message_cache.ml
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module Sliding_message_id_map (C : Gossipsub_intf.AUTOMATON_SUBCONFIG) : sig
(** A data structure containing a mapping from message ids to values of type
['a]. Message ids are grouped by topic and by slot (which is a just an
integer). The grouping by slots is used to remove entries from old slots,
thus it allows to use this data structure as a sliding window. *)
type 'a t
(** [make ~window_size] creates an empty map with window size [window_size].
This means that the values will be removed from the map after [window_size] shifts. *)
val make : window_size:int -> 'a t
(** [add topic message_id ~update_value t] adds an entry to the map for [message_id] with [topic].
[update_value] is used to update the value stored for [message_id]. *)
val add :
C.Topic.t ->
C.Message_id.t ->
update_value:('a option -> 'a option) ->
'a t ->
'a t
(** [update_value message_id f t] updates the value stored for key [message_id]
by applying [f] to the stored value. Returns [None] if no value was stored
for the [message_id], and otherwise returns [Some (t, value)] where [t] is the new map
and [value] is the updated value. *)
val update_value : C.Message_id.t -> ('a -> 'a) -> 'a t -> ('a t * 'a) option
(** [get_value message_id t] returns the value stored for key [message_id].
Returns [None] if nothing is stored. *)
val get_value : C.Message_id.t -> 'a t -> 'a option
(** [get_message_ids ~slots t] returns the [topic] to [message list] mapping
for the past [slots] slots. *)
val get_latest_message_ids :
slots:int -> 'a t -> (Int64.t * C.Message_id.t list C.Topic.Map.t) Seq.t
(** Shifts the sliding window by one slot. *)
val shift : 'a t -> 'a t
module Internal_for_tests : sig
val get_values : 'a t -> (C.Message_id.t * 'a) Seq.t
end
end = struct
module Topic = C.Topic
module Message_id = C.Message_id
(* TODO: https://gitlab.com/tezos/tezos/-/issues/5536
Transform the list into a set? *)
type slot_entry = Message_id.t list Topic.Map.t
(* A slot is just an index, normally a heartbeat tick, and this is why the
same type, namely [Int64], is used. Note that a bigger slot is a more
recent slot. *)
module Map = Map.Make (Int64)
type 'a value_with_counter = {
value : 'a;
store_counter : int;
(* This field is used to count how many times the message has been added to
the map. Normally the caller ensures that the same messages (that is,
with the same id) is not inserted twice; however, this module does not make
this assumption. *)
(* TODO: https://gitlab.com/tezos/tezos/-/issues/5536
Make the above assumption and remove this field? *)
}
type 'a t = {
values_with_counter : 'a value_with_counter Message_id.Map.t;
slot_entries : slot_entry Map.t;
(** The slot entries without the entry for the last slot, which is stored
separately, see next field. *)
latest_slot_entry : slot_entry;
latest_slot : Int64.t;
window_size : int;
}
let make ~window_size =
{
values_with_counter = Message_id.Map.empty;
slot_entries = Map.empty;
latest_slot_entry = Topic.Map.empty;
latest_slot = 0L;
window_size;
}
let add topic message_id ~update_value t =
let latest_slot_entry =
Topic.Map.update
topic
(function
| None -> Some [message_id]
| Some message_ids -> Some (message_id :: message_ids))
t.latest_slot_entry
in
let values_with_counter =
Message_id.Map.update
message_id
(function
| None ->
update_value None
|> Option.map (fun value -> {value; store_counter = 1})
| Some {value; store_counter} ->
update_value (Some value)
|> Option.map (fun value ->
{value; store_counter = store_counter + 1}))
t.values_with_counter
in
{t with latest_slot_entry; values_with_counter}
let update_value message_id f t =
let updated_value = ref None in
let values_with_counter =
Message_id.Map.update
message_id
(function
| None -> None
| Some {value; store_counter} ->
let value = f value in
updated_value := Some value ;
Some {value; store_counter})
t.values_with_counter
in
!updated_value
|> Option.map (fun value -> ({t with values_with_counter}, value))
let get_value message_id t =
Message_id.Map.find message_id t.values_with_counter
|> Option.map (fun {value; _} -> value)
let get_latest_message_ids ~slots t =
let slots =
Map.to_rev_seq t.slot_entries
