Node.js update client-accessible JSON file - javascript

A beginner's question as I am new to web programming. I am using the MEAN stack and writing a JSON file within the server in order to make some weather information available to any connected clients.
I am updating the JSON file every hour using the node-schedule library. Will the constant updating of the file from the server cause any concurrency issues if the clients happen to be attempting to access the file's data at the same time?
Code snippet below:
server.js
function updateWeatherFile() {
var weather = require('weather-js');
var w = "";
weather.find({search: weatherSearch, degreeType: 'C'}, function(err, result) {
if(err)
console.log(err);
w = JSON.stringify(result, null, 2);
fs.writeFile('public/weather.json', w, function(err) {
if(err) {
console.log(err);
}
});
});
}
if(scheduleWeather) {
var schedule = require('node-schedule');
var sequence = '1 * * * *'; // cron string to specify first minute of every hour
var j = schedule.scheduleJob(sequence, function(){
updateWeatherFile();
console.log('weather is updated to public/weather.json at ' + new Date());
});
}
else {
updateWeatherFile();
}
client_sample.js
// get the current weather from the server
$http.get('weather.json').then(function(response) {
console.log(response['data'][0]['current']);
vm.weather = response['data'][0]["current"].skytext;
vm.temperature = response['data'][0]["current"].temperature;
});

NodeJs is single threaded environment.
However To read and write files Node starts external processes and eventually the file can be accessed to read and write simultaneously. In this case the concurrency is not handled by Node, but by the Operational System.
If you think this concurrency may harm you program, consider using a lock file as commented and explained here.

Related

Request Size is too large

I have written the Stored procedure for bulkInsert where I am handling the SP's timeout as well. Still I am getting "Request size is too large" exception while executing the SP. Giving below the SP. Please help me, where I am wrong. I have taken all the code from pluralsight only. and handling in the same way like they have.
function spBulkInsert(docs){
if (!docs) {
throw new Error('Documents array is null or not defined!');
}
var context = getContext();
var collection = context.getCollection();
var response = context.getResponse();
var docCount = docs.length;
if (docCount == 0) {
response.setBody(0);
return;
}
var count = 0;
createDoc(docs[0]);
function createDoc(doc) {
var isAccepted = collection.createDoucument(collection.getSelfLink(), doc, docCreated);
if (!isAccepted) {
response.setBody(count);
}
}
function docCreated(err, doc) {
if (err) throw err;
count++;
if (count == docCount) response.setBody(count);
else createDoc(docs[count]);
}
};
Code for handling above SP:
var totalInsertedCount=0;
while (totalInsertedCount < data.Count)
{
var insertedCount = await client.ExecuteStoredProcedureAsync<int>(
UriFactory.CreateStoredProcedureUri("TestDoc", "coll", "spBulkInsert"),
new RequestOptions { PartitionKey = new PartitionKey("partitionKey") }, data);
totalInsertedCount += insertedCount;
Console.WriteLine("Inserted {0} documents ({1} total, {2} remaining)", insertedCount, totalInsertedCount, data.Count - totalInsertedCount);
data= data.GetRange(insertedCount, data.Count - insertedCount);
}
Just as summary,The document size in the request exceeded the allowable document size for a request. The max allowable document size is 2MB. which mentioned here .
Stored Procedure Bulk importing data is a process of executing Stored Procedure, just only one HTTP request, and the size of the requested documents per HTTP request is limited by Cosmos DB below 2MB.
Suggestions:
1.You can split your document data and import them in batches.
2.You can try to simplify your document data, such as removing unnecessary ' ' and '\n' etc.
Regardless of where the write occurs (SP or API or in the portal) there's always 2MB limitation for the document size in Cosmos DB. The documents must be split/disembedded/chained/linked/etc on the client side before submitting to Cosmos DB.

