/*

 * Copyright 2020 Google LLC

 *

 * Use of this source code is governed by a BSD-style

 * license that can be found in the LICENSE file or at

 * https://developers.google.com/open-source/licenses/bsd

 */

#include "block.h"

#include "blocksource.h"

#include "constants.h"

#include "iter.h"

#include "record.h"

#include "reftable-error.h"

#include "system.h"

size_t header_size(int version)

{

  switch (version) {

  case 1:

    return 24;

  case 2:

    return 28;

  }

  abort();

}

size_t footer_size(int version)

{

  switch (version) {

  case 1:

    return 68;

  case 2:

    return 72;

  }

  abort();

}

static int block_writer_register_restart(struct block_writer *w, int n,

           int is_restart, struct reftable_buf *key)

{

  uint32_t rlen;

  int err;

  rlen = w->restart_len;

  if (rlen >= MAX_RESTARTS)

    is_restart = 0;

  if (is_restart)

    rlen++;

  if (2 + 3 * rlen + n > w->block_size - w->next)

    return REFTABLE_ENTRY_TOO_BIG_ERROR;

  if (is_restart) {

    REFTABLE_ALLOC_GROW_OR_NULL(w->restarts, w->restart_len + 1,

              w->restart_cap);

    if (!w->restarts)

      return REFTABLE_OUT_OF_MEMORY_ERROR;

    w->restarts[w->restart_len++] = w->next;

  }

  w->next += n;

  reftable_buf_reset(&w->last_key);

  err = reftable_buf_add(&w->last_key, key->buf, key->len);

  if (err < 0)

    return err;

  w->entries++;

  return 0;

}

int block_writer_init(struct block_writer *bw, uint8_t typ, uint8_t *block,

          uint32_t block_size, uint32_t header_off, uint32_t hash_size)

{

  bw->block = block;

  bw->hash_size = hash_size;

  bw->block_size = block_size;

  bw->header_off = header_off;

  bw->block[header_off] = typ;

  bw->next = header_off + 4;

  bw->restart_interval = 16;

  bw->entries = 0;

  bw->restart_len = 0;

  bw->last_key.len = 0;

  if (!bw->zstream) {

    REFTABLE_CALLOC_ARRAY(bw->zstream, 1);

    if (!bw->zstream)

      return REFTABLE_OUT_OF_MEMORY_ERROR;

    deflateInit(bw->zstream, 9);

  }

  return 0;

}

uint8_t block_writer_type(struct block_writer *bw)

{

  return bw->block[bw->header_off];

}

/*

 * Adds the reftable_record to the block. Returns 0 on success and

 * appropriate error codes on failure.

 */

int block_writer_add(struct block_writer *w, struct reftable_record *rec)

{

  struct reftable_buf empty = REFTABLE_BUF_INIT;

  struct reftable_buf last =

    w->entries % w->restart_interval == 0 ? empty : w->last_key;

  struct string_view out = {

    .buf = w->block + w->next,

    .len = w->block_size - w->next,

  };

  struct string_view start = out;

  int is_restart = 0;

  int n = 0;

  int err;

  err = reftable_record_key(rec, &w->scratch);

  if (err < 0)

    goto done;

  if (!w->scratch.len) {

    err = REFTABLE_API_ERROR;

    goto done;

  }

  n = reftable_encode_key(&is_restart, out, last, w->scratch,

        reftable_record_val_type(rec));

  if (n < 0) {

    err = n;

    goto done;

  }

  string_view_consume(&out, n);

  n = reftable_record_encode(rec, out, w->hash_size);

  if (n < 0) {

    err = n;

    goto done;

  }

  string_view_consume(&out, n);

  err = block_writer_register_restart(w, start.len - out.len, is_restart,

              &w->scratch);

done:

  return err;

}

int block_writer_finish(struct block_writer *w)

{

  for (uint32_t i = 0; i < w->restart_len; i++) {

    reftable_put_be24(w->block + w->next, w->restarts[i]);

    w->next += 3;

  }

  reftable_put_be16(w->block + w->next, w->restart_len);

  w->next += 2;

  reftable_put_be24(w->block + 1 + w->header_off, w->next);

  /*

   * Log records are stored zlib-compressed. Note that the compression

   * also spans over the restart points we have just written.

