controller.rb

@foo = Foo.new
@foo.data = [params[:data].read].pack("H*")
@foo.save

node.js

var fs = require('fs');
var request = require('request')

var file = fs.readFileSync("/path/to/request.dat");
var body = file.toString('hex');

request.post({
  method: 'POST',
  uri: 'http://localhost:3000/foos',
  multipart: [{
    'Content-Disposition': 'attachment; name="data"; filename="data"',
    'Content-Type': 'application/octet-stream;',
    'Content-Length': body.length,
    'body': body
  }]},

  function(error, response, body) {

  }
);