reftable/block.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 "block.h"
  10
  11 #include "blocksource.h"
  12 #include "constants.h"
  13 #include "record.h"
  14 #include "reftable-error.h"
  15 #include "system.h"
  16 #include <zlib.h>
  17
  18 int header_size(int version)
  19 {
  20         switch (version) {
  21         case 1:
  22                 return 24;
  23         case 2:
  24                 return 28;
  25         }
  26         abort();
  27 }
  28
  29 int footer_size(int version)
  30 {
  31         switch (version) {
  32         case 1:
  33                 return 68;
  34         case 2:
  35                 return 72;
  36         }
  37         abort();
  38 }
  39
  40 static int block_writer_register_restart(struct block_writer *w, int n,
  41                                          int is_restart, struct strbuf *key)
  42 {
  43         int rlen = w->restart_len;
  44         if (rlen >= MAX_RESTARTS) {
  45                 is_restart = 0;
  46         }
  47
  48         if (is_restart) {
  49                 rlen++;
  50         }
  51         if (2 + 3 * rlen + n > w->block_size - w->next)
  52                 return -1;
  53         if (is_restart) {
  54                 REFTABLE_ALLOC_GROW(w->restarts, w->restart_len + 1, w->restart_cap);
  55                 w->restarts[w->restart_len++] = w->next;
  56         }
  57
  58         w->next += n;
  59
  60         strbuf_reset(&w->last_key);
  61         strbuf_addbuf(&w->last_key, key);
  62         w->entries++;
  63         return 0;
  64 }
  65
  66 void block_writer_init(struct block_writer *bw, uint8_t typ, uint8_t *buf,
  67                        uint32_t block_size, uint32_t header_off, int hash_size)
  68 {
  69         bw->buf = buf;
  70         bw->hash_size = hash_size;
  71         bw->block_size = block_size;
  72         bw->header_off = header_off;
  73         bw->buf[header_off] = typ;
  74         bw->next = header_off + 4;
  75         bw->restart_interval = 16;
  76         bw->entries = 0;
  77         bw->restart_len = 0;
  78         bw->last_key.len = 0;
  79 }
  80
  81 uint8_t block_writer_type(struct block_writer *bw)
  82 {
  83         return bw->buf[bw->header_off];
  84 }
  85
  86 /* Adds the reftable_record to the block. Returns -1 if it does not fit, 0 on
  87    success. Returns REFTABLE_API_ERROR if attempting to write a record with
  88    empty key. */
  89 int block_writer_add(struct block_writer *w, struct reftable_record *rec)
  90 {
  91         struct strbuf empty = STRBUF_INIT;
  92         struct strbuf last =
  93                 w->entries % w->restart_interval == 0 ? empty : w->last_key;
  94         struct string_view out = {
  95                 .buf = w->buf + w->next,
  96                 .len = w->block_size - w->next,
  97         };
  98
  99         struct string_view start = out;
 100
 101         int is_restart = 0;
 102         struct strbuf key = STRBUF_INIT;
 103         int n = 0;
 104         int err = -1;
 105
 106         reftable_record_key(rec, &key);
 107         if (!key.len) {
 108                 err = REFTABLE_API_ERROR;
 109                 goto done;
 110         }
 111
 112         n = reftable_encode_key(&is_restart, out, last, key,
 113                                 reftable_record_val_type(rec));
 114         if (n < 0)
 115                 goto done;
 116         string_view_consume(&out, n);
 117
 118         n = reftable_record_encode(rec, out, w->hash_size);
 119         if (n < 0)
 120                 goto done;
 121         string_view_consume(&out, n);
 122
 123         err = block_writer_register_restart(w, start.len - out.len, is_restart,
 124                                             &key);
 125 done:
 126         strbuf_release(&key);
 127         return err;
 128 }
 129
 130 int block_writer_finish(struct block_writer *w)
 131 {
 132         int i;
 133         for (i = 0; i < w->restart_len; i++) {
 134                 put_be24(w->buf + w->next, w->restarts[i]);
 135                 w->next += 3;
 136         }
 137
 138         put_be16(w->buf + w->next, w->restart_len);
 139         w->next += 2;
 140         put_be24(w->buf + 1 + w->header_off, w->next);
 141
 142         if (block_writer_type(w) == BLOCK_TYPE_LOG) {
 143                 int block_header_skip = 4 + w->header_off;
 144                 uLongf src_len = w->next - block_header_skip;
 145                 uLongf dest_cap = src_len * 1.001 + 12;
 146                 uint8_t *compressed;
 147
 148                 REFTABLE_ALLOC_ARRAY(compressed, dest_cap);
 149
 150                 while (1) {
