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// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package icmp
import (
"encoding/binary"
"net"
"runtime"
"golang.org/x/net/internal/socket"
"golang.org/x/net/ipv4"
)
// freebsdVersion is set in sys_freebsd.go.
// See http://www.freebsd.org/doc/en/books/porters-handbook/freebsd-versions.html.
var freebsdVersion uint32
// ParseIPv4Header returns the IPv4 header of the IPv4 packet that
// triggered an ICMP error message.
// This is found in the Data field of the ICMP error message body.
//
// The provided b must be in the format used by a raw ICMP socket on
// the local system.
// This may differ from the wire format, and the format used by a raw
// IP socket, depending on the system.
//
// To parse an IPv6 header, use ipv6.ParseHeader.
func ParseIPv4Header(b []byte) (*ipv4.Header, error) {
if len(b) < ipv4.HeaderLen {
return nil, errHeaderTooShort
}
hdrlen := int(b[0]&0x0f) << 2
if hdrlen > len(b) {
return nil, errBufferTooShort
}
h := &ipv4.Header{
Version: int(b[0] >> 4),
Len: hdrlen,
TOS: int(b[1]),
ID: int(binary.BigEndian.Uint16(b[4:6])),
FragOff: int(binary.BigEndian.Uint16(b[6:8])),
TTL: int(b[8]),
Protocol: int(b[9]),
Checksum: int(binary.BigEndian.Uint16(b[10:12])),
Src: net.IPv4(b[12], b[13], b[14], b[15]),
Dst: net.IPv4(b[16], b[17], b[18], b[19]),
}
switch runtime.GOOS {
case "darwin":
h.TotalLen = int(socket.NativeEndian.Uint16(b[2:4]))
case "freebsd":
if freebsdVersion >= 1000000 {
h.TotalLen = int(binary.BigEndian.Uint16(b[2:4]))
} else {
h.TotalLen = int(socket.NativeEndian.Uint16(b[2:4]))
}
default:
h.TotalLen = int(binary.BigEndian.Uint16(b[2:4]))
}
h.Flags = ipv4.HeaderFlags(h.FragOff&0xe000) >> 13
h.FragOff = h.FragOff & 0x1fff
if hdrlen-ipv4.HeaderLen > 0 {
h.Options = make([]byte, hdrlen-ipv4.HeaderLen)
copy(h.Options, b[ipv4.HeaderLen:])
}
return h, nil
}
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