(*
 * Copyright (c) 2013-2015 David Sheets <sheets@alum.mit.edu>
 *
 * 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.
 *
 *)

exception Parse_error of string * string

type scope = Point | Interface | Link | Admin | Site | Organization | Global

let try_with_result fn a =
  try Ok (fn a) with Parse_error (msg, _) -> Error (`Msg ("Ipaddr: " ^ msg))

let failwith_msg = function Ok x -> x | Error (`Msg m) -> failwith m

let string_of_scope = function
  | Point -> "point"
  | Interface -> "interface"
  | Link -> "link"
  | Admin -> "admin"
  | Site -> "site"
  | Organization -> "organization"
  | Global -> "global"

let scope_of_string = function
  | "point" -> Ok Point
  | "interface" -> Ok Interface
  | "link" -> Ok Link
  | "admin" -> Ok Admin
  | "site" -> Ok Site
  | "organization" -> Ok Organization
  | "global" -> Ok Global
  | s -> Error (`Msg ("unknown scope: " ^ s))

let pp_scope fmt s = Format.pp_print_string fmt (string_of_scope s)
let ( ~| ) = Int32.of_int
let ( |~ ) = Int32.to_int
let ( &&& ) x y = Int32.logand x y
let ( ||| ) x y = Int32.logor x y
let ( <|< ) x y = Int32.shift_left x y
let ( >|> ) x y = Int32.shift_right_logical x y
let ( >! ) x y = x >|> y &&& 0xFF_l
let ( <! ) x y = x &&& 0xFF_l <|< y
let need_more x = Parse_error ("not enough data", x)
let char_0 = int_of_char '0'
let char_a = int_of_char 'a'
let char_A = int_of_char 'A'

let int_of_char c =
  match c with
  | '0' .. '9' -> Stdlib.int_of_char c - char_0
  | 'a' .. 'f' -> 10 + Stdlib.int_of_char c - char_a
  | 'A' .. 'F' -> 10 + Stdlib.int_of_char c - char_A
  | _ -> -1

let bad_char i s =
  let msg = Printf.sprintf "invalid character '%c' at %d" s.[i] i in
  Parse_error (msg, s)

let octal_notation s =
  let msg = Printf.sprintf "octal notation disallowed" in
  Parse_error (msg, s)

let is_number base n = n >= 0 && n < base

let parse_int base s i =
  let len = String.length s in
  let rec next prev =
    let j = !i in
    if j >= len then prev
    else
      let c = s.[j] in
      let k = int_of_char c in
      if is_number base k then (
        incr i;
        next ((prev * base) + k))
      else prev
  in
  let i = !i in
  if i < len then
    if is_number base (int_of_char s.[i]) then next 0 else raise (bad_char i s)
  else raise (need_more s)

let parse_dec_int s i = parse_int 10 s i
let parse_hex_int s i = parse_int 16 s i

let expect_char s i c =
  if !i < String.length s then
    if s.[!i] <> c then raise (bad_char !i s) else incr i
  else raise (need_more s)

let expect_end s i = if String.length s <= !i then () else raise (bad_char !i s)

let reject_octal s i =
  if !i + 1 < String.length s then
    if s.[!i] == '0' && is_number 10 (int_of_char s.[!i + 1]) then
      raise (octal_notation s)

module V4 = struct
  type t = int32

  let compare = Int32.unsigned_compare
  let make a b c d = ~|a <! 24 ||| (~|b <! 16) ||| (~|c <! 8 ||| (~|d <! 0))

  (* parsing *)

  let parse_dotted_quad s i =
    reject_octal s i;
    let a = parse_dec_int s i in
    expect_char s i '.';
    reject_octal s i;
    let b = parse_dec_int s i in
    expect_char s i '.';
    reject_octal s i;
    let c = parse_dec_int s i in
    expect_char s i '.';
    reject_octal s i;
    let d = parse_dec_int s i in
    let valid a = a land 0xff <> a in
    if valid a then raise (Parse_error ("first octet out of bounds", s))
    else if valid b then raise (Parse_error ("second octet out of bounds", s))
    else if valid c then raise (Parse_error ("third octet out of bounds", s))
    else if valid d then raise (Parse_error ("fourth octet out of bounds", s))
    else make a b c d

  (* string conversion *)

  let of_string_raw = parse_dotted_quad

  let of_string_exn s =
    let o = ref 0 in
    let x = of_string_raw s o in
    expect_end s o;
    x

  let of_string s = try_with_result of_string_exn s

  let with_port_of_string ~default s =
    try
      let len = String.length s and o = ref 0 in
      let ipv4 = of_string_raw s o in
      if !o < len && s.[!o] = ':' then (
        incr o;
        let port = parse_dec_int s o in
        expect_end s o;
        Ok (ipv4, port))
      else (
        expect_end s o;
        Ok (ipv4, default))
    with Parse_error (msg, _) -> Error (`Msg ("Ipaddr: " ^ msg))

  let to_buffer b i =
    Printf.bprintf b "%ld.%ld.%ld.%ld" (i >! 24) (i >! 16) (i >! 8) (i >! 0)

  let to_string i =
    let b = Buffer.create 15 in
    to_buffer b i;
    Buffer.contents b

  let pp ppf i = Format.fprintf ppf "%s" (to_string i)

  (* Octets conversion *)

  let of_octets_exn ?(off = 0) bs =
    try
      make
        (Char.code bs.[0 + off])
        (Char.code bs.[1 + off])
        (Char.code bs.[2 + off])
        (Char.code bs.[3 + off])
    with _ -> raise (need_more bs)

  let of_octets ?off bs = try_with_result (of_octets_exn ?off) bs

  let write_octets_exn ?(off = 0) i b =
    try
      Bytes.set b (0 + off) (Char.chr (( |~ ) (i >! 24)));
      Bytes.set b (1 + off) (Char.chr (( |~ ) (i >! 16)));
      Bytes.set b (2 + off) (Char.chr (( |~ ) (i >! 8)));
      Bytes.set b (3 + off) (Char.chr (( |~ ) (i >! 0)))
    with _ -> raise (need_more (Bytes.to_string b))

  let write_octets ?off i bs = try_with_result (write_octets_exn ?off i) bs

  let to_octets i =
    String.init 4 (function
      | 0 -> Char.chr (( |~ ) (i >! 24))
      | 1 -> Char.chr (( |~ ) (i >! 16))
      | 2 -> Char.chr (( |~ ) (i >! 8))
      | 3 -> Char.chr (( |~ ) (i >! 0))
      | _ -> assert false)

