| /* |
| * 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; |
| * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND |
| * 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 "pch.hpp" |
| #include "hdlc.tmh" |
| |
| /** |
| * FCS lookup table |
| */ |
| enum |
| { |
| kInitFcs = 0xffff, ///< Initial FCS value. |
| kGoodFcs = 0xf0b8, ///< Good FCS value. |
| }; |
| |
| static bool |
| hdlc_byte_needs_escape(UCHAR byte) |
| { |
| switch (byte) |
| { |
| case HdlcXOn: |
| case HdlcXOff: |
| case HdlcEscapeSequence: |
| case HdlcFlagSequence: |
| case HdlcSpecial: |
| return true; |
| |
| default: |
| return false; |
| } |
| } |
| |
| /** |
| * This method updates an FCS. |
| * |
| * @param[in] aFcs The FCS to update. |
| * @param[in] aByte The input byte value. |
| * |
| * @returns The updated FCS. |
| */ |
| USHORT UpdateFcs(USHORT aFcs, UCHAR aByte) |
| { |
| const USHORT 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]; |
| } |
| |
| ULONG |
| HdlcComputeEncodedByteLength( |
| _In_ UCHAR aByte |
| ) |
| { |
| return hdlc_byte_needs_escape(aByte) ? 2 : 1; |
| } |
| |
| ULONG |
| HdlcComputeEncodedLength( |
| _In_reads_bytes_(DecodedBufferLength) |
| PUCHAR DecodedBuffer, |
| _In_ ULONG DecodedBufferLength |
| ) |
| { |
| USHORT Fcs = kInitFcs; |
| ULONG Length = 2; // Start and end sequence |
| |
| for (ULONG i = 0; i < DecodedBufferLength; i++) |
| { |
| Length += HdlcComputeEncodedByteLength(DecodedBuffer[i]); |
| Fcs = UpdateFcs(Fcs, DecodedBuffer[i]); |
| } |
| |
| Fcs ^= 0xffff; |
| |
| Length += HdlcComputeEncodedByteLength(Fcs & 0xff); |
| Length += HdlcComputeEncodedByteLength(Fcs >> 8); |
| |
| return Length; |
| } |
| |
| bool |
| HdlcEncodeByte( |
| _In_ UCHAR aByte, |
| _Inout_ ULONG& Offset, |
| _In_ ULONG EncodedBufferLength, |
| _Out_writes_bytes_(EncodedBufferLength) |
| PUCHAR EncodedBuffer |
| ) |
| { |
| if (hdlc_byte_needs_escape(aByte)) |
| { |
| if (Offset + 2 > EncodedBufferLength) return false; |
| |
| EncodedBuffer[Offset++] = HdlcEscapeSequence; |
| EncodedBuffer[Offset++] = (aByte ^ 0x20); |
| } |
| else |
| { |
| if (Offset + 1 > EncodedBufferLength) return false; |
| |
| EncodedBuffer[Offset++] = aByte; |
| } |
| |
| return true; |
| } |
| |
| _Success_(return == true) |
| bool |
| HdlcEncodeBuffer( |
| _In_reads_bytes_(DecodedBufferLength) |
| PUCHAR DecodedBuffer, |
| _In_ ULONG DecodedBufferLength, |
| _Out_writes_bytes_(EncodedBufferLength) |
| PUCHAR EncodedBuffer, |
| _In_ ULONG EncodedBufferLength |
| ) |
| { |
| USHORT Fcs = kInitFcs; |
| ULONG Offset = 0; |
| bool Complete = false; |
| |
| if (Offset + 1 > EncodedBufferLength) goto error; |
| EncodedBuffer[Offset++] = HdlcFlagSequence; |
| |
| for (ULONG i = 0; i < DecodedBufferLength; i++) |
| { |
| UCHAR aByte = DecodedBuffer[i]; |
| |
| if (!HdlcEncodeByte(aByte, Offset, EncodedBufferLength, EncodedBuffer)) { |
| goto error; |
| } |
| |
