C# HttpClient: How to send query strings in POST Requests

Question

This is the POST Request, it works.

curl -X POST --header 'Accept: application/json' 

'http://mywebsite.com/api/CompleteService?refId=12345&productPrice=600'

How to send this request using C# => HttpClient => client.PostAsync() method? Two methods have been tried but both failed.

Method 1 (Failed, Response 404)

string url = "http://mywebsite.com/api/CompleteService";
string refId = "12345";
string price= "600";
string param = $"refId ={refId}&productPrice={price}";
HttpContent content = new StringContent(param, Encoding.UTF8, "application/json");
HttpResponseMessage response = client.PostAsync(url, content).Result;

This would only work if API is to accept a request body, not query strings.

Method 2 (Failed, Response 404) https://stackoverflow.com/a/37443799/7768490

var parameters = new Dictionary<string, string> { { "refId ", refId }, { "productPrice", price} };
var encodedContent = new FormUrlEncodedContent(parameters);
HttpResponseMessage response = client.PostAsync(url, encodedContent)

Since 404, you have to post your controller and actions headers — Serge, Sep 18 '21 at 00:53

A Farmanbar · Accepted Answer · 2021-09-18T01:45:37.350

3

Apparently, None of the tried approaches put parameters in the URL!. You are posting on the below URL

"http://mywebsite.com/api/CompleteService"

However, something that works

string url = "http://mywebsite.com/api/CompleteService?";
string refId = "12345";
string price= "600";
string param = $"refId={refId}&productPrice={price}";
HttpContent content = new StringContent(param, Encoding.UTF8, "application/json");

Attach Parameters to URL and to get Response's Body, Use:

  try   
  {
     HttpResponseMessage response = await client.PostAsync(url + param, content);
     response.EnsureSuccessStatusCode();
     string responseBody = await response.Content.ReadAsStringAsync();
     Console.WriteLine(responseBody);
  }
  catch(HttpRequestException e)
  {
     Console.WriteLine("Message :{0} ",e.Message);
  }

edited Sep 18 '21 at 01:45

answered Sep 18 '21 at 00:59

A Farmanbar

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You probably don't want the space in `refId =` – Rowan Smith Sep 18 '21 at 01:05
@RowanSmith I reused OP codes, and edition welcome. – A Farmanbar Sep 18 '21 at 01:06
Thanks for the effort, but nope this did not work. Same result. I cannot post my production API URL here, but I don't think this is a formatting issue. – Gary Bao 鲍昱彤 Sep 18 '21 at 01:06
Drop a Breakpoint in your debugger on the HttpResponseMessage line and check that the value of `content` is correctly formatted and what you expect. – Rowan Smith Sep 18 '21 at 01:08
@JayPow if you need to have URL parameters so you should attach, `URL + Param` – A Farmanbar Sep 18 '21 at 01:08
@AFarmanbar actually I think this is also wrong here: client.PostAsync(url + param, content), what's the purpose of doing param plus a content including param?thanks – Gary Bao 鲍昱彤 Sep 18 '21 at 01:11
@JayPow content is your request's body – A Farmanbar Sep 18 '21 at 01:12
@AFarmanbar but request body should be null in this case because my endpoint was but to only accept request parameters – Gary Bao 鲍昱彤 Sep 18 '21 at 01:13
@JayPow make it null. no problem – A Farmanbar Sep 18 '21 at 01:14
@AFarmanbar, actually I think it worked. ``URL+Param``, but I still need to add the empty HttpContent to ``client.PostAsync(url + para, content).Result.`` – Gary Bao 鲍昱彤 Sep 18 '21 at 01:19
@AFarmanbar If you don't mind, can you also edit your answer and help me extract the response body out as well? it supposes to return a ``string`` response. Thanks! – Gary Bao 鲍昱彤 Sep 18 '21 at 01:20
2

@JayPow, it's recommended if your body is null, change the end-point to accept `GET` requests – A Farmanbar Sep 18 '21 at 01:21
@JayPow string or JSON? we have not string, it's plain text or json object – A Farmanbar Sep 18 '21 at 01:22
@AFarmanbar a string encoded to JSON. – Gary Bao 鲍昱彤 Sep 18 '21 at 01:23
@JayPow see update – A Farmanbar Sep 18 '21 at 01:29
I couldn't use ``await`` because my method is not ``async``, here is my code. And thanks to you @AFarmanbar response = client.PostAsync(url + param, encodedContent).Result; string returnCnum = response.Content.ReadAsStringAsync().Result; – Gary Bao 鲍昱彤 Sep 18 '21 at 01:31
@JayPow, I'm not sure but try `client.PostAsync(url + param, content).GetAwaiter().GetResult()` – A Farmanbar Sep 18 '21 at 01:39
@AFarmanbar it's already working. thank you. I used non-async methods. – Gary Bao 鲍昱彤 Sep 18 '21 at 01:43
1

@JayPow Depending on the context of your app, not awaiting your async call could cause [big problems](https://learn.microsoft.com/en-us/archive/blogs/jpsanders/asp-net-do-not-use-task-result-in-main-context). If you're going to make async calls, make your method async. If you don't need asynchrony, make a synchronous call ([Send](https://learn.microsoft.com/en-us/dotnet/api/system.net.http.httpclient.send?view=net-5.0)). – Chris Sep 18 '21 at 01:50

C# HttpClient: How to send query strings in POST Requests

1 Answers1