Fix native image build for the cases when io.netty.util.NetUtil is initialized at run-time (#10799)

Motivation:

In #10630, field substitutions were introduced for NetUtil.LOCALHOST4, NetUtil.LOCALHOST6 and NetUtil.LOCALHOST fields. They were required to allow a native image be built with most of Netty (including NetUtil) initialized at build time.

The substitutions created in #10630 only define getters, so the 3 fields can only be read in a native image.

But when NetUtil is initialized at run-time (this is what happens in #10797), its static initialization block is executed, and this block writes to all 3 fields. As the substitutions do not provide any setters, field stores are not valid, and such builds fail.

Modifications:

- Add netty-testsuite-native-image-client-runtime-init Maven module that builds a native image deferring NetUtil class initialization till run-time; this module is used to demonstrate the problem and verify the problem is gone with the fix
- Add no-op setters to substitutions for NetUtil.LOCALHOST4, NetUtil.LOCALHOST6 and NetUtil.LOCALHOST

Result:

A native image initializing NetUtil at run-time builds successfully.

Fixes #10797

common/src/main/java/io/netty/util/NetUtilSubstitutions.java

@@ -45,6 +45,10 @@ final class NetUtilSubstitutions {
             // using https://en.wikipedia.org/wiki/Initialization-on-demand_holder_idiom
             return NetUtilLocalhost4LazyHolder.LOCALHOST4;
         }
+
+        static void set(Inet4Address ignored) {
+            // a no-op setter to avoid exceptions when NetUtil is initialized at run-time
+        }
     }
 
     private static final class NetUtilLocalhost4LazyHolder {
@@ -56,6 +60,10 @@ final class NetUtilSubstitutions {
             // using https://en.wikipedia.org/wiki/Initialization-on-demand_holder_idiom
             return NetUtilLocalhost6LazyHolder.LOCALHOST6;
         }
+
+        static void set(Inet6Address ignored) {
+            // a no-op setter to avoid exceptions when NetUtil is initialized at run-time
+        }
     }
 
     private static final class NetUtilLocalhost6LazyHolder {
@@ -67,6 +75,10 @@ final class NetUtilSubstitutions {
             // using https://en.wikipedia.org/wiki/Initialization-on-demand_holder_idiom
             return NetUtilLocalhostLazyHolder.LOCALHOST;
         }
+
+        static void set(InetAddress ignored) {
+            // a no-op setter to avoid exceptions when NetUtil is initialized at run-time
+        }
     }
 
     private static final class NetUtilLocalhostLazyHolder {

pom.xml

@@ -444,6 +444,7 @@
     <module>testsuite-shading</module>
     <module>testsuite-native-image</module>
     <module>testsuite-native-image-client</module>
+    <module>testsuite-native-image-client-runtime-init</module>
     <module>transport-blockhound-tests</module>
     <module>microbench</module>
     <module>bom</module>

testsuite-native-image-client-runtime-init/pom.xml

@@ -0,0 +1,100 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ Copyright 2020 The Netty Project
+  ~
+  ~ The Netty Project licenses this file to you under the Apache License,
+  ~ version 2.0 (the "License"); you may not use this file except in compliance
+  ~ with the License. You may obtain a copy of the License at:
+  ~
+  ~   https://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing, software
+  ~ distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+  ~ WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+  ~ License for the specific language governing permissions and limitations
+  ~ under the License.
+  -->
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/maven-v4_0_0.xsd">
+
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>io.netty</groupId>
+    <artifactId>netty-parent</artifactId>
+    <version>4.1.55.Final-SNAPSHOT</version>
+  </parent>
+
+  <artifactId>netty-testsuite-native-image-client-runtime-init</artifactId>
+  <packaging>jar</packaging>
+
+  <name>Netty/Testsuite/NativeImage/ClientRuntimeInit</name>
+
+  <properties>
+    <skipJapicmp>true</skipJapicmp>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>${project.groupId}</groupId>
+      <artifactId>netty-common</artifactId>
+      <version>${project.version}</version>
+    </dependency>
+  </dependencies>
+
+  <profiles>
+    <profile>
+      <id>skipTests</id>
+      <activation>
+        <property>
+          <name>skipTests</name>
+        </property>
+      </activation>
+      <properties>
+        <skipNativeImageTestsuite>true</skipNativeImageTestsuite>
+      </properties>
+    </profile>
+  </profiles>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>com.oracle.substratevm</groupId>
+        <artifactId>native-image-maven-plugin</artifactId>
+        <version>${graalvm.version}</version>
+        <executions>
+          <execution>
+            <goals>
+              <goal>native-image</goal>
+            </goals>
+            <phase>package</phase>
+          </execution>
+        </executions>
+        <configuration>
+          <skip>${skipNativeImageTestsuite}</skip>
+          <imageName>${project.artifactId}</imageName>
+          <mainClass>io.netty.testsuite.svm.client.NativeClientWithNettyInitAtRuntime</mainClass>
+          <buildArgs>--report-unsupported-elements-at-runtime --allow-incomplete-classpath --no-fallback --initialize-at-run-time=io.netty.util.NetUtil</buildArgs>
+        </configuration>
+      </plugin>
+      <plugin>
+        <groupId>org.codehaus.mojo</groupId>
+        <artifactId>exec-maven-plugin</artifactId>
+        <version>1.6.0</version>
+        <executions>
+          <!-- This will do a whitesmoke test: if the substitutions are missing the binary will fail to run -->
+          <!-- If the metadata is missing the build above will fail -->
+          <execution>
+            <id>verify-native-image</id>
+            <phase>verify</phase>
+            <goals>
+              <goal>exec</goal>
+            </goals>
+          </execution>
+        </executions>
+        <configuration>
+          <skip>${skipNativeImageTestsuite}</skip>
+          <executable>${project.build.directory}/${project.artifactId}</executable>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>

testsuite-native-image-client-runtime-init/src/main/java/io/netty/testsuite/svm/client/NativeClientWithNettyInitAtRuntime.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2020 The Netty Project
+ *
+ * The Netty Project licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+ *
+ *   https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+package io.netty.testsuite.svm.client;
+
+import io.netty.util.NetUtil;
+
+/**
+ * A client that triggers runtime initialization of NetUtil when
+ * built to a native image.
+ */
+public final class NativeClientWithNettyInitAtRuntime {
+    /**
+     * Main entry point (not instantiable)
+     */
+    private NativeClientWithNettyInitAtRuntime() {
+    }
+
+    public static void main(String[] args) {
+        System.out.println(NetUtil.LOCALHOST4);
+        System.out.println(NetUtil.LOCALHOST6);
+        System.out.println(NetUtil.LOCALHOST);
+    }
+}

testsuite-native-image-client-runtime-init/src/main/java/io/netty/testsuite/svm/client/package-info.java

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2020 The Netty Project
+ *
+ * The Netty Project licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+ *
+ *   https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+
+/**
+ * A client that triggers runtime initialization of NetUtil when
+ * built to a native image.
+ */
+package io.netty.testsuite.svm.client;

testsuite-native-image-client/src/main/java/io/netty/testsuite/svm/client/package-info.java

@@ -15,6 +15,6 @@
  */
 
 /**
- * A hello world server that should be compiled to native.
+ * A client that uses netty-dns and gets compiled to a native image.
  */
 package io.netty.testsuite.svm.client;