git/reftable/block.c
Han-Wen Nienhuys 45c2fcc2a0 reftable: avoid writing empty keys at the block layer
The public interface (reftable_writer) already ensures that keys are
written in strictly increasing order, and an empty key by definition
fails this check.

However, by also enforcing this at the block layer, it is easier to
verify that records (which are written into blocks) never have to
consider the possibility of empty keys.

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2022-02-23 13:36:26 -08:00

453 lines
10 KiB
C

/*
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 "record.h"
#include "reftable-error.h"
#include "system.h"
#include <zlib.h>
int header_size(int version)
{
switch (version) {
case 1:
return 24;
case 2:
return 28;
}
abort();
}
int 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 strbuf *key)
{
int 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 -1;
if (is_restart) {
if (w->restart_len == w->restart_cap) {
w->restart_cap = w->restart_cap * 2 + 1;
w->restarts = reftable_realloc(
w->restarts, sizeof(uint32_t) * w->restart_cap);
}
w->restarts[w->restart_len++] = w->next;
}
w->next += n;
strbuf_reset(&w->last_key);
strbuf_addbuf(&w->last_key, key);
w->entries++;
return 0;
}
void block_writer_init(struct block_writer *bw, uint8_t typ, uint8_t *buf,
uint32_t block_size, uint32_t header_off, int hash_size)
{
bw->buf = buf;
bw->hash_size = hash_size;
bw->block_size = block_size;
bw->header_off = header_off;
bw->buf[header_off] = typ;
bw->next = header_off + 4;
bw->restart_interval = 16;
bw->entries = 0;
bw->restart_len = 0;
bw->last_key.len = 0;
}
uint8_t block_writer_type(struct block_writer *bw)
{
return bw->buf[bw->header_off];
}
/* Adds the reftable_record to the block. Returns -1 if it does not fit, 0 on
success. Returns REFTABLE_API_ERROR if attempting to write a record with
empty key. */
int block_writer_add(struct block_writer *w, struct reftable_record *rec)
{
struct strbuf empty = STRBUF_INIT;
struct strbuf last =
w->entries % w->restart_interval == 0 ? empty : w->last_key;
struct string_view out = {
.buf = w->buf + w->next,
.len = w->block_size - w->next,
};
struct string_view start = out;
int is_restart = 0;
struct strbuf key = STRBUF_INIT;
int n = 0;
int err = -1;
reftable_record_key(rec, &key);
if (!key.len) {
err = REFTABLE_API_ERROR;
goto done;
}
n = reftable_encode_key(&is_restart, out, last, key,
reftable_record_val_type(rec));
if (n < 0)
goto done;
string_view_consume(&out, n);
n = reftable_record_encode(rec, out, w->hash_size);
if (n < 0)
goto done;
string_view_consume(&out, n);
err = block_writer_register_restart(w, start.len - out.len, is_restart,
&key);
done:
strbuf_release(&key);
return err;
}
int block_writer_finish(struct block_writer *w)
{
int i;
for (i = 0; i < w->restart_len; i++) {
put_be24(w->buf + w->next, w->restarts[i]);
w->next += 3;
}
put_be16(w->buf + w->next, w->restart_len);
w->next += 2;
put_be24(w->buf + 1 + w->header_off, w->next);
if (block_writer_type(w) == BLOCK_TYPE_LOG) {
int block_header_skip = 4 + w->header_off;
uLongf src_len = w->next - block_header_skip;
uLongf dest_cap = src_len * 1.001 + 12;
uint8_t *compressed = reftable_malloc(dest_cap);
while (1) {
uLongf out_dest_len = dest_cap;
int zresult = compress2(compressed, &out_dest_len,
w->buf + block_header_skip,
src_len, 9);
if (zresult == Z_BUF_ERROR && dest_cap < LONG_MAX) {
dest_cap *= 2;
compressed =
reftable_realloc(compressed, dest_cap);
if (compressed)
continue;
}
if (Z_OK != zresult) {
reftable_free(compressed);
return REFTABLE_ZLIB_ERROR;
}
memcpy(w->buf + block_header_skip, compressed,
out_dest_len);
w->next = out_dest_len + block_header_skip;
reftable_free(compressed);
break;
}
}
return w->next;
}
uint8_t block_reader_type(struct block_reader *r)
{
return r->block.data[r->header_off];
}
int block_reader_init(struct block_reader *br, struct reftable_block *block,
uint32_t header_off, uint32_t table_block_size,
int hash_size)
{
uint32_t full_block_size = table_block_size;
uint8_t typ = block->data[header_off];
uint32_t sz = get_be24(block->data + header_off + 1);
int err = 0;
uint16_t restart_count = 0;
uint32_t restart_start = 0;
uint8_t *restart_bytes = NULL;
uint8_t *uncompressed = NULL;
if (!reftable_is_block_type(typ)) {
err = REFTABLE_FORMAT_ERROR;
goto done;
}
if (typ == BLOCK_TYPE_LOG) {
int block_header_skip = 4 + header_off;
uLongf dst_len = sz - block_header_skip; /* total size of dest
buffer. */
uLongf src_len = block->len - block_header_skip;
/* Log blocks specify the *uncompressed* size in their header.
*/
uncompressed = reftable_malloc(sz);
/* Copy over the block header verbatim. It's not compressed. */
memcpy(uncompressed, block->data, block_header_skip);
/* Uncompress */
if (Z_OK !=
uncompress2(uncompressed + block_header_skip, &dst_len,
block->data + block_header_skip, &src_len)) {
err = REFTABLE_ZLIB_ERROR;
goto done;
}
if (dst_len + block_header_skip != sz) {
