/*
 * Copyright 2014 - 2020 Rafael Winterhalter
 *
 * Licensed 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
 *
 *     http://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 net.bytebuddy.agent;

import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;

import java.io.*;
import java.lang.instrument.Instrumentation;
import java.lang.management.ManagementFactory;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.MalformedURLException;
import java.net.URISyntaxException;
import java.net.URL;
import java.net.URLClassLoader;
import java.security.AccessController;
import java.security.CodeSource;
import java.security.PrivilegedAction;
import java.security.ProtectionDomain;
import java.util.*;
import java.util.jar.*;

 The Byte Buddy agent provides a JVM Instrumentation in order to allow Byte Buddy the redefinition of already loaded classes. An agent must normally be specified via the command line via the javaagent parameter. As an argument to this parameter, one must specify the location of this agent's jar file such as for example in 


java -javaagent:byte-buddy-agent.jar -jar app.jar



Note: The runtime installation of a Java agent is not possible on all JVMs. See the documentation for install() for details on JVMs that are supported out of the box. 

Important: This class's name is known to the Byte Buddy main application and must not be altered.


Note: Byte Buddy does not execute code using an AccessController. If a security manager is present, the user of this class is responsible for assuring any required privileges. 
/**
 * <p>
 * The Byte Buddy agent provides a JVM {@link java.lang.instrument.Instrumentation} in order to allow Byte Buddy the
 * redefinition of already loaded classes. An agent must normally be specified via the command line via the
 * {@code javaagent} parameter. As an argument to this parameter, one must specify the location of this agent's jar
 * file such as for example in
 * </p>
 * <p>
 * <code>
 * java -javaagent:byte-buddy-agent.jar -jar app.jar
 * </code>
 * </p>
 * <p>
 * <b>Note</b>: The runtime installation of a Java agent is not possible on all JVMs. See the documentation for
 * {@link ByteBuddyAgent#install()} for details on JVMs that are supported out of the box.
 * </p>
 * <p>
 * <b>Important</b>: This class's name is known to the Byte Buddy main application and must not be altered.
 * </p>
 * <p>
 * <b>Note</b>: Byte Buddy does not execute code using an {@link java.security.AccessController}. If a security manager
 * is present, the user of this class is responsible for assuring any required privileges.
 * </p>
 */
public class ByteBuddyAgent {

    
Indicates that the agent should not resolve it's own code location for a self-attachment.
/**
     * Indicates that the agent should not resolve it's own code location for a self-attachment.
     */
    public static final String LATENT_RESOLVE = "net.bytebuddy.agent.latent";

    
The manifest property specifying the agent class.
/**
     * The manifest property specifying the agent class.
     */
    private static final String AGENT_CLASS_PROPERTY = "Agent-Class";

    
The manifest property specifying the can redefine property.
/**
     * The manifest property specifying the <i>can redefine</i> property.
     */
    private static final String CAN_REDEFINE_CLASSES_PROPERTY = "Can-Redefine-Classes";

    
The manifest property specifying the can retransform property.
/**
     * The manifest property specifying the <i>can retransform</i> property.
     */
    private static final String CAN_RETRANSFORM_CLASSES_PROPERTY = "Can-Retransform-Classes";

    
The manifest property specifying the can set native method prefix property.
/**
     * The manifest property specifying the <i>can set native method prefix</i> property.
     */
    private static final String CAN_SET_NATIVE_METHOD_PREFIX = "Can-Set-Native-Method-Prefix";

    
The manifest property value for the manifest version.
/**
     * The manifest property value for the manifest version.
     */
    private static final String MANIFEST_VERSION_VALUE = "1.0";

    
The size of the buffer for copying the agent installer file into another jar.
/**
     * The size of the buffer for copying the agent installer file into another jar.
     */
    private static final int BUFFER_SIZE = 1024;

    
Convenience indices for reading and writing to the buffer to make the code more readable.
/**
     * Convenience indices for reading and writing to the buffer to make the code more readable.
     */
    private static final int START_INDEX = 0, END_OF_FILE = -1;

    
The status code expected as a result of a successful attachment.
/**
     * The status code expected as a result of a successful attachment.
     */
    private static final int SUCCESSFUL_ATTACH = 0;

    
Base for access to a reflective member to make the code more readable.
/**
     * Base for access to a reflective member to make the code more readable.
     */
    private static final Object STATIC_MEMBER = null;

    
Representation of the bootstrap ClassLoader. /**
     * Representation of the bootstrap {@link java.lang.ClassLoader}.
     */
    private static final ClassLoader BOOTSTRAP_CLASS_LOADER = null;

    
Represents a no-op argument for a dynamic agent attachment.
/**
     * Represents a no-op argument for a dynamic agent attachment.
     */
    private static final String WITHOUT_ARGUMENT = null;

    
The naming prefix of all artifacts for an attacher jar.
/**
     * The naming prefix of all artifacts for an attacher jar.
     */
    private static final String ATTACHER_FILE_NAME = "byteBuddyAttacher";

    
The file extension for a class file.
/**
     * The file extension for a class file.
     */
    private static final String CLASS_FILE_EXTENSION = ".class";

    
The file extension for a jar file.
/**
     * The file extension for a jar file.
     */
    private static final String JAR_FILE_EXTENSION = ".jar";

    
The class path argument to specify the class path elements.
/**
     * The class path argument to specify the class path elements.
     */
    private static final String CLASS_PATH_ARGUMENT = "-cp";

    
The Java property denoting the Java home directory.
/**
     * The Java property denoting the Java home directory.
     */
    private static final String JAVA_HOME = "java.home";

    
The Java property denoting the operating system name.
/**
     * The Java property denoting the operating system name.
     */
    private static final String OS_NAME = "os.name";

    
The name of the method for reading the installer's instrumentation.
/**
     * The name of the method for reading the installer's instrumentation.
     */
    private static final String INSTRUMENTATION_METHOD = "getInstrumentation";

    
Represents the file URL protocol. /**
     * Represents the {@code file} URL protocol.
     */
    private static final String FILE_PROTOCOL = "file";

    
An indicator variable to express that no instrumentation is available.
/**
     * An indicator variable to express that no instrumentation is available.
     */
    private static final Instrumentation UNAVAILABLE = null;

    
Represents a failed attempt to self-resolve a jar file location.
/**
     * Represents a failed attempt to self-resolve a jar file location.
     */
    private static final File CANNOT_SELF_RESOLVE = null;

    
The attachment type evaluator to be used for determining if an attachment requires an external process.
/**
     * The attachment type evaluator to be used for determining if an attachment requires an external process.
     */
    private static final AttachmentTypeEvaluator ATTACHMENT_TYPE_EVALUATOR = AccessController.doPrivileged(AttachmentTypeEvaluator.InstallationAction.INSTANCE);

    
The agent provides only static utility methods and should not be instantiated. /**
     * The agent provides only {@code static} utility methods and should not be instantiated.
     */
    private ByteBuddyAgent() {
        throw new UnsupportedOperationException("This class is a utility class and not supposed to be instantiated");
    }

    
 Looks up the Instrumentation instance of an installed Byte Buddy agent. Note that this method implies reflective lookup and reflective invocation such that the returned value should be cached rather than calling this method several times. 

Note: This method throws an IllegalStateException If the Byte Buddy agent is not properly installed. 
Returns:
The Instrumentation instance which is provided by an installed Byte Buddy agent./**
     * <p>
     * Looks up the {@link java.lang.instrument.Instrumentation} instance of an installed Byte Buddy agent. Note that
     * this method implies reflective lookup and reflective invocation such that the returned value should be cached
     * rather than calling this method several times.
     * </p>
     * <p>
     * <b>Note</b>: This method throws an {@link java.lang.IllegalStateException} If the Byte Buddy agent is not
     * properly installed.
     * </p>
     *
     * @return The {@link java.lang.instrument.Instrumentation} instance which is provided by an installed
     * Byte Buddy agent.
     */
    public static Instrumentation getInstrumentation() {
        Instrumentation instrumentation = doGetInstrumentation();
        if (instrumentation == null) {
            throw new IllegalStateException("The Byte Buddy agent is not initialized");
        }
        return instrumentation;
    }

    
 Attaches the given agent Jar on the target process which must be a virtual machine process. The default attachment provider is used for applying the attachment. This operation blocks until the attachment is complete. If the current VM does not supply any known form of attachment to a remote VM, an IllegalStateException is thrown. The agent is not provided an argument. 

Important: It is only possible to attach to processes that are executed by the same operating system user.

Params:
agentJar –  The agent jar file.
processId – The target process id./**
     * <p>
     * Attaches the given agent Jar on the target process which must be a virtual machine process. The default attachment provider
     * is used for applying the attachment. This operation blocks until the attachment is complete. If the current VM does not supply
     * any known form of attachment to a remote VM, an {@link IllegalStateException} is thrown. The agent is not provided an argument.
     * </p>
     * <p>
     * <b>Important</b>: It is only possible to attach to processes that are executed by the same operating system user.
     * </p>
     *
     * @param agentJar  The agent jar file.
     * @param processId The target process id.
     */
    public static void attach(File agentJar, String processId) {
        attach(agentJar, processId, WITHOUT_ARGUMENT);
    }

    
 Attaches the given agent Jar on the target process which must be a virtual machine process. The default attachment provider is used for applying the attachment. This operation blocks until the attachment is complete. If the current VM does not supply any known form of attachment to a remote VM, an IllegalStateException is thrown. 

