Request + LRU Cache

request_cache.js

var request = require('request');
var LRU = require('lru-cache');

/*

Request + LRU Cache
- request_cache(target, callback() {})

*/

var cache = LRU({
	max:    10000,
	maxAge: 10 * 60 * 1000
});

var
	KEY_PREFIX = 'rcache:',
	STATE_PENDING = 'pending',
	STATE_DONE = 'done',
	REQUEST_TIMEOUT = 4000,
	PENDING_REQUEST_TIMEOUT = 8000,
	REQUEST_EXPIRY = 12000;

function RCacheItem(callback) {
	this.state = STATE_PENDING;
	this.callbacks = [callback];
	this.res = null;
}

function Result(error, response, body) {
	this.error = error;
	this.response = response;
	this.body = body;
}

function request_cache(uri, callback) {
	var key = KEY_PREFIX + uri;
	var hit = cache.get(key);

	if (hit) {
		if (hit.state === STATE_PENDING) {
			return hit.callbacks.push(callback);
		}
		else if (hit.state === STATE_DONE) {
			var res = hit.res;
			callback(res.error, res.response, res.body);
		}
		return;
	}

	var item = new RCacheItem(callback);
	cache.set(key, item, PENDING_REQUEST_TIMEOUT);

	var target = {
		uri: uri,
		timeout: REQUEST_TIMEOUT
	};

	request(target, handleResponse);
	
	function handleResponse(error, response, body) {
		// TODO handle retries here
		
		handleDone(error, response, body);
	}
	
	function handleDone(error, response, body) {
		item.res = new Result(error, response, body);
		item.state = STATE_DONE;
		
		cache.set(key, item, REQUEST_EXPIRY);
		items.callbacks.forEach(function(callback) {
			callback(error, response, body);
		});
	}
}