  (* Int32 *)
  let of_int32 i = i
  let to_int32 i = i

  (* Int16 *)
  let of_int16 (a, b) = ~|a <|< 16 ||| ~|b
  let to_int16 a = (( |~ ) (a >|> 16), ( |~ ) (a &&& 0xFF_FF_l))

  (* MAC *)
  (* {{:http://tools.ietf.org/html/rfc1112#section-6.2}RFC 1112}. *)
  let multicast_to_mac i =
    let macb = Bytes.create 6 in
    Bytes.set macb 0 (Char.chr 0x01);
    Bytes.set macb 1 (Char.chr 0x00);
    Bytes.set macb 2 (Char.chr 0x5E);
    Bytes.set macb 3 (Char.chr (( |~ ) (i >|> 16 &&& 0x7F_l)));
    Bytes.set macb 4 (Char.chr (( |~ ) (i >! 8)));
    Bytes.set macb 5 (Char.chr (( |~ ) (i >! 0)));
    Macaddr.of_octets_exn (Bytes.to_string macb)

  (* Host *)
  let to_domain_name i =
    let name =
      [
        Int32.to_string (i >! 0);
        Int32.to_string (i >! 8);
        Int32.to_string (i >! 16);
        Int32.to_string (i >! 24);
        "in-addr";
        "arpa";
      ]
    in
    Domain_name.(host_exn (of_strings_exn name))

  let of_domain_name n =
    match Domain_name.to_strings n with
    | [ a; b; c; d; in_addr; arpa ]
      when Domain_name.(
             equal_label arpa "arpa" && equal_label in_addr "in-addr") -> (
        let conv bits data =
          let i = Int32.of_int (parse_dec_int data (ref 0)) in
          if i > 0xFFl then
            raise (Parse_error ("label with a too big number", data))
          else i <! bits
        in
        try
          let ( + ) = Int32.add in
          Some (conv 0 a + conv 8 b + conv 16 c + conv 24 d)
        with Parse_error _ -> None)
    | _ -> None

  let succ t =
    if Int32.equal t 0xFF_FF_FF_FFl then
      Error (`Msg "Ipaddr: highest address has been reached")
    else Ok (Int32.succ t)

  let pred t =
    if Int32.equal t 0x00_00_00_00l then
      Error (`Msg "Ipaddr: lowest address has been reached")
    else Ok (Int32.pred t)

  (* constant *)

  let any = make 0 0 0 0
  let unspecified = make 0 0 0 0
  let broadcast = make 255 255 255 255
  let localhost = make 127 0 0 1
  let nodes = make 224 0 0 1
  let routers = make 224 0 0 2

  module Prefix = struct
    type addr = t
    type t = addr * int

    let compare (pre, sz) (pre', sz') =
      let c = compare pre pre' in
      if c = 0 then Stdlib.compare sz sz' else c

    let ip = make

    let mask sz =
      if sz <= 0 then 0_l
      else if sz >= 32 then 0x0_FF_FF_FF_FF_l
      else 0x0_FF_FF_FF_FF_l <|< 32 - sz

    let prefix (pre, sz) = (pre &&& mask sz, sz)
    let make sz pre = (pre, sz)

    let network_address (pre, sz) addr =
      pre &&& mask sz ||| (addr &&& Int32.lognot (mask sz))

    (* string conversion *)

    let _of_string_raw s i =
      let quad = of_string_raw s i in
      expect_char s i '/';
      let p = parse_dec_int s i in
      if p > 32 || p < 0 then raise (Parse_error ("invalid prefix size", s));
      (p, quad)

    let of_string_raw s i =
      let p, quad = _of_string_raw s i in
      make p quad

    let _of_string_exn s =
      let i = ref 0 in
      let res = _of_string_raw s i in
      expect_end s i;
      res

    let of_string_exn s =
      let p, quad = _of_string_exn s in
      make p quad

    let of_string s = try_with_result of_string_exn s

    let _of_netmask_exn ~netmask address =
      let rec find_greatest_one bits i =
        if bits = 0_l then i - 1 else find_greatest_one (bits >|> 1) (i + 1)
      in
      let one = netmask &&& Int32.neg netmask in
      let sz = 32 - find_greatest_one one (if one = 0_l then 33 else 0) in
      if netmask <> mask sz then
        raise (Parse_error ("invalid netmask", to_string netmask))
      else make sz address

    let of_netmask_exn ~netmask ~address = _of_netmask_exn ~netmask address

    let of_netmask ~netmask ~address =
      try_with_result (_of_netmask_exn ~netmask) address

    let to_buffer buf (pre, sz) = Printf.bprintf buf "%a/%d" to_buffer pre sz

    let to_string subnet =
      let b = Buffer.create 18 in
      to_buffer b subnet;
      Buffer.contents b

    let pp ppf i = Format.fprintf ppf "%s" (to_string i)

    let mem ip (pre, sz) =
      let m = mask sz in
      ip &&& m = (pre &&& m)

    let subset ~subnet:(pre1, sz1) ~network:(pre2, sz2) =
      sz1 >= sz2 && mem pre1 (pre2, sz2)

    let of_addr ip = make 32 ip
    let global = make 0 (ip 0 0 0 0)
    let relative = make 8 (ip 0 0 0 0)
    let loopback = make 8 (ip 127 0 0 0)
    let link = make 16 (ip 169 254 0 0)
    let multicast = make 4 (ip 224 0 0 0)
    let multicast_org = make 14 (ip 239 192 0 0)
    let multicast_admin = make 16 (ip 239 255 0 0)
    let multicast_link = make 24 (ip 224 0 0 0)

