How do you setup an Erlang NIF project with rebar? - erlang

Question

I looked through the questions here on StackOverflow and Googled around for an example of setting up a Basic NIF project in rebar for wrapping a C++ library.
I used to library project on GitHub as a guide:
https://github.com/tuncer/re2
My project is here:
https://github.com/project-z/emutton/
When I do a rebar compile && rebar eunit, I get a failure in the eunit test because it cannot find emtn.so:
$ rebar compile && rebar eunit
==> emutton (compile)
==> emutton (eunit)
undefined
*** test module not found ***
**emtn
=ERROR REPORT==== 25-Jun-2013::12:21:55 ===
The on_load function for module emtn returned {error,
{load_failed,
"Failed to load NIF library: 'dlopen(/.../source/emutton/priv/emtn.so, 2): image not found'"}}
=======================================================
Failed: 0. Skipped: 0. Passed: 0.
One or more tests were cancelled.
ERROR: One or more eunit tests failed.
ERROR: eunit failed while processing /.../source/emutton: rebar_abort
When I call rebar compile, it is only producing a single driver file, emtn_drv.so and no emtn.so:
$ tree priv
priv
└── emtn_drv.so
0 directories, 1 file
I have an echo statement in c_src/build_deps.sh that I don't see output when I call rebar clean. It seems to behave as though my pre_hook and post_hook in rebar.config are completely ignored:
{pre_hooks, [{compile, "c_src/build_deps.sh"}]}.
{post_hooks, [{clean, "c_src/build_deps.sh clean"}]}.
Examples of no output shown from rebar:
$ rebar compile
==> emutton (compile)
$ rebar clean
==> emutton (clean)
Because I have cloned tuncer's RE2 bindings project and when I do a rebar compile see output from his build_deps.sh script. The permissions on mine match those on his:
-rwxr-xr-x 1 ajl staff 891B Jun 25 12:30 c_src/build_deps.sh
Any idea what I'm missing here? I believe that rebar is configured correctly to call out to the script and do the compilation.

Answer 1

Your problem is that the line in your rebar.config
https://github.com/project-z/emutton/blob/master/rebar.config%20#L1
Doesn't match what you attempt to load
https://github.com/project-z/emutton/blob/master/src/emtn.erl#L25
You should either change the rebar.config to
{port_specs, [{"priv/emtn.so",["c_src/emtn_nif.c"]}]}.
and change emtn.erl to
erlang:load_nif(filename:join(PrivDir, "emtn"), 0). % ?MODULE is an atom, I believe you need a string
Or change emtn.erl to
erlang:load_nif(filename:join(PrivDir, "emtn_drv"), 0).