mkdelta.c

   1 /*
   2  * Deltafication of a GIT database.
   3  *
   4  * (C) 2005 Nicolas Pitre <nico@cam.org>
   5  *
   6  * This code is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 as
   8  * published by the Free Software Foundation.
   9  */
  10
  11 #include "cache.h"
  12 #include "delta.h"
  13
  14 static int replace_object(char *buf, unsigned long size, unsigned char *sha1)
  15 {
  16         char tmpfile[PATH_MAX];
  17         int fd;
  18
  19         snprintf(tmpfile, sizeof(tmpfile), "%s/obj_XXXXXX", get_object_directory());
  20         fd = mkstemp(tmpfile);
  21         if (fd < 0)
  22                 return error("%s: %s\n", tmpfile, strerror(errno));
  23         if (write(fd, buf, size) != size) {
  24                 perror("unable to write file");
  25                 close(fd);
  26                 unlink(tmpfile);
  27                 return -1;
  28         }
  29         fchmod(fd, 0444);
  30         close(fd);
  31         if (rename(tmpfile, sha1_file_name(sha1))) {
  32                 perror("unable to replace original object");
  33                 unlink(tmpfile);
  34                 return -1;
  35         }
  36         return 0;
  37 }
  38
  39 static void *create_object(char *buf, unsigned long len, char *hdr, int hdrlen,
  40                            unsigned long *retsize)
  41 {
  42         char *compressed;
  43         unsigned long size;
  44         z_stream stream;
  45
  46         /* Set it up */
  47         memset(&stream, 0, sizeof(stream));
  48         deflateInit(&stream, Z_BEST_COMPRESSION);
  49         size = deflateBound(&stream, len+hdrlen);
  50         compressed = xmalloc(size);
  51
  52         /* Compress it */
  53         stream.next_out = compressed;
  54         stream.avail_out = size;
  55
  56         /* First header.. */
  57         stream.next_in = hdr;
  58         stream.avail_in = hdrlen;
  59         while (deflate(&stream, 0) == Z_OK)
  60                 /* nothing */;
  61
  62         /* Then the data itself.. */
  63         stream.next_in = buf;
  64         stream.avail_in = len;
  65         while (deflate(&stream, Z_FINISH) == Z_OK)
  66                 /* nothing */;
  67         deflateEnd(&stream);
  68         *retsize = stream.total_out;
  69         return compressed;
  70 }
  71
  72 static int restore_original_object(char *buf, unsigned long len,
  73                                    char *type, unsigned char *sha1)
  74 {
  75         char hdr[50];
  76         int hdrlen, ret;
  77         void *compressed;
  78         unsigned long size;
  79
  80         hdrlen = sprintf(hdr, "%s %lu", type, len)+1;
  81         compressed = create_object(buf, len, hdr, hdrlen, &size);
  82         ret = replace_object(compressed, size, sha1);
  83         free(compressed);
  84         return ret;
  85 }
  86
  87 static void *create_delta_object(char *buf, unsigned long len,
  88                                  unsigned char *sha1_ref, unsigned long *size)
  89 {
  90         char hdr[50];
  91         int hdrlen;
  92
  93         /* Generate the header + sha1 of reference for delta */
  94         hdrlen = sprintf(hdr, "delta %lu", len+20)+1;
  95         memcpy(hdr + hdrlen, sha1_ref, 20);
  96         hdrlen += 20;
  97
  98         return create_object(buf, len, hdr, hdrlen, size);
  99 }
 100
 101 static void *get_buffer(unsigned char *sha1, char *type,
 102                         unsigned long *size, unsigned long *compsize)
 103 {
 104         unsigned long mapsize;
 105         void *map = map_sha1_file(sha1, &mapsize);
 106         if (map) {
 107                 void *buffer = unpack_sha1_file(map, mapsize, type, size);
 108                 munmap(map, mapsize);
 109                 if (compsize)
 110                         *compsize = mapsize;
 111                 if (buffer)
 112                         return buffer;
 113         }
 114         error("unable to get object %s", sha1_to_hex(sha1));
 115         return NULL;
 116 }
 117
 118 static void *expand_delta(void *delta, unsigned long *size, char *type,
 119                           unsigned int *depth, unsigned char **links)
 120 {
 121         void *buf = NULL;
 122         unsigned int level = (*depth)++;
 123         if (*size < 20) {
 124                 error("delta object is bad");
 125                 free(delta);
 126         } else {
 127                 unsigned long ref_size;
 128                 void *ref = get_buffer(delta, type, &ref_size, NULL);
 129                 if (ref && !strcmp(type, "delta"))
 130                         ref = expand_delta(ref, &ref_size, type, depth, links);
 131                 else if (ref)
 132 {
 133                         *links = xmalloc(*depth * 20);
 134 }
 135                 if (ref) {
 136                         buf = patch_delta(ref, ref_size, delta+20, *size-20, size);
 137                         free(ref);
 138                         if (buf)
 139                                 memcpy(*links + level*20, delta, 20);
 140                         else
 141                                 free(*links);
 142                 }
 143                 free(delta);
 144         }
 145         return buf;
 146 }
 147
 148 static char *mkdelta_usage =
 149 "mkdelta [--max-depth=N] [--max-behind=N] <reference_sha1> <target_sha1> [<next_sha1> ...]";
 150
 151 struct delta {
 152         unsigned char sha1[20];         /* object sha1 */
 153         unsigned long size;             /* object size */
