Resource injection for class loader getResourceAsStream

instrumentation/internal/internal-class-loader/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/internal/classloader/ResourceInjectionInstrumentation.java

@@ -14,6 +14,8 @@
 import io.opentelemetry.javaagent.bootstrap.HelperResources;
 import io.opentelemetry.javaagent.extension.instrumentation.TypeInstrumentation;
 import io.opentelemetry.javaagent.extension.instrumentation.TypeTransformer;
+import java.io.IOException;
+import java.io.InputStream;
 import java.net.URL;
 import java.util.Collections;
 import java.util.Enumeration;
@@ -47,6 +49,12 @@ public void transform(TypeTransformer transformer) {
             .and(takesArguments(String.class))
             .and(returns(Enumeration.class)),
         ResourceInjectionInstrumentation.class.getName() + "$GetResourcesAdvice");
+    transformer.applyAdviceToMethod(
+        isMethod()
+            .and(named("getResourceAsStream"))
+            .and(takesArguments(String.class))
+            .and(returns(InputStream.class)),
+        ResourceInjectionInstrumentation.class.getName() + "$GetResourceAsStreamAdvice");
   }
 
   @SuppressWarnings("unused")
@@ -57,6 +65,9 @@ public static void onExit(
         @Advice.This ClassLoader classLoader,
         @Advice.Argument(0) String name,
         @Advice.Return(readOnly = false) URL resource) {
+      if (resource != null) {
+        return;
+      }
 
       URL helper = HelperResources.loadOne(classLoader, name);
       if (helper != null) {
@@ -101,4 +112,27 @@ public static void onExit(
       resources = Collections.enumeration(result);
     }
   }
+
+  @SuppressWarnings("unused")
+  public static class GetResourceAsStreamAdvice {
+
+    @Advice.OnMethodExit(suppress = Throwable.class)
+    public static void onExit(
+        @Advice.This ClassLoader classLoader,
+        @Advice.Argument(0) String name,
+        @Advice.Return(readOnly = false) InputStream inputStream) {
+      if (inputStream != null) {
+        return;
+      }
+
+      URL helper = HelperResources.loadOne(classLoader, name);
+      if (helper != null) {
+        try {
+          inputStream = helper.openStream();
+        } catch (IOException ignored) {
+          // ClassLoader.getResourceAsStream also ignores io exceptions from opening the stream
+        }
+      }
+    }
+  }
 }

instrumentation/internal/internal-class-loader/javaagent/src/test/groovy/TomcatClassloadingTest.groovy

@@ -4,28 +4,68 @@
  */
 
 import io.opentelemetry.instrumentation.test.AgentInstrumentationSpecification
+import io.opentelemetry.javaagent.bootstrap.HelperResources
+import java.nio.charset.StandardCharsets
+import java.nio.file.Files
+import java.util.stream.Collectors
 import org.apache.catalina.WebResource
 import org.apache.catalina.WebResourceRoot
 import org.apache.catalina.loader.ParallelWebappClassLoader
+import spock.lang.Shared
 
 class TomcatClassloadingTest extends AgentInstrumentationSpecification {
 
-  WebResourceRoot resources = Mock(WebResourceRoot) {
-    getResource(_) >> Mock(WebResource)
-    listResources(_) >> []
-    // Looks like 9.x.x needs this one:
-    getResources(_) >> []
-  }
-  ParallelWebappClassLoader classloader = new ParallelWebappClassLoader(null)
+  @Shared
+  ParallelWebappClassLoader classloader
 
-  def "tomcat class loading delegates to parent for agent classes"() {
-    setup:
+  def setupSpec() {
+    WebResourceRoot resources = Mock(WebResourceRoot) {
+      getResource(_) >> Mock(WebResource)
+      getClassLoaderResource(_) >> Mock(WebResource)
+      listResources(_) >> []
+      // Looks like 9.x.x needs this one:
+      getResources(_) >> []
+      getClassLoaderResources(_) >> []
+    }
+    def parentClassLoader = new ClassLoader(null) {
+    }
+    classloader = new ParallelWebappClassLoader(parentClassLoader)
     classloader.setResources(resources)
     classloader.init()
     classloader.start()
+  }
 
+  def "tomcat class loading delegates to parent for agent classes"() {
     expect:
     // If instrumentation didn't work this would blow up with NPE due to incomplete resources mocking
     classloader.loadClass("io.opentelemetry.javaagent.bootstrap.Java8BytecodeBridge")
   }
+
+  def "test resource injection"() {
+    setup:
+    def tmpFile = Files.createTempFile("hello", "tmp")
+    Files.write(tmpFile, "hello".getBytes(StandardCharsets.UTF_8))
+    def url = tmpFile.toUri().toURL()
+    HelperResources.register(classloader, "hello.txt", Arrays.asList(url))
+
+    expect:
+    classloader.getResource("hello.txt") != null
+
+    and:
+    def resources = classloader.getResources("hello.txt")
+    resources != null
+    resources.hasMoreElements()
+
+    and:
+    def inputStream = classloader.getResourceAsStream("hello.txt")
+    inputStream != null
+    String text = new BufferedReader(
+      new InputStreamReader(inputStream, StandardCharsets.UTF_8))
+      .lines()
+      .collect(Collectors.joining("\n"))
+    text == "hello"
+
+    cleanup:
+    inputStream?.close()
+  }
 }