Develop Reference

Reconnect raspberry pi's bluetooth to an HC-06 in a processing sketch

I have a working setup in which a raspberry pi runs a headless processing sketch upon booting. This sketch connects the Pi's onboard bluetooth to an HC-06. The Pi also sets up a serial connection to an arduino nano through a USB cable. The processing sketch acts as a relay. It relays bytes from the arduino to the Hc-06 and vice versa.
The device with the HC-06 is an arduino nano. This device sends out a handshaking signal so the arduino on the Pi's end knows it's connected and sends a respons.
This all works like a charm but on one condition. The Hc-06 needs to be 'on' before the processing sketch boots. If I turn on the HC-06 too late or if I turn it on/off I cannot reconnect and the processing sketch is to be rebooted.
I want to program a more advanced hand shaking protocol with an time-out feature. So both device will be aware that the connection is severed.
I start the processing sketch via a shell script
sudo rfcomm bind hci0 20:14:04:15:23:75
sudo killall java
xvfb-run processing-java --sketch=/home/pi/Documents/bluetooth --run # runs headless
The rfcomm bind command is only yo be run once upon booting.
And the bluetooth script:
import processing.serial.*;
Serial handController;
Serial central;
byte mode;
void setup()
{
printArray(Serial.list());
size(200,200);
background(0); // black
central = new Serial( this, Serial.list()[3], 115200);
handController = new Serial( this , Serial.list()[0] , 115200 );
}
long prev;
byte tgl = 0;
void draw()
{
if(handController.available() > 0) {
int c = handController.read();
println(" handcontroller:\t" + (char) c + "\t" + c); // as well char as dec value
central.write(c);
}
....
Is it possible that from within this sketch that I terminate the serial connection to rfcomm0 and then restart it?
It seems that this line sets up the bluetooth connection.
handController = new Serial( this , Serial.list()[0] , 115200 ); // rfcomm0
I am not extremely familiar with java. How can I destroy the serial object? And can I do 'new' a 2nd time from out a function?
Kind regards,
Bas

You can use the Serial's stop() method to close the serial connection.
You can then re-initialise the port as required.
Here's a rough(untested example):
void restartSerialPort(Serial reference,String portName, int baudRate){
// pause rendering (draw loop)
noLoop();
// stop previous connection
if(reference != null){
reference.stop();
reference = null;
}
// start connection anew
try{
reference = new Serial( this, portName, baudRate);
}catch(Exception e){
println("error opening serial port: " + portName);
e.printStackTrace();
}
// resume rendering
loop();
}
Bare in mind this needs to be tested/tweaked: I'm not 100% the passed reference will update that easily (otherwise the new Serial object probably needs to be returned by the method and re-assigned to the original reference).
Also not that Processing requires a windowing environment, so it's not quite fully headless.
As a quick alternative to a pure commandline option you can look at Python and the pyserial module

How to detect if docker container crashed

I am running a process every 5 minutes and checking to make sure every container. If the container does not respond I can flag it as down. I have the containers IP address and I loop through each ip and check if it responds to a ping. If not I flag it as down. Is there a better way to do this? My code:
#Transactional
#Scheduled(fixedRate = 1000 * 60) //5 min
public void monitorHosts(){
Iterable<Ncl> ncls = nclRepository.findAll();
for(Ncl ncl: ncls){
for(String host: ncl.getHosts()){
Boolean isHostAlive = isHostAlive(host);
if(!isHostAlive){
Ncl nclWorking = nclRepository.findOne(ncl.getUuid());
if(nclWorking != null){
Set<String> hosts = nclWorking.getHosts().stream().filter(x -> x.equals(host)).collect(Collectors.toSet());
nclWorking.getHosts().clear();
nclWorking = nclRepository.save(nclWorking);
nclWorking.setHosts(hosts);
nclRepository.save(nclWorking);
}
}
}
}
}
private Boolean isHostAlive(String host){
try{
InetAddress address = InetAddress.getByName(host);
boolean reachable = address.isReachable(10000);
return reachable;
} catch (Exception e){
e.printStackTrace();
return false;
}
}

It mostly depends on what you need to do with the information about your containers.
There is a number of monitoring solutions available, which can monitor your containers and notify some one if there are some troubles.
If you have to use this info in some application, then you can use some solutions like Consul.io and let them check your services statuses, not containers (in most cases man aware of the service availability in the container, not container itself). Or you can use docker-api for Java, because ICMP-protocol is not always a good solution, especially in distributed networks.

