third_party/grpc/src/core/ext/transport/chttp2/transport/hpack_table.h

/*
 *
 * Copyright 2015 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

#ifndef GRPC_CORE_EXT_TRANSPORT_CHTTP2_TRANSPORT_HPACK_TABLE_H
#define GRPC_CORE_EXT_TRANSPORT_CHTTP2_TRANSPORT_HPACK_TABLE_H

#include <grpc/support/port_platform.h>

#include <grpc/slice.h>
#include "src/core/lib/iomgr/error.h"
#include "src/core/lib/transport/metadata.h"

/* HPACK header table */

/* last index in the static table */
#define GRPC_CHTTP2_LAST_STATIC_ENTRY 61

/* Initial table size as per the spec */
#define GRPC_CHTTP2_INITIAL_HPACK_TABLE_SIZE 4096
/* Maximum table size that we'll use */
#define GRPC_CHTTP2_MAX_HPACK_TABLE_SIZE GRPC_CHTTP2_INITIAL_HPACK_TABLE_SIZE
/* Per entry overhead bytes as per the spec */
#define GRPC_CHTTP2_HPACK_ENTRY_OVERHEAD 32
#if 0
/* Maximum number of entries we could possibly fit in the table, given defined
   overheads */
#define GRPC_CHTTP2_MAX_TABLE_COUNT                                            \
  ((GRPC_CHTTP2_MAX_HPACK_TABLE_SIZE + GRPC_CHTTP2_HPACK_ENTRY_OVERHEAD - 1) / \
   GRPC_CHTTP2_HPACK_ENTRY_OVERHEAD)
#endif

/* hpack decoder table */
typedef struct {
  /* the first used entry in ents */
  uint32_t first_ent;
  /* how many entries are in the table */
  uint32_t num_ents;
  /* the amount of memory used by the table, according to the hpack algorithm */
  uint32_t mem_used;
  /* the max memory allowed to be used by the table, according to the hpack
     algorithm */
  uint32_t max_bytes;
  /* the currently agreed size of the table, according to the hpack algorithm */
  uint32_t current_table_bytes;
  /* Maximum number of entries we could possibly fit in the table, given defined
     overheads */
  uint32_t max_entries;
  /* Number of entries allocated in ents */
  uint32_t cap_entries;
  /* a circular buffer of headers - this is stored in the opposite order to
     what hpack specifies, in order to simplify table management a little...
     meaning lookups need to SUBTRACT from the end position */
  grpc_mdelem* ents;
  grpc_mdelem static_ents[GRPC_CHTTP2_LAST_STATIC_ENTRY];
} grpc_chttp2_hptbl;

/* initialize a hpack table */
void grpc_chttp2_hptbl_init(grpc_chttp2_hptbl* tbl);
void grpc_chttp2_hptbl_destroy(grpc_chttp2_hptbl* tbl);
void grpc_chttp2_hptbl_set_max_bytes(grpc_chttp2_hptbl* tbl,
                                     uint32_t max_bytes);
grpc_error* grpc_chttp2_hptbl_set_current_table_size(grpc_chttp2_hptbl* tbl,
                                                     uint32_t bytes);

/* lookup a table entry based on its hpack index */
grpc_mdelem grpc_chttp2_hptbl_lookup(const grpc_chttp2_hptbl* tbl,
                                     uint32_t index);
/* add a table entry to the index */
grpc_error* grpc_chttp2_hptbl_add(grpc_chttp2_hptbl* tbl,
                                  grpc_mdelem md) GRPC_MUST_USE_RESULT;

size_t grpc_chttp2_get_size_in_hpack_table(grpc_mdelem elem,
                                           bool use_true_binary_metadata);

/* Returns the static hpack table index that corresponds to /a elem. Returns 0
  if /a elem is not statically stored or if it is not in the static hpack
  table */
uint8_t grpc_chttp2_get_static_hpack_table_index(grpc_mdelem md);

/* Find a key/value pair in the table... returns the index in the table of the
   most similar entry, or 0 if the value was not found */
typedef struct {
  uint32_t index;
  int has_value;
} grpc_chttp2_hptbl_find_result;
grpc_chttp2_hptbl_find_result grpc_chttp2_hptbl_find(
    const grpc_chttp2_hptbl* tbl, grpc_mdelem md);

#endif /* GRPC_CORE_EXT_TRANSPORT_CHTTP2_TRANSPORT_HPACK_TABLE_H */