| Fcs = UpdateFcs(Fcs, aByte); |
| } |
| |
| Fcs ^= 0xffff; |
| |
| if (!HdlcEncodeByte(Fcs & 0xff, Offset, EncodedBufferLength, EncodedBuffer) || |
| !HdlcEncodeByte(Fcs >> 8, Offset, EncodedBufferLength, EncodedBuffer)) { |
| goto error; |
| } |
| |
| if (Offset + 1 > EncodedBufferLength) goto error; |
| EncodedBuffer[Offset++] = HdlcFlagSequence; |
| |
| NT_ASSERT(Offset == EncodedBufferLength); |
| Complete = true; |
| |
| error: |
| |
| return Complete; |
| } |
| |
| enum HdlcDecodeState |
| { |
| kStateNoSync = 0, |
| kStateSync, |
| kStateEscaped, |
| }; |
| |
| _Success_(return == true) |
| bool |
| HdlcDecodeBuffer( |
| _In_reads_bytes_(*EncodedBufferLength) |
| PUCHAR EncodedBuffer, |
| _Inout_ PULONG EncodedBufferLength, |
| _Inout_ PULONG DecodedBufferLength, |
| _Out_writes_bytes_opt_(*DecodedBufferLength) |
| PUCHAR DecodedBuffer, |
| _Out_ bool* IsGood |
| ) |
| { |
| UCHAR byte; |
| HdlcDecodeState state = kStateNoSync; |
| ULONG DecodedLength = 0; |
| USHORT Fcs = kInitFcs; |
| |
| for (ULONG i = 0; i < *EncodedBufferLength; i++) |
| { |
| byte = EncodedBuffer[i]; |
| |
| switch (state) |
| { |
| case kStateNoSync: |
| { |
| if (byte == HdlcFlagSequence) |
| { |
| if (i != 0) |
| { |
| // Set the output for junk length |
| *EncodedBufferLength = i; |
| |
| // Set the output 'IsGood' flag based on FCS |
| *IsGood = false; |
| |
| return true; |
| } |
| else |
| { |
| state = kStateSync; |
| } |
| } |
| break; |
| } |
| case kStateSync: |
| { |
| switch (byte) |
| { |
| case HdlcEscapeSequence: |
| { |
| state = kStateEscaped; |
| break; |
| } |
| case HdlcFlagSequence: |
| { |
| // If it wasn't enough buffer to be a complete sequence, maybe we are |
| // actually between sequences. Leave the trailing escape character. |
| if (i < sizeof(USHORT) + 2) |
| { |
| // Set the output encoded buffer length |
| *EncodedBufferLength = i; |
| |
| *IsGood = false; |
| } |
| else |
| { |
| // Set the output encoded buffer length |
| *EncodedBufferLength = i + 1; |
| |
| // Set the decoded buffer length (subtract 2 for the FCS) |
| *DecodedBufferLength = DecodedLength - 2; |
| |
| // Set the output 'IsGood' flag based on FCS |
| *IsGood = (Fcs == kGoodFcs); |
| } |
| |
| return true; |
| } |
| default: |
| { |
| Fcs = UpdateFcs(Fcs, byte); |
| DecodedLength++; |
| if (DecodedBuffer) |
| { |
| if (*DecodedBufferLength >= DecodedLength) |
| { |
| DecodedBuffer[DecodedLength - 1] = byte; |
| } |
| } |
| break; |
| } |
| } |
| break; |
| } |
| case kStateEscaped: |
| { |
| if (i + 1 < *EncodedBufferLength) |
| { |
| byte ^= 0x20; |
| Fcs = UpdateFcs(Fcs, byte); |
| DecodedLength++; |
| if (DecodedBuffer) |
| { |
| if (*DecodedBufferLength >= DecodedLength) |
| { |
| DecodedBuffer[DecodedLength - 1] = byte; |
| } |
| } |
| |
| state = kStateSync; |
| } |
| else |
| { |
| // Not enough buffer |
| } |
| break; |
| } |
| } |
| } |
| |
| return false; |
| } |
