create text map propagators from registry

removing undocumented dependency between sdk and extension by adding text map propagators to a registry
as part of composer autoloading, similar to how exporters, transports etc are treated.

composer.json

@@ -67,7 +67,9 @@
             "src/Contrib/Grpc/_register.php",
             "src/Contrib/Newrelic/_register.php",
             "src/Contrib/Zipkin/_register.php",
+            "src/Extension/Propagator/B3/_register.php",
             "src/SDK/Metrics/MetricExporter/_register.php",
+            "src/SDK/Propagation/_register.php",
             "src/SDK/Trace/SpanExporter/_register.php",
             "src/SDK/Common/Dev/Compatibility/_load.php",
             "src/SDK/Common/Util/functions.php",

examples/autoload_sdk.php

@@ -9,6 +9,7 @@
 putenv('OTEL_EXPORTER_OTLP_METRICS_PROTOCOL=grpc');
 putenv('OTEL_EXPORTER_OTLP_ENDPOINT=http://collector:4317');
 putenv('OTEL_PHP_TRACES_PROCESSOR=batch');
+putenv('OTEL_PROPAGATORS=b3,baggage,tracecontext');
 
 echo 'autoloading SDK example starting...' . PHP_EOL;
 

src/API/Baggage/Propagation/BaggagePropagatorFactory.php

@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\API\Baggage\Propagation;
+
+use OpenTelemetry\Context\Propagation\TextMapPropagatorInterface;
+
+class BaggagePropagatorFactory implements \OpenTelemetry\Context\Propagation\TextMapPropagatorFactoryInterface
+{
+    public function create(): TextMapPropagatorInterface
+    {
+        return BaggagePropagator::getInstance();
+    }
+}

src/API/Trace/Propagation/TraceContextPropagatorFactory.php

@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\API\Trace\Propagation;
+
+use OpenTelemetry\Context\Propagation\TextMapPropagatorFactoryInterface;
+use OpenTelemetry\Context\Propagation\TextMapPropagatorInterface;
+
+class TraceContextPropagatorFactory implements TextMapPropagatorFactoryInterface
+{
+    public function create(): TextMapPropagatorInterface
+    {
+        return TraceContextPropagator::getInstance();
+    }
+}

src/Context/Propagation/NoopTextMapPropagatorFactory.php

@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\Context\Propagation;
+
+class NoopTextMapPropagatorFactory implements TextMapPropagatorFactoryInterface
+{
+    public function create(): TextMapPropagatorInterface
+    {
+        return NoopTextMapPropagator::getInstance();
+    }
+}

src/Context/Propagation/TextMapPropagatorFactoryInterface.php

@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\Context\Propagation;
+
+interface TextMapPropagatorFactoryInterface
+{
+    public function create(): TextMapPropagatorInterface;
+}

src/Extension/Propagator/B3/B3MultiPropagatorFactory.php

@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\Extension\Propagator\B3;
+
+use OpenTelemetry\Context\Propagation\TextMapPropagatorFactoryInterface;
+use OpenTelemetry\Context\Propagation\TextMapPropagatorInterface;
+
+class B3MultiPropagatorFactory implements TextMapPropagatorFactoryInterface
+{
+    public function create(): TextMapPropagatorInterface
+    {
+        return B3Propagator::getB3MultiHeaderInstance();
+    }
+}

src/Extension/Propagator/B3/B3SinglePropagatorFactory.php

@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\Extension\Propagator\B3;
+
+use OpenTelemetry\Context\Propagation\TextMapPropagatorFactoryInterface;
+use OpenTelemetry\Context\Propagation\TextMapPropagatorInterface;
+
+class B3SinglePropagatorFactory implements TextMapPropagatorFactoryInterface
+{
+    public function create(): TextMapPropagatorInterface
+    {
+        return B3Propagator::getB3SingleHeaderInstance();
+    }
+}

