short circuit out of a few places where we would allocate zero bytes
[git.git] / pack-objects.c
1 #include "cache.h"
2 #include "object.h"
3 #include "delta.h"
4 #include "pack.h"
5 #include "csum-file.h"
6
7 static const char pack_usage[] = "git-pack-objects [--non-empty] [--local] [--incremental] [--window=N] [--depth=N] {--stdout | base-name} < object-list";
8
9 struct object_entry {
10         unsigned char sha1[20];
11         unsigned long size;
12         unsigned long offset;
13         unsigned int depth;
14         unsigned int hash;
15         enum object_type type;
16         unsigned long delta_size;
17         struct object_entry *delta;
18 };
19
20 static unsigned char object_list_sha1[20];
21 static int non_empty = 0;
22 static int local = 0;
23 static int incremental = 0;
24 static struct object_entry **sorted_by_sha, **sorted_by_type;
25 static struct object_entry *objects = NULL;
26 static int nr_objects = 0, nr_alloc = 0;
27 static const char *base_name;
28 static unsigned char pack_file_sha1[20];
29
30 static void *delta_against(void *buf, unsigned long size, struct object_entry *entry)
31 {
32         unsigned long othersize, delta_size;
33         char type[10];
34         void *otherbuf = read_sha1_file(entry->delta->sha1, type, &othersize);
35         void *delta_buf;
36
37         if (!otherbuf)
38                 die("unable to read %s", sha1_to_hex(entry->delta->sha1));
39         delta_buf = diff_delta(otherbuf, othersize,
40                                buf, size, &delta_size, 0);
41         if (!delta_buf || delta_size != entry->delta_size)
42                 die("delta size changed");
43         free(buf);
44         free(otherbuf);
45         return delta_buf;
46 }
47
48 /*
49  * The per-object header is a pretty dense thing, which is
50  *  - first byte: low four bits are "size", then three bits of "type",
51  *    and the high bit is "size continues".
52  *  - each byte afterwards: low seven bits are size continuation,
53  *    with the high bit being "size continues"
54  */
55 static int encode_header(enum object_type type, unsigned long size, unsigned char *hdr)
56 {
57         int n = 1;
58         unsigned char c;
59
60         if (type < OBJ_COMMIT || type > OBJ_DELTA)
61                 die("bad type %d", type);
62
63         c = (type << 4) | (size & 15);
64         size >>= 4;
65         while (size) {
66                 *hdr++ = c | 0x80;
67                 c = size & 0x7f;
68                 size >>= 7;
69                 n++;
70         }
71         *hdr = c;
72         return n;
73 }
74
75 static unsigned long write_object(struct sha1file *f, struct object_entry *entry)
76 {
77         unsigned long size;
78         char type[10];
79         void *buf = read_sha1_file(entry->sha1, type, &size);
80         unsigned char header[10];
81         unsigned hdrlen, datalen;
82         enum object_type obj_type;
83
84         if (!buf)
85                 die("unable to read %s", sha1_to_hex(entry->sha1));
86         if (size != entry->size)
87                 die("object %s size inconsistency (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
88
89         /*
90          * The object header is a byte of 'type' followed by zero or
91          * more bytes of length.  For deltas, the 20 bytes of delta sha1
92          * follows that.
93          */
94         obj_type = entry->type;
95         if (entry->delta) {
96                 buf = delta_against(buf, size, entry);
97                 size = entry->delta_size;
98                 obj_type = OBJ_DELTA;
99         }
100         hdrlen = encode_header(obj_type, size, header);
101         sha1write(f, header, hdrlen);
102         if (entry->delta) {
103                 sha1write(f, entry->delta, 20);
104                 hdrlen += 20;
105         }
106         datalen = sha1write_compressed(f, buf, size);
107         free(buf);
108         return hdrlen + datalen;
109 }
110
111 static unsigned long write_one(struct sha1file *f,
112                                struct object_entry *e,
113                                unsigned long offset)
114 {
115         if (e->offset)
116                 /* offset starts from header size and cannot be zero
117                  * if it is written already.