Important: It is only possible to attach to processes that are executed by the same operating system user.

Params:
agentJar –  The agent jar file.
processId – The target process id.
argument –  The argument to provide to the agent./**
     * <p>
     * Attaches the given agent Jar on the target process which must be a virtual machine process. The default attachment provider
     * is used for applying the attachment. This operation blocks until the attachment is complete. If the current VM does not supply
     * any known form of attachment to a remote VM, an {@link IllegalStateException} is thrown.
     * </p>
     * <p>
     * <b>Important</b>: It is only possible to attach to processes that are executed by the same operating system user.
     * </p>
     *
     * @param agentJar  The agent jar file.
     * @param processId The target process id.
     * @param argument  The argument to provide to the agent.
     */
    public static void attach(File agentJar, String processId, String argument) {
        attach(agentJar, processId, argument, AttachmentProvider.DEFAULT);
    }

    

Attaches the given agent Jar on the target process which must be a virtual machine process. This operation blocks until the
attachment is complete. The agent is not provided an argument.


Important: It is only possible to attach to processes that are executed by the same operating system user.

Params:
agentJar –           The agent jar file.
processId –          The target process id.
attachmentProvider – The attachment provider to use./**
     * <p>
     * Attaches the given agent Jar on the target process which must be a virtual machine process. This operation blocks until the
     * attachment is complete. The agent is not provided an argument.
     * </p>
     * <p>
     * <b>Important</b>: It is only possible to attach to processes that are executed by the same operating system user.
     * </p>
     *
     * @param agentJar           The agent jar file.
     * @param processId          The target process id.
     * @param attachmentProvider The attachment provider to use.
     */
    public static void attach(File agentJar, String processId, AttachmentProvider attachmentProvider) {
        attach(agentJar, processId, WITHOUT_ARGUMENT, attachmentProvider);
    }

    

Attaches the given agent Jar on the target process which must be a virtual machine process. This operation blocks until the
attachment is complete.


Important: It is only possible to attach to processes that are executed by the same operating system user.

Params:
agentJar –           The agent jar file.
processId –          The target process id.
argument –           The argument to provide to the agent.
attachmentProvider – The attachment provider to use./**
     * <p>
     * Attaches the given agent Jar on the target process which must be a virtual machine process. This operation blocks until the
     * attachment is complete.
     * </p>
     * <p>
     * <b>Important</b>: It is only possible to attach to processes that are executed by the same operating system user.
     * </p>
     *
     * @param agentJar           The agent jar file.
     * @param processId          The target process id.
     * @param argument           The argument to provide to the agent.
     * @param attachmentProvider The attachment provider to use.
     */
    public static void attach(File agentJar, String processId, String argument, AttachmentProvider attachmentProvider) {
        install(attachmentProvider, processId, argument, new AgentProvider.ForExistingAgent(agentJar), false);
    }

    
 Attaches the given agent Jar on the target process which must be a virtual machine process. The default attachment provider is used for applying the attachment. This operation blocks until the attachment is complete. If the current VM does not supply any known form of attachment to a remote VM, an IllegalStateException is thrown. The agent is not provided an argument. 

Important: It is only possible to attach to processes that are executed by the same operating system user.

Params:
agentJar –        The agent jar file.
processProvider – A provider of the target process id./**
     * <p>
     * Attaches the given agent Jar on the target process which must be a virtual machine process. The default attachment provider
     * is used for applying the attachment. This operation blocks until the attachment is complete. If the current VM does not supply
     * any known form of attachment to a remote VM, an {@link IllegalStateException} is thrown. The agent is not provided an argument.
     * </p>
     * <p>
     * <b>Important</b>: It is only possible to attach to processes that are executed by the same operating system user.
     * </p>
     *
     * @param agentJar        The agent jar file.
     * @param processProvider A provider of the target process id.
     */
    public static void attach(File agentJar, ProcessProvider processProvider) {
        attach(agentJar, processProvider, WITHOUT_ARGUMENT);
    }

    
 Attaches the given agent Jar on the target process which must be a virtual machine process. The default attachment provider is used for applying the attachment. This operation blocks until the attachment is complete. If the current VM does not supply any known form of attachment to a remote VM, an IllegalStateException is thrown. 

Important: It is only possible to attach to processes that are executed by the same operating system user.

Params:
agentJar –        The agent jar file.
processProvider – A provider of the target process id.
argument –        The argument to provide to the agent./**
     * <p>
     * Attaches the given agent Jar on the target process which must be a virtual machine process. The default attachment provider
     * is used for applying the attachment. This operation blocks until the attachment is complete. If the current VM does not supply
     * any known form of attachment to a remote VM, an {@link IllegalStateException} is thrown.
     * </p>
     * <p>
     * <b>Important</b>: It is only possible to attach to processes that are executed by the same operating system user.
     * </p>
     *
     * @param agentJar        The agent jar file.
     * @param processProvider A provider of the target process id.
     * @param argument        The argument to provide to the agent.
     */
    public static void attach(File agentJar, ProcessProvider processProvider, String argument) {
        attach(agentJar, processProvider, argument, AttachmentProvider.DEFAULT);
    }

    

Attaches the given agent Jar on the target process which must be a virtual machine process. This operation blocks until the
attachment is complete. The agent is not provided an argument.


Important: It is only possible to attach to processes that are executed by the same operating system user.

Params:
agentJar –           The agent jar file.
processProvider –    A provider of the target process id.
attachmentProvider – The attachment provider to use./**
     * <p>
     * Attaches the given agent Jar on the target process which must be a virtual machine process. This operation blocks until the
     * attachment is complete. The agent is not provided an argument.
     * </p>
     * <p>
     * <b>Important</b>: It is only possible to attach to processes that are executed by the same operating system user.
     * </p>
     *
     * @param agentJar           The agent jar file.
     * @param processProvider    A provider of the target process id.
     * @param attachmentProvider The attachment provider to use.
     */
    public static void attach(File agentJar, ProcessProvider processProvider, AttachmentProvider attachmentProvider) {
        attach(agentJar, processProvider, WITHOUT_ARGUMENT, attachmentProvider);
    }

    

Attaches the given agent Jar on the target process which must be a virtual machine process. This operation blocks until the
attachment is complete.


Important: It is only possible to attach to processes that are executed by the same operating system user.

Params:
agentJar –           The agent jar file.
processProvider –    A provider of the target process id.
argument –           The argument to provide to the agent.
attachmentProvider – The attachment provider to use./**
     * <p>
     * Attaches the given agent Jar on the target process which must be a virtual machine process. This operation blocks until the
     * attachment is complete.
     * </p>
     * <p>
     * <b>Important</b>: It is only possible to attach to processes that are executed by the same operating system user.
     * </p>
     *
     * @param agentJar           The agent jar file.
     * @param processProvider    A provider of the target process id.
     * @param argument           The argument to provide to the agent.
     * @param attachmentProvider The attachment provider to use.
     */
    public static void attach(File agentJar, ProcessProvider processProvider, String argument, AttachmentProvider attachmentProvider) {
        install(attachmentProvider, processProvider.resolve(), argument, new AgentProvider.ForExistingAgent(agentJar), false);
    }

    
 Attaches the given agent library on the target process which must be a virtual machine process. The default attachment provider is used for applying the attachment. This operation blocks until the attachment is complete. If the current VM does not supply any known form of attachment to a remote VM, an IllegalStateException is thrown. The agent is not provided an argument. 

Important: It is only possible to attach to processes that are executed by the same operating system user.

Params:
agentLibrary – The agent jar file.
processId –    The target process id./**
     * <p>
     * Attaches the given agent library on the target process which must be a virtual machine process. The default attachment provider
     * is used for applying the attachment. This operation blocks until the attachment is complete. If the current VM does not supply
     * any known form of attachment to a remote VM, an {@link IllegalStateException} is thrown. The agent is not provided an argument.
     * </p>
     * <p>
     * <b>Important</b>: It is only possible to attach to processes that are executed by the same operating system user.
     * </p>
     *
     * @param agentLibrary The agent jar file.
     * @param processId    The target process id.
     */
    public static void attachNative(File agentLibrary, String processId) {
        attachNative(agentLibrary, processId, WITHOUT_ARGUMENT);
    }

    
 Attaches the given agent library on the target process which must be a virtual machine process. The default attachment provider is used for applying the attachment. This operation blocks until the attachment is complete. If the current VM does not supply any known form of attachment to a remote VM, an IllegalStateException is thrown. 

Important: It is only possible to attach to processes that are executed by the same operating system user.

Params:
agentLibrary – The agent library.
processId –    The target process id.
argument –     The argument to provide to the agent./**
     * <p>
     * Attaches the given agent library on the target process which must be a virtual machine process. The default attachment provider
     * is used for applying the attachment. This operation blocks until the attachment is complete. If the current VM does not supply
     * any known form of attachment to a remote VM, an {@link IllegalStateException} is thrown.
     * </p>
     * <p>
     * <b>Important</b>: It is only possible to attach to processes that are executed by the same operating system user.
     * </p>
     *
     * @param agentLibrary The agent library.
     * @param processId    The target process id.
     * @param argument     The argument to provide to the agent.
     */
    public static void attachNative(File agentLibrary, String processId, String argument) {
        attachNative(agentLibrary, processId, argument, AttachmentProvider.DEFAULT);
    }

    

Attaches the given agent library on the target process which must be a virtual machine process. This operation blocks until the
attachment is complete. The agent is not provided an argument.


