1// Standard COBS/rCOBS:
2// 00000000 => end of frame
3// nnnnnnnn => output n-1 bytes from stream, output 0x00
4// 11111111 => output 254 bytes from stream
5//
6// zCOBS/rzCOBS:
7// 00000000 => end of frame
8// 0xxxxxxx => foreach x from LSB to MSB: if x=0 output 1 byte from stream, if x=1 output 0x00
9// 1nnnnnnn => output n+7 bytes from stream, output 0x00
10// 11111111 => output 134 bytes from stream
11
12pub(crate) struct Encoder {
13 run: u8,
14 zeros: u8,
15 started: bool,
16}
17
18impl Encoder {
19 pub const fn new() -> Self {
20 Self {
21 run: 0,
22 zeros: 0,
23 started: false,
24 }
25 }
26
27 pub fn start_frame(&mut self, mut write: impl FnMut(&[u8])) {
28 let mut write_byte = move |b: u8| write(&[b]);
29 if !self.started {
30 self.started = true;
31
32 // Write a frame-separator at the very beginning. This allows the
33 // decoder to correctly decode the first frame if a previous boot had left a
34 // partly-written frame.
35 write_byte(0x00);
36 }
37 }
38
39 pub fn end_frame(&mut self, mut write: impl FnMut(&[u8])) {
40 let mut write_byte = move |b: u8| write(&[b]);
41
42 // Finish writing the previous symbol if needed.
43 match self.run {
44 0 => {}
45 1..=6 => write_byte((self.zeros | (0xFF << self.run)) & 0x7F),
46 _ => write_byte((self.run - 7) | 0x80),
47 }
48
49 // Write frame-separator.
50 write_byte(0x00);
51
52 self.run = 0;
53 self.zeros = 0;
54 }
55
56 pub fn write(&mut self, data: &[u8], mut write: impl FnMut(&[u8])) {
57 let mut write_byte = move |b: u8| write(&[b]);
58
59 for &byte in data {
60 if self.run < 7 {
61 if byte == 0 {
62 self.zeros |= 1 << self.run;
63 } else {
64 write_byte(byte);
65 }
66
67 self.run += 1;
68 if self.run == 7 && self.zeros != 0x00 {
69 write_byte(self.zeros);
70 self.run = 0;
71 self.zeros = 0;
72 }
73 } else if byte == 0 {
74 write_byte((self.run - 7) | 0x80);
75 self.run = 0;
76 self.zeros = 0;
77 } else {
78 write_byte(byte);
79 self.run += 1;
80 if self.run == 134 {
81 write_byte(0xFF);
82 self.run = 0;
83 self.zeros = 0;
84 }
85 }
86 }
87 }
88}
89
90#[cfg(feature = "unstable-test")]
91#[cfg(test)]
92mod tests {
93 use super::*;
94
95 #[test]
96 fn it_works() {
97 let tests: &[(&[u8], &[u8])] = &[
98 (&[], &[0x00]),
99 (&[0x00], &[0x7f, 0x00]),
100 (&[0x00, 0x00], &[0x7f, 0x00]),
101 (&[0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00], &[0x7f, 0x00]),
102 (
103 &[0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00],
104 &[0x7f, 0x7f, 0x00],
105 ),
106 (&[0x01], &[0x01, 0x7e, 0x00]),
107 (&[0x01, 0x00], &[0x01, 0x7e, 0x00]),
108 (&[0x00, 0x01], &[0x01, 0x7d, 0x00]),
109 (&[0x01, 0x02], &[0x01, 0x02, 0x7c, 0x00]),
110 (
111 &[0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x00],
112 &[0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x40, 0x00],
113 ),
114 (
115 &[0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77],
116 &[0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x80, 0x00],
117 ),
118 (
119 &[0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x00],
120 &[0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x80, 0x00],
121 ),
122 (
123 &[0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88],
124 &[0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x81, 0x00],
125 ),
126 (
127 &[
128 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
129 0xff,
130 ],
131 &[0x7f, 0xff, 0x3f, 0x00],
132 ),
133 (
134 &[
135 0x00, 0x00, 0x00, 0x00, 0x00, 0x44, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
136 0xff,
137 ],
138 &[0x44, 0x5f, 0xff, 0x3f, 0x00],
139 ),
140 (
141 &[
142 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d,
143 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a,
144 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
145 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 0x34,
146 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f, 0x40, 0x41,
147 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e,
148 0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x5b,
149 0x5c, 0x5d, 0x5e, 0x5f, 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,
150 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75,
151 0x76, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 0x80, 0x81, 0x82,
152 0x83, 0x84, 0x85,
153 ],
154 &[
155 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d,
156 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a,
157 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
158 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 0x34,
159 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f, 0x40, 0x41,
160 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e,
161 0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x5b,
162 0x5c, 0x5d, 0x5e, 0x5f, 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,
163 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75,
