pack-objects.c

   1 #include "cache.h"
   2 #include "object.h"
   3 #include "delta.h"
   4
   5 static const char pack_usage[] = "git-pack-objects [--window=N] base-name < object-list";
   6
   7 enum object_type {
   8         OBJ_NONE,
   9         OBJ_COMMIT,
  10         OBJ_TREE,
  11         OBJ_BLOB,
  12         OBJ_DELTA       // NOTE! This is _not_ the same as a "delta" object in the filesystem
  13 };
  14
  15 struct object_entry {
  16         unsigned char sha1[20];
  17         unsigned long size;
  18         unsigned long offset;
  19         unsigned int depth;
  20         unsigned int flags;
  21         enum object_type type;
  22         unsigned long delta_size;
  23         struct object_entry *delta;
  24 };
  25
  26 static struct object_entry **sorted_by_sha, **sorted_by_type;
  27 static struct object_entry *objects = NULL;
  28 static int nr_objects = 0, nr_alloc = 0;
  29 static int delta_window = 10;
  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(buf, size, otherbuf, othersize, &delta_size);
  87         if (delta_size != entry->delta_size)
  88                 die("delta size changed");
  89         free(buf);
  90         free(otherbuf);
  91         return delta_buf;
  92 }
  93
  94 static unsigned long write_object(FILE *f, struct object_entry *entry)
  95 {
  96         unsigned long size;
  97         char type[10];
  98         void *buf = read_sha1_file(entry->sha1, type, &size);
  99         char header[21];
 100         unsigned hdrlen, datalen;
 101
 102         if (!buf)
 103                 die("unable to read %s", sha1_to_hex(entry->sha1));
 104         if (size != entry->size)
 105                 die("object %s size inconsistency (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
 106
 107         /*
 108          * The object header is a byte of 'type' followed by four bytes of
 109          * length, except for deltas that has the 20 bytes of delta sha
 110          * instead.
 111          */
 112         header[0] = ".CTB"[entry->type];
 113         datalen = htonl(size);
 114         memcpy(header+1, &datalen, 4);
 115         hdrlen = 5;
 116         if (entry->delta) {
 117                 memcpy(header+1, entry->delta, 20);
 118                 buf = delta_against(buf, size, entry);
 119                 size = entry->delta_size;
 120                 hdrlen = 21;
 121         }
 122         fwrite(header, hdrlen, 1, f);
 123         datalen = fwrite_compressed(buf, size, f);
 124         free(buf);
 125         return hdrlen + datalen;
 126 }
 127
 128 static void write_pack_file(void)
 129 {
 130         int i;
 131         FILE *f = create_file("pack");
 132         unsigned long offset = 0;
 133         unsigned long mb;
 134
 135         for (i = 0; i < nr_objects; i++) {
 136                 struct object_entry *entry = objects + i;
 137                 entry->offset = offset;
 138                 offset += write_object(f, entry);
 139         }
 140         fclose(f);
 141         mb = offset >> 20;
 142         offset &= 0xfffff;
 143 }
 144
 145 static void write_index_file(void)
 146 {
 147         int i;
 148         FILE *f = create_file("idx");
 149         struct object_entry **list = sorted_by_sha;
 150         struct object_entry **last = list + nr_objects;
 151         unsigned int array[256];
 152
 153         /*
 154          * Write the first-level table (the list is sorted,
 155          * but we use a 256-entry lookup to be able to avoid
 156          * having to do eight extra binary search iterations)
 157          */
 158         for (i = 0; i < 256; i++) {
 159                 struct object_entry **next = list;
 160                 while (next < last) {
 161                         struct object_entry *entry = *next;
 162                         if (entry->sha1[0] != i)
 163                                 break;
 164                         next++;
 165                 }
 166                 array[i] = htonl(next - sorted_by_sha);
 167                 list = next;
 168         }
 169         fwrite(array, 256, sizeof(int), f);
 170
 171         /*
 172          * Write the actual SHA1 entries..
