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