 154         void *buf;                      /* object content */
 155         unsigned char *links;           /* delta reference links */
 156         unsigned int depth;             /* delta depth */
 157 };
 158
 159 int main(int argc, char **argv)
 160 {
 161         struct delta *ref, trg;
 162         char ref_type[20], trg_type[20], *skip_reason;
 163         void *best_buf;
 164         unsigned long best_size, orig_size, orig_compsize;
 165         unsigned int r, orig_ref, best_ref, nb_refs, next_ref, max_refs = 0;
 166         unsigned int i, duplicate, skip_lvl, verbose = 0, quiet = 0;
 167         unsigned int max_depth = -1;
 168
 169         for (i = 1; i < argc; i++) {
 170                 if (!strcmp(argv[i], "-v")) {
 171                         verbose = 1;
 172                         quiet = 0;
 173                 } else if (!strcmp(argv[i], "-q")) {
 174                         quiet = 1;
 175                         verbose = 0;
 176                 } else if (!strcmp(argv[i], "-d") && i+1 < argc) {
 177                         max_depth = atoi(argv[++i]);
 178                 } else if (!strncmp(argv[i], "--max-depth=", 12)) {
 179                         max_depth = atoi(argv[i]+12);
 180                 } else if (!strcmp(argv[i], "-b") && i+1 < argc) {
 181                         max_refs = atoi(argv[++i]);
 182                 } else if (!strncmp(argv[i], "--max-behind=", 13)) {
 183                         max_refs = atoi(argv[i]+13);
 184                 } else
 185                         break;
 186         }
 187
 188         if (i + (max_depth != 0) >= argc)
 189                 usage(mkdelta_usage);
 190
 191         if (!max_refs || max_refs > argc - i)
 192                 max_refs = argc - i;
 193         ref = xmalloc(max_refs * sizeof(*ref));
 194         for (r = 0; r < max_refs; r++)
 195                 ref[r].buf = ref[r].links = NULL;
 196         next_ref = nb_refs = 0;
 197
 198         do {
 199                 if (get_sha1(argv[i], trg.sha1))
 200                         die("bad sha1 %s", argv[i]);
 201                 trg.buf = get_buffer(trg.sha1, trg_type, &trg.size, &orig_compsize);
 202                 if (trg.buf && !trg.size) {
 203                         if (verbose)
 204                                 printf("skip    %s (object is empty)\n", argv[i]);
 205                         continue;
 206                 }
 207                 orig_size = trg.size;
 208                 orig_ref = -1;
 209                 trg.depth = 0;
 210                 trg.links = NULL;
 211                 if (trg.buf && !strcmp(trg_type, "delta")) {
 212                         for (r = 0; r < nb_refs; r++)
 213                                 if (!memcmp(trg.buf, ref[r].sha1, 20))
 214                                         break;
 215                         if (r < nb_refs) {
 216                                 /* no need to reload the reference object */
 217                                 trg.depth = ref[r].depth + 1;
 218                                 trg.links = xmalloc(trg.depth*20);
 219                                 memcpy(trg.links, trg.buf, 20);
 220                                 memcpy(trg.links+20, ref[r].links, ref[r].depth*20);
 221                                 trg.buf = patch_delta(ref[r].buf, ref[r].size,
 222                                                       trg.buf+20, trg.size-20,
 223                                                       &trg.size);
 224                                 strcpy(trg_type, ref_type);
 225                                 orig_ref = r;
 226                         } else {
 227                                 trg.buf = expand_delta(trg.buf, &trg.size, trg_type,
 228                                                        &trg.depth, &trg.links);
 229                         }
 230                 }
 231                 if (!trg.buf)
 232                         die("unable to read target object %s", argv[i]);
 233
 234                 if (!nb_refs) {
 235                         strcpy(ref_type, trg_type);
 236                 } else if (max_depth && strcmp(ref_type, trg_type)) {
 237                         die("type mismatch for object %s", argv[i]);
 238                 }
 239
 240                 duplicate = 0;
 241                 best_buf = NULL;
 242                 best_size = -1;
 243                 best_ref = -1;
 244                 skip_lvl = 0;
 245                 skip_reason = NULL;
 246                 for (r = 0; max_depth && r < nb_refs; r++) {
 247                         void *delta_buf, *comp_buf;
 248                         unsigned long delta_size, comp_size;
 249                         unsigned int l;
 250
 251                         duplicate = !memcmp(trg.sha1, ref[r].sha1, 20);
 252                         if (duplicate) {
 253                                 skip_reason = "already seen";
 254                                 break;
 255                         }
 256                         if (ref[r].depth >= max_depth) {
 257                                 if (skip_lvl < 1) {
 258                                         skip_reason = "exceeding max link depth";
 259                                         skip_lvl = 1;
 260                                 }
 261                                 continue;
 262                         }
 263                         for (l = 0; l < ref[r].depth; l++)
