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This section show example how to calling API using HttpClient in C#.

ApiCallerHelper.cs

using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Net.Http.Headers;

namespace WebApplicationMvcApi.Helper
{
    public class ApiCallerHelper
    {
        private static string endpointName = "endpoint";
        public static HttpResponseMessage getResult(HttpRequestMessage request)
        {

            var queryStringNvp = request.GetQueryNameValuePairs();
            var endpoint = getEndpoint(queryStringNvp);
            var requestParam = getRequestParams(queryStringNvp);
            var actualEndpointWithParam = concatUrlWithParam(endpoint, requestParam);
            
            var headers = request.Headers;

            var newRequest = new HttpRequestMessage(request.Method, actualEndpointWithParam);
            if(request.Method != HttpMethod.Get && request.Method != HttpMethod.Delete)
            {
                newRequest.Content = request.Content;
            }

            var ignoreClientHeaders = new List<string> { "Accept", "Accept-Charset", "Accept-Encoding", "Accept-Language", "Host", "Connection", "Cache-Control", "Origin" };
            
            var headersEnumerable = (IEnumerable<KeyValuePair<string, IEnumerable<string>>>)headers;
            foreach (var header in headersEnumerable)
            {
                if(!ignoreClientHeaders.Exists(item => item.ToLower().Equals(header.Key.ToLower())))
                    newRequest.Headers.Add(header.Key, header.Value);
            }

            return doRequest(newRequest);
        }
        
        private static string concatUrlWithParam(string url, string queryString)
        {
            return string.IsNullOrEmpty(queryString) ? url : string.Format("{0}?{1}", url, queryString);
        }

        private static string getRequestParams(IEnumerable<KeyValuePair<string, string>> nameValuePairs)
        {
            var requestParams = nameValuePairs.Where(item => !item.Key.ToLower().Equals(endpointName.ToLower()))
                .Select(item => string.Format("{0}={1}", item.Key, item.Value));
            return string.Join("&", requestParams); ;
        }

        private static string getEndpoint(IEnumerable<KeyValuePair<string, string>> nameValuePairs)
        {
            var endpointKvp = nameValuePairs.FirstOrDefault(item => item.Key.ToLower().Equals(endpointName.ToLower()));
            if(!endpointKvp.Equals(default(KeyValuePair<string, string>)))
            {
                return endpointKvp.Value;
            }
            return null;
        }

        public static HttpResponseMessage doRequest(HttpRequestMessage request)
        {
            using (HttpClient client = new HttpClient())
            {
                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                return client.SendAsync(request).Result;
            }
        }
    }
        
}

API Caller Usage

[RoutePrefix("api/caller")]
public class CallerController : ApiController
{
    [Route("do")]
    [HttpGet, HttpPost, HttpPut, HttpPatch, HttpDelete]
    public HttpResponseMessage Do()
    {
        return ApiCallerHelper.getResult(Request);
    }
}

Example: POST Request

POST /api/caller/do?endpoint=https://reqres.in/api/register HTTP/1.1
Host: localhost:57596
Content-Type: application/json
Cache-Control: no-cache
Postman-Token: 58b8c84f-89a5-ec5d-5196-17f2814cabee

{
    "email": "alex@son.com",
    "password": "Lex_One"
}

POST Response

{
    "token": "QpwL5tke4Pnpja7X"
}

Environment
Windows 10 Home 64bit
Visual Studio 2017 (Version 15.8.4)
Target .Net Framework 4.5.2

This post shows how to break simple captcha using Tesseract in C#. Challenges in the captcha solving is how to train or make a good algorithm so that the computer more better in recognizing the text, such as a human can read the captcha.

 To use MailChimp API V3.0 in C# language, do the steps below:

1. Create C# Web Form Project called 'MailChimpV3'.
2. Add Json.NET Framework to project Reference. Here I use  Json 8.0.2 version from Newtonsoft.
3. Create folder called `MailChimp` on the project.
4. Add C# class called `MailChimpManager.cs` in the `MailChimp` folder, location would be like `\MailChimpV3\MailChimp\MailChimpManager.cs`. Then copy the code below.

List Class defined in System.Collections.Generic Namespace in mscorlib.dll assembly, it provide methods to search, sort and manipulate lists. Elements in List can be accessed using an integer index, index start from 0 (zero-based). We can create object list from this class with syntax :
List<T>
where T is The type of elements in the list, example : List<int>.