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49 lines
1.5 KiB
Go
49 lines
1.5 KiB
Go
// Copyright (c) 2020 Tailscale Inc & 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 packet
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import (
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"errors"
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"math"
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)
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const tcpHeaderLength = 20
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// maxPacketLength is the largest length that all headers support.
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// IPv4 headers using uint16 for this forces an upper bound of 64KB.
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const maxPacketLength = math.MaxUint16
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var (
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errSmallBuffer = errors.New("buffer too small")
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errLargePacket = errors.New("packet too large")
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)
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// Header is a packet header capable of marshaling itself into a byte buffer.
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type Header interface {
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// Len returns the length of the header after marshaling.
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Len() int
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// Marshal serializes the header into buf in wire format.
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// It clobbers the header region, which is the first h.Length() bytes of buf.
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// It explicitly initializes every byte of the header region,
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// so pre-zeroing it on reuse is not required. It does not allocate memory.
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// It fails if and only if len(buf) < Length().
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Marshal(buf []byte) error
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// ToResponse transforms the header into one for a response packet.
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// For instance, this swaps the source and destination IPs.
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ToResponse()
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}
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// Generate generates a new packet with the given header and payload.
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// Unlike Header.Marshal, this does allocate memory.
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func Generate(h Header, payload []byte) []byte {
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hlen := h.Len()
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buf := make([]byte, hlen+len(payload))
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copy(buf[hlen:], payload)
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h.Marshal(buf)
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return buf
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}
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