Use correct 'sample_rate' key when deriving sampleRand (#1874)

Author: cleptric

src/Tracing/PropagationContext.php

@@ -231,7 +231,7 @@ private static function parseTraceparentAndBaggage(string $traceparent, string $
                     $context->sampleRand = round(mt_rand(0, mt_getrandmax() - 1) / mt_getrandmax() * (float) $samplingContext->get('sample_rate'), 6);
                 } else {
                     // [rate, 1)
-                    $context->sampleRand = round(mt_rand(0, mt_getrandmax() - 1) / mt_getrandmax() * (1 - (float) $samplingContext->get('sample_rate')) + (float) $samplingContext->get('sample-rate'), 6);
+                    $context->sampleRand = round(mt_rand(0, mt_getrandmax() - 1) / mt_getrandmax() * (1 - (float) $samplingContext->get('sample_rate')) + (float) $samplingContext->get('sample_rate'), 6);
                 }
             } elseif ($context->parentSampled !== null) {
                 // [0, 1)

src/Tracing/TransactionContext.php

@@ -196,7 +196,7 @@ private static function parseTraceAndBaggage(string $sentryTrace, string $baggag
                     $context->getMetadata()->setSampleRand(round(mt_rand(0, mt_getrandmax() - 1) / mt_getrandmax() * (float) $samplingContext->get('sample_rate'), 6));
                 } else {
                     // [rate, 1)
-                    $context->getMetadata()->setSampleRand(round(mt_rand(0, mt_getrandmax() - 1) / mt_getrandmax() * (1 - (float) $samplingContext->get('sample_rate')) + (float) $samplingContext->get('sample-rate'), 6));
+                    $context->getMetadata()->setSampleRand(round(mt_rand(0, mt_getrandmax() - 1) / mt_getrandmax() * (1 - (float) $samplingContext->get('sample_rate')) + (float) $samplingContext->get('sample_rate'), 6));
                 }
             } elseif ($context->parentSampled !== null) {
                 // [0, 1)

tests/Tracing/PropagationContextTest.php

@@ -136,6 +136,21 @@ public function testGetTraceContext()
         ], $propagationContext->getTraceContext());
     }
 
+    public function testSampleRandRangeWhenParentNotSampledAndSampleRateProvided(): void
+    {
+        $propagationContext = PropagationContext::fromHeaders(
+            '566e3688a61d4bc888951642d6f14a19-566e3688a61d4bc8-0',
+            'sentry-sample_rate=0.4'
+        );
+
+        $sampleRand = $propagationContext->getSampleRand();
+
+        $this->assertNotNull($sampleRand);
+        // Should be within [rate, 1) and rounded to 6 decimals
+        $this->assertGreaterThanOrEqual(0.4, $sampleRand);
+        $this->assertLessThanOrEqual(0.999999, $sampleRand);
+    }
+
     /**
      * @dataProvider gettersAndSettersDataProvider
      */

tests/Tracing/TransactionContextTest.php

@@ -137,4 +137,19 @@ public static function tracingDataProvider(): iterable
             true,
         ];
     }
+
+    public function testSampleRandRangeWhenParentNotSampledAndSampleRateProvided(): void
+    {
+        $context = TransactionContext::fromHeaders(
+            '566e3688a61d4bc888951642d6f14a19-566e3688a61d4bc8-0',
+            'sentry-sample_rate=0.4'
+        );
+
+        $sampleRand = $context->getMetadata()->getSampleRand();
+
+        $this->assertNotNull($sampleRand);
+        // Should be within [rate, 1) and rounded to 6 decimals
+        $this->assertGreaterThanOrEqual(0.4, $sampleRand);
+        $this->assertLessThanOrEqual(0.999999, $sampleRand);
+    }
 }