Add traceresponse propagator (#143)

- Cleanup dependencies
- Add PHPStan config and clean code
- Allow PHP 7 compatible symfony/http-client
- Add TraceResponse to .gitsplit
- Fix test method casing

Author: cedricziel

.php-cs-fixer.php

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+<?php
+$finder = PhpCsFixer\Finder::create()
+    ->exclude('vendor')
+    ->exclude('var/cache')
+    ->in(__DIR__);
+
+$config = new PhpCsFixer\Config();
+return $config->setRules([
+    'concat_space' => ['spacing' => 'one'],
+    'declare_equal_normalize' => ['space' => 'none'],
+    'is_null' => true,
+    'modernize_types_casting' => true,
+    'ordered_imports' => true,
+    'php_unit_construct' => true,
+    'single_line_comment_style' => true,
+    'yoda_style' => false,
+    '@PSR2' => true,
+    'array_syntax' => ['syntax' => 'short'],
+    'blank_line_after_opening_tag' => true,
+    'blank_line_before_statement' => true,
+    'cast_spaces' => true,
+    'declare_strict_types' => true,
+    'function_typehint_space' => true,
+    'include' => true,
+    'lowercase_cast' => true,
+    'new_with_braces' => true,
+    'no_extra_blank_lines' => true,
+    'no_leading_import_slash' => true,
+    'echo_tag_syntax' => true,
+    'no_unused_imports' => true,
+    'no_useless_else' => true,
+    'no_useless_return' => true,
+    'phpdoc_order' => true,
+    'phpdoc_scalar' => true,
+    'phpdoc_types' => true,
+    'short_scalar_cast' => true,
+    'single_blank_line_before_namespace' => true,
+    'single_quote' => true,
+    'trailing_comma_in_multiline' => true,
+    ])
+    ->setRiskyAllowed(true)
+    ->setFinder($finder);
+

README.md

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+# OpenTelemetry TraceResponse Propagator
+
+**Note:** This package is experimental as `traceresponse` is currently an editors' draft.
+
+This package provides a [Trace Context HTTP Response Headers Format](https://w3c.github.io/trace-context/#trace-context-http-response-headers-format)
+propagator to inject the current span context into Response datastructures.
+
+The main goal is to allow client-side technology (Real User Monitoring, HTTP Clients) to record
+the server side context in order to allow referencing it.
+
+## Requirements
+
+* OpenTelemetry SDK and exporters (required to actually export traces)
+
+Optional:
+* OpenTelemetry extension (Some instrumentations can automatically use the `TraceResponsePropagator`)
+
+## Usage
+
+Assuming there is an active `SpanContext`, you can inject it into your response as follows:
+
+```php
+// your framework probably provides a datastructure to model HTTP responses
+// and allows you to hook into the end of a request / listen to a matching event.
+$response = new Response();
+
+// get the current scope, bail out if none
+$scope = Context::storage()->scope();
+if (null === $scope) {
+    return;
+}
+
+// create a PropagationSetterInterface that knows how to inject response headers
+$propagationSetter = new class implements OpenTelemetry\Context\Propagation\PropagationSetterInterface {
+    public function set(&$carrier, string $key, string $value) : void {
+        $carrier->headers->set($key, $value);
+    }
+};
+$propagator = new TraceResponseProgator();
+$propagator->inject($response, $propagationSetter, $scope->context());
+```
+
+## Installation via composer
+
+```bash
+$ composer require open-telemetry/opentelemetry-propagation-traceresponse
+```
+
+## Installing dependencies and executing tests
+
+From TraceResponse subdirectory:
+
+```bash
+$ composer install
+$ ./vendor/bin/phpunit tests
+```

composer.json

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+{
+  "name": "open-telemetry/opentelemetry-propagation-traceresponse",
+  "description": "OpenTelemetry traceresponse propagator.",
+  "keywords": ["opentelemetry", "otel", "open-telemetry", "propagator", "traceresponse"],
+  "type": "library",
+  "homepage": "https://opentelemetry.io/docs/php",
+  "readme": "./README.md",
+  "license": "Apache-2.0",
+  "minimum-stability": "dev",
+  "prefer-stable": true,
+  "require": {
+    "php": "^7.0|^8.0",
+    "open-telemetry/context": "^1.0"
+  },
+  "autoload": {
+    "psr-4": {
+      "OpenTelemetry\\Contrib\\Propagation\\TraceResponse\\": "src/"
+    }
+  },
+  "require-dev": {
+    "friendsofphp/php-cs-fixer": "^3",
+    "phan/phan": "^5.0",
+    "phpstan/phpstan": "^1.1",
+    "phpstan/phpstan-phpunit": "^1.0",
+    "psalm/plugin-phpunit": "^0.16",
+    "open-telemetry/sdk": "^1.0",
+    "phpunit/phpunit": "^9.5",
+    "vimeo/psalm": "^4.0",
+    "symfony/http-client": "^5.4|^6.0",
+    "guzzlehttp/promises": "^1.5",
+    "php-http/message-factory": "^1.0",
+    "nyholm/psr7": "^1.5"
+  },
+  "config": {
+    "allow-plugins": {
+      "php-http/discovery": true
+    }
+  }
+}