src/Extension/Propagator/B3/_register.php

@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+\OpenTelemetry\SDK\FactoryRegistry::registerTextMapPropagatorFactory(
+    \OpenTelemetry\SDK\Common\Configuration\KnownValues::VALUE_B3,
+    \OpenTelemetry\Extension\Propagator\B3\B3SinglePropagatorFactory::class
+);
+\OpenTelemetry\SDK\FactoryRegistry::registerTextMapPropagatorFactory(
+    \OpenTelemetry\SDK\Common\Configuration\KnownValues::VALUE_B3_MULTI,
+    \OpenTelemetry\Extension\Propagator\B3\B3MultiPropagatorFactory::class
+);

src/Extension/Propagator/B3/composer.json

@@ -18,6 +18,9 @@
     "autoload": {
         "psr-4": {
             "OpenTelemetry\\Extension\\Propagator\\B3\\": "."
-        }
+        },
+        "files": [
+            "_register.php"
+        ]
     }
 }

src/SDK/FactoryRegistry.php

@@ -4,6 +4,7 @@
 
 namespace OpenTelemetry\SDK;
 
+use OpenTelemetry\Context\Propagation\TextMapPropagatorFactoryInterface;
 use OpenTelemetry\SDK\Common\Export\TransportFactoryInterface;
 use OpenTelemetry\SDK\Metrics\MetricExporterFactoryInterface;
 use OpenTelemetry\SDK\Trace\SpanExporter\SpanExporterFactoryInterface;
@@ -14,6 +15,7 @@ class FactoryRegistry
     private static array $spanExporterFactories = [];
     private static array $transportFactories = [];
     private static array $metricExporterFactories = [];
+    private static array $textMapPropagatorFactories = [];
 
     /**
      * @param TransportFactoryInterface|class-string<TransportFactoryInterface> $factory
@@ -84,6 +86,26 @@ public static function registerMetricExporterFactory(string $exporter, $factory,
         self::$metricExporterFactories[$exporter] = $factory;
     }
 
+    public static function registerTextMapPropagatorFactory(string $name, $factory, bool $clobber = false): void
+    {
+        if (!$clobber && array_key_exists($name, self::$textMapPropagatorFactories)) {
+            return;
+        }
+        if (!is_subclass_of($factory, TextMapPropagatorFactoryInterface::class)) {
+            trigger_error(
+                sprintf(
+                    'Cannot register text map propagator factory: %s must exist and implement %s',
+                    is_string($factory) ? $factory : get_class($factory),
+                    TextMapPropagatorFactoryInterface::class
+                ),
+                E_USER_WARNING
+            );
+
+            return;
+        }
+        self::$textMapPropagatorFactories[$name] = $factory;
+    }
+
     public static function spanExporterFactory(string $exporter): SpanExporterFactoryInterface
     {
         if (!array_key_exists($exporter, self::$spanExporterFactories)) {
@@ -124,4 +146,16 @@ public static function metricExporterFactory(string $exporter): MetricExporterFa
 
         return $factory;
     }
+
+    public static function textMapPropagatorFactory(string $name): TextMapPropagatorFactoryInterface
+    {
+        if (!array_key_exists($name, self::$textMapPropagatorFactories)) {
+            throw new RuntimeException('Text map propagator factory not registered for: ' . $name);
+        }
+        $class = self::$textMapPropagatorFactories[$name];
+        $factory = (is_callable($class)) ? $class : new $class();
+        assert($factory instanceof TextMapPropagatorFactoryInterface);
+
+        return $factory;
+    }
 }

src/SDK/Propagation/PropagatorFactory.php

@@ -9,28 +9,21 @@
 use OpenTelemetry\Context\Propagation\TextMapPropagatorInterface;
 use OpenTelemetry\SDK\Behavior\LogsMessagesTrait;
 use OpenTelemetry\SDK\Common\Configuration\Configuration;
-use OpenTelemetry\SDK\Common\Configuration\KnownValues;
 use OpenTelemetry\SDK\Common\Configuration\Variables;
+use OpenTelemetry\SDK\FactoryRegistry;
 
 class PropagatorFactory
 {
     use LogsMessagesTrait;
 
