reftable/reader.c

   1 /*
   2 Copyright 2020 Google LLC
   3
   4 Use of this source code is governed by a BSD-style
   5 license that can be found in the LICENSE file or at
   6 https://developers.google.com/open-source/licenses/bsd
   7 */
   8
   9 #include "reader.h"
  10
  11 #include "system.h"
  12 #include "block.h"
  13 #include "constants.h"
  14 #include "generic.h"
  15 #include "iter.h"
  16 #include "record.h"
  17 #include "reftable-error.h"
  18 #include "reftable-generic.h"
  19
  20 uint64_t block_source_size(struct reftable_block_source *source)
  21 {
  22         return source->ops->size(source->arg);
  23 }
  24
  25 int block_source_read_block(struct reftable_block_source *source,
  26                             struct reftable_block *dest, uint64_t off,
  27                             uint32_t size)
  28 {
  29         int result = source->ops->read_block(source->arg, dest, off, size);
  30         dest->source = *source;
  31         return result;
  32 }
  33
  34 void block_source_close(struct reftable_block_source *source)
  35 {
  36         if (!source->ops) {
  37                 return;
  38         }
  39
  40         source->ops->close(source->arg);
  41         source->ops = NULL;
  42 }
  43
  44 static struct reftable_reader_offsets *
  45 reader_offsets_for(struct reftable_reader *r, uint8_t typ)
  46 {
  47         switch (typ) {
  48         case BLOCK_TYPE_REF:
  49                 return &r->ref_offsets;
  50         case BLOCK_TYPE_LOG:
  51                 return &r->log_offsets;
  52         case BLOCK_TYPE_OBJ:
  53                 return &r->obj_offsets;
  54         }
  55         abort();
  56 }
  57
  58 static int reader_get_block(struct reftable_reader *r,
  59                             struct reftable_block *dest, uint64_t off,
  60                             uint32_t sz)
  61 {
  62         if (off >= r->size)
  63                 return 0;
  64
  65         if (off + sz > r->size) {
  66                 sz = r->size - off;
  67         }
  68
  69         return block_source_read_block(&r->source, dest, off, sz);
  70 }
  71
  72 uint32_t reftable_reader_hash_id(struct reftable_reader *r)
  73 {
  74         return r->hash_id;
  75 }
  76
  77 const char *reader_name(struct reftable_reader *r)
  78 {
  79         return r->name;
  80 }
  81
  82 static int parse_footer(struct reftable_reader *r, uint8_t *footer,
  83                         uint8_t *header)
  84 {
  85         uint8_t *f = footer;
  86         uint8_t first_block_typ;
  87         int err = 0;
  88         uint32_t computed_crc;
  89         uint32_t file_crc;
  90
  91         if (memcmp(f, "REFT", 4)) {
  92                 err = REFTABLE_FORMAT_ERROR;
  93                 goto done;
  94         }
  95         f += 4;
  96
  97         if (memcmp(footer, header, header_size(r->version))) {
  98                 err = REFTABLE_FORMAT_ERROR;
  99                 goto done;
 100         }
 101
 102         f++;
 103         r->block_size = get_be24(f);
 104
 105         f += 3;
 106         r->min_update_index = get_be64(f);
 107         f += 8;
 108         r->max_update_index = get_be64(f);
 109         f += 8;
 110
 111         if (r->version == 1) {
 112                 r->hash_id = GIT_SHA1_FORMAT_ID;
 113         } else {
 114                 r->hash_id = get_be32(f);
 115                 switch (r->hash_id) {
 116                 case GIT_SHA1_FORMAT_ID:
 117                         break;
 118                 case GIT_SHA256_FORMAT_ID:
 119                         break;
 120                 default:
 121                         err = REFTABLE_FORMAT_ERROR;
 122                         goto done;
 123                 }
 124                 f += 4;
 125         }
 126
 127         r->ref_offsets.index_offset = get_be64(f);
 128         f += 8;
 129
 130         r->obj_offsets.offset = get_be64(f);
 131         f += 8;
 132
 133         r->object_id_len = r->obj_offsets.offset & ((1 << 5) - 1);
 134         r->obj_offsets.offset >>= 5;
 135
 136         r->obj_offsets.index_offset = get_be64(f);
 137         f += 8;
 138         r->log_offsets.offset = get_be64(f);
 139         f += 8;
