Node.js async text files search

file_type_search.js

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

function file_type_search(path, mime_match, callback_all, callback_each) {
    var file_list = [];
    var level = 0;

    if (typeof callback_all !== 'function') callback_all = false;
    if (typeof callback_each !== 'function') callback_each = false;

    function enter() {
        level += 1;
    }

    function leave() {
        level -= 1;

        if ((level == 0) && callback_all) callback_all(file_list);
    }

    function scan_directory(path, file_list) {
        path = (path.charAt(path.length - 1) == '/') ? path : path + '/';

        fs.readdir(path, function (err, files) {
            if (err) {
                console.error(err.message);
                leave();
                return;
            }

            for (var index in files) {
                process_directory_entry(path + files[index], file_list);
            }

            leave();
        });
    }

    function process_directory_entry(path, file_list) {
        enter();

        fs.stat(path, function (err, stats) {
            if (err) {
                console.error(err.message);
                leave();
                return
            }

            if (stats.isDirectory()) {
                scan_directory(path, file_list);
            } else {
                if (stats.isFile) {
                    if (mime.lookup(path).match(mime_match)) {
                        if (callback_all) file_list.push(path);
                        if (callback_each) callback_each(path);
                    }
                }

                leave();
            }
        });
    }

    process_directory_entry(path, file_list);
}

module.exports = file_type_search;