kernel/src/user.erl

%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 1996-2020. All Rights Reserved.
%%
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%%
%%     http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
%%
%% %CopyrightEnd%
%%
-module(user).
-compile(inline).

%% Basic standard i/o server for user interface port.

-export([start/0, start/1, start_out/0]).
-export([interfaces/1]).

-define(NAME, user).

%% Defines for control ops
-define(ERTS_TTYSL_DRV_CONTROL_MAGIC_NUMBER, 16#018b0900).
-define(CTRL_OP_GET_WINSIZE, (100 + ?ERTS_TTYSL_DRV_CONTROL_MAGIC_NUMBER)).

%%
%% The basic server and start-up.
%%

start() ->
    start_port([eof,binary]).

start([Mod,Fun|Args]) ->
    %% Mod,Fun,Args should return a pid. That process is supposed to act
    %% as the io port.
    Pid = apply(Mod, Fun, Args),  % This better work!
    Id = spawn(fun() -> server(Pid) end),
    register(?NAME, Id),
    Id.

start_out() ->
    %% Output-only version of start/0
    start_port([out,binary]).

start_port(PortSettings) ->
    Id = spawn(fun() -> server({fd,0,1}, PortSettings) end),
    register(?NAME, Id),
    Id.

%% Return the pid of the shell process.
%% Note: We can't ask the user process for this info since it
%% may be busy waiting for data from the port.
interfaces(User) ->
    case process_info(User, dictionary) of
	{dictionary,Dict} ->
	    case lists:keysearch(shell, 1, Dict) of
		{value,Sh={shell,Shell}} when is_pid(Shell) ->
		    [Sh];
		_ ->
		    []
	    end;
	_ ->
	    []
    end.

server(Pid) when is_pid(Pid) ->
    process_flag(trap_exit, true),
    link(Pid),
    run(Pid).

server(PortName,PortSettings) ->
    process_flag(trap_exit, true),
    Port = open_port(PortName,PortSettings),
    run(Port).

run(P) ->
    put(read_mode,list),
    put(encoding,latin1),
    case init:get_argument(noshell) of
	%% non-empty list -> noshell
	{ok, [_|_]} ->
	    put(shell, noshell),
	    server_loop(P, queue:new());
	_ ->
	    group_leader(self(), self()),
	    catch_loop(P, start_init_shell())
    end.

catch_loop(Port, Shell) ->
    catch_loop(Port, Shell, queue:new()).

catch_loop(Port, Shell, Q) ->
    case catch server_loop(Port, Q) of
	new_shell ->
	    exit(Shell, kill),
	    catch_loop(Port, start_new_shell());
	{unknown_exit,{Shell,Reason},_} ->		 % shell has exited
	    case Reason of
		normal ->
                    put_port(<<"*** ">>, Port);
		_ ->
                    put_port(<<"*** ERROR: ">>, Port)
	    end,
	    put_port(<<"Shell process terminated! ***\n">>, Port),
	    catch_loop(Port, start_new_shell());
	{unknown_exit,_,Q1} ->
	    catch_loop(Port, Shell, Q1);
	{'EXIT',R} ->
	    exit(R)
    end.

link_and_save_shell(Shell) ->
    link(Shell),
    put(shell, Shell),
    Shell.

start_init_shell() ->
    link_and_save_shell(shell:start(init)).

start_new_shell() ->
    link_and_save_shell(shell:start()).

server_loop(Port, Q) ->
    receive
	{io_request,From,ReplyAs,Request} when is_pid(From) ->
	    server_loop(Port, do_io_request(Request, From, ReplyAs, Port, Q));
	{Port,{data,Bytes}} ->
	    case get(shell) of
		noshell ->
		    server_loop(Port, queue:snoc(Q, Bytes));
		_ ->
		    case contains_ctrl_g_or_ctrl_c(Bytes) of
			false ->
			    server_loop(Port, queue:snoc(Q, Bytes));
			_ ->
			    throw(new_shell)
		    end
	    end;
	{Port, eof} ->
	    put(eof, true),
	    server_loop(Port, Q);

	%% Ignore messages from port here.
	{'EXIT',Port,badsig} ->			% Ignore badsig errors
	    server_loop(Port, Q);
	{'EXIT',Port,What} ->			% Port has exited
	    exit(What);

	%% Check if shell has exited
	{'EXIT',SomePid,What} ->
	    case get(shell) of
		noshell ->
		    server_loop(Port, Q);	% Ignore
		_ ->
		    throw({unknown_exit,{SomePid,What},Q})
	    end;

	_Other ->				% Ignore other messages
	    server_loop(Port, Q)
    end.


get_fd_geometry(Port) ->
    case (catch port_control(Port,?CTRL_OP_GET_WINSIZE,[])) of
	List when length(List) =:= 8 ->
	    <<W:32/native,H:32/native>> = list_to_binary(List),
	    {W,H};
	_ ->
	    error
    end.


