59 lines
1.4 KiB
Go
59 lines
1.4 KiB
Go
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package pmtud
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import (
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cryptorand "crypto/rand"
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"encoding/binary"
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"fmt"
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"math/rand/v2"
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"golang.org/x/net/icmp"
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"golang.org/x/net/ipv4"
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"golang.org/x/net/ipv6"
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)
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func buildMessageToSend(ipVersion string, mtu int) (id uint16, message *icmp.Message) {
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var seed [32]byte
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_, _ = cryptorand.Read(seed[:])
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randomSource := rand.NewChaCha8(seed)
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const uint16Bytes = 2
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idBytes := make([]byte, uint16Bytes)
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_, _ = randomSource.Read(idBytes)
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id = binary.BigEndian.Uint16(idBytes)
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var ipHeaderLength int
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var icmpType icmp.Type
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switch ipVersion {
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case "v4":
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ipHeaderLength = ipv4.HeaderLen
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icmpType = ipv4.ICMPTypeEcho
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case "v6":
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ipHeaderLength = ipv6.HeaderLen
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icmpType = ipv6.ICMPTypeEchoRequest
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default:
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panic(fmt.Sprintf("IP version %q not supported", ipVersion))
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}
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const pingHeaderLength = 0 +
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1 + // type
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1 + // code
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2 + // checksum
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2 + // identifier
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2 // sequence number
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pingBodyDataSize := mtu - ipHeaderLength - pingHeaderLength
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messageBodyData := make([]byte, pingBodyDataSize)
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_, _ = randomSource.Read(messageBodyData)
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// See https://www.iana.org/assignments/icmp-parameters/icmp-parameters.xhtml#icmp-parameters-types
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message = &icmp.Message{
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Type: icmpType, // echo request
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Code: 0, // no code
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Checksum: 0, // calculated at encoding (ipv4) or sending (ipv6)
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Body: &icmp.Echo{
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ID: int(id),
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Seq: 0, // only one packet
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Data: messageBodyData,
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},
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}
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return id, message
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}
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