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// Copyright 2018 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package header provides the implementation of the encoding and decoding of
// network protocol headers.
package header
import (
"encoding/binary"
"gvisor.googlesource.com/gvisor/pkg/tcpip"
"gvisor.googlesource.com/gvisor/pkg/tcpip/buffer"
)
func calculateChecksum(buf []byte, initial uint32) uint16 {
v := initial
l := len(buf)
if l&1 != 0 {
l--
v += uint32(buf[l]) << 8
}
for i := 0; i < l; i += 2 {
v += (uint32(buf[i]) << 8) + uint32(buf[i+1])
}
return ChecksumCombine(uint16(v), uint16(v>>16))
}
// Checksum calculates the checksum (as defined in RFC 1071) of the bytes in the
// given byte array.
//
// The initial checksum must have been computed on an even number of bytes.
func Checksum(buf []byte, initial uint16) uint16 {
return calculateChecksum(buf, uint32(initial))
}
// ChecksumVV calculates the checksum (as defined in RFC 1071) of the bytes in
// the given VectorizedView.
//
// The initial checksum must have been computed on an even number of bytes.
func ChecksumVV(vv buffer.VectorisedView, initial uint16) uint16 {
var odd bool
sum := initial
for _, v := range vv.Views() {
if len(v) == 0 {
continue
}
s := uint32(sum)
if odd {
s += uint32(v[0])
v = v[1:]
}
odd = len(v)&1 != 0
sum = calculateChecksum(v, s)
}
return sum
}
// ChecksumCombine combines the two uint16 to form their checksum. This is done
// by adding them and the carry.
//
// Note that checksum a must have been computed on an even number of bytes.
func ChecksumCombine(a, b uint16) uint16 {
v := uint32(a) + uint32(b)
return uint16(v + v>>16)
}
// PseudoHeaderChecksum calculates the pseudo-header checksum for the given
// destination protocol and network address. Pseudo-headers are needed by
// transport layers when calculating their own checksum.
func PseudoHeaderChecksum(protocol tcpip.TransportProtocolNumber, srcAddr tcpip.Address, dstAddr tcpip.Address, totalLen uint16) uint16 {
xsum := Checksum([]byte(srcAddr), 0)
xsum = Checksum([]byte(dstAddr), xsum)
// Add the length portion of the checksum to the pseudo-checksum.
tmp := make([]byte, 2)
binary.BigEndian.PutUint16(tmp, totalLen)
xsum = Checksum(tmp, xsum)
return Checksum([]byte{0, uint8(protocol)}, xsum)
}
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