   */

  if (block_writer_type(w) == REFTABLE_BLOCK_TYPE_LOG) {

    int block_header_skip = 4 + w->header_off;

    uLongf src_len = w->next - block_header_skip, compressed_len;

    int ret;

    ret = deflateReset(w->zstream);

    if (ret != Z_OK)

      return REFTABLE_ZLIB_ERROR;

    /*

     * Precompute the upper bound of how many bytes the compressed

     * data may end up with. Combined with `Z_FINISH`, `deflate()`

     * is guaranteed to return `Z_STREAM_END`.

     */

    compressed_len = deflateBound(w->zstream, src_len);

    REFTABLE_ALLOC_GROW_OR_NULL(w->compressed, compressed_len,

              w->compressed_cap);

    if (!w->compressed) {

      ret = REFTABLE_OUT_OF_MEMORY_ERROR;

      return ret;

    }

    w->zstream->next_out = w->compressed;

    w->zstream->avail_out = compressed_len;

    w->zstream->next_in = w->block + block_header_skip;

    w->zstream->avail_in = src_len;

    /*

     * We want to perform all decompression in a single step, which

     * is why we can pass Z_FINISH here. As we have precomputed the

     * deflated buffer's size via `deflateBound()` this function is

     * guaranteed to succeed according to the zlib documentation.

     */

    ret = deflate(w->zstream, Z_FINISH);

    if (ret != Z_STREAM_END)

      return REFTABLE_ZLIB_ERROR;

    /*

     * Overwrite the uncompressed data we have already written and

     * adjust the `next` pointer to point right after the

     * compressed data.

     */

    memcpy(w->block + block_header_skip, w->compressed,

           w->zstream->total_out);

    w->next = w->zstream->total_out + block_header_skip;

  }

  return w->next;

}

static int read_block(struct reftable_block_source *source,

          struct reftable_block_data *dest, uint64_t off,

          uint32_t sz)

{

  size_t size = block_source_size(source);

  block_source_release_data(dest);

  if (off >= size)

    return 0;

  if (off + sz > size)

    sz = size - off;

  return block_source_read_data(source, dest, off, sz);

}

int reftable_block_init(struct reftable_block *block,

      struct reftable_block_source *source,

      uint32_t offset, uint32_t header_size,

      uint32_t table_block_size, uint32_t hash_size,

      uint8_t want_type)

{

  uint32_t guess_block_size = table_block_size ?

    table_block_size : DEFAULT_BLOCK_SIZE;

  uint32_t full_block_size = table_block_size;

  uint16_t restart_count;

  uint32_t restart_off;

  uint32_t block_size;

  uint8_t block_type;

  int err;

  err = read_block(source, &block->block_data, offset, guess_block_size);

  if (err < 0)

    goto done;

  block_type = block->block_data.data[header_size];

  if (!reftable_is_block_type(block_type)) {

    err = REFTABLE_FORMAT_ERROR;

    goto done;

  }

  if (want_type != REFTABLE_BLOCK_TYPE_ANY && block_type != want_type) {

    err = 1;

    goto done;

  }

  block_size = reftable_get_be24(block->block_data.data + header_size + 1);

  if (block_size > guess_block_size) {

    err = read_block(source, &block->block_data, offset, block_size);

    if (err < 0)

      goto done;

  }

  /*

   * Verify that the block size covers at least the table header, block

   * header and the 2 byte restart counter.

