pack-objects.c

   1 #include <ctype.h>
   2 #include "cache.h"
   3 #include "object.h"
   4 #include "delta.h"
   5 #include "csum-file.h"
   6
   7 static const char pack_usage[] = "git-pack-objects [--window=N] [--depth=N] base-name < object-list";
   8
   9 /*
  10  * The object type is a single-character shorthand:
  11  *  - 'C' for "Commit"
  12  *  - 'T' for "Tree"
  13  *  - 'B' for "Blob"
  14  *  - 'G' for "taG"
  15  *  - 'D' for "Delta"
  16  */
  17 struct object_entry {
  18         unsigned char sha1[20];
  19         unsigned long size;
  20         unsigned long offset;
  21         unsigned int depth;
  22         unsigned int hash;
  23         unsigned char type;
  24         unsigned long delta_size;
  25         struct object_entry *delta;
  26 };
  27
  28 static struct object_entry **sorted_by_sha, **sorted_by_type;
  29 static struct object_entry *objects = NULL;
  30 static int nr_objects = 0, nr_alloc = 0;
  31 static const char *base_name;
  32 static unsigned char pack_file_sha1[20];
  33
  34 static void *delta_against(void *buf, unsigned long size, struct object_entry *entry)
  35 {
  36         unsigned long othersize, delta_size;
  37         char type[10];
  38         void *otherbuf = read_sha1_file(entry->delta->sha1, type, &othersize);
  39         void *delta_buf;
  40
  41         if (!otherbuf)
  42                 die("unable to read %s", sha1_to_hex(entry->delta->sha1));
  43         delta_buf = diff_delta(otherbuf, othersize,
  44                                buf, size, &delta_size, ~0UL);
  45         if (!delta_buf || delta_size != entry->delta_size)
  46                 die("delta size changed");
  47         free(buf);
  48         free(otherbuf);
  49         return delta_buf;
  50 }
  51
  52 static unsigned long write_object(struct sha1file *f, struct object_entry *entry)
  53 {
  54         unsigned long size;
  55         char type[10];
  56         void *buf = read_sha1_file(entry->sha1, type, &size);
  57         char header[25];
  58         unsigned hdrlen, datalen;
  59
  60         if (!buf)
  61                 die("unable to read %s", sha1_to_hex(entry->sha1));
  62         if (size != entry->size)
  63                 die("object %s size inconsistency (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
  64
  65         /*
  66          * The object header is a byte of 'type' followed by four bytes of
  67          * length, except for deltas that has the 20 bytes of delta sha
  68          * instead.
  69          */
  70         header[0] = entry->type;
  71         hdrlen = 5;
  72         if (entry->delta) {
  73                 header[0] = 'D';
  74                 memcpy(header+5, entry->delta, 20);
  75                 buf = delta_against(buf, size, entry);
  76                 size = entry->delta_size;
  77                 hdrlen = 25;
  78         }
  79         datalen = htonl(size);
  80         memcpy(header+1, &datalen, 4);
  81         sha1write(f, header, hdrlen);
  82         datalen = sha1write_compressed(f, buf, size);
  83         free(buf);
  84         return hdrlen + datalen;
  85 }
  86
  87 static void write_pack_file(void)
  88 {
  89         int i;
  90         struct sha1file *f = sha1create("%s.%s", base_name, "pack");
  91         unsigned long offset = 0;
  92         unsigned long mb;
  93
  94         for (i = 0; i < nr_objects; i++) {
  95                 struct object_entry *entry = objects + i;
  96                 entry->offset = offset;
  97                 offset += write_object(f, entry);
  98         }
  99         sha1close(f, pack_file_sha1, 1);
 100         mb = offset >> 20;
 101         offset &= 0xfffff;
 102 }
 103
 104 static void write_index_file(void)
 105 {
 106         int i;
 107         struct sha1file *f = sha1create("%s.%s", base_name, "idx");
 108         struct object_entry **list = sorted_by_sha;
 109         struct object_entry **last = list + nr_objects;
 110         unsigned int array[256];
 111
 112         /*
 113          * Write the first-level table (the list is sorted,
 114          * but we use a 256-entry lookup to be able to avoid
 115          * having to do eight extra binary search iterations).
 116          */
 117         for (i = 0; i < 256; i++) {
 118                 struct object_entry **next = list;
 119                 while (next < last) {
 120                         struct object_entry *entry = *next;
 121                         if (entry->sha1[0] != i)
 122                                 break;
 123                         next++;
 124                 }
 125                 array[i] = htonl(next - sorted_by_sha);
 126                 list = next;
 127         }
 128         sha1write(f, array, 256 * sizeof(int));
 129
 130         /*
 131          * Write the actual SHA1 entries..
