84 lines
2.4 KiB
Go
84 lines
2.4 KiB
Go
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package pmtud
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import (
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"bytes"
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"errors"
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"fmt"
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"golang.org/x/net/icmp"
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)
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var (
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ErrICMPNextHopMTUTooLow = errors.New("ICMP Next Hop MTU is too low")
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ErrICMPNextHopMTUTooHigh = errors.New("ICMP Next Hop MTU is too high")
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)
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func checkMTU(mtu, minMTU, physicalLinkMTU int) (err error) {
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switch {
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case mtu < minMTU:
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return fmt.Errorf("%w: %d", ErrICMPNextHopMTUTooLow, mtu)
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case mtu > physicalLinkMTU:
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return fmt.Errorf("%w: %d is larger than physical link MTU %d",
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ErrICMPNextHopMTUTooHigh, mtu, physicalLinkMTU)
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default:
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return nil
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}
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}
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func checkInvokingReplyIDMatch(icmpProtocol int, received []byte,
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outboundMessage *icmp.Message,
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) (match bool, err error) {
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inboundMessage, err := icmp.ParseMessage(icmpProtocol, received)
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if err != nil {
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return false, fmt.Errorf("parsing invoking packet: %w", err)
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}
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inboundBody, ok := inboundMessage.Body.(*icmp.Echo)
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if !ok {
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return false, fmt.Errorf("%w: %T", ErrICMPBodyUnsupported, inboundMessage.Body)
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}
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outboundBody := outboundMessage.Body.(*icmp.Echo) //nolint:forcetypeassert
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return inboundBody.ID == outboundBody.ID, nil
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}
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var ErrICMPIDMismatch = errors.New("ICMP id mismatch")
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func checkEchoReply(icmpProtocol int, received []byte,
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outboundMessage *icmp.Message, truncatedBody bool,
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) (err error) {
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inboundMessage, err := icmp.ParseMessage(icmpProtocol, received)
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if err != nil {
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return fmt.Errorf("parsing invoking packet: %w", err)
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}
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inboundBody, ok := inboundMessage.Body.(*icmp.Echo)
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if !ok {
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return fmt.Errorf("%w: %T", ErrICMPBodyUnsupported, inboundMessage.Body)
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}
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outboundBody := outboundMessage.Body.(*icmp.Echo) //nolint:forcetypeassert
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if inboundBody.ID != outboundBody.ID {
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return fmt.Errorf("%w: sent id %d and received id %d",
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ErrICMPIDMismatch, outboundBody.ID, inboundBody.ID)
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}
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err = checkEchoBodies(outboundBody.Data, inboundBody.Data, truncatedBody)
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if err != nil {
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return fmt.Errorf("checking sent and received bodies: %w", err)
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}
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return nil
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}
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var ErrICMPEchoDataMismatch = errors.New("ICMP data mismatch")
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func checkEchoBodies(sent, received []byte, receivedTruncated bool) (err error) {
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if len(received) > len(sent) {
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return fmt.Errorf("%w: sent %d bytes and received %d bytes",
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ErrICMPEchoDataMismatch, len(sent), len(received))
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}
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if receivedTruncated {
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sent = sent[:len(received)]
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}
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if !bytes.Equal(received, sent) {
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return fmt.Errorf("%w: sent %x and received %x",
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ErrICMPEchoDataMismatch, sent, received)
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}
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return nil
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}
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