System.Net.HttpListenerRequest.Helpers.GetAttributeFromHeader C# (CSharp) Method

            internal static string GetAttributeFromHeader(string headerValue, string attrName)
            {
                if (headerValue == null)
                    return null;

                int l = headerValue.Length;
                int k = attrName.Length;

                // find properly separated attribute name
                int i = 1; // start searching from 1

                while (i < l)
                {
                    i = CultureInfo.InvariantCulture.CompareInfo.IndexOf(headerValue, attrName, i, CompareOptions.IgnoreCase);
                    if (i < 0)
                        break;
                    if (i + k >= l)
                        break;

                    char chPrev = headerValue[i - 1];
                    char chNext = headerValue[i + k];
                    if ((chPrev == ';' || chPrev == ',' || char.IsWhiteSpace(chPrev)) && (chNext == '=' || char.IsWhiteSpace(chNext)))
                        break;

                    i += k;
                }

                if (i < 0 || i >= l)
                    return null;

                // skip to '=' and the following whitespaces
                i += k;
                while (i < l && char.IsWhiteSpace(headerValue[i]))
                    i++;
                if (i >= l || headerValue[i] != '=')
                    return null;
                i++;
                while (i < l && char.IsWhiteSpace(headerValue[i]))
                    i++;
                if (i >= l)
                    return null;

                // parse the value
                string attrValue = null;

                int j;

                if (i < l && headerValue[i] == '"')
                {
                    if (i == l - 1)
                        return null;
                    j = headerValue.IndexOf('"', i + 1);
                    if (j < 0 || j == i + 1)
                        return null;

                    attrValue = headerValue.Substring(i + 1, j - i - 1).Trim();
                }
                else
                {
                    for (j = i; j < l; j++)
                    {
                        if (headerValue[j] == ' ' || headerValue[j] == ',')
                            break;
                    }

                    if (j == i)
                        return null;

                    attrValue = headerValue.Substring(i, j - i).Trim();
                }

                return attrValue;
            }