Punycode (RFC3492) in OCaml
Add fuzz tests for ax25, cookeio, hostname, punycode, xff, x509
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fuzz/dune
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fuzz/dune
···
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; Crowbar fuzz testing for punycode
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;
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; To run: dune exec ocaml-punycode/fuzz/fuzz_punycode.exe
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; With AFL: afl-fuzz -i fuzz/corpus -o fuzz/findings -- ./_build/default/ocaml-punycode/fuzz/fuzz_punycode.exe @@
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(executable
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(name fuzz_punycode)
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(modules fuzz_punycode)
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(libraries punycode crowbar))
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(rule
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(alias fuzz)
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(deps fuzz_punycode.exe)
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(action
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(run %{exe:fuzz_punycode.exe})))
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fuzz/fuzz_punycode.ml
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fuzz/fuzz_punycode.ml
···
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(*---------------------------------------------------------------------------
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Copyright (c) 2025 Thomas Gazagnaire. All rights reserved.
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SPDX-License-Identifier: MIT
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---------------------------------------------------------------------------*)
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(* Crowbar-based fuzz testing for Punycode encoding/decoding *)
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open Crowbar
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(* Test that encode_utf8 never crashes on arbitrary input *)
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let test_encode_no_crash input =
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let _ = Punycode.encode_utf8 input in
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()
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(* Test that decode_utf8 never crashes on arbitrary input *)
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let test_decode_no_crash input =
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let _ = Punycode.decode_utf8 input in
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()
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(* Test roundtrip: encode then decode should give back original *)
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let test_roundtrip input =
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match Punycode.encode_utf8 input with
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| Ok encoded -> (
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match Punycode.decode_utf8 encoded with
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| Ok decoded -> check_eq ~pp:Format.pp_print_string input decoded
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| Error _ ->
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(* Some encoded values might not decode, that's ok for fuzz testing *)
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())
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| Error _ ->
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(* Some inputs might not encode, that's ok *)
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()
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(* Test that error printing never crashes *)
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let () =
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let pos = { Punycode.byte_offset = 0; char_index = 0 } in
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let errors =
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[
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Punycode.Overflow pos;
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Punycode.Invalid_character (pos, Uchar.of_int 0x1F600);
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Punycode.Invalid_digit (pos, 'x');
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Punycode.Unexpected_end pos;
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Punycode.Invalid_utf8 pos;
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Punycode.Label_too_long 100;
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Punycode.Empty_label;
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]
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in
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List.iter
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(fun e ->
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let _ = Format.asprintf "%a" Punycode.pp_error e in
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let _ = Punycode.error_to_string e in
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())
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errors
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(* Test ASCII-only strings (should pass through mostly unchanged) *)
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let test_ascii_string input =
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let ascii_only =
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String.init
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(String.length input mod 64)
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(fun i -> Char.chr (Char.code input.[i mod String.length input] mod 128))
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in
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if String.length ascii_only > 0 then
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match Punycode.encode ascii_only with Ok _ -> () | Error _ -> ()
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(* Test inputs starting with ACE prefix "xn--" *)
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let test_ace_prefix input =
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let ace_input = "xn--" ^ input in
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let _ = Punycode.decode_utf8 ace_input in
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()
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let () =
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add_test ~name:"punycode: encode no crash" [ bytes ] test_encode_no_crash;
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add_test ~name:"punycode: decode no crash" [ bytes ] test_decode_no_crash;
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add_test ~name:"punycode: roundtrip" [ bytes ] test_roundtrip;
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add_test ~name:"punycode: ascii string" [ bytes ] test_ascii_string;
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add_test ~name:"punycode: ace prefix" [ bytes ] test_ace_prefix