Respect Datadog DD_TRACE_SAMPLE_RATE rate limiting environment variable

src/Profiler/DatadogProfiler.php

@@ -21,10 +21,19 @@ class DatadogProfiler implements ProfilerInterface
     private ?Scope $scope = null;
 
     private LoggerInterface $logger;
+    private ?float $sampleRate;
 
     public function __construct(LoggerInterface $logger)
     {
         $this->logger = $logger;
+
+        $sampleRateString = getenv('DD_TRACE_SAMPLE_RATE');
+        if(is_numeric($sampleRateString)) {
+            $sampleRate = floatval($sampleRateString);
+            $this->sampleRate = $sampleRate;
+        } else {
+            $this->sampleRate = null;
+        }
     }
 
     public function start(string $name, ?string $kind = null): void
@@ -33,6 +42,10 @@ public function start(string $name, ?string $kind = null): void
             return;
         }
 
+        if($this->rateLimited()) {
+            return;
+        }
+
         if (dd_trace_env_config('DD_TRACE_GENERATE_ROOT_SPAN')) {
             $this->logger->error(
                 sprintf('You should set DD_TRACE_GENERATE_ROOT_SPAN=0 when using %s.', self::class)
@@ -89,6 +102,15 @@ public function stopAndIgnore(): void
         GlobalTracer::set(new Tracer());
     }
 
+    private function rateLimited(): bool
+    {
+        if($this->sampleRate) {
+            $randomFloat = mt_rand() / mt_getrandmax(); // between 0 and 1
+            return $randomFloat > $this->sampleRate;
+        }  
+        return false;
+    }
+
     private function isEnabled(): bool
     {
         return \extension_loaded('ddtrace')