using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    private static Dictionary<string, string> DecodeQueryParameters(string query)

    {

        //From https://stackoverflow.com/a/20134983 other methods had been tried, like using the result of HttpUtility.ParseQueryString().

        //However it did not give the consistency like the below

​

        return query.TrimStart('?')

            .Split(new[] { '&' }, StringSplitOptions.RemoveEmptyEntries)

            .Select(parameter => parameter.Split(new[] { '=' }, StringSplitOptions.RemoveEmptyEntries))

            .GroupBy(parts => parts[0],

                     parts => parts.Length > 2 ? string.Join("=", parts, 1, parts.Length - 1) : (parts.Length > 1 ? parts[1] : ""))

            .ToDictionary(grouping => grouping.Key,

                          grouping => string.Join(",", grouping));

    }

    public static void Main()

    {

        var res = DecodeQueryParameters("/upload/presignedurl?originalFileName=test%26plus%2Bsome_stuff.aif&ws=a59a3061-3d1a-4de6-97a7-0cbed0f9fde5&destination=music_manager&onlyUploadAsset=false&destinationId=");

        Console.WriteLine(string.Join(" ", res.Keys));

    }

}