Quarkus: java.net.URL not supported in native mode

[jefrajames]

Describe the bug
java.net.URL is not supported by GraalVM 20.2.0. Packaging a Quarkus native image is not possible and produces the following error:

Error: com.oracle.svm.hosted.substitute.DeletedElementException: Unsupported field java.net.URL.handlers is reachable

This seems to be a GraalVM limitation/decision as described in this issue .

Having URL data is common place. Is there any standard recommandation, workaround for Quarkus users?

Expected behavior

mvn package -Pnative
working with java.net.URL data

Actual behavior

mvn package -Pnative
not working with java.net.URL data

To Reproduce

This simple GitHub project reproduces this issue.

Configuration

# Add your application.properties here, if applicable.
quarkus.native.additional-build-args=--initialize-at-run-time=io.smallrye.graphql.cdi.validation.ValidationService

Environment (please complete the following information):

• Output of uname -a or ver: Darwin MBP-de-powerj 17.7.0 Darwin Kernel Version 17.7.0: Mon Aug 31 22:11:23 PDT 2020; root:xnu-4570.71.82.6~1/RELEASE_X86_64 x86_64
• Output of java -version: openjdk version "11.0.7" 2020-04-14
  OpenJDK Runtime Environment AdoptOpenJDK (build 11.0.7+10)
  Eclipse OpenJ9 VM AdoptOpenJDK (build openj9-0.20.0, JRE 11 Mac OS X amd64-64-Bit Compressed References 20200428_567 (JIT enabled, AOT enabled)
  OpenJ9 - 05fa2d361
  OMR - d4365f371
  JCL - 838028fc9d based on jdk-11.0.7+10)
• GraalVM version (if different from Java): 20.2.0
• Quarkus version or git rev: 1.8.1.Final
• Build tool (ie. output of mvnw --version or gradlew --version): Maven home: /Users/powerj/.m2/wrapper/dists/apache-maven-3.6.3-bin/1iopthnavndlasol9gbrbg6bf2/apache-maven-3.6.3
  Java version: 11.0.7, vendor: Eclipse OpenJ9, runtime: /Library/Java/JavaVirtualMachines/adoptopenjdk-11-openj9.jdk/Contents/Home
  Default locale: fr_FR, platform encoding: UTF-8
  OS name: "mac os x", version: "10.13.6", arch: "x86_64", family: "mac"

Additional context
java.net.URL is supported in JVM mode.

[phillip-kruger]

@jefrajames - not sure how to fix this one. Asking on Zulip.

[Sanne]

Just to clarify, that error doesn't mean that you can't use URL, it means you can't use its handlers field.

The code will need to be refactored a bit to avoid using the handlers field. Hopefully that's possible?

[dmlloyd]

It's not really clear what is causing the failure; we need to determine how that deleted field was considered reachable.

[jaikiran]

I looked into this a bit and what seems to be happening is that this appears to be triggering a potential bug in GraalVM. The call tree with that reproducer application (the one linked in this issue) is extremely large so it isn't easy to copy/paste here. I was however able to easily narrow this down to a simple application which when built as a native-image runs into this same issue. Here's the trivial Java code:

import javax.enterprise.util.AnnotationLiteral;
import java.net.URL;

public class URLProxyTest {

    public static void main(final String[] args) throws Exception {
        final AnnotationLiteral dummy = new AnnotationLiteral() {
        };
        final URL url = new URL("file://ignore");
        System.out.println("Just here to keep this reachable " + dummy + " " + url.getPath());      
    }
}

and then (importantly) add java.net.URL as marked for reflection, using this reflection.json file:

[
  {
    "name" : "java.net.URL",
    "allDeclaredConstructors" : true,
    "allPublicConstructors" : true,
    "allDeclaredMethods" : true,
    "allPublicMethods" : true,
    "allDeclaredClasses" : true,
    "allPublicClasses" : true
  }
]

Run the native-image generation command:

$GRAALVM_HOME/bin/native-image -classpath lib/cdi-api-1.0.jar:. URLProxyTest --no-server -H:+ReportExceptionStackTraces --no-fallback -H:ReflectionConfigurationFiles=reflection.json -H:+PrintAnalysisCallTree

(make sure you have cdi-api jar in the lib directory)

and you should see this same exception:

Caused by: com.oracle.graal.pointsto.constraints.UnsupportedFeatureException: com.oracle.svm.hosted.substitute.DeletedElementException: Unsupported field java.net.URL.handlers is reachable
To diagnose the issue, you can add the option --report-unsupported-elements-at-runtime. The unsupported element is then reported at run time when it is accessed the first time.
Detailed message:
Trace: 
    at parsing java.net.URL.setURLStreamHandlerFactory(URL.java:1213)
Call path from entry point to java.net.URL.setURLStreamHandlerFactory(URLStreamHandlerFactory): 
    at java.net.URL.setURLStreamHandlerFactory(URL.java:1205)
    at com.oracle.svm.reflect.URL_setURLStreamHandlerFactory_8b4d2aa28c41f22bcb499464d696277608a31df4_24.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Method.java:566)
    at javax.enterprise.util.AnnotationLiteral.invoke(AnnotationLiteral.java:333)
    at javax.enterprise.util.AnnotationLiteral.toString(AnnotationLiteral.java:134)
    at java.lang.String.valueOf(String.java:2951)
    at java.io.PrintStream.print(PrintStream.java:745)
    at java.io.PrintStream.println(PrintStream.java:882)
    at com.oracle.svm.jni.functions.JNIFunctions.ExceptionDescribe(JNIFunctions.java:759)
    at com.oracle.svm.core.code.IsolateEnterStub.JNIFunctions_ExceptionDescribe_b5412f7570bccae90b000bc37855f00408b2ad73(generated:0)

    at com.oracle.graal.pointsto.constraints.UnsupportedFeatures.report(UnsupportedFeatures.java:126)
    at com.oracle.svm.hosted.NativeImageGenerator.runPointsToAnalysis(NativeImageGenerator.java:750)
    ... 8 more

The AnnotationLiteral in combination with marking URL for reflective access seems to trigger this issue. The root cause is this (IMO, incomplete subsititution) https://github.com/oracle/graal/blob/master/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/JavaNetSubstitutions.java#L59. It marks handlers field as deleted and then substitutes getURLStreamHandler (one of the methods that would have used this handlers) but it doesn't substitute or @Delete the setURLStreamHandlerFactory[1] which too uses this handlers field.

The reason why it shows up in the user's Quarkus application, I guess is because of this endpoint:

@GET
    @Produces(MediaType.TEXT_PLAIN)
    @Path("url")
    public URL quarkusURL() throws MalformedURLException {
        return new URL("http://quarkus.io");
    }

The return type gets marked for reflection from what I remember.

[1] https://github.com/openjdk/jdk11/blob/master/src/java.base/share/classes/java/net/URL.java#L1181

[jaikiran]

I've opened a PR in graal repo with a potential fix for this https://github.com/oracle/graal/pull/2889. Given how URL protocols need special handling in native image[1], AFAIK, URL.setURLStreamHandlerFactory isn't supported at runtime anyway. So I think that PR should be OK.
I've given that change a try both against my trivial reproducer as well as the linked Quarkus application reproducer. Both of them pass with this change.

[1] https://github.com/oracle/graal/blob/master/substratevm/URLProtocols.md