jellyfin/SocketHttpListener/Ext.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.IO.Compression;
using System.Net;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using MediaBrowser.Model.Services;
using HttpStatusCode = SocketHttpListener.Net.HttpStatusCode;
using WebSocketState = System.Net.WebSockets.WebSocketState;

namespace SocketHttpListener
{
    /// <summary>
    /// Provides a set of static methods for the websocket-sharp.
    /// </summary>
    public static class Ext
    {
        #region Private Const Fields

        private const string _tspecials = "()<>@,;:\\\"/[]?={} \t";

        #endregion

        #region Private Methods

        private static MemoryStream compress(this Stream stream)
        {
            var output = new MemoryStream();
            if (stream.Length == 0)
                return output;

            stream.Position = 0;
            using (var ds = new DeflateStream(output, CompressionMode.Compress, true))
            {
                stream.CopyTo(ds);
                //ds.Close(); // "BFINAL" set to 1.
                output.Position = 0;

                return output;
            }
        }

        private static byte[] decompress(this byte[] value)
        {
            if (value.Length == 0)
                return value;

            using (var input = new MemoryStream(value))
            {
                return input.decompressToArray();
            }
        }

        private static MemoryStream decompress(this Stream stream)
        {
            var output = new MemoryStream();
            if (stream.Length == 0)
                return output;

            stream.Position = 0;
            using (var ds = new DeflateStream(stream, CompressionMode.Decompress, true))
            {
                ds.CopyTo(output, true);
                return output;
            }
        }

        private static byte[] decompressToArray(this Stream stream)
        {
            using (var decomp = stream.decompress())
            {
                return decomp.ToArray();
            }
        }

        private static byte[] readBytes(this Stream stream, byte[] buffer, int offset, int length)
        {
            var len = stream.Read(buffer, offset, length);
            if (len < 1)
                return buffer.SubArray(0, offset);

            var tmp = 0;
            while (len < length)
            {
                tmp = stream.Read(buffer, offset + len, length - len);
                if (tmp < 1)
                    break;

                len += tmp;
            }

            return len < length
                   ? buffer.SubArray(0, offset + len)
                   : buffer;
        }

        private static async Task<byte[]> ReadBytesAsync(this Stream stream, byte[] buffer, int offset, int length)
        {
            var len = await stream.ReadAsync(buffer, offset, length).ConfigureAwait(false);
            if (len < 1)
                return buffer.SubArray(0, offset);

            var tmp = 0;
            while (len < length)
            {
                tmp = await stream.ReadAsync(buffer, offset + len, length - len).ConfigureAwait(false);
                if (tmp < 1)
                {
                    break;
                }

                len += tmp;
            }

            return len < length
                   ? buffer.SubArray(0, offset + len)
                   : buffer;
        }

        private static bool readBytes(this Stream stream, byte[] buffer, int offset, int length, Stream dest)
        {
            var bytes = stream.readBytes(buffer, offset, length);
            var len = bytes.Length;
            dest.Write(bytes, 0, len);

            return len == offset + length;
        }

        private static async Task<bool> ReadBytesAsync(this Stream stream, byte[] buffer, int offset, int length, Stream dest)
        {
            var bytes = await stream.ReadBytesAsync(buffer, offset, length).ConfigureAwait(false);
            var len = bytes.Length;
            dest.Write(bytes, 0, len);

            return len == offset + length;
        }

        #endregion

        #region Internal Methods

        internal static byte[] Append(this ushort code, string reason)
        {
            using (var buffer = new MemoryStream())
            {
                var tmp = code.ToByteArrayInternally(ByteOrder.Big);
                buffer.Write(tmp, 0, 2);
                if (reason != null && reason.Length > 0)
                {
                    tmp = Encoding.UTF8.GetBytes(reason);
                    buffer.Write(tmp, 0, tmp.Length);
                }

                return buffer.ToArray();
            }
        }

        internal static string CheckIfClosable(this WebSocketState state)
        {
            return state == WebSocketState.CloseSent
                   ? "While closing the WebSocket connection."
                   : state == WebSocketState.Closed
                     ? "The WebSocket connection has already been closed."
                     : null;
        }

