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How check my device is connected (IOTCore - GCP) [duplicate]

Does anybody know of an easy way to trigger an event when a device on Google Core IoT goes offline? Before I switched to Google's IoT implementation, this was very easily handled by triggering an event when MQTT disconnects, but it seems Google has no easy way of doing this.
Does anybody know if there is something planned for this?
Who's back do I need to scratch to get them to see that something like this is a basic requirement for IoT device management!
Other platforms like AWS and Microsoft already have this implemented (or some way to handle it easily):
https://docs.aws.amazon.com/iot/latest/developerguide/life-cycle-events.html
Device connectivity(online/offline)status with the Auzure iot hub
I wish I had known this before writing all my code and implementing my setup using Google's IoT platform, I guess that's my fault for assuming something so simple and that should be standard for IoT devices would be available.
How are you going to compete with other IoT providers if you can't even provide basic offline/online events?!
My reply in this SO question shows how I had to write 100+ lines of code just to create a firebase function to check if a device is online (but that still doesn't handle offline events, and is just a hack for something that should be native to ANY IoT service provider!):
https://stackoverflow.com/a/54609628/378506
I'm hoping someone else has figured out a way to do this, as i've spent numerous days searching SO, Google, Google Core IoT Documentation, and still have not found anything.
Even if MQTT Last Will was supported we could make that work, but even that IS NOT SUPPORTED by Google (https://cloud.google.com/iot/docs/requirements) ... come on guys!

Your cloud project does have access to the individual MQTT connect/disconnect events, but currently they only show up in the Stackdriver logs. Within the cloud console, you can create an exporter that will publish these events to a Pub/Sub topic:
Visit the Stackdriver Logs in the
Cloud Console.
Enter the following advanced filter:
resource.type="cloudiot_device"
jsonPayload.eventType="DISCONNECT" OR "CONNECT"
Click CREATE EXPORT
Enter a value for Sink Name
Select Cloud Pub/Sub for Sink Service
Create a new Cloud Pub/Sub topic as the Sink Destination
The exporter publishes the full LogEntry, which you can then consume from a cloud function subscribed to the same Pub/Sub topic:
export const checkDeviceOnline = functions.pubsub.topic('online-state').onPublish(async (message) => {
const logEntry = JSON.parse(Buffer.from(message.data, 'base64').toString());
const deviceId = logEntry.labels.device_id;
let online;
switch (logEntry.jsonPayload.eventType) {
case 'CONNECT':
online = true;
break;
case 'DISCONNECT':
online = false;
break;
default:
throw new Error('Invalid message type');
}
// ...write updated state to Firebase...
});
Note that in cases of connectivity loss, the time lag between the device being unreachable and an actual DISCONNECT event could be as long the MQTT keep-alive interval. If you need an immediate check on whether a device is reachable, you can send a command to that device.

The best solution i think is that
We need 3 things
cloud sheduler ,
and 2 cloud functions
The first function will be the #devunwired answer but instant of
// ...write updated state to Firebase... schedule a second function to trigger in 2-3 min (let device to recconect)
the seccond function will send a command to device
if the device resposne to command
if stored status is connected dont do nothing
else if the stored status is disconnected then update the status to connected and do what ever you want maybe email
else
if stored status is disconnected dont do nothing
if stored status is connected change the status alert by email or something

