webauthn/cbor/CBOR.ml

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OCaml
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2021-09-29 14:34:09 +00:00
(** CBOR encoder/decoder, RFC 7049 *)
open Printf
module BE = EndianBytes.BigEndian_unsafe
module SE = EndianString.BigEndian_unsafe
exception Error of string
let (@@) f x = f x
let (|>) x f = f x
let list_iteri f l = let i = ref 0 in List.iter (fun x -> f !i x; incr i) l
let fail fmt = ksprintf (fun s -> raise (Error s)) fmt
module Encode = struct
let start () = Buffer.create 10
let init b ~maj add =
assert (maj >= 0 && maj < 8);
assert (add >= 0 && add < 32);
Buffer.add_char b @@ char_of_int @@ (maj lsl 5) lor add
let put_n b n f x =
let s = Bytes.create n in
f s 0 x;
Buffer.add_string b (Bytes.unsafe_to_string s)
let max_uint32 =
match Sys.word_size with
| 32 -> max_int (* max signed int, but on 32-bit this is enough *)
| _ -> int_of_string "0xFF_FF_FF_FF" (* so that it compiles on 32-bit *)
let put b ~maj n =
assert (n >= 0);
if n < 24 then
init b ~maj n
else if n < 256 then
begin init b ~maj 24; Buffer.add_char b @@ char_of_int n end
else if n < 65536 then
begin init b ~maj 25; put_n b 2 BE.set_int16 n end
else if n <= max_uint32 then
begin init b ~maj 26; put_n b 4 BE.set_int32 @@ Int32.of_int n end
else
begin init b ~maj 27; put_n b 8 BE.set_int64 @@ Int64.of_int n end
let int b n =
let (maj,n) = if n < 0 then 1, -1 - n else 0, n in
put b ~maj n
let hex_char x =
assert (x >= 0 && x < 16);
if x <= 9 then Char.chr @@ Char.code '0' + x
else Char.chr @@ Char.code 'a' + x - 10
let to_hex s =
let r = Bytes.create (String.length s * 2) in
for i = 0 to String.length s - 1 do
Bytes.set r (i*2) @@ hex_char @@ Char.code s.[i] lsr 4;
Bytes.set r (i*2+1) @@ hex_char @@ Char.code s.[i] land 0b1111;
done;
Bytes.to_string r
end
module Simple = struct
type t =
[ `Null
| `Undefined
| `Simple of int
| `Bool of bool
| `Int of int
| `Float of float
| `Bytes of string
| `Text of string
| `Array of t list
| `Map of (t * t) list
]
let encode item =
let open Encode in
let b = start () in
let rec write = function
| `Null -> put b ~maj:7 22;
| `Undefined -> put b ~maj:7 23;
| `Bool false -> put b ~maj:7 20;
| `Bool true -> put b ~maj:7 21;
| `Simple n when (n >= 0 && n <= 23) || (n >= 32 && n <= 255) -> put b ~maj:7 n
| `Simple n -> fail "encode: simple(%d)" n
| `Int n -> int b n
| `Float f -> init b ~maj:7 27; put_n b 8 BE.set_double f
| `Bytes s -> put b ~maj:2 (String.length s); Buffer.add_string b s
| `Text s -> put b ~maj:3 (String.length s); Buffer.add_string b s
| `Array l -> put b ~maj:4 (List.length l); List.iter write l
| `Map m -> put b ~maj:5 (List.length m); List.iter (fun (a,b) -> write a; write b) m
in
write item;
Buffer.contents b
let need (s,i) n =
if n > String.length s || !i + n > String.length s then
fail "truncated: len %d pos %d need %d" (String.length s) !i n;
let j = !i in
i := !i + n;
j
let get_byte (s,_ as r) = int_of_char @@ s.[need r 1]
let get_n (s,_ as r) n f = f s @@ need r n
let get_s (s,_ as r) n = String.sub s (need r n) n
let get_additional byte1 = byte1 land 0b11111
let is_indefinite byte1 = get_additional byte1 = 31
let int64_max_int = Int64.of_int max_int
let two_min_int32 = 2 * Int32.to_int Int32.min_int
let extract_number byte1 r =
match get_additional byte1 with
