hpack_table.h

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 *
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#ifndef GRPC_INTERNAL_CORE_TRANSPORT_CHTTP2_HPACK_TABLE_H
#define GRPC_INTERNAL_CORE_TRANSPORT_CHTTP2_HPACK_TABLE_H

#include "src/core/transport/metadata.h"
#include <grpc/support/port_platform.h>
#include <grpc/support/slice.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
/* 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)

/* hpack decoder table */
typedef struct {
  grpc_mdctx *mdctx;
  /* the first used entry in ents */
  gpr_uint16 first_ent;
  /* the last used entry in ents */
  gpr_uint16 last_ent;
  /* how many entries are in the table */
  gpr_uint16 num_ents;
  /* the amount of memory used by the table, according to the hpack algorithm */
  gpr_uint16 mem_used;
  /* the max memory allowed to be used by the table, according to the hpack
     algorithm */
  gpr_uint16 max_bytes;
  /* 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_CHTTP2_MAX_TABLE_COUNT];
  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, grpc_mdctx *mdctx);
void grpc_chttp2_hptbl_destroy(grpc_chttp2_hptbl *tbl);

/* lookup a table entry based on its hpack index */
grpc_mdelem *grpc_chttp2_hptbl_lookup(const grpc_chttp2_hptbl *tbl,
                                      gpr_uint32 index);
/* add a table entry to the index */
void grpc_chttp2_hptbl_add(grpc_chttp2_hptbl *tbl, 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 {
  gpr_uint16 index;
  gpr_uint8 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_INTERNAL_CORE_TRANSPORT_CHTTP2_HPACK_TABLE_H */