Java usb4java reading from usb device on windows 10 platform

I am trying to read a message from RFID reader connected via USB to windows 10pro machine with usb4java library.
I have managed to claim the interface, opened pipe and registered listener for the data, however the listener is never triggered. The reader acts as keyboard and whatever it reads ends up in active application, such as IDE i have open, instead of in listener.
UsbInterface usbInterface = activeInteface(device);
// there is only one endpoint in the list
UsbEndpoint endpoint = (UsbEndpoint)usbInterface.getUsbEndpoints().get(0);
UsbPipe pipe = endpoint.getUsbPipe();
try {
usbInterface.claim();
// true
System.out.println("claimed usb interface: " + usbInterface.isClaimed());
pipe.open();
// true
System.out.println("pipe open: " + pipe.isOpen());
pipe.addUsbPipeListener(new MessageListener());
// true
System.out.println("pipe active: " + pipe.isActive());
// keep main thread alive, async call should be done from another thread i guess
Thread.sleep(15000);
}
catch (Exception any) {System.out.println(any);}
}
And the listener:
private static class MessageListener implements UsbPipeListener {
#Override
public void errorEventOccurred(UsbPipeErrorEvent event) {
System.out.println(event.toString() + " , " +event.getUsbException());
}
#Override
public void dataEventOccurred(UsbPipeDataEvent event) {
// this code block never triggers
System.out.println("listener ...);
int actualLength = event.getActualLength();
System.out.println("length: " + actualLength);
byte[] data = event.getData();
System.out.println("data length " + data.length);
}
}
i have also tried synchronous read instead of asynchronous in the block above, like this:
byte[] buffer = new data[8];
// this fails on its own, don't even need to read something with RFID reader
int received = pipe.syncSubmit(buffer);
fails with:
USB error1: Transfer error on interrupt endpoint: Input/Output error
There is some windows specific property that library supports: org.usb4java.javax.useUSBDK = true
but this fails when i try to set it with an exception.
I have 0 experience with USB devices so not sure how to proceed from here. Is there something wrong with the code, do i need USBDK or device does not support libUSB driver ? Sadly this is not my device and i don't have access to documentation of the device so cannot be sure if it is device driver issue.

I know that this is 2 years old, but i've had similar issue and this was one of the first questions that i ran into looking for solution, which took me hours.
So, basically, windows doesn't let to read/write keyboard devices directly, to do so, you have to override it's driver (That's why you're getting Input/Output error, and it's written in the hid4java's FAQ).
First way to override device driver is described in libusb wiki.
As far as i know you would have to install a new driver every time you connect the device to a new USB port, which is why i recommend you to read further.
Second way is what you've already mentioned, which is using UsbDk (Usb Drivers Development Kit for Windows). It makes the device accessible for you by detaching the kernel driver and reattaching it back after you're done playing with it.
In order to use it, you need to do two things:
Set the org.usb4java.javax.useUSBDK = true in you javax.usb.properties file as stated in the manual (this can also be done manually in low-level usb4java, see OPTION_USE_USBDK and setOption(Context, int)).
Download and install UsbDk on your system (simplest way is to download x64 or x86 version msi installer which has GUI and is fully automated), which is sadly not in the manual (maybe it's obvious for some people, but took me amount of time that i am not proud of to realize).
Im guessing that the lack of second step is why OP has been getting an exception.
Hope that this will help someone, knowing all this two days ago would save me a lot of headache.

RFID readers operate in keyboard emulation mode by default.
You can normally get a tool from the manufacturer's website to configure the RFID reader.
This will allow you to change the reader to HID mode.
This should resolve your issues.
Sorry for the late response but I hope it helps others.

How to receive data from a python ZeroMQ PUB server on a Java SUB client (ZMQ)

I'm working with Pupil Labs, a huge open source for eye/pupil tracking. The entire code is written in Python. The so-called Pupil Remote is based on ZeroMQ.
If I start running the Filter Messages everything is fine. For my purposes I need to "translate" Filter Messages into Java because I created an Android app, which should call a client, which has the purpose to serve as the python client.
Here's what I've done so far:
import android.annotation.SuppressLint;
import org.zeromq.ZMQ;
import java.nio.charset.Charset;
import static java.lang.Thread.sleep;
public class ZeroMQClient {
#SuppressLint("NewApi")
public static void requestGazeData() {
ZMQ.Context context = ZMQ.context(1);
ZMQ.Socket subscriber = context.socket(ZMQ.SUB);
System.out.println("Connecting to server...");
subscriber.connect("tcp://xxx.x.x.x:50020");
System.out.println("Connected");
String gaze = "gaze";
subscriber.subscribe(gaze.getBytes(Charset.forName("UTF-8")));
while (true) {
String msg = subscriber.recvStr();
System.out.println(msg);
subscriber.close();
context.term();
}
}
}
Now as you can expect, why I'm asking you, nothing happens, I don't receive any data from the Pupil Labs server. I oriented myself on this post, but unfortunately, it didn't work out for me. Also the IP-Address and port are the same as on the server. It works neither locally nor remotely.
Happy about any answer, since I stuck at this.

Due to the correct establishment in terms of my implementation the actual issue was the firewall, which just blocked the connection. By posting my solution I'm hopefully able to help future visitors of this question.

