forked from mystiq/dex
132 lines
3.8 KiB
Go
132 lines
3.8 KiB
Go
// Copyright 2012 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 ipv4
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import (
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"encoding/binary"
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"fmt"
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"net"
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"runtime"
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"syscall"
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)
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const (
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Version = 4 // protocol version
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HeaderLen = 20 // header length without extension headers
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maxHeaderLen = 60 // sensible default, revisit if later RFCs define new usage of version and header length fields
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)
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type HeaderFlags int
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const (
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MoreFragments HeaderFlags = 1 << iota // more fragments flag
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DontFragment // don't fragment flag
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)
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// A Header represents an IPv4 header.
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type Header struct {
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Version int // protocol version
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Len int // header length
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TOS int // type-of-service
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TotalLen int // packet total length
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ID int // identification
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Flags HeaderFlags // flags
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FragOff int // fragment offset
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TTL int // time-to-live
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Protocol int // next protocol
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Checksum int // checksum
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Src net.IP // source address
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Dst net.IP // destination address
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Options []byte // options, extension headers
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}
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func (h *Header) String() string {
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if h == nil {
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return "<nil>"
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}
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return fmt.Sprintf("ver=%d hdrlen=%d tos=%#x totallen=%d id=%#x flags=%#x fragoff=%#x ttl=%d proto=%d cksum=%#x src=%v dst=%v", h.Version, h.Len, h.TOS, h.TotalLen, h.ID, h.Flags, h.FragOff, h.TTL, h.Protocol, h.Checksum, h.Src, h.Dst)
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}
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// Marshal returns the binary encoding of the IPv4 header h.
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func (h *Header) Marshal() ([]byte, error) {
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if h == nil {
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return nil, syscall.EINVAL
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}
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if h.Len < HeaderLen {
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return nil, errHeaderTooShort
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}
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hdrlen := HeaderLen + len(h.Options)
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b := make([]byte, hdrlen)
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b[0] = byte(Version<<4 | (hdrlen >> 2 & 0x0f))
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b[1] = byte(h.TOS)
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flagsAndFragOff := (h.FragOff & 0x1fff) | int(h.Flags<<13)
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switch runtime.GOOS {
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case "darwin", "dragonfly", "freebsd", "netbsd":
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nativeEndian.PutUint16(b[2:4], uint16(h.TotalLen))
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nativeEndian.PutUint16(b[6:8], uint16(flagsAndFragOff))
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default:
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binary.BigEndian.PutUint16(b[2:4], uint16(h.TotalLen))
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binary.BigEndian.PutUint16(b[6:8], uint16(flagsAndFragOff))
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}
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binary.BigEndian.PutUint16(b[4:6], uint16(h.ID))
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b[8] = byte(h.TTL)
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b[9] = byte(h.Protocol)
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binary.BigEndian.PutUint16(b[10:12], uint16(h.Checksum))
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if ip := h.Src.To4(); ip != nil {
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copy(b[12:16], ip[:net.IPv4len])
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}
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if ip := h.Dst.To4(); ip != nil {
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copy(b[16:20], ip[:net.IPv4len])
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} else {
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return nil, errMissingAddress
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}
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if len(h.Options) > 0 {
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copy(b[HeaderLen:], h.Options)
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}
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return b, nil
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}
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// ParseHeader parses b as an IPv4 header.
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func ParseHeader(b []byte) (*Header, error) {
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if len(b) < 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 := &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(binary.BigEndian.Uint16(b[4:6])),
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TTL: int(b[8]),
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Protocol: int(b[9]),
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Checksum: int(binary.BigEndian.Uint16(b[10:12])),
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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", "dragonfly", "netbsd":
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h.TotalLen = int(nativeEndian.Uint16(b[2:4])) + hdrlen
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h.FragOff = int(nativeEndian.Uint16(b[6:8]))
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case "freebsd":
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h.TotalLen = int(nativeEndian.Uint16(b[2:4]))
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if freebsdVersion < 1000000 {
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h.TotalLen += hdrlen
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}
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h.FragOff = int(nativeEndian.Uint16(b[6:8]))
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default:
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h.TotalLen = int(binary.BigEndian.Uint16(b[2:4]))
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h.FragOff = int(binary.BigEndian.Uint16(b[6:8]))
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}
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h.Flags = HeaderFlags(h.FragOff&0xe000) >> 13
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h.FragOff = h.FragOff & 0x1fff
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if hdrlen-HeaderLen > 0 {
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h.Options = make([]byte, hdrlen-HeaderLen)
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copy(h.Options, b[HeaderLen:])
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}
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return h, nil
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}
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