%% NewSaveBuffer = io_request(Request, FromPid, ReplyAs, Port, SaveBuffer)

do_io_request(Req, From, ReplyAs, Port, Q0) ->
    case io_request(Req, Port, Q0) of
	{_Status,Reply,Q1} ->
	    _ = io_reply(From, ReplyAs, Reply),
	    Q1;
	{exit,What} ->
	    ok = send_port(Port, close),
	    exit(What)
    end.

%% New in R13B
%% Encoding option (unicode/latin1)
io_request({put_chars,unicode,Chars}, Port, Q) -> % Binary new in R9C
    case wrap_characters_to_binary(Chars, unicode, get(encoding)) of
        error ->
            {error,{error,put_chars},Q};
        Bin ->
           put_chars(Bin, Port, Q)
    end;
io_request({put_chars,unicode,Mod,Func,Args}, Port, Q) ->
    case catch apply(Mod,Func,Args) of
        Data when is_list(Data); is_binary(Data) ->
            case wrap_characters_to_binary(Data, unicode, get(encoding)) of
                Bin when is_binary(Bin) ->
                    put_chars(Bin, Port, Q);
                error ->
                    {error,{error,put_chars},Q}
            end;
        Undef ->
            put_chars(Undef, Port, Q)
    end;
io_request({put_chars,latin1,Chars}, Port, Q) -> % Binary new in R9C
    case catch unicode:characters_to_binary(Chars, latin1, get(encoding)) of
        Data when is_binary(Data) ->
            put_chars(Data, Port, Q);
        _ ->
            {error,{error,put_chars},Q}
    end;
io_request({put_chars,latin1,Mod,Func,Args}, Port, Q) ->
    case catch apply(Mod,Func,Args) of
        Data when is_list(Data); is_binary(Data) ->
            case
                catch unicode:characters_to_binary(Data,latin1,get(encoding))
            of
                Bin when is_binary(Bin) ->
                    put_chars(Bin, Port, Q);
                _ ->
                    {error,{error,put_chars},Q}
            end;
        Undef ->
            put_chars(Undef, Port, Q)
    end;
io_request({get_chars,Enc,Prompt,N}, Port, Q) -> % New in R9C
    get_chars(Prompt, io_lib, collect_chars, N, Port, Q, Enc);
io_request({get_line,Enc,Prompt}, Port, Q) ->
    case get(read_mode) of
	binary ->
	    get_line_bin(Prompt,Port,Q,Enc);
	_ ->
	    get_chars(Prompt, io_lib, collect_line, [], Port, Q, Enc)
    end;
io_request({get_until,Enc,Prompt,M,F,As}, Port, Q) ->
    get_chars(Prompt, io_lib, get_until, {M,F,As}, Port, Q, Enc);
%%  End New in R13B
io_request(getopts, Port, Q) ->
    getopts(Port, Q);
io_request({setopts,Opts}, Port, Q) when is_list(Opts) ->
    setopts(Opts, Port, Q);
io_request({requests,Reqs}, Port, Q) ->
    io_requests(Reqs, {ok,ok,Q}, Port);

%% New in R12
io_request({get_geometry,columns},Port,Q) ->
    case get_fd_geometry(Port) of
	{W,_H} ->
	    {ok,W,Q};
	_ ->
	    {error,{error,enotsup},Q}
    end;
io_request({get_geometry,rows},Port,Q) ->
    case get_fd_geometry(Port) of
	{_W,H} ->
	    {ok,H,Q};
	_ ->
	    {error,{error,enotsup},Q}
    end;
%% BC with pre-R13 nodes
io_request({put_chars,Chars}, Port, Q) ->
    io_request({put_chars,latin1,Chars}, Port, Q);
io_request({put_chars,Mod,Func,Args}, Port, Q) ->
    io_request({put_chars,latin1,Mod,Func,Args}, Port, Q);
io_request({get_chars,Prompt,N}, Port, Q) ->
    io_request({get_chars,latin1,Prompt,N}, Port, Q);
io_request({get_line,Prompt}, Port, Q) ->
    io_request({get_line,latin1,Prompt}, Port, Q);
io_request({get_until,Prompt,M,F,As}, Port, Q) ->
    io_request({get_until,latin1,Prompt,M,F,As}, Port, Q);

io_request(R, _Port, Q) ->                      %Unknown request
    {error,{error,{request,R}},Q}.		%Ignore but give error (?)