 264                                 if (!memcmp(trg.sha1, ref[r].links + l*20, 20))
 265                                         break;
 266                         if (l != ref[r].depth) {
 267                                 if (skip_lvl < 2) {
 268                                         skip_reason = "would create a loop";
 269                                         skip_lvl = 2;
 270                                 }
 271                                 continue;
 272                         }
 273                         if (trg.depth < max_depth && r == orig_ref) {
 274                                 if (skip_lvl < 3) {
 275                                         skip_reason = "delta already in place";
 276                                         skip_lvl = 3;
 277                                 }
 278                                 continue;
 279                         }
 280                         delta_buf = diff_delta(ref[r].buf, ref[r].size,
 281                                                trg.buf, trg.size, &delta_size);
 282                         if (!delta_buf)
 283                                 die("out of memory");
 284                         if (trg.depth < max_depth &&
 285                             delta_size+20 >= orig_size) {
 286                                 /* no need to even try to compress if original
 287                                    object is smaller than this delta */
 288                                 free(delta_buf);
 289                                 if (skip_lvl < 4) {
 290                                         skip_reason = "no size reduction";
 291                                         skip_lvl = 4;
 292                                 }
 293                                 continue;
 294                         }
 295                         comp_buf = create_delta_object(delta_buf, delta_size,
 296                                                        ref[r].sha1, &comp_size);
 297                         if (!comp_buf)
 298                                 die("out of memory");
 299                         free(delta_buf);
 300                         if (trg.depth < max_depth &&
 301                             comp_size >= orig_compsize) {
 302                                 free(comp_buf);
 303                                 if (skip_lvl < 5) {
 304                                         skip_reason = "no size reduction";
 305                                         skip_lvl = 5;
 306                                 }
 307                                 continue;
 308                         }
 309                         if ((comp_size < best_size) ||
 310                             (comp_size == best_size &&
 311                              ref[r].depth < ref[best_ref].depth)) {
 312                                 free(best_buf);
 313                                 best_buf = comp_buf;
 314                                 best_size = comp_size;
 315                                 best_ref = r;
 316                         }
 317                 }
 318
 319                 if (best_buf) {
 320                         if (replace_object(best_buf, best_size, trg.sha1))
 321                                 die("unable to write delta for %s", argv[i]);
 322                         free(best_buf);
 323                         free(trg.links);
 324                         trg.depth = ref[best_ref].depth + 1;
 325                         trg.links = xmalloc(trg.depth*20);
 326                         memcpy(trg.links, ref[best_ref].sha1, 20);
 327                         memcpy(trg.links+20, ref[best_ref].links, ref[best_ref].depth*20);
 328                         if (!quiet)
 329                                 printf("delta   %s (size=%ld.%02ld%% depth=%d dist=%d)\n",
 330                                        argv[i], best_size*100 / orig_compsize,
 331                                        (best_size*10000 / orig_compsize)%100,
 332                                        trg.depth,
 333                                        (next_ref - best_ref + max_refs)
 334                                        % (max_refs + 1) + 1);
 335                 } else if (trg.depth > max_depth) {
 336                         if (restore_original_object(trg.buf, trg.size, trg_type, trg.sha1))
 337                                 die("unable to restore %s", argv[i]);
 338                         if (!quiet)
 339                                 printf("undelta %s (depth was %d)\n",
 340                                        argv[i], trg.depth);
 341                         trg.depth = 0;
 342                         free(trg.links);
 343                         trg.links = NULL;
 344                 } else if (skip_reason && verbose) {
 345                         printf("skip    %s (%s)\n", argv[i], skip_reason);
 346                 }
 347
 348                 if (!duplicate) {
 349                         free(ref[next_ref].buf);
 350                         free(ref[next_ref].links);
 351                         ref[next_ref] = trg;
 352                         if (++next_ref > nb_refs)
 353                                 nb_refs = next_ref;
 354                         if (next_ref == max_refs)
 355                                 next_ref = 0;
 356                 } else {
 357                         free(trg.buf);
 358                         free(trg.links);
 359                 }
 360         } while (++i < argc);
 361
 362         return 0;
 363 }