code: function sendFile(params) {
      const p = params;
      
      checkParams(params);
      
      fs.lstat(p.name, (error, stat) => {
          if (error)
              return sendError(error, params);
          
          const isGzip = isGZIP(p.request) && p.gzip;
          const time = stat.mtime.toUTCString();
          const length = stat.size;
          const range = getRange(p.request, length);
          
          if (range)
              assign(p, {
                  range,
                  status: RANGE
              });
          
          assign(p, {
              time
          });
          
          if (!isGzip)
              p.length = length;
          
          setHeader(params);
          
          const options = {
              gzip    : isGzip,
              range,
          };
          
          files.pipe(p.name, p.response, options).catch((error) => {
              sendError(error, params);
          });
      });
  }
docs: send file to client thru pipe
  and gzip it if client support