[bug] binary stdin/stdout mode cannot be enabled on windows

[ZeeWanderer]

Describe the bug
Even when open_port is called with binary there is a CRLF -> LF transformation as if the mode is text

To Reproduce
Try this

%% File: stdio_port_repro.erl
-module(stdio_port_repro).
-export([run/0, child/0]).

run() ->
    {ok, Erl} = find_erl(),
    Port = open_port(
      {spawn_executable, Erl},
      [{args, ["-noshell","-noinput","-s","stdio_port_repro","child"]},
       use_stdio, stderr_to_stdout, exit_status, binary]
    ),
    wait_ready(Port),
    lists:foreach(
      fun({Name, Payload}) -> do_test(Port, Name, Payload) end,
      [{"CRLF", <<13,10>>}, {"LF", <<10>>}, {"CR", <<13>>}]
    ),
    port_close(Port),
    receive {Port, {exit_status, _}} -> ok after 1000 -> ok end.

find_erl() ->
    case os:find_executable("erl") of
        false -> exit(no_erl_in_path);
        Path  -> {ok, Path}
    end.

wait_ready(Port) ->
    receive
        {Port, {data, <<"READY">>}} -> ok;
        {Port, _} -> wait_ready(Port)
    after 5000 ->
        exit(timeout_wait_ready)
    end.

do_test(Port, Name, Payload) ->
    port_command(Port, Payload),
    Echo = receive {Port, {data, Bin}} -> Bin after 2000 -> timeout end,
    io:format("~s sent: ~s echoed: ~s~n", [Name, hex(Payload), hex(Echo)]),
    case Echo of
        Payload -> io:format("~s => OK~n", [Name]);
        _       -> io:format("~s => MISMATCH~n", [Name])
    end.

hex(timeout) -> <<"timeout">>;
hex(Bin) when is_binary(Bin) ->
    iolist_to_binary([io_lib:format("~2.16.0B ", [B]) || <<B:8>> <= Bin]).

child() ->
    io:setopts([binary]),
    P = open_port({fd, 0, 1}, [binary, stream, eof]),
    port_command(P, <<"READY">>),
    loop(P).

loop(P) ->
    receive
        {P, {data, Bin}} -> port_command(P, Bin), loop(P);
        {P, eof} -> ok
    end.

Output is

CRLF sent: 0D 0A  echoed: 0A
CRLF => MISMATCH
LF sent: 0A  echoed: 0A
LF => OK
CR sent: 0D  echoed: 0A
CR => MISMATCH

Expected behavior

CRLF sent: 0D 0A  echoed: 0D 0A 
CRLF => OK
LF sent: 0A  echoed: 0A 
LF => OK
CR sent: 0D  echoed: 0D 
CR => OK

Affected versions
OTP 28

Additional context
WhatsApp/edb#8

[jhogberg]

Thanks for raising this issue!

There is no "binary" or "text" mode with ports. The binary option says that you want the payload to be a bitstring instead of a list, it does not do anything else. The same goes for io:setopts([binary]).

From what I can tell the problem is that on Windows, console handles are special, and things like line feed conversion is enabled by default, and we cannot disable this without changing application behavior. I'll need to mull this for a while.

[jcpetruzza]

@jhogberg Would it make sense to be able to control text/binary mode for a file descriptor from io:setopts() (which on posix platforms would be a no-op)?

[jhogberg]

I don't think so, the descriptors are global and any change in behavior will affect everything else, including the shell.