Important: It is only possible to attach to processes that are executed by the same operating system user.

Params:
agentLibrary –       The agent library.
processId –          The target process id.
attachmentProvider – The attachment provider to use./**
     * <p>
     * Attaches the given agent library on the target process which must be a virtual machine process. This operation blocks until the
     * attachment is complete. The agent is not provided an argument.
     * </p>
     * <p>
     * <b>Important</b>: It is only possible to attach to processes that are executed by the same operating system user.
     * </p>
     *
     * @param agentLibrary       The agent library.
     * @param processId          The target process id.
     * @param attachmentProvider The attachment provider to use.
     */
    public static void attachNative(File agentLibrary, String processId, AttachmentProvider attachmentProvider) {
        attachNative(agentLibrary, processId, WITHOUT_ARGUMENT, attachmentProvider);
    }

    

Attaches the given agent library on the target process which must be a virtual machine process. This operation blocks until the
attachment is complete.


Important: It is only possible to attach to processes that are executed by the same operating system user.

Params:
agentLibrary –       The agent library.
processId –          The target process id.
argument –           The argument to provide to the agent.
attachmentProvider – The attachment provider to use./**
     * <p>
     * Attaches the given agent library on the target process which must be a virtual machine process. This operation blocks until the
     * attachment is complete.
     * </p>
     * <p>
     * <b>Important</b>: It is only possible to attach to processes that are executed by the same operating system user.
     * </p>
     *
     * @param agentLibrary       The agent library.
     * @param processId          The target process id.
     * @param argument           The argument to provide to the agent.
     * @param attachmentProvider The attachment provider to use.
     */
    public static void attachNative(File agentLibrary, String processId, String argument, AttachmentProvider attachmentProvider) {
        install(attachmentProvider, processId, argument, new AgentProvider.ForExistingAgent(agentLibrary), true);
    }

    
 Attaches the given agent library on the target process which must be a virtual machine process. The default attachment provider is used for applying the attachment. This operation blocks until the attachment is complete. If the current VM does not supply any known form of attachment to a remote VM, an IllegalStateException is thrown. The agent is not provided an argument. 

Important: It is only possible to attach to processes that are executed by the same operating system user.

Params:
agentLibrary –    The agent library.
processProvider – A provider of the target process id./**
     * <p>
     * Attaches the given agent library on the target process which must be a virtual machine process. The default attachment provider
     * is used for applying the attachment. This operation blocks until the attachment is complete. If the current VM does not supply
     * any known form of attachment to a remote VM, an {@link IllegalStateException} is thrown. The agent is not provided an argument.
     * </p>
     * <p>
     * <b>Important</b>: It is only possible to attach to processes that are executed by the same operating system user.
     * </p>
     *
     * @param agentLibrary    The agent library.
     * @param processProvider A provider of the target process id.
     */
    public static void attachNative(File agentLibrary, ProcessProvider processProvider) {
        attachNative(agentLibrary, processProvider, WITHOUT_ARGUMENT);
    }

    
 Attaches the given agent library on the target process which must be a virtual machine process. The default attachment provider is used for applying the attachment. This operation blocks until the attachment is complete. If the current VM does not supply any known form of attachment to a remote VM, an IllegalStateException is thrown. 

Important: It is only possible to attach to processes that are executed by the same operating system user.

Params:
agentLibrary –    The agent library.
processProvider – A provider of the target process id.
argument –        The argument to provide to the agent./**
     * <p>
     * Attaches the given agent library on the target process which must be a virtual machine process. The default attachment provider
     * is used for applying the attachment. This operation blocks until the attachment is complete. If the current VM does not supply
     * any known form of attachment to a remote VM, an {@link IllegalStateException} is thrown.
     * </p>
     * <p>
     * <b>Important</b>: It is only possible to attach to processes that are executed by the same operating system user.
     * </p>
     *
     * @param agentLibrary    The agent library.
     * @param processProvider A provider of the target process id.
     * @param argument        The argument to provide to the agent.
     */
    public static void attachNative(File agentLibrary, ProcessProvider processProvider, String argument) {
        attachNative(agentLibrary, processProvider, argument, AttachmentProvider.DEFAULT);
    }

    

Attaches the given agent library on the target process which must be a virtual machine process. This operation blocks until the
attachment is complete. The agent is not provided an argument.


Important: It is only possible to attach to processes that are executed by the same operating system user.

Params:
agentLibrary –       The agent library.
processProvider –    A provider of the target process id.
attachmentProvider – The attachment provider to use./**
     * <p>
     * Attaches the given agent library on the target process which must be a virtual machine process. This operation blocks until the
     * attachment is complete. The agent is not provided an argument.
     * </p>
     * <p>
     * <b>Important</b>: It is only possible to attach to processes that are executed by the same operating system user.
     * </p>
     *
     * @param agentLibrary       The agent library.
     * @param processProvider    A provider of the target process id.
     * @param attachmentProvider The attachment provider to use.
     */
    public static void attachNative(File agentLibrary, ProcessProvider processProvider, AttachmentProvider attachmentProvider) {
        attachNative(agentLibrary, processProvider, WITHOUT_ARGUMENT, attachmentProvider);
    }

    

Attaches the given agent library on the target process which must be a virtual machine process. This operation blocks until the
attachment is complete.


Important: It is only possible to attach to processes that are executed by the same operating system user.

Params:
agentLibrary –       The agent library.
processProvider –    A provider of the target process id.
argument –           The argument to provide to the agent.
attachmentProvider – The attachment provider to use./**
     * <p>
     * Attaches the given agent library on the target process which must be a virtual machine process. This operation blocks until the
     * attachment is complete.
     * </p>
     * <p>
     * <b>Important</b>: It is only possible to attach to processes that are executed by the same operating system user.
     * </p>
     *
     * @param agentLibrary       The agent library.
     * @param processProvider    A provider of the target process id.
     * @param argument           The argument to provide to the agent.
     * @param attachmentProvider The attachment provider to use.
     */
    public static void attachNative(File agentLibrary, ProcessProvider processProvider, String argument, AttachmentProvider attachmentProvider) {
        install(attachmentProvider, processProvider.resolve(), argument, new AgentProvider.ForExistingAgent(agentLibrary), true);
    }

    

Installs an agent on the currently running Java virtual machine. Unfortunately, this does
not always work. The runtime installation of a Java agent is supported for:


JVM version 9+: For Java VM of at least version 9, the attachment API was moved into a module and the runtime installation is possible if the jdk.attach module is available to Byte Buddy which is typically only available for VMs shipped with a JDK.
OpenJDK / Oracle JDK / IBM J9 versions 8-: The installation for HotSpot is only possible when bundled with a JDK and requires a tools.jar bundled with the VM which is typically only available for JDK-versions of the JVM.
When running Linux and including the optional junixsocket-native-common depedency,
Byte Buddy emulates a Unix socket connection to attach to the target VM.

 If an agent cannot be installed, an IllegalStateException is thrown. 

Important: This is a rather computation-heavy operation. Therefore, this operation is not repeated after an agent was successfully installed for the first time. Instead, the previous instrumentation instance is returned. However, invoking this method requires synchronization such that subsequently to an installation, getInstrumentation() should be invoked instead. 
Returns:
An instrumentation instance representing the currently running JVM./**
     * <p>
     * Installs an agent on the currently running Java virtual machine. Unfortunately, this does
     * not always work. The runtime installation of a Java agent is supported for:
     * </p>
     * <ul>
     * <li><b>JVM version 9+</b>: For Java VM of at least version 9, the attachment API was moved
     * into a module and the runtime installation is possible if the {@code jdk.attach} module is
     * available to Byte Buddy which is typically only available for VMs shipped with a JDK.</li>
     * <li><b>OpenJDK / Oracle JDK / IBM J9 versions 8-</b>: The installation for HotSpot is only
     * possible when bundled with a JDK and requires a {@code tools.jar} bundled with the VM which
     * is typically only available for JDK-versions of the JVM.</li>
     * <li>When running Linux and including the optional <i>junixsocket-native-common</i> depedency,
     * Byte Buddy emulates a Unix socket connection to attach to the target VM.</li>
     * </ul>
     * <p>
     * If an agent cannot be installed, an {@link IllegalStateException} is thrown.
     * </p>
     * <p>
     * <b>Important</b>: This is a rather computation-heavy operation. Therefore, this operation is
     * not repeated after an agent was successfully installed for the first time. Instead, the previous
     * instrumentation instance is returned. However, invoking this method requires synchronization
     * such that subsequently to an installation, {@link ByteBuddyAgent#getInstrumentation()} should
     * be invoked instead.
     * </p>
     *
     * @return An instrumentation instance representing the currently running JVM.
     */
    public static Instrumentation install() {
        return install(AttachmentProvider.DEFAULT);
    }

    

Installs an agent on the currently running Java virtual machine using the supplied
attachment provider.

 If an agent cannot be installed, an IllegalStateException is thrown. 

