net: ipv6 support, merge unix+ip;[pack:x] attribute (#9904)

examples/tcp_echo_server.v

@@ -0,0 +1,40 @@
+import io
+import net
+
+// This file shows how a basic TCP echo server can be implemented using
+// the net module. You can connect to the server by using netcat or telnet,
+// in separate shells, for example:
+// nc 127.0.0.1 12345
+// or
+// telnet 127.0.0.1 12345
+
+fn main() {
+	mut server := net.listen_tcp(.ip6, ':12345') ?
+	laddr := server.addr() ?
+	eprintln('Listen on $laddr ...')
+	for {
+		mut socket := server.accept() ?
+		go handle_client(mut socket)
+	}
+}
+
+fn handle_client(mut socket net.TcpConn) {
+	defer {
+		socket.close() or { panic(err) }
+	}
+	client_addr := socket.peer_addr() or { return }
+	eprintln('> new client: $client_addr')
+	mut reader := io.new_buffered_reader(reader: socket)
+	defer {
+		reader.free()
+	}
+	socket.write_string('server: hello\n') or { return }
+	for {
+		received_line := reader.read_line() or { return }
+		if received_line == '' {
+			return
+		}
+		println('client $client_addr: $received_line')
+		socket.write_string('server: $received_line\n') or { return }
+	}
+}