adding OTEL_PHP_EXCLUDED_URLS (#1226)

Modeled on python's feature to turn off all instrumentation for specific URLs,
https://opentelemetry.io/docs/languages/python/automatic/agent-config/#excluded-urls
this feature will effectively disable SDK autoloading if there is a request URI that
matches one of the provided excluded URLs, and no-op implementations will be used
for tracer/logger/meter providers.

examples/traces/features/ignore_request_urls.php

@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\Example;
+
+use OpenTelemetry\API\Globals;
+
+/**
+ * Define OTEL_PHP_EXCLUDED_URLS to include a pattern that matches
+ * REQUEST_URI, which effectively disables the SDK autoloader for some URLs,
+ * meaning no telemetry signals will be emitted.
+ */
+putenv('OTEL_PHP_AUTOLOAD_ENABLED=true');
+putenv('OTEL_TRACES_EXPORTER=console');
+putenv('OTEL_PHP_EXCLUDED_URLS=client/.*/info,healthcheck');
+$_SERVER['REQUEST_URI'] = 'https://example.com/v1/healthcheck';
+
+require __DIR__ . '/../../../vendor/autoload.php';
+
+$tracer = Globals::tracerProvider()->getTracer('demo');
+$tracer->spanBuilder('healthcheck')->startSpan()->end();

src/SDK/Common/Configuration/Variables.php

@@ -139,4 +139,5 @@ interface Variables
     public const OTEL_PHP_AUTOLOAD_ENABLED = 'OTEL_PHP_AUTOLOAD_ENABLED';
     public const OTEL_PHP_INTERNAL_METRICS_ENABLED = 'OTEL_PHP_INTERNAL_METRICS_ENABLED'; //whether the SDK should emit its own metrics
     public const OTEL_PHP_DISABLED_INSTRUMENTATIONS = 'OTEL_PHP_DISABLED_INSTRUMENTATIONS';
+    public const OTEL_PHP_EXCLUDED_URLS = 'OTEL_PHP_EXCLUDED_URLS';
 }

src/SDK/SdkAutoloader.php

@@ -31,7 +31,7 @@ public static function autoload(): bool
             //invalid setting, assume false
             self::$enabled = false;
         }
-        if (!self::$enabled) {
+        if (!self::$enabled || self::isIgnoredUrl()) {
             return false;
         }
         Globals::registerInitializer(function (Configurator $configurator) {
@@ -69,6 +69,30 @@ public static function autoload(): bool
         return true;
     }
 
+    /**
+     * Test whether a request URI is set, and if it matches the excluded urls configuration option
+     *
+     * @internal
+     */
+    public static function isIgnoredUrl(): bool
+    {
+        $ignoreUrls = Configuration::getList(Variables::OTEL_PHP_EXCLUDED_URLS, []);
+        if ($ignoreUrls === []) {
+            return false;
+        }
+        $url = $_SERVER['REQUEST_URI'] ?? null;
+        if (!$url) {
+            return false;
+        }
+        foreach ($ignoreUrls as $ignore) {
+            if (preg_match(sprintf('|%s|', $ignore), $url) === 1) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     /**
      * @internal
      */

tests/Unit/SDK/SdkAutoloaderTest.php

@@ -69,4 +69,59 @@ public function test_enabled_by_configuration(): void
         $this->assertNotInstanceOf(NoopTracerProvider::class, Globals::tracerProvider());
         $this->assertNotInstanceOf(NoopLoggerProvider::class, Globals::loggerProvider());
     }
+
+    public function test_ignore_urls_without_request_uri(): void
+    {
+        $this->setEnvironmentVariable(Variables::OTEL_PHP_AUTOLOAD_ENABLED, 'true');
+        $this->setEnvironmentVariable(Variables::OTEL_PHP_EXCLUDED_URLS, '*');
+        unset($_SERVER['REQUEST_URI']);
+        $this->assertFalse(SdkAutoloader::isIgnoredUrl());
+    }
+
+    /**
+     * @dataProvider ignoreUrlsProvider
+     */
+    public function test_ignore_urls(string $ignore, string $uri, bool $expected): void
+    {
+        $this->setEnvironmentVariable(Variables::OTEL_PHP_AUTOLOAD_ENABLED, 'true');
+        $this->setEnvironmentVariable(Variables::OTEL_PHP_EXCLUDED_URLS, $ignore);
+        $_SERVER['REQUEST_URI'] = $uri;
+        $this->assertSame($expected, SdkAutoloader::isIgnoredUrl());
+    }
+
+    public static function ignoreUrlsProvider(): array
+    {
+        return [
+            [
+                'foo',
+                '/foo?bar=baz',
+                true,
+            ],
+            [
+                'foo',
+                '/bar',
+                false,
+            ],
+            [
+                'foo,bar',
+                'https://example.com/bar?p1=2',
+                true,
+            ],
+            [
+                'foo,bar',
+                'https://example.com/baz?p1=2',
+                false,
+            ],
+            [
+                'client/.*/info,healthcheck',
+                'https://site/client/123/info',
+                true,
+            ],
+            [
+                'client/.*/info,healthcheck',
+                'https://site/xyz/healthcheck',
+                true,
+            ],
+        ];
+    }
 }