   */

  if (block_size < header_size + 4 + 2) {

    err = REFTABLE_FORMAT_ERROR;

    goto done;

  }

  if (block_type == REFTABLE_BLOCK_TYPE_LOG) {

    uint32_t block_header_skip = 4 + header_size;

    uLong dst_len = block_size - block_header_skip;

    uLong src_len = block->block_data.len - block_header_skip;

    /* Log blocks specify the *uncompressed* size in their header. */

    REFTABLE_ALLOC_GROW_OR_NULL(block->uncompressed_data, block_size,

              block->uncompressed_cap);

    if (!block->uncompressed_data) {

      err = REFTABLE_OUT_OF_MEMORY_ERROR;

      goto done;

    }

    /* Copy over the block header verbatim. It's not compressed. */

    memcpy(block->uncompressed_data, block->block_data.data, block_header_skip);

    if (!block->zstream) {

      REFTABLE_CALLOC_ARRAY(block->zstream, 1);

      if (!block->zstream) {

        err = REFTABLE_OUT_OF_MEMORY_ERROR;

        goto done;

      }

      err = inflateInit(block->zstream);

    } else {

      err = inflateReset(block->zstream);

    }

    if (err != Z_OK) {

      err = REFTABLE_ZLIB_ERROR;

      goto done;

    }

    block->zstream->next_in = block->block_data.data + block_header_skip;

    block->zstream->avail_in = src_len;

    block->zstream->next_out = block->uncompressed_data + block_header_skip;

    block->zstream->avail_out = dst_len;

    /*

     * We know both input as well as output size, and we know that

     * the sizes should never be bigger than `uInt_MAX` because

     * blocks can at most be 16MB large. We can thus use `Z_FINISH`

     * here to instruct zlib to inflate the data in one go, which

     * is more efficient than using `Z_NO_FLUSH`.

     */

    err = inflate(block->zstream, Z_FINISH);

    if (err != Z_STREAM_END) {

      err = REFTABLE_ZLIB_ERROR;

      goto done;

    }

    err = 0;

    if (block->zstream->total_out + block_header_skip != block_size) {

      err = REFTABLE_FORMAT_ERROR;

      goto done;

    }

    /* We're done with the input data. */

    block_source_release_data(&block->block_data);

    block->block_data.data = block->uncompressed_data;

    block->block_data.len = block_size;

    full_block_size = src_len + block_header_skip - block->zstream->avail_in;

  } else if (full_block_size == 0) {

    full_block_size = block_size;

  } else if (block_size < full_block_size && block_size < block->block_data.len &&

       block->block_data.data[block_size] != 0) {

    /* If the block is smaller than the full block size, it is

       padded (data followed by '\0') or the next block is

       unaligned. */

    full_block_size = block_size;

  }

  /*

   * Ensure that we have sufficient data available now to satisfy the

   * claimed block size.

   */

  if (block_size > block->block_data.len) {

    err = REFTABLE_FORMAT_ERROR;

    goto done;

  }

  restart_count = reftable_get_be16(block->block_data.data + block_size - 2);

  restart_off = block_size - 2 - 3 * restart_count;

  if (restart_off < header_size + 4 || restart_off > block_size - 2) {

    err = REFTABLE_FORMAT_ERROR;

    goto done;

  }

  block->block_type = block_type;

  block->hash_size = hash_size;

  block->restart_off = restart_off;

  block->full_block_size = full_block_size;

  block->header_off = header_size;

  block->restart_count = restart_count;

  err = 0;

done:

  if (err < 0)

    reftable_block_release(block);

  return err;

}

void reftable_block_release(struct reftable_block *block)

{

  inflateEnd(block->zstream);

  reftable_free(block->zstream);

  reftable_free(block->uncompressed_data);

  block_source_release_data(&block->block_data);

  memset(block, 0, sizeof(*block));

}

uint8_t reftable_block_type(const struct reftable_block *b)

{

  return b->block_data.data[b->header_off];

}

int reftable_block_first_key(const struct reftable_block *block, struct reftable_buf *key)

{

  int off = block->header_off + 4, n;

  struct string_view in = {

    .buf = block->block_data.data + off,

    .len = block->restart_off - off,

  };

  uint8_t extra = 0;

  reftable_buf_reset(key);

  n = reftable_decode_key(key, &extra, in);

  if (n < 0)

    return n;

  if (!key->len)

    return REFTABLE_FORMAT_ERROR;

  return 0;