 173          */
 174         list = sorted_by_sha;
 175         for (i = 0; i < nr_objects; i++) {
 176                 struct object_entry *entry = *list++;
 177                 unsigned int offset = htonl(entry->offset);
 178                 fwrite(&offset, 4, 1, f);
 179                 fwrite(entry->sha1, 20, 1, f);
 180         }
 181         fclose(f);
 182 }
 183
 184 static void add_object_entry(unsigned char *sha1)
 185 {
 186         unsigned int idx = nr_objects;
 187         struct object_entry *entry;
 188
 189         if (idx >= nr_alloc) {
 190                 unsigned int needed = (idx + 1024) * 3 / 2;
 191                 objects = xrealloc(objects, needed * sizeof(*entry));
 192                 nr_alloc = needed;
 193         }
 194         entry = objects + idx;
 195         memset(entry, 0, sizeof(*entry));
 196         memcpy(entry->sha1, sha1, 20);
 197         nr_objects = idx+1;
 198 }
 199
 200 static void check_object(struct object_entry *entry)
 201 {
 202         char buffer[128];
 203         char type[10];
 204         unsigned long mapsize;
 205         z_stream stream;
 206         void *map;
 207
 208         map = map_sha1_file(entry->sha1, &mapsize);
 209         if (!map)
 210                 die("unable to map %s", sha1_to_hex(entry->sha1));
 211         if (unpack_sha1_header(&stream, map, mapsize, buffer, sizeof(buffer)) < 0)
 212                 die("unable to unpack %s header", sha1_to_hex(entry->sha1));
 213         munmap(map, mapsize);
 214         if (parse_sha1_header(buffer, type, &entry->size) < 0)
 215                 die("unable to parse %s header", sha1_to_hex(entry->sha1));
 216         if (!strcmp(type, "commit")) {
 217                 entry->type = OBJ_COMMIT;
 218         } else if (!strcmp(type, "tree")) {
 219                 entry->type = OBJ_TREE;
 220         } else if (!strcmp(type, "blob")) {
 221                 entry->type = OBJ_BLOB;
 222         } else
 223                 die("unable to pack object %s of type %s", sha1_to_hex(entry->sha1), type);
 224 }
 225
 226 static void get_object_details(void)
 227 {
 228         int i;
 229         struct object_entry *entry = objects;
 230
 231         for (i = 0; i < nr_objects; i++)
 232                 check_object(entry++);
 233 }
 234
 235 typedef int (*entry_sort_t)(const struct object_entry *, const struct object_entry *);
 236
 237 static entry_sort_t current_sort;
 238
 239 static int sort_comparator(const void *_a, const void *_b)
 240 {
 241         struct object_entry *a = *(struct object_entry **)_a;
 242         struct object_entry *b = *(struct object_entry **)_b;
 243         return current_sort(a,b);
 244 }
 245
 246 static struct object_entry **create_sorted_list(entry_sort_t sort)
 247 {
 248         struct object_entry **list = xmalloc(nr_objects * sizeof(struct object_entry *));
 249         int i;
 250
 251         for (i = 0; i < nr_objects; i++)
 252                 list[i] = objects + i;
 253         current_sort = sort;
 254         qsort(list, nr_objects, sizeof(struct object_entry *), sort_comparator);
 255         return list;
 256 }
 257
 258 static int sha1_sort(const struct object_entry *a, const struct object_entry *b)
 259 {
 260         return memcmp(a->sha1, b->sha1, 20);
 261 }
 262
 263 static int type_size_sort(const struct object_entry *a, const struct object_entry *b)
 264 {
 265         if (a->type < b->type)
 266                 return -1;
 267         if (a->type > b->type)
 268                 return 1;
 269         if (a->size < b->size)
 270                 return -1;
 271         if (a->size > b->size)
 272                 return 1;
 273         return a < b ? -1 : (a > b);
 274 }
 275
 276 struct unpacked {
 277         struct object_entry *entry;
 278         void *data;
 279 };
 280
 281 /*
 282  * We search for deltas in a list sorted by type and by size, and
 283  * walk the "old" chain backwards in the list, so if the type
 284  * has changed or the size difference is too big, there's no point
 285  * in even continuing the walk, since the other old objects are
 286  * going to be even smaller or of a different type. So return -1
 287  * once we determine that there's no point even trying.