I would use docker events
extract from the doc
https://docs.docker.com/engine/reference/commandline/events/#examples
use something like
docker events --filter 'event=stop'

This is more obtrusive but is a nice one:
Using HEALTHCHECK that docker provides
You can customize it for each application. Something like:
HEALTHCHECK --interval=5m --timeout=3s \
CMD curl -f http://localhost/ || exit 1
Then you can check the health status as this:
docker inspect --format='{{json .State.Health}}' <container_id>
Or you can use docker ps and see the STATUS column:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
225426fc7c93 ubuntu "tail -f /dev/null" 5 seconds ago Up 4 seconds (healthy)
Or you can query the docker API:
curl --unix-socket /var/run/docker.sock http:/v1.24/containers/json
PS: You can set the healthcheck at docker run time (without modifying the Dockerfile). Docs

check accessibility of all nodes in a network in java

I want to check all of nodes accessibility in a network using java. I have read This and This Questions and I have write my method by helping these questions, I have at least two tested Ips in my network which are accessible, one of them is 192.168.1.1 and another is 192.168.1.102 you can see test of 192.168.1.1 in the below picture:
Odk but when I run my code my app says that 192.168.1.1 is not reachable. here is the image, I have pointed at it with a red arrow:
ok , and here is my java code:
private void checkNetworkAccessibility(){
int timeout = 1000;
String subnet = firstSubnet.getText() + "." + secondSubnet.getText() + "." + thirdSubnet.getText() + ".";
DefaultTableModel model = (DefaultTableModel)networkTable.getModel();
for(int i=1;i<=254;i++){
try {
if(InetAddress.getByName(subnet+i).isReachable(timeout)){
model.addRow(new Object[]{subnet + i, subnet + i, "بله", "بله"});
}
else{
model.addRow(new Object[]{subnet + i, "نامشخص", "خیر", "بله"});
}
} catch (IOException ex) {
System.out.println(ex.getMessage());
}
}
}
what is wrong with my code?

The problem is that .isReachable() is not reliable. Its implementation is totally OS dependent!
Let's take Linux as an example; this method uses the echo TCP service (port 7). Do you actually know of a server which has even that running today? I don't.
It cannot use ping; look at this:
$ ls -l $(which ping)
-rwsr-xr-x 1 root root 44168 May 7 2014 /bin/ping
Yes, that's right; the sticky bit. The reason for this is that the ping command sends an ICMP echo request packet along the wire, and this requires that you be able to access raw sockets.
Which you can't do unless you have the necessary privileges, and which you can't do in Java! Except if you use native libraries. And you run with the necessary privileges. Which more often than not means you need to be admin. Which you don't want.
And of course, a sysadmin may even decide to block incoming echo request packets on a host, so even ping is not reliable...

How to control the handset using AT commands in java

I know that by using AT commands we can control the handset.As example unlocking screen we can give a specific AT command or moving right to the menu or left or bottom or up we can give specific AT commands. What all are the AT commands for doing this kind of control.
Thank you.

From what I understand, the AT commands are more used for phone-type functions (making calls, or sending SMS, etc), rather than menu navigation, etc.
I'm not entirely sure if that was your end-goal after menu navigation, but you can find more details here: http://en.wikipedia.org/wiki/Hayes_command_set (the original +AT command set)
If you wanted to send SMS from a handset connected to your computer you might want to take a peek at this page: http://www.developershome.com/sms/atCommandsIntro.asp
If you wanted more control when performing functions, like sending SMS, etc, you might want to investigate "PDU Mode."
It is entirely possible that some handset manufacturers may have implemented additional +AT commands to allow other functions to be performed, so you might do better by specifically searching for the commands related to the handset you are using.
(Of course, if you're having issues connecting to the handset hardware itself, you need to ensure you have either the javax.comm extension or some favoured Java USB API installed)
If post doesn't help, perhaps you could provide more details in your question? (eg. what you are ultimately trying to do, if you think it would help)

List of AT commands
sample java code to use AT command
public void servicesDiscovered(int transID, ServiceRecord serviceRecord[])
{
String url = serviceRecord[0].getConnectionURL(1, false);
try
{
//ClientSession conn= (ClientSession)Connector.open(url);
StreamConnection meineVerbindung = (StreamConnection) Connector.open(url);
if(conn== null)
System.out.println("Kann Service URL nicht oeffnen\n");
else
{
OutputStream out = conn.openOutputStream();
InputStream in = conn.openInputStream();
String message = "AT+CGMI\r\n";
// send AT-command
System.out.println("send AT Comand request: "+message);
out.write(message.getBytes());
out.flush();
out.close();
byte buffer[] = new byte[10000];
// read the response from mobile phone
in.read(buffer);
System.out.println("AT Comand response: "+buffer.toString());}
}
catch(IOException e)
{
System.out.println("Service Error(3): "+e.getMessage());
}
}

How can I emulate a COM port, write data to it and read data from it?

