#47: Initial POC of connecting to another VM

.gitignore

@@ -92,4 +92,6 @@ gradle-app.setting
 # VSCode Project
 .classpath
 .project
-.settings
+.settings
+
+*.hprof

agent/src/main/java/com/octogonapus/omj/agent/AgentLibJarExtractor.java

@@ -16,19 +16,12 @@
  */
 package com.octogonapus.omj.agent;
 
-import com.octogonapus.omj.util.Util;
+import com.octogonapus.omj.util.JarExtractor;
 import java.io.File;
 import java.io.IOException;
-import java.io.InputStream;
-import java.nio.file.Files;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 public final class AgentLibJarExtractor {
 
-  private static File agentLibAllJar = null;
-  private static final Logger logger = LoggerFactory.getLogger(AgentLibJarExtractor.class);
-
   /**
    * Extracts the agent-lib jar from our jar and into a file.
    *
@@ -37,40 +30,6 @@ public final class AgentLibJarExtractor {
    */
   @SuppressWarnings("ResultOfMethodCallIgnored")
   public static File extractJar() throws IOException {
-    try (final var agentLib = ClassLoader.getSystemResourceAsStream("agent-lib-all")) {
-      if (agentLib == null) {
-        throw new IOException("Could not locate agent-lib-all resource.");
-      }
-
-      // Extract the Jar and save it to agentLibAllJar so that subsequent calls do not try to
-      // extract the Jar again.
-      if (agentLibAllJar == null) {
-        Util.getAgentLibJarDir().toFile().mkdirs();
-        final var file = Util.getAgentLibJarDir().resolve("agent-lib-all.jar").toFile();
-        logger.debug("Extracting agent-lib-all.jar into {}", file.getAbsolutePath());
-        file.createNewFile();
-        copyStreamToFile(file, agentLib);
-        agentLibAllJar = file;
-      }
-
-      return agentLibAllJar;
-    }
-  }
-
-  private static void copyStreamToFile(File file, InputStream lib) throws IOException {
-    try (final var os = Files.newOutputStream(file.toPath())) {
-      final var buffer = new byte[0xFFFF];
-      int readBytes;
-      while (true) {
-        readBytes = lib.read(buffer);
-
-        // -1 means end of stream
-        if (readBytes == -1) {
-          break;
-        }
-
-        os.write(buffer, 0, readBytes);
-      }
-    }
+    return JarExtractor.extractJar("agent-lib-all");
   }
 }

agent/src/main/kotlin/com/octogonapus/omj/agent/Agent.kt

@@ -31,6 +31,15 @@ object Agent {
 
     @JvmStatic
     fun premain(args: String?, instrumentation: Instrumentation) {
+        mainImpl(instrumentation)
+    }
+
+    @JvmStatic
+    fun agentmain(args: String?, instrumentation: Instrumentation) {
+        mainImpl(instrumentation)
+    }
+
+    private fun mainImpl(instrumentation: Instrumentation) {
         OMJKoinContext.koinApp = koinApplication {
             modules(
                 module {

ui/src/main/kotlin/com/octogonapus/omj/ui/AgentLoader.kt

@@ -0,0 +1,45 @@
+/*
+ * This file is part of OMJ.
+ *
+ * OMJ is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * OMJ is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with OMJ.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package com.octogonapus.omj.ui
+
+import com.octogonapus.omj.util.JarExtractor
+import com.sun.tools.attach.AttachNotSupportedException
+import com.sun.tools.attach.VirtualMachine
+import java.io.IOException
+import java.lang.management.ManagementFactory
+
+object AgentLoader {
+
+    fun loadAgent() {
+        val name = ManagementFactory.getRuntimeMXBean().name
+        val pid = name.substring(0, name.indexOf('@'))
+        try {
+            val virtualMachine = VirtualMachine.attach(pid)
+            val agentJar = JarExtractor.extractJar("agent-all")
+            virtualMachine.loadAgent(agentJar.absolutePath, null)
+            virtualMachine.detach()
+        } catch (e: AttachNotSupportedException) {
+            e.printStackTrace()
+        } catch (e: IOException) {
+            e.printStackTrace()
+        }
+    }
+}
+
+fun main() {
+    AgentLoader.loadAgent()
+}

util/src/main/java/com/octogonapus/omj/util/JarExtractor.java

@@ -0,0 +1,71 @@
+/*
+ * This file is part of OMJ.
+ *
+ * OMJ is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * OMJ is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with OMJ.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package com.octogonapus.omj.util;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.file.Files;
+import java.util.HashMap;
+import java.util.Map;
+
+public class JarExtractor {
+
+  private static final Map<String, File> resourceMap = new HashMap<>();
+
+  /**
+   * Extracts the agent-lib jar from our jar and into a file.
+   *
+   * @return The file the agent-lib jar is extracted into.
+   * @throws IOException Any IO problems along the way. All fatal.
+   */
+  public static File extractJar(final String resourceName) throws IOException {
+    try (final var agentLib = ClassLoader.getSystemResourceAsStream(resourceName)) {
+      if (agentLib == null) {
+        throw new IOException("Could not locate resource: " + resourceName);
+      }
+
+      // Extract the Jar and save it so that subsequent calls do not try to extract the Jar again.
+      if (!resourceMap.containsKey(resourceName)) {
+        final var file =
+            Files.createTempFile(Util.getAgentLibJarDir(), resourceName + '_', ".jar").toFile();
+        file.deleteOnExit();
+        copyStreamToFile(file, agentLib);
+        resourceMap.put(resourceName, file);
+      }
+
+      return resourceMap.get(resourceName);
+    }
+  }
+
+  private static void copyStreamToFile(File file, InputStream lib) throws IOException {
+    try (final var os = Files.newOutputStream(file.toPath())) {
+      final var buffer = new byte[0xFFFF];
+      int readBytes;
+      while (true) {
+        readBytes = lib.read(buffer);
+
+        // -1 means end of stream
+        if (readBytes == -1) {
+          break;
+        }
+
+        os.write(buffer, 0, readBytes);
+      }
+    }
+  }
+}