 288  */
 289 static int try_delta(struct unpacked *cur, struct unpacked *old)
 290 {
 291         struct object_entry *cur_entry = cur->entry;
 292         struct object_entry *old_entry = old->entry;
 293         unsigned long size, oldsize, delta_size;
 294         void *delta_buf;
 295
 296         /* Don't bother doing diffs between different types */
 297         if (cur_entry->type != old_entry->type)
 298                 return -1;
 299
 300         /* Size is guaranteed to be larger than or equal to oldsize */
 301         size = cur_entry->size;
 302         oldsize = old_entry->size;
 303         if (size - oldsize > oldsize / 4)
 304                 return -1;
 305
 306         /*
 307          * NOTE!
 308          *
 309          * We always delta from the bigger to the smaller, since that's
 310          * more space-efficient (deletes don't have to say _what_ they
 311          * delete).
 312          */
 313         delta_buf = diff_delta(cur->data, size, old->data, oldsize, &delta_size);
 314         if (!delta_buf)
 315                 die("unable to create delta");
 316         if (delta_size + 20 < size / 2) {
 317                 if (!cur_entry->delta || cur_entry->delta_size > delta_size) {
 318                         cur_entry->delta = old_entry;
 319                         cur_entry->delta_size = delta_size;
 320                 }
 321         }
 322         free(delta_buf);
 323 }
 324
 325 static void find_deltas(struct object_entry **list, int window)
 326 {
 327         unsigned int i;
 328         unsigned int array_size = window * sizeof(struct unpacked);
 329         struct unpacked *array = xmalloc(array_size);
 330
 331         memset(array, 0, array_size);
 332         for (i = 0; i < nr_objects; i++) {
 333                 unsigned int idx = i % window;
 334                 struct object_entry *entry = list[i];
 335                 struct unpacked *n = array + idx;
 336                 unsigned long size;
 337                 char type[10];
 338                 int j;
 339
 340                 free(n->data);
 341                 n->entry = entry;
 342                 n->data = read_sha1_file(entry->sha1, type, &size);
 343                 if (size != entry->size)
 344                         die("object %s inconsistent object length (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
 345                 for (j = 0; j < window; j++) {
 346                         unsigned int other_idx = idx - 1 - j;
 347                         struct unpacked *m;
 348                         if (other_idx < 0)
 349                                 other_idx += window;
 350                         m = array + other_idx;
 351                         if (!m->entry)
 352                                 break;
 353                         if (try_delta(n, m) < 0)
 354                                 break;
 355                 }
 356         }
 357 }
 358
 359 int main(int argc, char **argv)
 360 {
 361         char line[128];
 362         int i;
 363
 364         for (i = 1; i < argc; i++) {
 365                 const char *arg = argv[i];
 366
 367                 if (*arg == '-') {
 368                         if (!strncmp("--window=", arg, 9)) {
 369                                 char *end;
 370                                 delta_window = strtoul(arg+9, &end, 0);
 371                                 if (!arg[9] || *end)
 372                                         usage(pack_usage);
 373                                 continue;
 374                         }
 375                         usage(pack_usage);
 376                 }
 377                 if (base_name)
 378                         usage(pack_usage);
 379                 base_name = arg;
 380         }
 381
 382         if (!base_name)
 383                 usage(pack_usage);
 384
 385         while (fgets(line, sizeof(line), stdin) != NULL) {
 386                 unsigned char sha1[20];
 387                 if (get_sha1_hex(line, sha1))
 388                         die("expected sha1, got garbage");
 389                 add_object_entry(sha1);
 390         }
 391         get_object_details();
 392
 393         printf("Packing %d objects\n", nr_objects);
 394
 395         sorted_by_sha = create_sorted_list(sha1_sort);
 396         sorted_by_type = create_sorted_list(type_size_sort);
 397         if (delta_window)
 398                 find_deltas(sorted_by_type, delta_window);
 399
 400         write_pack_file();
 401         write_index_file();
 402         return 0;
 403 }