The final solution, after having debugged the root-cause issue is below
Happy about having answer, you have to set a subscription Policy:
ZeroMQ expects each SUB-side to first explicitly say, what this SUB-side wants to receive from PUB ( Yes, what it to subscribes to ).
Like your mailbox will never get newspapers in, without first subscribing to any. :o)
So setup an empty string "" in the subscriber and you are done:
// String filterPermitANY = ""; // WAS AN EXAMPLE TO TEST
// subscriber.subscribe( filterPermitANY.getBytes() );// IF PUB.send()-s ANY
String gaze = "gaze"; // WAS ON TOPIC
subscriber.subscribe( gaze.getBytes() ); //
Voilá.
Having zero-warranty what python version is running on the opposite side, tweaking may take place for string-representation matching...
( Also recommended to setup LINGER to 1, that prevents from hanging terminations
and preferably it is the best time to turn the process
into using a non-blocking .poll() + .recv( ..., ZMQ_DONTWAIT ) in a soft-realtime maintained event-loop )
[ 1 ] We have got confirmed the Android/ZeroMQ side is working fine
if the PUB-side was mocked by a plain python-PUB infinite-sender and the Android-SUB was subscribed to String filterPermitANY ="";
This makes the above claim "It's an issue from the android side" actually void if not misleading.
[ 2 ] Next comes the question why it still does not work?
And the answer is: because the above designed code does not follow the published principles, how to connect and use the Pupil Labs API.
A careful reader will notice that the Pupil Labs API is not connected by the SUB-side ( be it an Android or python or whatever else implementation of such a peer ) on a port :50020, but on another port, which is first asked about via another dialogue, held over an REQ/REP-formal communication archetype ( lines 13/14/15+19 ).
Epilogue
Knocking on a wrong door will never make the intended interview happen.
One first has to ask onto which door to knock next, so as to get the Pupil Labs API into the game.

ELM327 returns `?` when trying to use it with ODB Java API

I'm trying to use ODB Java API (this library) to get the data from ELM327 via Bluetooth from my car, but in returns ? on every request, and library raises MisunderstoodException
Here is my code:
socket = device.createInsecureRfcommSocketToServiceRecord(uuid);
socket.connect();
final CustomRPMCommand engineRpmCommand = new CustomRPMCommand();
final SpeedObdCommand speedObdCommand = new SpeedObdCommand();
while (!Thread.currentThread().isInterrupted()) {
engineRpmCommand.run(socket.getInputStream(), socket.getOutputStream());
speedObdCommand.run(socket.getInputStream(), socket.getOutputStream());
runOnUiThread(new Runnable() {
#Override
public void run() {
speedometerGauge.setSpeed(engineRpmCommand.getRPM(), true);
rpmGauge.setSpeed(speedObdCommand.getMetricSpeed(), true);
}
});
}
What's wrong?

I also used the same library for the first steps into trying out OBD, so I can say at least at the time I used it, it worked fine.
From my experience however, getting ? back can sometimes happen with cheap Bluetooth devices (maybe even with expensive ones? never had one). I guess this happens, if some bits are lost during the transmission, because then command will be misunderstood.
What I did to circumvent this problem is setting up a process where I sent all AT commands up to 10 times until I get the desired response of OK (except for ATZ, which will respond with ELM327). As for value requests like RPM etc. I usually just throw away the erroneous values.
That's the short answer, but since such problems with the devices can annoy a lot, I will guide you into debugging the whole process...
Setting up a terminal on windows
First of all to test the functionality of the ELM device, you can send commands to the serial interface directly. On windows, this is possible using for example TeraTerm and then setting up new Bluetooth connection on your windows as a COM device (search for Bluetooth in start -> search box and then choose Change Bluetooth settings or similar). From there, go to COM connections and then add a new one Outgoing for the Bluetooth OBDII device. Wait a bit for windows to calculate the new COM port number, you will need it.
If you cannot find OBDII in the dropdown box, you have to bond your PC with your Bluetooth device first. This can be done via devices and printers, there you should see the OBDII device, so you only have to connect it (PIN usually is 1234).
If you're on Linux, it might be somewhat easier, but I haven't done it :)
Sending some commands via terminal
Once you have your Bluetooth connection and TeraTerm installed, you can start TeraTerm and connect to the adapter. Choose Serial and then the port you just set up. Ensure, that no other device is connected to the OBD adapter (also not your phone). Only one device can be connected at a time.
If connection was successful, you should be able to type letters. Usually, in default settings you should be able to see the letters you type (Echo mode on), but since this is not certain, just type ATZ and hit <Enter>. The ELM should respond with "ELM327" in the same line now (which for me usually results in odd display if echo mode was on, but you should get any response).
From terminal I usually send these commands in order:
ATZ
E1
L1
010c
This will trigger:
Reset of the OBD device
Make sure that echo is on, so I see what I am typing
Make sure Line feed is on, so we get responses in the next line
Request RPM from the vehicle
Between each command I'll check what is the reply of the device. For all AT commands (1., 2. and 3.) it must be OK. If I get back ?, which can happen, I will repeat the command another time. You will see that in such a case the device indeed did not follow the instructions, e.g. did not set line feed on if it was off. So we really have to send it again.
In programming mode on the other hand, we will set e0 and l0 (echo mode off and line feed off), because we do not want to get sent back what we already sent out.

