add an spi to get access to bootstrap proxy from muzzle module

javaagent-tooling/src/main/java/io/opentelemetry/javaagent/tooling/AgentInstaller.java

@@ -137,7 +137,6 @@ public static ResettableClassFileTransformer installBytebuddyAgent(
       runBeforeAgentListeners(agentListeners, config, autoConfiguredSdk);
     }
 
-    AgentTooling.init(Utils.getBootstrapProxy());
     AgentBuilder agentBuilder =
         new AgentBuilder.Default()
             .disableClassFormatChanges()

javaagent-tooling/src/main/java/io/opentelemetry/javaagent/tooling/bootstrap/BootstrapProxyProviderImpl.java

@@ -0,0 +1,19 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.javaagent.tooling.bootstrap;
+
+import com.google.auto.service.AutoService;
+import io.opentelemetry.javaagent.tooling.Utils;
+import io.opentelemetry.javaagent.tooling.muzzle.BootstrapProxyProvider;
+
+@AutoService(BootstrapProxyProvider.class)
+public class BootstrapProxyProviderImpl implements BootstrapProxyProvider {
+
+  @Override
+  public ClassLoader getBootstrapProxy() {
+    return Utils.getBootstrapProxy();
+  }
+}

muzzle/src/main/java/io/opentelemetry/javaagent/tooling/muzzle/AgentTooling.java

@@ -5,6 +5,8 @@
 
 package io.opentelemetry.javaagent.tooling.muzzle;
 
+import java.util.Iterator;
+import java.util.ServiceLoader;
 import net.bytebuddy.agent.builder.AgentBuilder;
 
 /**
@@ -14,7 +16,8 @@
  */
 public final class AgentTooling {
 
-  private static volatile ClassLoader bootstrapProxy;
+  private static final AgentBuilder.PoolStrategy POOL_STRATEGY =
+      new AgentCachingPoolStrategy(locationStrategy(getBootstrapProxy()));
 
   public static AgentLocationStrategy locationStrategy() {
     return locationStrategy(null);
@@ -25,17 +28,19 @@ public static AgentLocationStrategy locationStrategy(ClassLoader bootstrapProxy)
   }
 
   public static AgentBuilder.PoolStrategy poolStrategy() {
-    return PoolStrategyHolder.POOL_STRATEGY;
+    return POOL_STRATEGY;
   }
 
-  public static void init(ClassLoader classLoader) {
-    bootstrapProxy = classLoader;
+  private static ClassLoader getBootstrapProxy() {
+    Iterator<BootstrapProxyProvider> iterator =
+        ServiceLoader.load(BootstrapProxyProvider.class).iterator();
+    if (iterator.hasNext()) {
+      BootstrapProxyProvider bootstrapProxyProvider = iterator.next();
+      return bootstrapProxyProvider.getBootstrapProxy();
+    }
+
+    return null;
   }
 
   private AgentTooling() {}
-
-  private static class PoolStrategyHolder {
-    private static final AgentBuilder.PoolStrategy POOL_STRATEGY =
-        new AgentCachingPoolStrategy(locationStrategy(bootstrapProxy));
-  }
 }

muzzle/src/main/java/io/opentelemetry/javaagent/tooling/muzzle/BootstrapProxyProvider.java

@@ -0,0 +1,13 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.javaagent.tooling.muzzle;
+
+/** This SPI can be used to find a class loader which can be used to look up bootstrap resources. */
+public interface BootstrapProxyProvider {
+
+  /** Provide a class loader which can be used to look up bootstrap resources. */
+  ClassLoader getBootstrapProxy();
+}