%% Status = io_requests(RequestList, PrevStat, Port)
%%  Process a list of output requests as long as the previous status is 'ok'.

io_requests([R|Rs], {ok,_Res,Q}, Port) ->
    io_requests(Rs, io_request(R, Port, Q), Port);
io_requests([_|_], Error, _) ->
    Error;
io_requests([], Stat, _) ->
    Stat.

%% put_port(DeepList, Port)
%%  Take a deep list of characters, flatten and output them to the
%%  port.

put_port(List, Port) ->
    true = port_command(Port, List),
    ok.

%% send_port(Port, Command)

send_port(Port, Command) ->
    Port ! {self(),Command},
    ok.

%% io_reply(From, ReplyAs, Reply)
%%  The function for sending i/o command acknowledgement.
%%  The ACK contains the return value.

io_reply(From, ReplyAs, Reply) ->
    From ! {io_reply,ReplyAs,Reply}.

%% put_chars
put_chars(Chars, Port, Q) when is_binary(Chars) ->
    ok = put_port(Chars, Port),
    {ok,ok,Q};
put_chars(Chars, Port, Q) ->
    case catch list_to_binary(Chars) of
	Binary when is_binary(Binary) ->
	    put_chars(Binary, Port, Q);
	_ ->
	    {error,{error,put_chars},Q}
    end.

expand_encoding([]) ->
    [];
expand_encoding([latin1 | T]) ->
    [{encoding,latin1} | expand_encoding(T)];
expand_encoding([unicode | T]) ->
    [{encoding,unicode} | expand_encoding(T)];
expand_encoding([H|T]) ->
    [H|expand_encoding(T)].

%% setopts
setopts(Opts0,Port,Q) ->
    Opts = proplists:unfold(
	     proplists:substitute_negations(
	       [{list,binary}],
	       expand_encoding(Opts0))),
    case check_valid_opts(Opts) of
	true ->
	    do_setopts(Opts,Port,Q);
	false ->
	    {error,{error,enotsup},Q}
    end.
check_valid_opts([]) ->
    true;
check_valid_opts([{binary,_}|T]) ->
    check_valid_opts(T);
check_valid_opts([{encoding,Valid}|T]) when Valid =:= latin1; Valid =:= utf8; Valid =:= unicode ->
    check_valid_opts(T);
check_valid_opts(_) ->
    false.

do_setopts(Opts, _Port, Q) ->
    case proplists:get_value(encoding,Opts) of
	Valid when Valid =:= unicode; Valid =:= utf8 ->
	    put(encoding,unicode);
	latin1 ->
	    put(encoding,latin1);
	undefined ->
	    ok
    end,
    case proplists:get_value(binary, Opts) of
	true ->
	    put(read_mode,binary),
	    {ok,ok,Q};
	false ->
	    put(read_mode,list),
	    {ok,ok,Q};
	_ ->
	    {ok,ok,Q}
    end.

getopts(_Port,Q) ->
    Bin = {binary, get(read_mode) =:= binary},
    Uni = {encoding, get(encoding)},
    {ok,[Bin,Uni],Q}.

get_line_bin(Prompt,Port,Q, Enc) ->
    case prompt(Port, Prompt) of
        error ->
	    {error,{error,get_line},Q};
        ok ->
            case {get(eof),queue:is_empty(Q)} of
                {true,true} ->
                    {ok,eof,Q};
                _ ->
                    get_line(Prompt,Port, Q, [], Enc)
            end
    end.

get_line(Prompt, Port, Q, Acc, Enc) ->
    case queue:is_empty(Q) of
	true ->
	    receive
		{Port,{data,Bytes}} ->
		    get_line_bytes(Prompt, Port, Q, Acc, Bytes, Enc);
		{Port, eof} ->
		    put(eof, true),
		    {ok, eof, queue:new()};
                {io_request,From,ReplyAs,{get_geometry,_}=Req} when is_pid(From) ->
                    do_io_request(Req, From, ReplyAs, Port,
                                  queue:new()),
                    %% No prompt.
                    get_line(Prompt, Port, Q, Acc, Enc);
		{io_request,From,ReplyAs,Request} when is_pid(From) ->
		    do_io_request(Request, From, ReplyAs, Port, queue:new()),
                    case prompt(Port, Prompt) of
                        error ->
                            {error,{error,get_line},Q};
                        ok ->
                            get_line(Prompt, Port, Q, Acc, Enc)
                    end;
		{'EXIT',From,What} when node(From) =:= node() ->
		    {exit,What}
	    end;
	false ->
	    get_line_doit(Prompt, Port, Q, Acc, Enc)
    end.

