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
– Serge, Commented Sep 18, 2021 at 0:53

A Farmanbar · Accepted Answer · 2021-09-18 01:45:37Z

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, 2021 at 1:45

answered Sep 18, 2021 at 0:59

A Farmanbar

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19 Comments

Rowan Smith Over a year ago

You probably don't want the space in refId =

A Farmanbar Over a year ago

@RowanSmith I reused OP codes, and edition welcome.

Jay 鲍昱彤 Over a year ago

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.

A Farmanbar Over a year ago

@JayPow, it's recommended if your body is null, change the end-point to accept GET requests

Chris Over a year ago

@JayPow Depending on the context of your app, not awaiting your async call could cause big problems. If you're going to make async calls, make your method async. If you don't need asynchrony, make a synchronous call (Send).

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