 151                         uLongf out_dest_len = dest_cap;
 152                         int zresult = compress2(compressed, &out_dest_len,
 153                                                 w->buf + block_header_skip,
 154                                                 src_len, 9);
 155                         if (zresult == Z_BUF_ERROR && dest_cap < LONG_MAX) {
 156                                 dest_cap *= 2;
 157                                 compressed =
 158                                         reftable_realloc(compressed, dest_cap);
 159                                 if (compressed)
 160                                         continue;
 161                         }
 162
 163                         if (Z_OK != zresult) {
 164                                 reftable_free(compressed);
 165                                 return REFTABLE_ZLIB_ERROR;
 166                         }
 167
 168                         memcpy(w->buf + block_header_skip, compressed,
 169                                out_dest_len);
 170                         w->next = out_dest_len + block_header_skip;
 171                         reftable_free(compressed);
 172                         break;
 173                 }
 174         }
 175         return w->next;
 176 }
 177
 178 uint8_t block_reader_type(struct block_reader *r)
 179 {
 180         return r->block.data[r->header_off];
 181 }
 182
 183 int block_reader_init(struct block_reader *br, struct reftable_block *block,
 184                       uint32_t header_off, uint32_t table_block_size,
 185                       int hash_size)
 186 {
 187         uint32_t full_block_size = table_block_size;
 188         uint8_t typ = block->data[header_off];
 189         uint32_t sz = get_be24(block->data + header_off + 1);
 190         int err = 0;
 191         uint16_t restart_count = 0;
 192         uint32_t restart_start = 0;
 193         uint8_t *restart_bytes = NULL;
 194         uint8_t *uncompressed = NULL;
 195
 196         if (!reftable_is_block_type(typ)) {
 197                 err =  REFTABLE_FORMAT_ERROR;
 198                 goto done;
 199         }
 200
 201         if (typ == BLOCK_TYPE_LOG) {
 202                 int block_header_skip = 4 + header_off;
 203                 uLongf dst_len = sz - block_header_skip; /* total size of dest
 204                                                             buffer. */
 205                 uLongf src_len = block->len - block_header_skip;
 206
 207                 /* Log blocks specify the *uncompressed* size in their header. */
 208                 REFTABLE_ALLOC_ARRAY(uncompressed, sz);
 209
 210                 /* Copy over the block header verbatim. It's not compressed. */
 211                 memcpy(uncompressed, block->data, block_header_skip);
 212
 213                 /* Uncompress */
 214                 if (Z_OK !=
 215                     uncompress2(uncompressed + block_header_skip, &dst_len,
 216                                 block->data + block_header_skip, &src_len)) {
 217                         err = REFTABLE_ZLIB_ERROR;
 218                         goto done;
 219                 }
 220
 221                 if (dst_len + block_header_skip != sz) {
 222                         err = REFTABLE_FORMAT_ERROR;
 223                         goto done;
 224                 }
 225
 226                 /* We're done with the input data. */
 227                 reftable_block_done(block);
 228                 block->data = uncompressed;
 229                 uncompressed = NULL;
 230                 block->len = sz;
 231                 block->source = malloc_block_source();
 232                 full_block_size = src_len + block_header_skip;
 233         } else if (full_block_size == 0) {
 234                 full_block_size = sz;
 235         } else if (sz < full_block_size && sz < block->len &&
 236                    block->data[sz] != 0) {
 237                 /* If the block is smaller than the full block size, it is
 238                    padded (data followed by '\0') or the next block is
 239                    unaligned. */
 240                 full_block_size = sz;
 241         }
 242
 243         restart_count = get_be16(block->data + sz - 2);
 244         restart_start = sz - 2 - 3 * restart_count;
 245         restart_bytes = block->data + restart_start;
 246
 247         /* transfer ownership. */
 248         br->block = *block;
 249         block->data = NULL;
 250         block->len = 0;
 251
 252         br->hash_size = hash_size;
 253         br->block_len = restart_start;
 254         br->full_block_size = full_block_size;
 255         br->header_off = header_off;