SDP message construction?

I was wondering can anyone point me to a good tutorial on how to construct a SDP message.
I have read the basics and can construct and understand the parameters but I just can't seem to get it to work.
I either get a not acceptable here reply or no reply at all, this is after I get 100 Trying and 180 ringing back.
So my SIP works but it doesn't like the SDP Data.
Its currently constructed like this:
String sdpData = "v=0\r\n"
+ "o=- 019078020 0"
+ " IN IP4 sip.ciceronetworks.com\r\n" + "s=MySession\r\n"
+ "c=IN IP4 sip.ciceronetworks.com\r\n"
+ "t=0 0\r\n" + "m=audio 6002 RTP/AVP 0\r\n"
+ "a=sendrecv\r\n" + "a=rtpmap:0 PCMU/8000\r\n" + "a=ptime:20\r\n"+ "a=fmtp:97 mode=20\r\n";
byte[] contents = sdpData.getBytes();
request.setContent(contents, contentTypeHeader);
And while like that I get 100 trying then 180 ringing but when I accept the call on the other end I get nothing back at all, it seems to just crash, I also get "Audio device Error" on the pc client that I try ringing.
Anyone any ideas?

The issue could be really simple: you seem to forgot the newline after "a=sendrecv". :-)
Anyway, here's an advice:
For testing purposes you are probably better off using a tool rather than jumping right in and writing parts of the protocol. You can use sipp for this purpose, it makes a great tool for testing SIP networks. Other than that you could of course just sniff the network traffic between two working SIP devices and see how it differs from your traffic.
EDIT:
I missed this one before:
You should omit a=fmtp:97 mode=20, as the session description is invalid this way: You may only use the format parameter attribute for codecs that are mentioned in the media line. Codecs are identified via the payload type number (0=PCMU, 8=PCMA, 18=G723, ...). Some codecs don't have officially assigned numbers, for these the dynamic range 96-127 should be used: user agents are free to assign a number in this range via an rtpmap attribute. So, unless you specify which codec you mean by 97, there is no way for the other user agent to know which codec the format parameters should be applied to.

Paprika is right: the a=fmtp:97 mode=20 is simply wrong (and looks like it's part of an iLBC codec offer). You didn't offer codec 97, you offered codec 0 (PCMU).
Note that the a=fmtp:97 shouldn't hurt you, it's just spurious.
The most likely problem is that you are not sip.ciceronetworks.com - i.e. your c= line (and m= line) said "send my media to port 6002 at sip.ciceronetworks.com". I suspect your PC's IP address is not the same as sip.ciceronetworks.com, and/or there's a firewall/NAT between you and the other end.
It probably isn't your problem, but the o= line is wrong per the spec
From RFC 4566:
o=<username> <sess-id> <sess-version> <nettype> <addrtype> <unicast-address>
Getting VoIP to work is not as simple as the RFCs or cookbook explanations would imply....

I found a good article which deals with SDP (Session Description Protocol). It is also in relationship with an SDK which is called Ozeki VoIP SIP SDK. If you combine these things you will be able to create a softphone for instance.
There is also a brief overall about SDP.
Working with SDP in VoIP SIP calls is an interesting topic for those who wish to develop their own softphone or webphone application or what you desire.
SDP describes multimedia communication session for the purposes of session announcement, session invitation, and parameter negotiation.
The usage of an SDK can take a lot of burden from one's shoulder bucasue flexibility and high compatibility is assured.
For more information regarding SDP in connection with an SDK to build own applications you can have a look at the mentioned article if you Google for: "Working with SDP in VoIP SIP calls"