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->root->diff_flags | right->root->diff_flags);
110 	bool ignore_whitespace = (flags & DIFF_FLAG_IGNORE_WHITESPACE);
111 
112 	if (!left->len && !right->len) {
113 		*cmp = 0;
114 		return 0;
115 	}
116 	if (!ignore_whitespace) {
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->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->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;
202 	if (left->hash != right->hash) {
203 		*same = false;
204 		return 0;
205 	}
206 	r = diff_atom_cmp(&cmp, left, right);
207 	if (r) {
208 		*same = true;
209 		return r;
210 	}
211 	*same = (cmp == 0);
212 	return 0;
213 }
214 
215 static struct diff_chunk *
216 diff_state_add_solved_chunk(struct diff_state *state,
217 			    const struct diff_chunk *chunk)
218 {
219 	diff_chunk_arraylist_t *result;
220 	struct diff_chunk *new_chunk;
221 	enum diff_chunk_type last_t;
222 	enum diff_chunk_type new_t;
223 	struct diff_chunk *last;
224 
225 	/* Append to solved chunks; make sure that adjacent chunks of same type are combined, and that a minus chunk
226 	 * never directly follows a plus chunk. */
227 	result = &state->result->chunks;
228 
229 	last_t = result->len ? diff_chunk_type(&result->head[result->len - 1])
230 		: CHUNK_EMPTY;
231 	new_t = diff_chunk_type(chunk);
232 
233 	debug("ADD %s chunk #%u:\n", chunk->solved ? "solved" : "UNSOLVED",
234 	      result->len);
235 	debug("L\n");
236 	debug_dump_atoms(&state->left, chunk->left_start, chunk->left_count);
237 	debug("R\n");
238 	debug_dump_atoms(&state->right, chunk->right_start, chunk->right_count);
239 
240 	if (result->len) {
241 		last = &result->head[result->len - 1];
242 		assert(chunk->left_start
243 		       == last->left_start + last->left_count);
244 		assert(chunk->right_start
245 		       == last->right_start + last->right_count);
246 	}
247 
248 	if (new_t == last_t) {
249 		new_chunk = &result->head[result->len - 1];
250 		new_chunk->left_count += chunk->left_count;
251 		new_chunk->right_count += chunk->right_count;
252 		debug("  - added chunk touches previous one of same type, joined:\n");
253 		debug("L\n");
254 		debug_dump_atoms(&state->left, new_chunk->left_start, new_chunk->left_count);
255 		debug("R\n");
256 		debug_dump_atoms(&state->right, new_chunk->right_start, new_chunk->right_count);
257 	} else if (last_t == CHUNK_PLUS && new_t == CHUNK_MINUS) {
258 		enum diff_chunk_type prev_last_t =
259 			result->len > 1 ?
260 				diff_chunk_type(&result->head[result->len - 2])
261 				: CHUNK_EMPTY;
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 
269 			debug("  - added minus-chunk follows plus-chunk,"
270 			      " put before that plus-chunk and joined"
271 			      " with preceding minus-chunk:\n");
272 			debug("L\n");
273 			debug_dump_atoms(&state->left, new_chunk->left_start, new_chunk->left_count);
274 			debug("R\n");
275 			debug_dump_atoms(&state->right, new_chunk->right_start, new_chunk->right_count);
276 		} else {
277 			ARRAYLIST_INSERT(new_chunk, *result, result->len - 1);
278 			if (!new_chunk)
279 				return NULL;
280 			*new_chunk = *chunk;
281 
282 			/* The new minus chunk indicates to which position on
283 			 * the right it corresponds, even though it doesn't add
284 			 * any lines on the right. By moving above a plus chunk,
285 			 * that position on the right has shifted. */
286 			last = &result->head[result->len - 1];
287 			new_chunk->right_start = last->right_start;
288 
289 			debug("  - added minus-chunk follows plus-chunk,"
290 			      " put before that plus-chunk\n");
291 		}
292 
293 		/* That last_t == CHUNK_PLUS indicates to which position on the
294 		 * left it corresponds, even though it doesn't add any lines on
295 		 * the left. By inserting/extending the prev_last_t ==
296 		 * CHUNK_MINUS, that position on the left has shifted. */
297 		last = &result->head[result->len - 1];
298 		last->left_start = new_chunk->left_start
299 			+ new_chunk->left_count;
300 
301 	} else {
302 		ARRAYLIST_ADD(new_chunk, *result);
303 		if (!new_chunk)
304 			return NULL;
305 		*new_chunk = *chunk;
306 	}
307 	return new_chunk;
308 }
309 
310 /* Even if a left or right side is empty, diff output may need to know the
311  * position in that file.