get_line_bytes(Prompt, Port, Q, Acc, Bytes, Enc) ->
    case get(shell) of
	noshell ->
	    get_line_doit(Prompt, Port, queue:snoc(Q, Bytes),Acc,Enc);
	_ ->
	    case contains_ctrl_g_or_ctrl_c(Bytes) of
		false ->
		    get_line_doit(Prompt, Port, queue:snoc(Q, Bytes), Acc, Enc);
		_ ->
		    throw(new_shell)
	    end
    end.
is_cr_at(Pos,Bin) ->
    case Bin of
  	<<_:Pos/binary,$\r,_/binary>> ->
  	    true;
  	_ ->
  	    false
    end.
srch(<<>>,_,_) ->
    nomatch;
srch(<<X:8,_/binary>>,X,N) ->
    {match,[{N,1}]};
srch(<<_:8,T/binary>>,X,N) ->
    srch(T,X,N+1).

get_line_doit(Prompt, Port, Q, Accu, Enc) ->
    case queue:is_empty(Q) of
	true ->
	    case get(eof) of
		true ->
		   case Accu of
		       [] ->
			   {ok,eof,Q};
		       _ ->
			   {ok,binrev(Accu,[]),Q}
		   end;
		_ ->
		    get_line(Prompt, Port, Q, Accu, Enc)
	    end;
	false ->
	    Bin = queue:head(Q),
	    case srch(Bin,$\n,0) of
		nomatch ->
		    X = byte_size(Bin)-1,
		    case is_cr_at(X,Bin) of
			true ->
			    <<D:X/binary,_/binary>> = Bin,
			    get_line_doit(Prompt, Port, queue:tail(Q),
					  [<<$\r>>,D|Accu], Enc);
			false ->
			    get_line_doit(Prompt, Port, queue:tail(Q),
					  [Bin|Accu], Enc)
		    end;
		{match,[{Pos,1}]} ->
		    %% We are done
		    PosPlus = Pos + 1,
		    case Accu of
			[] ->
			    {Head,Tail} =
				case is_cr_at(Pos - 1,Bin) of
				    false ->
					<<H:PosPlus/binary,
					 T/binary>> = Bin,
					{H,T};
				    true ->
					PosMinus = Pos - 1,
					<<H:PosMinus/binary,
					 _,_,T/binary>> = Bin,
					{binrev([],[H,$\n]),T}
				end,
			    case Tail of
				<<>> ->
				    {ok, cast(Head,Enc), queue:tail(Q)};
				_ ->
				    {ok, cast(Head,Enc),
				     queue:cons(Tail, queue:tail(Q))}
			    end;
			[<<$\r>>|Stack1] when Pos =:= 0 ->
			    <<_:PosPlus/binary,Tail/binary>> = Bin,
			    case Tail of
				<<>> ->
				    {ok, cast(binrev(Stack1, [$\n]),Enc),
				     queue:tail(Q)};
				_ ->
				    {ok, cast(binrev(Stack1, [$\n]),Enc),
				     queue:cons(Tail, queue:tail(Q))}
			    end;
			_ ->
			    {Head,Tail} =
				case is_cr_at(Pos - 1,Bin) of
				    false ->
					<<H:PosPlus/binary,
					 T/binary>> = Bin,
					{H,T};
				    true ->
					PosMinus = Pos - 1,
					<<H:PosMinus/binary,
					 _,_,T/binary>> = Bin,
					{[H,$\n],T}
				end,
			    case Tail of
				<<>> ->
				    {ok, cast(binrev(Accu,[Head]),Enc),
				     queue:tail(Q)};
				_ ->
				    {ok, cast(binrev(Accu,[Head]),Enc),
				     queue:cons(Tail, queue:tail(Q))}
			    end
		    end
	    end
    end.

binrev(L, T) ->
    list_to_binary(lists:reverse(L, T)).

