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fix bug in right aligned field extraction

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This commit is contained in:
Patricio Whittingslow
2025-12-31 02:58:09 -03:00
parent 5f0edf62a9
commit 02ca576e14
2 changed files with 251 additions and 4 deletions
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internet/pcap/capture.go
+8 -4
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@@ -590,10 +590,14 @@ func appendField(dst, pkt []byte, fieldBitStart, bitlen int, rightAligned bool)
dst = append(dst, pkt[octetsStart+1:octetsStart+octets]...)
return dst, nil
}
// Right aligned with trailing bits. i.e: ???
for i := 1; i < octets; i++ {
b := pkt[octetsStart+i] >> (8 - lastOctetExcessBits)
b |= pkt[octetsStart+i-1] & mask
// Right aligned with trailing bits. i.e: IPv6 Traffic Class.
// Field spans an extra byte, so need octets+1 bytes from packet.
if octets+octetsStart+1 > len(pkt) {
return dst, errors.New("buffer overflow")
}
for i := 0; i < octets; i++ {
b := (pkt[octetsStart+i] & mask) << (8 - firstBitOffset)
b |= pkt[octetsStart+i+1] >> firstBitOffset
dst = append(dst, b)
}
return dst, nil