ClassNotFoundException for java.net.http.HttpClient in SpanExporter extension

[v-chernyshev]

Describe the bug

I'm developing a custom OpenTelemetry agent extension that provides a SpanExporter that bridges OpenTelemetry with our proprietary telemetry solution. Implementation-wise, the encoded Collection<SpanData> must be sent over HTTP. I've tried using the built-in java.net.http.HttpClient for this purpose and, quite surprisingly, got a ClassNotFoundException from the extension class loader.

As far as I understand, it's caused by the class name filtering here:

opentelemetry-java-instrumentation/javaagent-bootstrap/src/main/java/io/opentelemetry/javaagent/bootstrap/AgentClassLoader.java

Lines 486 to 495 in 3100f0b

	@Override
	protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
	// prometheus exporter uses jdk http server, load it from the platform class loader
	// some custom extensions use java.sql classes, make these available to agent and extensions
	if (name != null
	&& (name.startsWith("com.sun.net.httpserver.") || name.startsWith("java.sql."))) {
	return platformClassLoader.loadClass(name);
	}
	return Class.forName(name, false, null);
	}

Is there a particular reason why the filter does not allow all java. classes to reach the platform class loader?

Steps to reproduce

This dummy exporter provider implementation always throws the exception for me:

public final class CustomExporterProvider implements ConfigurableSpanExporterProvider {
    @Override
    public SpanExporter createExporter(ConfigProperties properties) {
        java.net.http.HttpClient.newBuilder().build();
        return null;
    }

    @Override
    public String getName() {
        return "custom-exporter";
    }
}

Expected behavior

I believe that java.net.http.HttpClient should be usable as it's a platform-provided class.

Actual behavior

The java.net.http.HttpClient class can't be loaded.

Javaagent or library instrumentation version

v2.9.0

Environment

JDK: Zulu21.38+21-CA (build 21.0.5+11-LTS)
OS: macOS Sonoma 14.6.1

Additional context

No response

[laurit]

Is there a particular reason why the filter does not allow all java. classes to reach the platform class loader?

See

opentelemetry-java-instrumentation/javaagent-bootstrap/src/main/java/io/opentelemetry/javaagent/bootstrap/AgentClassLoader.java

Lines 468 to 470 in 3100f0b

	// We don't always delegate to platform loader because platform class loader also contains user
	// classes when running a modular application. We don't want these classes interfering with the
	// agent.

I create a PR that changes delegation to all java classes instead of just java.sql.