bytesconv.go
func AppendHTTPDate(dst []byte, date time.Time) []byte {
	dst = date.In(time.UTC).AppendFormat(dst, time.RFC1123)
	copy(dst[len(dst)-3:], strGMT)
	return dst
}
func AppendHTTPDate(dst []byte, date time.Time) []byte {
	dst = date.In(time.UTC).AppendFormat(dst, time.RFC1123)
	copy(dst[len(dst)-3:], strGMT)
	return dst
}
// AppendHTTPDate appends HTTP-compliant (RFC1123) representation of date
// to dst and returns the extended dst.