HttpClientService.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Net.Http;
using System.Net.Http.Formatting;
using System.Threading.Tasks;

namespace Infrastructure.Services
{
    public class HttpClientService : IHttpClientService
    {
        public HttpClientService()
        {
        }

        public async Task<T> GetAsync<T>(HttpClient httpClient, string url, Dictionary<string, string> queryParams = null, Dictionary<string, string> headers = null)
        {
            try
            {
                var request = CreateGetRequest(url, queryParams, headers);
                var response = await httpClient.SendAsync(request);
                if (response.IsSuccessStatusCode)
                {
                    return await response.Content.ReadAsAsync<T>();
                }
                return default(T);
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

        public async Task<Stream> GetStreamAsync(HttpClient httpClient, string url, Dictionary<string, string> queryParams = null, Dictionary<string, string> headers = null)
        {
            try
            {
                // TODO: Handle queryParams, headers
                return await httpClient.GetStreamAsync(url);
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

        public async Task<T> PostAsJsonAsync<T>(HttpClient httpClient, string url, object data, Dictionary<string, string> queryParams = null, Dictionary<string, string> headers = null)
        {
            try
            {
                var request = CreatePostAsJsonRequest(url, data, queryParams, headers);
                var response = await httpClient.SendAsync(request);
                if (response.IsSuccessStatusCode)
                {
                    return await response.Content.ReadAsAsync<T>();
                }
                return default(T);
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

        public async Task<T> PostAsFormUrlEncodedAsync<T>(HttpClient httpClient, string url, Dictionary<string, string> data, Dictionary<string, string> queryParams = null, Dictionary<string, string> headers = null)
        {
            try
            {
                var request = CreatePostAsFormUrlEncodedRequest(url, data, queryParams, headers);
                var response = await httpClient.SendAsync(request);
                if (response.IsSuccessStatusCode)
                {
                    return await response.Content.ReadAsAsync<T>();
                }
                return default(T);
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

        #region Private Method
        private HttpRequestMessage CreatePostAsJsonRequest(string url, object data, Dictionary<string, string> queryParams, Dictionary<string, string> headers)
        {
            // TODO: Handle queryParams
            MediaTypeFormatter jsonFormatter = new JsonMediaTypeFormatter();
            HttpContent content = new ObjectContent<object>(data, jsonFormatter);
            var request = new HttpRequestMessage(HttpMethod.Post, url)
            {
                Content = content,
            };
            if (headers != null)
            {
                foreach (KeyValuePair<string, string> entry in headers)
                {
                    request.Headers.Add(entry.Key, entry.Value);
                }
            }
            return request;
        }

        private HttpRequestMessage CreatePostAsFormUrlEncodedRequest(string url, Dictionary<string, string> data, Dictionary<string, string> queryParams, Dictionary<string, string> headers)
        {
            // TODO: Handle queryParams
            var request = new HttpRequestMessage(HttpMethod.Post, url)
            {
                Content = new FormUrlEncodedContent(data),
            };
            if (headers != null)
            {
                foreach (KeyValuePair<string, string> entry in headers)
                {
                    request.Headers.Add(entry.Key, entry.Value);
                }
            }
            return request;
        }

        private HttpRequestMessage CreateGetRequest(string url, Dictionary<string, string> queryParams, Dictionary<string, string> headers)
        {
            // TODO: Handle queryParams
            var request = new HttpRequestMessage(HttpMethod.Get, url);
            foreach (KeyValuePair<string, string> entry in headers)
            {
                request.Headers.Add(entry.Key, entry.Value);
            }
            return request;
        }
        #endregion
    }
}

IHttpClientService.cs

using System.Collections.Generic;
using System.IO;
using System.Net.Http;
using System.Threading.Tasks;

namespace Infrastructure.Services
{
    public interface IHttpClientService
    {
        Task<T> GetAsync<T>(HttpClient httpClient, string url, Dictionary<string, string> queryParams = null, Dictionary<string, string> headers = null);
        Task<T> PostAsJsonAsync<T>(HttpClient httpClient, string url, object data, Dictionary<string, string> queryParams = null, Dictionary<string, string> headers = null);
        Task<T> PostAsFormUrlEncodedAsync<T>(HttpClient httpClient, string url, Dictionary<string, string> data, Dictionary<string, string> queryParams = null, Dictionary<string, string> headers = null);
        Task<Stream> GetStreamAsync(HttpClient httpClient, string url, Dictionary<string, string> queryParams = null, Dictionary<string, string> headers = null);
    }
}

TestController.cs

namespace Web.Controllers
{
    [Produces("application/json")]
    [Route("api/[controller]")]
    public class ToolController: Controller
    {
        private readonly IHttpClientFactory _httpClientFactory;
        private readonly IHttpClientService _httpClientService;
        private readonly HttpClient _httpClientA;
        public ToolController(
            IHttpClientFactory httpClientFactory,
            IHttpClientService httpClientService
        )
        {
            _httpClientFactory = httpClientFactory;
            _httpClientService = httpClientService;
            _httpClientA = _httpClientFactory.CreateClient("A");
        }
    }
    
    [HttpGet("hello-world")]
    public async Task<IActionResult> HelloWorld()
    {
        var response = await _httpClientService.GetAsync(_httpClientA, "/api/hello-world");
        return Ok("Hello World");
    }
}