        internal static string CheckIfOpen(this WebSocketState state)
        {
            return state == WebSocketState.Connecting
                   ? "A WebSocket connection isn't established."
                   : state == WebSocketState.CloseSent
                     ? "While closing the WebSocket connection."
                     : state == WebSocketState.Closed
                       ? "The WebSocket connection has already been closed."
                       : null;
        }

        internal static string CheckIfValidControlData(this byte[] data, string paramName)
        {
            return data.Length > 125
                   ? string.Format("'{0}' length must be less.", paramName)
                   : null;
        }

        internal static Stream Compress(this Stream stream, CompressionMethod method)
        {
            return method == CompressionMethod.Deflate
                   ? stream.compress()
                   : stream;
        }

        internal static bool Contains<T>(this IEnumerable<T> source, Func<T, bool> condition)
        {
            foreach (T elm in source)
                if (condition(elm))
                    return true;

            return false;
        }

        internal static void CopyTo(this Stream src, Stream dest, bool setDefaultPosition)
        {
            var readLen = 0;
            var bufferLen = 256;
            var buffer = new byte[bufferLen];
            while ((readLen = src.Read(buffer, 0, bufferLen)) > 0)
            {
                dest.Write(buffer, 0, readLen);
            }

            if (setDefaultPosition)
                dest.Position = 0;
        }

        internal static byte[] Decompress(this byte[] value, CompressionMethod method)
        {
            return method == CompressionMethod.Deflate
                   ? value.decompress()
                   : value;
        }

        internal static byte[] DecompressToArray(this Stream stream, CompressionMethod method)
        {
            return method == CompressionMethod.Deflate
                   ? stream.decompressToArray()
                   : stream.ToByteArray();
        }

        /// <summary>
        /// Determines whether the specified <see cref="int"/> equals the specified <see cref="char"/>,
        /// and invokes the specified Action&lt;int&gt; delegate at the same time.
        /// </summary>
        /// <returns>
        /// <c>true</c> if <paramref name="value"/> equals <paramref name="c"/>;
        /// otherwise, <c>false</c>.
        /// </returns>
        /// <param name="value">
        /// An <see cref="int"/> to compare.
        /// </param>
        /// <param name="c">
        /// A <see cref="char"/> to compare.
        /// </param>
        /// <param name="action">
        /// An Action&lt;int&gt; delegate that references the method(s) called at
        /// the same time as comparing. An <see cref="int"/> parameter to pass to
        /// the method(s) is <paramref name="value"/>.
        /// </param>
        /// <exception cref="ArgumentOutOfRangeException">
        /// <paramref name="value"/> isn't between 0 and 255.
        /// </exception>
        internal static bool EqualsWith(this int value, char c, Action<int> action)
        {
            if (value < 0 || value > 255)
                throw new ArgumentOutOfRangeException(nameof(value));

            action(value);
            return value == c - 0;
        }

        internal static string GetMessage(this CloseStatusCode code)
        {
            return code == CloseStatusCode.ProtocolError
                   ? "A WebSocket protocol error has occurred."
                   : code == CloseStatusCode.IncorrectData
                     ? "An incorrect data has been received."
                     : code == CloseStatusCode.Abnormal
                       ? "An exception has occurred."
                       : code == CloseStatusCode.InconsistentData
                         ? "An inconsistent data has been received."
                         : code == CloseStatusCode.PolicyViolation
                           ? "A policy violation has occurred."
                           : code == CloseStatusCode.TooBig
                             ? "A too big data has been received."
                             : code == CloseStatusCode.IgnoreExtension
                               ? "WebSocket client did not receive expected extension(s)."
                               : code == CloseStatusCode.ServerError
                                 ? "WebSocket server got an internal error."
                                 : code == CloseStatusCode.TlsHandshakeFailure
                                   ? "An error has occurred while handshaking."
                                   : string.Empty;
        }

        internal static string GetNameInternal(this string nameAndValue, string separator)
        {
            var i = nameAndValue.IndexOf(separator);
            return i > 0
                   ? nameAndValue.Substring(0, i).Trim()
                   : null;
        }