phpstan.neon.dist

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+includes:
+    - vendor/phpstan/phpstan-phpunit/extension.neon
+
+parameters:
+    tmpDir: var/cache/phpstan
+    level: 5
+    paths:
+        - src
+        - tests

phpunit.xml.dist

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+<?xml version="1.0" encoding="UTF-8"?>
+
+<phpunit
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.5/phpunit.xsd"
+    backupGlobals="false"
+    backupStaticAttributes="false"
+    cacheResult="false"
+    colors="false"
+    convertErrorsToExceptions="true"
+    convertNoticesToExceptions="true"
+    convertWarningsToExceptions="true"
+    forceCoversAnnotation="false"
+    processIsolation="false"
+    stopOnError="false"
+    stopOnFailure="false"
+    stopOnIncomplete="false"
+    stopOnSkipped="false"
+    stopOnRisky="false"
+    timeoutForSmallTests="1"
+    timeoutForMediumTests="10"
+    timeoutForLargeTests="60"
+    verbose="true">
+
+    <coverage processUncoveredFiles="true" disableCodeCoverageIgnore="false">
+        <include>
+            <directory>src</directory>
+        </include>
+    </coverage>
+
+    <php>
+        <ini name="date.timezone" value="UTC" />
+        <ini name="display_errors" value="On" />
+        <ini name="display_startup_errors" value="On" />
+        <ini name="error_reporting" value="E_ALL" />
+    </php>
+
+    <testsuites>
+        <testsuite name="unit">
+            <directory>tests/Unit</directory>
+        </testsuite>
+    </testsuites>
+
+</phpunit>

psalm.xml.dist

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+<?xml version="1.0"?>
+<psalm
+    errorLevel="3"
+    cacheDirectory="var/cache/psalm"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xmlns="https://getpsalm.org/schema/config"
+    xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd">
+    <projectFiles>
+        <directory name="src"/>
+        <directory name="tests"/>
+    </projectFiles>
+    <plugins>
+        <pluginClass class="Psalm\PhpUnitPlugin\Plugin"/>
+    </plugins>
+</psalm>

src/ResponsePropagator.php

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+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\Contrib\Propagation\TraceResponse;
+
+use OpenTelemetry\Context\ContextInterface;
+use OpenTelemetry\Context\Propagation\PropagationSetterInterface;
+
+/**
+ * This propagator type is used to inject the trace-context into HTTP responses.
+ */
+interface ResponsePropagator
+{
+    /**
+     * Injects specific values from the provided {@see ContextInterface} into the provided carrier
+     * via an {@see PropagationSetterInterface}.
+     *
+     * @see https://github.com/open-telemetry/opentelemetry-specification/blob/v1.6.1/specification/context/api-propagators.md#textmap-inject
+     *
+     * @param mixed $carrier
+     */
+    public function inject(&$carrier, PropagationSetterInterface $setter = null, ContextInterface $context = null): void;
+}

src/TraceResponsePropagator.php

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+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\Contrib\Propagation\TraceResponse;
+
+use OpenTelemetry\API\Trace\Span;
+use OpenTelemetry\Context\Context;
+use OpenTelemetry\Context\ContextInterface;
+use OpenTelemetry\Context\Propagation\ArrayAccessGetterSetter;
+use OpenTelemetry\Context\Propagation\PropagationSetterInterface;
+
+/**
+ * Provides a ResponsePropagator for the Trace Context HTTP Response Headers Format
+ *
+ * @see https://w3c.github.io/trace-context/#trace-context-http-response-headers-format
+ */
+final class TraceResponsePropagator implements ResponsePropagator
+{
+    const IS_SAMPLED = '1';
+    const NOT_SAMPLED = '0';
+    const SUPPORTED_VERSION = '00';
+    const TRACERESPONSE = 'traceresponse';
+
+    public function fields(): array
+    {
+        return [
+            self::TRACERESPONSE,
+        ];
+    }
+
+    public function inject(&$carrier, ?PropagationSetterInterface $setter = null, ?ContextInterface $context = null): void
+    {
+        $setter = $setter ?? ArrayAccessGetterSetter::getInstance();
+        $context = $context ?? Context::getCurrent();
+        $spanContext = Span::fromContext($context)->getContext();
+
+        if (!$spanContext->isValid()) {
+            return;
+        }
+
+        $traceId = $spanContext->getTraceId();
+        $spanId = $spanContext->getSpanId();
+
+        $samplingFlag = $spanContext->isSampled() ? self::IS_SAMPLED : self::NOT_SAMPLED;
+
+        $header = self::SUPPORTED_VERSION . '-' . $traceId . '-' . $spanId . '-' . $samplingFlag;
+        $setter->set($carrier, self::TRACERESPONSE, $header);
+    }
+}