-    private const KNOWN_PROPAGATORS = [
-        KnownValues::VALUE_TRACECONTEXT => ['\OpenTelemetry\API\Trace\Propagation\TraceContextPropagator', 'getInstance'],
-        KnownValues::VALUE_BAGGAGE => ['\OpenTelemetry\API\Baggage\Propagation\BaggagePropagator', 'getInstance'],
-        KnownValues::VALUE_B3 => ['\OpenTelemetry\Extension\Propagator\B3\B3Propagator', 'getB3SingleHeaderInstance'],
-        KnownValues::VALUE_B3_MULTI => ['\OpenTelemetry\Extension\Propagator\B3\B3Propagator', 'getB3MultiHeaderInstance'],
-    ];
-
     public function create(): TextMapPropagatorInterface
     {
         $propagators = Configuration::getList(Variables::OTEL_PROPAGATORS);
         switch (count($propagators)) {
             case 0:
                 return new NoopTextMapPropagator();
             case 1:
-                return $this->buildPropagator($propagators[0]) ?? new NoopTextMapPropagator();
+                return $this->buildPropagator($propagators[0]);
             default:
                 return new MultiTextMapPropagator($this->buildPropagators($propagators));
         }
@@ -43,41 +36,22 @@ private function buildPropagators(array $names): array
     {
         $propagators = [];
         foreach ($names as $name) {
-            $propagator = $this->buildPropagator($name);
-            if ($propagator !== null) {
-                $propagators[] = $propagator;
-            }
+            $propagators[] = $this->buildPropagator($name);
         }
 
         return $propagators;
     }
 
-    private function buildPropagator(string $name): ?TextMapPropagatorInterface
+    private function buildPropagator(string $name): TextMapPropagatorInterface
     {
-        switch ($name) {
-            case KnownValues::VALUE_NONE:
-                return null;
-            case KnownValues::VALUE_XRAY:
-            case KnownValues::VALUE_OTTRACE:
-                self::logWarning('Unimplemented propagator: ' . $name);
-
-                return null;
-            default:
-                if (!array_key_exists($name, self::KNOWN_PROPAGATORS)) {
-                    self::logWarning('Unknown propagator: ' . $name);
-
-                    return null;
-                }
-                $parts = self::KNOWN_PROPAGATORS[$name];
-
-                try {
-                    return call_user_func($parts);
-                } catch (\Throwable $e) {
-                    self::logError(sprintf('Unable to create %s propagator: %s', $name, $e->getMessage()));
-
-                    return null;
-                }
+        try {
+            $factory = FactoryRegistry::textMapPropagatorFactory($name);
 
+            return $factory->create();
+        } catch (\RuntimeException $e) {
+            self::logWarning($e->getMessage());
         }
+
+        return NoopTextMapPropagator::getInstance();
     }
 }

src/SDK/Propagation/_register.php

@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+\OpenTelemetry\SDK\FactoryRegistry::registerTextMapPropagatorFactory(
+    \OpenTelemetry\SDK\Common\Configuration\KnownValues::VALUE_BAGGAGE,
+    \OpenTelemetry\API\Baggage\Propagation\BaggagePropagatorFactory::class
+);
+\OpenTelemetry\SDK\FactoryRegistry::registerTextMapPropagatorFactory(
+    \OpenTelemetry\SDK\Common\Configuration\KnownValues::VALUE_TRACECONTEXT,
+    \OpenTelemetry\API\Trace\Propagation\TraceContextPropagatorFactory::class
+);
+\OpenTelemetry\SDK\FactoryRegistry::registerTextMapPropagatorFactory(
+    \OpenTelemetry\SDK\Common\Configuration\KnownValues::VALUE_NONE,
+    \OpenTelemetry\Context\Propagation\NoopTextMapPropagatorFactory::class
+);

src/SDK/composer.json

@@ -32,6 +32,7 @@
         "files": [
             "Common/Util/functions.php",
             "Metrics/MetricExporter/_register.php",
+            "Propagation/_register.php",
             "Trace/SpanExporter/_register.php",
             "_autoload.php"
         ]