backwater

%% Copyright (c) 2017-2026 Guilherme Andrade <backwater@gandrade.net>
%%
%% Permission is hereby granted, free of charge, to any person obtaining a
%% copy  of this software and associated documentation files (the "Software"),
%% to deal in the Software without restriction, including without limitation
%% the rights to use, copy, modify, merge, publish, distribute, sublicense,
%% and/or sell copies of the Software, and to permit persons to whom the
%% Software is furnished to do so, subject to the following conditions:
%%
%% The above copyright notice and this permission notice shall be included in
%% all copies or substantial portions of the Software.
%%
%% THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
%% IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
%% FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
%% AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
%% LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
%% FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
%% DEALINGS IN THE SOFTWARE.

-module(backwater_encoding_gzip).

-ifdef(E48).
-moduledoc false.
-endif.

%% ------------------------------------------------------------------
%% API Function Exports
%% ------------------------------------------------------------------

-export([encode/1]).
-export([decode/2]).

%% ------------------------------------------------------------------
%% Macro Definitions
%% ------------------------------------------------------------------

% taken from zlib.erl at Erlang/OTP source code
-define(MAX_WBITS, 15).

%% ------------------------------------------------------------------
%% API Function Definitions
%% ------------------------------------------------------------------

-spec encode(iodata()) -> binary().
encode(Data) ->
    zlib:gzip(Data).

-spec decode(iodata(), non_neg_integer()) -> {ok, binary()} | {error, too_big} | {error, term()}.
decode(Data, MaxUncompressedSize) ->
    Z = zlib:open(),
    try
        zlib:inflateInit(Z, 16 + ?MAX_WBITS),
        decode_recur(Z, zlib:safeInflate(Z, Data), [], 0, MaxUncompressedSize)
    catch
        error:Reason ->
            {error, Reason}
    after
        zlib:close(Z)
    end.

%% ------------------------------------------------------------------
%% Internal Function Definitions
%% ------------------------------------------------------------------

decode_recur(Z, {Stage, Chunk}, OutputAcc, OutputSize, MaxUncompressedSize) when
    Stage =:= continue;
    Stage =:= finished
->
    UpdatedOutputAcc = [Chunk | OutputAcc],
    UpdatedOutputSize = OutputSize + iolist_size(Chunk),
    case UpdatedOutputSize > MaxUncompressedSize of
        true ->
            {error, too_big};
        _ when Stage =:= continue ->
            decode_recur(
                Z,
                zlib:safeInflate(Z, ""),
                UpdatedOutputAcc,
                UpdatedOutputSize,
                MaxUncompressedSize
            );
        _ ->
            zlib:inflateEnd(Z),
            Output = iolist_to_binary(lists:reverse(UpdatedOutputAcc)),
            {ok, Output}
    end.