        internal static string GetValueInternal(this string nameAndValue, string separator)
        {
            var i = nameAndValue.IndexOf(separator);
            return i >= 0 && i < nameAndValue.Length - 1
                   ? nameAndValue.Substring(i + 1).Trim()
                   : null;
        }

        internal static bool IsCompressionExtension(this string value, CompressionMethod method)
        {
            return value.StartsWith(method.ToExtensionString());
        }

        internal static bool IsPortNumber(this int value)
        {
            return value > 0 && value < 65536;
        }

        internal static bool IsReserved(this ushort code)
        {
            return code == (ushort)CloseStatusCode.Undefined ||
                   code == (ushort)CloseStatusCode.NoStatusCode ||
                   code == (ushort)CloseStatusCode.Abnormal ||
                   code == (ushort)CloseStatusCode.TlsHandshakeFailure;
        }

        internal static bool IsReserved(this CloseStatusCode code)
        {
            return code == CloseStatusCode.Undefined ||
                   code == CloseStatusCode.NoStatusCode ||
                   code == CloseStatusCode.Abnormal ||
                   code == CloseStatusCode.TlsHandshakeFailure;
        }

        internal static bool IsText(this string value)
        {
            var len = value.Length;
            for (var i = 0; i < len; i++)
            {
                char c = value[i];
                if (c < 0x20 && !"\r\n\t".Contains(c))
                    return false;

                if (c == 0x7f)
                    return false;

                if (c == '\n' && ++i < len)
                {
                    c = value[i];
                    if (!" \t".Contains(c))
                        return false;
                }
            }

            return true;
        }

        internal static bool IsToken(this string value)
        {
            foreach (char c in value)
                if (c < 0x20 || c >= 0x7f || _tspecials.Contains(c))
                    return false;

            return true;
        }

        internal static string Quote(this string value)
        {
            return value.IsToken()
                   ? value
                   : string.Format("\"{0}\"", value.Replace("\"", "\\\""));
        }

        internal static Task<byte[]> ReadBytesAsync(this Stream stream, int length)
            => stream.ReadBytesAsync(new byte[length], 0, length);

        internal static async Task<byte[]> ReadBytesAsync(this Stream stream, long length, int bufferLength)
        {
            using (var result = new MemoryStream())
            {
                var count = length / bufferLength;
                var rem = (int)(length % bufferLength);

                var buffer = new byte[bufferLength];
                var end = false;
                for (long i = 0; i < count; i++)
                {
                    if (!await stream.ReadBytesAsync(buffer, 0, bufferLength, result).ConfigureAwait(false))
                    {
                        end = true;
                        break;
                    }
                }

                if (!end && rem > 0)
                {
                    await stream.ReadBytesAsync(new byte[rem], 0, rem, result).ConfigureAwait(false);
                }

                return result.ToArray();
            }
        }

        internal static string RemovePrefix(this string value, params string[] prefixes)
        {
            var i = 0;
            foreach (var prefix in prefixes)
            {
                if (value.StartsWith(prefix))
                {
                    i = prefix.Length;
                    break;
                }
            }

            return i > 0
                   ? value.Substring(i)
                   : value;
        }

        internal static T[] Reverse<T>(this T[] array)
        {
            var len = array.Length;
            T[] reverse = new T[len];

            var end = len - 1;
            for (var i = 0; i <= end; i++)
                reverse[i] = array[end - i];

            return reverse;
        }

        internal static IEnumerable<string> SplitHeaderValue(
          this string value, params char[] separator)
        {
            var len = value.Length;
            var separators = new string(separator);

            var buffer = new StringBuilder(32);
            var quoted = false;
            var escaped = false;

            char c;
            for (var i = 0; i < len; i++)
            {
                c = value[i];
                if (c == '"')
                {
                    if (escaped)
                        escaped = !escaped;
                    else
                        quoted = !quoted;
                }
                else if (c == '\\')
                {
                    if (i < len - 1 && value[i + 1] == '"')
                        escaped = true;
                }
                else if (separators.Contains(c))
                {
                    if (!quoted)
                    {
                        yield return buffer.ToString();
                        buffer.Length = 0;