Important: This is a rather computation-heavy operation. Therefore, this operation is not repeated after an agent was successfully installed for the first time. Instead, the previous instrumentation instance is returned. However, invoking this method requires synchronization such that subsequently to an installation, getInstrumentation() should be invoked instead. 
Params:
attachmentProvider – The attachment provider to use for the installation.
Returns:
An instrumentation instance representing the currently running JVM./**
     * <p>
     * Installs an agent on the currently running Java virtual machine using the supplied
     * attachment provider.
     * </p>
     * <p>
     * If an agent cannot be installed, an {@link IllegalStateException} is thrown.
     * </p>
     * <p>
     * <b>Important</b>: This is a rather computation-heavy operation. Therefore, this operation is
     * not repeated after an agent was successfully installed for the first time. Instead, the previous
     * instrumentation instance is returned. However, invoking this method requires synchronization
     * such that subsequently to an installation, {@link ByteBuddyAgent#getInstrumentation()} should
     * be invoked instead.
     * </p>
     *
     * @param attachmentProvider The attachment provider to use for the installation.
     * @return An instrumentation instance representing the currently running JVM.
     */
    public static Instrumentation install(AttachmentProvider attachmentProvider) {
        return install(attachmentProvider, ProcessProvider.ForCurrentVm.INSTANCE);
    }


    

Installs an agent on the Java virtual machine resolved by the process provider. Unfortunately, this does
not always work. The runtime installation of a Java agent is supported for:


JVM version 9+: For Java VM of at least version 9, the attachment API was moved into a module and the runtime installation is possible if the jdk.attach module is available to Byte Buddy which is typically only available for VMs shipped with a JDK.
OpenJDK / Oracle JDK / IBM J9 versions 8-: The installation for HotSpot is only possible when bundled with a JDK and requires a tools.jar bundled with the VM which is typically only available for JDK-versions of the JVM.
When running Linux and including the optional junixsocket-native-common depedency,
Byte Buddy emulates a Unix socket connection to attach to the target VM.

 If an agent cannot be installed, an IllegalStateException is thrown. 
Params:
processProvider – The provider for the current JVM's process id.
Returns:
An instrumentation instance representing the currently running JVM./**
     * <p>
     * Installs an agent on the Java virtual machine resolved by the process provider. Unfortunately, this does
     * not always work. The runtime installation of a Java agent is supported for:
     * </p>
     * <ul>
     * <li><b>JVM version 9+</b>: For Java VM of at least version 9, the attachment API was moved
     * into a module and the runtime installation is possible if the {@code jdk.attach} module is
     * available to Byte Buddy which is typically only available for VMs shipped with a JDK.</li>
     * <li><b>OpenJDK / Oracle JDK / IBM J9 versions 8-</b>: The installation for HotSpot is only
     * possible when bundled with a JDK and requires a {@code tools.jar} bundled with the VM which
     * is typically only available for JDK-versions of the JVM.</li>
     * <li>When running Linux and including the optional <i>junixsocket-native-common</i> depedency,
     * Byte Buddy emulates a Unix socket connection to attach to the target VM.</li>
     * </ul>
     * <p>
     * If an agent cannot be installed, an {@link IllegalStateException} is thrown.
     * </p>
     *
     * @param processProvider The provider for the current JVM's process id.
     * @return An instrumentation instance representing the currently running JVM.
     */
    public static Instrumentation install(ProcessProvider processProvider) {
        return install(AttachmentProvider.DEFAULT, processProvider);
    }

    

Installs an agent on the currently running Java virtual machine using the supplied
attachment provider and process provider.

 If an agent cannot be installed, an IllegalStateException is thrown. 
Params:
attachmentProvider – The attachment provider to use for the installation.
processProvider –    The provider for the current JVM's process id.
Returns:
An instrumentation instance representing the currently running JVM./**
     * <p>
     * Installs an agent on the currently running Java virtual machine using the supplied
     * attachment provider and process provider.
     * </p>
     * <p>
     * If an agent cannot be installed, an {@link IllegalStateException} is thrown.
     * </p>
     *
     * @param attachmentProvider The attachment provider to use for the installation.
     * @param processProvider    The provider for the current JVM's process id.
     * @return An instrumentation instance representing the currently running JVM.
     */
    public static synchronized Instrumentation install(AttachmentProvider attachmentProvider, ProcessProvider processProvider) {
        Instrumentation instrumentation = doGetInstrumentation();
        if (instrumentation != null) {
            return instrumentation;
        }
        install(attachmentProvider, processProvider.resolve(), WITHOUT_ARGUMENT, AgentProvider.ForByteBuddyAgent.INSTANCE, false);
        return doGetInstrumentation();
    }

    
Installs a Java agent on a target VM.
Params:
attachmentProvider – The attachment provider to use.
processId –          The process id of the target JVM process.
argument –           The argument to provide to the agent.
agentProvider –      The agent provider for the agent jar or library.
isNative –  true if the agent is native./**
     * Installs a Java agent on a target VM.
     *
     * @param attachmentProvider The attachment provider to use.
     * @param processId          The process id of the target JVM process.
     * @param argument           The argument to provide to the agent.
     * @param agentProvider      The agent provider for the agent jar or library.
     * @param isNative           {@code true} if the agent is native.
     */
    private static void install(AttachmentProvider attachmentProvider, String processId, String argument, AgentProvider agentProvider, boolean isNative) {
        AttachmentProvider.Accessor attachmentAccessor = attachmentProvider.attempt();
        if (!attachmentAccessor.isAvailable()) {
            throw new IllegalStateException("No compatible attachment provider is available");
        }
        try {
            if (attachmentAccessor.isExternalAttachmentRequired() && ATTACHMENT_TYPE_EVALUATOR.requiresExternalAttachment(processId)) {
                installExternal(attachmentAccessor.getExternalAttachment(), processId, agentProvider.resolve(), isNative, argument);
            } else {
                Attacher.install(attachmentAccessor.getVirtualMachineType(), processId, agentProvider.resolve().getAbsolutePath(), isNative, argument);
            }
        } catch (RuntimeException exception) {
            throw exception;
        } catch (Exception exception) {
            throw new IllegalStateException("Error during attachment using: " + attachmentProvider, exception);
        }
    }

    
Installs a Java agent to the current VM via an external process. This is typically required starting with OpenJDK 9 when the jdk.attach.allowAttachSelf property is set to false what is the default setting. 
Params:
externalAttachment – A description of the external attachment.
processId –          The process id of the current process.
agent –              The Java agent to install.
isNative –  true if the agent is native.
argument –  The argument to provide to the agent or null if no argument should be supplied.
Throws:
Exception – If an exception occurs during the attachment or the external process fails the attachment./**
     * Installs a Java agent to the current VM via an external process. This is typically required starting with OpenJDK 9
     * when the {@code jdk.attach.allowAttachSelf} property is set to {@code false} what is the default setting.
     *
     * @param externalAttachment A description of the external attachment.
     * @param processId          The process id of the current process.
     * @param agent              The Java agent to install.
     * @param isNative           {@code true} if the agent is native.
     * @param argument           The argument to provide to the agent or {@code null} if no argument should be supplied.
     * @throws Exception If an exception occurs during the attachment or the external process fails the attachment.
     */
    private static void installExternal(AttachmentProvider.Accessor.ExternalAttachment externalAttachment,
                                        String processId,
                                        File agent,
                                        boolean isNative,
                                        String argument) throws Exception {
        File selfResolvedJar = trySelfResolve(), attachmentJar = null;
        try {
            if (selfResolvedJar == null) {
                InputStream inputStream = Attacher.class.getResourceAsStream('/' + Attacher.class.getName().replace('.', '/') + CLASS_FILE_EXTENSION);
                if (inputStream == null) {
                    throw new IllegalStateException("Cannot locate class file for Byte Buddy installation process");
                }
                try {
                    attachmentJar = File.createTempFile(ATTACHER_FILE_NAME, JAR_FILE_EXTENSION);
                    JarOutputStream jarOutputStream = new JarOutputStream(new FileOutputStream(attachmentJar));
                    try {
                        jarOutputStream.putNextEntry(new JarEntry(Attacher.class.getName().replace('.', '/') + CLASS_FILE_EXTENSION));
                        byte[] buffer = new byte[BUFFER_SIZE];
                        int index;
                        while ((index = inputStream.read(buffer)) != END_OF_FILE) {
                            jarOutputStream.write(buffer, START_INDEX, index);
                        }
                        jarOutputStream.closeEntry();
                    } finally {
                        jarOutputStream.close();
                    }
                } finally {
                    inputStream.close();
                }
            }
            StringBuilder classPath = new StringBuilder().append(quote((selfResolvedJar == null
                    ? attachmentJar
                    : selfResolvedJar).getCanonicalPath()));
            for (File jar : externalAttachment.getClassPath()) {
                classPath.append(File.pathSeparatorChar).append(quote(jar.getCanonicalPath()));
            }
            if (new ProcessBuilder(System.getProperty(JAVA_HOME)
                    + File.separatorChar + "bin"
                    + File.separatorChar + (System.getProperty(OS_NAME, "").toLowerCase(Locale.US).contains("windows") ? "java.exe" : "java"),
                    CLASS_PATH_ARGUMENT,
                    classPath.toString(),
                    Attacher.class.getName(),
                    externalAttachment.getVirtualMachineType(),
                    processId,
                    quote(agent.getAbsolutePath()),
                    Boolean.toString(isNative),
                    argument == null ? "" : ("=" + argument)).start().waitFor() != SUCCESSFUL_ATTACH) {
                throw new IllegalStateException("Could not self-attach to current VM using external process");
            }
        } finally {
            if (attachmentJar != null) {
                if (!attachmentJar.delete()) {
                    attachmentJar.deleteOnExit();
                }
            }
        }
    }