err = REFTABLE_FORMAT_ERROR;
goto done;
}
/* We're done with the input data. */
reftable_block_done(block);
block->data = uncompressed;
uncompressed = NULL;
block->len = sz;
block->source = malloc_block_source();
full_block_size = src_len + block_header_skip;
} else if (full_block_size == 0) {
full_block_size = sz;
} else if (sz < full_block_size && sz < block->len &&
block->data[sz] != 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 = sz;
}
restart_count = get_be16(block->data + sz - 2);
restart_start = sz - 2 - 3 * restart_count;
restart_bytes = block->data + restart_start;
/* transfer ownership. */
br->block = *block;
block->data = NULL;
block->len = 0;
br->hash_size = hash_size;
br->block_len = restart_start;
br->full_block_size = full_block_size;
br->header_off = header_off;
br->restart_count = restart_count;
br->restart_bytes = restart_bytes;
done:
reftable_free(uncompressed);
return err;
}
static uint32_t block_reader_restart_offset(struct block_reader *br, int i)
{
return get_be24(br->restart_bytes + 3 * i);
}
void block_reader_start(struct block_reader *br, struct block_iter *it)
{
it->br = br;
strbuf_reset(&it->last_key);
it->next_off = br->header_off + 4;
}
struct restart_find_args {
int error;
struct strbuf key;
struct block_reader *r;
};
static int restart_key_less(size_t idx, void *args)
{
struct restart_find_args *a = args;
uint32_t off = block_reader_restart_offset(a->r, idx);
struct string_view in = {
.buf = a->r->block.data + off,
.len = a->r->block_len - off,
};
/* the restart key is verbatim in the block, so this could avoid the
alloc for decoding the key */
struct strbuf rkey = STRBUF_INIT;
struct strbuf last_key = STRBUF_INIT;
uint8_t unused_extra;
int n = reftable_decode_key(&rkey, &unused_extra, last_key, in);
int result;
if (n < 0) {
a->error = 1;
return -1;
}
result = strbuf_cmp(&a->key, &rkey);
strbuf_release(&rkey);
return result;
}
void block_iter_copy_from(struct block_iter *dest, struct block_iter *src)
{
dest->br = src->br;
dest->next_off = src->next_off;
strbuf_reset(&dest->last_key);
strbuf_addbuf(&dest->last_key, &src->last_key);
}
int block_iter_next(struct block_iter *it, struct reftable_record *rec)
{
struct string_view in = {
.buf = it->br->block.data + it->next_off,
.len = it->br->block_len - it->next_off,
};
struct string_view start = in;
struct strbuf key = STRBUF_INIT;
uint8_t extra = 0;
int n = 0;
if (it->next_off >= it->br->block_len)
return 1;
n = reftable_decode_key(&key, &extra, it->last_key, in);
if (n < 0)
return -1;
if (!key.len)
return REFTABLE_FORMAT_ERROR;
string_view_consume(&in, n);
n = reftable_record_decode(rec, key, extra, in, it->br->hash_size);
if (n < 0)
return -1;
string_view_consume(&in, n);
strbuf_reset(&it->last_key);
strbuf_addbuf(&it->last_key, &key);
it->next_off += start.len - in.len;
strbuf_release(&key);
return 0;
}
int block_reader_first_key(struct block_reader *br, struct strbuf *key)
{
struct strbuf empty = STRBUF_INIT;
int off = br->header_off + 4;
struct string_view in = {
.buf = br->block.data + off,
.len = br->block_len - off,
};
uint8_t extra = 0;
int n = reftable_decode_key(key, &extra, empty, in);
if (n < 0)
return n;
if (!key->len)
return REFTABLE_FORMAT_ERROR;
return 0;
}
int block_iter_seek(struct block_iter *it, struct strbuf *want)
{
return block_reader_seek(it->br, it, want);
}
void block_iter_close(struct block_iter *it)
{
strbuf_release(&it->last_key);
}
int block_reader_seek(struct block_reader *br, struct block_iter *it,
struct strbuf *want)
{
struct restart_find_args args = {
.key = *want,
.r = br,
};
struct reftable_record rec = reftable_new_record(block_reader_type(br));
struct strbuf key = STRBUF_INIT;
int err = 0;
struct block_iter next = {
.last_key = STRBUF_INIT,
};
int i = binsearch(br->restart_count, &restart_key_less, &args);
if (args.error) {
err = REFTABLE_FORMAT_ERROR;
goto done;
}
it->br = br;
if (i > 0) {
i--;
it->next_off = block_reader_restart_offset(br, i);
} else {
it->next_off = br->header_off + 4;
}
/* We're looking for the last entry less/equal than the wanted key, so
we have to go one entry too far and then back up.
*/
while (1) {
block_iter_copy_from(&next, it);
err = block_iter_next(&next, &rec);
if (err < 0)
goto done;
reftable_record_key(&rec, &key);
if (err > 0 || strbuf_cmp(&key, want) >= 0) {
err = 0;
goto done;
}
block_iter_copy_from(it, &next);
}
done:
strbuf_release(&key);
strbuf_release(&next.last_key);
reftable_record_release(&rec);
return err;
}
void block_writer_release(struct block_writer *bw)
{
FREE_AND_NULL(bw->restarts);
strbuf_release(&bw->last_key);
/* the block is not owned. */
}
void reftable_block_done(struct reftable_block *blockp)
{
struct reftable_block_source source = blockp->source;
if (blockp && source.ops)
source.ops->return_block(source.arg, blockp);
blockp->data = NULL;
blockp->len = 0;
blockp->source.ops = NULL;
blockp->source.arg = NULL;
}