118                  */
119                 return offset;
120         e->offset = offset;
121         offset += write_object(f, e);
122         /* if we are delitified, write out its base object. */
123         if (e->delta)
124                 offset = write_one(f, e->delta, offset);
125         return offset;
126 }
127
128 static void write_pack_file(void)
129 {
130         int i;
131         struct sha1file *f;
132         unsigned long offset;
133         unsigned long mb;
134         struct pack_header hdr;
135
136         if (!base_name)
137                 f = sha1fd(1, "<stdout>");
138         else
139                 f = sha1create("%s-%s.%s", base_name, sha1_to_hex(object_list_sha1), "pack");
140         hdr.hdr_signature = htonl(PACK_SIGNATURE);
141         hdr.hdr_version = htonl(PACK_VERSION);
142         hdr.hdr_entries = htonl(nr_objects);
143         sha1write(f, &hdr, sizeof(hdr));
144         offset = sizeof(hdr);
145         for (i = 0; i < nr_objects; i++)
146                 offset = write_one(f, objects + i, offset);
147
148         sha1close(f, pack_file_sha1, 1);
149         mb = offset >> 20;
150         offset &= 0xfffff;
151 }
152
153 static void write_index_file(void)
154 {
155         int i;
156         struct sha1file *f = sha1create("%s-%s.%s", base_name, sha1_to_hex(object_list_sha1), "idx");
157         struct object_entry **list = sorted_by_sha;
158         struct object_entry **last = list + nr_objects;
159         unsigned int array[256];
160
161         /*
162          * Write the first-level table (the list is sorted,
163          * but we use a 256-entry lookup to be able to avoid
164          * having to do eight extra binary search iterations).
165          */
166         for (i = 0; i < 256; i++) {
167                 struct object_entry **next = list;
168                 while (next < last) {
169                         struct object_entry *entry = *next;
170                         if (entry->sha1[0] != i)
171                                 break;
172                         next++;
173                 }
174                 array[i] = htonl(next - sorted_by_sha);
175                 list = next;
176         }
177         sha1write(f, array, 256 * sizeof(int));
178
179         /*
180          * Write the actual SHA1 entries..
181          */
182         list = sorted_by_sha;
183         for (i = 0; i < nr_objects; i++) {
184                 struct object_entry *entry = *list++;
185                 unsigned int offset = htonl(entry->offset);
186                 sha1write(f, &offset, 4);
187                 sha1write(f, entry->sha1, 20);
188         }
189         sha1write(f, pack_file_sha1, 20);
190         sha1close(f, NULL, 1);
191 }
192
193 static int add_object_entry(unsigned char *sha1, unsigned int hash)
194 {
195         unsigned int idx = nr_objects;
196         struct object_entry *entry;
197
198         if (incremental || local) {
199                 struct packed_git *p;
200
201                 for (p = packed_git; p; p = p->next) {
202                         struct pack_entry e;
203
204                         if (find_pack_entry_one(sha1, &e, p)) {
205                                 if (incremental)
206                                         return 0;
207                                 if (local && !p->pack_local)
208                                         return 0;
209                         }
210                 }
211         }
212
213         if (idx >= nr_alloc) {
214                 unsigned int needed = (idx + 1024) * 3 / 2;
215                 objects = xrealloc(objects, needed * sizeof(*entry));
216                 nr_alloc = needed;
217         }
218         entry = objects + idx;
219         memset(entry, 0, sizeof(*entry));
220         memcpy(entry->sha1, sha1, 20);
221         entry->hash = hash;
222         nr_objects = idx+1;
223         return 1;
224 }
225
226 static void check_object(struct object_entry *entry)
227 {
228         char type[20];
229
230         if (!sha1_object_info(entry->sha1, type, &entry->size)) {
231                 if (!strcmp(type, "commit")) {
232                         entry->type = OBJ_COMMIT;
233                 } else if (!strcmp(type, "tree")) {
234                         entry->type = OBJ_TREE;
235                 } else if (!strcmp(type, "blob")) {
236                         entry->type = OBJ_BLOB;
237                 } else if (!strcmp(type, "tag")) {
238                         entry->type = OBJ_TAG;
239                 } else
240                         die("unable to pack object %s of type %s",
241                             sha1_to_hex(entry->sha1), type);
242         }
243         else
244                 die("unable to get type of object %s",
245                     sha1_to_hex(entry->sha1));
246 }
247
248 static void get_object_details(void)
249 {
250         int i;
251         struct object_entry *entry = objects;
252
253         for (i = 0; i < nr_objects; i++)
254                 check_object(entry++);
255 }
256
257 typedef int (*entry_sort_t)(const struct object_entry *, const struct object_entry *);
258
259 static entry_sort_t current_sort;
260
261 static int sort_comparator(const void *_a, const void *_b)
262 {
263         struct object_entry *a = *(struct object_entry **)_a;
264         struct object_entry *b = *(struct object_entry **)_b;
265         return current_sort(a,b);
266 }
267
268 static struct object_entry **create_sorted_list(entry_sort_t sort)
269 {
270         struct object_entry **list = xmalloc(nr_objects * sizeof(struct object_entry *));
271         int i;
272
273         for (i = 0; i < nr_objects; i++)
274                 list[i] = objects + i;
275         current_sort = sort;
276         qsort(list, nr_objects, sizeof(struct object_entry *), sort_comparator);
277         return list;
278 }
279
280 static int sha1_sort(const struct object_entry *a, const struct object_entry *b)
281 {
282         return memcmp(a->sha1, b->sha1, 20);
283 }
284
285 static int type_size_sort(const struct object_entry *a, const struct object_entry *b)
286 {
287         if (a->type < b->type)
288                 return -1;
289         if (a->type > b->type)
290                 return 1;
291         if (a->hash < b->hash)
292                 return -1;
293         if (a->hash > b->hash)
294                 return 1;
295         if (a->size < b->size)
296                 return -1;
297         if (a->size > b->size)
298                 return 1;
299         return a < b ? -1 : (a > b);
300 }
301
302 struct unpacked {
303         struct object_entry *entry;
304         void *data;
305 };
306
307 /*
308  * We search for deltas _backwards_ in a list sorted by type and
309  * by size, so that we see progressively smaller and smaller files.
