I have a simple script in my nodejs app which is managing file. When application is started it works indefinitely and on fixed intervals its saving current value (that is a number).
Lets say we have counter.dat file and its content is number 6570.
App is launched and its working, file is being updated properly for days.
In some occasions i have to restart the process and sometimes (rarely) i find NaN inside instead of proper number.
I made some tests and it seems that starting file and exiting it can indeed sometimes store NaN.
const init = async () => {
...
const readCounter = await files.getContent("counter.dat");
...
};
const saveCounter = (counter) => {
// this value (counter) was never found NaN, but sometimes file has NaN inside
let stream = fs.createWriteStream("counter.dat");
stream.once('open', () => {
stream.write(counter);
stream.end();
});
};
Can it be that exiting script (for example with CTRL + C in MAC terminal) can cause number to be saved as NaN and if so, what could be done to prevent it?
Yes, It's clear if you enter CTRL + c then your process will close.
You must keep your script alive even if you close the terminal.
There is a module called pm2, you can start your script by pm2.
Related
complete noob picking up NodeJS over the last few days here, and I've gotten myself in big trouble, it looks like. I've currently got a working Node JS+Express server instance, running on a Raspberry Pi, acting as a web interface for a local data acquisition script ("the DAQ"). When executed, the script writes out data to a local file on the Pi, in .csv format, writing out in real-time every second.
My Node app is a simple web interface to start (on-click) the data acquisition script, as well as to plot previously acquired data logs, and visualize the actively being collected data in real time. Plotting of old logs was simple, and I wrote a JS function (using Plotly + d3) to read a local csv file via AJAX call, and plot it - using this script as a starting point, but using the logs served by express rather than an external file.
When I went to translate this into a real-time plot, I started out using the setInterval() method to update the graph periodically, based on other examples. After dealing with a few unwanted recursion issues, and adjusting the interval to a more reasonable setting, I eliminated the memory/traffic issues which were crashing the browser after a minute or two, and things are mostly stable.
However, I need help with one thing primarily:
Improving the efficiency of my first attempt approach: This acquisition script absolutely needs to be written to file every second, but considering that a typical run might last 1-2 weeks, the file size being requested on every Interval loop will quickly start to balloon. I'm completely new to Node/Express, so I'm sure there's a much better way of doing the real-time rendering aspect of this - that's the real issue here. Any pointers of a better way to go about doing this would be massively helpful!
Right now, the killDAQ() call issued by the "Stop" button kills the underlying python process writing out the data to disk. Is there a way to hook into using that same button click to also terminate the setInterval() loop updating the graph? There's no need for it to be updated any longer after the data acquisition has been stopped so having the single click do double duty would be ideal. I think that setting up a listener or res/req approach would be an option, but pointers in the right direction would be massively helpful.
(Edit: I solved #2, using global window. variables. It's a hack, but it seems to work:
window.refreshIntervalId = setInterval(foo);
...
clearInterval(window.refreshIntervalId);
)
Thanks for much for the help!
MWE:
html (using Pug as a template engine):
doctype html
html
body.default
.container-fluid
.row
.col-md-5
.row.text-center
.col-md-6
button#start_button(type="button", onclick="makeCallToDAQ()") Start Acquisition
.col-md-6
button#stop_button(type="button", onclick="killDAQ()") Stop Acquisition
.col-md-7
#myDAQDiv(style='width: 980px; height: 500px;')
javascript (start/stop acquisition):
function makeCallToDAQ() {
fetch('/start_daq', {
// call to app to start the acquisition script
})
.then(console.log(dateTime))
.then(function(response) {
console.log(response)
setInterval(function(){ callPlotly(dateTime.concat('.csv')); }, 5000);
});
}
function killDAQ() {
fetch('/stop_daq')
// kills the process
.then(function(response) {
// Use the response sent here
alert('DAQ has stopped!')
})
}
javascript (call to Plotly for plotting):
function callPlotly(filename) {
var csv_filename = filename;
console.log(csv_filename)
function makeplot(csv_filename) {
// Read data via AJAX call and grab header names
var headerNames = [];
d3.csv(csv_filename, function(error, data) {
headerNames = d3.keys(data[0]);
processData(data, headerNames)
});
};
function processData(allRows, headerNames) {
// Plot data from relevant columns
var plotDiv = document.getElementById("plot");
var traces = [{
x: x,
y: y
}];
Plotly.newPlot('myDAQDiv', traces, plotting_options);
};
makeplot(filename);
}
node.js (the actual Node app):
// Start the DAQ
app.use(express.json());
var isDaqRunning = true;
var pythonPID = 0;
const { spawn } = require('child_process')
var process;
app.post('/start_daq', function(req, res) {
isDaqRunning = true;
// Call the python script here.
const process = spawn('python', ['../private/BIC_script.py', arg1, arg2])
pythonPID = process.pid;
process.stdout.on('data', (myData) => {
res.send("Done!")
