Attempt to fix the JvmOptions in native-image

Author: jbachorik

components/environment/src/main/java/datadog/environment/JvmOptions.java

@@ -15,7 +15,6 @@
 import java.nio.file.Paths;
 import java.util.ArrayList;
 import java.util.List;
-import java.util.ListIterator;
 import java.util.StringTokenizer;
 
 /** Fetches and captures the JVM options. */
@@ -41,28 +40,35 @@ private String[] readProcFsCmdLine() {
     return null;
   }
 
-  @SuppressForbidden // Class.forName() as backup
   private List<String> findVmOptions() {
+    return findVmOptions(PROCFS_CMDLINE);
+  }
+
+  @SuppressForbidden // Class.forName() as backup
+  // Visible for testing
+  List<String> findVmOptions(String[] procfsCmdline) {
     // Try ProcFS on Linux
-    if (PROCFS_CMDLINE != null) {
+    // Be aware that when running a native image, the command line in /proc/self/cmdline is just the
+    // executable
+    if (procfsCmdline != null) {
+      // Create list of VM options
+      List<String> vmOptions = new ArrayList<>();
       // Start at 1 to skip "java" command itself
       int index = 1;
       // Look for main class or "-jar", end of VM options
-      for (; index < PROCFS_CMDLINE.length; index++) {
-        if (!PROCFS_CMDLINE[index].startsWith("-") || "-jar".equals(PROCFS_CMDLINE[index])) {
-          break;
+      // Simultaneously, collect all arguments in the VM options
+      for (; index < procfsCmdline.length; index++) {
+        String argument = procfsCmdline[index];
+        if (argument.startsWith("@")) {
+          vmOptions.addAll(getArgumentsFromFile(argument));
+        } else {
+          vmOptions.add(argument);
         }
-      }
-      // Create list of VM options
-      List<String> vmOptions = new ArrayList<>(asList(PROCFS_CMDLINE).subList(1, index + 1));
-      ListIterator<String> iterator = vmOptions.listIterator();
-      while (iterator.hasNext()) {
-        String vmOption = iterator.next();
-        if (vmOption.startsWith("@")) {
-          iterator.remove();
-          for (String argument : getArgumentsFromFile(vmOption)) {
-            iterator.add(argument);
+        if (!argument.startsWith("-") || "-jar".equals(argument)) {
+          if (index + 1 < procfsCmdline.length) {
+            vmOptions.add(procfsCmdline[index + 1]); // jar file or the main class
           }
+          break;
         }
       }
       // Insert JDK_JAVA_OPTIONS at the start if present and supported

components/environment/src/test/java/datadog/environment/JvmOptionsTest.java

@@ -105,6 +105,42 @@ void testFindVmOptions(
     assertEquals(expectedArguments.jvmOptions, result.jvmOptions, "Failed to get JVM options");
   }
 
+  @MethodSource
+  private static Stream<Arguments> procFsCmdLine() {
+    // spotless:off
+    return Stream.of(
+        arguments(
+            "No arguments",
+            new String[0],
+            emptyList()
+        ),
+        arguments(
+            "Native image launcher",
+            new String[]{"native-image-launcher", "-Xmx512m"},
+            singletonList("-Xmx512m")
+        ),
+        arguments(
+            "Java with JAR and options",
+            new String[]{"java", "-Xmx512m", "-Xms256m", "-jar", "app.jar"},
+            asList("-Xmx512m", "-Xms256m", "-jar", "app.jar")
+        ),
+        arguments(
+            "Java from class and options",
+            new String[]{"java", "-Xmx512m", "-Xms256m", "-cp", "app.jar", "Main"},
+            asList("-Xmx512m", "-Xms256m", "-cp", "app.jar", "Main")
+        ));
+    // spotless:on
+  }
+
+  @ParameterizedTest(name = "[{index}] {0}")
+  @MethodSource("procFsCmdLine")
+  void testFindVmOptionsWithProcFsCmdLine(
+      String useCase, String[] procfsCmdline, List<String> expected) throws Exception {
+    JvmOptions vmOptions = new JvmOptions();
+    List<String> found = vmOptions.findVmOptions(procfsCmdline);
+    assertEquals(expected, found);
+  }
+
   private void skipJdkJavaOptionsOnJava8(Map<String, String> environmentVariables) {
     assumeTrue(
         JavaVirtualMachine.isJavaVersionAtLeast(9)