}

static uint32_t block_restart_offset(const struct reftable_block *b, size_t idx)

{

  return reftable_get_be24(b->block_data.data + b->restart_off + 3 * idx);

}

void block_iter_init(struct block_iter *it, const struct reftable_block *block)

{

  it->block = block;

  block_iter_seek_start(it);

}

void block_iter_seek_start(struct block_iter *it)

{

  reftable_buf_reset(&it->last_key);

  it->next_off = it->block->header_off + 4;

}

struct restart_needle_less_args {

  int error;

  struct reftable_buf needle;

  const struct reftable_block *block;

};

static int restart_needle_less(size_t idx, void *_args)

{

  struct restart_needle_less_args *args = _args;

  uint32_t off = block_restart_offset(args->block, idx);

  struct string_view in = {

    .buf = args->block->block_data.data + off,

    .len = args->block->restart_off - off,

  };

  uint64_t prefix_len, suffix_len;

  uint8_t extra;

  int n;

  /*

   * The restart offset must point to a record, which is stored before

   * the restart table. Verify that this is the case.

   */

  if (off >= args->block->restart_off) {

    args->error = 1;

    return -1;

  }

  /*

   * Records at restart points are stored without prefix compression, so

   * there is no need to fully decode the record key here. This removes

   * the need for allocating memory.

   */

  n = reftable_decode_keylen(in, &prefix_len, &suffix_len, &extra);

  if (n < 0 || prefix_len) {

    args->error = 1;

    return -1;

  }

  string_view_consume(&in, n);

  if (suffix_len > in.len) {

    args->error = 1;

    return -1;

  }

  n = memcmp(args->needle.buf, in.buf,

       args->needle.len < suffix_len ? args->needle.len : suffix_len);

  if (n)

    return n < 0;

  return args->needle.len < suffix_len;

}

int block_iter_next(struct block_iter *it, struct reftable_record *rec)

{

  struct string_view in = {

    .buf = (unsigned char *) it->block->block_data.data + it->next_off,

    .len = it->block->restart_off - it->next_off,

  };

  struct string_view start = in;

  uint8_t extra = 0;

  int n = 0;

  if (it->next_off >= it->block->restart_off)

    return 1;

  n = reftable_decode_key(&it->last_key, &extra, in);

  if (n < 0)

    return -1;

  if (!it->last_key.len)

    return REFTABLE_FORMAT_ERROR;

  string_view_consume(&in, n);

  n = reftable_record_decode(rec, it->last_key, extra, in, it->block->hash_size,

           &it->scratch);

  if (n < 0)

    return -1;

  string_view_consume(&in, n);

  it->next_off += start.len - in.len;

  return 0;

}

void block_iter_reset(struct block_iter *it)

{

  reftable_buf_reset(&it->last_key);

  it->next_off = 0;

  it->block = NULL;

}

void block_iter_close(struct block_iter *it)

{

  reftable_buf_release(&it->last_key);

  reftable_buf_release(&it->scratch);

}

int block_iter_seek_key(struct block_iter *it, struct reftable_buf *want)

{

  struct restart_needle_less_args args = {

    .needle = *want,

    .block = it->block,

  };

  struct reftable_record rec;

  int err = 0;

  size_t i;

  err = reftable_record_init(&rec, reftable_block_type(it->block));

  if (err < 0)

    goto done;

  /*

   * Perform a binary search over the block's restart points, which

   * avoids doing a linear scan over the whole block. Like this, we

   * identify the section of the block that should contain our key.

   *

   * Note that we explicitly search for the first restart point _greater_

   * than the sought-after record, not _greater or equal_ to it. In case

   * the sought-after record is located directly at the restart point we

   * would otherwise start doing the linear search at the preceding

   * restart point. While that works alright, we would end up scanning

   * too many record.

