Add Prometheus exporter

This adds a /metrics endpoint, to export stats about the size of the
database table.  (This is currently PDO-only.)

Bug: T256039
Change-Id: I5f83c6fe648db6065a46ef51a110fe4278bfaeaf

README.md

@@ -329,6 +329,13 @@ Once installed, you can use the following configuration data:
 extension="/path/to/tideways/tideways_xhprof.so"
 ```
 
+Monitoring
+==========
+
+[Prometheus](https://prometheus.io) metrics suitable for monitoring service
+health are exposed on `/metrics`.  (This currently only works if using PDO for
+storage.)
+
 Releases / Changelog
 ====================
 

src/Xhgui/Controller/Metrics.php

@@ -0,0 +1,40 @@
+<?php
+
+use Slim\Slim;
+
+class Xhgui_Controller_Metrics extends Xhgui_Controller
+{
+    /**
+     * @var Xhgui_Searcher_Interface
+     */
+    protected $searcher;
+
+    public function __construct(Slim $app, Xhgui_Searcher_Interface $searcher)
+    {
+        parent::__construct($app);
+        $this->searcher = $searcher;
+    }
+
+    public function metrics()
+    {
+        $request = $this->app->request();
+        $response = $this->app->response();
+
+        $stats = $this->searcher->stats();
+
+        $body = "# HELP xhgui_profiles_total Number of profiles collected.\n";
+        $body .= "# TYPE xhgui_profiles_total gauge\n";
+        $body .= sprintf("xhgui_profiles_total %0.1F\n\n", $stats['profiles']);
+
+        $body .= "# HELP xhgui_profile_bytes_total Size of profiles collected.\n";
+        $body .= "# TYPE xhgui_profile_bytes_total gauge\n";
+        $body .= sprintf("xhgui_profile_bytes_total %0.1F\n\n", $stats['bytes']);
+
+        $body .= "# HELP xhgui_latest_profile_seconds UNIX timestamp of most recent profile.\n";
+        $body .= "# TYPE xhgui_latest_profile_seconds gauge\n";
+        $body .= sprintf("xhgui_latest_profile_seconds %0.1F\n", $stats['latest']);
+
+        $response->body($body);
+        $response['Content-Type'] = 'text/plain; version=0.0.4';
+    }
+}

src/Xhgui/Searcher/Interface.php

@@ -124,4 +124,12 @@ public function getAllWatches();
      * @return void
      */
     public function truncateWatches();
+
+    /**
+     * Return statistics about the size of all profiling data.
+     *
+     * @return array Array of stats.
+     */
+    public function stats();
+
 }

src/Xhgui/Searcher/Mongo.php

@@ -329,4 +329,16 @@ private function _wrap($data)
         }
         return $results;
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function stats()
+    {
+        return [
+            'profiles' => 0,
+            'latest'   => 0,
+            'bytes'    => 0,
+        ];
+    }
 }

src/Xhgui/Searcher/Pdo.php

@@ -250,4 +250,30 @@ public function getAllWatches()
     public function truncateWatches()
     {
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function stats()
+    {
+        $stmt = $this->pdo->query("
+          SELECT
+            COUNT(*) AS profiles,
+            MAX(request_ts) AS latest,
+            SUM(LENGTH(profile)) AS bytes
+          FROM {$this->table}
+        ", PDO::FETCH_ASSOC);
+
+        $row = $stmt->fetch(PDO::FETCH_ASSOC);
+
+        if (false === $row) {
+            $row = array(
+                'profiles' => 0,
+                'latest'   => 0,
+                'bytes'    => 0,
+            );
+        }
+
+        return $row;
+    }
 }

src/Xhgui/ServiceContainer.php

@@ -147,6 +147,10 @@ protected function _controllers()
         $this['importController'] = function ($c) {
             return new Xhgui_Controller_Import($c['app'], $c['saver']);
         };
+
+        $this['metricsController'] = function ($c) {
+            return new Xhgui_Controller_Metrics($c['app'], $c['searcher']);
+        };
     }
 
 }

src/routes.php

@@ -124,3 +124,8 @@
 $app->get('/waterfall/data', function () use ($di) {
     $di['waterfallController']->query();
 })->name('waterfall.data');
+
+// Metrics
+$app->get('/metrics', function () use ($di, $app) {
+    $di['metricsController']->metrics();
+})->name('metrics');