    (* http://tools.ietf.org/html/rfc2365 *)

    let private_10 = make 8 (ip 10 0 0 0)
    let private_172 = make 12 (ip 172 16 0 0)
    let private_192 = make 16 (ip 192 168 0 0)

    let private_blocks =
      [ loopback; link; private_10; private_172; private_192 ]

    let broadcast (pre, sz) =
      Int32.logor pre (Int32.logxor (mask sz) 0xFF_FF_FF_FFl)

    let network (pre, sz) = pre &&& mask sz
    let address (addr, _) = addr
    let bits (_, sz) = sz
    let netmask subnet = mask (bits subnet)
    let hostmask cidr = Int32.logxor (netmask cidr) 0xFF_FF_FF_FFl

    let first ((_, sz) as cidr) =
      if sz > 30 then network cidr else network cidr |> succ |> failwith_msg

    let last ((_, sz) as cidr) =
      if sz > 30 then broadcast cidr else broadcast cidr |> pred |> failwith_msg

    let hosts ?(usable = true) ((_, sz) as cidr) =
      let rec iter_seq start stop =
        if compare (start, 32) (stop, 32) > 0 then Seq.Nil
        else
          match succ start with
          | Ok start_succ -> Seq.Cons (start, fun () -> iter_seq start_succ stop)
          | Error _ -> Seq.Cons (start, fun () -> Seq.Nil)
      in
      if usable && sz = 32 then fun () -> Seq.Nil
      else
        let start, stop =
          if usable then (first cidr, last cidr)
          else (network cidr, broadcast cidr)
        in
        fun () -> iter_seq start stop

    let subnets n ((_, sz) as cidr) =
      let rec iter_seq start stop steps =
        if compare (start, 32) (stop, 32) > 0 then Seq.Nil
        else
          let prefix = make n start in
          let start_succ = Int32.add start steps in
          if start_succ = 0l then Seq.Cons (prefix, fun () -> Seq.Nil)
          else Seq.Cons (prefix, fun () -> iter_seq start_succ stop steps)
      in
      if sz > n || n > 32 then fun () -> Seq.Nil
      else
        let start = network cidr in
        let stop = broadcast cidr in
        let steps = Int32.add (hostmask cidr) 1l >|> n - sz in
        fun () -> iter_seq start stop steps
  end

  (* TODO: this could be optimized with something trie-like *)
  let scope i =
    let mem = Prefix.mem i in
    if mem Prefix.loopback then Interface
    else if mem Prefix.link then Link
    else if List.exists mem Prefix.private_blocks then Organization
    else if i = unspecified then Point
    else if i = broadcast then Admin
    else if mem Prefix.relative then Admin
    else if mem Prefix.multicast then
      if mem Prefix.multicast_org then Organization
      else if mem Prefix.multicast_admin then Admin
      else if mem Prefix.multicast_link then Link
      else Global
    else Global

  let is_global i = scope i = Global
  let is_multicast i = Prefix.(mem i multicast)
  let is_private i = scope i <> Global

  module Set = Set.Make (struct
    type nonrec t = t

    let compare (a : t) (b : t) = compare a b
  end)

  module Map = Map.Make (struct
    type nonrec t = t

    let compare (a : t) (b : t) = compare a b
  end)
end

module S128 : sig
  exception Overflow

  type t

  val zero : t [@@ocaml.warning "-32"]
  val max_int : t
  val compare : t -> t -> int
  val equal : t -> t -> bool
  val fold_left : ('a -> int -> 'a) -> 'a -> t -> 'a
  val of_octets_exn : string -> t
  val to_octets : t -> string
  val of_int64 : int64 * int64 -> t
  val to_int64 : t -> int64 * int64
  val of_int32 : int32 * int32 * int32 * int32 -> t
  val to_int32 : t -> int32 * int32 * int32 * int32
  val of_int16 : int * int * int * int * int * int * int * int -> t
  val to_int16 : t -> int * int * int * int * int * int * int * int
  val add_exn : t -> t -> t [@@ocaml.warning "-32"]
  val pred_exn : t -> t [@@ocaml.warning "-32"]
  val add : t -> t -> t option
  val logand : t -> t -> t
  val logor : t -> t -> t
  val logxor : t -> t -> t
  val lognot : t -> t

  module Byte : sig
    val get_lsbits : int -> int -> int [@@ocaml.warning "-32"]
    val get_msbits : int -> int -> int [@@ocaml.warning "-32"]
    val set_msbits : int -> int -> int -> int [@@ocaml.warning "-32"]
    val fold_left : ('a -> bool -> 'a) -> 'a -> int -> 'a
  end

  val shift_right : t -> int -> t
  val shift_left : t -> int -> t
  val write_octets_exn : ?off:int -> t -> bytes -> unit
  val succ_exn : t -> t
  val succ : t -> (t, [> `Msg of string ]) result
  val pred : t -> (t, [> `Msg of string ]) result
end = struct
  exception Overflow

  type t = string

  let mk_zero () = Bytes.make 16 '\x00'
  let zero = Bytes.unsafe_to_string (mk_zero ())
  let max_int = String.make 16 '\xff'
  let compare = String.compare
  let equal = String.equal

  let fold_left f init s =
    (* With OCaml>=4.13.0:
       [String.fold_left (fun acc c -> f acc (Char.code c)) init s] *)
    let a = ref init in
    for i = 0 to 15 do
      a := f !a (Char.code (String.get s i))
    done;
    !a

  let iteri_right2 f x y =
    for i = 15 downto 0 do
      let x' = Char.code (String.get x i) in
      let y' = Char.code (String.get y i) in
      f i x' y'
    done

  let of_octets_exn s =
    if String.length s <> 16 then invalid_arg "not 16 bytes long";
    s

  let to_octets = Fun.id

  let of_int64 (a, b) =
    let b' = mk_zero () in
    Bytes.set_int64_be b' 0 a;
    Bytes.set_int64_be b' 8 b;
    Bytes.unsafe_to_string b'