I'm trying to test my code that reads from a USB port (COM25 when the device is connected) that is created when a device is connected to my computer and to a boat. I cannot power the USB device when not on the boat so testing is difficult. Can someone let me know how to simulate a COM port and write data to it so my test program is able to connect to that simulated COM port and read that data?
I'm reading this from a Java program but the simulation doesn't need to be in Java or any specific language. Just a program that will simulate the COM port and allow me to connect to it. I downloaded a COM port emulator from AGG Software and it appears that it's writing to what I deem COM25 but I'm not able to connect to it from my Java test.

The general answer for this kind of problem is to wrap the code that talks to the COM port in a class that implements an interface. If you do this as a Facade (pattern) then you can also make the COM methods you call sensible from your end.
The interface can then be mocked or faked for the test. (There is a great article on test objects, but I haven't been able to find it yet.) One advantage here is that you can create a fake version that throws exceptions or otherwise does things that are possible for the port to do but hard to get it to do in practice.

Where I work, we solved a similar issue by having our emulator not spoof a COM port at all. Here's how you can do it:
Define an interface for talking with your COM port, something like IUsbCommService
Implement your real COM-communcation service, using the standard Java Comm API
For your emulator, simply kick of a thread that spits out the same sort of data you can expect from your USB device at regular intervals.
Use your IOC framework of choice (e.g., Spring) to wire up either the emulator or the real service.
As long as you hide your implementation logic appropriately, and as long as you code to your interface, your service-consumer code won't care whether it's talking to the real USB device or to the emulator.
For example:
import yourpackage.InaccessibleDeviceException;
import yourpackage.NoDataAvailableException;
public interface IUsbProviderService {
public void initDevice() throws InaccessibleDeviceException;
public UsbData getUsbData()
throws InaccessibleDeviceException, NoDataAvailableException;
}
// The real service
import javax.comm.SerialPort; //....and the rest of the java comm API
public class UsbService implements IUsbProviderService {
.
.
.
}
// The emulator
public class UsbServiceEmulator implements IUsbProviderService {
private Thread listenerThread;
private static final Long WAITTIMEMS = 10L;
private String usbData;
public UsbServiceEmulator(long maxWaitTime) throws InaccessibleDeviceException{
initialize();
boolean success = false;
long slept = 0;
while (!success && slept < maxWaitTime) {
Thread.sleep(WAITTIMEMS);
slept += WAITTIMEMS;
}
}
private void initialize() throws InaccessibleDeviceException{
listenerThread = new Thread();
listenerThread.start();
}
private class UsbRunner implements Runnable {
private String[] lines = {"Data line 1", "Data line 2", "Data line 3"};
public void run() {
int line = 0;
while(true) {
serialEvent(lines[line]);
if(line == 3) {
line = 0;
} else {
line++;
}
try {
Thread.sleep(200);
} catch (InterruptedException e) {
//handle the error
}
}
private void serialEvent(String line) {
if(/*you have detected you have enough data */) {
synchronized(this) {
usbData = parser.getUsbData();
}
}
}
}
Hope this helps!

Thanks to all the answers so far! Here's what I ended up doing as a result of recommendations from someone at work.
Downloaded the COM Port Data Emulator (CPDE) from AGG Software
Downloaded the Virtual Serial Port Driver (VSPD) from Eltima Software
(I just randomly picked a free data emulator and virtual serial port package. There are plenty of alternatives out there)
Using VSPD, created virtual serial ports 24 and 25 and connected them via a virtual null modem cable. This effectively creates a write port at 24 and a read port at 25.
Ran the CPDE, connected to 24 and started writing my test data.
Ran my test program, connected to 25 and was able to read the test data from it

There are plenty of relevant answers in this section. But as for me, I personally use Virtual Serial Port Driver, which works perfect for me. But I must admit that there are plenty alternatives when it comes to creating virtual ports: freevirtualserialports.com; comOcom to name a few. But I haven't got a chance to use them, so my recommendation for solving this problem is Virtual Serial Port Driver.

I recommend fabulatech's virtual modem.
Get it at http://www.virtual-modem.com
You might also want to get a COM port monitor for your tests - You can find it at
http://www.serial-port-monitor.com
Good luck with the boat! :)

I use com0com and it works great for what I need.

In addition all others, I would like to added this nice, free emulator https://sites.google.com/site/terminalbpp/ I do use. I do also use AGG Com port data emulator.