title: why does http use CRLF as line delimiter?
body: <p>As I know, use <code>LF</code> as line delimiter is quite popular, but I'm wondering why many text protocol like HTTP, FTP use <code>CRLF</code> as its line delimiter?</p>
  
  <p>I don't think these protocols are invented for old typewriters, so is there any historic reason for this? I tried to search it over google and stackoverflow and wikipedia but do not get any reasonable information.</p>
  
  <p>Thanks</p>