Keep the original Netty package intact when shading

AGENTS.md

@@ -11,8 +11,10 @@ The Java client and its dependencies are bundled as a single shaded JAR under `l
 `lib/ext/rabbitmq-client-netty-shaded.jar` is a shaded uber-JAR, produced by `mvn package`
 via the Maven Shade plugin (see `pom.xml`). It bundles the RabbitMQ Java client with all
 Netty modules. Netty classes are relocated from `io.netty.*` to
-`com.rabbitmq.marchhare.shaded.netty.*`, so another JRuby gem's own Netty version
+`com.rabbitmq.marchhare.shaded.io.netty.*`, so another JRuby gem's own Netty version
 (Logstash plugins, for example) cannot conflict with March Hare's.
+Keep `io.netty` in the relocated package name: Netty's native library loader only
+supports adding a prefix to the original package.
 
 The SLF4J JARs (`slf4j-api.jar` and `slf4j-simple.jar`) are not shaded and stay separate,
 so the RabbitMQ client's logging goes through whatever SLF4J backend the application uses.

lib/march_hare.rb

@@ -8,7 +8,7 @@
 
 # Single shaded JAR bundling the RabbitMQ Java client together with all Netty
 # dependencies.  Netty classes are relocated from io.netty.* to
-# com.rabbitmq.marchhare.shaded.netty.* so they cannot conflict with other gems
+# com.rabbitmq.marchhare.shaded.io.netty.* so they cannot conflict with other gems
 # (e.g. Logstash plugins) that bundle a different Netty version on the same JVM.
 require 'ext/rabbitmq-client-netty-shaded'
 

pom.xml

@@ -47,10 +47,13 @@
                   Relocate every io.netty class to a private package so that other gems
                   bundling a different Netty version do not clash with ours.
                   The RabbitMQ client's internal references are rewritten automatically.
+                  Keep the original io.netty package intact: Netty's native library
+                  loader supports prepending a namespace, but not replacing the
+                  original package.
                 -->
                 <relocation>
                   <pattern>io.netty</pattern>
-                  <shadedPattern>com.rabbitmq.marchhare.shaded.netty</shadedPattern>
+                  <shadedPattern>com.rabbitmq.marchhare.shaded.io.netty</shadedPattern>
                 </relocation>
               </relocations>
 

spec/java_dependencies_spec.rb

@@ -0,0 +1,19 @@
+RSpec.describe "Shaded Netty dependencies" do
+  it "preserves the package suffix required by Netty's native library loader" do
+    jar = java.util.jar.JarFile.new(File.expand_path("../lib/ext/rabbitmq-client-netty-shaded.jar", __dir__))
+    begin
+      loader_entry = jar.entries.to_a.map(&:name).find do |name|
+        name.end_with?("/netty/util/internal/NativeLibraryLoader.class")
+      end
+    ensure
+      jar.close
+    end
+
+    expect(loader_entry).not_to be_nil
+    loader = JavaUtilities.get_proxy_class(loader_entry.delete_suffix(".class").tr("/", "."))
+    # Exercise the prefix check without requiring a platform-specific native library
+    prefix_method = loader.java_class.declared_method("calculateMangledPackagePrefix")
+    prefix_method.accessible = true
+    expect(prefix_method.invoke_static).to eq("com_rabbitmq_marchhare_shaded_")
+  end
+end