src/java.base/unix/classes/sun/nio/ch/InheritedChannel.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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
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 * by Oracle in the LICENSE file that accompanied this code.
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 * 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).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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package sun.nio.ch;

import java.lang.reflect.Constructor;
import java.io.FileDescriptor;
import java.io.IOException;
import java.net.InetAddress;
import java.net.Inet6Address;
import java.net.InetSocketAddress;
import java.net.ProtocolFamily;
import java.net.SocketAddress;
import java.net.UnixDomainSocketAddress;
import java.nio.channels.Channel;
import java.nio.channels.spi.SelectorProvider;
import static java.net.StandardProtocolFamily.INET6;
import static java.net.StandardProtocolFamily.INET;
import static java.net.StandardProtocolFamily.UNIX;

class InheritedChannel {

    // the "types" of socket returned by soType0
    private static final int UNKNOWN            = -1;
    private static final int SOCK_STREAM        = 1;
    private static final int SOCK_DGRAM         = 2;

    // socket address type
    static final int AF_UNKNOWN         = -1;
    static final int AF_INET            = 1;
    static final int AF_INET6           = 2;
    static final int AF_UNIX            = 3;

    // oflag values when opening a file
    private static final int O_RDONLY           = 0;
    private static final int O_WRONLY           = 1;
    private static final int O_RDWR             = 2;

    /*
     * In order to "detach" the standard streams we dup them to /dev/null.
     * In order to reduce the possibility of an error at close time we
     * open /dev/null early - that way we know we won't run out of file
     * descriptors at close time. This makes the close operation a
     * simple dup2 operation for each of the standard streams.
     */
    private static int devnull = -1;

    private static void detachIOStreams() {
        try {
            dup2(devnull, 0);
            dup2(devnull, 1);
            dup2(devnull, 2);
        } catch (IOException ioe) {
            // this shouldn't happen
            throw new InternalError(ioe);
        }
    }

    static ProtocolFamily protocolFamily(SocketAddress sa) {
        if (sa instanceof UnixDomainSocketAddress) {
            return UNIX;
        } else {
            InetSocketAddress isa = (InetSocketAddress) sa;
            return (isa.getAddress() instanceof Inet6Address) ? INET6 : INET;
        }
    }

    static ProtocolFamily protocolFamily(int family) {
        return switch (family) {
            case AF_INET -> INET;
            case AF_INET6 -> INET6;
            case AF_UNIX -> UNIX;
            default -> throw new IllegalArgumentException();
        };
    }

    /*
     * Override the implCloseSelectableChannel for each channel type - this
     * allows us to "detach" the standard streams after closing and ensures
     * that the underlying socket really closes.
     */
    public static class InheritedSocketChannelImpl extends SocketChannelImpl {

        InheritedSocketChannelImpl(SelectorProvider sp,
                                   FileDescriptor fd,
                                   SocketAddress remote)
            throws IOException
        {
            super(sp, protocolFamily(remote), fd, remote);
        }

        protected void implCloseSelectableChannel() throws IOException {
            super.implCloseSelectableChannel();
            detachIOStreams();
        }
    }

    public static class InheritedServerSocketChannelImpl extends ServerSocketChannelImpl {

        InheritedServerSocketChannelImpl(SelectorProvider sp,
                                         ProtocolFamily family,
                                         FileDescriptor fd)
            throws IOException
        {
            super(sp, family, fd, true);
        }

        @Override
        protected void implCloseSelectableChannel() throws IOException {
            super.implCloseSelectableChannel();
            detachIOStreams();
        }
    }

    public static class InheritedDatagramChannelImpl extends DatagramChannelImpl {

        InheritedDatagramChannelImpl(SelectorProvider sp,
                                     FileDescriptor fd)
            throws IOException
        {
            super(sp, fd);
        }

        protected void implCloseSelectableChannel() throws IOException {
            super.implCloseSelectableChannel();
            detachIOStreams();
        }
    }