 140         r->log_offsets.index_offset = get_be64(f);
 141         f += 8;
 142
 143         computed_crc = crc32(0, footer, f - footer);
 144         file_crc = get_be32(f);
 145         f += 4;
 146         if (computed_crc != file_crc) {
 147                 err = REFTABLE_FORMAT_ERROR;
 148                 goto done;
 149         }
 150
 151         first_block_typ = header[header_size(r->version)];
 152         r->ref_offsets.is_present = (first_block_typ == BLOCK_TYPE_REF);
 153         r->ref_offsets.offset = 0;
 154         r->log_offsets.is_present = (first_block_typ == BLOCK_TYPE_LOG ||
 155                                      r->log_offsets.offset > 0);
 156         r->obj_offsets.is_present = r->obj_offsets.offset > 0;
 157         if (r->obj_offsets.is_present && !r->object_id_len) {
 158                 err = REFTABLE_FORMAT_ERROR;
 159                 goto done;
 160         }
 161
 162         err = 0;
 163 done:
 164         return err;
 165 }
 166
 167 int init_reader(struct reftable_reader *r, struct reftable_block_source *source,
 168                 const char *name)
 169 {
 170         struct reftable_block footer = { NULL };
 171         struct reftable_block header = { NULL };
 172         int err = 0;
 173         uint64_t file_size = block_source_size(source);
 174
 175         /* Need +1 to read type of first block. */
 176         uint32_t read_size = header_size(2) + 1; /* read v2 because it's larger.  */
 177         memset(r, 0, sizeof(struct reftable_reader));
 178
 179         if (read_size > file_size) {
 180                 err = REFTABLE_FORMAT_ERROR;
 181                 goto done;
 182         }
 183
 184         err = block_source_read_block(source, &header, 0, read_size);
 185         if (err != read_size) {
 186                 err = REFTABLE_IO_ERROR;
 187                 goto done;
 188         }
 189
 190         if (memcmp(header.data, "REFT", 4)) {
 191                 err = REFTABLE_FORMAT_ERROR;
 192                 goto done;
 193         }
 194         r->version = header.data[4];
 195         if (r->version != 1 && r->version != 2) {
 196                 err = REFTABLE_FORMAT_ERROR;
 197                 goto done;
 198         }
 199
 200         r->size = file_size - footer_size(r->version);
 201         r->source = *source;
 202         r->name = xstrdup(name);
 203         r->hash_id = 0;
 204
 205         err = block_source_read_block(source, &footer, r->size,
 206                                       footer_size(r->version));
 207         if (err != footer_size(r->version)) {
 208                 err = REFTABLE_IO_ERROR;
 209                 goto done;
 210         }
 211
 212         err = parse_footer(r, footer.data, header.data);
 213 done:
 214         reftable_block_done(&footer);
 215         reftable_block_done(&header);
 216         return err;
 217 }
 218
 219 struct table_iter {
 220         struct reftable_reader *r;
 221         uint8_t typ;
 222         uint64_t block_off;
 223         struct block_iter bi;
 224         int is_finished;
 225 };
 226 #define TABLE_ITER_INIT { \
 227         .bi = BLOCK_ITER_INIT \
 228 }
 229
 230 static void table_iter_copy_from(struct table_iter *dest,
 231                                  struct table_iter *src)
 232 {
 233         dest->r = src->r;
 234         dest->typ = src->typ;
 235         dest->block_off = src->block_off;
 236         dest->is_finished = src->is_finished;
 237         block_iter_copy_from(&dest->bi, &src->bi);
 238 }
 239
 240 static int table_iter_next_in_block(struct table_iter *ti,
 241                                     struct reftable_record *rec)
 242 {
 243         int res = block_iter_next(&ti->bi, rec);
 244         if (res == 0 && reftable_record_type(rec) == BLOCK_TYPE_REF) {
 245                 rec->u.ref.update_index += ti->r->min_update_index;
 246         }
 247
 248         return res;
 249 }
 250
 251 static void table_iter_block_done(struct table_iter *ti)
 252 {
 253         if (!ti->bi.br) {
 254                 return;
 255         }
 256         reftable_block_done(&ti->bi.br->block);
 257         FREE_AND_NULL(ti->bi.br);
 258
 259         ti->bi.last_key.len = 0;
 260         ti->bi.next_off = 0;
 261 }
 262