  let to_int64 s =
    (* with OCaml>=4.13, use String.get_int64_be *)
    let b = Bytes.unsafe_of_string s in
    (Bytes.get_int64_be b 0, Bytes.get_int64_be b 8)

  let of_int32 (a, b, c, d) =
    let b' = mk_zero () in
    Bytes.set_int32_be b' 0 a;
    Bytes.set_int32_be b' 4 b;
    Bytes.set_int32_be b' 8 c;
    Bytes.set_int32_be b' 12 d;
    Bytes.unsafe_to_string b'

  let to_int32 s =
    (* with OCaml>=4.13, use String.get_int32_be *)
    let b = Bytes.unsafe_of_string s in
    ( Bytes.get_int32_be b 0,
      Bytes.get_int32_be b 4,
      Bytes.get_int32_be b 8,
      Bytes.get_int32_be b 12 )

  let of_int16 (a, b, c, d, e, f, g, h) =
    let b' = mk_zero () in
    Bytes.set_uint16_be b' 0 a;
    Bytes.set_uint16_be b' 2 b;
    Bytes.set_uint16_be b' 4 c;
    Bytes.set_uint16_be b' 6 d;
    Bytes.set_uint16_be b' 8 e;
    Bytes.set_uint16_be b' 10 f;
    Bytes.set_uint16_be b' 12 g;
    Bytes.set_uint16_be b' 14 h;
    Bytes.unsafe_to_string b'

  let to_int16 s =
    (* with OCaml>=4.13, use String.get_uint16_be *)
    let b = Bytes.unsafe_of_string s in
    ( Bytes.get_uint16_be b 0,
      Bytes.get_uint16_be b 2,
      Bytes.get_uint16_be b 4,
      Bytes.get_uint16_be b 6,
      Bytes.get_uint16_be b 8,
      Bytes.get_uint16_be b 10,
      Bytes.get_uint16_be b 12,
      Bytes.get_uint16_be b 14 )

  let add_exn x y =
    let b = mk_zero () in
    let carry = ref 0 in
    iteri_right2
      (fun i x' y' ->
        let sum = x' + y' + !carry in
        if sum >= 256 then (
          carry := 1;
          Bytes.set_uint8 b i (sum - 256))
        else (
          carry := 0;
          Bytes.set_uint8 b i sum))
      x y;
    if !carry <> 0 then raise Overflow else Bytes.unsafe_to_string b

  let add x y = try Some (add_exn x y) with Overflow -> None

  let pred_exn x =
    if equal x zero then raise Overflow;
    let b = Bytes.of_string x in
    let rec go i =
      Bytes.set_uint8 b i (Char.code (String.get x i) - 1);
      if Char.code (String.get x i) = 0 then go (Stdlib.pred i)
    in
    go 15;
    Bytes.unsafe_to_string b

  let logand x y =
    let b = mk_zero () in
    iteri_right2 (fun i x y -> Bytes.set_uint8 b i (x land y)) x y;
    Bytes.unsafe_to_string b

  let logor x y =
    let b = mk_zero () in
    iteri_right2 (fun i x y -> Bytes.set_uint8 b i (x lor y)) x y;
    Bytes.unsafe_to_string b

  let logxor x y =
    let b = mk_zero () in
    iteri_right2 (fun i x y -> Bytes.set_uint8 b i (x lxor y)) x y;
    Bytes.unsafe_to_string b

  let lognot x =
    let b = mk_zero () in
    String.iteri
      (fun i _ -> Bytes.set_uint8 b i (lnot (Char.code (String.get x i))))
      x;
    Bytes.unsafe_to_string b

  module Byte = struct
    (* Extract the [n] least significant bits from [i] *)
    let get_lsbits n i =
      if n <= 0 || n > 8 then invalid_arg "out of bounds";
      i land ((1 lsl n) - 1)

    (* Extract the [n] most significant bits from [i] *)
    let get_msbits n i =
      if n <= 0 || n > 8 then invalid_arg "out of bounds";
      (i land (255 lsl (8 - n))) lsr (8 - n)

    (* Set value [x] in [i]'s [n] most significant bits *)
    let set_msbits n x i =
      if n < 0 || n > 8 then raise (Invalid_argument "n must be >= 0 && <= 8")
      else if n = 0 then i
      else if n = 8 then x
      else (x lsl (8 - n)) lor i

    (* set bits are represented as true *)
    let fold_left f a i =
      let bitmask = ref 0b1000_0000 in
      let a' = ref a in
      for _ = 0 to 7 do
        a' := f !a' (i land !bitmask > 0);
        bitmask := !bitmask lsr 1
      done;
      !a'
  end

  let shift_right x n =
    match n with
    | 0 -> x
    | 128 -> zero
    | n when n > 0 && n < 128 ->
        let b = mk_zero () in
        let shift_bytes, shift_bits = (n / 8, n mod 8) in
        (if shift_bits = 0 then
           Bytes.blit_string x 0 b shift_bytes (16 - shift_bytes)
         else
           let carry = ref 0 in
           for i = 0 to 15 - shift_bytes do
             let x' = Char.code (String.get x i) in
             let new_carry = Byte.get_lsbits shift_bits x' in
             let shifted_value = x' lsr shift_bits in
             let new_value = Byte.set_msbits shift_bits !carry shifted_value in
             Bytes.set_uint8 b (i + shift_bytes) new_value;
             carry := new_carry
           done);
        Bytes.unsafe_to_string b
    | _ -> raise (Invalid_argument "n must be >= 0 && <= 128")

  let shift_left x n =
    match n with
    | 0 -> x
    | 128 -> zero
    | n when n > 0 && n < 128 ->
        let b = mk_zero () in
        let shift_bytes, shift_bits = (n / 8, n mod 8) in
        (if shift_bits = 0 then
           Bytes.blit_string x shift_bytes b 0 (16 - shift_bytes)
         else
           let carry = ref 0 in
           for i = 15 downto 0 + shift_bytes do
             let x' = Char.code (String.get x i) in
             let new_carry = Byte.get_msbits shift_bits x' in
             let shifted_value = x' lsl shift_bits in
             let new_value = shifted_value lor !carry in
             Bytes.set_uint8 b (i - shift_bytes) new_value;
             carry := new_carry
           done);
        Bytes.unsafe_to_string b
    | _ -> raise (Invalid_argument "n must be >= 0 && <= 128")

