inet.af/netstack@v0.0.0-20220214151720-7585b01ddccf/tcpip/link/sniffer/pcap.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 sniffer 16 17 import ( 18 "encoding" 19 "encoding/binary" 20 "time" 21 22 "inet.af/netstack/tcpip" 23 "inet.af/netstack/tcpip/stack" 24 ) 25 26 type pcapHeader struct { 27 // MagicNumber is the file magic number. 28 MagicNumber uint32 29 30 // VersionMajor is the major version number. 31 VersionMajor uint16 32 33 // VersionMinor is the minor version number. 34 VersionMinor uint16 35 36 // Thiszone is the GMT to local correction. 37 Thiszone int32 38 39 // Sigfigs is the accuracy of timestamps. 40 Sigfigs uint32 41 42 // Snaplen is the max length of captured packets, in octets. 43 Snaplen uint32 44 45 // Network is the data link type. 46 Network uint32 47 } 48 49 var _ encoding.BinaryMarshaler = (*pcapPacket)(nil) 50 51 type pcapPacket struct { 52 timestamp time.Time 53 packet *stack.PacketBuffer 54 maxCaptureLen int 55 } 56 57 func (p *pcapPacket) MarshalBinary() ([]byte, error) { 58 packetSize := p.packet.Size() 59 captureLen := p.maxCaptureLen 60 if packetSize < captureLen { 61 captureLen = packetSize 62 } 63 b := make([]byte, 16+captureLen) 64 binary.BigEndian.PutUint32(b[0:4], uint32(p.timestamp.Unix())) 65 binary.BigEndian.PutUint32(b[4:8], uint32(p.timestamp.Nanosecond()/1000)) 66 binary.BigEndian.PutUint32(b[8:12], uint32(captureLen)) 67 binary.BigEndian.PutUint32(b[12:16], uint32(packetSize)) 68 w := tcpip.SliceWriter(b[16:]) 69 for _, v := range p.packet.Views() { 70 if captureLen == 0 { 71 break 72 } 73 if len(v) > captureLen { 74 v = v[:captureLen] 75 } 76 n, err := w.Write(v) 77 if err != nil { 78 panic(err) 79 } 80 captureLen -= n 81 } 82 return b, nil 83 }