public synchronized String createDisplay()

in sshd-core/src/main/java/org/apache/sshd/server/x11/DefaultX11ForwardSupport.java [69:174]
92 lines of code
18 McCabe index (conditional complexity)

    public synchronized String createDisplay(
            boolean singleConnection, String authenticationProtocol, String authenticationCookie, int screen)
            throws IOException {
        boolean debugEnabled = log.isDebugEnabled();
        if (isClosed()) {
            throw new IllegalStateException("X11ForwardSupport is closed");
        }
        if (isClosing()) {
            throw new IllegalStateException("X11ForwardSupport is closing");
        }

        // only support non windows systems
        if (OsUtils.isWin32()) {
            if (debugEnabled) {
                log.debug("createDisplay(auth={}, cookie={}, screen={}) Windows O/S N/A",
                        authenticationProtocol, authenticationCookie, screen);
            }
            return null;
        }

        Session session = Objects.requireNonNull(service.getSession(), "No session");
        if (acceptor == null) {
            FactoryManager manager = Objects.requireNonNull(session.getFactoryManager(), "No factory manager");
            IoServiceFactory factory = Objects.requireNonNull(manager.getIoServiceFactory(), "No I/O service factory");
            acceptor = factory.createAcceptor(this);
        }

        int minDisplayNumber = CoreModuleProperties.X11_DISPLAY_OFFSET.getRequired(session);
        int maxDisplayNumber = CoreModuleProperties.X11_MAX_DISPLAYS.getRequired(session);
        int basePort = CoreModuleProperties.X11_BASE_PORT.getRequired(session);
        String bindHost = CoreModuleProperties.X11_BIND_HOST.getRequired(session);
        InetSocketAddress addr = null;

        // try until bind successful or max is reached
        for (int displayNumber = minDisplayNumber; displayNumber < maxDisplayNumber; displayNumber++) {
            int port = basePort + displayNumber;
            addr = new InetSocketAddress(bindHost, port);
            try {
                acceptor.bind(addr);
                break;
            } catch (BindException bindErr) {
                if (debugEnabled) {
                    log.debug("createDisplay(auth={}, cookie={}, screen={}) failed ({}) to bind to address={}: {}",
                            authenticationProtocol, authenticationCookie, screen,
                            bindErr.getClass().getSimpleName(), addr, bindErr.getMessage());
                }

                addr = null;
            }
        }

        if (addr == null) {
            log.warn("createDisplay(auth={}, cookie={}, screen={})"
                     + " failed to allocate internet-domain X11 display socket in range {}-{}",
                    authenticationProtocol, authenticationCookie, screen,
                    minDisplayNumber, maxDisplayNumber);
            Collection<SocketAddress> boundAddresses = acceptor.getBoundAddresses();
            if (GenericUtils.isEmpty(boundAddresses)) {
                if (debugEnabled) {
                    log.debug("createDisplay(auth={}, cookie={}, screen={}) closing - no more bound addresses",
                            authenticationProtocol, authenticationCookie, screen);
                }
                close();
            } else {
                if (debugEnabled) {
                    log.debug("createDisplay(auth={}, cookie={}, screen={}) closing - remaining bound addresses: {}",
                            authenticationProtocol, authenticationCookie, screen, boundAddresses);
                }
            }

            return null;
        }

        int port = addr.getPort();
        int displayNumber = port - basePort;
        String authDisplay = "unix:" + displayNumber + "." + screen;
        try {
            ProcessBuilder processBuilder = new ProcessBuilder(XAUTH_COMMAND, "remove", authDisplay);
            Process p = processBuilder.start();
            int result = p.waitFor();
            if (debugEnabled) {
                log.debug("createDisplay({}) {} remove result={}", authDisplay, XAUTH_COMMAND, result);
            }

            if (result == 0) {
                processBuilder = new ProcessBuilder(
                        XAUTH_COMMAND, "add", authDisplay, authenticationProtocol, authenticationCookie);
                p = processBuilder.start();
                result = p.waitFor();

                if (debugEnabled) {
                    log.debug("createDisplay({}) {} add result={}", authDisplay, XAUTH_COMMAND, result);
                }
            }

            if (result != 0) {
                throw new IllegalStateException("Bad " + XAUTH_COMMAND + " invocation result: " + result);
            }

            return bindHost + ":" + displayNumber + "." + screen;
        } catch (Throwable e) {
            warn("createDisplay({}) failed ({}) run xauth: {}",
                    authDisplay, e.getClass().getSimpleName(), e.getMessage(), e);
            return null;
        }
    }