Erlang/Elixir BEAM decompiler

b2f.erl

#! /usr/bin/env escript

%% -*- mode: erlang -*-
%% -*- tab-width: 4;erlang-indent-level: 4;indent-tabs-mode: nil -*-
%% ex: ts=4 sw=4 ft=erlang et
%%
%% Copyright 2016 Operable, Inc. All Rights Reserved.
%%
%% This file is provided to you 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.
%%

main([Cmd]) when Cmd == "help";
                 Cmd == "--help";
                 Cmd == "-h" ->
    io:format("b2f: Beam To Function decompiler~n"),
    io:format("Usage: b2f beam_file [function_names]~n"),
    io:format("Notes: beam_file must be a valid path to a BEAM file with debug info.~n"),
    io:format("       function_names are optional. If given, they must be a space-delimited list of~n"),
    io:format("       function names to dump.~n");
main([FileName|Funs]) ->
    case file:read_file(FileName) of
        {error, Reason} ->
            exit(Reason);
        {ok, Contents} ->
            {ok, Chunk} = beam_lib:chunks(Contents, [abstract_code]),
            {Mod, [{abstract_code, {raw_abstract_v1, Code}}]} = Chunk,
            dump_function(Mod, Code, Funs)
    end.

dump_function(Mod, Code, Funs) ->
    MaskF = function_mask(Funs),
    FinalFuns = [F || F <- Code,
                      MaskF(F) == true],
    pretty_print(Mod, FinalFuns).

function_mask("") ->
    fun({function, _, _, _, _}) ->
            true;
       (_) ->
            false
    end;
function_mask(Names0) ->
    Names = [list_to_atom(N) || N <- Names0],
    fun({function, _, Name, _, _}) ->
            lists:member(Name, Names);
       (_) ->
            false
    end.

pretty_print(_Mod, []) ->
    ok;
pretty_print(Mod, [{function, _Line, Name, _Arity, Body0}|T]) ->
    Body = erl_prettypr:format(erl_syntax:form_list(Body0)),
    io:format("~p~s~n", [Name, Body]),
    case T of
        [] ->
            ok;
        _ ->
            pretty_print(Mod, T)
    end.