Function urlencode

dlib/server/server_http.cpp:20–43

        }

        const std::string urlencode( const std::string& s )  
        {
            std::ostringstream os;

            for ( std::string::const_iterator ci = s.begin(); ci != s.end(); ++ci )
            {
                if ( (*ci >= 'a' && *ci <= 'z') ||
                     (*ci >= 'A' && *ci <= 'Z') ||
                     (*ci >= '0' && *ci <= '9') )
                { // allowed
                    os << *ci;
                }
                else if ( *ci == ' ')
                {
                    os << '+';
                }
                else
                {
                    os << '%' << to_hex(*ci >> 4) << to_hex(*ci % 16);
                }
            }

            return os.str();
        }

        inline unsigned char from_hex (
            unsigned char ch