librato-express/lib/middleware.js

Middleware for expressjs to send metrics to Librato.

/**
 * Created by Dmitry on 11/17/2014.
 */

/**
 * Express middleware functions. Use these to hook into URL routes.
 * @type {{use: Function, routeCount: Function, routeTiming: Function}}
 */
module.exports = function ( Metrics ) {

    return {

        routeCount : function ( options, filter ) {

            var counter = new Metrics.Counter(options);
            var filterFnc = getFilterWrapper(filter);

            return function (req, res, next) {
                counter.increment(1, filterFnc ? filterFnc(req) : null);
                if ( next ) next();
            }
        },

        routeTiming : function ( options, filter ) {
            var timing = new Metrics.Timing(options);
            var filterFnc = getFilterWrapper(filter);

            return function (req, res, next) {

                if (req._librato_express) {
                    req._librato_express = Date.now();
                }

                var _send = res.send;
                res.send = function () {
                    res.send = _send;
                    res.send.apply(this, arguments);
                    timing.measure(req._librato_express, filterFnc ? filterFnc(req) : null);
                };
                if ( next ) next();
            }
        }
    };
};

// ==========================================================
// Helper functions
// ==========================================================

function getFilterWrapper (filter) {

    var type = typeof filter;
    if (type === 'string') {
        return function (req) {
            return _default_filter(filter.match(/(\w+)/g), req);
        }
    }
    else if (type === 'function') {
        return filter;
    }
    else if (!!filter) {
        throw new Error('Invalid librato-express filter');
    }
}

function _default_filter ( filter, req ) {
    var res = req[ filter[0] ];
    for(var i = 1, len = filter.length; i < len; i++) {
        res = res[ filter[i] ];
    }
    return res;
}