1 /*
2 * Copyright (c) 2016, The OpenThread Authors.
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 * 3. Neither the name of the copyright holder nor the
13 * names of its contributors may be used to endorse or promote products
14 * derived from this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
18 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
19 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY
20 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
21 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
22 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
23 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
25 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28 /**
29 * @file
30 * This file implements an HDLC-lite encoder and decoder.
31 */
32
33 #include "hdlc.hpp"
34
35 #include <stdlib.h>
36
37 #include "common/code_utils.hpp"
38
39 namespace ot {
40 namespace Hdlc {
41
42 /**
43 * This method updates an FCS.
44 *
45 * @param[in] aFcs The FCS to update.
46 * @param[in] aByte The input byte value.
47 *
48 * @returns The updated FCS.
49 *
50 */
51 static uint16_t UpdateFcs(uint16_t aFcs, uint8_t aByte);
52
53 enum
54 {
55 kFlagXOn = 0x11,
56 kFlagXOff = 0x13,
57 kFlagSequence = 0x7e, ///< HDLC Flag value
58 kEscapeSequence = 0x7d, ///< HDLC Escape value
59 kFlagSpecial = 0xf8,
60 };
61
62 /**
63 * FCS lookup table
64 *
65 */
66 enum
67 {
68 kInitFcs = 0xffff, ///< Initial FCS value.
69 kGoodFcs = 0xf0b8, ///< Good FCS value.
70 kFcsSize = 2, ///< FCS size (number of bytes).
71 };
72
UpdateFcs(uint16_t aFcs,uint8_t aByte)73 uint16_t UpdateFcs(uint16_t aFcs, uint8_t aByte)
74 {
75 static const uint16_t sFcsTable[256] = {
76 0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf, 0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5,
77 0xe97e, 0xf8f7, 0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e, 0x9cc9, 0x8d40, 0xbfdb, 0xae52,
78 0xdaed, 0xcb64, 0xf9ff, 0xe876, 0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd, 0xad4a, 0xbcc3,
79 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5, 0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
80 0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974, 0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9,
81 0x2732, 0x36bb, 0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3, 0x5285, 0x430c, 0x7197, 0x601e,
82 0x14a1, 0x0528, 0x37b3, 0x263a, 0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72, 0x6306, 0x728f,
83 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9, 0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
84 0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738, 0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862,
85 0x9af9, 0x8b70, 0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7, 0x0840, 0x19c9, 0x2b52, 0x3adb,
86 0x4e64, 0x5fed, 0x6d76, 0x7cff, 0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036, 0x18c1, 0x0948,
87 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e, 0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
88 0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd, 0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226,
89 0xd0bd, 0xc134, 0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c, 0xc60c, 0xd785, 0xe51e, 0xf497,
90 0x8028, 0x91a1, 0xa33a, 0xb2b3, 0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb, 0xd68d, 0xc704,
91 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232, 0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
92 0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1, 0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb,
93 0x0e70, 0x1ff9, 0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330, 0x7bc7, 0x6a4e, 0x58d5, 0x495c,
94 0x3de3, 0x2c6a, 0x1ef1, 0x0f78};
95 return (aFcs >> 8) ^ sFcsTable[(aFcs ^ aByte) & 0xff];
96 }
97
HdlcByteNeedsEscape(uint8_t aByte)98 static bool HdlcByteNeedsEscape(uint8_t aByte)
99 {
100 bool rval;
101
102 switch (aByte)
103 {
104 case kFlagXOn:
105 case kFlagXOff:
106 case kEscapeSequence:
107 case kFlagSequence:
108 case kFlagSpecial:
109 rval = true;
