47 lines
1.4 KiB
Go
47 lines
1.4 KiB
Go
// Copyright 2016 The Netstack Authors. 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 header provides the implementation of the encoding and decoding of
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// network protocol headers.
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package header
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import (
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"gvisor.googlesource.com/gvisor/pkg/tcpip"
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)
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// Checksum calculates the checksum (as defined in RFC 1071) of the bytes in the
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// given byte array.
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func Checksum(buf []byte, initial uint16) uint16 {
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v := uint32(initial)
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l := len(buf)
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if l&1 != 0 {
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l--
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v += uint32(buf[l]) << 8
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}
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for i := 0; i < l; i += 2 {
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v += (uint32(buf[i]) << 8) + uint32(buf[i+1])
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}
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return ChecksumCombine(uint16(v), uint16(v>>16))
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}
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// ChecksumCombine combines the two uint16 to form their checksum. This is done
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// by adding them and the carry.
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func ChecksumCombine(a, b uint16) uint16 {
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v := uint32(a) + uint32(b)
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return uint16(v + v>>16)
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}
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// PseudoHeaderChecksum calculates the pseudo-header checksum for the
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// given destination protocol and network address, ignoring the length
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// field. Pseudo-headers are needed by transport layers when calculating
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// their own checksum.
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func PseudoHeaderChecksum(protocol tcpip.TransportProtocolNumber, srcAddr tcpip.Address, dstAddr tcpip.Address) uint16 {
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xsum := Checksum([]byte(srcAddr), 0)
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xsum = Checksum([]byte(dstAddr), xsum)
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return Checksum([]byte{0, uint8(protocol)}, xsum)
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}
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