164 0x76, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 0x80, 0x81, 0x82,
165 0x83, 0x84, 0x85, 0xfe, 0x00,
166 ],
167 ),
168 (
169 &[
170 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d,
171 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a,
172 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
173 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 0x34,
174 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f, 0x40, 0x41,
175 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e,
176 0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x5b,
177 0x5c, 0x5d, 0x5e, 0x5f, 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,
178 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75,
179 0x76, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 0x80, 0x81, 0x82,
180 0x83, 0x84, 0x85, 0x00,
181 ],
182 &[
183 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d,
184 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a,
185 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
186 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 0x34,
187 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f, 0x40, 0x41,
188 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e,
189 0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x5b,
190 0x5c, 0x5d, 0x5e, 0x5f, 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,
191 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75,
192 0x76, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 0x80, 0x81, 0x82,
193 0x83, 0x84, 0x85, 0xfe, 0x00,
194 ],
195 ),
196 (
197 &[
198 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d,
199 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a,
200 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
201 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 0x34,
202 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f, 0x40, 0x41,
203 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e,
204 0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x5b,
205 0x5c, 0x5d, 0x5e, 0x5f, 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,
206 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75,
207 0x76, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 0x80, 0x81, 0x82,
208 0x83, 0x84, 0x85, 0x86,
209 ],
210 &[
211 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d,
212 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a,
213 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
214 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 0x34,
215 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f, 0x40, 0x41,
216 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e,
217 0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x5b,
218 0x5c, 0x5d, 0x5e, 0x5f, 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,
219 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75,
220 0x76, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 0x80, 0x81, 0x82,
221 0x83, 0x84, 0x85, 0x86, 0xff, 0x00,
222 ],
223 ),
224 (
225 &[
226 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d,
227 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a,
228 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
229 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 0x34,
230 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f, 0x40, 0x41,
231 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e,
232 0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x5b,
233 0x5c, 0x5d, 0x5e, 0x5f, 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,
234 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75,
235 0x76, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 0x80, 0x81, 0x82,
236 0x83, 0x84, 0x85, 0x86, 0x00,
237 ],
238 &[
239 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d,
240 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a,
241 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
242 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 0x34,
243 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f, 0x40, 0x41,
244 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e,
245 0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x5b,
246 0x5c, 0x5d, 0x5e, 0x5f, 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,
247 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75,
248 0x76, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 0x80, 0x81, 0x82,
249 0x83, 0x84, 0x85, 0x86, 0xff, 0x7f, 0x00,
250 ],
251 ),
252 ];
253
254 for (dec, enc) in tests {
255 let mut res: Vec<u8> = Vec::new();
256
257 let mut e = Encoder::new();
258 e.started = true; // simulate that this is not the first frame.
259
260 e.start_frame(|data| res.extend(data));
261 e.write(dec, |data| res.extend(data));
262 e.end_frame(|data| res.extend(data));
263
264 assert_eq!(enc, &res);
265 }
266 }
267}
268