110 break;
111
112 default:
113 rval = false;
114 break;
115 }
116
117 return rval;
118 }
119
Encoder(FrameWritePointer & aWritePointer)120 Encoder::Encoder(FrameWritePointer &aWritePointer)
121 : mWritePointer(aWritePointer)
122 , mFcs(0)
123 {
124 }
125
BeginFrame(void)126 otError Encoder::BeginFrame(void)
127 {
128 mFcs = kInitFcs;
129
130 return mWritePointer.WriteByte(kFlagSequence);
131 }
132
Encode(uint8_t aByte)133 otError Encoder::Encode(uint8_t aByte)
134 {
135 otError error = OT_ERROR_NONE;
136
137 if (HdlcByteNeedsEscape(aByte))
138 {
139 VerifyOrExit(mWritePointer.CanWrite(2), error = OT_ERROR_NO_BUFS);
140
141 IgnoreError(mWritePointer.WriteByte(kEscapeSequence));
142 IgnoreError(mWritePointer.WriteByte(aByte ^ 0x20));
143 }
144 else
145 {
146 SuccessOrExit(error = mWritePointer.WriteByte(aByte));
147 }
148
149 mFcs = UpdateFcs(mFcs, aByte);
150
151 exit:
152 return error;
153 }
154
Encode(const uint8_t * aData,uint16_t aLength)155 otError Encoder::Encode(const uint8_t *aData, uint16_t aLength)
156 {
157 otError error = OT_ERROR_NONE;
158 uint16_t oldFcs = mFcs;
159 FrameWritePointer oldPointer = mWritePointer;
160
161 while (aLength--)
162 {
163 SuccessOrExit(error = Encode(*aData++));
164 }
165
166 exit:
167
168 if (error != OT_ERROR_NONE)
169 {
170 mWritePointer = oldPointer;
171 mFcs = oldFcs;
172 }
173
174 return error;
175 }
176
EndFrame(void)177 otError Encoder::EndFrame(void)
178 {
179 otError error = OT_ERROR_NONE;
180 FrameWritePointer oldPointer = mWritePointer;
181 uint16_t oldFcs = mFcs;
182 uint16_t fcs = mFcs;
183
184 fcs ^= 0xffff;
185
186 SuccessOrExit(error = Encode(fcs & 0xff));
187 SuccessOrExit(error = Encode(fcs >> 8));
188
189 SuccessOrExit(error = mWritePointer.WriteByte(kFlagSequence));
190
191 exit:
192
193 if (error != OT_ERROR_NONE)
194 {
195 mWritePointer = oldPointer;
196 mFcs = oldFcs;
197 }
198
199 return error;
200 }
201
Decoder(FrameWritePointer & aFrameWritePointer,FrameHandler aFrameHandler,void * aContext)202 Decoder::Decoder(FrameWritePointer &aFrameWritePointer, FrameHandler aFrameHandler, void *aContext)
203 : mState(kStateNoSync)
204 , mWritePointer(aFrameWritePointer)
205 , mFrameHandler(aFrameHandler)
206 , mContext(aContext)
207 , mFcs(0)
208 , mDecodedLength(0)
209 {
210 }
211
Reset(void)212 void Decoder::Reset(void)
213 {
214 mState = kStateNoSync;
215 mFcs = 0;
216 mDecodedLength = 0;
217 }
218
Decode(const uint8_t * aData,uint16_t aLength)219 void Decoder::Decode(const uint8_t *aData, uint16_t aLength)
220 {
221 while (aLength--)
222 {
223 uint8_t byte = *aData++;
224
225 switch (mState)
226 {
227 case kStateNoSync:
228 if (byte == kFlagSequence)
229 {
230 mState = kStateSync;
231 mDecodedLength = 0;
232 mFcs = kInitFcs;
233 }
234
235 break;
236
237 case kStateSync:
238 switch (byte)
239 {
240 case kEscapeSequence:
241 mState = kStateEscaped;
242 break;
243
244 case kFlagSequence:
245
246 if (mDecodedLength > 0)
247 {
248 otError error = OT_ERROR_PARSE;
249
250 if ((mDecodedLength >= kFcsSize)
251 #ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
252 && (mFcs == kGoodFcs)
253 #endif
254 )
255 {
256 // Remove the FCS from the frame.
257 mWritePointer.UndoLastWrites(kFcsSize);
258 error = OT_ERROR_NONE;
259 }
260
261 mFrameHandler(mContext, error);
262 }
263
264 mDecodedLength = 0;
265 mFcs = kInitFcs;
266 break;
267
268 default:
269 if (mWritePointer.CanWrite(sizeof(uint8_t)))
270 {
271 mFcs = UpdateFcs(mFcs, byte);
272 IgnoreError(mWritePointer.WriteByte(byte));
273 mDecodedLength++;
274 }
275 else
276 {
277 mFrameHandler(mContext, OT_ERROR_NO_BUFS);
278 mState = kStateNoSync;
279 }
280
281 break;
282 }
283
284 break;
285
286 case kStateEscaped:
287 if (mWritePointer.CanWrite(sizeof(uint8_t)))
288 {
289 byte ^= 0x20;
290 mFcs = UpdateFcs(mFcs, byte);
291 IgnoreError(mWritePointer.WriteByte(byte));
292 mDecodedLength++;
293 mState = kStateSync;
294 }
295 else
296 {
297 mFrameHandler(mContext, OT_ERROR_NO_BUFS);
298 mState = kStateNoSync;
299 }
300
301 break;
302 }
303 }
304 }
305
306 } // namespace Hdlc
307 } // namespace ot
308