310  * That's because we prefer deltas to be from the bigger file
311  * to the smaller - deletes are potentially cheaper, but perhaps
312  * more importantly, the bigger file is likely the more recent
313  * one.
314  */
315 static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_depth)
316 {
317         struct object_entry *cur_entry = cur->entry;
318         struct object_entry *old_entry = old->entry;
319         unsigned long size, oldsize, delta_size, sizediff;
320         long max_size;
321         void *delta_buf;
322
323         /* Don't bother doing diffs between different types */
324         if (cur_entry->type != old_entry->type)
325                 return -1;
326
327         size = cur_entry->size;
328         if (size < 50)
329                 return -1;
330         oldsize = old_entry->size;
331         sizediff = oldsize > size ? oldsize - size : size - oldsize;
332         if (sizediff > size / 8)
333                 return -1;
334         if (old_entry->depth >= max_depth)
335                 return 0;
336
337         /*
338          * NOTE!
339          *
340          * We always delta from the bigger to the smaller, since that's
341          * more space-efficient (deletes don't have to say _what_ they
342          * delete).
343          */
344         max_size = size / 2 - 20;
345         if (cur_entry->delta)
346                 max_size = cur_entry->delta_size-1;
347         if (sizediff >= max_size)
348                 return -1;
349         delta_buf = diff_delta(old->data, oldsize,
350                                cur->data, size, &delta_size, max_size);
351         if (!delta_buf)
352                 return 0;
353         cur_entry->delta = old_entry;
354         cur_entry->delta_size = delta_size;
355         cur_entry->depth = old_entry->depth + 1;
356         free(delta_buf);
357         return 0;
358 }
359
360 static void find_deltas(struct object_entry **list, int window, int depth)
361 {
362         int i, idx;
363         unsigned int array_size = window * sizeof(struct unpacked);
364         struct unpacked *array = xmalloc(array_size);
365
366         memset(array, 0, array_size);
367         i = nr_objects;
368         idx = 0;
369         while (--i >= 0) {
370                 struct object_entry *entry = list[i];
371                 struct unpacked *n = array + idx;
372                 unsigned long size;
373                 char type[10];
374                 int j;
375
376                 free(n->data);
377                 n->entry = entry;
378                 n->data = read_sha1_file(entry->sha1, type, &size);
379                 if (size != entry->size)
380                         die("object %s inconsistent object length (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
381                 j = window;
382                 while (--j > 0) {
383                         unsigned int other_idx = idx + j;
384                         struct unpacked *m;
385                         if (other_idx >= window)
386                                 other_idx -= window;
387                         m = array + other_idx;
388                         if (!m->entry)
389                                 break;
390                         if (try_delta(n, m, depth) < 0)
391                                 break;
392                 }
393                 idx++;
394                 if (idx >= window)
395                         idx = 0;
396         }
397
398         for (i = 0; i < window; ++i)
399                 free(array[i].data);
400         free(array);
401 }
402
403 static void prepare_pack(int window, int depth)
404 {
405         get_object_details();
406
407         fprintf(stderr, "Packing %d objects\n", nr_objects);
408
409         sorted_by_type = create_sorted_list(type_size_sort);
410         if (window && depth)
411                 find_deltas(sorted_by_type, window+1, depth);
412         write_pack_file();
413 }
414
415 static int reuse_cached_pack(unsigned char *sha1, int pack_to_stdout)
416 {
417         static const char cache[] = "pack-cache/pack-%s.%s";
418         char *cached_pack, *cached_idx;
419         int ifd, ofd, ifd_ix = -1;
420
421         cached_pack = git_path(cache, sha1_to_hex(sha1), "pack");
422         ifd = open(cached_pack, O_RDONLY);
423         if (ifd < 0)
424                 return 0;
425
426         if (!pack_to_stdout) {
427                 cached_idx = git_path(cache, sha1_to_hex(sha1), "idx");
428                 ifd_ix = open(cached_idx, O_RDONLY);
429                 if (ifd_ix < 0) {
430                         close(ifd);
431                         return 0;
432                 }
433         }
434
435         fprintf(stderr, "Reusing %d objects pack %s\n", nr_objects,
436                 sha1_to_hex(sha1));
437
438         if (pack_to_stdout) {
439                 if (copy_fd(ifd, 1))
