/*

 * Copyright (c) 2005, 2018, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package sun.tools.attach;

import com.sun.tools.attach.AttachOperationFailedException;

import com.sun.tools.attach.AgentLoadException;

import com.sun.tools.attach.AttachNotSupportedException;

import com.sun.tools.attach.spi.AttachProvider;

import java.io.InputStream;

import java.io.IOException;

import java.io.File;

import java.nio.charset.StandardCharsets;

import java.nio.file.Path;

import java.nio.file.Paths;

import java.nio.file.Files;

/*

 * Linux implementation of HotSpotVirtualMachine

 */

public class VirtualMachineImpl extends HotSpotVirtualMachine {

    // "/tmp" is used as a global well-known location for the files

    // .java_pid<pid>. and .attach_pid<pid>. It is important that this

    // location is the same for all processes, otherwise the tools

    // will not be able to find all Hotspot processes.

    // Any changes to this needs to be synchronized with HotSpot.

    private static final String tmpdir = "/tmp";

    String socket_path;

    /**

     * Attaches to the target VM

     */

    VirtualMachineImpl(AttachProvider provider, String vmid)

        throws AttachNotSupportedException, IOException

    {

        super(provider, vmid);

        // This provider only understands pids

        int pid;

        try {

            pid = Integer.parseInt(vmid);

        } catch (NumberFormatException x) {

            throw new AttachNotSupportedException("Invalid process identifier");

        }

        // Try to resolve to the "inner most" pid namespace

        int ns_pid = getNamespacePid(pid);

        // Find the socket file. If not found then we attempt to start the

        // attach mechanism in the target VM by sending it a QUIT signal.

        // Then we attempt to find the socket file again.

        File socket_file = findSocketFile(pid, ns_pid);

        socket_path = socket_file.getPath();

        if (!socket_file.exists()) {

            File f = createAttachFile(pid, ns_pid);

            try {

                sendQuitTo(pid);

                // give the target VM time to start the attach mechanism

                final int delay_step = 100;

                final long timeout = attachTimeout();

                long time_spend = 0;

                long delay = 0;

                do {

                    // Increase timeout on each attempt to reduce polling

                    delay += delay_step;

                    try {

                        Thread.sleep(delay);

                    } catch (InterruptedException x) { }

                    time_spend += delay;

                    if (time_spend > timeout/2 && !socket_file.exists()) {

                        // Send QUIT again to give target VM the last chance to react

                        sendQuitTo(pid);

                    }

                } while (time_spend <= timeout && !socket_file.exists());

                if (!socket_file.exists()) {

                    throw new AttachNotSupportedException(

                        String.format("Unable to open socket file %s: " +

                          "target process %d doesn't respond within %dms " +

                          "or HotSpot VM not loaded", socket_path, pid,

                                      time_spend));

                }

            } finally {

                f.delete();

            }

        }

        // Check that the file owner/permission to avoid attaching to

        // bogus process

        checkPermissions(socket_path);

        // Check that we can connect to the process

        // - this ensures we throw the permission denied error now rather than

        // later when we attempt to enqueue a command.

        int s = socket();

        try {

            connect(s, socket_path);

        } finally {

            close(s);

        }

    }

    /**

     * Detach from the target VM

     */

    public void detach() throws IOException {

        synchronized (this) {

            if (socket_path != null) {

                socket_path = null;

            }

        }

    }

    // protocol version

    private final static String PROTOCOL_VERSION = "1";

    // known errors

    private final static int ATTACH_ERROR_BADVERSION = 101;

    /**

     * Execute the given command in the target VM.

     */

    InputStream execute(String cmd, Object ... args) throws AgentLoadException, IOException {

        assert args.length <= 3;                // includes null

        // did we detach?

        synchronized (this) {

            if (socket_path == null) {

                throw new IOException("Detached from target VM");

            }

        }

        // create UNIX socket

        int s = socket();

        // connect to target VM

        try {

            connect(s, socket_path);

        } catch (IOException x) {

            close(s);

            throw x;

        }

        IOException ioe = null;

        // connected - write request

        // <ver> <cmd> <args...>

        try {

            writeString(s, PROTOCOL_VERSION);

            writeString(s, cmd);

            for (int i=0; i<3; i++) {

                if (i < args.length && args[i] != null) {

                    writeString(s, (String)args[i]);

                } else {

                    writeString(s, "");

                }

            }

        } catch (IOException x) {

            ioe = x;

        }

        // Create an input stream to read reply

        SocketInputStream sis = new SocketInputStream(s);

        // Read the command completion status

        int completionStatus;

        try {

            completionStatus = readInt(sis);

        } catch (IOException x) {

            sis.close();

            if (ioe != null) {

                throw ioe;

            } else {

                throw x;

            }

        }

        if (completionStatus != 0) {

            // read from the stream and use that as the error message

            String message = readErrorMessage(sis);

            sis.close();

            // In the event of a protocol mismatch then the target VM

            // returns a known error so that we can throw a reasonable

            // error.