    
Attempts to resolve the location of the Attacher class for a self-attachment. Doing so avoids the creation of a temporary jar file. 
Returns:
The self-resolved jar file or null if the jar file cannot be located./**
     * Attempts to resolve the location of the {@link Attacher} class for a self-attachment. Doing so avoids the creation of a temporary jar file.
     *
     * @return The self-resolved jar file or {@code null} if the jar file cannot be located.
     */
    @SuppressFBWarnings(value = "REC_CATCH_EXCEPTION", justification = "Exception should not be rethrown but trigger a fallback")
    private static File trySelfResolve() {
        try {
            if (Boolean.getBoolean(LATENT_RESOLVE)) {
                return CANNOT_SELF_RESOLVE;
            }
            ProtectionDomain protectionDomain = Attacher.class.getProtectionDomain();
            if (protectionDomain == null) {
                return CANNOT_SELF_RESOLVE;
            }
            CodeSource codeSource = protectionDomain.getCodeSource();
            if (codeSource == null) {
                return CANNOT_SELF_RESOLVE;
            }
            URL location = codeSource.getLocation();
            if (!location.getProtocol().equals(FILE_PROTOCOL)) {
                return CANNOT_SELF_RESOLVE;
            }
            try {
                return new File(location.toURI());
            } catch (URISyntaxException ignored) {
                return new File(location.getPath());
            }
        } catch (Exception ignored) {
            return CANNOT_SELF_RESOLVE;
        }
    }

    
Quotes a value if it contains a white space.
Params:
value – The value to quote.
Returns:
The value being quoted if necessary./**
     * Quotes a value if it contains a white space.
     *
     * @param value The value to quote.
     * @return The value being quoted if necessary.
     */
    private static String quote(String value) {
        return value.contains(" ")
                ? '"' + value + '"'
                : value;
    }

    
Performs the actual lookup of the Instrumentation from an installed Byte Buddy agent. 
Returns:
The Byte Buddy agent's Instrumentation instance./**
     * Performs the actual lookup of the {@link java.lang.instrument.Instrumentation} from an installed
     * Byte Buddy agent.
     *
     * @return The Byte Buddy agent's {@link java.lang.instrument.Instrumentation} instance.
     */
    @SuppressFBWarnings(value = "REC_CATCH_EXCEPTION", justification = "Legal outcome where reflection communicates errors by throwing an exception")
    private static Instrumentation doGetInstrumentation() {
        try {
            return (Instrumentation) ClassLoader.getSystemClassLoader()
                    .loadClass(Installer.class.getName())
                    .getMethod(INSTRUMENTATION_METHOD)
                    .invoke(STATIC_MEMBER);
        } catch (Exception ignored) {
            return UNAVAILABLE;
        }
    }

    
An attachment provider is responsible for making the Java attachment API available.
/**
     * An attachment provider is responsible for making the Java attachment API available.
     */
    @SuppressFBWarnings(value = "IC_SUPERCLASS_USES_SUBCLASS_DURING_INITIALIZATION", justification = "Safe initialization is implied")
    public interface AttachmentProvider {

        
The default attachment provider to be used.
/**
         * The default attachment provider to be used.
         */
        AttachmentProvider DEFAULT = new Compound(ForModularizedVm.INSTANCE,
                ForJ9Vm.INSTANCE,
                ForStandardToolsJarVm.JVM_ROOT,
                ForStandardToolsJarVm.JDK_ROOT,
                ForStandardToolsJarVm.MACINTOSH,
                ForUserDefinedToolsJar.INSTANCE,
                ForEmulatedAttachment.INSTANCE);

        
Attempts the creation of an accessor for a specific JVM's attachment API.
Returns:
The accessor this attachment provider can supply for the currently running JVM./**
         * Attempts the creation of an accessor for a specific JVM's attachment API.
         *
         * @return The accessor this attachment provider can supply for the currently running JVM.
         */
        Accessor attempt();

        
An accessor for a JVM's attachment API.
/**
         * An accessor for a JVM's attachment API.
         */
        interface Accessor {

            
The name of the VirtualMachine class on any OpenJDK or Oracle JDK implementation. /**
             * The name of the {@code VirtualMachine} class on any OpenJDK or Oracle JDK implementation.
             */
            String VIRTUAL_MACHINE_TYPE_NAME = "com.sun.tools.attach.VirtualMachine";

            
The name of the VirtualMachine class on IBM J9 VMs. /**
             * The name of the {@code VirtualMachine} class on IBM J9 VMs.
             */
            String VIRTUAL_MACHINE_TYPE_NAME_J9 = "com.ibm.tools.attach.VirtualMachine";

            
Determines if this accessor is applicable for the currently running JVM.
Returns:
true if this accessor is available./**
             * Determines if this accessor is applicable for the currently running JVM.
             *
             * @return {@code true} if this accessor is available.
             */
            boolean isAvailable();

            
Returns true if this accessor prohibits attachment to the same virtual machine in Java 9 and later. 
Returns:
true if this accessor prohibits attachment to the same virtual machine in Java 9 and later./**
             * Returns {@code true} if this accessor prohibits attachment to the same virtual machine in Java 9 and later.
             *
             * @return {@code true} if this accessor prohibits attachment to the same virtual machine in Java 9 and later.
             */
            boolean isExternalAttachmentRequired();

            
Returns a VirtualMachine class. This method must only be called for available accessors. 
Returns:
The virtual machine type./**
             * Returns a {@code VirtualMachine} class. This method must only be called for available accessors.
             *
             * @return The virtual machine type.
             */
            Class<?> getVirtualMachineType();

            
Returns a description of a virtual machine class for an external attachment.
Returns:
A description of the external attachment./**
             * Returns a description of a virtual machine class for an external attachment.
             *
             * @return A description of the external attachment.
             */
            ExternalAttachment getExternalAttachment();

            
A canonical implementation of an unavailable accessor.
/**
             * A canonical implementation of an unavailable accessor.
             */
            enum Unavailable implements Accessor {

                
The singleton instance.
/**
                 * The singleton instance.
                 */
                INSTANCE;

                
{@inheritDoc}
/**
                 * {@inheritDoc}
                 */
                public boolean isAvailable() {
                    return false;
                }

                
{@inheritDoc}
/**
                 * {@inheritDoc}
                 */
                public boolean isExternalAttachmentRequired() {
                    throw new IllegalStateException("Cannot read the virtual machine type for an unavailable accessor");
                }

                
{@inheritDoc}
/**
                 * {@inheritDoc}
                 */
                public Class<?> getVirtualMachineType() {
                    throw new IllegalStateException("Cannot read the virtual machine type for an unavailable accessor");
                }

                
{@inheritDoc}
/**
                 * {@inheritDoc}
                 */
                public ExternalAttachment getExternalAttachment() {
                    throw new IllegalStateException("Cannot read the virtual machine type for an unavailable accessor");
                }
            }

            
Describes an external attachment to a Java virtual machine.
/**
             * Describes an external attachment to a Java virtual machine.
             */
            class ExternalAttachment {

                
The fully-qualified binary name of the virtual machine type.
/**
                 * The fully-qualified binary name of the virtual machine type.
                 */
                private final String virtualMachineType;

                
The class path elements required for loading the supplied virtual machine type.
/**
                 * The class path elements required for loading the supplied virtual machine type.
                 */
                private final List<File> classPath;

                
Creates an external attachment.
Params:
virtualMachineType – The fully-qualified binary name of the virtual machine type.
classPath –          The class path elements required for loading the supplied virtual machine type./**
                 * Creates an external attachment.
                 *
                 * @param virtualMachineType The fully-qualified binary name of the virtual machine type.
                 * @param classPath          The class path elements required for loading the supplied virtual machine type.
                 */
                public ExternalAttachment(String virtualMachineType, List<File> classPath) {
                    this.virtualMachineType = virtualMachineType;
                    this.classPath = classPath;
                }

                
Returns the fully-qualified binary name of the virtual machine type.
Returns:
The fully-qualified binary name of the virtual machine type./**
                 * Returns the fully-qualified binary name of the virtual machine type.
                 *
                 * @return The fully-qualified binary name of the virtual machine type.
                 */
                public String getVirtualMachineType() {
                    return virtualMachineType;
                }

                
Returns the class path elements required for loading the supplied virtual machine type.
Returns:
The class path elements required for loading the supplied virtual machine type./**
                 * Returns the class path elements required for loading the supplied virtual machine type.
                 *
                 * @return The class path elements required for loading the supplied virtual machine type.
                 */
                public List<File> getClassPath() {
                    return classPath;
                }
            }

            
A simple implementation of an accessible accessor.
/**
             * A simple implementation of an accessible accessor.
             */
            abstract class Simple implements Accessor {

                
A VirtualMachine class. /**
                 * A {@code VirtualMachine} class.
                 */
                protected final Class<?> virtualMachineType;

                
Creates a new simple accessor.
Params:
virtualMachineType – A VirtualMachine class./**
                 * Creates a new simple accessor.
                 *
                 * @param virtualMachineType A {@code VirtualMachine} class.
                 */
                protected Simple(Class<?> virtualMachineType) {
                    this.virtualMachineType = virtualMachineType;
                }

                
 Creates an accessor by reading the process id from the JMX runtime bean and by attempting to load the com.sun.tools.attach.VirtualMachine class from the provided class loader. 