  let write_octets_exn ?(off = 0) s dest =
    if Bytes.length dest - off < 16 then
      raise (Parse_error ("larger including offset than target bytes", s))
    else Bytes.blit_string s 0 dest off (String.length s)

  let succ_exn x = add_exn x (of_int64 (0L, 1L))

  let succ x =
    try Ok (succ_exn x)
    with Overflow -> Error (`Msg "Ipaddr: highest address has been reached")

  let pred x =
    try Ok (pred_exn x)
    with Overflow | Invalid_argument _ ->
      Error (`Msg "Ipaddr: lowest address has been reached")
end

module V6 = struct
  include S128

  let make a b c d e f g h = of_int16 (a, b, c, d, e, f, g, h)

  (* parsing *)
  let parse_ipv6 s i =
    let compressed = ref false in
    (* :: *)
    let len = String.length s in
    if len < !i + 1 then raise (need_more s);
    let use_bracket = s.[!i] = '[' in
    if use_bracket then incr i;
    if len < !i + 2 then raise (need_more s);
    (* check if it starts with :: *)
    let l =
      if s.[!i] = ':' then (
        incr i;
        if s.[!i] = ':' then (
          compressed := true;
          incr i;
          [ -1 ])
        else raise (bad_char !i s))
      else []
    in

    let rec loop nb acc =
      if nb >= 8 then acc
      else if !i >= len then acc
      else
        let pos = !i in
        let x = try parse_hex_int s i with _ -> -1 in
        if x < 0 then acc
        else if nb = 7 then x :: acc
        else if !i < len && s.[!i] = ':' then (
          incr i;
          if !i < len then
            if s.[!i] = ':' then
              if !compressed then (
                decr i;
                x :: acc (* trailing :: *))
              else (
                compressed := true;
                incr i;
                loop (nb + 2) (-1 :: x :: acc))
            else if is_number 16 (int_of_char s.[!i]) then
              loop (nb + 1) (x :: acc)
            else raise (bad_char !i s)
          else raise (need_more s))
        else if !i < len && s.[!i] = '.' then (
          i := pos;
          let v4 = V4.of_string_raw s i in
          let hi, lo = V4.to_int16 v4 in
          lo :: hi :: acc)
        else x :: acc
    in

    let res = loop (List.length l) l in
    let res_len = List.length res in
    if res_len > 8 then raise (Parse_error ("too many components", s))
    else if res_len = 0 then raise (need_more s)
    else
      let a = Array.make 8 0 in
      let missing =
        if !compressed then 8 - (res_len - 1)
        else if res_len <> 8 then
          if !i < len then raise (bad_char !i s) else raise (need_more s)
        else 0
      in
      let _ =
        List.fold_left
          (fun i x ->
            if x = -1 then i - missing
            else (
              if x land 0xffff <> x then
                raise
                  (Parse_error (Printf.sprintf "component %d out of bounds" i, s));
              a.(i) <- x;
              i - 1))
          7 res
      in
      if use_bracket then expect_char s i ']';
      a

  (* string conversion *)

  let of_string_raw s offset =
    let a = parse_ipv6 s offset in
    make a.(0) a.(1) a.(2) a.(3) a.(4) a.(5) a.(6) a.(7)

  let of_string_exn s =
    let o = ref 0 in
    let x = of_string_raw s o in
    expect_end s o;
    x

  let of_string s = try_with_result of_string_exn s

  let with_port_of_string ~default s =
    let len = String.length s and o = ref 0 in
    try
      let ipv6 = of_string_raw s o in
      if !o < len && s.[!o] = ':' then (
        incr o;
        let port = parse_dec_int s o in
        expect_end s o;
        Ok (ipv6, port))
      else (
        expect_end s o;
        Ok (ipv6, default))
    with Parse_error (msg, _) -> Error (`Msg ("Ipaddr: " ^ msg))

  (* http://tools.ietf.org/html/rfc5952 *)
  let to_buffer buf addr =
    let ((a, b, c, d, e, f, g, h) as comp) = to_int16 addr in

    let v4 =
      match comp with 0, 0, 0, 0, 0, 0xffff, _, _ -> true | _ -> false
    in

    let rec loop elide zeros acc = function
      | 0 :: xs -> loop elide (zeros - 1) acc xs
      | n :: xs when zeros = 0 -> loop elide 0 (n :: acc) xs
      | n :: xs -> loop (min elide zeros) 0 (n :: zeros :: acc) xs
      | [] ->
          let elide = min elide zeros in
          ( (if elide < -1 then Some elide else None),
            if zeros = 0 then acc else zeros :: acc )
    in

    let elide, l = loop 0 0 [] [ h; g; f; e; d; c; b; a ] in
    assert (match elide with Some x when x < -8 -> false | _ -> true);

    let rec cons_zeros l x =
      if x >= 0 then l else cons_zeros (Some 0 :: l) (x + 1)
    in

    let _, lrev =
      List.fold_left
        (fun (patt, l) x ->
          if Some x = patt then (None, None :: l)
          else if x < 0 then (patt, cons_zeros l x)
          else (patt, Some x :: l))
        (elide, []) l
    in

    let rec fill = function
      | [ Some hi; Some lo ] when v4 ->
          let addr = V4.of_int16 (hi, lo) in
          V4.to_buffer buf addr
      | None :: xs ->
          Buffer.add_string buf "::";
          fill xs
      | [ Some n ] -> Printf.bprintf buf "%x" n
      | Some n :: None :: xs ->
          Printf.bprintf buf "%x::" n;
          fill xs
      | Some n :: xs ->
          Printf.bprintf buf "%x:" n;
          fill xs
      | [] -> ()
    in
    fill (List.rev lrev)

  let to_string l =
    let buf = Buffer.create 39 in
    to_buffer buf l;
    Buffer.contents buf

  let pp ppf i = Format.fprintf ppf "%s" (to_string i)