%% get_chars(Prompt, Module, Function, XtraArg, Port, Queue, Encoding)
%%  Gets characters from the input port until the applied function
%%  returns {stop,Result,RestBuf}. Does not block output until input
%%  has been received. Encoding is the encoding of the data sent to
%%  the client and to Function.
%%  Returns:
%%	{Status,Result,NewQueue}
%%	{exit,Reason}

%% Entry function.
get_chars(Prompt, M, F, Xa, Port, Q, Enc) ->
    case prompt(Port, Prompt) of
        error ->
            {error,{error,get_chars},Q};
        ok ->
            case {get(eof),queue:is_empty(Q)} of
                {true,true} ->
                    {ok,eof,Q};
                _ ->
                    get_chars(Prompt, M, F, Xa, Port, Q, start, Enc)
            end
    end.

%% First loop. Wait for port data. Respond to output requests.
get_chars(Prompt, M, F, Xa, Port, Q, State, Enc) ->
    case queue:is_empty(Q) of
	true ->
	    receive
		{Port,{data,Bytes}} ->
		    get_chars_bytes(State, M, F, Xa, Port, Q, Bytes, Enc);
		{Port, eof} ->
		    put(eof, true),
		    {ok, eof, queue:new()};
                {io_request,From,ReplyAs,{get_geometry,_}=Req} when is_pid(From) ->
                    do_io_request(Req, From, ReplyAs, Port,
                                  queue:new()), %Keep Q over this call
                    %% No prompt.
                    get_chars(Prompt, M, F, Xa, Port, Q, State, Enc);
		{io_request,From,ReplyAs,Request} when is_pid(From) ->
		    get_chars_req(Prompt, M, F, Xa, Port, Q, State,
				  Request, From, ReplyAs, Enc);
		{'EXIT',From,What} when node(From) =:= node() ->
		    {exit,What}
	    end;
	false ->
	    get_chars_apply(State, M, F, Xa, Port, Q, Enc)
    end.

get_chars_req(Prompt, M, F, XtraArg, Port, Q, State,
	      Req, From, ReplyAs, Enc) ->
    do_io_request(Req, From, ReplyAs, Port, queue:new()), %Keep Q over this call
    case prompt(Port, Prompt) of
        error ->
            {error,{error,get_chars},Q};
        ok ->
            get_chars(Prompt, M, F, XtraArg, Port, Q, State, Enc)
    end.

%% Second loop. Pass data to client as long as it wants more.
%% A ^G in data interrupts loop if 'noshell' is not undefined.
get_chars_bytes(State, M, F, Xa, Port, Q, Bytes, Enc) ->
    case get(shell) of
	noshell ->
	    get_chars_apply(State, M, F, Xa, Port, queue:snoc(Q, Bytes),Enc);
	_ ->
	    case contains_ctrl_g_or_ctrl_c(Bytes) of
		false ->
		    get_chars_apply(State, M, F, Xa, Port,
				    queue:snoc(Q, Bytes),Enc);
		_ ->
		    throw(new_shell)
	    end
    end.

get_chars_apply(State0, M, F, Xa, Port, Q, Enc) ->
    case catch M:F(State0, cast(queue:head(Q),Enc), Enc, Xa) of
	{stop,Result,<<>>} ->
	    {ok,Result,queue:tail(Q)};
	{stop,Result,[]} ->
	    {ok,Result,queue:tail(Q)};
	{stop,Result,eof} ->
	    {ok,Result,queue:tail(Q)};
	{stop,Result,Buf} ->
	    {ok,Result,queue:cons(Buf, queue:tail(Q))};
	{'EXIT',_Why} ->
	    {error,{error,err_func(M, F, Xa)},queue:new()};
	State1 ->
	    get_chars_more(State1, M, F, Xa, Port, queue:tail(Q), Enc)
    end.

get_chars_more(State, M, F, Xa, Port, Q, Enc) ->
    case queue:is_empty(Q) of
	true ->
	    case get(eof) of
		undefined ->
		    receive
			{Port,{data,Bytes}} ->
			    get_chars_bytes(State, M, F, Xa, Port, Q, Bytes, Enc);
			{Port,eof} ->
			    put(eof, true),
			    get_chars_apply(State, M, F, Xa, Port,
					    queue:snoc(Q, eof), Enc);
			{'EXIT',From,What} when node(From) =:= node() ->
			    {exit,What}
		    end;
		_ ->
		    get_chars_apply(State, M, F, Xa, Port, queue:snoc(Q, eof), Enc)
	    end;
	false ->
	    get_chars_apply(State, M, F, Xa, Port, Q, Enc)
    end.