This accessor is supposed to work on any implementation of the OpenJDK or Oracle JDK.

Params:
classLoader – A class loader that is capable of loading the virtual machine type.
classPath –   The class path required to load the virtual machine class.
Returns:
An appropriate accessor./**
                 * <p>
                 * Creates an accessor by reading the process id from the JMX runtime bean and by attempting
                 * to load the {@code com.sun.tools.attach.VirtualMachine} class from the provided class loader.
                 * </p>
                 * <p>
                 * This accessor is supposed to work on any implementation of the OpenJDK or Oracle JDK.
                 * </p>
                 *
                 * @param classLoader A class loader that is capable of loading the virtual machine type.
                 * @param classPath   The class path required to load the virtual machine class.
                 * @return An appropriate accessor.
                 */
                public static Accessor of(ClassLoader classLoader, File... classPath) {
                    try {
                        return new Simple.WithExternalAttachment(classLoader.loadClass(VIRTUAL_MACHINE_TYPE_NAME),
                                Arrays.asList(classPath));
                    } catch (ClassNotFoundException ignored) {
                        return Unavailable.INSTANCE;
                    }
                }

                
 Creates an accessor by reading the process id from the JMX runtime bean and by attempting to load the com.ibm.tools.attach.VirtualMachine class from the provided class loader. 

This accessor is supposed to work on any implementation of IBM's J9.

Returns:
An appropriate accessor./**
                 * <p>
                 * Creates an accessor by reading the process id from the JMX runtime bean and by attempting
                 * to load the {@code com.ibm.tools.attach.VirtualMachine} class from the provided class loader.
                 * </p>
                 * <p>
                 * This accessor is supposed to work on any implementation of IBM's J9.
                 * </p>
                 *
                 * @return An appropriate accessor.
                 */
                public static Accessor ofJ9() {
                    try {
                        return new Simple.WithExternalAttachment(ClassLoader.getSystemClassLoader().loadClass(VIRTUAL_MACHINE_TYPE_NAME_J9),
                                Collections.<File>emptyList());
                    } catch (ClassNotFoundException ignored) {
                        return Unavailable.INSTANCE;
                    }
                }

                
{@inheritDoc}
/**
                 * {@inheritDoc}
                 */
                public boolean isAvailable() {
                    return true;
                }

                
{@inheritDoc}
/**
                 * {@inheritDoc}
                 */
                public Class<?> getVirtualMachineType() {
                    return virtualMachineType;
                }

                
A simple implementation of an accessible accessor that allows for external attachment.
/**
                 * A simple implementation of an accessible accessor that allows for external attachment.
                 */
                protected static class WithExternalAttachment extends Simple {

                    
The class path required for loading the virtual machine type.
/**
                     * The class path required for loading the virtual machine type.
                     */
                    private final List<File> classPath;

                    
Creates a new simple accessor that allows for external attachment.
Params:
virtualMachineType – The com.sun.tools.attach.VirtualMachine class.
classPath –          The class path required for loading the virtual machine type./**
                     * Creates a new simple accessor that allows for external attachment.
                     *
                     * @param virtualMachineType The {@code com.sun.tools.attach.VirtualMachine} class.
                     * @param classPath          The class path required for loading the virtual machine type.
                     */
                    public WithExternalAttachment(Class<?> virtualMachineType, List<File> classPath) {
                        super(virtualMachineType);
                        this.classPath = classPath;
                    }

                    
{@inheritDoc}
/**
                     * {@inheritDoc}
                     */
                    public boolean isExternalAttachmentRequired() {
                        return true;
                    }

                    
{@inheritDoc}
/**
                     * {@inheritDoc}
                     */
                    public ExternalAttachment getExternalAttachment() {
                        return new ExternalAttachment(virtualMachineType.getName(), classPath);
                    }
                }

                
A simple implementation of an accessible accessor that attaches using a virtual machine emulation that does not require external attachment.
/**
                 * A simple implementation of an accessible accessor that attaches using a virtual machine emulation that does not require external attachment.
                 */
                protected static class WithDirectAttachment extends Simple {

                    
Creates a new simple accessor that implements direct attachment.
Params:
virtualMachineType – A VirtualMachine class./**
                     * Creates a new simple accessor that implements direct attachment.
                     *
                     * @param virtualMachineType A {@code VirtualMachine} class.
                     */
                    public WithDirectAttachment(Class<?> virtualMachineType) {
                        super(virtualMachineType);
                    }

                    
{@inheritDoc}
/**
                     * {@inheritDoc}
                     */
                    public boolean isExternalAttachmentRequired() {
                        return false;
                    }

                    
{@inheritDoc}
/**
                     * {@inheritDoc}
                     */
                    public ExternalAttachment getExternalAttachment() {
                        throw new IllegalStateException("Cannot apply external attachment");
                    }
                }
            }
        }

        
An attachment provider that locates the attach API directly from the system class loader, as possible since introducing the Java module system via the jdk.attach module. /**
         * An attachment provider that locates the attach API directly from the system class loader, as possible since
         * introducing the Java module system via the {@code jdk.attach} module.
         */
        enum ForModularizedVm implements AttachmentProvider {

            
The singleton instance.
/**
             * The singleton instance.
             */
            INSTANCE;

            
{@inheritDoc}
/**
             * {@inheritDoc}
             */
            public Accessor attempt() {
                return Accessor.Simple.of(ClassLoader.getSystemClassLoader());
            }
        }

        
An attachment provider that locates the attach API directly from the system class loader expecting
an IBM J9 VM.
/**
         * An attachment provider that locates the attach API directly from the system class loader expecting
         * an IBM J9 VM.
         */
        enum ForJ9Vm implements AttachmentProvider {

            
The singleton instance.
/**
             * The singleton instance.
             */
            INSTANCE;

            
{@inheritDoc}
/**
             * {@inheritDoc}
             */
            public Accessor attempt() {
                return Accessor.Simple.ofJ9();
            }
        }

        
An attachment provider that is dependant on the existence of a tools.jar file on the local
file system.
/**
         * An attachment provider that is dependant on the existence of a <i>tools.jar</i> file on the local
         * file system.
         */
        enum ForStandardToolsJarVm implements AttachmentProvider {

            
An attachment provider that locates the tools.jar from a Java home directory.
/**
             * An attachment provider that locates the <i>tools.jar</i> from a Java home directory.
             */
            JVM_ROOT("../lib/tools.jar"),

            
An attachment provider that locates the tools.jar from a Java installation directory.
In practice, several virtual machines do not return the JRE's location for the
java.home property against the property's specification.
/**
             * An attachment provider that locates the <i>tools.jar</i> from a Java installation directory.
             * In practice, several virtual machines do not return the JRE's location for the
             * <i>java.home</i> property against the property's specification.
             */
            JDK_ROOT("lib/tools.jar"),

            
An attachment provider that locates the tools.jar as it is set for several JVM
installations on Apple Macintosh computers.
/**
             * An attachment provider that locates the <i>tools.jar</i> as it is set for several JVM
             * installations on Apple Macintosh computers.
             */
            MACINTOSH("../Classes/classes.jar");

            
The Java home system property.
/**
             * The Java home system property.
             */
            private static final String JAVA_HOME_PROPERTY = "java.home";

            
The path to the tools.jar file, starting from the Java home directory.
/**
             * The path to the <i>tools.jar</i> file, starting from the Java home directory.
             */
            private final String toolsJarPath;

            
Creates a new attachment provider that loads the virtual machine class from the tools.jar.
Params:
toolsJarPath – The path to the tools.jar file, starting from the Java home directory./**
             * Creates a new attachment provider that loads the virtual machine class from the <i>tools.jar</i>.
             *
             * @param toolsJarPath The path to the <i>tools.jar</i> file, starting from the Java home directory.
             */
            ForStandardToolsJarVm(String toolsJarPath) {
                this.toolsJarPath = toolsJarPath;
            }

            
{@inheritDoc}
/**
             * {@inheritDoc}
             */
            @SuppressFBWarnings(value = "DP_CREATE_CLASSLOADER_INSIDE_DO_PRIVILEGED", justification = "Privilege is explicit user responsibility")
            public Accessor attempt() {
                File toolsJar = new File(System.getProperty(JAVA_HOME_PROPERTY), toolsJarPath);
                try {
                    return toolsJar.isFile() && toolsJar.canRead()
                            ? Accessor.Simple.of(new URLClassLoader(new URL[]{toolsJar.toURI().toURL()}, BOOTSTRAP_CLASS_LOADER), toolsJar)
                            : Accessor.Unavailable.INSTANCE;
                } catch (MalformedURLException exception) {
                    throw new IllegalStateException("Could not represent " + toolsJar + " as URL");
                }
            }
        }

        
An attachment provider that attempts to locate a tools.jar from a custom location set via a system property. /**
         * An attachment provider that attempts to locate a {@code tools.jar} from a custom location set via a system property.
         */
        enum ForUserDefinedToolsJar implements AttachmentProvider {

            
The singelton instance.
/**
             * The singelton instance.
             */
            INSTANCE;

            
The property being read for locating tools.jar. /**
             * The property being read for locating {@code tools.jar}.
             */
            public static final String PROPERTY = "net.bytebuddy.agent.toolsjar";

