.GetBalance(request)
.ConfigureAwait(false)
.GetAwaiter()
.GetResult();
sw.Stop();
_logger.Log($"GetBalance -> method duration: { sw.ElapsedMilliseconds }");
I don't see the log in my logs at all, and I don't seem to ever get a response or any code executed after the .GetAwaiter().GetResult(). Switching the last block of code to be asynchronous and await the GetBalance() method is not really an option for me, sadly.
I am unable to figure out why nothing is changing, even after using the .ConfigureAwait(false) method.
You're experiencing the common deadlock that happens when you block on asynchronous code (described in detail on my blog). There are a variety of ways to get around it, but they're all hacks and none of them work in every situation.
In your case, I'd say either use the direct blocking hack or use the boolean argument hack.
The direct blocking hack requires you to use ConfigureAwait(false) everywhere. Note that your current code only uses ConfigureAwait(false) where it doesn't do anything; ConfigureAwait configures the await, so it needs to go where the awaits are. All of them.
The boolean argument hack means that your code will take a bool parameter that determines whether it executes synchronously or asynchronously. Note that HttpClient (for now) has an async-only API, so your custom delegating handler will need to support direct blocking, using ConfigureAwait(false). Similarly, Log will either need a synchronous equivalent or also support direct blocking. Your code would end up looking something like this:
public Task<TResponse> PostAsync<TResponse, TRequest>(string method, TRequest body) => PostCoreAsync(method, body, sync: false);
public TResponse Post<TResponse, TRequest>(string method, TRequest body) => PostCoreAsync(method, body, sync: true).GetAwaiter().GetResult();
private async Task<TResponse> PostCoreAsync<TResponse, TRequest>(string method, TRequest body, bool sync)
{
_logger.Log($"Method {method}, body {JsonConvert.SerializeObject(body)} on url {_configuration.ApiUrl}");
using (var customDelegatingHandler = new HMACDelegatingHandler(_configuration, _apiId))
{
using (var client = new HttpClient(customDelegatingHandler))
{
var responseTask = client.PostAsync($"{_configuration.ApiUrl}/{method}",
new StringContent(JsonConvert.SerializeObject(body), Encoding.UTF8, "application/json"));
var response = sync ? responseTask.GetAwaiter().GetResult() : await responseTask;
if (response.StatusCode == HttpStatusCode.OK)
{
var content = sync ? response.Content.ReadAsStringAsync().GetAwaiter().GetResult() : await response.Content.ReadAsStringAsync();
return JsonConvert.DeserializeObject<TResponse>(content);
}
else
{
var logTask = Log(body, response);
if (sync)
logTask.GetAwaiter().GetResult();
else
await logTask;
}
return default;
}
}
}
public Task<decimal> GetBalanceAsync(Request request) => GetBalanceCoreAsync(request, sync: false);
public decimal GetBalance(Request request) => GetBalanceCoreAsync(request, sync: true).GetAwaiter().GetResult();
private async Task<decimal> GetBalanceCoreAsync(Request request, bool sync)
{
// = new MyCustomClient...
QueryFundsResponse response = sync ?
customClient.Post<Response, Request>("testAction", request) :
await customClient.PostAsync<Response, Request>("testAction", request);
if (response == default)
return 0.0m;
return response.Amount;
}
var sw = new Stopwatch();
sw.Start();
var balance = _provider
.GetBalance(request);
sw.Stop();
_logger.Log($"GetBalance -> method duration: { sw.ElapsedMilliseconds }");
I'm trying to build a dynamic http client using dynamic proxy to intercept the calls and create an http request with it.
The issue i had was with Async methods:
private Task<object> PostAsync(HttpClient client, string url, HttpRequestParameters parameters, Type returnType)
{
return Task.Run(async () =>
{
var requestContent = new StringContent(Serializer.Serialize(parameters.BodyParameters));
var httpResponse = await client.PostAsync(url, requestContent);
var responseContent = await httpResponse.Content.ReadAsStringAsync();
return Serializer.Deserialize(responseContent, returnType);
});
}
My task returns dynamic/object and not the T of the Interception return type.