312  * So left_start or right_start must never be NULL -- pass left_count or
313  * right_count as zero to indicate staying at that position without consuming
314  * any lines. */
315 struct diff_chunk *
316 diff_state_add_chunk(struct diff_state *state, bool solved,
317 		     struct diff_atom *left_start, unsigned int left_count,
318 		     struct diff_atom *right_start, unsigned int right_count)
319 {
320 	struct diff_chunk *new_chunk;
321 	struct diff_chunk chunk = {
322 		.solved = solved,
323 		.left_start = left_start,
324 		.left_count = left_count,
325 		.right_start = right_start,
326 		.right_count = right_count,
327 	};
328 
329 	/* An unsolved chunk means store as intermediate result for later
330 	 * re-iteration.
331 	 * If there already are intermediate results, that means even a
332 	 * following solved chunk needs to go to intermediate results, so that
333 	 * it is later put in the final correct position in solved chunks.
334 	 */
335 	if (!solved || state->temp_result.len) {
336 		/* Append to temp_result */
337 		debug("ADD %s chunk to temp result:\n",
338 		      chunk.solved ? "solved" : "UNSOLVED");
339 		debug("L\n");
340 		debug_dump_atoms(&state->left, left_start, left_count);
341 		debug("R\n");
342 		debug_dump_atoms(&state->right, right_start, right_count);
343 		ARRAYLIST_ADD(new_chunk, state->temp_result);
344 		if (!new_chunk)
345 			return NULL;
346 		*new_chunk = chunk;
347 		return new_chunk;
348 	}
349 
350 	return diff_state_add_solved_chunk(state, &chunk);
351 }
352 
353 static void
354 diff_data_init_root(struct diff_data *d, FILE *f, const uint8_t *data,
355     unsigned long long len, int diff_flags)
356 {
357 	*d = (struct diff_data){
358 		.f = f,
359 		.pos = 0,
360 		.data = data,
361 		.len = len,
362 		.root = d,
363 		.diff_flags = diff_flags,
364 	};
365 }
366 
367 void
368 diff_data_init_subsection(struct diff_data *d, struct diff_data *parent,
369 			  struct diff_atom *from_atom, unsigned int atoms_count)
370 {
371 	struct diff_atom *last_atom;
372 
373 	debug("diff_data %p  parent %p  from_atom %p  atoms_count %u\n",
374 	      d, parent, from_atom, atoms_count);
375 	debug("  from_atom ");
376 	debug_dump_atom(parent, NULL, from_atom);
377 
378 	if (atoms_count == 0) {
379 		*d = (struct diff_data){
380 			.f = NULL,
381 			.pos = 0,
382 			.data = NULL,
383 			.len = 0,
384 			.root = parent->root,
385 			.atoms.head = NULL,
386 			.atoms.len = atoms_count,
387 		};
388 
389 		return;
390 	}
391 
392 	last_atom = from_atom + atoms_count - 1;
393 	*d = (struct diff_data){
394 		.f = NULL,
395 		.pos = from_atom->pos,
396 		.data = from_atom->at,
397 		.len = (last_atom->pos + last_atom->len) - from_atom->pos,
398 		.root = parent->root,
399 		.atoms.head = from_atom,
400 		.atoms.len = atoms_count,
401 	};
402 
403 	debug("subsection:\n");
404 	debug_dump(d);
405 }
406 
407 void
408 diff_data_free(struct diff_data *diff_data)
409 {
410 	if (!diff_data)
411 		return;
412 	if (diff_data->atoms.allocated)
413 		ARRAYLIST_FREE(diff_data->atoms);
414 }
415 
416 int
417 diff_algo_none(const struct diff_algo_config *algo_config,
