I am trying to use zbarcam to monitor the usb cam and shoot back the QR Codes it sees.
I am new to both Zbarcam and Nodejs, but have done a fair amount of research and cannot see what is wrong. I am running this on Ubuntu 12.04 LTS and it works fine from the command line, but when run in a child process in Node it returns nothing.
if I run the following on the command line it works great, sees the QR Codes and shoots back the code:
zbarcam /dev/video0 --prescale=1280x720 -q --raw --nodisplay
but when I run it in a small nodejs script it just hangs, I can see the cam enable, but the response does not route back.
var exec = require('child_process').exec,child;
child = exec('zbarcam /dev/video0 --prescale=640x480 -q --raw --nodisplay', function (error, stdout, stderr) {
if (error) {
console.log(error.stack);
console.log('Error code: '+error.code);
console.log('Signal received: '+error.signal);
}
console.log('Child Process STDOUT: '+stdout);
console.log('Child Process STDERR: '+stderr);
});
child.on('exit', function (code) {
console.log('Child process exited with exit code '+code);
});
I suspect it's the way I start it in Node and how node tracks the stdout.
Thanks to all in advance.
you can use the zbar npm, here's my fork on github https://github.com/flatr0ze/node-zbar with updated readme file
run npm install zbar and follow the readme, it should work fine
here's an Npm-less example: https://github.com/cloudpower/qr2wifi/blob/f28f3bf7062b58c8adca2751faaf4e070fa124b4/index.js
good luck!
Related
I've been browsing around but to no success. I've found some npm packages like nodemon and forever but documentation doesn't explain how to call a restart inside the script properly.
I've found this code snippet on another question but I'm not using Express or other frameworks since the script is using a pulling service not a response one.
This is code I've made so far using internal Node.js dependencies but no luck.
'use strict'
process.on('uncaughtException', (error) => {
console.error('Global uncaughtException error caught')
console.error(error.message)
console.log('Killing server with restart...')
process.exit(0)
})
process.on('exit', () => {
console.log('on exit detected')
const exec = require('child_process').exec
var command = 'node app.js'
exec(command, (error, stdout, stderr) => {
console.log(`error: ${error.message}`)
console.log(`stdout: ${stdout}`)
console.log(`stderr: ${stderr}`)
})
})
setTimeout(() => {
errorTriggerTimeBomb() // Dummy error for testing triggering uncaughtException
}, 3000)
Just to note I'm running the server on Termux, a Linux terminal app for android. I know it's better to run from desktop but I'm always at a WiFi or mobile data area and that I don't like leaving my PC on overnight.
A typical restart using something like nodemon or forever would be triggered by calling process.exit() in your script.
This would exit the current script and then the monitoring agent would see that it exited and would restart it for you. It's the same principal as if it crashed on its own, but if you're trying to orchestrate it shutting down, you just exit the process and then the monitoring agent will restart it.
I have a home automation server that is being monitored using forever. If it crashes forever will automatically restart it. I also have it set so that at 4am every morning, it will call process.exit() and then forever will automatically restart it. I do this to prevent any memory leak accumulation over a long period of time and 30 seconds of down time in the middle of the night for my application is no big deal.
I'm using mocha with Nodejs to test my restApi.
When I run mocha, I tell my test to create a child_process and run the API so I can make requests to it.
The problem is whenever the test exits (finishing or crashing), it seems that the API keeps running on background. I've seen some answers here that instructs to manually kill the child process whenever the main process exits. So I did it like this:
export function startProcess(done) {
const child = spawn('babel-node', ["app.js"]);
child.stdout.on("data", function(data) {
data = data.toString();
// console.log(data.toString());
if(data.indexOf("Server online") > -1) done();
});
child.stderr.on('data', function(err) {
console.log("ERROR: ", err.toString());
});
child.on('exit', function(code) {
console.log("PROPERLY EXITING");
console.log("Child process exited with code", code);
});
process.on('exit', function(code) {
console.log("Killing child process");
child.kill();
console.log("Main process exited with code", code);
});
}
When the main process exits it does log "Killing child process", meaning that child.kill() was indeed called. But if I try to run my test again, when the spawn command gets called, the API throws an error
Error: listen EADDRINUSE :::3300
, meaning that the API is still running and that port address is taken.
So I have to run sudo pkill node to really kill all node process and then npm test works again.
Am I missing something? Is this really the way to achieve what I'm expecting?
I thought about using child_process.exec to run sudo pkill node on my process.on('exit') listener, but that doesnt seem like a smart thing to do.
This is happening both in Mac and Ubuntu.
Any suggestions?
Thanks
"exit" is an event that gets triggered when node finishes it's event loop internally, it's not triggered when you terminate the process externally.
What you're looking for is executing something on a SIGINT.
Have a look at http://nodejs.org/api/process.html#process_signal_events
This may sound rather crazy,
but I cannot find a solution to automate taking screenshots on a cordova application.
I know I can take and save a screenshot of the emulator using
adb shell /system/bin/screencap -p /sdcard/screenshot.png
adb pull /sdcard/screenshot.png screenshot.png
in the terminal, my crazy question is.
Can I trigger these commands from a nodeJS automation script? or is this too far fetched and a terrible idea?
