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112 lines
3.5 KiB
Go
112 lines
3.5 KiB
Go
/*
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* Copyright (c) 2014, Yawning Angel <yawning at torproject dot org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* * Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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*
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* * Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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package obfs4
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import (
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"encoding/binary"
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"fmt"
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"log"
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"github.com/yawning/obfs4/framing"
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)
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const (
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packetOverhead = 2 + 1
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maxPacketPayloadLength = framing.MaximumFramePayloadLength - packetOverhead
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maxPacketPaddingLength = maxPacketPayloadLength
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)
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const (
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packetTypePayload = iota
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packetTypePrngSeed
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)
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// InvalidPacketLengthError is the error returned when decodePacket detects a
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// invalid packet length/
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type InvalidPacketLengthError int
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func (e InvalidPacketLengthError) Error() string {
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return fmt.Sprintf("packet: Invalid packet length: %d", int(e))
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}
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// InvalidPayloadLengthError is the error returned when decodePacket rejects the
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// payload length.
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type InvalidPayloadLengthError int
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func (e InvalidPayloadLengthError) Error() string {
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return fmt.Sprintf("packet: Invalid payload length: %d", int(e))
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}
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var zeroPadBytes [maxPacketPaddingLength]byte
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func makePacket(pkt []byte, pktType uint8, data []byte, padLen uint16) int {
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pktLen := packetOverhead + len(data) + int(padLen)
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if len(data)+int(padLen) > maxPacketPayloadLength {
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log.Panicf("BUG: makePacket() len(data) + padLen > maxPacketPayloadLength: %d + %d > %d",
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len(data), padLen, maxPacketPayloadLength)
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}
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// Packets are:
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// uint8_t type packetTypePayload (0x00)
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// uint16_t length Length of the payload (Big Endian).
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// uint8_t[] payload Data payload.
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// uint8_t[] padding Padding.
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pkt[0] = pktType
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binary.BigEndian.PutUint16(pkt[1:], uint16(len(data)))
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copy(pkt[3:], data[:])
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copy(pkt[3+len(data):], zeroPadBytes[:padLen])
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return pktLen
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}
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func (c *Obfs4Conn) decodePacket(pkt []byte) error {
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if len(pkt) < packetOverhead {
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return InvalidPacketLengthError(len(pkt))
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}
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pktType := pkt[0]
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payloadLen := binary.BigEndian.Uint16(pkt[1:])
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if int(payloadLen) > len(pkt)-packetOverhead {
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return InvalidPayloadLengthError(int(payloadLen))
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}
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payload := pkt[3 : 3+payloadLen]
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switch pktType {
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case packetTypePayload:
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// packetTypePayload
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c.receiveDecodedBuffer.Write(payload)
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default:
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// Ignore unrecognised packet types.
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log.Printf("[INFO] - Ignoring packet type: %d", pktType)
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}
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return nil
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}
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