418 	       struct diff_state *state)
419 {
420 	debug("\n** %s\n", __func__);
421 	debug("left:\n");
422 	debug_dump(&state->left);
423 	debug("right:\n");
424 	debug_dump(&state->right);
425 	debug_dump_myers_graph(&state->left, &state->right, NULL, NULL, 0, NULL,
426 			       0);
427 
428 	/* Add a chunk of equal lines, if any */
429 	struct diff_atom *l = state->left.atoms.head;
430 	unsigned int l_len = state->left.atoms.len;
431 	struct diff_atom *r = state->right.atoms.head;
432 	unsigned int r_len = state->right.atoms.len;
433 	unsigned int equal_atoms_start = 0;
434 	unsigned int equal_atoms_end = 0;
435 	unsigned int l_idx = 0;
436 	unsigned int r_idx = 0;
437 
438 	while (equal_atoms_start < l_len
439 	       && equal_atoms_start < r_len) {
440 		int err;
441 		bool same;
442 		err = diff_atom_same(&same, &l[equal_atoms_start],
443 				     &r[equal_atoms_start]);
444 		if (err)
445 			return err;
446 		if (!same)
447 			break;
448 		equal_atoms_start++;
449 	}
450 	while (equal_atoms_end < (l_len - equal_atoms_start)
451 	       && equal_atoms_end < (r_len - equal_atoms_start)) {
452 		int err;
453 		bool same;
454 		err = diff_atom_same(&same, &l[l_len - 1 - equal_atoms_end],
455 				   &r[r_len - 1 - equal_atoms_end]);
456 		if (err)
457 			return err;
458 		if (!same)
459 			break;
460 		equal_atoms_end++;
461 	}
462 
463 	/* Add a chunk of equal lines at the start */
464 	if (equal_atoms_start) {
465 		if (!diff_state_add_chunk(state, true,
466 					  l, equal_atoms_start,
467 					  r, equal_atoms_start))
468 			return ENOMEM;
469 		l_idx += equal_atoms_start;
470 		r_idx += equal_atoms_start;
471 	}
472 
473 	/* Add a "minus" chunk with all lines from the left. */
474 	if (equal_atoms_start + equal_atoms_end < l_len) {
475 		unsigned int add_len = l_len - equal_atoms_start - equal_atoms_end;
476 		if (!diff_state_add_chunk(state, true,
477 					  &l[l_idx], add_len,
478 					  &r[r_idx], 0))
479 			return ENOMEM;
480 		l_idx += add_len;
481 	}
482 
483 	/* Add a "plus" chunk with all lines from the right. */
484 	if (equal_atoms_start + equal_atoms_end < r_len) {
485 		unsigned int add_len = r_len - equal_atoms_start - equal_atoms_end;
486 		if (!diff_state_add_chunk(state, true,
487 					  &l[l_idx], 0,
488 					  &r[r_idx], add_len))
489 			return ENOMEM;
490 		r_idx += add_len;
491 	}
492 
493 	/* Add a chunk of equal lines at the end */
494 	if (equal_atoms_end) {
495 		if (!diff_state_add_chunk(state, true,
496 					  &l[l_idx], equal_atoms_end,
497 					  &r[r_idx], equal_atoms_end))
498 			return ENOMEM;
499 	}
500 
501 	return DIFF_RC_OK;
502 }
503 
504 static int
505 diff_run_algo(const struct diff_algo_config *algo_config,
506 	      struct diff_state *state)
507 {
508 	int rc;
509 
510 	if (!algo_config || !algo_config->impl
511 	    || !state->recursion_depth_left
512 	    || !state->left.atoms.len || !state->right.atoms.len) {
513 		debug("Fall back to diff_algo_none():%s%s%s\n",
514 		      (!algo_config || !algo_config->impl) ? " no-cfg" : "",
515 		      (!state->recursion_depth_left) ? " max-depth" : "",
516 		      (!state->left.atoms.len || !state->right.atoms.len)?