Simplest way to execute terminal commands from node.js would be to use child_process.exec
const exec = require('child_process').exec;
exec('adb shell /system/bin/screencap -p /sdcard/screenshot.png', (error, stdout, stderr) => {
if (error) {
console.error(`exec error: ${error}`);
return;
}
console.log(`stdout: ${stdout}`);
console.log(`stderr: ${stderr}`);
});
The built-in child_process module in node.js provides many functions such child_process.spawn, child_process.exec, child_process.execFile which can be used to execute terminal commands or other script files (.sh, .bat).
I am using node.js/express.js on windows and I have a command I execute when a user takes a image and uploads up from there phone. Once it is uploaded I run myApp.exe to perform some openCV image processing and I output the updated images to a output directory that is a argument in the command below.
I am able to kick this off from my webapp using child_process.exec, but the performance is 60x slower if I run it at command line by itself. To increase the performance I was hoping to use Spawn, but I don't know if this is an accurate assumption, please let me know if it is not.
var exec = require('child_process').exec;
var child = exec('C:\\opt\\package_v030_package\\myApp.exe
--user="C:\\opt\\package_v030_package\\Phone\\'+file.filename+'"
--mv="C:\\opt\\package_v030_package\\mv\\'+req.body.detectionString+'.bmp"
--outPath="C:\\opt\\package_v030_package\\output"
--outputScaled
--outputScaledOverlaid');
child.stdout.on('data', function(data) {
console.log('stdout: ' + data);
});
child.stderr.on('data', function(data) {
console.log('stdout: ' + data);
});
child.on('close', function(code) {
console.log('closing code: ' + code);
//res.json("success")
});
I have tried to kick it off using spawn, but it fails to execute with the following: "error child process exited with code 4294967295". The code is below:
var spawn = require('child_process').spawn;
var cmd = spawn('cmd', ['/s',
'/c',
'C:\\opt\\package_v030_package\\myApp.exe',
'--user="C:\\opt\\package_v030_package\\Phone\\'+file.filename+'"',
'--mv="C:\\opt\\package_v030_package\\mv\\'+req.body.detectionString+'.bmp"',
'--outPath="C:\\opt\\package_v030_package\\output"',
'--outputScaled',
'--outputScaledOverlaid'
]);
cmd.stdout.on('data', (data) => {
console.log(`stdout: ${data}`);
});
cmd.stderr.on('data', (data) => {
console.log(`stderr: ${data}`);
});
cmd.on('close', (code) => {
console.log(`child process exited with code ${code}`);
});
It seems I am able to execute just myApp.exe from spawn because when I add any of my arguments it fails. Even when I hard code the variables that I inject. Is there an issue with my arguments or am I spawning myApp.exe incorrectly?
Update 1
I placed the command in a .bat and was able to execute it from node.js using spawn. It does not increase performance which leads me to believe that the decrease in performance is a limitation of node.js on the windows platform.
In addition, I performed a few tests using postman to see if I could optimize the call without anything else happening, but I did not succeed. I will leave this question open in the event this changes and node.js is able to better handle performance of a CPU intensive child process.
Update 2 & Answer
I was able to fix this by placing the command that we run at the command line into a java class taking in the detectionString as a parameter. Then from node I use spawn to kick off the .jar file. This caused the speed to increase significantly and run as if I was running it myself at command line.
I was able to fix this by placing the command that we run at the command line into a java class taking in the detectionString as a parameter. Then from node I use spawn to kick off the .jar file. This caused the speed to increase significantly and run as if I was running it myself at command line.
Here is a short overview to help you experts understand the situation I am in - sorry that its too verbose, but it might help resolving this issue:
So I have a Linux machine, and it runs Apache properly.
Under '/var/www/html', I put my project files which are HTML (index.html) , and a javaScript file with utility functions.
httpd runs and everyone can view the content when 'http:///index.html' from their PC's.
I want to run a bash script from my Linux machine by letting the users provide the parameters from the front end user interface.
Reading how to do that, I saw tons of examples of how node.js can do that, so I downloaded Node.JS to my Linux machine, and it can be run from:
"
~/Desktop/node-v4.2.1-linux-x64/bin/node --version
v4.2.1
~/Desktop/node-v4.2.1-linux-x64/bin/npm --version
2.14.7
"
So it seems like its properly installed...
Note: I did not put anything in my Linux path after extracting the node.js tar.gz file.
Now, from my Linux machine, under '/var/www/html' , I have an HTML file, and I created an 'onclick' event to invoke a javascript function, in which I wrote a call to run this bash script which is located in my Linux machine under "/" - here it is:
function start_run(pTopoFile, pEmailAddress) {
var childProcess = require('child_process');
var run_command;
run_command = childProcess.exec('/run.sh ' + pTopoFile + ' ' + pEmailAddress, function (error, stdout, stderr) {
if (error) {
console.log(error.stack);
console.log('Error code: '+error.code);
console.log('Signal received: '+error.signal);
}
console.log('Child Process STDOUT: '+stdout);
console.log('Child Process STDERR: '+stderr);
});
ls.on('exit', function (code) {
console.log('Child process exited with exit code '+code);
});
}
When I run the above I get this error:
"ReferenceError: require is not defined"
Which means that even though Node.js was installed properly (as I showed you above), I cannot access its methods from /var/www/html on my Linux machine ...
Can anyone let me know how to link between the great features that node.js has to my scripts?
I hope that I was clear enough with the info I provided...
Thanks,
Tom