1 /* Generic infrastructure to implement various diff algorithms (implementation). */
2 /*
3  * Copyright (c) 2020 Neels Hofmeyr <neels@hofmeyr.de>
4  *
5  * Permission to use, copy, modify, and distribute this software for any
6  * purpose with or without fee is hereby granted, provided that the above
7  * copyright notice and this permission notice appear in all copies.
8  *
9  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16  */
17 
18 
19 #include <sys/queue.h>
20 #include <ctype.h>
21 #include <errno.h>
22 #include <stdint.h>
23 #include <stdlib.h>
24 #include <stdbool.h>
25 #include <stdio.h>
26 #include <string.h>
27 #include <limits.h>
28 #include <unistd.h>
29 
30 #include <assert.h>
31 
32 #include <arraylist.h>
33 #include <diff_main.h>
34 
35 #include "diff_internal.h"
36 #include "diff_debug.h"
37 
38 static int
39 read_at(FILE *f, off_t at_pos, unsigned char *buf, size_t len)
40 {
41 	int r;
42 	if (fseeko(f, at_pos, SEEK_SET) == -1)
43 		return errno;
44 	r = fread(buf, sizeof(char), len, f);
45 	if ((r == 0 || r < len) && ferror(f))
46 		return errno;
47 	if (r != len)
48 		return EIO;
49 	return 0;
50 }
51 
52 static int
53 buf_cmp(const unsigned char *left, size_t left_len,
54 	const unsigned char *right, size_t right_len,
55 	bool ignore_whitespace)
56 {
57 	int cmp;
58 
59 	if (ignore_whitespace) {
60 		int il = 0, ir = 0;
61 		while (il < left_len && ir < right_len) {
62 			unsigned char cl = left[il];
63 			unsigned char cr = right[ir];
64 
65 			if (isspace(cl) && il < left_len) {
66 				il++;
67 				continue;
68 			}
69 			if (isspace(cr) && ir < right_len) {
70 				ir++;
71 				continue;
72 			}
73 
74 			if (cl > cr)
75 				return 1;
76 			if (cr > cl)
77 				return -1;
78 			il++;
79 			ir++;
80 		}
81 		while (il < left_len) {
82 			unsigned char cl = left[il++];
83 			if (!isspace(cl))
84 				return 1;
85 		}
86 		while (ir < right_len) {
87 			unsigned char cr = right[ir++];
88 			if (!isspace(cr))
89 				return -1;
90 		}
91 
92 		return 0;
93 	}
94 
95 	cmp = memcmp(left, right, MIN(left_len, right_len));
96 	if (cmp)
97 		return cmp;
98 	if (left_len == right_len)
99 		return 0;
100 	return (left_len > right_len) ? 1 : -1;
101 }
102 
103 int
104 diff_atom_cmp(int *cmp,
105 	      const struct diff_atom *left,
106 	      const struct diff_atom *right)
107 {
108 	off_t remain_left, remain_right;
109 	int flags = (left->d->root->diff_flags | right->d->root->diff_flags);
110 	bool ignore_whitespace = (flags & DIFF_FLAG_IGNORE_WHITESPACE);
111 
112 	if (!ignore_whitespace) {
113 		if (!left->len && !right->len) {
114 			*cmp = 0;
115 			return 0;
116 		}
117 		if (!right->len) {
118 			*cmp = 1;
119 			return 0;
120 		}
121 		if (!left->len) {
122 			*cmp = -1;
123 			return 0;
124 		}
125 	}
126 
127 	if (left->at != NULL && right->at != NULL) {
128 		*cmp = buf_cmp(left->at, left->len, right->at, right->len,
129 		    ignore_whitespace);
130 		return 0;
131 	}
132 
133 	remain_left = left->len;
134 	remain_right = right->len;
135 	while (remain_left > 0 || remain_right > 0) {
136 		const size_t chunksz = 8192;
137 		unsigned char buf_left[chunksz], buf_right[chunksz];
138 		const uint8_t *p_left, *p_right;
139 		off_t n_left, n_right;
140 		ssize_t r;
141 
142 		if (!remain_right) {
143 			*cmp = 1;
144 			return 0;
145 		}
146 		if (!remain_left) {
147 			*cmp = -1;