 132          */
 133         list = sorted_by_sha;
 134         for (i = 0; i < nr_objects; i++) {
 135                 struct object_entry *entry = *list++;
 136                 unsigned int offset = htonl(entry->offset);
 137                 sha1write(f, &offset, 4);
 138                 sha1write(f, entry->sha1, 20);
 139         }
 140         sha1write(f, pack_file_sha1, 20);
 141         sha1close(f, NULL, 1);
 142 }
 143
 144 static void add_object_entry(unsigned char *sha1, unsigned int hash)
 145 {
 146         unsigned int idx = nr_objects;
 147         struct object_entry *entry;
 148
 149         if (idx >= nr_alloc) {
 150                 unsigned int needed = (idx + 1024) * 3 / 2;
 151                 objects = xrealloc(objects, needed * sizeof(*entry));
 152                 nr_alloc = needed;
 153         }
 154         entry = objects + idx;
 155         memset(entry, 0, sizeof(*entry));
 156         memcpy(entry->sha1, sha1, 20);
 157         entry->hash = hash;
 158         nr_objects = idx+1;
 159 }
 160
 161 static void check_object(struct object_entry *entry)
 162 {
 163         char type[20];
 164
 165         if (!sha1_object_info(entry->sha1, type, &entry->size)) {
 166                 if (!strcmp(type, "commit")) {
 167                         entry->type = 'C';
 168                 } else if (!strcmp(type, "tree")) {
 169                         entry->type = 'T';
 170                 } else if (!strcmp(type, "blob")) {
 171                         entry->type = 'B';
 172                 } else if (!strcmp(type, "tag")) {
 173                         entry->type = 'G';
 174                 } else
 175                         die("unable to pack object %s of type %s",
 176                             sha1_to_hex(entry->sha1), type);
 177         }
 178         else
 179                 die("unable to get type of object %s",
 180                     sha1_to_hex(entry->sha1));
 181 }
 182
 183 static void get_object_details(void)
 184 {
 185         int i;
 186         struct object_entry *entry = objects;
 187
 188         for (i = 0; i < nr_objects; i++)
 189                 check_object(entry++);
 190 }
 191
 192 typedef int (*entry_sort_t)(const struct object_entry *, const struct object_entry *);
 193
 194 static entry_sort_t current_sort;
 195
 196 static int sort_comparator(const void *_a, const void *_b)
 197 {
 198         struct object_entry *a = *(struct object_entry **)_a;
 199         struct object_entry *b = *(struct object_entry **)_b;
 200         return current_sort(a,b);
 201 }
 202
 203 static struct object_entry **create_sorted_list(entry_sort_t sort)
 204 {
 205         struct object_entry **list = xmalloc(nr_objects * sizeof(struct object_entry *));
 206         int i;
 207
 208         for (i = 0; i < nr_objects; i++)
 209                 list[i] = objects + i;
 210         current_sort = sort;
 211         qsort(list, nr_objects, sizeof(struct object_entry *), sort_comparator);
 212         return list;
 213 }
 214
 215 static int sha1_sort(const struct object_entry *a, const struct object_entry *b)
 216 {
 217         return memcmp(a->sha1, b->sha1, 20);
 218 }
 219
 220 static int type_size_sort(const struct object_entry *a, const struct object_entry *b)
 221 {
 222         if (a->type < b->type)
 223                 return -1;
 224         if (a->type > b->type)
 225                 return 1;
 226         if (a->hash < b->hash)
 227                 return -1;
 228         if (a->hash > b->hash)
 229                 return 1;
 230         if (a->size < b->size)
 231                 return -1;
 232         if (a->size > b->size)
 233                 return 1;
 234         return a < b ? -1 : (a > b);
 235 }
 236
 237 struct unpacked {
 238         struct object_entry *entry;
 239         void *data;
 240 };
 241
 242 /*
 243  * We search for deltas _backwards_ in a list sorted by type and
 244  * by size, so that we see progressively smaller and smaller files.
 245  * That's because we prefer deltas to be from the bigger file
 246  * to the smaller - deletes are potentially cheaper, but perhaps
 247  * more importantly, the bigger file is likely the more recent
 248  * one.
