Metrics: Add support for histogram

src/Controllers/Metrics/MetricsEngine.php

@@ -6,11 +6,15 @@ use Engelsystem\Renderer\EngineInterface;
 
 class MetricsEngine implements EngineInterface
 {
+    /** @var string */
+    protected $prefix = 'engelsystem_';
+
     /**
      * Render metrics
      *
      * @param string  $path
      * @param mixed[] $data
+     *
      * @return string
      *
      * @example $data = ['foo' => [['labels' => ['foo'=>'bar'], 'value'=>42]], 'bar'=>123]
@@ -25,21 +29,29 @@ class MetricsEngine implements EngineInterface
             }
 
             $list = is_array($list) ? $list : [$list];
-            $name = 'engelsystem_' . $name;
+            $name = $this->prefix . $name;
 
             if (isset($list['help'])) {
                 $return[] = sprintf('# HELP %s %s', $name, $this->escape($list['help']));
                 unset($list['help']);
             }
 
+            $type = null;
             if (isset($list['type'])) {
+                $type = $list['type'];
                 $return[] = sprintf('# TYPE %s %s', $name, $list['type']);
                 unset($list['type']);
             }
 
             $list = (!isset($list['value']) || !isset($list['labels'])) ? $list : [$list];
             foreach ($list as $row) {
-                $row = is_array($row) ? $row : [$row];
+                $row = $this->expandData($row);
+
+                if ($type == 'histogram') {
+                    $return = array_merge($return, $this->formatHistogram($row, $name));
+
+                    continue;
+                }
 
                 $return[] = $this->formatData($name, $row);
             }
@@ -49,17 +61,72 @@ class MetricsEngine implements EngineInterface
     }
 
     /**
-     * @param string $path
+     * @param array  $row
-     * @return bool
+     * @param string $name
+     *
+     * @return array[]
      */
-    public function canRender(string $path): bool
+    protected function formatHistogram(array $row, string $name): array
     {
-        return $path == '/metrics';
+        $return = [];
+        $data = ['labels' => $row['labels']];
+
+        if (!isset($row['value']['+Inf'])) {
+            $row['value']['+Inf'] = !empty($row['value']) ? max($row['value']) : 'NaN';
+        }
+        asort($row['value']);
+
+        foreach ($row['value'] as $le => $value) {
+            $return[] = $this->formatData(
+                $name . '_bucket',
+                array_merge_recursive($data, ['value' => $value, 'labels' => ['le' => $le]])
+            );
+        }
+
+        $sum = isset($row['sum']) ? $row['sum'] : 'NaN';
+        $count = $row['value']['+Inf'];
+        $return[] = $this->formatData($name . '_sum', $data + ['value' => $sum]);
+        $return[] = $this->formatData($name . '_count', $data + ['value' => $count]);
+
+        return $return;
+    }
+
+    /**
+     * Expand the value to be an array
+     *
+     * @param $data
+     *
+     * @return array
+     */
+    protected function expandData($data): array
+    {
+        $data = is_array($data) ? $data : [$data];
+        $return = ['labels' => [], 'value' => null];
+
+        if (isset($data['labels'])) {
+            $return['labels'] = $data['labels'];
+            unset($data['labels']);
+        }
+
+        if (isset($data['sum'])) {
+            $return['sum'] = $data['sum'];
+            unset($data['sum']);
+        }
+
+        if (isset($data['value'])) {
+            $return['value'] = $data['value'];
+            unset($data['value']);
+        } else {
+            $return['value'] = $data;
+        }
+
+        return $return;
     }
 
     /**
      * @param string      $name
      * @param array|mixed $row
+     *
      * @return string
      * @see https://prometheus.io/docs/instrumenting/exposition_formats/
      */
@@ -68,23 +135,23 @@ class MetricsEngine implements EngineInterface
         return sprintf(
             '%s%s %s',
             $name,
-            $this->renderLabels($row),
+            $this->renderLabels($row['labels']),
-            $this->renderValue($row)
+            $this->renderValue($row['value'])
         );
     }
 
     /**
-     * @param array|mixed $row
+     * @param array $labels
+     *
      * @return mixed
      */
-    protected function renderLabels($row): string
+    protected function renderLabels(array $labels): string
     {
-        $labels = [];
+        if (empty($labels)) {
-        if (!is_array($row) || empty($row['labels'])) {
             return '';
         }
 
-        foreach ($row['labels'] as $type => $value) {
+        foreach ($labels as $type => $value) {
             $labels[$type] = $type . '="' . $this->formatValue($value) . '"';
         }
 
@@ -93,19 +160,21 @@ class MetricsEngine implements EngineInterface
 
     /**
      * @param array|mixed $row
+     *
      * @return mixed
      */
     protected function renderValue($row)
     {
-        if (isset($row['value'])) {
+        if (is_array($row)) {
-            return $this->formatValue($row['value']);
+            $row = array_pop($row);
         }
 
