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90 lines
2.3 KiB
Go
90 lines
2.3 KiB
Go
// Copyright 2015 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 "encoding/binary"
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// An Extension represents an ICMP extension.
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type Extension interface {
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// Len returns the length of ICMP extension.
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// Proto must be either the ICMPv4 or ICMPv6 protocol number.
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Len(proto int) int
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// Marshal returns the binary encoding of ICMP extension.
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// Proto must be either the ICMPv4 or ICMPv6 protocol number.
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Marshal(proto int) ([]byte, error)
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}
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const extensionVersion = 2
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func validExtensionHeader(b []byte) bool {
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v := int(b[0]&0xf0) >> 4
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s := binary.BigEndian.Uint16(b[2:4])
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if s != 0 {
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s = checksum(b)
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}
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if v != extensionVersion || s != 0 {
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return false
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}
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return true
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}
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// parseExtensions parses b as a list of ICMP extensions.
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// The length attribute l must be the length attribute field in
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// received icmp messages.
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//
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// It will return a list of ICMP extensions and an adjusted length
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// attribute that represents the length of the padded original
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// datagram field. Otherwise, it returns an error.
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func parseExtensions(b []byte, l int) ([]Extension, int, error) {
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// Still a lot of non-RFC 4884 compliant implementations are
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// out there. Set the length attribute l to 128 when it looks
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// inappropriate for backwards compatibility.
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//
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// A minimal extension at least requires 8 octets; 4 octets
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// for an extension header, and 4 octets for a single object
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// header.
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//
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// See RFC 4884 for further information.
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if 128 > l || l+8 > len(b) {
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l = 128
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}
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if l+8 > len(b) {
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return nil, -1, errNoExtension
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}
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if !validExtensionHeader(b[l:]) {
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if l == 128 {
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return nil, -1, errNoExtension
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}
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l = 128
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if !validExtensionHeader(b[l:]) {
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return nil, -1, errNoExtension
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}
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}
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var exts []Extension
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for b = b[l+4:]; len(b) >= 4; {
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ol := int(binary.BigEndian.Uint16(b[:2]))
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if 4 > ol || ol > len(b) {
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break
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}
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switch b[2] {
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case classMPLSLabelStack:
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ext, err := parseMPLSLabelStack(b[:ol])
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if err != nil {
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return nil, -1, err
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}
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exts = append(exts, ext)
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case classInterfaceInfo:
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ext, err := parseInterfaceInfo(b[:ol])
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if err != nil {
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return nil, -1, err
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}
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exts = append(exts, ext)
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}
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b = b[ol:]
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}
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return exts, l, nil
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}
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