I thought that i will be able to use it like so
var task = PostAsync(client, url, parameters, returnType);
invocation.ReturnValue = task;
Since the task that will be returned is the original task and it is still pending i thought it would work but all i'm getting is an exception that Task cant be converted to task of my type (Which is string in that case).
Thanks for the helpers
Edit:
I did see Intercept async method, that's what i tried to do but i was unable to call the Task even using reflection, i still got the same exception.
I solved it eventually with a few modifications:
Creating the interceptor with a base object, i used Moq objects to lazy create them and store them in a ConcurrentDictionary for caching.
var mock = new Mock<T>();
var pg = new ProxyGenerator();
return pg.CreateInterfaceProxyWithTarget<T>(GetTarget(clientType), _gatewayInterceptor);
I passed the invocation's return value (in that case Task of T) to a method and got the T.
I wrapped the http call with a new Task of T, await the http call and
return desirialized T result from the task.
Assign the new Task of T back to the return value.
invocation.ReturnValue = GetAsync((dynamic)invocation.ReturnValue, serializer, headers, req);
internal static Task<T> GetAsync<T>(Task<T> originalTask, ISerializer serializer, Headers headers, InvokeHttpRequest req)
{
return Task.Run(async () =>
{
using (HttpClient client = new HttpClient())
{
var httpResponse = await PerformGetAsync(headers, req, client);
var jsonResponse = await httpResponse.Content.ReadAsStringAsync();
return ProcessResult<T>(serializer, jsonResponse);
}
});
}
I know its not the best way to go but it worked for me.
The solution is here if anyone needs it https://github.com/ErezLevip/SimpleProxyClient
Hello I dont get the difference between the following two asnyc functions, could someone explain it to me? Both of them doesnt return IRestResponse, so I cant access StatusCode field. Do I have to cast here?
public async Task<IRestResponse> Post<T>(string Ressource, T ObjTOPost) where T : new()
{
return await Task.Factory.StartNew(() =>
{
var client = new RestClient("test.com");
var request = new RestRequest(Ressource, Method.POST);
var response = client.Execute(request);
return response;
});
}
And this:
public async Task<IRestResponse> Post<T>(string Ressource, T ObjTOPost) where T : new()
{
var client = new RestClient("test.com");
var request = new RestRequest(Ressource, Method.POST);
var response = await client.ExecuteTaskAsync<T>(request);
return response;
}
Both of them doesnt return IRestResponse, so I cant access StatusCode field.
They return a Task<IRestResponse>. You can get the interface by awaiting the task, e.g.
var task = Post(resource, objectToPost);
IRestResponse response = await task;
Or in one line (more common):
var response = await Post(resource, objectToPost);
Difference between these two async functions
The second example is far more straightforward. The first example spins up an additional task and passes its awaitable back to the caller, whereas the second example awaits the RestClient directly. I see no reason to use the structure in the first example.
I'm completely new to using async calls and await. I have the below unit test function:
public async static void POSTDataHttpContent(string jsonString, string webAddress)
{
HttpClient client = new HttpClient();
StringContent stringContent = new StringContent(jsonString);
HttpResponseMessage response = await client.PostAsync(
webAddress,
stringContent);
Console.WriteLine("response is: " + response);
}
The test completes without error, but I never see the Console.WriteLine print statement show up in output - I'm not sure why. I've been looking around and it sounds like I may need to set this up as a task? Could someone point me in the proper direction?