 256         br->restart_count = restart_count;
 257         br->restart_bytes = restart_bytes;
 258
 259 done:
 260         reftable_free(uncompressed);
 261         return err;
 262 }
 263
 264 static uint32_t block_reader_restart_offset(struct block_reader *br, int i)
 265 {
 266         return get_be24(br->restart_bytes + 3 * i);
 267 }
 268
 269 void block_reader_start(struct block_reader *br, struct block_iter *it)
 270 {
 271         it->br = br;
 272         strbuf_reset(&it->last_key);
 273         it->next_off = br->header_off + 4;
 274 }
 275
 276 struct restart_needle_less_args {
 277         int error;
 278         struct strbuf needle;
 279         struct block_reader *reader;
 280 };
 281
 282 static int restart_needle_less(size_t idx, void *_args)
 283 {
 284         struct restart_needle_less_args *args = _args;
 285         uint32_t off = block_reader_restart_offset(args->reader, idx);
 286         struct string_view in = {
 287                 .buf = args->reader->block.data + off,
 288                 .len = args->reader->block_len - off,
 289         };
 290         struct strbuf kth_restart_key = STRBUF_INIT;
 291         uint8_t unused_extra;
 292         int result, n;
 293
 294         /*
 295          * TODO: The restart key is verbatim in the block, so we can in theory
 296          * avoid decoding the key and thus save some allocations.
 297          */
 298         n = reftable_decode_key(&kth_restart_key, &unused_extra, in);
 299         if (n < 0) {
 300                 args->error = 1;
 301                 return -1;
 302         }
 303
 304         result = strbuf_cmp(&args->needle, &kth_restart_key);
 305         strbuf_release(&kth_restart_key);
 306         return result < 0;
 307 }
 308
 309 void block_iter_copy_from(struct block_iter *dest, struct block_iter *src)
 310 {
 311         dest->br = src->br;
 312         dest->next_off = src->next_off;
 313         strbuf_reset(&dest->last_key);
 314         strbuf_addbuf(&dest->last_key, &src->last_key);
 315 }
 316
 317 int block_iter_next(struct block_iter *it, struct reftable_record *rec)
 318 {
 319         struct string_view in = {
 320                 .buf = it->br->block.data + it->next_off,
 321                 .len = it->br->block_len - it->next_off,
 322         };
 323         struct string_view start = in;
 324         uint8_t extra = 0;
 325         int n = 0;
 326
 327         if (it->next_off >= it->br->block_len)
 328                 return 1;
 329
 330         n = reftable_decode_key(&it->last_key, &extra, in);
 331         if (n < 0)
 332                 return -1;
 333         if (!it->last_key.len)
 334                 return REFTABLE_FORMAT_ERROR;
 335
 336         string_view_consume(&in, n);
 337         n = reftable_record_decode(rec, it->last_key, extra, in, it->br->hash_size,
 338                                    &it->scratch);
 339         if (n < 0)
 340                 return -1;
 341         string_view_consume(&in, n);
 342
 343         it->next_off += start.len - in.len;
 344         return 0;
 345 }
 346
 347 int block_reader_first_key(struct block_reader *br, struct strbuf *key)
 348 {
 349         int off = br->header_off + 4, n;
 350         struct string_view in = {
 351                 .buf = br->block.data + off,
 352                 .len = br->block_len - off,
 353         };
 354         uint8_t extra = 0;
 355
 356         strbuf_reset(key);
 357
 358         n = reftable_decode_key(key, &extra, in);
 359         if (n < 0)
 360                 return n;
 361         if (!key->len)
 362                 return REFTABLE_FORMAT_ERROR;
 363
 364         return 0;
 365 }
 366
 367 int block_iter_seek(struct block_iter *it, struct strbuf *want)
 368 {
 369         return block_reader_seek(it->br, it, want);
 370 }
 371
 372 void block_iter_close(struct block_iter *it)
 373 {
 374         strbuf_release(&it->last_key);
 375         strbuf_release(&it->scratch);
 376 }
 377
 378 int block_reader_seek(struct block_reader *br, struct block_iter *it,
 379                       struct strbuf *want)
 380 {
 381         struct restart_needle_less_args args = {
 382                 .needle = *want,
 383                 .reader = br,
 384         };
 385         struct block_iter next = BLOCK_ITER_INIT;
 386         struct reftable_record rec;
 387         int err = 0;
 388         size_t i;
 389
 390         /*
 391          * Perform a binary search over the block's restart points, which
 392          * avoids doing a linear scan over the whole block. Like this, we
 393          * identify the section of the block that should contain our key.
