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rawmsg.go
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rawmsg.go
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package dns
// These raw* functions do not use reflection, they directly set the values
// in the buffer. There are faster than their reflection counterparts.
// RawSetId sets the message id in buf.
func rawSetId(msg []byte, i uint16) bool {
if len(msg) < 2 {
return false
}
msg[0], msg[1] = packUint16(i)
return true
}
// rawSetQuestionLen sets the length of the question section.
func rawSetQuestionLen(msg []byte, i uint16) bool {
if len(msg) < 6 {
return false
}
msg[4], msg[5] = packUint16(i)
return true
}
// rawSetAnswerLen sets the lenght of the answer section.
func rawSetAnswerLen(msg []byte, i uint16) bool {
if len(msg) < 8 {
return false
}
msg[6], msg[7] = packUint16(i)
return true
}
// rawSetsNsLen sets the lenght of the authority section.
func rawSetNsLen(msg []byte, i uint16) bool {
if len(msg) < 10 {
return false
}
msg[8], msg[9] = packUint16(i)
return true
}
// rawSetExtraLen sets the lenght of the additional section.
func rawSetExtraLen(msg []byte, i uint16) bool {
if len(msg) < 12 {
return false
}
msg[10], msg[11] = packUint16(i)
return true
}
// 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
}
msg[off], msg[off+1] = packUint16(uint16(rdatalen))
return true
}