110 lines
3 KiB
Go
110 lines
3 KiB
Go
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// 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 "golang.org/x/net/internal/iana"
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// multipartMessageBodyDataLen takes b as an original datagram and
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// exts as extensions, and returns a required length for message body
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// and a required length for a padded original datagram in wire
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// format.
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func multipartMessageBodyDataLen(proto int, b []byte, exts []Extension) (bodyLen, dataLen int) {
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for _, ext := range exts {
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bodyLen += ext.Len(proto)
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}
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if bodyLen > 0 {
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dataLen = multipartMessageOrigDatagramLen(proto, b)
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bodyLen += 4 // length of extension header
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} else {
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dataLen = len(b)
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}
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bodyLen += dataLen
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return bodyLen, dataLen
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}
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// multipartMessageOrigDatagramLen takes b as an original datagram,
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// and returns a required length for a padded orignal datagram in wire
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// format.
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func multipartMessageOrigDatagramLen(proto int, b []byte) int {
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roundup := func(b []byte, align int) int {
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// According to RFC 4884, the padded original datagram
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// field must contain at least 128 octets.
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if len(b) < 128 {
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return 128
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}
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r := len(b)
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return (r + align - 1) & ^(align - 1)
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}
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switch proto {
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case iana.ProtocolICMP:
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return roundup(b, 4)
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case iana.ProtocolIPv6ICMP:
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return roundup(b, 8)
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default:
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return len(b)
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}
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}
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// marshalMultipartMessageBody takes data as an original datagram and
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// exts as extesnsions, and returns a binary encoding of message body.
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// It can be used for non-multipart message bodies when exts is nil.
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func marshalMultipartMessageBody(proto int, data []byte, exts []Extension) ([]byte, error) {
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bodyLen, dataLen := multipartMessageBodyDataLen(proto, data, exts)
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b := make([]byte, 4+bodyLen)
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copy(b[4:], data)
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off := dataLen + 4
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if len(exts) > 0 {
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b[dataLen+4] = byte(extensionVersion << 4)
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off += 4 // length of object header
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for _, ext := range exts {
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switch ext := ext.(type) {
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case *MPLSLabelStack:
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if err := ext.marshal(proto, b[off:]); err != nil {
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return nil, err
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}
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off += ext.Len(proto)
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case *InterfaceInfo:
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attrs, l := ext.attrsAndLen(proto)
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if err := ext.marshal(proto, b[off:], attrs, l); err != nil {
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return nil, err
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}
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off += ext.Len(proto)
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}
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}
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s := checksum(b[dataLen+4:])
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b[dataLen+4+2] ^= byte(s)
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b[dataLen+4+3] ^= byte(s >> 8)
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switch proto {
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case iana.ProtocolICMP:
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b[1] = byte(dataLen / 4)
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case iana.ProtocolIPv6ICMP:
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b[0] = byte(dataLen / 8)
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}
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}
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return b, nil
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}
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// parseMultipartMessageBody parses b as either a non-multipart
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// message body or a multipart message body.
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func parseMultipartMessageBody(proto int, b []byte) ([]byte, []Extension, error) {
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var l int
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switch proto {
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case iana.ProtocolICMP:
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l = 4 * int(b[1])
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case iana.ProtocolIPv6ICMP:
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l = 8 * int(b[0])
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}
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if len(b) == 4 {
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return nil, nil, nil
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}
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exts, l, err := parseExtensions(b[4:], l)
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if err != nil {
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l = len(b) - 4
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}
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data := make([]byte, l)
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copy(data, b[4:])
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return data, exts, nil
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}
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