                        continue;
                    }
                }
                else
                {
                }

                buffer.Append(c);
            }

            if (buffer.Length > 0)
                yield return buffer.ToString();
        }

        internal static byte[] ToByteArray(this Stream stream)
        {
            using (var output = new MemoryStream())
            {
                stream.Position = 0;
                stream.CopyTo(output);

                return output.ToArray();
            }
        }

        internal static byte[] ToByteArrayInternally(this ushort value, ByteOrder order)
        {
            var bytes = BitConverter.GetBytes(value);
            if (!order.IsHostOrder())
                Array.Reverse(bytes);

            return bytes;
        }

        internal static byte[] ToByteArrayInternally(this ulong value, ByteOrder order)
        {
            var bytes = BitConverter.GetBytes(value);
            if (!order.IsHostOrder())
                Array.Reverse(bytes);

            return bytes;
        }

        internal static string ToExtensionString(
          this CompressionMethod method, params string[] parameters)
        {
            if (method == CompressionMethod.None)
                return string.Empty;

            var m = string.Format("permessage-{0}", method.ToString().ToLowerInvariant());
            if (parameters == null || parameters.Length == 0)
                return m;

            return string.Format("{0}; {1}", m, parameters.ToString("; "));
        }

        internal static ushort ToUInt16(this byte[] src, ByteOrder srcOrder)
        {
            src.ToHostOrder(srcOrder);
            return BitConverter.ToUInt16(src, 0);
        }

        internal static ulong ToUInt64(this byte[] src, ByteOrder srcOrder)
        {
            src.ToHostOrder(srcOrder);
            return BitConverter.ToUInt64(src, 0);
        }

        internal static string TrimEndSlash(this string value)
        {
            value = value.TrimEnd('/');
            return value.Length > 0
                   ? value
                   : "/";
        }

        internal static string Unquote(this string value)
        {
            var start = value.IndexOf('\"');
            var end = value.LastIndexOf('\"');
            if (start < end)
                value = value.Substring(start + 1, end - start - 1).Replace("\\\"", "\"");

            return value.Trim();
        }

        internal static void WriteBytes(this Stream stream, byte[] value)
        {
            using (var src = new MemoryStream(value))
            {
                src.CopyTo(stream);
            }
        }

        #endregion

        #region Public Methods

        /// <summary>
        /// Determines whether the specified <see cref="string"/> contains any of characters
        /// in the specified array of <see cref="char"/>.
        /// </summary>
        /// <returns>
        /// <c>true</c> if <paramref name="value"/> contains any of <paramref name="chars"/>;
        /// otherwise, <c>false</c>.
        /// </returns>
        /// <param name="value">
        /// A <see cref="string"/> to test.
        /// </param>
        /// <param name="chars">
        /// An array of <see cref="char"/> that contains characters to find.
        /// </param>
        public static bool Contains(this string value, params char[] chars)
        {
            return chars == null || chars.Length == 0
                   ? true
                   : value == null || value.Length == 0
                     ? false
                     : value.IndexOfAny(chars) != -1;
        }

        /// <summary>
        /// Determines whether the specified <see cref="QueryParamCollection"/> contains the entry
        /// with the specified <paramref name="name"/>.
        /// </summary>
        /// <returns>
        /// <c>true</c> if <paramref name="collection"/> contains the entry
        /// with <paramref name="name"/>; otherwise, <c>false</c>.
        /// </returns>
        /// <param name="collection">
        /// A <see cref="QueryParamCollection"/> to test.
        /// </param>
        /// <param name="name">
        /// A <see cref="string"/> that represents the key of the entry to find.
        /// </param>
        public static bool Contains(this QueryParamCollection collection, string name)
        {
            return collection == null || collection.Count == 0
                   ? false
                   : collection[name] != null;
        }

