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ASP.NET Core synchronously wait for http request

I have an external endpoint which I call to get some Json response.
This endpoint will initiate a session to a POS device, so the device will show the request details and ask the customer to enter his credit card to complete the payment, then when the customer finishes; the POS will call the endpoint and it will return the result back to my application.
The problem here is that I need the operation to complete as described in this scenario (synchronously).
When I do the call to this endpoint from postman; it waits a lot of time (until the POS receives the request and customer do his entries then returns the results back to endpoint and endpoint returns the results back to Postman) ... this is all works fine.
The problem is when I do this from an ASP.NET Core app, the request is not waited for endpoint and the response is returned with null directly.
I need something to wait for it.
using (var client = new HttpClient())
{
client.DefaultRequestHeaders.Add("x-API-Key", "ApiKey");
client.DefaultRequestHeaders.Add("Connection", "keep-alive");
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
var postTask = client.PostAsJsonAsync(new Uri("terminalEndpoint here"), dto);//dto is the request payload
postTask.Wait();
var result = postTask.Result;
if (result.IsSuccessStatusCode)
{
//Should hang after this line to wait for POS
var terminalPaymentResponseDto = result.Content.ReadAsAsync<InitiateTerminalPaymentResponseDto>().Result;
//Should hit this line after customer finishes with POS device
return terminalPaymentResponseDto;
}
}

First of all, there's no need to block. In fact, in an ASP.NET Core application you should avoid blocking as much as possible. Use async and await instead. This allows ASP.NET Core to use the freed threadpool thread for other work.
Second, HttpClient is thread-safe and meant to be reused. Creating a new one every time in a using block leaks sockets. You could use a static instance but a better solution is to use IHttpClientFactory as Make HTTP requests using IHttpClientFactory in ASP.NET Core shows, to both reuse and recycle HttpClient instances automatically.
Finally, there's no reason to add these headers on every call. The Content-Type is set by PostAsJsonAsync anyway. I also suspect the API key doesn't change when calling the same server either.
In your Startup.cs or Program.cs you can use AddHttpClient to configure the API Key :
builder.Services.AddHttpClient(client=>{
client.DefaultRequestHeaders.Add("x-API-Key", "ApiKey");
});
After that you can inject IHttpClientFactory into your controllers or pages and call it asynchronously in asynchronous actions or handlers :
public class MyController:ControllerBase
{
private readonly IHttpClientFactory _httpClientFactory;
public MyController:ControllerBase(IHttpClientFactory httpClientFactory) =>
_httpClientFactory = httpClientFactory;
public async Task<InitiateTerminalPaymentResponseDto> PostAsync(MyDTO dto)
{
var client=_httpClientFactory.CreateClient();
var uri=new Uri("terminalEndpoint here");
var result = client.PostAsJsonAsync(uri, dto);payload
if (result.IsSuccessStatusCode)
{
//Should hang after this line to wait for POS
var paymentDto= await result.Content.ReadAsAsync<InitiateTerminalPaymentResponseDto>();
//Should hit this line after customer finishes with POS device
return paymentDto;
}
else {
//Do whatever is needed in case of error
}
}
}
Using HttpClientFactory allows adding retry strategies using Polly eg, to recover from a temporary network disconnection.

Why not use the await like below? And make sure to change the function to async
var postTask = await client.PostAsJsonAsync(new Uri("terminalEndpoint here"), dto);

How to use Post to get data from API?

I wrote a function which consumes Web API. This function works great for GET requests. However, I need to get some other resources from API which, according to API provider's docs, requires POST method. So I've simply changed HttpMethod from Get to HttpMethod.Post. When I call the API then I get Error 400 Bad Request.
CallAPI
private static async Task<T> CallAPI<T>(string endpoint, string accessToken)
{
var request = new HttpRequestMessage(HttpMethod.Post,
new Uri(ApiUri, endpoint));
request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", accessToken);
var _httpClient = new HttpClient();
var response = await _httpClient.SendAsync(request);
response.EnsureSuccessStatusCode();
var responseStream = await response.Content.ReadAsStreamAsync();
var responseObject = await JsonSerializer.DeserializeAsync<T>(responseStream);
return responseObject;
}
I call this API:
var result = await CallAPI<SomeDataModel>("cars/locations", accessToken);
Don't know where is a problem. It works great for GET as I said. Moreover, I don't understand why there's a need to use POST instead of GETto get data. I think it's against REST best-practices. According to provider's API docs, I don't need to attach any parameters to POST request, it's just raw endpoint. Anyways, I need to use POST here to get data.

"Pass through" controller action (gets and returns JSON) in .NET Core 3.1

Someone's probably done this before but I can't seem to formulate the question properly to find results. I want to make AJAX calls from a view, but I can't directly call the external API from javascript because there's a key that I can't expose. My idea is to have another controller action that I call from the page that calls the actual external REST API I want to get data from and just passes it on as a JSON. I see lots of examples of getting a JSON through C# and deserializing it but not many where you get a JSON and then return it and consume it from the view. Any help appreciated.
public JsonResult GetStuff()
{
HttpClient client = new HttpClient();
client.BaseAddress = new Uri(URL);
client.DefaultRequestHeaders.Accept.Add(
new MediaTypeWithQualityHeaderValue("application/json"));
HttpResponseMessage response = client.GetAsync("Stuff/?Id=" + id).Result;
*code to take response and pass it on as a JSON that I can consume from Javascript
}

Here is what I recommend.
[HttpGet("myapi/{id}");
public async Task MyApi(int id) {
// Replace these lines as needed to make your API call properly.
using HttpClient client = new() {
BaseAddress = REMOTE_SERVER_BASE
}
// Make sure to properly encode url parameters if needed
using HttpResponseMessage response = await client.GetAsync($"myapi/{id}");
this.HttpContext.Response.StatusCode = (int)response.StatusCode;
foreach (KeyValuePair<string, IEnumerable<string>> header in response.Headers) {
this.HttpContext.Response.Headers[header.Key] = new StringValues(header.Value.ToArray());
}
await response.Content.CopyToAsync(this.HttpContext.Response.Body);
}
This will copy all the common response fields such as status code, headers, and body content, over to your response.
This code isn't tested so you might have to tweak it a bit but it should be enough to get you started.