 263 static int32_t extract_block_size(uint8_t *data, uint8_t *typ, uint64_t off,
 264                                   int version)
 265 {
 266         int32_t result = 0;
 267
 268         if (off == 0) {
 269                 data += header_size(version);
 270         }
 271
 272         *typ = data[0];
 273         if (reftable_is_block_type(*typ)) {
 274                 result = get_be24(data + 1);
 275         }
 276         return result;
 277 }
 278
 279 int reader_init_block_reader(struct reftable_reader *r, struct block_reader *br,
 280                              uint64_t next_off, uint8_t want_typ)
 281 {
 282         int32_t guess_block_size = r->block_size ? r->block_size :
 283                                                          DEFAULT_BLOCK_SIZE;
 284         struct reftable_block block = { NULL };
 285         uint8_t block_typ = 0;
 286         int err = 0;
 287         uint32_t header_off = next_off ? 0 : header_size(r->version);
 288         int32_t block_size = 0;
 289
 290         if (next_off >= r->size)
 291                 return 1;
 292
 293         err = reader_get_block(r, &block, next_off, guess_block_size);
 294         if (err < 0)
 295                 goto done;
 296
 297         block_size = extract_block_size(block.data, &block_typ, next_off,
 298                                         r->version);
 299         if (block_size < 0) {
 300                 err = block_size;
 301                 goto done;
 302         }
 303         if (want_typ != BLOCK_TYPE_ANY && block_typ != want_typ) {
 304                 err = 1;
 305                 goto done;
 306         }
 307
 308         if (block_size > guess_block_size) {
 309                 reftable_block_done(&block);
 310                 err = reader_get_block(r, &block, next_off, block_size);
 311                 if (err < 0) {
 312                         goto done;
 313                 }
 314         }
 315
 316         err = block_reader_init(br, &block, header_off, r->block_size,
 317                                 hash_size(r->hash_id));
 318 done:
 319         reftable_block_done(&block);
 320
 321         return err;
 322 }
 323
 324 static int table_iter_next_block(struct table_iter *dest,
 325                                  struct table_iter *src)
 326 {
 327         uint64_t next_block_off = src->block_off + src->bi.br->full_block_size;
 328         struct block_reader br = { 0 };
 329         int err = 0;
 330
 331         dest->r = src->r;
 332         dest->typ = src->typ;
 333         dest->block_off = next_block_off;
 334
 335         err = reader_init_block_reader(src->r, &br, next_block_off, src->typ);
 336         if (err > 0) {
 337                 dest->is_finished = 1;
 338                 return 1;
 339         }
 340         if (err != 0)
 341                 return err;
 342         else {
 343                 struct block_reader *brp =
 344                         reftable_malloc(sizeof(struct block_reader));
 345                 *brp = br;
 346
 347                 dest->is_finished = 0;
 348                 block_reader_start(brp, &dest->bi);
 349         }
 350         return 0;
 351 }
 352
 353 static int table_iter_next(struct table_iter *ti, struct reftable_record *rec)
 354 {
 355         if (reftable_record_type(rec) != ti->typ)
 356                 return REFTABLE_API_ERROR;
 357
 358         while (1) {
 359                 struct table_iter next = TABLE_ITER_INIT;
 360                 int err;
 361
 362                 if (ti->is_finished)
 363                         return 1;
 364
 365                 /*
 366                  * Check whether the current block still has more records. If
 367                  * so, return it. If the iterator returns positive then the
 368                  * current block has been exhausted.
 369                  */
 370                 err = table_iter_next_in_block(ti, rec);
 371                 if (err <= 0)
 372                         return err;
 373
 374                 /*
 375                  * Otherwise, we need to continue to the next block in the
 376                  * table and retry. If there are no more blocks then the
 377                  * iterator is drained.