148 			return 0;
149 		}
150 
151 		n_left = MIN(chunksz, remain_left);
152 		n_right = MIN(chunksz, remain_right);
153 
154 		if (left->at == NULL) {
155 			r = read_at(left->d->root->f,
156 				    left->pos + (left->len - remain_left),
157 				    buf_left, n_left);
158 			if (r) {
159 				*cmp = 0;
160 				return r;
161 			}
162 			p_left = buf_left;
163 		} else {
164 			p_left = left->at + (left->len - remain_left);
165 		}
166 
167 		if (right->at == NULL) {
168 			r = read_at(right->d->root->f,
169 				    right->pos + (right->len - remain_right),
170 				    buf_right, n_right);
171 			if (r) {
172 				*cmp = 0;
173 				return r;
174 			}
175 			p_right = buf_right;
176 		} else {
177 			p_right = right->at + (right->len - remain_right);
178 		}
179 
180 		r = buf_cmp(p_left, n_left, p_right, n_right,
181 		    ignore_whitespace);
182 		if (r) {
183 			*cmp = r;
184 			return 0;
185 		}
186 
187 		remain_left -= n_left;
188 		remain_right -= n_right;
189 	}
190 
191 	*cmp = 0;
192 	return 0;
193 }
194 
195 int
196 diff_atom_same(bool *same,
197 	       const struct diff_atom *left,
198 	       const struct diff_atom *right)
199 {
200 	int cmp;
201 	int r = diff_atom_cmp(&cmp, left, right);
202 	if (r) {
203 		*same = true;
204 		return r;
205 	}
206 	*same = (cmp == 0);
207 	return 0;
208 }
209 
210 /* Even if a left or right side is empty, diff output may need to know the
211  * position in that file.
212  * So left_start or right_start must never be NULL -- pass left_count or
213  * right_count as zero to indicate staying at that position without consuming
214  * any lines. */
215 struct diff_chunk *
216 diff_state_add_chunk(struct diff_state *state, bool solved,
217 		     struct diff_atom *left_start, unsigned int left_count,
218 		     struct diff_atom *right_start, unsigned int right_count)
219 {
220 	diff_chunk_arraylist_t *result = NULL;
221 	struct diff_chunk *new_chunk;
222 	struct diff_chunk chunk = {
223 		.solved = solved,
224 		.left_start = left_start,
225 		.left_count = left_count,
226 		.right_start = right_start,
227 		.right_count = right_count,
228 	};
229 	enum diff_chunk_type last_t;
230 	enum diff_chunk_type prev_last_t;
231 	enum diff_chunk_type new_t;
232 
233 	if (!solved || state->temp_result.len) {
234 		/* Append to temp_result */
235 		result = &state->temp_result;
236 	} else if (!state->result->chunks.len) {
237 		/* Append to final result */
238 		result = &state->result->chunks;
239 	}
240 	if (result) {
241 		ARRAYLIST_ADD(new_chunk, *result);
242 		if (!new_chunk)
243 			return NULL;
244 		*new_chunk = chunk;
245 		goto chunk_added;
246 	}
247 
248 	/* Append to solved chunks; make sure that adjacent chunks of same type are combined, and that a minus chunk
249 	 * never directly follows a plus chunk. */
250 	result = &state->result->chunks;
251 
252 	prev_last_t = result->len > 1 ?
253 		diff_chunk_type(&result->head[result->len - 2]) : CHUNK_EMPTY;
254 	last_t = diff_chunk_type(&result->head[result->len - 1]);
255 	new_t = diff_chunk_type(&chunk);
256 
257 	if (new_t == last_t) {
258 		new_chunk = &result->head[result->len - 1];
259 		new_chunk->left_count += chunk.left_count;
260 		new_chunk->right_count += chunk.right_count;
261 	} else if (last_t == CHUNK_PLUS && new_t == CHUNK_MINUS) {
262 		/* If a minus-chunk follows a plus-chunk, place it above the plus-chunk.
