pack-objects.c

   1 #include <ctype.h>
   2 #include "cache.h"
   3 #include "object.h"
   4 #include "delta.h"
   5
   6 static const char pack_usage[] = "git-pack-objects [--window=N] [--depth=N] base-name < object-list";
   7
   8 enum object_type {
   9         OBJ_NONE,
  10         OBJ_COMMIT,
  11         OBJ_TREE,
  12         OBJ_BLOB,
  13         OBJ_DELTA       // NOTE! This is _not_ the same as a "delta" object in the filesystem
  14 };
  15
  16 struct object_entry {
  17         unsigned char sha1[20];
  18         unsigned long size;
  19         unsigned long offset;
  20         unsigned int depth;
  21         unsigned int hash;
  22         enum object_type type;
  23         unsigned long delta_size;
  24         struct object_entry *delta;
  25 };
  26
  27 static struct object_entry **sorted_by_sha, **sorted_by_type;
  28 static struct object_entry *objects = NULL;
  29 static int nr_objects = 0, nr_alloc = 0;
  30 static const char *base_name;
  31
  32 struct myfile {
  33         int fd;
  34         unsigned long chars;
  35         unsigned char buffer[8192];
  36 };
  37
  38 static FILE *create_file(const char *suffix)
  39 {
  40         static char filename[PATH_MAX];
  41         unsigned len;
  42
  43         len = snprintf(filename, PATH_MAX, "%s.%s", base_name, suffix);
  44         if (len >= PATH_MAX)
  45                 die("you wascally wabbit, you");
  46         return fopen(filename, "w");
  47 }
  48
  49 static unsigned long fwrite_compressed(void *in, unsigned long size, FILE *f)
  50 {
  51         z_stream stream;
  52         unsigned long maxsize;
  53         void *out;
  54
  55         memset(&stream, 0, sizeof(stream));
  56         deflateInit(&stream, Z_DEFAULT_COMPRESSION);
  57         maxsize = deflateBound(&stream, size);
  58         out = xmalloc(maxsize);
  59
  60         /* Compress it */
  61         stream.next_in = in;
  62         stream.avail_in = size;
  63
  64         stream.next_out = out;
  65         stream.avail_out = maxsize;
  66
  67         while (deflate(&stream, Z_FINISH) == Z_OK)
  68                 /* nothing */;
  69         deflateEnd(&stream);
  70
  71         size = stream.total_out;
  72         fwrite(out, size, 1, f);
  73         free(out);
  74         return size;
  75 }
  76
  77 static void *delta_against(void *buf, unsigned long size, struct object_entry *entry)
  78 {
  79         unsigned long othersize, delta_size;
  80         char type[10];
  81         void *otherbuf = read_sha1_file(entry->delta->sha1, type, &othersize);
  82         void *delta_buf;
  83
  84         if (!otherbuf)
  85                 die("unable to read %s", sha1_to_hex(entry->delta->sha1));
  86         delta_buf = diff_delta(otherbuf, othersize,
  87                                buf, size, &delta_size, ~0UL);
  88         if (!delta_buf || delta_size != entry->delta_size)
  89                 die("delta size changed");
  90         free(buf);
  91         free(otherbuf);
  92         return delta_buf;
  93 }
  94
  95 static unsigned long write_object(FILE *f, struct object_entry *entry)
  96 {
  97         unsigned long size;
  98         char type[10];
  99         void *buf = read_sha1_file(entry->sha1, type, &size);
 100         char header[25];
 101         unsigned hdrlen, datalen;
 102
 103         if (!buf)
 104                 die("unable to read %s", sha1_to_hex(entry->sha1));
 105         if (size != entry->size)
 106                 die("object %s size inconsistency (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
 107
 108         /*
 109          * The object header is a byte of 'type' followed by four bytes of
 110          * length, except for deltas that has the 20 bytes of delta sha
 111          * instead.
