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class IO::Socket::Async::ListenSocket is Tap {}

IO::Socket::Async::ListenSocket represents a listening TCP socket. Instances of this are returned by the tap method of the supply returned by IO::Socket::Async.listen:

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my IO::Socket::Async::ListenSocket:D $server =
    IO::Socket::Async.listen('127.0.0.1', 0).tap(-> $peer {
        await $peer.print: "Hello. Goodbye!\r\n";
        $peer.close;
    });

my (Str:D $host, Int:D $port) = await $server.socket-host, $server.socket-port;
say "The rude service is listening on $host:$port for the next 10 seconds...";
await Promise.in(10).then({ $server.close });
say "I'm done now.";

Alternatively, by using the do prefix with whenever, you can also use it from within a react block:

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react {
    my IO::Socket::Async::ListenSocket:D $server =
        do whenever IO::Socket::Async.listen('127.0.0.1', 0) -> IO::Socket::Async:D $connection {
            await $connection.print: "Hello. Goodbye!\r\n";
            $connection.close;
            QUIT { $server.close; .rethrow }
        };
    # Use $server here somehow.
}