pack-objects.c

   1 #include <ctype.h>
   2 #include "cache.h"
   3 #include "object.h"
   4 #include "delta.h"
   5 #include "pack.h"
   6 #include "csum-file.h"
   7
   8 static const char pack_usage[] = "git-pack-objects [--incremental] [--window=N] [--depth=N] {--stdout | base-name} < object-list";
   9
  10 struct object_entry {
  11         unsigned char sha1[20];
  12         unsigned long size;
  13         unsigned long offset;
  14         unsigned int depth;
  15         unsigned int hash;
  16         enum object_type type;
  17         unsigned long delta_size;
  18         struct object_entry *delta;
  19 };
  20
  21 static unsigned char object_list_sha1[20];
  22 static int non_empty = 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 && has_sha1_pack(sha1))
 199                 return 0;
 200
 201         if (idx >= nr_alloc) {
 202                 unsigned int needed = (idx + 1024) * 3 / 2;
 203                 objects = xrealloc(objects, needed * sizeof(*entry));
 204                 nr_alloc = needed;
 205         }
 206         entry = objects + idx;
 207         memset(entry, 0, sizeof(*entry));
 208         memcpy(entry->sha1, sha1, 20);
 209         entry->hash = hash;
 210         nr_objects = idx+1;
 211         return 1;
 212 }
 213
 214 static void check_object(struct object_entry *entry)
 215 {
 216         char type[20];
 217
 218         if (!sha1_object_info(entry->sha1, type, &entry->size)) {
 219                 if (!strcmp(type, "commit")) {
 220                         entry->type = OBJ_COMMIT;
 221                 } else if (!strcmp(type, "tree")) {
 222                         entry->type = OBJ_TREE;
 223                 } else if (!strcmp(type, "blob")) {
 224                         entry->type = OBJ_BLOB;
 225                 } else if (!strcmp(type, "tag")) {
 226                         entry->type = OBJ_TAG;
 227                 } else
 228                         die("unable to pack object %s of type %s",
 229                             sha1_to_hex(entry->sha1), type);
 230         }
 231         else
 232                 die("unable to get type of object %s",
 233                     sha1_to_hex(entry->sha1));
 234 }
 235
 236 static void get_object_details(void)
 237 {
 238         int i;
 239         struct object_entry *entry = objects;
 240
 241         for (i = 0; i < nr_objects; i++)
 242                 check_object(entry++);
 243 }
 244
 245 typedef int (*entry_sort_t)(const struct object_entry *, const struct object_entry *);
 246
 247 static entry_sort_t current_sort;
 248
 249 static int sort_comparator(const void *_a, const void *_b)
 250 {
 251         struct object_entry *a = *(struct object_entry **)_a;
 252         struct object_entry *b = *(struct object_entry **)_b;
 253         return current_sort(a,b);
 254 }
 255
 256 static struct object_entry **create_sorted_list(entry_sort_t sort)
 257 {
 258         struct object_entry **list = xmalloc(nr_objects * sizeof(struct object_entry *));
 259         int i;
 260
 261         for (i = 0; i < nr_objects; i++)
 262                 list[i] = objects + i;
 263         current_sort = sort;
 264         qsort(list, nr_objects, sizeof(struct object_entry *), sort_comparator);
 265         return list;
 266 }
 267
 268 static int sha1_sort(const struct object_entry *a, const struct object_entry *b)
 269 {
 270         return memcmp(a->sha1, b->sha1, 20);
 271 }
 272
 273 static int type_size_sort(const struct object_entry *a, const struct object_entry *b)
 274 {
 275         if (a->type < b->type)
 276                 return -1;
 277         if (a->type > b->type)
 278                 return 1;
 279         if (a->hash < b->hash)
 280                 return -1;
 281         if (a->hash > b->hash)
 282                 return 1;
 283         if (a->size < b->size)
 284                 return -1;
 285         if (a->size > b->size)
 286                 return 1;
 287         return a < b ? -1 : (a > b);
 288 }
 289
 290 struct unpacked {
 291         struct object_entry *entry;
 292         void *data;
 293 };
 294
 295 /*
 296  * We search for deltas _backwards_ in a list sorted by type and
 297  * by size, so that we see progressively smaller and smaller files.
 298  * That's because we prefer deltas to be from the bigger file
 299  * to the smaller - deletes are potentially cheaper, but perhaps
 300  * more importantly, the bigger file is likely the more recent
 301  * one.
 302  */
 303 static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_depth)
 304 {
 305         struct object_entry *cur_entry = cur->entry;
 306         struct object_entry *old_entry = old->entry;
 307         unsigned long size, oldsize, delta_size, sizediff;
 308         long max_size;
 309         void *delta_buf;
 310
 311         /* Don't bother doing diffs between different types */
 312         if (cur_entry->type != old_entry->type)
 313                 return -1;
 314
 315         size = cur_entry->size;
 316         if (size < 50)
 317                 return -1;
 318         oldsize = old_entry->size;
 319         sizediff = oldsize > size ? oldsize - size : size - oldsize;
 320         if (sizediff > size / 8)
 321                 return -1;
 322         if (old_entry->depth >= max_depth)
 323                 return 0;
 324
 325         /*
 326          * NOTE!