  (* byte conversion *)

  let of_octets_exn ?(off = 0) bs =
    if String.length bs - off < 16 then raise (need_more bs)
    else S128.of_octets_exn (String.sub bs off 16)

  let of_octets ?off bs = try_with_result (of_octets_exn ?off) bs
  let write_octets ?off i bs = try_with_result (write_octets_exn ?off i) bs
  let to_octets = S128.to_octets

  (* MAC *)
  (* {{:https://tools.ietf.org/html/rfc2464#section-7}RFC 2464}. *)
  let multicast_to_mac s =
    let macb = Bytes.make 6 (Char.chr 0x33) in
    Bytes.blit_string (S128.to_octets s) 12 macb 2 4;
    Macaddr.of_octets_exn (Bytes.to_string macb)

  (* Host *)
  let to_domain_name b =
    let hexstr_of_int = Printf.sprintf "%x" in
    let name =
      S128.fold_left
        (fun acc b ->
          let x = hexstr_of_int (b land ((1 lsl 4) - 1)) in
          let y = hexstr_of_int (b lsr 4) in
          x :: y :: acc)
        [ "ip6"; "arpa" ] b
    in
    Domain_name.(host_exn (of_strings_exn name))

  let of_domain_name n =
    let int_of_char_string = function
      | "0" -> 0
      | "1" -> 1
      | "2" -> 2
      | "3" -> 3
      | "4" -> 4
      | "5" -> 5
      | "6" -> 6
      | "7" -> 7
      | "8" -> 8
      | "9" -> 9
      | "a" -> 10
      | "b" -> 11
      | "c" -> 12
      | "d" -> 13
      | "e" -> 14
      | "f" -> 15
      | _ -> failwith "int_of_char_string: invalid hexadecimal string"
    in
    let labels = Domain_name.to_array n in
    if
      Array.length labels = 34
      && Domain_name.equal_label labels.(0) "arpa"
      && Domain_name.equal_label labels.(1) "ip6"
    then
      let b = Bytes.create 16 in
      try
        for bi = 0 to 15 do
          let i = 2 * Int.succ bi in
          let x = int_of_char_string labels.(i) in
          let y = int_of_char_string labels.(i + 1) in
          Bytes.set_uint8 b bi (Int.logor (Int.shift_left x 4) y)
        done;
        Some (S128.of_octets_exn (Bytes.unsafe_to_string b))
      with Failure _ -> None
    else None

  (* constant *)

  let unspecified = make 0 0 0 0 0 0 0 0
  let localhost = make 0 0 0 0 0 0 0 1
  let interface_nodes = make 0xff01 0 0 0 0 0 0 1
  let link_nodes = make 0xff02 0 0 0 0 0 0 1
  let interface_routers = make 0xff01 0 0 0 0 0 0 2
  let link_routers = make 0xff02 0 0 0 0 0 0 2
  let site_routers = make 0xff05 0 0 0 0 0 0 2

  module Prefix = struct
    type addr = t
    type t = addr * int

    let compare (pre, sz) (pre', sz') =
      let c = compare pre pre' in
      if c = 0 then Stdlib.compare sz sz' else c

    let ip = make
    let mask sz = shift_left max_int (128 - sz)
    let prefix (pre, sz) = (logand pre (mask sz), sz)
    let make sz pre = (pre, sz)

    let network_address (pre, sz) addr =
      logor (logand pre (mask sz)) (logand addr (lognot (mask sz)))

    let _of_string_raw s i =
      let v6 = of_string_raw s i in
      expect_char s i '/';
      let p = parse_dec_int s i in
      if p > 128 || p < 0 then raise (Parse_error ("invalid prefix size", s));
      (p, v6)

    let of_string_raw s i =
      let p, v6 = _of_string_raw s i in
      make p v6

    let _of_string_exn s =
      let i = ref 0 in
      let res = _of_string_raw s i in
      expect_end s i;
      res

    let of_string_exn s =
      let p, v6 = _of_string_exn s in
      make p v6

    let of_string s = try_with_result of_string_exn s

    let _of_netmask_exn ~netmask address =
      let count_bits bits is_last_bit_set i =
        S128.Byte.fold_left
          (fun (a, is_last_bit_set) e ->
            match (is_last_bit_set, e) with
            | true, false | false, false -> (a, false)
            | true, true -> (a + 1, true)
            | false, true ->
                (* netmask is not contiguous *)
                raise (Parse_error ("invalid netmask", to_string netmask)))
          (bits, is_last_bit_set) i
      in
      let nm_bits_set, _ =
        S128.fold_left
          (fun (a, is_last_bit_set) e -> count_bits a is_last_bit_set e)
          (0, true) netmask
      in
      make nm_bits_set address

    let of_netmask_exn ~netmask ~address = _of_netmask_exn ~netmask address

    let of_netmask ~netmask ~address =
      try_with_result (_of_netmask_exn ~netmask) address

    let to_buffer buf (pre, sz) = Printf.bprintf buf "%a/%d" to_buffer pre sz

    let to_string subnet =
      let buf = Buffer.create 43 in
      to_buffer buf subnet;
      Buffer.contents buf

    let pp ppf i = Format.fprintf ppf "%s" (to_string i)

    let mem ip (pre, sz) =
      let m = mask sz in
      logand ip m = logand pre m

    let subset ~subnet:(pre1, sz1) ~network:(pre2, sz2) =
      sz1 >= sz2 && mem pre1 (pre2, sz2)

    let of_addr ip = make 128 ip
    let global_unicast_001 = make 3 (ip 0x2000 0 0 0 0 0 0 0)
    let link = make 64 (ip 0xfe80 0 0 0 0 0 0 0)
    let unique_local = make 7 (ip 0xfc00 0 0 0 0 0 0 0)
    let multicast = make 8 (ip 0xff00 0 0 0 0 0 0 0)
    let ipv4_mapped = make 96 (ip 0 0 0 0 0 0xffff 0 0)
    let noneui64_interface = make 3 (ip 0x0000 0 0 0 0 0 0 0)
    let solicited_node = make 104 (ip 0xff02 0 0 0 0 1 0xff00 0)
    let network (pre, sz) = logand pre (mask sz)
    let address (addr, _) = addr
    let bits (_, sz) = sz
    let netmask subnet = mask (bits subnet)
    let hostmask cidr = S128.logxor (netmask cidr) S128.max_int