Since you are already awaiting an HttpResponseMessage, a simple (and consistent) solution is to return Task<HttpResponseMessage>.
var x = await POSTDataHttpContent("test", "http://api/");
public async Task<HttpResponseMessage> POSTDataHttpContent(
string jsonString, string webAddress)
{
using (HttpClient client = new HttpClient())
{
StringContent stringContent = new StringContent(jsonString);
HttpResponseMessage response = await client.PostAsync(
webAddress,
stringContent);
Console.WriteLine("response is: " + response);
return response;
}
}
That said, you also need to ensure that your test setup is correct. You cannot properly call an async method from a synchronous test. Instead, mark your test async as well and await the method you are calling. Furthermore, your test method must be marked as async Task as well since neither MS Test Runner nor other tools (NCrunch, NUnit) will properly deal with an async void test method:
[TestMethod]
public async Task TestAsyncHttpCall()
{
var x = await POSTDataHttpContent("test", "http://api/");
Assert.IsTrue(x.IsSuccessStatusCode);
}
I think the best thing to do here for you would be to opt for a Task return type instead of a void.
public async Task POSTDataHttpContent(string jsonString, string webAddress)
{
using (HttpClient client = new HttpClient())
{
StringContent stringContent = new StringContent(jsonString);
HttpResponseMessage response = await client.PostAsync(
webAddress,
stringContent);
// Assert your response may be?
}
}
And if you are really adamant about not using Tasks (which is not a good idea):
public void POSTDataHttpContent(string jsonString, string webAddress)
{
var Task = Task<HttpResponseMessage>.Run(async () => {
using (HttpClient client = new HttpClient())
{
StringContent stringContent = new StringContent(jsonString);
HttpResponseMessage response = await client.PostAsync(
webAddress,
stringContent);
return response;
}
});
Task.Wait();
Assert.IsNotNull(Task.Result);
}
I have a Portable Class Library (PCL) method like this:
public async Task<string> GetLineStatuses()
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url);
using (HttpWebResponse response = (HttpWebResponse)await request.GetResponseAsync())
{
return response.GetResponseStream().ReadAllText();
}
}
My ASP.NET Web Api method looks like this:
public async Task<HttpResponseMessage> Get()
{
HttpResponseMessage response = new HttpResponseMessage();
string statuses = await service.GetStatuses();
response.Content = new StringContent(statuses);
return response;
}
What are the implications of returning a Task in Web API. Is this allowed? The only reason I want to use await is so I can use a Portable Class Library (PCL). What is the best practice? Should I have a syncronous version of my method and an asyncronous version? What are the performance and code readability and maintainability implications?
Also would I have the same effect if I returned Task<string> rather than Task<HttpResponseMessage>?
Async and await are perfectly acceptable in ASP.NET. Here's a Scott Handselman video demoing it: http://www.asp.net/vnext/overview/aspnet/async-and-await
"Also would I have the same effect if I returned Task<string> rather than Task<HttpResponseMessage>?"
Not really sure what you mean by this. The Task is like a container for the object, so a Task<string> would contain your string result and a Task<HttpResponseMessage> would contain your HttpResponseMessage result... Is that what you mean? I think either method is perfectly acceptable. If you just need the string, then go with that. No point in returning more than you need.
as alternative:
public static async Task<string> CallGET(string requestUri, string id = "")
{
string responseData;
using (var client = new HttpClient(new HttpClientHandler() { UseDefaultCredentials = true }))
{
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
Uri.TryCreate(new Uri(baseURI), $"{requestUri}{(string.IsNullOrEmpty(id) ? string.Empty : $"/{id}")}", out Uri fullRequestUri);
using (var response = await client.GetAsync(fullRequestUri))
{
responseData = await response.Content.ReadAsStringAsync();
}
return responseData;
}
}
and call would be:
var getListUsersResult = Utils.CallGET($"/v1/users").Result;
var resultset= JsonConvert.DeserializeObject(getListUsersResult, typeof(List<UsersDTO>)) as List<UsersDTO>;
UserDTO r = users.Where(d => d.Name.ToLower().Contains("test")).FirstOrDefault();
and another call for one item:
var getUser = Utils.CallGET($"/v1/users", $"{USER_ID}").Result;
var getUserResponse = JsonConvert.DeserializeObject(getUser, typeof(UserDTO)) as UserDTO;