mirror of
https://github.com/SagerNet/sing-tun.git
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68 lines
1.9 KiB
Go
68 lines
1.9 KiB
Go
// Copyright 2018 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package checksum provides the implementation of the encoding and decoding of
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// network protocol headers.
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package checksum
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import (
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"encoding/binary"
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)
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// Size is the size of a checksum.
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//
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// The checksum is held in a uint16 which is 2 bytes.
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const Size = 2
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// Put puts the checksum in the provided byte slice.
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func Put(b []byte, xsum uint16) {
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binary.BigEndian.PutUint16(b, xsum)
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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. This function uses an optimized version of the checksum
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// algorithm.
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//
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// The initial checksum must have been computed on an even number of bytes.
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func Checksum(buf []byte, initial uint16) uint16 {
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s, _ := calculateChecksum(buf, false, initial)
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return s
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}
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// Checksumer calculates checksum defined in RFC 1071.
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type Checksumer struct {
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sum uint16
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odd bool
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}
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// Add adds b to checksum.
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func (c *Checksumer) Add(b []byte) {
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if len(b) > 0 {
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c.sum, c.odd = calculateChecksum(b, c.odd, c.sum)
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}
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}
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// Checksum returns the latest checksum value.
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func (c *Checksumer) Checksum() uint16 {
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return c.sum
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}
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// Combine 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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//
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// Note that checksum a must have been computed on an even number of bytes.
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func Combine(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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