LanguageServerProtocol.cs

using System;
using System.Text;

namespace ConsoleApp6
{
    class Program
    {
        static void Main(string[] args)
        {
            while (true)
            {
                var lenStr = Console.ReadLine();
                var contentLength = int.Parse(lenStr.Substring(16));
                Console.ReadLine();
                var sb = new StringBuilder();
                for(var j = 0; j < contentLength; ++j)
                {
                    sb.Append((char)Console.Read());
                }
                var req = sb.ToString();

                string response = null;
                if (req.Contains("\"initialize\""))
                {
                    response = "{\"jsonrpc\":\"2.0\",\"id\":0,\"result\":{\"capabilities\":{\"textDocumentSync\":1,\"completionProvider\":{\"resolveProvider\":true}}}}";
                }
                else if (req.Contains("\"initialized\""))
                {
                    response = "{\"jsonrpc\":\"2.0\",\"method\":\"window/showMessage\",\"params\":{\"type\":1,\"message\":\"Hello from server\"}}";
                }
                if(response != null)
                {
                    Console.Write($"Content-Length: {response.Length}\r\n\r\n{response}");
                }
            }
        }
    }
}