-        return $this->formatValue(array_pop($row));
+        return $this->formatValue($row);
     }
 
     /**
      * @param mixed $value
+     *
      * @return mixed
      */
     protected function formatValue($value)
@@ -119,6 +188,7 @@ class MetricsEngine implements EngineInterface
 
     /**
      * @param mixed $value
+     *
      * @return mixed
      */
     protected function escape($value)
@@ -136,6 +206,16 @@ class MetricsEngine implements EngineInterface
         );
     }
 
+    /**
+     * @param string $path
+     *
+     * @return bool
+     */
+    public function canRender(string $path): bool
+    {
+        return $path == '/metrics';
+    }
+
     /**
      * Does nothing as shared data will only result in unexpected behaviour
      *

tests/Unit/Controllers/Metrics/MetricsEngineTest.php

@@ -55,6 +55,85 @@ class MetricsEngineTest extends TestCase
         );
     }
 
+    /**
+     * @covers \Engelsystem\Controllers\Metrics\MetricsEngine::expandData
+     * @covers \Engelsystem\Controllers\Metrics\MetricsEngine::formatHistogram
+     * @covers \Engelsystem\Controllers\Metrics\MetricsEngine::get
+     */
+    public function testGetHistogram()
+    {
+        $engine = new MetricsEngine();
+
+        $this->assertEquals(
+            <<<'EOD'
+# TYPE engelsystem_test_minimum_histogram histogram
+engelsystem_test_minimum_histogram_bucket{le="3"} 4
+engelsystem_test_minimum_histogram_bucket{le="+Inf"} 4
+engelsystem_test_minimum_histogram_sum 1.337
+engelsystem_test_minimum_histogram_count 4
+EOD,
+            $engine->get('/metrics', [
+                'test_minimum_histogram' => [
+                    'type'  => 'histogram', [3 => 4, 'sum' => 1.337]
+                ],
+            ])
+        );
+
+        $this->assertEquals(
+            <<<'EOD'
+# TYPE engelsystem_test_short_histogram histogram
+engelsystem_test_short_histogram_bucket{le="0"} 0
+engelsystem_test_short_histogram_bucket{le="60"} 10
+engelsystem_test_short_histogram_bucket{le="120"} 19
+engelsystem_test_short_histogram_bucket{le="+Inf"} 300
+engelsystem_test_short_histogram_sum 123.456
+engelsystem_test_short_histogram_count 300
+EOD,
+            $engine->get('/metrics', [
+                'test_short_histogram' => [
+                    'type'  => 'histogram',
+                    'value' => [120 => 19, '+Inf' => 300, 60 => 10, 0 => 0, 'sum' => 123.456]
+                ],
+            ])
+        );
+
+        $this->assertEquals(
+            <<<'EOD'
+# TYPE engelsystem_test_multiple_histogram histogram
+engelsystem_test_multiple_histogram_bucket{handler="foo",le="0.1"} 32
+engelsystem_test_multiple_histogram_bucket{handler="foo",le="3"} 99
+engelsystem_test_multiple_histogram_bucket{handler="foo",le="+Inf"} 99
+engelsystem_test_multiple_histogram_sum{handler="foo"} 42
+engelsystem_test_multiple_histogram_count{handler="foo"} 99
+engelsystem_test_multiple_histogram_bucket{handler="bar",le="0.2"} 0
+engelsystem_test_multiple_histogram_bucket{handler="bar",le="+Inf"} 3
+engelsystem_test_multiple_histogram_sum{handler="bar"} 3
+engelsystem_test_multiple_histogram_count{handler="bar"} 3
+EOD,
+            $engine->get('/metrics', [
+                'test_multiple_histogram' => [
+                    'type' => 'histogram',
+                    ['labels' => ['handler' => 'foo'], 'sum' => '42', 'value' => ['0.1' => 32, 3 => 99]],
+                    ['labels' => ['handler' => 'bar'], 'sum' => '3', 'value' => ['0.2' => 0, '+Inf' => 3]],
+                ],
+            ])
+        );
+
+        $this->assertEquals(
+            <<<'EOD'
+# TYPE engelsystem_test_minimum_histogram histogram
+engelsystem_test_minimum_histogram_bucket{le="+Inf"} NaN
+engelsystem_test_minimum_histogram_sum NaN
+engelsystem_test_minimum_histogram_count NaN
+EOD,
+            $engine->get('/metrics', [
+                'test_minimum_histogram' => [
+                    'type'  => 'histogram', []
+                ],
+            ])
+        );
+    }
+
     /**
      * @covers \Engelsystem\Controllers\Metrics\MetricsEngine::canRender
      */