| package dns |
| |
| import "encoding/binary" |
| |
| // rawSetRdlength sets the rdlength in the header of |
| // the RR. The offset 'off' must be positioned at the |
| // start of the header of the RR, 'end' must be the |
| // end of the RR. |
| func rawSetRdlength(msg []byte, off, end int) bool { |
| l := len(msg) |
| Loop: |
| for { |
| if off+1 > l { |
| return false |
| } |
| c := int(msg[off]) |
| off++ |
| switch c & 0xC0 { |
| case 0x00: |
| if c == 0x00 { |
| // End of the domainname |
| break Loop |
| } |
| if off+c > l { |
| return false |
| } |
| off += c |
| |
| case 0xC0: |
| // pointer, next byte included, ends domainname |
| off++ |
| break Loop |
| } |
| } |
| // The domainname has been seen, we at the start of the fixed part in the header. |
| // Type is 2 bytes, class is 2 bytes, ttl 4 and then 2 bytes for the length. |
| off += 2 + 2 + 4 |
| if off+2 > l { |
| return false |
| } |
| //off+1 is the end of the header, 'end' is the end of the rr |
| //so 'end' - 'off+2' is the length of the rdata |
| rdatalen := end - (off + 2) |
| if rdatalen > 0xFFFF { |
| return false |
| } |
| binary.BigEndian.PutUint16(msg[off:], uint16(rdatalen)) |
| return true |
| } |