Source file ack.ml

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
(*
 * Copyright (c) 2010 Anil Madhavapeddy <anil@recoil.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *)

open Lwt.Infix

(* General signature for all the ack modules *)
module type M = sig
  type t

  (* ack: put mvar to trigger the transmission of an ack *)
  val t : send_ack:Sequence.t Lwt_mvar.t -> last:Sequence.t -> t

  (* called when new data is received *)
  val receive: t -> Sequence.t -> unit Lwt.t

  (* called when new data is received *)
  val pushack: t -> Sequence.t -> unit Lwt.t

  (* called when an ack is transmitted from elsewhere *)
  val transmit: t -> Sequence.t -> unit Lwt.t
end

(* Transmit ACKs immediately, the dumbest (and simplest) way *)
module Immediate : M = struct

  type t = {
    send_ack: Sequence.t Lwt_mvar.t;
    mutable pushpending: bool;
  }

  let t ~send_ack ~last:_ =
    let pushpending = false in
    {send_ack; pushpending}

  let pushack t ack_number =
    t.pushpending <- true;
    Lwt_mvar.put t.send_ack ack_number

  let receive t ack_number =
    match t.pushpending with
    | true  -> Lwt.return_unit
    | false -> pushack t ack_number

  let transmit t _ =
    t.pushpending <- false;
    Lwt.return_unit
end


(* Delayed ACKs *)
module Delayed (Time:Mirage_time.S) : M = struct

  module TT = Tcptimer.Make(Time)

  type delayed_r = {
    send_ack: Sequence.t Lwt_mvar.t;
    mutable delayedack: Sequence.t;
    mutable delayed: bool;
    mutable pushpending: bool;
  }

  type t = {
    r: delayed_r;
    timer: Tcptimer.t;
  }

  let transmitacknow r ack_number =
    Lwt_mvar.put r.send_ack ack_number

  let transmitack r ack_number =
    match r.pushpending with
    | true  -> Lwt.return_unit
    | false ->
      r.pushpending <- true;
      transmitacknow r ack_number

  let ontimer r s  =
    match r.delayed with
    | false -> Lwt.return Tcptimer.Stoptimer
    | true  ->
      match r.delayedack = s with
      | false ->
        Lwt.return (Tcptimer.Continue r.delayedack)
      | true ->
        r.delayed <- false;
        transmitack r s >>= fun () ->
        Lwt.return Tcptimer.Stoptimer

  let t ~send_ack ~last : t =
    let pushpending = false in
    let delayed = false in
    let delayedack = last in
    let r = {send_ack; delayedack; delayed; pushpending} in
    let expire = ontimer r in
    let period_ns = Duration.of_ms 100 in
    let timer = TT.t ~period_ns ~expire in
    {r; timer}


  (* Advance the received ACK count *)
  let receive t ack_number =
    match t.r.delayed with
    | true ->
      t.r.delayed <- false;
      transmitack t.r ack_number
    | false ->
      t.r.delayed <- true;
      t.r.delayedack <- ack_number;
      TT.start t.timer ack_number


  (* Force out an ACK *)
  let pushack t ack_number =
    transmitacknow t.r ack_number


  (* Indicate that an ACK has been transmitted *)
  let transmit t _ =
    t.r.delayed <- false;
    t.r.pushpending <- false;
    Lwt.return_unit

end