440                         exit(1);
441                 close(ifd);
442         }
443         else {
444                 char name[PATH_MAX];
445                 snprintf(name, sizeof(name),
446                          "%s-%s.%s", base_name, sha1_to_hex(sha1), "pack");
447                 ofd = open(name, O_CREAT | O_EXCL | O_WRONLY, 0666);
448                 if (ofd < 0)
449                         die("unable to open %s (%s)", name, strerror(errno));
450                 if (copy_fd(ifd, ofd))
451                         exit(1);
452                 close(ifd);
453
454                 snprintf(name, sizeof(name),
455                          "%s-%s.%s", base_name, sha1_to_hex(sha1), "idx");
456                 ofd = open(name, O_CREAT | O_EXCL | O_WRONLY, 0666);
457                 if (ofd < 0)
458                         die("unable to open %s (%s)", name, strerror(errno));
459                 if (copy_fd(ifd_ix, ofd))
460                         exit(1);
461                 close(ifd_ix);
462                 puts(sha1_to_hex(sha1));
463         }
464
465         return 1;
466 }
467
468 int main(int argc, char **argv)
469 {
470         SHA_CTX ctx;
471         char line[PATH_MAX + 20];
472         int window = 10, depth = 10, pack_to_stdout = 0;
473         struct object_entry **list;
474         int i;
475
476         setup_git_directory();
477
478         for (i = 1; i < argc; i++) {
479                 const char *arg = argv[i];
480
481                 if (*arg == '-') {
482                         if (!strcmp("--non-empty", arg)) {
483                                 non_empty = 1;
484                                 continue;
485                         }
486                         if (!strcmp("--local", arg)) {
487                                 local = 1;
488                                 continue;
489                         }
490                         if (!strcmp("--incremental", arg)) {
491                                 incremental = 1;
492                                 continue;
493                         }
494                         if (!strncmp("--window=", arg, 9)) {
495                                 char *end;
496                                 window = strtoul(arg+9, &end, 0);
497                                 if (!arg[9] || *end)
498                                         usage(pack_usage);
499                                 continue;
500                         }
501                         if (!strncmp("--depth=", arg, 8)) {
502                                 char *end;
503                                 depth = strtoul(arg+8, &end, 0);
504                                 if (!arg[8] || *end)
505                                         usage(pack_usage);
506                                 continue;
507                         }
508                         if (!strcmp("--stdout", arg)) {
509                                 pack_to_stdout = 1;
510                                 continue;
511                         }
512                         usage(pack_usage);
513                 }
514                 if (base_name)
515                         usage(pack_usage);
516                 base_name = arg;
517         }
518
519         if (pack_to_stdout != !base_name)
520                 usage(pack_usage);
521
522         prepare_packed_git();
523         while (fgets(line, sizeof(line), stdin) != NULL) {
524                 unsigned int hash;
525                 char *p;
526                 unsigned char sha1[20];
527
528                 if (get_sha1_hex(line, sha1))
529                         die("expected sha1, got garbage:\n %s", line);
530                 hash = 0;
531                 p = line+40;
532                 while (*p) {
533                         unsigned char c = *p++;
534                         if (isspace(c))
535                                 continue;
536                         hash = hash * 11 + c;
537                 }
538                 add_object_entry(sha1, hash);
539         }
540         if (non_empty && !nr_objects)
541                 return 0;
542
543         sorted_by_sha = create_sorted_list(sha1_sort);
544         SHA1_Init(&ctx);
545         list = sorted_by_sha;
546         for (i = 0; i < nr_objects; i++) {
547                 struct object_entry *entry = *list++;
548                 SHA1_Update(&ctx, entry->sha1, 20);
549         }
550         SHA1_Final(object_list_sha1, &ctx);
551
552         if (reuse_cached_pack(object_list_sha1, pack_to_stdout))
553                 ;
554         else {
555                 prepare_pack(window, depth);
556                 if (!pack_to_stdout) {
557                         write_index_file();
558                         puts(sha1_to_hex(object_list_sha1));
559                 }
560         }
561         return 0;
562 }