Update HTML object with node.js and javascript

I'm new to nodejs and jquery, and I'm trying to update one single html object using a script.
I am using a Raspberry pi 2 and a ultrasonic sensor, to measure distance. I want to measure continuous, and update the html document at the same time with the real time values.
When I try to run my code it behaves like a server and not a client. Everything that i console.log() prints in the cmd and not in the browesers' console. When I run my code now i do it with "sudo node surveyor.js", but nothing happens in the html-document. I have linked it properly to the script. I have also tried document.getElementsByTagName("h6").innerHTML = distance.toFixed(2), but the error is "document is not defiend".
Is there any easy way to fix this?
My code this far is:
var statistics = require('math-statistics');
var usonic = require('r-pi-usonic');
var fs = require("fs");
var path = require("path");
var jsdom = require("jsdom");
var htmlSource = fs.readFileSync("../index.html", "utf8");
var init = function(config) {
usonic.init(function (error) {
if (error) {
console.log('error');
} else {
var sensor = usonic.createSensor(config.echoPin, config.triggerPin, config.timeout);
//console.log(config);
var distances;
(function measure() {
if (!distances || distances.length === config.rate) {
if (distances) {
print(distances);
}
distances = [];
}
setTimeout(function() {
distances.push(sensor());
measure();
}, config.delay);
}());
}
});
};
var print = function(distances) {
var distance = statistics.median(distances);
process.stdout.clearLine();
process.stdout.cursorTo(0);
if (distance < 0) {
process.stdout.write('Error: Measurement timeout.\n');
} else {
process.stdout.write('Distance: ' + distance.toFixed(2) + ' cm');
call_jsdom(htmlSource, function (window) {
var $ = window.$;
$("h6").replaceWith(distance.toFixed(2));
console.log(documentToSource(window.document));
});
}
};
function documentToSource(doc) {
// The non-standard window.document.outerHTML also exists,
// but currently does not preserve source code structure as well
// The following two operations are non-standard
return doc.doctype.toString()+doc.innerHTML;
}
function call_jsdom(source, callback) {
jsdom.env(
source,
[ 'jquery-1.7.1.min.js' ],
function(errors, window) {
process.nextTick(
function () {
if (errors) {
throw new Error("There were errors: "+errors);
}
callback(window);
}
);
}
);
}
init({
echoPin: 15, //Echo pin
triggerPin: 14, //Trigger pin
timeout: 1000, //Measurement timeout in µs
delay: 60, //Measurement delay in ms
rate: 5 //Measurements per sample
});
Node.js is a server-side implementation of JavaScript. It's ok to do all the sensors operations and calculations on server-side, but you need some mechanism to provide the results to your clients. If they are going to use your application by using a web browser, you must run a HTTP server, like Express.js, and create a route (something like http://localhost/surveyor or just http://localhost/) that calls a method you have implemented on server-side and do something with the result. One possible way to return this resulting data to the clients is by rendering an HTML page that shows them. For that you should use a Template Engine.
Any DOM manipulation should be done on client-side (you could, for example, include a <script> tag inside your template HTML just to try and understand how it works, but it is not recommended to do this in production environments).
Try searching google for Node.js examples and tutorials and you will get it :)