 378                  */
 379                 err = table_iter_next_block(&next, ti);
 380                 table_iter_block_done(ti);
 381                 if (err) {
 382                         ti->is_finished = 1;
 383                         return err;
 384                 }
 385
 386                 table_iter_copy_from(ti, &next);
 387                 block_iter_close(&next.bi);
 388         }
 389 }
 390
 391 static int table_iter_next_void(void *ti, struct reftable_record *rec)
 392 {
 393         return table_iter_next(ti, rec);
 394 }
 395
 396 static void table_iter_close(void *p)
 397 {
 398         struct table_iter *ti = p;
 399         table_iter_block_done(ti);
 400         block_iter_close(&ti->bi);
 401 }
 402
 403 static struct reftable_iterator_vtable table_iter_vtable = {
 404         .next = &table_iter_next_void,
 405         .close = &table_iter_close,
 406 };
 407
 408 static void iterator_from_table_iter(struct reftable_iterator *it,
 409                                      struct table_iter *ti)
 410 {
 411         assert(!it->ops);
 412         it->iter_arg = ti;
 413         it->ops = &table_iter_vtable;
 414 }
 415
 416 static int reader_table_iter_at(struct reftable_reader *r,
 417                                 struct table_iter *ti, uint64_t off,
 418                                 uint8_t typ)
 419 {
 420         struct block_reader br = { 0 };
 421         struct block_reader *brp = NULL;
 422
 423         int err = reader_init_block_reader(r, &br, off, typ);
 424         if (err != 0)
 425                 return err;
 426
 427         brp = reftable_malloc(sizeof(struct block_reader));
 428         *brp = br;
 429         ti->r = r;
 430         ti->typ = block_reader_type(brp);
 431         ti->block_off = off;
 432         block_reader_start(brp, &ti->bi);
 433         return 0;
 434 }
 435
 436 static int reader_start(struct reftable_reader *r, struct table_iter *ti,
 437                         uint8_t typ, int index)
 438 {
 439         struct reftable_reader_offsets *offs = reader_offsets_for(r, typ);
 440         uint64_t off = offs->offset;
 441         if (index) {
 442                 off = offs->index_offset;
 443                 if (off == 0) {
 444                         return 1;
 445                 }
 446                 typ = BLOCK_TYPE_INDEX;
 447         }
 448
 449         return reader_table_iter_at(r, ti, off, typ);
 450 }
 451
 452 static int reader_seek_linear(struct table_iter *ti,
 453                               struct reftable_record *want)
 454 {
 455         struct strbuf want_key = STRBUF_INIT;
 456         struct strbuf got_key = STRBUF_INIT;
 457         struct table_iter next = TABLE_ITER_INIT;
 458         struct reftable_record rec;
 459         int err = -1;
 460
 461         reftable_record_init(&rec, reftable_record_type(want));
 462         reftable_record_key(want, &want_key);
 463
 464         while (1) {
 465                 err = table_iter_next_block(&next, ti);
 466                 if (err < 0)
 467                         goto done;
 468
 469                 if (err > 0) {
 470                         break;
 471                 }
 472
 473                 err = block_reader_first_key(next.bi.br, &got_key);
 474                 if (err < 0)
 475                         goto done;
 476
 477                 if (strbuf_cmp(&got_key, &want_key) > 0) {
 478                         table_iter_block_done(&next);
 479                         break;
 480                 }
 481
 482                 table_iter_block_done(ti);
 483                 table_iter_copy_from(ti, &next);
 484         }
 485
 486         err = block_iter_seek(&ti->bi, &want_key);
 487         if (err < 0)
 488                 goto done;
 489         err = 0;
 490
 491 done:
 492         block_iter_close(&next.bi);
 493         reftable_record_release(&rec);
 494         strbuf_release(&want_key);
 495         strbuf_release(&got_key);
 496         return err;
 497 }
 498
 499 static int reader_seek_indexed(struct reftable_reader *r,
 500                                struct reftable_iterator *it,
 501                                struct reftable_record *rec)
 502 {
 503         struct reftable_record want_index = {
 504                 .type = BLOCK_TYPE_INDEX, .u.idx = { .last_key = STRBUF_INIT }
 505         };
 506         struct reftable_record index_result = {
 507                 .type = BLOCK_TYPE_INDEX,
 508                 .u.idx = { .last_key = STRBUF_INIT },
 509         };
 510         struct table_iter index_iter = TABLE_ITER_INIT;
 511         struct table_iter next = TABLE_ITER_INIT;
 512         int err = 0;
 513
 514         reftable_record_key(rec, &want_index.u.idx.last_key);
 515         err = reader_start(r, &index_iter, reftable_record_type(rec), 1);
 516         if (err < 0)
 517                 goto done;
 518
 519         /*
 520          * The index may consist of multiple levels, where each level may have
 521          * multiple index blocks. We start by doing a linear search in the
 522          * highest layer that identifies the relevant index block as well as
 523          * the record inside that block that corresponds to our wanted key.
