Added rate limiting sampler

Author: allflame

src/Sampler/ConstGenerator.php

@@ -0,0 +1,12 @@
+<?php
+declare(strict_types=1);
+
+namespace Jaeger\Sampler;
+
+class ConstGenerator implements GeneratorInterface
+{
+    public function generate(int $traceId, string $operationName): string
+    {
+        return 'const';
+    }
+}

src/Sampler/GeneratorInterface.php

@@ -0,0 +1,9 @@
+<?php
+declare(strict_types=1);
+
+namespace Jaeger\Sampler;
+
+interface GeneratorInterface
+{
+    public function generate(int $traceId, string $operationName) : string;
+}

src/Sampler/OperationGenerator.php

@@ -0,0 +1,12 @@
+<?php
+declare(strict_types=1);
+
+namespace Jaeger\Sampler;
+
+class OperationGenerator implements GeneratorInterface
+{
+    public function generate(int $traceId, string $operationName): string
+    {
+        return $operationName;
+    }
+}

src/Sampler/RateLimitingSampler.php

@@ -0,0 +1,57 @@
+<?php
+declare(strict_types=1);
+
+namespace Jaeger\Sampler;
+
+class RateLimitingSampler extends AbstractSampler
+{
+    private $rate;
+
+    private $generator;
+
+    public function __construct(float $rate, GeneratorInterface $generator)
+    {
+        $this->rate = $rate;
+        $this->generator = $generator;
+    }
+
+    public function doDecide(int $traceId, string $operationName): SamplerResult
+    {
+        $key = $this->generator->generate($traceId, $operationName);
+        if (false !== ($current = apcu_add($key, sprintf('%s:%d', time(), 1), 1 / $this->rate))) {
+            return new SamplerResult(
+                true, 0x01, [
+                        new SamplerTypeTag('ratelimiting'),
+                        new SamplerDecisionTag(true),
+                        new SamplerFlagsTag(0x01),
+                        new SamplerParamTag((string)$this->rate)
+                    ]
+            );
+        }
+
+        while (true) {
+            if (false === ($current = apcu_fetch($key))) {
+                return $this->doDecide($traceId, $operationName);
+            }
+            list ($timestamp, $count) = explode(':', $current);
+            if ($count / (time() - $timestamp) > $this->rate) {
+                return new SamplerResult(false, 0);
+            }
+            if (false === apcu_cas($key, $current, sprintf('%s:%d', $timestamp, $count + 1))) {
+                continue;
+            }
+
+            return new SamplerResult(
+                true, 0x01, [
+                        new SamplerTypeTag('ratelimiting'),
+                        new SamplerDecisionTag(true),
+                        new SamplerFlagsTag(0x01),
+                        new SamplerParamTag($key),
+                        new SamplerParamTag((string)$this->rate)
+                    ]
+            );
+        }
+
+        return new SamplerResult(false, 0);
+    }
+}