62 lines
1.7 KiB
Go
62 lines
1.7 KiB
Go
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// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package icmp
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import (
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"net"
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"runtime"
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"unsafe"
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"golang.org/x/net/ipv4"
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)
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// See http://www.freebsd.org/doc/en/books/porters-handbook/freebsd-versions.html.
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var freebsdVersion uint32
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// ParseIPv4Header parses b as an IPv4 header of ICMP error message
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// invoking packet, which is contained in ICMP error message.
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func ParseIPv4Header(b []byte) (*ipv4.Header, error) {
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if len(b) < ipv4.HeaderLen {
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return nil, errHeaderTooShort
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}
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hdrlen := int(b[0]&0x0f) << 2
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if hdrlen > len(b) {
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return nil, errBufferTooShort
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}
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h := &ipv4.Header{
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Version: int(b[0] >> 4),
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Len: hdrlen,
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TOS: int(b[1]),
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ID: int(b[4])<<8 | int(b[5]),
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FragOff: int(b[6])<<8 | int(b[7]),
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TTL: int(b[8]),
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Protocol: int(b[9]),
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Checksum: int(b[10])<<8 | int(b[11]),
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Src: net.IPv4(b[12], b[13], b[14], b[15]),
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Dst: net.IPv4(b[16], b[17], b[18], b[19]),
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}
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switch runtime.GOOS {
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case "darwin":
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// TODO(mikio): fix potential misaligned memory access
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h.TotalLen = int(*(*uint16)(unsafe.Pointer(&b[2:3][0])))
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case "freebsd":
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if freebsdVersion >= 1000000 {
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h.TotalLen = int(b[2])<<8 | int(b[3])
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} else {
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// TODO(mikio): fix potential misaligned memory access
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h.TotalLen = int(*(*uint16)(unsafe.Pointer(&b[2:3][0])))
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}
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default:
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h.TotalLen = int(b[2])<<8 | int(b[3])
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}
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h.Flags = ipv4.HeaderFlags(h.FragOff&0xe000) >> 13
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h.FragOff = h.FragOff & 0x1fff
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if hdrlen-ipv4.HeaderLen > 0 {
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h.Options = make([]byte, hdrlen-ipv4.HeaderLen)
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copy(h.Options, b[ipv4.HeaderLen:])
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}
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return h, nil
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}
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