54 lines
1.5 KiB
Go
54 lines
1.5 KiB
Go
// Copyright 2012 Miek Gieben. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package dns
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// Function defined in this subpackage work on []byte and but still
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// provide some higher level functions.
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// RawSetId sets the message ID in buf. The offset 'off' must
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// be positioned at the beginning of the message.
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func RawSetId(msg []byte, off int, id uint16) bool {
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msg[off], msg[off+1] = packUint16(id)
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return true
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}
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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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// We are at the start of the header, walk the domainname (might be compressed)
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Loop:
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for {
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if off > len(msg) {
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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 & 0xC00 {
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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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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+1 > len(msg) {
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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 lenght of the rdata
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msg[off], msg[off+1] = packUint16(uint16(end - (off + 2)))
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return true
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}
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