            
{@inheritDoc}
/**
             * {@inheritDoc}
             */
            @SuppressFBWarnings(value = "DP_CREATE_CLASSLOADER_INSIDE_DO_PRIVILEGED", justification = "Privilege is explicit user responsibility")
            public Accessor attempt() {
                String location = System.getProperty(PROPERTY);
                if (location == null) {
                    return Accessor.Unavailable.INSTANCE;
                } else {
                    File toolsJar = new File(location);
                    try {
                        return Accessor.Simple.of(new URLClassLoader(new URL[]{toolsJar.toURI().toURL()}, BOOTSTRAP_CLASS_LOADER), toolsJar);
                    } catch (MalformedURLException exception) {
                        throw new IllegalStateException("Could not represent " + toolsJar + " as URL");
                    }
                }
            }
        }

        
An attachment provider that uses Byte Buddy's attachment API emulation. To use this feature, JNA is required.
/**
         * An attachment provider that uses Byte Buddy's attachment API emulation. To use this feature, JNA is required.
         */
        enum ForEmulatedAttachment implements AttachmentProvider {

            
The singleton instance.
/**
             * The singleton instance.
             */
            INSTANCE;

            
{@inheritDoc}
/**
             * {@inheritDoc}
             */
            public Accessor attempt() {
                try {
                    return new Accessor.Simple.WithDirectAttachment(AccessController.doPrivileged(VirtualMachine.Resolver.INSTANCE));
                } catch (Throwable ignored) {
                    return Accessor.Unavailable.INSTANCE;
                }
            }
        }

        
A compound attachment provider that attempts the attachment by delegation to other providers. If
none of the providers of this compound provider is capable of providing a valid accessor, an
non-available accessor is returned.
/**
         * A compound attachment provider that attempts the attachment by delegation to other providers. If
         * none of the providers of this compound provider is capable of providing a valid accessor, an
         * non-available accessor is returned.
         */
        class Compound implements AttachmentProvider {

            
A list of attachment providers in the order of their application.
/**
             * A list of attachment providers in the order of their application.
             */
            private final List<AttachmentProvider> attachmentProviders;

            
Creates a new compound attachment provider.
Params:
attachmentProvider – A list of attachment providers in the order of their application./**
             * Creates a new compound attachment provider.
             *
             * @param attachmentProvider A list of attachment providers in the order of their application.
             */
            public Compound(AttachmentProvider... attachmentProvider) {
                this(Arrays.asList(attachmentProvider));
            }

            
Creates a new compound attachment provider.
Params:
attachmentProviders – A list of attachment providers in the order of their application./**
             * Creates a new compound attachment provider.
             *
             * @param attachmentProviders A list of attachment providers in the order of their application.
             */
            public Compound(List<? extends AttachmentProvider> attachmentProviders) {
                this.attachmentProviders = new ArrayList<AttachmentProvider>();
                for (AttachmentProvider attachmentProvider : attachmentProviders) {
                    if (attachmentProvider instanceof Compound) {
                        this.attachmentProviders.addAll(((Compound) attachmentProvider).attachmentProviders);
                    } else {
                        this.attachmentProviders.add(attachmentProvider);
                    }
                }
            }

            
{@inheritDoc}
/**
             * {@inheritDoc}
             */
            public Accessor attempt() {
                for (AttachmentProvider attachmentProvider : attachmentProviders) {
                    Accessor accessor = attachmentProvider.attempt();
                    if (accessor.isAvailable()) {
                        return accessor;
                    }
                }
                return Accessor.Unavailable.INSTANCE;
            }
        }
    }

    
A process provider is responsible for providing the process id of the current VM.
/**
     * A process provider is responsible for providing the process id of the current VM.
     */
    public interface ProcessProvider {

        
Resolves a process id for the current JVM.
Returns:
The resolved process id./**
         * Resolves a process id for the current JVM.
         *
         * @return The resolved process id.
         */
        String resolve();

        
Supplies the current VM's process id.
/**
         * Supplies the current VM's process id.
         */
        enum ForCurrentVm implements ProcessProvider {

            
The singleton instance.
/**
             * The singleton instance.
             */
            INSTANCE;

            
The best process provider for the current VM.
/**
             * The best process provider for the current VM.
             */
            private final ProcessProvider dispatcher;

            
Creates a process provider that supplies the current VM's process id.
/**
             * Creates a process provider that supplies the current VM's process id.
             */
            ForCurrentVm() {
                dispatcher = ForJava9CapableVm.make();
            }

            
{@inheritDoc}
/**
             * {@inheritDoc}
             */
            public String resolve() {
                return dispatcher.resolve();
            }

            
A process provider for a legacy VM that reads the process id from its JMX properties.
/**
             * A process provider for a legacy VM that reads the process id from its JMX properties.
             */
            protected enum ForLegacyVm implements ProcessProvider {

                
The singleton instance.
/**
                 * The singleton instance.
                 */
                INSTANCE;

                
{@inheritDoc}
/**
                 * {@inheritDoc}
                 */
                public String resolve() {
                    String runtimeName = ManagementFactory.getRuntimeMXBean().getName();
                    int processIdIndex = runtimeName.indexOf('@');
                    if (processIdIndex == -1) {
                        throw new IllegalStateException("Cannot extract process id from runtime management bean");
                    } else {
                        return runtimeName.substring(0, processIdIndex);
                    }
                }
            }

            
A process provider for a Java 9 capable VM with access to the introduced process API.
/**
             * A process provider for a Java 9 capable VM with access to the introduced process API.
             */
            protected static class ForJava9CapableVm implements ProcessProvider {

                
The java.lang.ProcessHandle#current() method. /**
                 * The {@code java.lang.ProcessHandle#current()} method.
                 */
                private final Method current;

                
The java.lang.ProcessHandle#pid() method. /**
                 * The {@code java.lang.ProcessHandle#pid()} method.
                 */
                private final Method pid;

                
Creates a new Java 9 capable dispatcher for reading the current process's id.
Params:
current – The java.lang.ProcessHandle#current() method.
pid –  The java.lang.ProcessHandle#pid() method./**
                 * Creates a new Java 9 capable dispatcher for reading the current process's id.
                 *
                 * @param current The {@code java.lang.ProcessHandle#current()} method.
                 * @param pid     The {@code java.lang.ProcessHandle#pid()} method.
                 */
                protected ForJava9CapableVm(Method current, Method pid) {
                    this.current = current;
                    this.pid = pid;
                }

                
Attempts to create a dispatcher for a Java 9 VM and falls back to a legacy dispatcher
if this is not possible.
Returns:
A dispatcher for the current VM./**
                 * Attempts to create a dispatcher for a Java 9 VM and falls back to a legacy dispatcher
                 * if this is not possible.
                 *
                 * @return A dispatcher for the current VM.
                 */
                @SuppressFBWarnings(value = "REC_CATCH_EXCEPTION", justification = "Exception should not be rethrown but trigger a fallback")
                public static ProcessProvider make() {
                    try {
                        return new ForJava9CapableVm(Class.forName("java.lang.ProcessHandle").getMethod("current"),
                                Class.forName("java.lang.ProcessHandle").getMethod("pid"));
                    } catch (Exception ignored) {
                        return ForLegacyVm.INSTANCE;
                    }
                }

                
{@inheritDoc}
/**
                 * {@inheritDoc}
                 */
                public String resolve() {
                    try {
                        return pid.invoke(current.invoke(STATIC_MEMBER)).toString();
                    } catch (IllegalAccessException exception) {
                        throw new IllegalStateException("Cannot access Java 9 process API", exception);
                    } catch (InvocationTargetException exception) {
                        throw new IllegalStateException("Error when accessing Java 9 process API", exception.getCause());
                    }
                }
            }
        }
    }

    
An agent provider is responsible for handling and providing the jar file of an agent that is being attached.
/**
     * An agent provider is responsible for handling and providing the jar file of an agent that is being attached.
     */
    protected interface AgentProvider {

        
Provides an agent jar file for attachment.
Throws:
IOException – If the agent cannot be written to disk.
Returns:
The provided agent./**
         * Provides an agent jar file for attachment.
         *
         * @return The provided agent.
         * @throws IOException If the agent cannot be written to disk.
         */
        File resolve() throws IOException;

        
An agent provider for a temporary Byte Buddy agent.
/**
         * An agent provider for a temporary Byte Buddy agent.
         */
        enum ForByteBuddyAgent implements AgentProvider {

            
The singleton instance.
/**
             * The singleton instance.
             */
            INSTANCE;

            
The default prefix of the Byte Buddy agent jar file.
/**
             * The default prefix of the Byte Buddy agent jar file.
             */
            private static final String AGENT_FILE_NAME = "byteBuddyAgent";