263 		 * Is the one before that also a minus? combine. */
264 		if (prev_last_t == CHUNK_MINUS) {
265 			new_chunk = &result->head[result->len - 2];
266 			new_chunk->left_count += chunk.left_count;
267 			new_chunk->right_count += chunk.right_count;
268 		} else {
269 			ARRAYLIST_INSERT(new_chunk, *result, result->len - 2);
270 			if (!new_chunk)
271 				return NULL;
272 			*new_chunk = chunk;
273 		}
274 	} else {
275 		ARRAYLIST_ADD(new_chunk, *result);
276 		if (!new_chunk)
277 			return NULL;
278 		*new_chunk = chunk;
279 		goto chunk_added;
280 	}
281 
282 chunk_added:
283 	debug("Add %s chunk:\n", new_chunk->solved ? "solved" : "UNSOLVED");
284 	debug("L\n");
285 	debug_dump_atoms(&state->left, new_chunk->left_start, new_chunk->left_count);
286 	debug("R\n");
287 	debug_dump_atoms(&state->right, new_chunk->right_start, new_chunk->right_count);
288 	return new_chunk;
289 }
290 
291 void
292 diff_data_init_root(struct diff_data *d, FILE *f, const uint8_t *data,
293     unsigned long long len, int diff_flags)
294 {
295 	*d = (struct diff_data){
296 		.f = f,
297 		.pos = 0,
298 		.data = data,
299 		.len = len,
300 		.root = d,
301 		.diff_flags = diff_flags,
302 	};
303 }
304 
305 void
306 diff_data_init_subsection(struct diff_data *d, struct diff_data *parent,
307 			  struct diff_atom *from_atom, unsigned int atoms_count)
308 {
309 	struct diff_atom *last_atom;
310 
311 	if (atoms_count == 0) {
312 		*d = (struct diff_data){
313 			.f = NULL,
314 			.pos = 0,
315 			.data = "",
316 			.len = 0,
317 			.root = parent->root,
318 			.atoms.head = NULL,
319 			.atoms.len = atoms_count,
320 		};
321 
322 		return;
323 	}
324 
325 	last_atom = from_atom + atoms_count - 1;
326 	*d = (struct diff_data){
327 		.f = NULL,
328 		.pos = from_atom->pos,
329 		.data = from_atom->at,
330 		.len = (last_atom->pos + last_atom->len) - from_atom->pos,
331 		.root = parent->root,
332 		.atoms.head = from_atom,
333 		.atoms.len = atoms_count,
334 	};
335 
336 	debug("subsection:\n");
337 	debug_dump(d);
338 }
339 
340 void
341 diff_data_free(struct diff_data *diff_data)
342 {
343 	if (!diff_data)
344 		return;
345 	if (diff_data->atoms.allocated)
346 		ARRAYLIST_FREE(diff_data->atoms);
347 }
348 
349 int
350 diff_algo_none(const struct diff_algo_config *algo_config,
351 	       struct diff_state *state)
352 {
353 	debug("\n** %s\n", __func__);
354 	debug("left:\n");
355 	debug_dump(&state->left);
356 	debug("right:\n");
357 	debug_dump(&state->right);
358 	debug_dump_myers_graph(&state->left, &state->right, NULL, NULL, 0, NULL,
359 			       0);
360 
361 	/* Add a chunk of equal lines, if any */
362 	unsigned int equal_atoms = 0;
363 	while (equal_atoms < state->left.atoms.len
364 	       && equal_atoms < state->right.atoms.len) {
365 		int r;
366 		bool same;
367 		r = diff_atom_same(&same, &state->left.atoms.head[equal_atoms],
368 				   &state->right.atoms.head[equal_atoms]);
369 		if (r)
370 			return r;
371 		if (!same)
372 			break;
373 		equal_atoms++;
374 	}
375 	if (equal_atoms) {
376 		if (!diff_state_add_chunk(state, true,
377 					  &state->left.atoms.head[0],
378 					  equal_atoms,
379 					  &state->right.atoms.head[0],
380 					  equal_atoms))
381 			return ENOMEM;
382 	}
383 
384 	/* Add a "minus" chunk with all lines from the left. */
385 	if (equal_atoms < state->left.atoms.len) {
386 		if (!diff_state_add_chunk(state, true,
387 					  &state->left.atoms.head[equal_atoms],
388 					  state->left.atoms.len - equal_atoms,
389 					  NULL, 0))
390 		    return ENOMEM;
391 	}
392 
393 	/* Add a "plus" chunk with all lines from the right. */
394 	if (equal_atoms < state->right.atoms.len) {
395 		if (!diff_state_add_chunk(state, true,
396 					  NULL, 0,
397 					  &state->right.atoms.head[equal_atoms],
398 					  state->right.atoms.len - equal_atoms))