517 			      " trivial" : "");
518 		return diff_algo_none(algo_config, state);
519 	}
520 
521 	ARRAYLIST_FREE(state->temp_result);
522 	ARRAYLIST_INIT(state->temp_result, DIFF_RESULT_ALLOC_BLOCKSIZE);
523 	rc = algo_config->impl(algo_config, state);
524 	switch (rc) {
525 	case DIFF_RC_USE_DIFF_ALGO_FALLBACK:
526 		debug("Got DIFF_RC_USE_DIFF_ALGO_FALLBACK (%p)\n",
527 		      algo_config->fallback_algo);
528 		rc = diff_run_algo(algo_config->fallback_algo, state);
529 		goto return_rc;
530 
531 	case DIFF_RC_OK:
532 		/* continue below */
533 		break;
534 
535 	default:
536 		/* some error happened */
537 		goto return_rc;
538 	}
539 
540 	/* Pick up any diff chunks that are still unsolved and feed to
541 	 * inner_algo.  inner_algo will solve unsolved chunks and append to
542 	 * result, and subsequent solved chunks on this level are then appended
543 	 * to result afterwards. */
544 	int i;
545 	for (i = 0; i < state->temp_result.len; i++) {
546 		struct diff_chunk *c = &state->temp_result.head[i];
547 		if (c->solved) {
548 			diff_state_add_solved_chunk(state, c);
549 			continue;
550 		}
551 
552 		/* c is an unsolved chunk, feed to inner_algo */
553 		struct diff_state inner_state = {
554 			.result = state->result,
555 			.recursion_depth_left = state->recursion_depth_left - 1,
556 			.kd_buf = state->kd_buf,
557 			.kd_buf_size = state->kd_buf_size,
558 		};
559 		diff_data_init_subsection(&inner_state.left, &state->left,
560 					  c->left_start, c->left_count);
561 		diff_data_init_subsection(&inner_state.right, &state->right,
562 					  c->right_start, c->right_count);
563 
564 		rc = diff_run_algo(algo_config->inner_algo, &inner_state);
565 		state->kd_buf = inner_state.kd_buf;
566 		state->kd_buf_size = inner_state.kd_buf_size;
567 		if (rc != DIFF_RC_OK)
568 			goto return_rc;
569 	}
570 
571 	rc = DIFF_RC_OK;
572 return_rc:
573 	ARRAYLIST_FREE(state->temp_result);
574 	return rc;
575 }
576 
577 int
578 diff_atomize_file(struct diff_data *d,
579 		  const struct diff_config *config,
580 		  FILE *f, const uint8_t *data, off_t len, int diff_flags)
581 {
582 	if (!config->atomize_func)
583 		return EINVAL;
584 
585 	diff_data_init_root(d, f, data, len, diff_flags);
586 
587 	return config->atomize_func(config->atomize_func_data, d);
588 
589 }
590 
591 struct diff_result *
592 diff_main(const struct diff_config *config, struct diff_data *left,
593 	  struct diff_data *right)
594 {
595 	struct diff_result *result = malloc(sizeof(struct diff_result));
596 	if (!result)
597 		return NULL;
598 
599 	*result = (struct diff_result){};
600 	result->left = left;
601 	result->right = right;
602 
603 	struct diff_state state = {
604 		.result = result,
605 		.recursion_depth_left = config->max_recursion_depth ?
606 		    config->max_recursion_depth : UINT_MAX,
607 		.kd_buf = NULL,
608 		.kd_buf_size = 0,
609 	};
610 	diff_data_init_subsection(&state.left, left,
611 				  left->atoms.head,
612 				  left->atoms.len);
613 	diff_data_init_subsection(&state.right, right,
614 				  right->atoms.head,
615 				  right->atoms.len);
616 
617 	result->rc = diff_run_algo(config->algo, &state);
618 	free(state.kd_buf);
619 
620 	return result;
621 }
622 
623 void
624 diff_result_free(struct diff_result *result)
625 {
626 	if (!result)
627 		return;
628 	ARRAYLIST_FREE(result->chunks);
629 	free(result);
630 }