code: func httpParseHeaderLine(line []byte) (k, v []byte, ok bool) {
  	colon := bytes.IndexByte(line, ':')
  	if colon == -1 {
  		return
  	}
  
  	k = btrim(line[:colon])
  	// TODO(gobwas): maybe use just lower here?
  	canonicalizeHeaderKey(k)
  
  	v = btrim(line[colon+1:])
  
  	return k, v, true
  }
docs: // httpParseHeaderLine parses HTTP header as key-value pair. It returns parsed
  // values and true if parse is ok.