RabbitMQ for NodeJS with Express routing

My server is running NodeJS and uses the amqplib api to request data from another application. The NodeJS server is receiving the information successfully but there's a noticable delay and I'm trying to determine whether I am doing this in the most efficient manner. Specifically I'm concerned with the way that I open and close connections.
Project Layout
I have two controller files that handle receiving and requesting the data, request.img.server.controller.js and receive.img.server.controller.js. Finally the routes handle the controller methods when a button on the front end is pushed, oct.server.routes.js.
request.img.server.controller.js
'use strict';
var amqp = require('amqplib/callback_api');
var connReady = false;
var conn, ch;
amqp.connect('amqp://localhost:5672', function(err, connection) {
conn = connection;
connReady = true;
conn.createChannel(function(err, channel) {
ch = channel;
});
});
exports.sendRequest = function(message) {
console.log('sending request');
if(connReady) {
var ex = '';
var key = 'utils';
ch.publish(ex, key, new Buffer(message));
console.log(" [x] Sent %s: '%s'", key, message);
}
};
receive.img.server.controller.js
var amqp = require('amqplib/callback_api');
var fs = require('fs');
var wstream = fs.createWriteStream('C:\\Users\\yako\\desktop\\binarytest.txt');
var image, rows, cols;
exports.getResponse = function(resCallback) {
amqp.connect('amqp://localhost:5672', function(err, conn) {
conn.createChannel(function(err, ch) {
var ex = '';
ch.assertQueue('server', {}, function(err, q) {
console.log('waiting for images');
var d = new Date();
var n = d.getTime();
ch.consume(q.queue, function(msg) {
console.log(" [x] %s: '%s'", msg.fields.routingKey, msg.content.toJSON());
rows = msg.content.readInt16LE(0);
cols = msg.content.readInt16LE(2);
console.log("rows = %s", msg.content.readInt16LE(0));
console.log("cols = %s", msg.content.readInt16LE(2));
image = msg.content;
var currMax = 0;
for (var i = 4; i < image.length; i+=2) {
if (image.readInt16LE(i) > currMax) {
currMax = image.readInt16LE(i);
}
wstream.write(image.readInt16LE(i) + ',');
}
console.log('done writing max is', currMax);
//console.log(image);
resCallback(rows, cols, image);
}, {
noAck: true
});
});
});
});
};
oct.server.routes.js
'use strict';
module.exports = function(app) {
var request_img = require('../../app/controllers/image-tools/request.img.server.controller.js');
var receive_img = require('../../app/controllers/image-tools/receive.img.server.controller.js');
// oct routes
app.get('/load_slice', function(req, res) {
console.log('load slice hit');
receive_img.getResponse(function (rows, cols, image) {
res.end(image);
});
request_img.sendRequest('123:C:\\Users\\yako\\Documents\\Developer\\medicaldiag\\test_files\\RUS-01-035-09M-21.oct');
});
};
The way you're opening connections is bad, and is at least part of the performance problem.
Connections are expensive to open. They open a new TCP/IP connection on a TCP/IP port between the client and rabbitmq server. This takes time, and uses up a limited resource on both the client and server.
Because of this, a single connection to RabbitMQ should be created and used within each of your node.js processes. This one connection should be shared by all of the code in that process.
Whenever you need to do something with RabbitMQ, open a new channel on the shared connection and do your work. Channels are cheap and are meant to be opened and closed as needed, within a connection.
More specifically in your code, the receive.img.server.controller.js file is the major problem. This opens a new connection to RabbitMQ every time you call the getResponse method.
If you have 10 users hitting the site, you'll have 10 open RabbitMQ connections when 1 would be sufficient. If you have thousands of users hitting the site, you'll have thousands of open RabbitMQ connections when 1 would be sufficient. You also run the risk of exhausting your available TCP/IP connections on the RabbitMQ server or client.
Your receive.img.server.controller.js should look more like your request.img.server.controller.js - one connection open, and re-used all the time.
Also, FWIW - I recommend using the wascally library for RabbitMQ w/ node.js. This library sits on top of amqplib, but makes things significantly easier. It will manage your one connection for you, and make it easier for you to send and receive messages.
I also have some training material available for RabbitMQ and node.js that covers the basics of amqplib and then moves in to using wascally for real application development.

Node.js process out of memory

I have written a service to download files from an external partner site. There are around 1000 files of 1 MB each. My process is going out of memory every time I reach around 800 files.
How should I identify the root cause ?
var request = require('sync-request');
var fs = require('graceful-fs')
function find_starting_url(xyz_category){
feed_url = "<url>"
response = request("GET", feed_url).getBody().toString()
response = JSON.parse(response)
apiListings = response['apiGroups']['affiliate']['apiListings']
starting_url = apiListings[xyz_category]['availableVariants']['v0.1.0']['get']
return starting_url
}
function get_all_files(feed_category, count, next_url, retry_count){
var headers = {
'Id': '<my_header>',
'Token': '<my key>'
}
console.log(Date())
console.log(count)
if(next_url){
products_url = next_url
}
else{
products_url = find_starting_url(feed_category)
}
try{
var products = request("GET", products_url, {"headers": headers}).getBody().toString()
var parsed = JSON.parse(products)
var home = process.env.HOME
var fd = fs.openSync(home + "/data/abc/xyz/" + feed_category + "/" + count + ".json", 'w')
fs.writeSync(fd, products)
fs.closeSync(fd)
next_url = parsed['nextUrl']
count++;
if(next_url){
get_all_files(feed_category, count, next_url)
}
}catch(e){
if(retry_count >= 5){
console.log("TERRIBLE ENDING!!!", e)
}else{
retry_count++;
console.log("some error... retrying ..", e)
get_all_files(feed_category, count, next_url, retry_count)
}
}
}
var feed_category = process.argv[2]
get_all_files(feed_category, 1)
You're calling a synchronous function recursively so every single request you have and all the data from each request is retained in memory in your local variables until all of the requests are done and all the recursive calls can unwind and then finally free all the sets of local variables. This requires monster amounts of memory (as you have discovered).
It would be best to restructure your code so that the current request is processed, written to disk and then nothing from that request is retained when it goes onto the next request. The simplest way to do that would be to use a while loop instead of a recursive call. In pseudo code:
initialize counter
while (more to do) {
process the next item
increment counter
}
I don't understand the details of what your code is trying to do well enough to propose a rewrite, but hopefully you can see how you can replace the recursion with the type of non-recursive structure above.
It's because you are performing a recursive call to the get_all_files function and it's keeping the body variable in memory for every single execution, since every child execution needs to be completed before the memory is released.

