grpc/src/core/ext/transport/chttp2/transport/hpack_encoder.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_ENCODER_H
#define GRPC_CORE_EXT_TRANSPORT_CHTTP2_TRANSPORT_HPACK_ENCODER_H

#include <grpc/support/port_platform.h>

#include <grpc/slice.h>
#include <grpc/slice_buffer.h>
#include "src/core/ext/transport/chttp2/transport/frame.h"
#include "src/core/lib/transport/metadata.h"
#include "src/core/lib/transport/metadata_batch.h"
#include "src/core/lib/transport/transport.h"

// This should be <= 8. We use 6 to save space.
#define GRPC_CHTTP2_HPACKC_NUM_VALUES_BITS 6
#define GRPC_CHTTP2_HPACKC_NUM_VALUES (1 << GRPC_CHTTP2_HPACKC_NUM_VALUES_BITS)
/* initial table size, per spec */
#define GRPC_CHTTP2_HPACKC_INITIAL_TABLE_SIZE 4096
/* maximum table size we'll actually use */
#define GRPC_CHTTP2_HPACKC_MAX_TABLE_SIZE (1024 * 1024)

extern grpc_core::TraceFlag grpc_http_trace;

struct grpc_chttp2_hpack_compressor {
  uint32_t max_table_size;
  uint32_t max_table_elems;
  uint32_t cap_table_elems;
  /** maximum number of bytes we'll use for the decode table (to guard against
      peers ooming us by setting decode table size high) */
  uint32_t max_usable_size;
  /* one before the lowest usable table index */
  uint32_t tail_remote_index;
  uint32_t table_size;
  uint32_t table_elems;
  uint16_t* table_elem_size;
  /** if non-zero, advertise to the decoder that we'll start using a table
      of this size */
  uint8_t advertise_table_size_change;

  /* filter tables for elems: this tables provides an approximate
     popularity count for particular hashes, and are used to determine whether
     a new literal should be added to the compression table or not.
     They track a single integer that counts how often a particular value has
     been seen. When that count reaches max (255), all values are halved. */
  uint32_t filter_elems_sum;
  uint8_t filter_elems[GRPC_CHTTP2_HPACKC_NUM_VALUES];

  /* entry tables for keys & elems: these tables track values that have been
     seen and *may* be in the decompressor table */
  struct {
    struct {
      grpc_mdelem value;
      uint32_t index;
    } entries[GRPC_CHTTP2_HPACKC_NUM_VALUES];
  } elem_table; /* Metadata table management */
  struct {
    struct {
      /* Only store the slice refcount - we do not need the byte buffer or
         length of the slice since we only need to store a mapping between the
         identity of the slice and the corresponding HPACK index. Since the
         slice *must* be static or interned, the refcount is sufficient to
         establish identity. */
      grpc_slice_refcount* value;
      uint32_t index;
    } entries[GRPC_CHTTP2_HPACKC_NUM_VALUES];
  } key_table; /* Key table management */
};

void grpc_chttp2_hpack_compressor_init(grpc_chttp2_hpack_compressor* c);
void grpc_chttp2_hpack_compressor_destroy(grpc_chttp2_hpack_compressor* c);
void grpc_chttp2_hpack_compressor_set_max_table_size(
    grpc_chttp2_hpack_compressor* c, uint32_t max_table_size);
void grpc_chttp2_hpack_compressor_set_max_usable_size(
    grpc_chttp2_hpack_compressor* c, uint32_t max_table_size);

struct grpc_encode_header_options {
  uint32_t stream_id;
  bool is_eof;
  bool use_true_binary_metadata;
  size_t max_frame_size;
  grpc_transport_one_way_stats* stats;
};
void grpc_chttp2_encode_header(grpc_chttp2_hpack_compressor* c,
                               grpc_mdelem** extra_headers,
                               size_t extra_headers_size,
                               grpc_metadata_batch* metadata,
                               const grpc_encode_header_options* options,
                               grpc_slice_buffer* outbuf);

#endif /* GRPC_CORE_EXT_TRANSPORT_CHTTP2_TRANSPORT_HPACK_ENCODER_H */