Use angular js to submit file via rails paperclip

I'm trying to use angular to send a file as a param to rails, and then have rails save that file as a user attachment via paperclip. The furthest I've gotten is getting rails to upload something, but it ends up being a txt file with the single line 'object file'.

Here's the relevant Angular

a.uploadAnonRes = function(app){
  if(window.FileReader){ console.log("supported")};
  console.log(($('.anonUploadField'))[0].files);
  http = {
    method: "PUT",
    url: '/admin/upload_anon_res.json',
    params: {
      anon_file: btoa(($('.anonUploadField'))[0].files[0]),
      user_id: app.raw_app.user_id
    }
  };
  $http(http).success(function(data){
      console.log("success");
  });
};

Here's the relevant rails

def upload_anon_res
 user = User.find(params[:user_id])
 user.anon_resume = decode_res
 user.save
 respond_to do |format|
  format.json{ render json: user, root: false }
 end
end

def decode_res
 decoded_data = Base64.decode64(params[:anon_file])
 data = StringIO.new(decoded_data)
 return data
end

As a last note, the file types that I'm trying to work with are doc/docx. I'm trying to avoid adding new dependencies, but if there's no other good way, then so be it. I really appreciate any help/suggestions.