        /// <summary>
        /// Determines whether the specified <see cref="QueryParamCollection"/> contains the entry
        /// with the specified both <paramref name="name"/> and <paramref name="value"/>.
        /// </summary>
        /// <returns>
        /// <c>true</c> if <paramref name="collection"/> contains the entry
        /// with both <paramref name="name"/> and <paramref name="value"/>;
        /// otherwise, <c>false</c>.
        /// </returns>
        /// <param name="collection">
        /// A <see cref="QueryParamCollection"/> to test.
        /// </param>
        /// <param name="name">
        /// A <see cref="string"/> that represents the key of the entry to find.
        /// </param>
        /// <param name="value">
        /// A <see cref="string"/> that represents the value of the entry to find.
        /// </param>
        public static bool Contains(this QueryParamCollection collection, string name, string value)
        {
            if (collection == null || collection.Count == 0)
                return false;

            var values = collection[name];
            if (values == null)
                return false;

            foreach (var v in values.Split(','))
                if (v.Trim().Equals(value, StringComparison.OrdinalIgnoreCase))
                    return true;

            return false;
        }

        /// <summary>
        /// Emits the specified <c>EventHandler&lt;TEventArgs&gt;</c> delegate
        /// if it isn't <see langword="null"/>.
        /// </summary>
        /// <param name="eventHandler">
        /// An <c>EventHandler&lt;TEventArgs&gt;</c> to emit.
        /// </param>
        /// <param name="sender">
        /// An <see cref="object"/> from which emits this <paramref name="eventHandler"/>.
        /// </param>
        /// <param name="e">
        /// A <c>TEventArgs</c> that represents the event data.
        /// </param>
        /// <typeparam name="TEventArgs">
        /// The type of the event data generated by the event.
        /// </typeparam>
        public static void Emit<TEventArgs>(
          this EventHandler<TEventArgs> eventHandler, object sender, TEventArgs e)
          where TEventArgs : EventArgs
        {
            if (eventHandler != null)
                eventHandler(sender, e);
        }

        /// <summary>
        /// Gets the description of the specified HTTP status <paramref name="code"/>.
        /// </summary>
        /// <returns>
        /// A <see cref="string"/> that represents the description of the HTTP status code.
        /// </returns>
        /// <param name="code">
        /// One of <see cref="HttpStatusCode"/> enum values, indicates the HTTP status codes.
        /// </param>
        public static string GetDescription(this HttpStatusCode code)
        {
            return ((int)code).GetStatusDescription();
        }

        /// <summary>
        /// Gets the description of the specified HTTP status <paramref name="code"/>.
        /// </summary>
        /// <returns>
        /// A <see cref="string"/> that represents the description of the HTTP status code.
        /// </returns>
        /// <param name="code">
        /// An <see cref="int"/> that represents the HTTP status code.
        /// </param>
        public static string GetStatusDescription(this int code)
        {
            switch (code)
            {
                case 100: return "Continue";
                case 101: return "Switching Protocols";
                case 102: return "Processing";
                case 200: return "OK";
                case 201: return "Created";
                case 202: return "Accepted";
                case 203: return "Non-Authoritative Information";
                case 204: return "No Content";
                case 205: return "Reset Content";
                case 206: return "Partial Content";
                case 207: return "Multi-Status";
                case 300: return "Multiple Choices";
                case 301: return "Moved Permanently";
                case 302: return "Found";
                case 303: return "See Other";
                case 304: return "Not Modified";
                case 305: return "Use Proxy";
                case 307: return "Temporary Redirect";
                case 400: return "Bad Request";
                case 401: return "Unauthorized";
                case 402: return "Payment Required";
                case 403: return "Forbidden";
                case 404: return "Not Found";
                case 405: return "Method Not Allowed";
                case 406: return "Not Acceptable";
                case 407: return "Proxy Authentication Required";
                case 408: return "Request Timeout";
                case 409: return "Conflict";
                case 410: return "Gone";
                case 411: return "Length Required";
                case 412: return "Precondition Failed";
                case 413: return "Request Entity Too Large";
                case 414: return "Request-Uri Too Long";
                case 415: return "Unsupported Media Type";
                case 416: return "Requested Range Not Satisfiable";
                case 417: return "Expectation Failed";
                case 422: return "Unprocessable Entity";
                case 423: return "Locked";
                case 424: return "Failed Dependency";
                case 500: return "Internal Server Error";
                case 501: return "Not Implemented";
                case 502: return "Bad Gateway";
                case 503: return "Service Unavailable";
                case 504: return "Gateway Timeout";
                case 505: return "Http Version Not Supported";
                case 507: return "Insufficient Storage";
            }