   */

  i = binsearch(it->block->restart_count, &restart_needle_less, &args);

  if (args.error) {

    err = REFTABLE_FORMAT_ERROR;

    goto done;

  }

  /*

   * Now there are multiple cases:

   *

   *   - `i == 0`: The wanted record is smaller than the record found at

   *     the first restart point. As the first restart point is the first

   *     record in the block, our wanted record cannot be located in this

   *     block at all. We still need to position the iterator so that the

   *     next call to `block_iter_next()` will yield an end-of-iterator

   *     signal.

   *

   *   - `i == restart_count`: The wanted record was not found at any of

   *     the restart points. As there is no restart point at the end of

   *     the section the record may thus be contained in the last block.

   *

   *   - `i > 0`: The wanted record must be contained in the section

   *     before the found restart point. We thus do a linear search

   *     starting from the preceding restart point.

   */

  if (i > 0)

    it->next_off = block_restart_offset(it->block, i - 1);

  else

    it->next_off = it->block->header_off + 4;

  /*

   * We're looking for the last entry less than the wanted key so that

   * the next call to `block_reader_next()` would yield the wanted

   * record. We thus don't want to position our iterator at the sought

   * after record, but one before. To do so, we have to go one entry too

   * far and then back up.

   */

  while (1) {

    size_t prev_off = it->next_off;

    err = block_iter_next(it, &rec);

    if (err < 0)

      goto done;

    if (err > 0) {

      it->next_off = prev_off;

      err = 0;

      goto done;

    }

    err = reftable_record_key(&rec, &it->last_key);

    if (err < 0)

      goto done;

    /*

     * Check whether the current key is greater or equal to the

     * sought-after key. In case it is greater we know that the

     * record does not exist in the block and can thus abort early.

     * In case it is equal to the sought-after key we have found

     * the desired record.

     *

     * Note that we store the next record's key record directly in

     * `last_key` without restoring the key of the preceding record

     * in case we need to go one record back. This is safe to do as

     * `block_iter_next()` would return the ref whose key is equal

     * to `last_key` now, and naturally all keys share a prefix

     * with themselves.

     */

    if (reftable_buf_cmp(&it->last_key, want) >= 0) {

      it->next_off = prev_off;

      goto done;

    }

  }

done:

  reftable_record_release(&rec);

  return err;

}

static int block_iter_seek_void(void *it, struct reftable_record *want)

{

  struct reftable_buf buf = REFTABLE_BUF_INIT;

  struct block_iter *bi = it;

  int err;

  if (bi->block->block_type != want->type)

    return REFTABLE_API_ERROR;

  err = reftable_record_key(want, &buf);

  if (err < 0)

    goto out;

  err = block_iter_seek_key(it, &buf);

  if (err < 0)

    goto out;

  err = 0;

out:

  reftable_buf_release(&buf);

  return err;

}

static int block_iter_next_void(void *it, struct reftable_record *rec)

{

  return block_iter_next(it, rec);

}

static void block_iter_close_void(void *it)

{

  block_iter_close(it);

}

static struct reftable_iterator_vtable block_iter_vtable = {

  .seek = &block_iter_seek_void,

  .next = &block_iter_next_void,

  .close = &block_iter_close_void,

};

int reftable_block_init_iterator(const struct reftable_block *b,

         struct reftable_iterator *it)

{

  struct block_iter *bi;

  REFTABLE_CALLOC_ARRAY(bi, 1);

  block_iter_init(bi, b);

  assert(!it->ops);

  it->iter_arg = bi;

  it->ops = &block_iter_vtable;

  return 0;

}

void block_writer_release(struct block_writer *bw)

{

  deflateEnd(bw->zstream);

  REFTABLE_FREE_AND_NULL(bw->zstream);

  REFTABLE_FREE_AND_NULL(bw->restarts);

  REFTABLE_FREE_AND_NULL(bw->compressed);

  reftable_buf_release(&bw->scratch);

  reftable_buf_release(&bw->last_key);

  /* the block is not owned. */

}