    let first ((_, sz) as cidr) =
      if sz > 126 then network cidr else network cidr |> succ |> failwith_msg

    let last ((_, sz) as cidr) =
      let ffff = S128.max_int in
      logor (network cidr) (S128.shift_right ffff sz)

    let hosts ?(usable = true) ((_, sz) as cidr) =
      let rec iter_seq start stop =
        if S128.compare start stop > 0 then Seq.Nil
        else
          match succ start with
          | Ok start_succ -> Seq.Cons (start, fun () -> iter_seq start_succ stop)
          | Error _ -> Seq.Cons (start, fun () -> Seq.Nil)
      in
      if usable && sz = 128 then fun () -> Seq.Nil
      else
        let start, stop =
          if usable then (first cidr, last cidr) else (network cidr, last cidr)
        in
        fun () -> iter_seq start stop

    let subnets n ((_, sz) as cidr) =
      let rec iter_seq start stop steps =
        if S128.compare start stop > 0 then Seq.Nil
        else
          let prefix = make n start in
          if S128.equal start stop then Seq.Cons (prefix, fun () -> Seq.Nil)
          else
            match S128.add start steps with
            | None -> Seq.Cons (prefix, fun () -> Seq.Nil)
            | Some start_succ ->
                Seq.Cons (prefix, fun () -> iter_seq start_succ stop steps)
      in
      if sz > n || n > 128 then fun () -> Seq.Nil
      else
        let start = network cidr in
        let stop = last cidr in
        let steps = S128.(succ_exn (shift_right (hostmask cidr) (n - sz))) in
        fun () -> iter_seq start stop steps
  end

  (* TODO: This could be optimized with something trie-like *)
  let scope i =
    let mem = Prefix.mem i in
    if mem Prefix.global_unicast_001 then Global
    else if
      mem Prefix.ipv4_mapped (* rfc says they are technically global but... *)
    then
      V4.scope
        (let _, _, _, v4 = to_int32 i in
         V4.of_int32 v4)
    else if mem Prefix.multicast then
      let x, _, _, _, _, _, _, _ = to_int16 i in
      match x land 0xf with
      | 0 -> Point
      | 1 -> Interface
      | 2 | 3 -> Link
      | 4 -> Admin
      | 5 | 6 | 7 -> Site
      | 8 | 9 | 10 | 11 | 12 | 13 -> Organization
      | 14 | 15 -> Global
      | _ -> assert false
    else if mem Prefix.link then Link
    else if mem Prefix.unique_local then Global
    else if i = localhost then Interface
    else if i = unspecified then Point
    else Global

  let link_address_of_mac =
    let c b i = Char.code b.[i] in
    fun mac ->
      let bmac = Macaddr.to_octets mac in
      let c_0 = c bmac 0 lxor 2 in
      let addr =
        make 0 0 0 0
          ((c_0 lsl 8) + c bmac 1)
          ((c bmac 2 lsl 8) + 0xff)
          (0xfe00 + c bmac 3)
          ((c bmac 4 lsl 8) + c bmac 5)
      in
      Prefix.(network_address link addr)

  let is_global i = scope i = Global
  let is_multicast i = Prefix.(mem i multicast)
  let is_private i = scope i <> Global

  module Set = Set.Make (struct
    type nonrec t = t

    let compare (a : t) (b : t) = compare a b
  end)

  module Map = Map.Make (struct
    type nonrec t = t

    let compare (a : t) (b : t) = compare a b
  end)
end

type ('v4, 'v6) v4v6 = V4 of 'v4 | V6 of 'v6
type t = (V4.t, V6.t) v4v6

let compare a b =
  match (a, b) with
  | V4 a, V4 b -> V4.compare a b
  | V6 a, V6 b -> V6.compare a b
  | V4 _, V6 _ -> -1
  | V6 _, V4 _ -> 1

module Set = Set.Make (struct
  type nonrec t = t

  let compare (a : t) (b : t) = compare a b
end)

module Map = Map.Make (struct
  type nonrec t = t

  let compare (a : t) (b : t) = compare a b
end)

let to_string = function V4 x -> V4.to_string x | V6 x -> V6.to_string x

let to_buffer buf = function
  | V4 x -> V4.to_buffer buf x
  | V6 x -> V6.to_buffer buf x

let pp ppf i = Format.fprintf ppf "%s" (to_string i)

let of_string_raw s offset =
  let len = String.length s in
  if len < !offset + 1 then raise (need_more s);
  match s.[0] with
  | '[' -> V6 (V6.of_string_raw s offset)
  | _ -> (
      let pos = !offset in
      try V4 (V4.of_string_raw s offset)
      with Parse_error (v4_msg, _) -> (
        offset := pos;
        try V6 (V6.of_string_raw s offset)
        with Parse_error (v6_msg, s) ->
          let msg =
            Printf.sprintf "not an IPv4 address: %s\nnot an IPv6 address: %s"
              v4_msg v6_msg
          in
          raise (Parse_error (msg, s))))

let of_string_exn s =
  let o = ref 0 in
  let x = of_string_raw s o in
  expect_end s o;
  x

let of_string s = try_with_result of_string_exn s

let with_port_of_string ~default s =
  let len = String.length s and o = ref 0 in
  try
    let ipv6 = of_string_raw s o in
    if !o < len && s.[!o] = ':' then (
      incr o;
      let port = parse_dec_int s o in
      expect_end s o;
      Ok (ipv6, port))
    else (
      expect_end s o;
      Ok (ipv6, default))
  with Parse_error (msg, _) -> Error (`Msg ("Ipaddr: " ^ msg))

