vendor/golang.org/x/net/icmp/ipv4.go

   1 // Copyright 2014 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 package icmp
   6
   7 import (
   8         "encoding/binary"
   9         "net"
  10         "runtime"
  11
  12         "golang.org/x/net/internal/socket"
  13         "golang.org/x/net/ipv4"
  14 )
  15
  16 // freebsdVersion is set in sys_freebsd.go.
  17 // See http://www.freebsd.org/doc/en/books/porters-handbook/freebsd-versions.html.
  18 var freebsdVersion uint32
  19
  20 // ParseIPv4Header returns the IPv4 header of the IPv4 packet that
  21 // triggered an ICMP error message.
  22 // This is found in the Data field of the ICMP error message body.
  23 //
  24 // The provided b must be in the format used by a raw ICMP socket on
  25 // the local system.
  26 // This may differ from the wire format, and the format used by a raw
  27 // IP socket, depending on the system.
  28 //
  29 // To parse an IPv6 header, use ipv6.ParseHeader.
  30 func ParseIPv4Header(b []byte) (*ipv4.Header, error) {
  31         if len(b) < ipv4.HeaderLen {
  32                 return nil, errHeaderTooShort
  33         }
  34         hdrlen := int(b[0]&0x0f) << 2
  35         if hdrlen > len(b) {
  36                 return nil, errBufferTooShort
  37         }
  38         h := &ipv4.Header{
  39                 Version:  int(b[0] >> 4),
  40                 Len:      hdrlen,
  41                 TOS:      int(b[1]),
  42                 ID:       int(binary.BigEndian.Uint16(b[4:6])),
  43                 FragOff:  int(binary.BigEndian.Uint16(b[6:8])),
  44                 TTL:      int(b[8]),
  45                 Protocol: int(b[9]),
  46                 Checksum: int(binary.BigEndian.Uint16(b[10:12])),
  47                 Src:      net.IPv4(b[12], b[13], b[14], b[15]),
  48                 Dst:      net.IPv4(b[16], b[17], b[18], b[19]),
  49         }
  50         switch runtime.GOOS {
  51         case "darwin":
  52                 h.TotalLen = int(socket.NativeEndian.Uint16(b[2:4]))
  53         case "freebsd":
  54                 if freebsdVersion >= 1000000 {
  55                         h.TotalLen = int(binary.BigEndian.Uint16(b[2:4]))
  56                 } else {
  57                         h.TotalLen = int(socket.NativeEndian.Uint16(b[2:4]))
  58                 }
  59         default:
  60                 h.TotalLen = int(binary.BigEndian.Uint16(b[2:4]))
  61         }
  62         h.Flags = ipv4.HeaderFlags(h.FragOff&0xe000) >> 13
  63         h.FragOff = h.FragOff & 0x1fff
  64         if hdrlen-ipv4.HeaderLen > 0 {
  65                 h.Options = make([]byte, hdrlen-ipv4.HeaderLen)
  66                 copy(h.Options, b[ipv4.HeaderLen:])
  67         }
  68         return h, nil
  69 }