            return string.Empty;
        }

        /// <summary>
        /// Determines whether the specified <see cref="ByteOrder"/> is host
        /// (this computer architecture) byte order.
        /// </summary>
        /// <returns>
        /// <c>true</c> if <paramref name="order"/> is host byte order;
        /// otherwise, <c>false</c>.
        /// </returns>
        /// <param name="order">
        /// One of the <see cref="ByteOrder"/> enum values, to test.
        /// </param>
        public static bool IsHostOrder(this ByteOrder order)
        {
            // true : !(true ^ true)  or !(false ^ false)
            // false: !(true ^ false) or !(false ^ true)
            return !(BitConverter.IsLittleEndian ^ (order == ByteOrder.Little));
        }

        /// <summary>
        /// Determines whether the specified <see cref="string"/> is a predefined scheme.
        /// </summary>
        /// <returns>
        /// <c>true</c> if <paramref name="value"/> is a predefined scheme; otherwise, <c>false</c>.
        /// </returns>
        /// <param name="value">
        /// A <see cref="string"/> to test.
        /// </param>
        public static bool IsPredefinedScheme(this string value)
        {
            if (value == null || value.Length < 2)
                return false;

            var c = value[0];
            if (c == 'h')
                return value == "http" || value == "https";

            if (c == 'w')
                return value == "ws" || value == "wss";

            if (c == 'f')
                return value == "file" || value == "ftp";

            if (c == 'n')
            {
                c = value[1];
                return c == 'e'
                       ? value == "news" || value == "net.pipe" || value == "net.tcp"
                       : value == "nntp";
            }

            return (c == 'g' && value == "gopher") || (c == 'm' && value == "mailto");
        }

        /// <summary>
        /// Determines whether the specified <see cref="string"/> is a URI string.
        /// </summary>
        /// <returns>
        /// <c>true</c> if <paramref name="value"/> may be a URI string; otherwise, <c>false</c>.
        /// </returns>
        /// <param name="value">
        /// A <see cref="string"/> to test.
        /// </param>
        public static bool MaybeUri(this string value)
        {
            if (value == null || value.Length == 0)
                return false;

            var i = value.IndexOf(':');
            if (i == -1)
                return false;

            if (i >= 10)
                return false;

            return value.Substring(0, i).IsPredefinedScheme();
        }

        /// <summary>
        /// Retrieves a sub-array from the specified <paramref name="array"/>.
        /// A sub-array starts at the specified element position.
        /// </summary>
        /// <returns>
        /// An array of T that receives a sub-array, or an empty array of T if any problems
        /// with the parameters.
        /// </returns>
        /// <param name="array">
        /// An array of T that contains the data to retrieve a sub-array.
        /// </param>
        /// <param name="startIndex">
        /// An <see cref="int"/> that contains the zero-based starting position of a sub-array
        /// in <paramref name="array"/>.
        /// </param>
        /// <param name="length">
        /// An <see cref="int"/> that contains the number of elements to retrieve a sub-array.
        /// </param>
        /// <typeparam name="T">
        /// The type of elements in the <paramref name="array"/>.
        /// </typeparam>
        public static T[] SubArray<T>(this T[] array, int startIndex, int length)
        {
            if (array == null || array.Length == 0)
                return new T[0];

            if (startIndex < 0 || length <= 0)
                return new T[0];

            if (startIndex + length > array.Length)
                return new T[0];

            if (startIndex == 0 && array.Length == length)
                return array;

