fix: Correctly register histograms with Redis (#47)

* fix: Correctly register histograms with Redis

Signed-off-by: Niels Grewe <niels@zasta.de>

* tests(redis histograms): Test for correct histogram observing/collecting values with unusual precision

Signed-off-by: Niels Grewe <niels@zasta.de>

Author: ngrewe

src/Prometheus/Storage/Redis.php

@@ -218,12 +218,13 @@ public function updateHistogram(array $data): void
 
         $this->redis->eval(
             <<<LUA
-local increment = redis.call('hIncrByFloat', KEYS[1], ARGV[1], ARGV[3])
+local result = redis.call('hIncrByFloat', KEYS[1], ARGV[1], ARGV[3])
 redis.call('hIncrBy', KEYS[1], ARGV[2], 1)
-if increment == ARGV[3] then
+if tonumber(result) >= tonumber(ARGV[3]) then
     redis.call('hSet', KEYS[1], '__meta', ARGV[4])
     redis.call('sAdd', KEYS[2], KEYS[1])
 end
+return result
 LUA
             ,
             [

tests/Test/Prometheus/AbstractHistogramTest.php

@@ -21,9 +21,28 @@ abstract class AbstractHistogramTest extends TestCase
      */
     public $adapter;
 
+
+    /**
+     * @var string
+     */
+    private $savedPrecision;
+
+    private const HIGH_PRECISION = "17";
+
     public function setUp(): void
     {
         $this->configureAdapter();
+        $savedPrecision = ini_get('serialize_precision');
+        if (!is_string($savedPrecision)) {
+            $savedPrecision = '-1';
+        }
+        $this->savedPrecision = $savedPrecision;
+        ini_set('serialize_precision', self::HIGH_PRECISION);
+    }
+
+    public function tearDown(): void
+    {
+        ini_set('serialize_precision', $this->savedPrecision);
     }
 
     abstract public function configureAdapter(): void;
@@ -237,6 +256,27 @@ public function itShouldObserveValuesOfTypeDouble(): void
         );
     }
 
+    /**
+     * @test
+     */
+    public function itShouldObserveValuesOfTypeDoubleWithUnusualPrecision(): void
+    {
+        $histogram = new Histogram(
+            $this->adapter,
+            'test',
+            'some_metric',
+            'this is for testing',
+            [],
+            [1.0]
+        );
+        ini_set("serialize_precision", "17");
+        $histogram->observe(1.1 * 2 ** 53);
+        self::assertThat(
+            $this->adapter->collect(),
+            self::logicalNot(self::isEmpty())
+        );
+    }
+
     /**
      * @test
      */