 524          */
 525         err = reader_seek_linear(&index_iter, &want_index);
 526         if (err < 0)
 527                 goto done;
 528
 529         /*
 530          * Traverse down the levels until we find a non-index entry.
 531          */
 532         while (1) {
 533                 /*
 534                  * In case we seek a record that does not exist the index iter
 535                  * will tell us that the iterator is over. This works because
 536                  * the last index entry of the current level will contain the
 537                  * last key it knows about. So in case our seeked key is larger
 538                  * than the last indexed key we know that it won't exist.
 539                  *
 540                  * There is one subtlety in the layout of the index section
 541                  * that makes this work as expected: the highest-level index is
 542                  * at end of the section and will point backwards and thus we
 543                  * start reading from the end of the index section, not the
 544                  * beginning.
 545                  *
 546                  * If that wasn't the case and the order was reversed then the
 547                  * linear seek would seek into the lower levels and traverse
 548                  * all levels of the index only to find out that the key does
 549                  * not exist.
 550                  */
 551                 err = table_iter_next(&index_iter, &index_result);
 552                 table_iter_block_done(&index_iter);
 553                 if (err != 0)
 554                         goto done;
 555
 556                 err = reader_table_iter_at(r, &next, index_result.u.idx.offset,
 557                                            0);
 558                 if (err != 0)
 559                         goto done;
 560
 561                 err = block_iter_seek(&next.bi, &want_index.u.idx.last_key);
 562                 if (err < 0)
 563                         goto done;
 564
 565                 if (next.typ == reftable_record_type(rec)) {
 566                         err = 0;
 567                         break;
 568                 }
 569
 570                 if (next.typ != BLOCK_TYPE_INDEX) {
 571                         err = REFTABLE_FORMAT_ERROR;
 572                         break;
 573                 }
 574
 575                 table_iter_copy_from(&index_iter, &next);
 576         }
 577
 578         if (err == 0) {
 579                 struct table_iter empty = TABLE_ITER_INIT;
 580                 struct table_iter *malloced = reftable_calloc(1, sizeof(*malloced));
 581                 *malloced = empty;
 582                 table_iter_copy_from(malloced, &next);
 583                 iterator_from_table_iter(it, malloced);
 584         }
 585 done:
 586         block_iter_close(&next.bi);
 587         table_iter_close(&index_iter);
 588         reftable_record_release(&want_index);
 589         reftable_record_release(&index_result);
 590         return err;
 591 }
 592
 593 static int reader_seek_internal(struct reftable_reader *r,
 594                                 struct reftable_iterator *it,
 595                                 struct reftable_record *rec)
 596 {
 597         struct reftable_reader_offsets *offs =
 598                 reader_offsets_for(r, reftable_record_type(rec));
 599         uint64_t idx = offs->index_offset;
 600         struct table_iter ti = TABLE_ITER_INIT;
 601         int err = 0;
 602         if (idx > 0)
 603                 return reader_seek_indexed(r, it, rec);
 604
 605         err = reader_start(r, &ti, reftable_record_type(rec), 0);
 606         if (err < 0)
 607                 return err;
 608         err = reader_seek_linear(&ti, rec);
 609         if (err < 0)
 610                 return err;
 611         else {
 612                 struct table_iter *p =
 613                         reftable_malloc(sizeof(struct table_iter));
 614                 *p = ti;
 615                 iterator_from_table_iter(it, p);
 616         }
 617
 618         return 0;
 619 }
 620