    /*
     * If standard inherited channel is connected to a socket then return a Channel
     * of the appropriate type based standard input.
     */
    private static Channel createChannel() throws IOException {

        // dup the file descriptor - we do this so that for two reasons :-
        // 1. Avoids any timing issues with FileDescriptor.in being closed
        //    or redirected while we create the channel.
        // 2. Allows streams based on file descriptor 0 to co-exist with
        //    the channel (closing one doesn't impact the other)

        int fdVal = dup(0);

        // Examine the file descriptor - if it's not a socket then we don't
        // create a channel so we release the file descriptor.

        int st;
        st = soType0(fdVal);
        if (st != SOCK_STREAM && st != SOCK_DGRAM) {
            close0(fdVal);
            return null;
        }

        // Next we create a FileDescriptor for the dup'ed file descriptor
        // Have to use reflection and also make assumption on how FD
        // is implemented.

        Class<?> paramTypes[] = { int.class };
        Constructor<?> ctr = Reflect.lookupConstructor("java.io.FileDescriptor",
                                                       paramTypes);
        Object args[] = { Integer.valueOf(fdVal) };
        FileDescriptor fd = (FileDescriptor)Reflect.invoke(ctr, args);


        // Now create the channel. If the socket is a streams socket then
        // we see if there is a peer (ie: connected). If so, then we
        // create a SocketChannel, otherwise a ServerSocketChannel.
        // If the socket is a datagram socket then create a DatagramChannel

        SelectorProvider provider = SelectorProvider.provider();
        assert provider instanceof sun.nio.ch.SelectorProviderImpl;

        Channel c;
        if (st == SOCK_STREAM) {
            int family = addressFamily(fdVal);
            if (family == AF_UNKNOWN)
                return null;
            ProtocolFamily pfamily = protocolFamily(family);
            if (family == AF_UNIX) {
                if (isConnected(fdVal)) {
                    var sa = UnixDomainSocketAddress.of(unixPeerAddress(fdVal));
                    return new InheritedSocketChannelImpl(provider, fd, sa);
                } else {
                    return new InheritedServerSocketChannelImpl(provider, pfamily, fd);
                }
            }
            InetAddress ia = inetPeerAddress0(fdVal);
            if (ia == null) {
               c = new InheritedServerSocketChannelImpl(provider, pfamily, fd);
            } else {
               int port = peerPort0(fdVal);

               assert port > 0;
               InetSocketAddress isa = new InetSocketAddress(ia, port);
               c = new InheritedSocketChannelImpl(provider, fd, isa);
            }
        } else {
            c = new InheritedDatagramChannelImpl(provider, fd);
        }
        return c;
    }

    private static boolean haveChannel = false;
    private static Channel channel = null;

    /*
     * Returns a Channel representing the inherited channel if the
     * inherited channel is a stream connected to a network socket.
     */
    public static synchronized Channel getChannel() throws IOException {
        if (devnull < 0) {
            devnull = open0("/dev/null", O_RDWR);
        }

        // If we don't have the channel try to create it
        if (!haveChannel) {
            channel = createChannel();
            haveChannel = true;
        }

        return channel;
    }

    private static String unixPeerAddress(int fd) throws IOException {
        byte[] bytes = unixPeerAddress0(fd);
        return new String(bytes);
    }

    // -- Native methods --

    private static native void initIDs();
    private static native int dup(int fd) throws IOException;
    private static native void dup2(int fd, int fd2) throws IOException;
    private static native int open0(String path, int oflag) throws IOException;
    private static native void close0(int fd) throws IOException;
    private static native int soType0(int fd);
    private static native int addressFamily(int fd);
    private static native InetAddress inetPeerAddress0(int fd);
    private static native byte[] unixPeerAddress0(int fd);
    private static native int peerPort0(int fd);

    // return true if socket is connected to a peer
    private static native boolean isConnected(int fd);

    static {
        IOUtil.load();
        initIDs();
    }
}