CODEWITHSUNDEEP
elixirdecompiling
mur762
mur762

Reputation: 120

get source code of escript executable

by mistake I deleted the source code of an Elixir escript that I wrote; as a last resort I'm trying to get the source (if possible at all) by decompiling the executable that I deployed on a server.

In case it matters, it was compiled on Ubuntu 16.04 running mix escript.build without additional arguments.

I would appreciate if somebody could give me any pointer how to do this or where to start!

Thanks

Upvotes: 3

Views: 868

Answers (1)

Dogbert
Dogbert

Reputation: 222348

Here's how you can get the compiled Erlang source of your files back. I don't think it's possible to get the original Elixir source back since it is not present in the escript at all; only the compiled Erlang bytecode is. The decompiled Erlang code should be fairly readable if you know some Erlang (if not, check out this quick Erlang <-> Elixir crash course).

The escript executable starts with #! /usr/bin/env escript followed by some lines and then the embedded compiled files are present as a binary zip file. Open the escript file in an editor and delete everything until the line starting with PK (the start of the zip).

$ mix escript.build
$ head -c 59 m
#! /usr/bin/env escript
%%
%%! -escript main m_escript
PK
$ vim m # remove everything until `PK`
$ head -c2 m
PK

Now you can extract the contents of the file with unzip and get all the compiled .beam files:

$ unzip m -d extracted
Archive:  m
  inflating: extracted/m_escript.beam
  inflating: extracted/Elixir.Version.Parser.DSL.beam
  inflating: extracted/Elixir.Kernel.LexicalTracker.beam
  inflating: extracted/Elixir.IO.ANSI.beam
  inflating: extracted/Elixir.Inspect.NaiveDateTime.beam
  inflating: extracted/Elixir.Protocol.beam
  inflating: extracted/Elixir.Inspect.Any.beam
  ...

Finally you can decompile the modules you want using decompile-beam:

$ decompile-beam extracted/Elixir.M.beam
-compile(no_auto_import).

-file("lib/m.ex", 1).

-module('Elixir.M').

-export(['__info__'/1, main/0, main/1]).

-spec '__info__'(attributes | compile | exports |
         functions | macros | md5 | module |
         native_addresses) -> atom() |
                      [{atom(), any()} |
                       {atom(), byte(), integer()}].

'__info__'(functions) -> [{main, 0}, {main, 1}];
'__info__'(macros) -> [];
'__info__'(info) ->
    erlang:get_module_info('Elixir.M', info).

main() -> main([]).

main(args@1) -> 'Elixir.IO':inspect({args@1, args@1}).

This was the original Elixir source:

$ cat lib/m.ex
defmodule M do
  def main(args \\ []) do
    IO.inspect {args, args}
  end
end

Upvotes: 4

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