            T[] subArray = new T[length];
            Array.Copy(array, startIndex, subArray, 0, length);

            return subArray;
        }

        /// <summary>
        /// Converts the order of the specified array of <see cref="byte"/> to the host byte order.
        /// </summary>
        /// <returns>
        /// An array of <see cref="byte"/> converted from <paramref name="src"/>.
        /// </returns>
        /// <param name="src">
        /// An array of <see cref="byte"/> to convert.
        /// </param>
        /// <param name="srcOrder">
        /// One of the <see cref="ByteOrder"/> enum values, indicates the byte order of
        /// <paramref name="src"/>.
        /// </param>
        /// <exception cref="ArgumentNullException">
        /// <paramref name="src"/> is <see langword="null"/>.
        /// </exception>
        public static void ToHostOrder(this byte[] src, ByteOrder srcOrder)
        {
            if (src == null)
            {
                throw new ArgumentNullException(nameof(src));
            }

            if (src.Length > 1 && !srcOrder.IsHostOrder())
            {
                Array.Reverse(src);
            }
        }

        /// <summary>
        /// Converts the specified <paramref name="array"/> to a <see cref="string"/> that
        /// concatenates the each element of <paramref name="array"/> across the specified
        /// <paramref name="separator"/>.
        /// </summary>
        /// <returns>
        /// A <see cref="string"/> converted from <paramref name="array"/>,
        /// or <see cref="String.Empty"/> if <paramref name="array"/> is empty.
        /// </returns>
        /// <param name="array">
        /// An array of T to convert.
        /// </param>
        /// <param name="separator">
        /// A <see cref="string"/> that represents the separator string.
        /// </param>
        /// <typeparam name="T">
        /// The type of elements in <paramref name="array"/>.
        /// </typeparam>
        /// <exception cref="ArgumentNullException">
        /// <paramref name="array"/> is <see langword="null"/>.
        /// </exception>
        public static string ToString<T>(this T[] array, string separator)
        {
            if (array == null)
                throw new ArgumentNullException(nameof(array));

            var len = array.Length;
            if (len == 0)
                return string.Empty;

            if (separator == null)
                separator = string.Empty;

            var buff = new StringBuilder(64);
            (len - 1).Times(i => buff.AppendFormat("{0}{1}", array[i].ToString(), separator));

            buff.Append(array[len - 1].ToString());
            return buff.ToString();
        }

        /// <summary>
        /// Executes the specified <c>Action&lt;int&gt;</c> delegate <paramref name="n"/> times.
        /// </summary>
        /// <param name="n">
        /// An <see cref="int"/> is the number of times to execute.
        /// </param>
        /// <param name="action">
        /// An <c>Action&lt;int&gt;</c> delegate that references the method(s) to execute.
        /// An <see cref="int"/> parameter to pass to the method(s) is the zero-based count of
        /// iteration.
        /// </param>
        public static void Times(this int n, Action<int> action)
        {
            if (n > 0 && action != null)
                for (int i = 0; i < n; i++)
                    action(i);
        }

        /// <summary>
        /// Converts the specified <see cref="string"/> to a <see cref="Uri"/>.
        /// </summary>
        /// <returns>
        /// A <see cref="Uri"/> converted from <paramref name="uriString"/>, or <see langword="null"/>
        /// if <paramref name="uriString"/> isn't successfully converted.
        /// </returns>
        /// <param name="uriString">
        /// A <see cref="string"/> to convert.
        /// </param>
        public static Uri ToUri(this string uriString)
        {
            return Uri.TryCreate(
                     uriString, uriString.MaybeUri() ? UriKind.Absolute : UriKind.Relative, out var res)
                   ? res
                   : null;
        }

        /// <summary>
        /// URL-decodes the specified <see cref="string"/>.
        /// </summary>
        /// <returns>
        /// A <see cref="string"/> that receives the decoded string, or the <paramref name="value"/>
        /// if it's <see langword="null"/> or empty.
        /// </returns>
        /// <param name="value">
        /// A <see cref="string"/> to decode.
        /// </param>
        public static string UrlDecode(this string value)
        {
            return value == null || value.Length == 0
                   ? value
                   : WebUtility.UrlDecode(value);
        }

        #endregion
    }
}