| n when n < 24 -> n
| 24 -> get_byte r
| 25 -> get_n r 2 SE.get_uint16
| 26 ->
let n = Int32.to_int @@ get_n r 4 SE.get_int32 in
if n < 0 then n - two_min_int32 else n
| 27 ->
let n = get_n r 8 SE.get_int64 in
if n > int64_max_int || n < 0L then fail "extract_number: %Lu" n;
Int64.to_int n
| n -> fail "bad additional %d" n
let get_float16 s i =
let half = Char.code s.[i] lsl 8 + Char.code s.[i+1] in
let mant = half land 0x3ff in
let value =
match (half lsr 10) land 0x1f with (* exp *)
| 31 when mant = 0 -> infinity
| 31 -> nan
| 0 -> ldexp (float mant) ~-24
| exp -> ldexp (float @@ mant + 1024) (exp - 25)
in
if half land 0x8000 = 0 then value else ~-. value
exception Break
let extract_list byte1 r f =
if is_indefinite byte1 then
let l = ref [] in
try while true do l := f r :: !l done; assert false with Break -> List.rev !l
else
let n = extract_number byte1 r in Array.to_list @@ Array.init n (fun _ -> f r)
let rec extract_pair r =
let a = extract r in
let b = try extract r with Break -> fail "extract_pair: unexpected break" in
a,b
and extract_string byte1 r f =
if is_indefinite byte1 then
let b = Buffer.create 10 in
try while true do Buffer.add_string b (f @@ extract r) done; assert false with Break -> Buffer.contents b
else
let n = extract_number byte1 r in get_s r n
and extract r =
let byte1 = get_byte r in
match byte1 lsr 5 with
| 0 -> `Int (extract_number byte1 r)
| 1 -> `Int (-1 - extract_number byte1 r)
| 2 -> `Bytes (extract_string byte1 r (function `Bytes s -> s | _ -> fail "extract: not a bytes chunk"))
| 3 -> `Text (extract_string byte1 r (function `Text s -> s | _ -> fail "extract: not a text chunk"))
| 4 -> `Array (extract_list byte1 r extract)
| 5 -> `Map (extract_list byte1 r extract_pair)
| 6 -> let _tag = extract_number byte1 r in extract r
| 7 ->
begin match get_additional byte1 with
| n when n < 20 -> `Simple n
| 20 -> `Bool false
| 21 -> `Bool true
| 22 -> `Null
| 23 -> `Undefined
| 24 -> `Simple (get_byte r)
| 25 -> `Float (get_n r 2 get_float16)
| 26 -> `Float (get_n r 4 SE.get_float)
| 27 -> `Float (get_n r 8 SE.get_double)
| 31 -> raise Break
| a -> fail "extract: (7,%d)" a
end
| _ -> assert false
let decode_partial s =
let i = ref 0 in
let x = try extract (s,i) with Break -> fail "decode: unexpected break" in
x, String.sub s !i (String.length s - !i)
let decode s : t =
let x, rest = decode_partial s in
if rest = "" then x
else fail "decode: extra data: len %d pos %d" (String.length s) (String.length s - String.length rest)
let to_diagnostic item =
let b = Buffer.create 10 in
let put = Buffer.add_string b in
let rec write = function
| `Null -> put "null"
| `Bool false -> put "false"
| `Bool true -> put "true"
| `Simple n -> bprintf b "simple(%d)" n
| `Undefined -> put "undefined"
| `Int n -> bprintf b "%d" n
| `Float f ->
begin match classify_float f with
| FP_nan -> put "NaN"
| FP_infinite -> put (if f < 0. then "-Infinity" else "Infinity")
| FP_zero | FP_normal | FP_subnormal -> bprintf b "%g" f
end
| `Bytes s -> bprintf b "h'%s'" (Encode.to_hex s)
| `Text s -> bprintf b "\"%s\"" s
| `Array l ->
put "[";
l |> list_iteri (fun i x -> if i <> 0 then put ", "; write x);
put "]"
| `Map m ->
put "{";
m |> list_iteri (fun i (k,v) -> if i <> 0 then put ", "; write k; put ": "; write v);
put "}"
in
write item;
Buffer.contents b
end (* Simple *)