 621 static int reader_seek(struct reftable_reader *r, struct reftable_iterator *it,
 622                        struct reftable_record *rec)
 623 {
 624         uint8_t typ = reftable_record_type(rec);
 625
 626         struct reftable_reader_offsets *offs = reader_offsets_for(r, typ);
 627         if (!offs->is_present) {
 628                 iterator_set_empty(it);
 629                 return 0;
 630         }
 631
 632         return reader_seek_internal(r, it, rec);
 633 }
 634
 635 int reftable_reader_seek_ref(struct reftable_reader *r,
 636                              struct reftable_iterator *it, const char *name)
 637 {
 638         struct reftable_record rec = {
 639                 .type = BLOCK_TYPE_REF,
 640                 .u.ref = {
 641                         .refname = (char *)name,
 642                 },
 643         };
 644         return reader_seek(r, it, &rec);
 645 }
 646
 647 int reftable_reader_seek_log_at(struct reftable_reader *r,
 648                                 struct reftable_iterator *it, const char *name,
 649                                 uint64_t update_index)
 650 {
 651         struct reftable_record rec = { .type = BLOCK_TYPE_LOG,
 652                                        .u.log = {
 653                                                .refname = (char *)name,
 654                                                .update_index = update_index,
 655                                        } };
 656         return reader_seek(r, it, &rec);
 657 }
 658
 659 int reftable_reader_seek_log(struct reftable_reader *r,
 660                              struct reftable_iterator *it, const char *name)
 661 {
 662         uint64_t max = ~((uint64_t)0);
 663         return reftable_reader_seek_log_at(r, it, name, max);
 664 }
 665
 666 void reader_close(struct reftable_reader *r)
 667 {
 668         block_source_close(&r->source);
 669         FREE_AND_NULL(r->name);
 670 }
 671
 672 int reftable_new_reader(struct reftable_reader **p,
 673                         struct reftable_block_source *src, char const *name)
 674 {
 675         struct reftable_reader *rd = reftable_calloc(1, sizeof(*rd));
 676         int err = init_reader(rd, src, name);
 677         if (err == 0) {
 678                 *p = rd;
 679         } else {
 680                 block_source_close(src);
 681                 reftable_free(rd);
 682         }
 683         return err;
 684 }
 685
 686 void reftable_reader_free(struct reftable_reader *r)
 687 {
 688         if (!r)
 689                 return;
 690         reader_close(r);
 691         reftable_free(r);
 692 }
 693
 694 static int reftable_reader_refs_for_indexed(struct reftable_reader *r,
 695                                             struct reftable_iterator *it,
 696                                             uint8_t *oid)
 697 {
 698         struct reftable_record want = {
 699                 .type = BLOCK_TYPE_OBJ,
 700                 .u.obj = {
 701                         .hash_prefix = oid,
 702                         .hash_prefix_len = r->object_id_len,
 703                 },
 704         };
 705         struct reftable_iterator oit = { NULL };
 706         struct reftable_record got = {
 707                 .type = BLOCK_TYPE_OBJ,
 708                 .u.obj = { 0 },
 709         };
 710         int err = 0;
 711         struct indexed_table_ref_iter *itr = NULL;
 712
 713         /* Look through the reverse index. */
 714         err = reader_seek(r, &oit, &want);
 715         if (err != 0)
 716                 goto done;
 717
 718         /* read out the reftable_obj_record */
 719         err = iterator_next(&oit, &got);
 720         if (err < 0)
 721                 goto done;
 722
 723         if (err > 0 || memcmp(want.u.obj.hash_prefix, got.u.obj.hash_prefix,
 724                               r->object_id_len)) {
 725                 /* didn't find it; return empty iterator */
 726                 iterator_set_empty(it);
 727                 err = 0;
 728                 goto done;
 729         }
 730
 731         err = new_indexed_table_ref_iter(&itr, r, oid, hash_size(r->hash_id),
 732                                          got.u.obj.offsets,