 112          */
 113         header[0] = ".CTB"[entry->type];
 114         hdrlen = 5;
 115         if (entry->delta) {
 116                 header[0] = 'D';
 117                 memcpy(header+5, entry->delta, 20);
 118                 buf = delta_against(buf, size, entry);
 119                 size = entry->delta_size;
 120                 hdrlen = 25;
 121         }
 122         datalen = htonl(size);
 123         memcpy(header+1, &datalen, 4);
 124         fwrite(header, hdrlen, 1, f);
 125         datalen = fwrite_compressed(buf, size, f);
 126         free(buf);
 127         return hdrlen + datalen;
 128 }
 129
 130 static void write_pack_file(void)
 131 {
 132         int i;
 133         FILE *f = create_file("pack");
 134         unsigned long offset = 0;
 135         unsigned long mb;
 136
 137         for (i = 0; i < nr_objects; i++) {
 138                 struct object_entry *entry = objects + i;
 139                 entry->offset = offset;
 140                 offset += write_object(f, entry);
 141         }
 142         fclose(f);
 143         mb = offset >> 20;
 144         offset &= 0xfffff;
 145 }
 146
 147 static void write_index_file(void)
 148 {
 149         int i;
 150         FILE *f = create_file("idx");
 151         struct object_entry **list = sorted_by_sha;
 152         struct object_entry **last = list + nr_objects;
 153         unsigned int array[256];
 154
 155         /*
 156          * Write the first-level table (the list is sorted,
 157          * but we use a 256-entry lookup to be able to avoid
 158          * having to do eight extra binary search iterations)
 159          */
 160         for (i = 0; i < 256; i++) {
 161                 struct object_entry **next = list;
 162                 while (next < last) {
 163                         struct object_entry *entry = *next;
 164                         if (entry->sha1[0] != i)
 165                                 break;
 166                         next++;
 167                 }
 168                 array[i] = htonl(next - sorted_by_sha);
 169                 list = next;
 170         }
 171         fwrite(array, 256, sizeof(int), f);
 172
 173         /*
 174          * Write the actual SHA1 entries..
 175          */
 176         list = sorted_by_sha;
 177         for (i = 0; i < nr_objects; i++) {
 178                 struct object_entry *entry = *list++;
 179                 unsigned int offset = htonl(entry->offset);
 180                 fwrite(&offset, 4, 1, f);
 181                 fwrite(entry->sha1, 20, 1, f);
 182         }
 183         fclose(f);
 184 }
 185
 186 static void add_object_entry(unsigned char *sha1, unsigned int hash)
 187 {
 188         unsigned int idx = nr_objects;
 189         struct object_entry *entry;
 190
 191         if (idx >= nr_alloc) {
 192                 unsigned int needed = (idx + 1024) * 3 / 2;
 193                 objects = xrealloc(objects, needed * sizeof(*entry));
 194                 nr_alloc = needed;
 195         }
 196         entry = objects + idx;
 197         memset(entry, 0, sizeof(*entry));
 198         memcpy(entry->sha1, sha1, 20);
 199         entry->hash = hash;
 200         nr_objects = idx+1;
 201 }
 202
 203 static void check_object(struct object_entry *entry)
 204 {
 205         char buffer[128];
 206         char type[10];
 207         unsigned long mapsize;
 208         z_stream stream;
 209         void *map;
 210
 211         map = map_sha1_file(entry->sha1, &mapsize);
 212         if (!map)
 213                 die("unable to map %s", sha1_to_hex(entry->sha1));
 214         if (unpack_sha1_header(&stream, map, mapsize, buffer, sizeof(buffer)) < 0)
 215                 die("unable to unpack %s header", sha1_to_hex(entry->sha1));
 216         munmap(map, mapsize);
 217         if (parse_sha1_header(buffer, type, &entry->size) < 0)
 218                 die("unable to parse %s header", sha1_to_hex(entry->sha1));
 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
 226                 die("unable to pack object %s of type %s", sha1_to_hex(entry->sha1), type);
 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;
 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                         usage(pack_usage);
 405                 }
 406                 if (base_name)
 407                         usage(pack_usage);
 408                 base_name = arg;
 409         }
 410
 411         if (!base_name)
 412                 usage(pack_usage);
 413
 414         while (fgets(line, sizeof(line), stdin) != NULL) {
 415                 unsigned int hash;
 416                 char *p;
 417                 unsigned char sha1[20];
 418
 419                 if (get_sha1_hex(line, sha1))
 420                         die("expected sha1, got garbage");
 421                 hash = 0;
 422                 p = line+40;
 423                 while (*p) {
 424                         unsigned char c = *p++;
 425                         if (isspace(c))
 426                                 continue;
 427                         hash = hash * 11 + c;
 428                 }
 429                 add_object_entry(sha1, hash);
 430         }
 431         get_object_details();
 432
 433         printf("Packing %d objects\n", nr_objects);
 434
 435         sorted_by_sha = create_sorted_list(sha1_sort);
 436         sorted_by_type = create_sorted_list(type_size_sort);
 437         if (window && depth)
 438                 find_deltas(sorted_by_type, window+1, depth);
 439
 440         write_pack_file();
 441         write_index_file();
 442         return 0;
 443 }