%% prompt(Port, Prompt)
%%  Print Prompt onto Port

%% common case, reduces execution time by 20%
prompt(_Port, '') -> ok;
prompt(Port, Prompt) ->
    Encoding = get(encoding),
    PromptString = io_lib:format_prompt(Prompt, Encoding),
    case wrap_characters_to_binary(PromptString, unicode, Encoding) of
        Bin when is_binary(Bin) ->
            put_port(Bin, Port);
        error ->
            error
    end.

%% Convert error code to make it look as before
err_func(io_lib, get_until, {_,F,_}) ->
    F;
err_func(_, F, _) ->
    F.

%% using regexp reduces execution time by >50% compared to old code
%% running two regexps in sequence is much faster than \\x03|\\x07
contains_ctrl_g_or_ctrl_c(BinOrList)->
    case {re:run(BinOrList, <<3>>),re:run(BinOrList, <<7>>)} of
	{nomatch, nomatch} -> false;
	_ -> true
    end.

%% Convert a buffer between list and binary
cast(Data, _Encoding) when is_atom(Data) ->
    Data;
cast(Data, Encoding) ->
    IoEncoding =  get(encoding),
    cast(Data, get(read_mode), IoEncoding, Encoding).

cast(B, binary, latin1, latin1) when is_binary(B) ->
    B;
cast(L, binary, latin1, latin1) ->
    case catch erlang:iolist_to_binary(L) of
        Bin when is_binary(Bin) -> Bin;
        _ -> exit({no_translation, latin1, latin1})
    end;
cast(Data, binary, unicode, latin1) when is_binary(Data); is_list(Data) ->
    case catch unicode:characters_to_binary(Data, unicode, latin1) of
        Bin when is_binary(Bin) -> Bin;
        _ -> exit({no_translation, unicode, latin1})
    end;
cast(Data, binary, latin1, unicode) when is_binary(Data); is_list(Data) ->
    case catch unicode:characters_to_binary(Data, latin1, unicode) of
        Bin when is_binary(Bin) -> Bin;
        _ -> exit({no_translation, latin1, unicode})
    end;
cast(B, binary, unicode, unicode) when is_binary(B) ->
    B;
cast(L, binary, unicode, unicode) ->
    case catch unicode:characters_to_binary(L, unicode) of
        Bin when is_binary(Bin) -> Bin;
        _ -> exit({no_translation, unicode, unicode})
    end;
cast(B, list, latin1, latin1) when is_binary(B) ->
    binary_to_list(B);
cast(L, list, latin1, latin1) ->
    case catch erlang:iolist_to_binary(L) of
        Bin when is_binary(Bin) -> binary_to_list(Bin);
        _ -> exit({no_translation, latin1, latin1})
    end;
cast(Data, list, unicode, latin1) when is_binary(Data); is_list(Data) ->
    case catch unicode:characters_to_list(Data, unicode) of
        Chars when is_list(Chars) ->
            [ case X of
                  High when High > 255 ->
                      exit({no_translation, unicode, latin1});
                  Low ->
                      Low
              end || X <- Chars ];
        _ ->
            exit({no_translation, unicode, latin1})
    end;
cast(Data, list, latin1, unicode) when is_binary(Data); is_list(Data) ->
    case catch unicode:characters_to_list(Data, latin1) of
        Chars when is_list(Chars) -> Chars;
        _ -> exit({no_translation, latin1, unicode})
    end;
cast(Data, list, unicode, unicode) when is_binary(Data); is_list(Data) ->
    case catch unicode:characters_to_list(Data, unicode) of
        Chars when is_list(Chars) -> Chars;
        _ -> exit({no_translation, unicode, unicode})
    end.

wrap_characters_to_binary(Chars, unicode, latin1) ->
    case catch unicode:characters_to_binary(Chars, unicode, latin1) of
        Bin when is_binary(Bin) ->
            Bin;
        _ ->
            case catch unicode:characters_to_list(Chars, unicode) of
                L when is_list(L) ->
                    list_to_binary(
                      [ case X of
                            High when High > 255 ->
                                ["\\x{",erlang:integer_to_list(X, 16),$}];
                            Low ->
                                Low
                        end || X <- L ]);
                _ ->
                    error
            end
    end;
wrap_characters_to_binary(Bin, From, From) when is_binary(Bin) ->
    Bin;
wrap_characters_to_binary(Chars, From, To) ->
    case catch unicode:characters_to_binary(Chars, From, To) of
        Bin when is_binary(Bin) ->
            Bin;
        _ ->
            error
    end.