|> Seq.take ~when_negative_length:() (slots - 1)
|> WithExceptions.Result.get_ok ~loc:__LOC__
in
Seq.cons (t.latest_slot, t.latest_slot_entry) slots
let shift t =
let drop_old_values oldest_entries =
Topic.Map.fold
(fun _topic message_ids messages ->
List.fold_left
(fun messages message_id ->
Message_id.Map.update
message_id
(function
| None -> None
| Some {value; store_counter} ->
if store_counter = 1 then None
else Some {value; store_counter = store_counter - 1})
messages)
messages
message_ids)
oldest_entries
t.values_with_counter
in
let slot_entries =
Map.add t.latest_slot t.latest_slot_entry t.slot_entries
in
let latest_slot = Int64.succ t.latest_slot in
let latest_slot_entry = Topic.Map.empty in
match Map.min_binding slot_entries with
| None -> {t with slot_entries; latest_slot; latest_slot_entry}
| Some (first_slot, entry) ->
if Int64.(sub latest_slot first_slot < of_int t.window_size) then
{
slot_entries;
latest_slot;
latest_slot_entry;
values_with_counter = t.values_with_counter;
window_size = t.window_size;
}
else
{
slot_entries = Map.remove first_slot slot_entries;
latest_slot_entry;
latest_slot;
values_with_counter = drop_old_values entry;
window_size = t.window_size;
}
module Internal_for_tests = struct
let get_values t =
t.values_with_counter |> Message_id.Map.to_seq
|> Seq.map (fun (message_id, {value; store_counter = _}) ->
(message_id, value))
end
end
module Make
(C : Gossipsub_intf.AUTOMATON_SUBCONFIG)
(Time : Gossipsub_intf.TIME) :
Gossipsub_intf.MESSAGE_CACHE
with module Peer = C.Peer
and module Topic = C.Topic
and module Message_id = C.Message_id
and module Message = C.Message
and module Time = Time = struct
module Peer = C.Peer
module Topic = C.Topic
module Message_id = C.Message_id
module Message = C.Message
module Time = Time
module Sliding_message_id_map = Sliding_message_id_map (C)
type message_with_access_counter = {
message : Message.t;
access_counters : int Peer.Map.t;
}
type t = {
gossip_slots : int;
messages : message_with_access_counter Sliding_message_id_map.t;
first_seen_times : Time.t Sliding_message_id_map.t;
}
let create ~history_slots ~gossip_slots ~seen_message_slots =
assert (gossip_slots > 0) ;
assert (gossip_slots <= history_slots) ;
assert (seen_message_slots > 0) ;
{
gossip_slots;
messages = Sliding_message_id_map.make ~window_size:history_slots;
first_seen_times =
Sliding_message_id_map.make ~window_size:seen_message_slots;
}
let add_message message_id message topic t =
let messages =
Sliding_message_id_map.add
topic
message_id
~update_value:(function
| None -> Some {message; access_counters = Peer.Map.empty}
| Some m -> Some m)
t.messages
in
let first_seen_times =
Sliding_message_id_map.add
topic
message_id
~update_value:(function
| None -> Some (Time.now ()) | Some time -> Some time)
t.first_seen_times
in
{t with messages; first_seen_times}
let get_message_for_peer peer message_id t =
let access_count = ref 0 in
let update_result =
Sliding_message_id_map.update_value
message_id
(fun {message; access_counters} ->
let access_counters =
Peer.Map.update
peer
(function
| None ->
access_count := 1 ;
Some !access_count
| Some c ->
access_count := c + 1 ;
Some !access_count)
access_counters
in
{message; access_counters})
t.messages
in
update_result
|> Option.map (fun (messages, {message; access_counters = _}) ->
({t with messages}, message, !access_count))
let get_message_ids_to_gossip topic t =
Sliding_message_id_map.get_latest_message_ids
~slots:t.gossip_slots
t.messages
|> Seq.fold_left
(fun acc_message_ids (_slot, entries) ->
match Topic.Map.find topic entries with
| None -> acc_message_ids
| Some message_ids -> List.rev_append message_ids acc_message_ids)
[]
let get_first_seen_time message_id t =
Sliding_message_id_map.get_value message_id t.first_seen_times
let seen_message message_id t =
Option.is_some
@@ Sliding_message_id_map.get_value message_id t.first_seen_times
let shift t =
{
t with
messages = Sliding_message_id_map.shift t.messages;
first_seen_times = Sliding_message_id_map.shift t.first_seen_times;
}
module Internal_for_tests = struct
let get_access_counters t =
Sliding_message_id_map.Internal_for_tests.get_values t.messages
|> Seq.map (fun (message_id, {access_counters; _}) ->
(message_id, access_counters))
end
end