})
process.stderr.on('data', (myErr) => {
// If anything gets written to stderr, it'll be in the myErr variable
})
res.status(200).send(); //.json(result);
})
// Stop the DAQ
app.get('/stop_daq', function(req, res) {
isDaqRunning = false;
process.on('close', (code, signal) => {
console.log(
`child process terminated due to receipt of signal ${signal}`);
});
// Send SIGTERM to process
process.kill('SIGTERM');
res.status(200).send();
})
I wrote a very simple typescript program, which does the following:
Transform users.csv into an array
For each element/user issue an API call to create that user on a 3rd party platform
Print any errors
The excel file has >160,000 rows and there is no way to create them all in one API call, so I wrote this program to run in the background of my computer for ~>20 hours.
The first time I ran this, the code stopped mid for loop without an exception or anything. So, I deleted the user rows from the csv file that were already uploaded and re-ran the code. Unfortunately, this kept happening.
Interestingly, the code has stopped at non-deterministic iterations, one time it was at i=812, another at i=27650, and so on.
This is the code:
const main = async () => {
const usersFile = await fsPromises.readFile("./users.csv", { encoding: "utf-8" });
const usersArr = makeArray(usersFile);
for (let i = 0; i < usersArr.length; i++) {
const [ userId, email ] = usersArr[i];
console.log(`uploading ${userId}. ${i}/${usersArr.length}`);
try {
await axios.post(/* create user */);
await sleep(150);
} catch (err) {
console.error(`Error uploading ${userId} -`, err.message);
}
}
};
main();
I should mention that exceptions are within the for-loop because many rows will fail to upload with a 400 error code. As such, I've preferred to have the code run non-stop and print any errors onto a file, so that I could later re-run it for the users that failed to upload. Otherwise I would have to check whether it halted because of an error every 10 minutes.
Why does this happen? and What can I do?
I run after compiling as: node build/index.js 2>>errors.txt
EDIT:
There is no code after main() and no code outside the try ... catch block within the loop. errors.txt only contains 400 errors. Even if it contained another run-time exception, it seems to me that this wouldn't/shouldn't halt execution, because it would execute catch and move on to the next iteration.
I think this may have been related to this post. The file I was reading was extremely large as noted, and it was saved into a runtime variable. Undeterministically, the OS could have decided that the memory demanded was too high. This is probably a situation to use a Readable Stream instead of a readFile.
I am preparing JavaScript code that shows a random number for user as follows: if the user spend more than two minutes to pass to the next web page or if the actual page has the GET parameter "&source", the random number is replaced by another one. otherwise, the same random number is displayed for all the web pages.
The problem is that the JavaScript code should be executed manually from browser console on each page load: I should prepare a code that can be integrated to any web page from console.
Is there any difference from the normal case (include script with<script></script>)
Thanks for posting! In future posts, please try to provide some code or an example of something you've tried previously.
Anyways, here is a brief example of a script that will check for an existing number, check to see if there is a &source parameter set, begin the timer if there isn't one, and generate a new number if the timer finishes or the parameter is set.
To save the information between pages, you should consider using window.localStorage. This will allow you to check for and save the number to be used on later loads.
Note that this snippet isn't going to work until you bring it into your own page. Also, as #Sorin-Vladu mentioned, you'll have to use a browser extension if you don't have access to modify the pages you're running the script on.
const timeout = 120000
// This can be replaced by your manual execution
window.onload = () => {
start()
}
function start() {
// Attempt to pull the code from storage
let code = localStorage.getItem('code')
console.log(code)
// Get the URL parameters
let urlParams = new URLSearchParams(window.location.search)
// Check to see if the source parameter exists
if (!urlParams.has('source')) {
// If not, begin the timer
setTimeout(() => {
setCode()
}, timeout)
} else {
setCode()
}
}
function setCode() {
const code = Math.floor(Math.random() * 1000000)
localStorage.setItem('code', code)
console.log(code)
}
I am trying to run a test where a file gets downloaded from our web application. The problem that I am running into however is that the file already exists and I have an if statement to handle it and delete it prior to downloading another one. The problem is though that it never goes into the if statement.
I know that my file path is correct. Is there something else I am doing wrong here?
const fs = require('fs')
fit('Download Visible Records', () => {
const filename = `C:\\Users\\me\\Downloads\\DataExport_2017-04-18-10-04am.csv`
if (fs.existsSync(filename)) {
console.log('Are we getting here??') // NEVER ACTUALLY GETS HERE EVEN THOUGH THE FILE DOES EXIST
// Make sure the browser doesn't have to rename the download
fs.unlink(filename)
console.log('how about here?')