            
Attempts to resolve the Installer class from this jar file if it can be located. Doing so, it is possible to avoid the creation of a temporary jar file which can remain undeleted on Windows operating systems where the agent is linked by a class loader such that File.deleteOnExit() does not have an effect. 
Throws:
IOException – If an I/O exception occurs.
Returns:
This jar file's location or null if this jar file's location is inaccessible./**
             * Attempts to resolve the {@link Installer} class from this jar file if it can be located. Doing so, it is possible
             * to avoid the creation of a temporary jar file which can remain undeleted on Windows operating systems where the agent
             * is linked by a class loader such that {@link File#deleteOnExit()} does not have an effect.
             *
             * @return This jar file's location or {@code null} if this jar file's location is inaccessible.
             * @throws IOException If an I/O exception occurs.
             */
            private static File trySelfResolve() throws IOException {
                ProtectionDomain protectionDomain = Installer.class.getProtectionDomain();
                if (Boolean.getBoolean(LATENT_RESOLVE)) {
                    return CANNOT_SELF_RESOLVE;
                }
                if (protectionDomain == null) {
                    return CANNOT_SELF_RESOLVE;
                }
                CodeSource codeSource = protectionDomain.getCodeSource();
                if (codeSource == null) {
                    return CANNOT_SELF_RESOLVE;
                }
                URL location = codeSource.getLocation();
                if (!location.getProtocol().equals(FILE_PROTOCOL)) {
                    return CANNOT_SELF_RESOLVE;
                }
                File agentJar;
                try {
                    agentJar = new File(location.toURI());
                } catch (URISyntaxException ignored) {
                    agentJar = new File(location.getPath());
                }
                if (!agentJar.isFile() || !agentJar.canRead()) {
                    return CANNOT_SELF_RESOLVE;
                }
                // It is necessary to check the manifest of the containing file as this code can be shaded into another artifact.
                JarInputStream jarInputStream = new JarInputStream(new FileInputStream(agentJar));
                try {
                    Manifest manifest = jarInputStream.getManifest();
                    if (manifest == null) {
                        return CANNOT_SELF_RESOLVE;
                    }
                    Attributes attributes = manifest.getMainAttributes();
                    if (attributes == null) {
                        return CANNOT_SELF_RESOLVE;
                    }
                    if (Installer.class.getName().equals(attributes.getValue(AGENT_CLASS_PROPERTY))
                            && Boolean.parseBoolean(attributes.getValue(CAN_REDEFINE_CLASSES_PROPERTY))
                            && Boolean.parseBoolean(attributes.getValue(CAN_RETRANSFORM_CLASSES_PROPERTY))
                            && Boolean.parseBoolean(attributes.getValue(CAN_SET_NATIVE_METHOD_PREFIX))) {
                        return agentJar;
                    } else {
                        return CANNOT_SELF_RESOLVE;
                    }
                } finally {
                    jarInputStream.close();
                }
            }

            
Creates an agent jar file containing the Installer class. 
Throws:
IOException – If an I/O exception occurs.
Returns:
The agent jar file./**
             * Creates an agent jar file containing the {@link Installer} class.
             *
             * @return The agent jar file.
             * @throws IOException If an I/O exception occurs.
             */
            private static File createJarFile() throws IOException {
                InputStream inputStream = Installer.class.getResourceAsStream('/' + Installer.class.getName().replace('.', '/') + CLASS_FILE_EXTENSION);
                if (inputStream == null) {
                    throw new IllegalStateException("Cannot locate class file for Byte Buddy installer");
                }
                try {
                    File agentJar = File.createTempFile(AGENT_FILE_NAME, JAR_FILE_EXTENSION);
                    agentJar.deleteOnExit(); // Agent jar is required until VM shutdown due to lazy class loading.
                    Manifest manifest = new Manifest();
                    manifest.getMainAttributes().put(Attributes.Name.MANIFEST_VERSION, MANIFEST_VERSION_VALUE);
                    manifest.getMainAttributes().put(new Attributes.Name(AGENT_CLASS_PROPERTY), Installer.class.getName());
                    manifest.getMainAttributes().put(new Attributes.Name(CAN_REDEFINE_CLASSES_PROPERTY), Boolean.TRUE.toString());
                    manifest.getMainAttributes().put(new Attributes.Name(CAN_RETRANSFORM_CLASSES_PROPERTY), Boolean.TRUE.toString());
                    manifest.getMainAttributes().put(new Attributes.Name(CAN_SET_NATIVE_METHOD_PREFIX), Boolean.TRUE.toString());
                    JarOutputStream jarOutputStream = new JarOutputStream(new FileOutputStream(agentJar), manifest);
                    try {
                        jarOutputStream.putNextEntry(new JarEntry(Installer.class.getName().replace('.', '/') + CLASS_FILE_EXTENSION));
                        byte[] buffer = new byte[BUFFER_SIZE];
                        int index;
                        while ((index = inputStream.read(buffer)) != END_OF_FILE) {
                            jarOutputStream.write(buffer, START_INDEX, index);
                        }
                        jarOutputStream.closeEntry();
                    } finally {
                        jarOutputStream.close();
                    }
                    return agentJar;
                } finally {
                    inputStream.close();
                }
            }

            
{@inheritDoc}
/**
             * {@inheritDoc}
             */
            public File resolve() throws IOException {
                try {
                    File agentJar = trySelfResolve();
                    return agentJar == null
                            ? createJarFile()
                            : agentJar;
                } catch (Exception ignored) {
                    return createJarFile();
                }
            }
        }

        
An agent provider that supplies an existing agent that is not deleted after attachment.
/**
         * An agent provider that supplies an existing agent that is not deleted after attachment.
         */
        class ForExistingAgent implements AgentProvider {

            
The supplied agent.
/**
             * The supplied agent.
             */
            private File agent;

            
Creates an agent provider for an existing agent.
Params:
agent – The supplied agent./**
             * Creates an agent provider for an existing agent.
             *
             * @param agent The supplied agent.
             */
            protected ForExistingAgent(File agent) {
                this.agent = agent;
            }

            
{@inheritDoc}
/**
             * {@inheritDoc}
             */
            public File resolve() {
                return agent;
            }
        }
    }

    
An attachment evaluator is responsible for deciding if an agent can be attached from the current process.
/**
     * An attachment evaluator is responsible for deciding if an agent can be attached from the current process.
     */
    protected interface AttachmentTypeEvaluator {

        
Checks if the current VM requires external attachment for the supplied process id.
Params:
processId – The process id of the process to which to attach.
Returns:
true if the current VM requires external attachment for the supplied process./**
         * Checks if the current VM requires external attachment for the supplied process id.
         *
         * @param processId The process id of the process to which to attach.
         * @return {@code true} if the current VM requires external attachment for the supplied process.
         */
        boolean requiresExternalAttachment(String processId);

        
An installation action for creating an attachment type evaluator.
/**
         * An installation action for creating an attachment type evaluator.
         */
        enum InstallationAction implements PrivilegedAction<AttachmentTypeEvaluator> {

            
The singleton instance.
/**
             * The singleton instance.
             */
            INSTANCE;

            
The OpenJDK's property for specifying the legality of self-attachment.
/**
             * The OpenJDK's property for specifying the legality of self-attachment.
             */
            private static final String JDK_ALLOW_SELF_ATTACH = "jdk.attach.allowAttachSelf";

            
{@inheritDoc}
/**
             * {@inheritDoc}
             */
            @SuppressFBWarnings(value = "REC_CATCH_EXCEPTION", justification = "Exception should not be rethrown but trigger a fallback")
            public AttachmentTypeEvaluator run() {
                try {
                    if (Boolean.getBoolean(JDK_ALLOW_SELF_ATTACH)) {
                        return Disabled.INSTANCE;
                    } else {
                        return new ForJava9CapableVm(Class.forName("java.lang.ProcessHandle").getMethod("current"),
                                Class.forName("java.lang.ProcessHandle").getMethod("pid"));
                    }
                } catch (Exception ignored) {
                    return Disabled.INSTANCE;
                }
            }
        }

        
An attachment type evaluator that never requires external attachment.
/**
         * An attachment type evaluator that never requires external attachment.
         */
        enum Disabled implements AttachmentTypeEvaluator {

            
The singleton instance.
/**
             * The singleton instance.
             */
            INSTANCE;

            
{@inheritDoc}
/**
             * {@inheritDoc}
             */
            public boolean requiresExternalAttachment(String processId) {
                return false;
            }
        }

        
An attachment type evaluator that checks a process id against the current process id.
/**
         * An attachment type evaluator that checks a process id against the current process id.
         */
        class ForJava9CapableVm implements AttachmentTypeEvaluator {

            
The java.lang.ProcessHandle#current() method. /**
             * The {@code java.lang.ProcessHandle#current()} method.
             */
            private final Method current;

            
The java.lang.ProcessHandle#pid() method. /**
             * The {@code java.lang.ProcessHandle#pid()} method.
             */
            private final Method pid;

            
Creates a new attachment type evaluator.
Params:
current – The java.lang.ProcessHandle#current() method.
pid –  The java.lang.ProcessHandle#pid() method./**
             * Creates a new attachment type evaluator.
             *
             * @param current The {@code java.lang.ProcessHandle#current()} method.
             * @param pid     The {@code java.lang.ProcessHandle#pid()} method.
             */
            protected ForJava9CapableVm(Method current, Method pid) {
                this.current = current;
                this.pid = pid;
            }

            
{@inheritDoc}
/**
             * {@inheritDoc}
             */
            public boolean requiresExternalAttachment(String processId) {
                try {
                    return pid.invoke(current.invoke(STATIC_MEMBER)).toString().equals(processId);
                } catch (IllegalAccessException exception) {
                    throw new IllegalStateException("Cannot access Java 9 process API", exception);
                } catch (InvocationTargetException exception) {
                    throw new IllegalStateException("Error when accessing Java 9 process API", exception.getCause());
                }
            }
        }
    }
}