System.Net.WebSockets.WebSocketHandle.BuildRequestHeader C# (CSharp) Method

        private static byte[] BuildRequestHeader(Uri uri, ClientWebSocketOptions options, string secKey)
        {
            StringBuilder builder = t_cachedStringBuilder ?? (t_cachedStringBuilder = new StringBuilder());
            Debug.Assert(builder.Length == 0, $"Expected builder to be empty, got one of length {builder.Length}");
            try
            {
                builder.Append("GET ").Append(uri.PathAndQuery).Append(" HTTP/1.1\r\n");

                // Add all of the required headers
                builder.Append("Host: ").Append(uri.IdnHost).Append(":").Append(uri.Port).Append("\r\n");
                builder.Append("Connection: Upgrade\r\n");
                builder.Append("Upgrade: websocket\r\n");
                builder.Append("Sec-WebSocket-Version: 13\r\n");
                builder.Append("Sec-WebSocket-Key: ").Append(secKey).Append("\r\n");

                // Add all of the additionally requested headers
                foreach (string key in options.RequestHeaders.AllKeys)
                {
                    builder.Append(key).Append(": ").Append(options.RequestHeaders[key]).Append("\r\n");
                }

                // Add the optional subprotocols header
                if (options.RequestedSubProtocols.Count > 0)
                {
                    builder.Append(HttpKnownHeaderNames.SecWebSocketProtocol).Append(": ");
                    builder.Append(options.RequestedSubProtocols[0]);
                    for (int i = 1; i < options.RequestedSubProtocols.Count; i++)
                    {
                        builder.Append(", ").Append(options.RequestedSubProtocols[i]);
                    }
                    builder.Append("\r\n");
                }

                // Add an optional cookies header
                if (options.Cookies != null)
                {
                    string header = options.Cookies.GetCookieHeader(uri);
                    if (!string.IsNullOrWhiteSpace(header))
                    {
                        builder.Append(HttpKnownHeaderNames.Cookie).Append(": ").Append(header).Append("\r\n");
                    }
                }

                // End the headers
                builder.Append("\r\n");

                // Return the bytes for the built up header
                return s_defaultHttpEncoding.GetBytes(builder.ToString());
            }
            finally
            {
                // Make sure we clear the builder
                builder.Clear();
            }
        }