1 // Copyright 2018 The gVisor Authors.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 15 // Package checksum provides the implementation of the encoding and decoding of
16 // network protocol headers.
17 package checksum
18 19 import (
20 "encoding/binary"
21 )
22 23 // Size is the size of a checksum.
24 //
25 // The checksum is held in a uint16 which is 2 bytes.
26 const Size = 2
27 28 // Put puts the checksum in the provided byte slice.
29 func Put(b []byte, xsum uint16) {
30 binary.BigEndian.PutUint16(b, xsum)
31 }
32 33 // Checksum calculates the checksum (as defined in RFC 1071) of the bytes in the
34 // given byte array. This function uses an optimized version of the checksum
35 // algorithm.
36 //
37 // The initial checksum must have been computed on an even number of bytes.
38 func Checksum(buf []byte, initial uint16) uint16 {
39 s, _ := calculateChecksum(buf, false, initial)
40 return s
41 }
42 43 // Checksumer calculates checksum defined in RFC 1071.
44 type Checksumer struct {
45 sum uint16
46 odd bool
47 }
48 49 // Add adds b to checksum.
50 func (c *Checksumer) Add(b []byte) {
51 if len(b) > 0 {
52 c.sum, c.odd = calculateChecksum(b, c.odd, c.sum)
53 }
54 }
55 56 // Checksum returns the latest checksum value.
57 func (c *Checksumer) Checksum() uint16 {
58 return c.sum
59 }
60 61 // Combine combines the two uint16 to form their checksum. This is done
62 // by adding them and the carry.
63 //
64 // Note that checksum a must have been computed on an even number of bytes.
65 func Combine(a, b uint16) uint16 {
66 v := uint32(a) + uint32(b)
67 return uint16(v + v>>16)
68 }
69