Provide default start & stop; custom limits.

Now you can request the most recent event as a simple GET request:

  /1.0/event?expression=random&limit=1

Or, get the value and apply a filter:

  /1.0/event?expression=random(random).gt(random,0)&limit=1

Likewise you can get the most recent metric for a given expression:

  /1.0/metric?expression=sum(random)&step=1e4&limit=1

This is convenient if you want to generate alerts based on recent events.

lib/cube/server/evaluator.js

@@ -4,7 +4,7 @@ var endpoint = require("./endpoint"),
 // To avoid running out of memory, the GET endpoints have a maximum number of
 // values they can return. If the limit is exceeded, only the most recent
 // results are returned.
-var limit = 1e4;
+var limitMax = 1e4;
 
 var headers = {
   "Content-Type": "application/json",
@@ -28,14 +28,15 @@ exports.register = function(db, endpoints) {
 
   function eventGet(request, response) {
     request = url.parse(request.url, true).query;
-    var data = [];
 
-    // A stop time is required for the REST API.
-    if (!("stop" in request)) {
-      response.writeHead(400, headers);
-      response.end(JSON.stringify({error: "invalid stop"}));
-      return;
-    }
+    var data = [],
+        limit = +request.limit;
+
+    // Provide default start and stop times for recent events.
+    // If the limit is not specified, or too big, use the maximum limit.
+    if (!("stop" in request)) request.stop = Date.now();
+    if (!("start" in request)) request.start = 0;
+    if (!(limit <= limitMax)) limit = limitMax;
 
     if (event(request, callback) < 0) {
       response.writeHead(400, headers);
@@ -52,15 +53,23 @@ exports.register = function(db, endpoints) {
 
   function metricGet(request, response) {
     request = url.parse(request.url, true).query;
+
     var data = [],
-        start = new Date(request.start),
-        stop = new Date(request.stop),
+        limit = +request.limit,
         step = +request.step;
 
+    // Provide default start and stop times for recent metrics.
+    // If the limit is not specified, or too big, use the maximum limit.
+    if (!("stop" in request)) request.stop = Math.floor(Date.now() / step) * step;
+    if (!("start" in request)) request.start = 0;
+    if (!(limit <= limitMax)) limit = limitMax;
+
     // If the time between start and stop is too long, then bring the start time
     // forward so that only the most recent results are returned. This is only
     // approximate in the case of months, but why would you want to return
     // exactly ten thousand months? Don't rely on exact limits!
+    var start = new Date(request.start),
+        stop = new Date(request.stop);
     if ((stop - start) / step > limit) request.start = new Date(stop - step * limit);
 
     if (metric(request, callback) < 0) {

lib/cube/server/metric.js

@@ -35,7 +35,7 @@ exports.getter = function(db) {
     }
 
     // Round start and stop to the appropriate time step.
-    var tier = tiers[request.step];
+    var tier = tiers[+request.step];
     if (!tier) return callback({error: "invalid step"}), -1;
     start = tier.floor(start);
     stop = tier.ceil(stop);