}
claims.downloadVizRecords()
browser.driver.wait(() => {
expect(fs.existsSync(filename)).toBe(true)
}, 10000)
})
My code works fine:
if (fs.existsSync('D:/CI/script/result/Report.html')) {
fs.unlinkSync('D:/CI/script/result/Report.html');
}
I am really new to Selenium. I managed to open a website using the below nodejs code
var webdriver = require('selenium-webdriver');
var driver = new webdriver.Builder()
.forBrowser('chrome')
.build();
console.log(driver);
driver.get('https://web.whatsapp.com');
//perform all other operations here.
https://web.whatsapp.com is opened and I manually scan a QR code and log in. Now I have different javascript files to perform actions like delete, clear chat inside web.whatsapp.com etc...
Now If I get some error, I debug and when I run the script again using node test.js, it takes another 2 minutes to load page and do the steps I needed. I just wanted to reopen the already opened tab and continue my script instead new window opens.
Edit day 2 : Still searching for solution. I tried below code to save object and reuse it.. Is this the correct approach ? I get a JSON parse error though.
var o = new chrome.Options();
o.addArguments("user-data-dir=/Users/vishnu/Library/Application Support/Google/Chrome/Profile 2");
o.addArguments("disable-infobars");
o.addArguments("--no-first-run");
var driver = new webdriver.Builder().withCapabilities(webdriver.Capabilities.chrome()).setChromeOptions(o).build();
var savefile = fs.writeFile('data.json', JSON.stringify(util.inspect(driver)) , 'utf-8');
var parsedJSON = require('./data.json');
console.log(parsedJSON);
It took me some time and a couple of different approaches, but I managed to work up something I think solves your problem and allows to develop tests in a rather nice way.
Because it does not directly answer the question of how to re-use a browser session in Selenium (using their JavaScript API), I will first present my proposed solution and then briefly discuss the other approaches I tried. It may give someone else an idea and help them to solve this problem in a nicer/better way. Who knows. At least my attempts will be documented.
Proposed solution (tested and works)
Because I did not manage to actually reuse a browser session (see below), I figured I could try something else. The approach will be the following.
Idea
Have a main loop in one file (say init.js) and tests in a separate file (test.js).
The main loop opens a browser instance and keeps it open. It also exposes some sort of CLI that allows one to run tests (from test.js), inspect errors as they occur and to close the browser instance and stop the main loop.
The test in test.js exports a test function that is being executed by the main loop. It is passed a driver instance to work with. Any errors that occur here are being caught by the main loop.
Because the browser instance is opened only once, we have to do the manual process of authenticating with WhatsApp (scanning a QR code) only once. After that, running a test will reload web.whatsapp.com, but it will have remembered that we authenticated and thus immediately be able to run whatever tests we define in test.js.
In order to keep the main loop alive, it is vital that we catch each and every error that might occur in our tests. I unfortunately had to resort to uncaughtException for that.
Implementation
This is the implementation of the above idea I came up with. It is possible to make this much fancier if you would want to do so. I went for simplicity here (hope I managed).
init.js
This is the main loop from the above idea.
var webdriver = require('selenium-webdriver'),
by = webdriver.By,
until = webdriver.until,
driver = null,
prompt = '> ',
testPath = 'test.js',
lastError = null;
function initDriver() {
return new Promise((resolve, reject) => {
// already opened a browser? done
if (driver !== null) {
resolve();
return;
}
// open a new browser, let user scan QR code
driver = new webdriver.Builder().forBrowser('chrome').build();
driver.get('https://web.whatsapp.com');
process.stdout.write("Please scan the QR code within 30 seconds...\n");
driver.wait(until.elementLocated(by.className('chat')), 30000)
.then(() => resolve())
.catch((timeout) => {
process.stdout.write("\b\bTimed out waiting for code to" +
" be scanned.\n");
driver.quit();
reject();
});
});
}
function recordError(err) {
process.stderr.write(err.name + ': ' + err.message + "\n");
lastError = err;
// let user know that test failed
process.stdout.write("Test failed!\n");
// indicate we are ready to read the next command
process.stdout.write(prompt);
}
process.stdout.write(prompt);
process.stdin.setEncoding('utf8');
process.stdin.on('readable', () => {
var chunk = process.stdin.read();
if (chunk === null) {
// happens on initialization, ignore
return;
}
// do various different things for different commands
var line = chunk.trim(),
cmds = line.split(/\s+/);
switch (cmds[0]) {
case 'error':
// print last error, when applicable
if (lastError !== null) {
console.log(lastError);
}
// indicate we are ready to read the next command
process.stdout.write(prompt);
break;
case 'run':
// open a browser if we didn't yet, execute tests
initDriver().then(() => {
// carefully load test code, report SyntaxError when applicable
var file = (cmds.length === 1 ? testPath : cmds[1] + '.js');
try {
var test = require('./' + file);
} catch (err) {
recordError(err);
return;
} finally {
// force node to read the test code again when we
// require it in the future
delete require.cache[__dirname + '/' + file];
}
// carefully execute tests, report errors when applicable
test.execute(driver, by, until)
.then(() => {
// indicate we are ready to read the next command
process.stdout.write(prompt);
})
.catch(recordError);
}).catch(() => process.stdin.destroy());
break;
case 'quit':
// close browser if it was opened and stop this process
if (driver !== null) {
driver.quit();
}
process.stdin.destroy();
return;
}
});
// some errors somehow still escape all catches we have...