399 		return ENOMEM;
400 	}
401 	return DIFF_RC_OK;
402 }
403 
404 int
405 diff_run_algo(const struct diff_algo_config *algo_config,
406 	      struct diff_state *state)
407 {
408 	int rc;
409 	ARRAYLIST_FREE(state->temp_result);
410 
411 	if (!algo_config || !algo_config->impl
412 	    || !state->recursion_depth_left) {
413 		debug("MAX RECURSION REACHED, just dumping diff chunks\n");
414 		return diff_algo_none(algo_config, state);
415 	}
416 
417 	ARRAYLIST_INIT(state->temp_result, DIFF_RESULT_ALLOC_BLOCKSIZE);
418 	rc = algo_config->impl(algo_config, state);
419 	switch (rc) {
420 	case DIFF_RC_USE_DIFF_ALGO_FALLBACK:
421 		debug("Got DIFF_RC_USE_DIFF_ALGO_FALLBACK (%p)\n",
422 		      algo_config->fallback_algo);
423 		rc = diff_run_algo(algo_config->fallback_algo, state);
424 		goto return_rc;
425 
426 	case DIFF_RC_OK:
427 		/* continue below */
428 		break;
429 
430 	default:
431 		/* some error happened */
432 		goto return_rc;
433 	}
434 
435 	/* Pick up any diff chunks that are still unsolved and feed to
436 	 * inner_algo.  inner_algo will solve unsolved chunks and append to
437 	 * result, and subsequent solved chunks on this level are then appended
438 	 * to result afterwards. */
439 	int i;
440 	for (i = 0; i < state->temp_result.len; i++) {
441 		struct diff_chunk *c = &state->temp_result.head[i];
442 		if (c->solved) {
443 			struct diff_chunk *final_c;
444 			ARRAYLIST_ADD(final_c, state->result->chunks);
445 			if (!final_c) {
446 				rc = ENOMEM;
447 				goto return_rc;
448 			}
449 			*final_c = *c;
450 			continue;
451 		}
452 
453 		/* c is an unsolved chunk, feed to inner_algo */
454 		struct diff_state inner_state = {
455 			.result = state->result,
456 			.recursion_depth_left = state->recursion_depth_left - 1,
457 		};
458 		diff_data_init_subsection(&inner_state.left, &state->left,
459 					  c->left_start, c->left_count);
460 		diff_data_init_subsection(&inner_state.right, &state->right,
461 					  c->right_start, c->right_count);
462 
463 		rc = diff_run_algo(algo_config->inner_algo, &inner_state);
464 
465 		if (rc != DIFF_RC_OK)
466 			goto return_rc;
467 	}
468 
469 	rc = DIFF_RC_OK;
470 return_rc:
471 	ARRAYLIST_FREE(state->temp_result);
472 	return rc;
473 }
474 
475 struct diff_result *
476 diff_main(const struct diff_config *config,
477 	  FILE *left_f, const uint8_t *left_data, off_t left_len,
478 	  FILE *right_f, const uint8_t *right_data, off_t right_len,
479 	  int diff_flags)
480 {
481 	struct diff_result *result = malloc(sizeof(struct diff_result));
482 	if (!result)
483 		return NULL;
484 
485 	*result = (struct diff_result){};
486 	diff_data_init_root(&result->left, left_f, left_data, left_len,
487 	    diff_flags);
488 	diff_data_init_root(&result->right, right_f, right_data, right_len,
489 	    diff_flags);
490 
491 	if (!config->atomize_func) {
492 		result->rc = EINVAL;
493 		return result;
494 	}
495 
496 	result->rc = config->atomize_func(config->atomize_func_data,
497 					  &result->left, &result->right);
498 	if (result->rc != DIFF_RC_OK)
499 		return result;
500 
501 	struct diff_state state = {
502 		.result = result,
503 		.recursion_depth_left = config->max_recursion_depth ? : 32,
504 	};
505 	diff_data_init_subsection(&state.left, &result->left,
506 				  result->left.atoms.head,
507 				  result->left.atoms.len);
508 	diff_data_init_subsection(&state.right, &result->right,
509 				  result->right.atoms.head,
510 				  result->right.atoms.len);
511 
512 	result->rc = diff_run_algo(config->algo, &state);
513 
514 	return result;
515 }
516 
517 void
518 diff_result_free(struct diff_result *result)
519 {
520 	if (!result)
521 		return;
522 	diff_data_free(&result->left);
523 	diff_data_free(&result->right);
524 	ARRAYLIST_FREE(result->chunks);
525 	free(result);
526 }