 733                                          got.u.obj.offset_len);
 734         if (err < 0)
 735                 goto done;
 736         got.u.obj.offsets = NULL;
 737         iterator_from_indexed_table_ref_iter(it, itr);
 738
 739 done:
 740         reftable_iterator_destroy(&oit);
 741         reftable_record_release(&got);
 742         return err;
 743 }
 744
 745 static int reftable_reader_refs_for_unindexed(struct reftable_reader *r,
 746                                               struct reftable_iterator *it,
 747                                               uint8_t *oid)
 748 {
 749         struct table_iter ti_empty = TABLE_ITER_INIT;
 750         struct table_iter *ti = reftable_calloc(1, sizeof(*ti));
 751         struct filtering_ref_iterator *filter = NULL;
 752         struct filtering_ref_iterator empty = FILTERING_REF_ITERATOR_INIT;
 753         int oid_len = hash_size(r->hash_id);
 754         int err;
 755
 756         *ti = ti_empty;
 757         err = reader_start(r, ti, BLOCK_TYPE_REF, 0);
 758         if (err < 0) {
 759                 reftable_free(ti);
 760                 return err;
 761         }
 762
 763         filter = reftable_malloc(sizeof(struct filtering_ref_iterator));
 764         *filter = empty;
 765
 766         strbuf_add(&filter->oid, oid, oid_len);
 767         reftable_table_from_reader(&filter->tab, r);
 768         filter->double_check = 0;
 769         iterator_from_table_iter(&filter->it, ti);
 770
 771         iterator_from_filtering_ref_iterator(it, filter);
 772         return 0;
 773 }
 774
 775 int reftable_reader_refs_for(struct reftable_reader *r,
 776                              struct reftable_iterator *it, uint8_t *oid)
 777 {
 778         if (r->obj_offsets.is_present)
 779                 return reftable_reader_refs_for_indexed(r, it, oid);
 780         return reftable_reader_refs_for_unindexed(r, it, oid);
 781 }
 782
 783 uint64_t reftable_reader_max_update_index(struct reftable_reader *r)
 784 {
 785         return r->max_update_index;
 786 }
 787
 788 uint64_t reftable_reader_min_update_index(struct reftable_reader *r)
 789 {
 790         return r->min_update_index;
 791 }
 792
 793 /* generic table interface. */
 794
 795 static int reftable_reader_seek_void(void *tab, struct reftable_iterator *it,
 796                                      struct reftable_record *rec)
 797 {
 798         return reader_seek(tab, it, rec);
 799 }
 800
 801 static uint32_t reftable_reader_hash_id_void(void *tab)
 802 {
 803         return reftable_reader_hash_id(tab);
 804 }
 805
 806 static uint64_t reftable_reader_min_update_index_void(void *tab)
 807 {
 808         return reftable_reader_min_update_index(tab);
 809 }
 810
 811 static uint64_t reftable_reader_max_update_index_void(void *tab)
 812 {
 813         return reftable_reader_max_update_index(tab);
 814 }
 815
 816 static struct reftable_table_vtable reader_vtable = {
 817         .seek_record = reftable_reader_seek_void,
 818         .hash_id = reftable_reader_hash_id_void,
 819         .min_update_index = reftable_reader_min_update_index_void,
 820         .max_update_index = reftable_reader_max_update_index_void,
 821 };
 822
 823 void reftable_table_from_reader(struct reftable_table *tab,
 824                                 struct reftable_reader *reader)
 825 {
 826         assert(!tab->ops);
 827         tab->ops = &reader_vtable;
 828         tab->table_arg = reader;
 829 }
 830
 831
 832 int reftable_reader_print_file(const char *tablename)
 833 {
 834         struct reftable_block_source src = { NULL };
 835         int err = reftable_block_source_from_file(&src, tablename);
 836         struct reftable_reader *r = NULL;
 837         struct reftable_table tab = { NULL };
 838         if (err < 0)
 839                 goto done;
 840
 841         err = reftable_new_reader(&r, &src, tablename);
 842         if (err < 0)
 843                 goto done;
 844
 845         reftable_table_from_reader(&tab, r);
 846         err = reftable_table_print(&tab);
 847 done:
 848         reftable_reader_free(r);
 849         return err;
 850 }