 249  */
 250 static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_depth)
 251 {
 252         struct object_entry *cur_entry = cur->entry;
 253         struct object_entry *old_entry = old->entry;
 254         unsigned long size, oldsize, delta_size, sizediff;
 255         long max_size;
 256         void *delta_buf;
 257
 258         /* Don't bother doing diffs between different types */
 259         if (cur_entry->type != old_entry->type)
 260                 return -1;
 261
 262         size = cur_entry->size;
 263         if (size < 50)
 264                 return -1;
 265         oldsize = old_entry->size;
 266         sizediff = oldsize > size ? oldsize - size : size - oldsize;
 267         if (sizediff > size / 8)
 268                 return -1;
 269         if (old_entry->depth >= max_depth)
 270                 return 0;
 271
 272         /*
 273          * NOTE!
 274          *
 275          * We always delta from the bigger to the smaller, since that's
 276          * more space-efficient (deletes don't have to say _what_ they
 277          * delete).
 278          */
 279         max_size = size / 2 - 20;
 280         if (cur_entry->delta)
 281                 max_size = cur_entry->delta_size-1;
 282         if (sizediff >= max_size)
 283                 return -1;
 284         delta_buf = diff_delta(old->data, oldsize,
 285                                cur->data, size, &delta_size, max_size);
 286         if (!delta_buf)
 287                 return 0;
 288         cur_entry->delta = old_entry;
 289         cur_entry->delta_size = delta_size;
 290         cur_entry->depth = old_entry->depth + 1;
 291         free(delta_buf);
 292         return 0;
 293 }
 294
 295 static void find_deltas(struct object_entry **list, int window, int depth)
 296 {
 297         int i, idx;
 298         unsigned int array_size = window * sizeof(struct unpacked);
 299         struct unpacked *array = xmalloc(array_size);
 300
 301         memset(array, 0, array_size);
 302         i = nr_objects;
 303         idx = 0;
 304         while (--i >= 0) {
 305                 struct object_entry *entry = list[i];
 306                 struct unpacked *n = array + idx;
 307                 unsigned long size;
 308                 char type[10];
 309                 int j;
 310
 311                 free(n->data);
 312                 n->entry = entry;
 313                 n->data = read_sha1_file(entry->sha1, type, &size);
 314                 if (size != entry->size)
 315                         die("object %s inconsistent object length (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
 316                 j = window;
 317                 while (--j > 0) {
 318                         unsigned int other_idx = idx + j;
 319                         struct unpacked *m;
 320                         if (other_idx >= window)
 321                                 other_idx -= window;
 322                         m = array + other_idx;
 323                         if (!m->entry)
 324                                 break;
 325                         if (try_delta(n, m, depth) < 0)
 326                                 break;
 327                 }
 328                 idx++;
 329                 if (idx >= window)
 330                         idx = 0;
 331         }
 332 }
 333
 334 int main(int argc, char **argv)
 335 {
 336         char line[PATH_MAX + 20];
 337         int window = 10, depth = 10;
 338         int i;
 339
 340         for (i = 1; i < argc; i++) {
 341                 const char *arg = argv[i];
 342
 343                 if (*arg == '-') {
 344                         if (!strncmp("--window=", arg, 9)) {
 345                                 char *end;
 346                                 window = strtoul(arg+9, &end, 0);
 347                                 if (!arg[9] || *end)
 348                                         usage(pack_usage);
 349                                 continue;
 350                         }
 351                         if (!strncmp("--depth=", arg, 8)) {
 352                                 char *end;
 353                                 depth = strtoul(arg+8, &end, 0);
 354                                 if (!arg[8] || *end)
 355                                         usage(pack_usage);
 356                                 continue;
 357                         }
 358                         usage(pack_usage);
 359                 }
 360                 if (base_name)
 361                         usage(pack_usage);
 362                 base_name = arg;
 363         }
 364
 365         if (!base_name)
 366                 usage(pack_usage);
 367
 368         while (fgets(line, sizeof(line), stdin) != NULL) {
 369                 unsigned int hash;
 370                 char *p;
 371                 unsigned char sha1[20];
 372
 373                 if (get_sha1_hex(line, sha1))
 374                         die("expected sha1, got garbage");
 375                 hash = 0;
 376                 p = line+40;
 377                 while (*p) {
 378                         unsigned char c = *p++;
 379                         if (isspace(c))
 380                                 continue;
 381                         hash = hash * 11 + c;
 382                 }
 383                 add_object_entry(sha1, hash);
 384         }
 385         get_object_details();
 386
 387         printf("Packing %d objects\n", nr_objects);
 388
 389         sorted_by_sha = create_sorted_list(sha1_sort);
 390         sorted_by_type = create_sorted_list(type_size_sort);
 391         if (window && depth)
 392                 find_deltas(sorted_by_type, window+1, depth);
 393
 394         write_pack_file();
 395         write_index_file();
 396         return 0;
 397 }