/*
* Copyright (c) 2016, The OpenThread Authors.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the copyright holder nor the
* names of its contributors may be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/**
* @file
* This file implements an HDLC-lite encoder and decoder.
*/
#include "hdlc.hpp"
#include <stdlib.h>
#include "lib/utils/utils.hpp"
namespace ot {
namespace Hdlc {
/**
* Updates an FCS.
*
* @param[in] aFcs The FCS to update.
* @param[in] aByte The input byte value.
*
* @returns The updated FCS.
*
*/
static uint16_t UpdateFcs(uint16_t aFcs, uint8_t aByte);
enum
{
kFlagXOn = 0x11,
kFlagXOff = 0x13,
kFlagSequence = 0x7e, ///< HDLC Flag value
kEscapeSequence = 0x7d, ///< HDLC Escape value
kFlagSpecial = 0xf8,
};
/**
* FCS lookup table
*
*/
enum
{
kInitFcs = 0xffff, ///< Initial FCS value.
kGoodFcs = 0xf0b8, ///< Good FCS value.
kFcsSize = 2, ///< FCS size (number of bytes).
};
uint16_t UpdateFcs(uint16_t aFcs, uint8_t aByte)
{
static const uint16_t sFcsTable[256] = {
0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf, 0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5,
0xe97e, 0xf8f7, 0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e, 0x9cc9, 0x8d40, 0xbfdb, 0xae52,
0xdaed, 0xcb64, 0xf9ff, 0xe876, 0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd, 0xad4a, 0xbcc3,
0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5, 0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974, 0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9,
0x2732, 0x36bb, 0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3, 0x5285, 0x430c, 0x7197, 0x601e,
0x14a1, 0x0528, 0x37b3, 0x263a, 0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72, 0x6306, 0x728f,
0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9, 0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738, 0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862,
0x9af9, 0x8b70, 0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7, 0x0840, 0x19c9, 0x2b52, 0x3adb,
0x4e64, 0x5fed, 0x6d76, 0x7cff, 0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036, 0x18c1, 0x0948,
0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e, 0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd, 0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226,
0xd0bd, 0xc134, 0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c, 0xc60c, 0xd785, 0xe51e, 0xf497,
0x8028, 0x91a1, 0xa33a, 0xb2b3, 0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb, 0xd68d, 0xc704,
0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232, 0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1, 0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb,
0x0e70, 0x1ff9, 0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330, 0x7bc7, 0x6a4e, 0x58d5, 0x495c,
0x3de3, 0x2c6a, 0x1ef1, 0x0f78};
return (aFcs >> 8) ^ sFcsTable[(aFcs ^ aByte) & 0xff];
}
static bool HdlcByteNeedsEscape(uint8_t aByte)
{
bool rval;
switch (aByte)
{
case kFlagXOn:
case kFlagXOff:
case kEscapeSequence:
case kFlagSequence:
case kFlagSpecial:
rval = true;
break;
default:
rval = false;
break;
}
return rval;
}
Encoder::Encoder(Spinel::FrameWritePointer &aWritePointer)
: mWritePointer(aWritePointer)
, mFcs(0)
{
}
otError Encoder::BeginFrame(void)
{
mFcs = kInitFcs;
return mWritePointer.WriteByte(kFlagSequence);
}
otError Encoder::Encode(uint8_t aByte)
{
otError error = OT_ERROR_NONE;
if (HdlcByteNeedsEscape(aByte))
{
EXPECT(mWritePointer.CanWrite(2), error = OT_ERROR_NO_BUFS);
IGNORE_RETURN(mWritePointer.WriteByte(kEscapeSequence));
IGNORE_RETURN(mWritePointer.WriteByte(aByte ^ 0x20));
}
else
{
EXPECT_NO_ERROR(error = mWritePointer.WriteByte(aByte));
}
mFcs = UpdateFcs(mFcs, aByte);
exit:
return error;
}
otError Encoder::Encode(const uint8_t *aData, uint16_t aLength)
{
otError error = OT_ERROR_NONE;
uint16_t oldFcs = mFcs;
Spinel::FrameWritePointer oldPointer = mWritePointer;
while (aLength--)
{
EXPECT_NO_ERROR(error = Encode(*aData++));
}
exit:
if (error != OT_ERROR_NONE)
{
mWritePointer = oldPointer;
mFcs = oldFcs;
}
return error;
}
otError Encoder::EndFrame(void)
{
otError error = OT_ERROR_NONE;
Spinel::FrameWritePointer oldPointer = mWritePointer;
uint16_t oldFcs = mFcs;
uint16_t fcs = mFcs;
fcs ^= 0xffff;
EXPECT_NO_ERROR(error = Encode(fcs & 0xff));
EXPECT_NO_ERROR(error = Encode(fcs >> 8));
EXPECT_NO_ERROR(error = mWritePointer.WriteByte(kFlagSequence));
exit:
if (error != OT_ERROR_NONE)
{
mWritePointer = oldPointer;
mFcs = oldFcs;
}
return error;
}
Decoder::Decoder(void)
: mState(kStateNoSync)
, mWritePointer(nullptr)
, mFrameHandler(nullptr)
, mContext(nullptr)
, mFcs(0)
, mDecodedLength(0)
{
}
void Decoder::Init(Spinel::FrameWritePointer &aFrameWritePointer, FrameHandler aFrameHandler, void *aContext)
{
mWritePointer = &aFrameWritePointer;
mFrameHandler = aFrameHandler;
mContext = aContext;
}
void Decoder::Reset(void)
{
mState = kStateNoSync;
mFcs = 0;
mDecodedLength = 0;
}
void Decoder::Decode(const uint8_t *aData, uint16_t aLength)
{
while (aLength--)
{
uint8_t byte = *aData++;
switch (mState)
{
case kStateNoSync:
if (byte == kFlagSequence)
{
mState = kStateSync;
mDecodedLength = 0;
mFcs = kInitFcs;
}
break;
case kStateSync:
switch (byte)
{
case kEscapeSequence:
mState = kStateEscaped;
break;
case kFlagSequence:
if (mDecodedLength > 0)
{
otError error = OT_ERROR_PARSE;
if ((mDecodedLength >= kFcsSize)
#ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
&& (mFcs == kGoodFcs)
#endif
)
{
// Remove the FCS from the frame.
mWritePointer->UndoLastWrites(kFcsSize);
error = OT_ERROR_NONE;
}
mFrameHandler(mContext, error);
}
mDecodedLength = 0;
mFcs = kInitFcs;
break;
default:
if (mWritePointer->CanWrite(sizeof(uint8_t)))
{
mFcs = UpdateFcs(mFcs, byte);
IGNORE_RETURN(mWritePointer->WriteByte(byte));
mDecodedLength++;
}
else
{
mFrameHandler(mContext, OT_ERROR_NO_BUFS);
mState = kStateNoSync;
}
break;
}
break;
case kStateEscaped:
if (mWritePointer->CanWrite(sizeof(uint8_t)))
{
byte ^= 0x20;
mFcs = UpdateFcs(mFcs, byte);
IGNORE_RETURN(mWritePointer->WriteByte(byte));
mDecodedLength++;
mState = kStateSync;
}
else
{
mFrameHandler(mContext, OT_ERROR_NO_BUFS);
mState = kStateNoSync;
}
break;
}
}
}
} // namespace Hdlc
} // namespace ot