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