process.on('uncaughtException', recordError);
test.js
This is the test from the above idea. I wrote some things just to test the main loop and some WebDriver functionality. Pretty much anything is possible here. I have used promises to make test execution work nicely with the main loop.
var driver, by, until,
timeout = 5000;
function waitAndClickElement(selector, index = 0) {
driver.wait(until.elementLocated(by.css(selector)), timeout)
.then(() => {
driver.findElements(by.css(selector)).then((els) => {
var element = els[index];
driver.wait(until.elementIsVisible(element), timeout);
element.click();
});
});
}
exports.execute = function(d, b, u) {
// make globally accessible for ease of use
driver = d;
by = b;
until = u;
// actual test as a promise
return new Promise((resolve, reject) => {
// open site
driver.get('https://web.whatsapp.com');
// make sure it loads fine
driver.wait(until.elementLocated(by.className('chat')), timeout);
driver.wait(until.elementIsVisible(
driver.findElement(by.className('chat'))), timeout);
// open menu
waitAndClickElement('.icon.icon-menu');
// click profile link
waitAndClickElement('.menu-shortcut', 1);
// give profile time to animate
// this prevents an error from occurring when we try to click the close
// button while it is still being animated (workaround/hack!)
driver.sleep(500);
// close profile
waitAndClickElement('.btn-close-drawer');
driver.sleep(500); // same for hiding profile
// click some chat
waitAndClickElement('.chat', 3);
// let main script know we are done successfully
// we do so after all other webdriver promise have resolved by creating
// another webdriver promise and hooking into its resolve
driver.wait(until.elementLocated(by.className('chat')), timeout)
.then(() => resolve());
});
};
Example output
Here is some example output. The first invocation of run test will open up an instance of Chrome. Other invocations will use that same instance. When an error occurs, it can be inspected as shown. Executing quit will close the browser instance and quit the main loop.
$ node init.js
> run test
> run test
WebDriverError: unknown error: Element <div class="chat">...</div> is not clickable at point (163, 432). Other element would receive the click: <div dir="auto" contenteditable="false" class="input input-text">...</div>
(Session info: chrome=57.0.2987.133)
(Driver info: chromedriver=2.29.461571 (8a88bbe0775e2a23afda0ceaf2ef7ee74e822cc5),platform=Linux 4.9.0-2-amd64 x86_64)
Test failed!
> error
<prints complete stacktrace>
> run test
> quit
You can run tests in other files by simply calling them. Say you have a file test-foo.js, then execute run test-foo in the above prompt to run it. All tests will share the same Chrome instance.
Failed attempt #1: saving and restoring storage
When inspecting the page using my development tools, I noticed that it appears to use the localStorage. It is possible to export this as JSON and write it to a file. On a next invocation, this file can be read, parsed and written to the new browser instance storage before reloading the page.
Unfortunately, WhatsApp still required me to scan the QR code. I have tried to figure out what I missed (cookies, sessionStorage, ...), but did not manage. It is possible that WhatsApp registers the browser as being disconnected after some time has passed. Or that it uses other browser properties (session ID?) to recognize the browser. This is pure speculating from my side though.
Failed attempt #2: switching session/window
Every browser instance started via WebDriver has a session ID. This ID can be retrieved, so I figured it may be possible to start a session and then connect to it from the test cases, which would then be run from a separate file (you can see this is the predecessor of the final solution). Unfortunately, I have not been able to figure out a way to set the session ID. This may actually be a security concern, I am not sure. People more expert in the usage of WebDriver might be able to clarify here.
I did find out that it is possible to retrieve a list of window handles and switch between them. Unfortunately, windows are only shared within a single session and not across sessions.