Source file tx_rollup_gas.ml

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(*****************************************************************************)
(*                                                                           *)
(* Open Source License                                                       *)
(* Copyright (c) 2022 Marigold <contact@marigold.dev>                        *)
(* Copyright (c) 2022 Nomadic Labs <contact@nomadic-labs.com>                *)
(* Copyright (c) 2022 Oxhead Alpha <info@oxhead-alpha.com>                   *)
(*                                                                           *)
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(* Software is furnished to do so, subject to the following conditions:      *)
(*                                                                           *)
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(* in all copies or substantial portions of the Software.                    *)
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(* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,  *)
(* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL   *)
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(* DEALINGS IN THE SOFTWARE.                                                 *)
(*                                                                           *)
(*****************************************************************************)

type error += Tx_rollup_negative_input_size

module S = Saturation_repr

(** The model in {!Michelson_v1_gas.N_IBlake2b}, plus the allocation
    of bytes from {!Storage_functor}. *)
let hash_cost input_size =
  error_unless Compare.Int.(0 <= input_size) Tx_rollup_negative_input_size
  >>? fun () ->
  let ( + ) = S.add in
  let cost_serialization = Gas_limit_repr.alloc_mbytes_cost input_size in
  let v0 = Saturation_repr.safe_int input_size in
  let cost_N_IBlake2b = S.safe_int 430 + v0 + S.shift_right v0 3 in
  let cost_blake2b = Gas_limit_repr.atomic_step_cost cost_N_IBlake2b in
  ok @@ (cost_serialization + cost_blake2b)

(** Model from {!Ticket_costs.Constants.cost_compare_ticket_hash} since they are
    Blake2B hashes too. *)
let compare_blake2b_hash = S.safe_int 10

let check_path_cost element_size path_depth =
  let ( + ) = S.add in
  error_unless Compare.Int.(0 <= path_depth) Tx_rollup_negative_input_size
  >>? fun () ->
  (* We hash the element *)
  hash_cost element_size >>? fun element_hash_cost ->
  (* At each step of the way, we hash 2 hashes together *)
  hash_cost 64 >>? fun hash_cost ->
  let rec acc_hash_cost acc i =
    if Compare.Int.(i <= 0) then acc else acc_hash_cost (hash_cost + acc) (i - 1)
  in

  ok (element_hash_cost + acc_hash_cost compare_blake2b_hash path_depth)

let consume_check_path_inbox_cost ctxt =
  let count_limit = Constants_storage.tx_rollup_max_messages_per_inbox ctxt in
  let max_depth = Merkle_list.max_depth ~count_limit in
  check_path_cost Tx_rollup_prefixes.message_hash.hash_size max_depth
  >>? fun cost -> Raw_context.consume_gas ctxt cost

let consume_check_path_commitment_cost ctxt =
  let count_limit = Constants_storage.tx_rollup_max_messages_per_inbox ctxt in
  let max_depth = Merkle_list.max_depth ~count_limit in
  check_path_cost Tx_rollup_prefixes.message_result_hash.hash_size max_depth
  >>? fun cost -> Raw_context.consume_gas ctxt cost

(** As generated by the model [inbox_add_message_codegen] in
    [lib_benchmarks_proto/tx_rollup_benchmarks.ml]. *)
let model_inbox_add_message_codegen inbox_length =
  (* We assume that the Merkle_tree implementation computes a tree
     whose depth is logarithmic in the number of leaves. The cost of
     inserting an element in this structure, in the worst case, is the
     cost of hashing the element and hashing the concatenation of two
     elements at each level in the tree, that is:

       cost_of_hashing(32 bytes) + log2(inbox_length) *
          inbox_max_length * cost_of_hashing(32 bytes + 32 bytes)

     This cost is captured by the following cost function which is
     inferred emperically through the benchmark & model mentioned
     above. *)
  let log2 n = S.safe_int (1 + S.numbits n) in
  S.mul (S.safe_int 445) (log2 (S.safe_int inbox_length))

let consume_add_message_cost ctxt =
  let max_messages_per_inbox =
    Constants_storage.tx_rollup_max_messages_per_inbox ctxt
  in
  (* as a safe, constant, over-approximation, suppose the inbox is
     the maximum size allowed *)
  let cost = model_inbox_add_message_codegen max_messages_per_inbox in
  Raw_context.consume_gas ctxt cost

(** As generated by the model [model_commitment_full_compact] in
    [lib_benchmarks_proto/tx_rollup_benchmarks.ml]. We add one to
    [inbox_length] so that the cost is never zero. *)
let model_commitment_full_compact inbox_length =
  S.mul (S.safe_int 915) (S.safe_int (1 + inbox_length))

let consume_compact_commitment_cost ctxt inbox_length =
  let cost = model_commitment_full_compact inbox_length in
  Raw_context.consume_gas ctxt cost

let hash ~hash_f ctxt encoding input =
  match Data_encoding.Binary.to_bytes_opt encoding input with
  | Some buffer ->
      let len = Bytes.length buffer in
      hash_cost len >>? fun cost ->
      Raw_context.consume_gas ctxt cost >>? fun ctxt ->
      ok (ctxt, hash_f [buffer])
  | None ->
      error
        (Tx_rollup_errors_repr.Internal_error
           "Cannot serialize input to hash function")

let () =
  let open Data_encoding in
  (* Tx_rollup_negative_message_size *)
  register_error_kind
    `Permanent
    ~id:"tx_rollup_negative_input_size"
    ~title:
      "The protocol has computed a negative size for the input of a hash \
       function"
    ~description:
      "The protocol has computed a negative size for the input of a hash \
       function. This is an internal error, and denotes a bug in the protocol \
       implementation."
    unit
    (function Tx_rollup_negative_input_size -> Some () | _ -> None)
    (fun () -> Tx_rollup_negative_input_size)