            if (completionStatus == ATTACH_ERROR_BADVERSION) {

                throw new IOException("Protocol mismatch with target VM");

            }

            // Special-case the "load" command so that the right exception is

            // thrown.

            if (cmd.equals("load")) {

                String msg = "Failed to load agent library";

                if (!message.isEmpty())

                    msg += ": " + message;

                throw new AgentLoadException(msg);

            } else {

                if (message.isEmpty())

                    message = "Command failed in target VM";

                throw new AttachOperationFailedException(message);

            }

        }

        // Return the input stream so that the command output can be read

        return sis;

    }

    /*

     * InputStream for the socket connection to get target VM

     */

    private class SocketInputStream extends InputStream {

        int s;

        public SocketInputStream(int s) {

            this.s = s;

        }

        public synchronized int read() throws IOException {

            byte b[] = new byte[1];

            int n = this.read(b, 0, 1);

            if (n == 1) {

                return b[0] & 0xff;

            } else {

                return -1;

            }

        }

        public synchronized int read(byte[] bs, int off, int len) throws IOException {

            if ((off < 0) || (off > bs.length) || (len < 0) ||

                ((off + len) > bs.length) || ((off + len) < 0)) {

                throw new IndexOutOfBoundsException();

            } else if (len == 0) {

                return 0;

            }

            return VirtualMachineImpl.read(s, bs, off, len);

        }

        public void close() throws IOException {

            VirtualMachineImpl.close(s);

        }

    }

    // Return the socket file for the given process.

    private File findSocketFile(int pid, int ns_pid) {

        // A process may not exist in the same mount namespace as the caller.

        // Instead, attach relative to the target root filesystem as exposed by

        // procfs regardless of namespaces.

        String root = "/proc/" + pid + "/root/" + tmpdir;

        return new File(root, ".java_pid" + ns_pid);

    }

    // On Linux a simple handshake is used to start the attach mechanism

    // if not already started. The client creates a .attach_pid<pid> file in the

    // target VM's working directory (or temp directory), and the SIGQUIT handler

    // checks for the file.

    private File createAttachFile(int pid, int ns_pid) throws IOException {

        String fn = ".attach_pid" + ns_pid;

        String path = "/proc/" + pid + "/cwd/" + fn;

        File f = new File(path);

        try {

            f.createNewFile();

        } catch (IOException x) {

            String root;

            if (pid != ns_pid) {

                // A process may not exist in the same mount namespace as the caller.

                // Instead, attach relative to the target root filesystem as exposed by

                // procfs regardless of namespaces.

                root = "/proc/" + pid + "/root/" + tmpdir;

            } else {

                root = tmpdir;

            }

            f = new File(root, fn);

            f.createNewFile();

        }

        return f;

    }

    /*

     * Write/sends the given to the target VM. String is transmitted in

     * UTF-8 encoding.

     */

    private void writeString(int fd, String s) throws IOException {

        if (s.length() > 0) {

            byte b[];

            try {

                b = s.getBytes("UTF-8");

            } catch (java.io.UnsupportedEncodingException x) {

                throw new InternalError(x);

            }

            VirtualMachineImpl.write(fd, b, 0, b.length);

        }

        byte b[] = new byte[1];

        b[0] = 0;

        write(fd, b, 0, 1);

    }

    // Return the inner most namespaced PID if there is one,

    // otherwise return the original PID.

    private int getNamespacePid(int pid) throws AttachNotSupportedException, IOException {

        // Assuming a real procfs sits beneath, reading this doesn't block

        // nor will it consume a lot of memory.

        String statusFile = "/proc/" + pid + "/status";

        File f = new File(statusFile);

        if (!f.exists()) {

            return pid; // Likely a bad pid, but this is properly handled later.

        }

        Path statusPath = Paths.get(statusFile);

        try {

            for (String line : Files.readAllLines(statusPath, StandardCharsets.UTF_8)) {

                String[] parts = line.split(":");

                if (parts.length == 2 && parts[0].trim().equals("NSpid")) {

                    parts = parts[1].trim().split("\\s+");

                    // The last entry represents the PID the JVM "thinks" it is.

                    // Even in non-namespaced pids these entries should be

                    // valid. You could refer to it as the inner most pid.

                    int ns_pid = Integer.parseInt(parts[parts.length - 1]);

                    return ns_pid;

                }

            }

            // Old kernels may not have NSpid field (i.e. 3.10).

            // Fallback to original pid in the event we cannot deduce.

            return pid;

        } catch (NumberFormatException | IOException x) {

            throw new AttachNotSupportedException("Unable to parse namespace");

        }

    }

    //-- native methods

    static native void sendQuitTo(int pid) throws IOException;

    static native void checkPermissions(String path) throws IOException;

    static native int socket() throws IOException;

    static native void connect(int fd, String path) throws IOException;

    static native void close(int fd) throws IOException;

    static native int read(int fd, byte buf[], int off, int bufLen) throws IOException;

    static native void write(int fd, byte buf[], int off, int bufLen) throws IOException;

    static {

        System.loadLibrary("attach");

    }

}