let of_octets_exn bs =
  match String.length bs with
  | 4 -> V4 (V4.of_octets_exn bs)
  | 16 -> V6 (V6.of_octets_exn bs)
  | _ -> raise (Parse_error ("octets must be of length 4 or 16", bs))

let of_octets bs = try_with_result of_octets_exn bs
let to_octets i = match i with V4 p -> V4.to_octets p | V6 p -> V6.to_octets p

let v6_of_v4 v4 =
  V6.(Prefix.(network_address ipv4_mapped (of_int32 (0l, 0l, 0l, v4))))

let v4_of_v6 v6 =
  if V6.Prefix.(mem v6 ipv4_mapped) then
    let _, _, _, v4 = V6.to_int32 v6 in
    Some V4.(of_int32 v4)
  else None

let to_v4 = function V4 v4 -> Some v4 | V6 v6 -> v4_of_v6 v6
let to_v6 = function V4 v4 -> v6_of_v4 v4 | V6 v6 -> v6
let scope = function V4 v4 -> V4.scope v4 | V6 v6 -> V6.scope v6
let is_global = function V4 v4 -> V4.is_global v4 | V6 v6 -> V6.is_global v6

let is_multicast = function
  | V4 v4 -> V4.is_multicast v4
  | V6 v6 -> V6.is_multicast v6

let is_private = function
  | V4 v4 -> V4.is_private v4
  | V6 v6 -> V6.is_private v6

let multicast_to_mac = function
  | V4 v4 -> V4.multicast_to_mac v4
  | V6 v6 -> V6.multicast_to_mac v6

let to_domain_name = function
  | V4 v4 -> V4.to_domain_name v4
  | V6 v6 -> V6.to_domain_name v6

let of_domain_name n =
  match Domain_name.count_labels n with
  | 6 -> (
      match V4.of_domain_name n with None -> None | Some x -> Some (V4 x))
  | 34 -> (
      match V6.of_domain_name n with None -> None | Some x -> Some (V6 x))
  | _ -> None

let succ = function
  | V4 addr -> Result.map (fun v -> V4 v) (V4.succ addr)
  | V6 addr -> Result.map (fun v -> V6 v) (V6.succ addr)

let pred = function
  | V4 addr -> Result.map (fun v -> V4 v) (V4.pred addr)
  | V6 addr -> Result.map (fun v -> V6 v) (V6.pred addr)

module Prefix = struct
  module Addr = struct
    let to_v6 = to_v6
  end

  type addr = t
  type t = (V4.Prefix.t, V6.Prefix.t) v4v6

  let compare a b =
    match (a, b) with
    | V4 a, V4 b -> V4.Prefix.compare a b
    | V6 a, V6 b -> V6.Prefix.compare a b
    | V4 _, V6 _ -> -1
    | V6 _, V4 _ -> 1

  let of_string_raw s offset =
    let len = String.length s in
    if len < !offset + 1 then raise (need_more s);
    match s.[0] with
    | '[' -> V6 (V6.Prefix.of_string_raw s offset)
    | _ -> (
        let pos = !offset in
        try V4 (V4.Prefix.of_string_raw s offset)
        with Parse_error (v4_msg, _) -> (
          offset := pos;
          try V6 (V6.Prefix.of_string_raw s offset)
          with Parse_error (v6_msg, s) ->
            let msg =
              Printf.sprintf "not an IPv4 prefix: %s\nnot an IPv6 prefix: %s"
                v4_msg v6_msg
            in
            raise (Parse_error (msg, s))))

  let of_string_exn s =
    let o = ref 0 in
    let x = of_string_raw s o in
    expect_end s o;
    x

  let of_string s = try_with_result of_string_exn s

  let v6_of_v4 v4 =
    V6.Prefix.make (96 + V4.Prefix.bits v4) (v6_of_v4 (V4.Prefix.network v4))

  let v4_of_v6 v6 =
    match v4_of_v6 (V6.Prefix.network v6) with
    | Some v4 -> Some (V4.Prefix.make (V6.Prefix.bits v6 - 96) v4)
    | None -> None

  let to_v4 = function V4 v4 -> Some v4 | V6 v6 -> v4_of_v6 v6
  let to_v6 = function V4 v4 -> v6_of_v4 v4 | V6 v6 -> v6
  let mem ip prefix = V6.Prefix.mem (Addr.to_v6 ip) (to_v6 prefix)

  let subset ~subnet ~network =
    V6.Prefix.subset ~subnet:(to_v6 subnet) ~network:(to_v6 network)

  let of_addr = function
    | V4 p -> V4 (V4.Prefix.of_addr p)
    | V6 p -> V6 (V6.Prefix.of_addr p)

  let to_string = function
    | V4 p -> V4.Prefix.to_string p
    | V6 p -> V6.Prefix.to_string p

  let to_buffer buf = function
    | V4 p -> V4.Prefix.to_buffer buf p
    | V6 p -> V6.Prefix.to_buffer buf p

  let network = function
    | V4 p -> V4 (V4.Prefix.network p)
    | V6 p -> V6 (V6.Prefix.network p)

  let netmask = function
    | V4 p -> V4 (V4.Prefix.netmask p)
    | V6 p -> V6 (V6.Prefix.netmask p)

  let address = function
    | V4 p -> V4 (V4.Prefix.address p)
    | V6 p -> V6 (V6.Prefix.address p)

  let bits = function V4 p -> V4.Prefix.bits p | V6 p -> V6.Prefix.bits p
  let pp ppf i = Format.fprintf ppf "%s" (to_string i)

  let first = function
    | V4 p -> V4 (V4.Prefix.first p)
    | V6 p -> V6 (V6.Prefix.first p)

  let last = function
    | V4 p -> V4 (V4.Prefix.last p)
    | V6 p -> V6 (V6.Prefix.last p)

  let hosts ?(usable = true) = function
    | V4 p -> V4 (V4.Prefix.hosts ~usable p)
    | V6 p -> V6 (V6.Prefix.hosts ~usable p)

  let subnets n = function
    | V4 p -> V4 (V4.Prefix.subnets n p)
    | V6 p -> V6 (V6.Prefix.subnets n p)
end