| // 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" |
| |
| "github.com/google/netstack/tcpip" |
| "github.com/google/netstack/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) |
| } |