 394          *
 395          * Note that we explicitly search for the first restart point _greater_
 396          * than the sought-after record, not _greater or equal_ to it. In case
 397          * the sought-after record is located directly at the restart point we
 398          * would otherwise start doing the linear search at the preceding
 399          * restart point. While that works alright, we would end up scanning
 400          * too many record.
 401          */
 402         i = binsearch(br->restart_count, &restart_needle_less, &args);
 403         if (args.error) {
 404                 err = REFTABLE_FORMAT_ERROR;
 405                 goto done;
 406         }
 407
 408         /*
 409          * Now there are multiple cases:
 410          *
 411          *   - `i == 0`: The wanted record is smaller than the record found at
 412          *     the first restart point. As the first restart point is the first
 413          *     record in the block, our wanted record cannot be located in this
 414          *     block at all. We still need to position the iterator so that the
 415          *     next call to `block_iter_next()` will yield an end-of-iterator
 416          *     signal.
 417          *
 418          *   - `i == restart_count`: The wanted record was not found at any of
 419          *     the restart points. As there is no restart point at the end of
 420          *     the section the record may thus be contained in the last block.
 421          *
 422          *   - `i > 0`: The wanted record must be contained in the section
 423          *     before the found restart point. We thus do a linear search
 424          *     starting from the preceding restart point.
 425          */
 426         if (i > 0)
 427                 it->next_off = block_reader_restart_offset(br, i - 1);
 428         else
 429                 it->next_off = br->header_off + 4;
 430         it->br = br;
 431
 432         reftable_record_init(&rec, block_reader_type(br));
 433
 434         /*
 435          * We're looking for the last entry less than the wanted key so that
 436          * the next call to `block_reader_next()` would yield the wanted
 437          * record. We thus don't want to position our reader at the sought
 438          * after record, but one before. To do so, we have to go one entry too
 439          * far and then back up.
 440          */
 441         while (1) {
 442                 block_iter_copy_from(&next, it);
 443                 err = block_iter_next(&next, &rec);
 444                 if (err < 0)
 445                         goto done;
 446                 if (err > 0) {
 447                         err = 0;
 448                         goto done;
 449                 }
 450
 451                 /*
 452                  * Check whether the current key is greater or equal to the
 453                  * sought-after key. In case it is greater we know that the
 454                  * record does not exist in the block and can thus abort early.
 455                  * In case it is equal to the sought-after key we have found
 456                  * the desired record.
 457                  */
 458                 reftable_record_key(&rec, &it->last_key);
 459                 if (strbuf_cmp(&it->last_key, want) >= 0)
 460                         goto done;
 461
 462                 block_iter_copy_from(it, &next);
 463         }
 464
 465 done:
 466         block_iter_close(&next);
 467         reftable_record_release(&rec);
 468
 469         return err;
 470 }
 471
 472 void block_writer_release(struct block_writer *bw)
 473 {
 474         FREE_AND_NULL(bw->restarts);
 475         strbuf_release(&bw->last_key);
 476         /* the block is not owned. */
 477 }
 478
 479 void reftable_block_done(struct reftable_block *blockp)
 480 {
 481         struct reftable_block_source source = blockp->source;
 482         if (blockp && source.ops)
 483                 source.ops->return_block(source.arg, blockp);
 484         blockp->data = NULL;
 485         blockp->len = 0;
 486         blockp->source.ops = NULL;
 487         blockp->source.arg = NULL;
 488 }