code: func MIMEType(hdr []byte) string {
  	hlen := len(hdr)
  	for _, pte := range matchTable {
  		if pte.fn != nil {
  			if pte.fn(hdr) {
  				return pte.mtype
  			}
  			continue
  		}
  		plen := pte.offset + len(pte.prefix)
  		if hlen > plen && bytes.Equal(hdr[pte.offset:plen], pte.prefix) {
  			return pte.mtype
  		}
  	}
  	t := http.DetectContentType(hdr)
  	t = strings.Replace(t, "; charset=utf-8", "", 1)
  	if t != "application/octet-stream" && t != "text/plain" {
  		return t
  	}
  	return ""
  }
docs: // MIMEType returns the MIME type from the data in the provided header
  // of the data.
  // It returns the empty string if the MIME type can't be determined.