CompositePropagator.php
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CompositePropagator.php
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	<?php
	namespace Wikimedia\Telemetry;

	use Wikimedia\Assert\Assert;
	use Wikimedia\Assert\ParameterAssertionException;

	/**
	* CompositePropagator accepts an array of other propagators.
	* It delegates to each of them in order when extracting or injecting.
	* When extracting, it returns the first non-null result.
	*/
	class CompositePropagator implements ContextPropagatorInterface {
	/** @var ContextPropagatorInterface[] */
	private $propagators;

	/**
	* @param ContextPropagatorInterface[] $propagators
	* @throws ParameterAssertionException if $propagators is empty
	*/
	public function __construct( array $propagators ) {
	Assert::parameter(
	count( $propagators ) > 0,
	'$propagators',
	'must not be empty'
	);
	$this->propagators = $propagators;
	}

	/**
	* @inheritDoc
	*/
	public function extract( array $carrier ): ?SpanContext {
	foreach ( $this->propagators as $propagator ) {
	$context = $propagator->extract( $carrier );
	if ( $context !== null ) {
	return $context;
	}
	}
	return null;
	}

	/**
	* @inheritDoc
	*/
	public function inject( ?SpanContext $context, array $carrier ): array {
	foreach ( $this->propagators as $propagator ) {
	$carrier = $propagator->inject( $context, $carrier );
	}
	return $carrier;
	}
	}