Unix-Domain Socket Channels

Unix-Domain Socket Channels, added in Java 16 (JEP 380), are a Java feature designed to improve inter-processor communication on the same host, over the usage of TCP/IP.

Same Host Communication

Synchronous communication between two discreet processes that are located on the same host is a somewhat common need. For Java, this has primarily been done through TCP/IP connections. TCP/IP connections have relatively high overhead in setup and also limited throughput. For an application that only ever communicates with a local process, this also opens a security vulnerability as they will need to accept remote connections.

Unix-Domain Socket Channels

Unix-Domain Socket Channels (Unix Sockets), added in Java 16, make use of the AF_UNIX (AF_LOCAL) socket family. Unix Sockets are strictly limited to intra-host communication, but offer:

• Faster setup and higher throughput than TCP/IP loopback connections

• Allow OS enforced controls filesystem controls

• Can work with containers via shared volumes

Also despite their name, Unix Sockets even work on Windows 10 and Windows Server 2019.

Configuring Communication

Setting up a Unix Socket appropriately requires configuring a “server” and a “client” like in the below examples.

Server

Configuring the “server” is pretty simple:

var address = UnixDomainSocketAddress.of("/mnt/server");
try (var serverChannel = ServerSocketChannel.open(UNIX)) {
    serverChannel.bind(address);
    try (var clientChannel = serverChannel.accept()) {
        ByteBuffer buf = ByteBuffer.allocate(64);
        clientChannel.read(buf);
        buf.flip();
        System.out.printf("Read %d bytes\n", buf.remaining());
    }
} finally {
    Files.deleteIfExists(address.getPath());
}

In the above example /mnt/server is the socket path.

The channel must then be opened: var serverChannel = ServerSocketChannel.open(UNIX)

The server must then be told to listen to communication coming from the channel: var clientChannel = serverChannel.accept()

To pull data sent on the data, use read(): clientChannel.read(buf)

Client

Configuration on the client side is even simpler:

var address = UnixDomainSocketAddress.of("/mnt/server");
try (var clientChannel = SocketChannel.open(address)) {
    ByteBuffer buf = ByteBuffer.wrap("Hello world".getBytes());
    clientChannel.write(buf);
}

The channel to the defined path /mnt/server must be opened: var clientChannel = SocketChannel.open(address)

To send data along the channel, use write(): clientChannel.write(buf);

Happy Coding!