Delete email using mailinator API

I am creating application to access public emails in mailinator. I can view emails but I have difficulties when I am trying to delete them.
https://mailinator.com/apidocs.jsp all examples from documentacion worked except this one.
I have code to POST Http request:
using (var client = new HttpClient())
{
var values = new Dictionary<string, string>
{
{ "msgid", id}
};
var content = new FormUrlEncodedContent(values);
var response = await client.PostAsync("https://api.mailinator.com/api/delete?", content);
var responseString = await response.Content.ReadAsStringAsync();
}
Only error it throws is (405) Method Not Allowed. or Method is not supported by this URL.
So I guess either my url that I'm sending is bad, either my code.
I need some help to figure it out.

According to the API docs you need to pass a valid token with every call. The delete API example looks like this:
curl "https://api.mailinator.com/api/delete?id=1373143878-0-test22&token=..."
The elipsis (...) there needs to be a valid token. So, add the token to your values dictionary.

401 Unauthorized on SECOND HttpClient/HttpWebRequest call

I have a application that uses the SharePoint 2010 REST API.
In the process of creating an Item there are multiple request done after each other:
1 Call: Getting Items from List: Succes
2 Call: Create Item: 401 Unauthorized
This is the same if I do it like this:
1 Call: Create Item: Succes
2 Call: Delete Item: 401 Unauthorized
What I know is that my functions work separately they DON'T work when they are called after each other.
When I close the application (Windows Phone 8.1 app) after creating a item and when restarted try to delete the item it works.
First I thought it had to do with the way I handle my fields so I changed them to NULL in a finally statement but that didn't work.
public async Task<bool> CreateNewItem(NewItem myNewItem)
{
try
{
StatusBar statusBar = await MyStatusBar.ShowStatusBar("Creating new List Item.");
//Retrieving Settings from Saved file
mySettings = await MyCredentials.GetMySettings();
myCred = new NetworkCredential(mySettings.UserName, mySettings.Password, mySettings.Domain);
using (var handler = new HttpClientHandler { Credentials = myCred })
{
HttpClient client = new HttpClient(handler);
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
NewItem newItem = myNewItem;
var jsonObject = JsonConvert.SerializeObject(newItem);
HttpResponseMessage response = await client.PostAsync(new Uri(baseUrl + listNameHourRegistration), new StringContent(jsonObject.ToString(), Encoding.Unicode, "application/json"));
response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/json");
response.EnsureSuccessStatusCode();
string responseMessage = await response.Content.ReadAsStringAsync();
client.Dispose();
if (responseMessage.Length > 0)
return true;
}
}
catch (Exception ex)
{
Debug.WriteLine(ex.Message);
return false;
}
finally
{
request = null;
response = null;
myCred = null;
mySettings = null;
}
return false;
}

Just run into the same problem.
Anyway, the 2nd request does not follow the same authentication procedure. Even if you initialize a new HttpClient object. I sniffed the HTTP traffic.
After the 1st request I am doing another with different credentials. This is also ending in a 401. I am really confused...
Seems the NTLM Handshake stucks at the 2nd of 6 steps
http://www.innovation.ch/personal/ronald/ntlm.html
Edit:
You may want to use the CSOM.
http://social.msdn.microsoft.com/Forums/office/en-US/efd12f11-cdb3-4b28-a9e0-32bfab71a419/windows-phone-81-sdk-for-sharepoint-csom?forum=sharepointdevelopment

While I still don't know what the actual problem is, at least I found a workaround: Use the WebRequest class instead of HttpClient.

I was running into this same error when I realized I was adding the headers each time I was calling the endpoint. Hopefully this will help someone.
Instead I initialized the HttpClient instance in my class constructor and set the headers there. Also I learned it is better practice to only use 1 instance instead of recreating with "using" (See this article https://www.aspnetmonsters.com/2016/08/2016-08-27-httpclientwrong/)
I'm invoking CallApiAsync from another class in a loop.
Here's my final solution:
class ApiShared
{
private HttpClient client;
public ApiShared() {
client = new HttpClient();
client.DefaultRequestHeaders.Add("x-api-key", ConfigurationManager.AppSettings["ApiKey"]);
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
}
public async Task<ApiResponse_Root> CallApiAsync(string endpoint)
{
// Make API call
Uri endpointUri = new Uri(endpoint);
var stringTask = client.GetStringAsync(endpointUri);
var data = JsonConvert.DeserializeObject<ApiResponse_Root>(await stringTask);
return data;
}
}

On a windows machine you can resolve this with this registry setting change:
Go to the following Registry entry:
Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
Now add a new DWORD to the Lsa folder called: DisableLoopBackCheck and set this to 1

I see that this question has been posted long back. But I don't see a correctly working solution posted yet to this thread.
I faced exactly the same issue where the next requests kept on failing returning me 401 UnAuthorized.
I figured out using fiddler that from SECOND request onwards, there was a Cookie added to the request which was possibly a result of Set-Cookie response sent by the server along with first response.
So here's how I tackled the situation - Make UseCookies false:
new HttpClientHandler { Credentials = myCred, UseCookies = false }
This should resolve your issue. Hope this helps someone who's looking for a solution to a similar issue.