github.com/metacubex/gvisor@v0.0.0-20240320004321-933faba989ec/pkg/tcpip/checksum/checksum.go (about)

     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  }