 327          *
 328          * We always delta from the bigger to the smaller, since that's
 329          * more space-efficient (deletes don't have to say _what_ they
 330          * delete).
 331          */
 332         max_size = size / 2 - 20;
 333         if (cur_entry->delta)
 334                 max_size = cur_entry->delta_size-1;
 335         if (sizediff >= max_size)
 336                 return -1;
 337         delta_buf = diff_delta(old->data, oldsize,
 338                                cur->data, size, &delta_size, max_size);
 339         if (!delta_buf)
 340                 return 0;
 341         cur_entry->delta = old_entry;
 342         cur_entry->delta_size = delta_size;
 343         cur_entry->depth = old_entry->depth + 1;
 344         free(delta_buf);
 345         return 0;
 346 }
 347
 348 static void find_deltas(struct object_entry **list, int window, int depth)
 349 {
 350         int i, idx;
 351         unsigned int array_size = window * sizeof(struct unpacked);
 352         struct unpacked *array = xmalloc(array_size);
 353
 354         memset(array, 0, array_size);
 355         i = nr_objects;
 356         idx = 0;
 357         while (--i >= 0) {
 358                 struct object_entry *entry = list[i];
 359                 struct unpacked *n = array + idx;
 360                 unsigned long size;
 361                 char type[10];
 362                 int j;
 363
 364                 free(n->data);
 365                 n->entry = entry;
 366                 n->data = read_sha1_file(entry->sha1, type, &size);
 367                 if (size != entry->size)
 368                         die("object %s inconsistent object length (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
 369                 j = window;
 370                 while (--j > 0) {
 371                         unsigned int other_idx = idx + j;
 372                         struct unpacked *m;
 373                         if (other_idx >= window)
 374                                 other_idx -= window;
 375                         m = array + other_idx;
 376                         if (!m->entry)
 377                                 break;
 378                         if (try_delta(n, m, depth) < 0)
 379                                 break;
 380                 }
 381                 idx++;
 382                 if (idx >= window)
 383                         idx = 0;
 384         }
 385
 386         for (i = 0; i < window; ++i)
 387                 free(array[i].data);
 388         free(array);
 389 }
 390
 391 int main(int argc, char **argv)
 392 {
 393         SHA_CTX ctx;
 394         char line[PATH_MAX + 20];
 395         int window = 10, depth = 10, pack_to_stdout = 0;
 396         struct object_entry **list;
 397         int i;
 398
 399         for (i = 1; i < argc; i++) {
 400                 const char *arg = argv[i];
 401
 402                 if (*arg == '-') {
 403                         if (!strcmp("--non-empty", arg)) {
 404                                 non_empty = 1;
 405                                 continue;
 406                         }
 407                         if (!strcmp("--incremental", arg)) {
 408                                 incremental = 1;
 409                                 continue;
 410                         }
 411                         if (!strncmp("--window=", arg, 9)) {
 412                                 char *end;
 413                                 window = strtoul(arg+9, &end, 0);
 414                                 if (!arg[9] || *end)
 415                                         usage(pack_usage);
 416                                 continue;
 417                         }
 418                         if (!strncmp("--depth=", arg, 8)) {
 419                                 char *end;
 420                                 depth = strtoul(arg+8, &end, 0);
 421                                 if (!arg[8] || *end)
 422                                         usage(pack_usage);
 423                                 continue;
 424                         }
 425                         if (!strcmp("--stdout", arg)) {
 426                                 pack_to_stdout = 1;
 427                                 continue;
 428                         }
 429                         usage(pack_usage);
 430                 }
 431                 if (base_name)
 432                         usage(pack_usage);
 433                 base_name = arg;
 434         }
 435
 436         if (pack_to_stdout != !base_name)
 437                 usage(pack_usage);
 438
 439         while (fgets(line, sizeof(line), stdin) != NULL) {
 440                 unsigned int hash;
 441                 char *p;
 442                 unsigned char sha1[20];
 443
 444                 if (get_sha1_hex(line, sha1))
 445                         die("expected sha1, got garbage");
 446                 hash = 0;
 447                 p = line+40;
 448                 while (*p) {
 449                         unsigned char c = *p++;
 450                         if (isspace(c))
 451                                 continue;
 452                         hash = hash * 11 + c;
 453                 }
 454                 add_object_entry(sha1, hash);
 455         }
 456         if (non_empty && !nr_objects)
 457                 return 0;
 458         get_object_details();
 459
 460         fprintf(stderr, "Packing %d objects\n", nr_objects);
 461
 462         sorted_by_sha = create_sorted_list(sha1_sort);
 463         SHA1_Init(&ctx);
 464         list = sorted_by_sha;
 465         for (i = 0; i < nr_objects; i++) {
 466                 struct object_entry *entry = *list++;
 467                 SHA1_Update(&ctx, entry->sha1, 20);
 468         }
 469         SHA1_Final(object_list_sha1, &ctx);
 470
 471         sorted_by_type = create_sorted_list(type_size_sort);
 472         if (window && depth)
 473                 find_deltas(sorted_by_type, window+1, depth);
 474
 475         write_pack_file();
 476         if (!pack_to_stdout) {
 477                 write_index_file();
 478                 puts(sha1_to_hex(object_list_sha1));
 479         }
 480         return 0;
 481 }