Node.js: Receiving too many UDP messages at a time, losing them

My node server receives about 400 UDP messages in one second, and it all works, and I am able to process all 400 of them.
However, when I start to receive about 700 UDP messages in one second, I lose 2-20 of the messages, and they never get parsed :(
I have thought about some options here:
Create a queue of all the socket messages, then consume one-by-one,
although I'm not sure how to implement this
Can't figure out how to implement
Find a setting in Node / Express / dgram socket where i can increase the memory size / buffer size, something like that
I couldn't find any settings like this, though :(
Use a different UDP receiver, stop using node's build in socket UDP receiver
Didn't find other receivers
Here's what my UDP sender looks like:
var dgram = require("dgram");
var udpserver = dgram.createSocket("udp4");
var seatStateStore = require("./SeatStateStore");
udpserver.on("message",
function (msg, rinfo)
{
seatStateStore.parseMessage(msg.toString());
});
Anyone have any ideas? I couldn't figure out any of the 3 options :/ Can someone help me out?
Node v0.10.29
Express v3.14.0
===============================
UPDATE / SOLUTION
Here's the code I ended up using (slightly modified #RoyHB 's solution):
var dgram = require("dgram");
var udpserver = dgram.createSocket("udp4");
var seatStateStore = require("./SeatStateStore");
var Dequeue = require('dequeue');
var FIFO = new Dequeue();
fetcher();
udpserver.on("message",
function (msg, rinfo)
{
FIFO.push(msg.toString());
});
udpserver.bind(43278);
function fetcher () {
while (FIFO.length > 0)
{
var msg = FIFO.shift();
seatStateStore.parseMessage(msg);
}
setImmediate(fetcher); //make this function continuously run
}
I know there is already an answer to this, but as of today, I found a way to increase the buffer on dgram from the official documentation: official doc.
socket.setRecvBufferSize(size);
Added in: v8.7.0
size <integer>
Sets the SO_RCVBUF socket option. Sets the maximum socket receive buffer in bytes.
socket.setSendBufferSize(size)
Added in: v8.7.0
size <integer>
Sets the SO_SNDBUF socket option. Sets the maximum socket send buffer in bytes.
Usage example:
var socket = dgram.createSocket('udp4');
socket.on("listening", () => {
socket.setRecvBufferSize(100000000); // 100mb
socket.setSendBufferSize(100000000); // 100mb
});
The default value is 65507
There is a NPM module called node-dequeue. I use it a lot for similar situations to yours.
basically,
your program pushes received messages onto the end of the queue.
an interval timer periodically activates another method or function ( a queue-fetcher) which checks to see if there are messages on the queue and if so, fetches one or more and processes it.
Alternatively (maybe better) no timer is used to schedule queue fetches. Instead the node process.nextTick method is used.
Alternatively, maybe preferably, you can use node process.nextTick to continuously check the queue for messages.
Ideally, seatStateStore.parseMessage would create a new object to asynchronously process one message so that parseMessage returns without delay while the actual message processing continues in the background. (see bottom of example code )
I haven't tested the code below, it's meant to illustrate, not to run
var FIFO = require ('dequeue');
var seatStateStore = require("./SeatStateStore");
var dgram = require("dgram");
setInterval(fetcher, 1);
var udpserver = dgram.createSocket("udp4");
udpserver.on("message",
function (msg, rinfo) {
FIFO.push(msg);
}
);
function fetcher () {
while (FIFO.length > 0) {
var msg = FIFO.shift();
seatStateStore.parseMessage(msg);
}
}
** OR (maybe better) **
var FIFO = require ('dequeue');
var seatStateStore = require("./SeatStateStore");
var dgram = require("dgram");
fetcher();
var udpserver = dgram.createSocket("udp4");
udpserver.on("message",
function (msg, rinfo) {
FIFO.push(msg);
}
);
function fetcher () {
while (FIFO.length > 0) {
var msg = FIFO.shift();
seatStateStore.parseMessage(msg);
process.nextTick(fetcher);
}
}
Outline of seatStateProcessor.parseMessage:
seatStateProcessor.parseMessage = function (msg) {
proc = new asyncProcHandler(msg, function (err) {
if (err) {
//handle the error
}
});
}

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