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Chaining routes in NodeJs with values after sending API response

I want to chain routes in NodeJs with values after sending API response to end-ser,
WHY: > The uploaded files would be somewhat large (5-50mb each) and require some processing, can not make my API user wait/timeout while my NodeJS code is working.. so need, 1: Upload files and send success immediately to user, Process files (few promises) and return/log success/failure for notification system.
My individual code blocks are done and working fine (i.e. upload service and file processing service both are good under tests and work nicely when tested individually.)
now with the API to upload in place, I've added following code:
router.post('/upload', upload.array('upload_data', multerMaxFiles), (req, res, next) => {
////some uploading and processing stuff - works nicely
res.json({ 'message': 'File uploaded successfully.' });// shown to API client nicely
console.log("what next? " + utilz.inspect(uploaded_file_paths)) //prints file names on console
next();
});
PROBLEM:
app.use('/api', uploadRoute); //The above code route
//want some processing to be done
app.use(function(req, res, next) {
**want those uploaded file names here**
tried with few response object options but stabs with error
});
OR
use something like ....
app.use(someFunction(uploaded_file_names)); **want those uploaded file names as params**
PS:
Any promise after the file upload success would result in 'Error: Can't set headers after they are sent.', so not helpful writing anything there.
Any suggestions folks.
--
N Baua

Once you've sent a response back to the browser (to keep it from timing out during your long processing time), that http request is done. You cannot send any more data on it and trying to do so will trigger a server-side error. You cannot "chain routes" the way you were asking as you seem to want to do because you simply can't send more data over that http request once you've sent the first response.
There are two common ways to deal with this issue.
As part of your initial response, send back a transaction ID and then have the client poll back every few seconds with an Ajax call asking what the final status is of that transaction. The server can return "in progress" until it is finally done and then it can return the final status.
You can connect a webSocket or socket.io connection from client to server. As part of your initial response to the upload, send back a transaction ID. Then, when the transaction is done server-side, it sends a notification on the webSocket or socket.io connection for that particular client with the transactionID with the final status. The client can then respond accordingly to that final status. You can either keep the webSocket/socket.io connection open for use with other requests or you can then close that connection.
Using either technique, you could also return/send a progress value (like percent complete) that the client could use to display completion progress. This is generally very helpful on the client-side to keep an impatient user from giving up or refreshing the page. If they can see that the processing is proceeding, they won't give up thinking that maybe it stopped working.

This should work with res.write(). But it does depend on your clients cache i think.
I tried this, but it does not work in my firefox.
app.get('/test', function(req, res) {
var count = 0;
var interval = setInterval(function() {
if (count++ === 100) {
clearInterval(interval);
res.end();
}
res.write('This is line #' + count + '\n');
}, 100);
});
After I increased frequency and number of writes it seems to work.
So try:
router.post('/upload', upload.array('upload_data', multerMaxFiles), (req, res, next) => {
////some uploading and processing stuff - works nicely
res.write(JSON.stringify({ 'message': 'File uploaded successfully.' }));// shown to API client nicely
console.log("what next? " + utilz.inspect(uploaded_file_paths)) //prints file names on console
next();
});

//STEP (1)
//Example simulate upload multiple files with chained api calls. In this example the parameters "idFile" and "arrayidFileExample" are helpful.
//You should create and send this data from view.
{
"idFile": "04fe640f6e4w", //id first file
"arrayidFileExample": ["04fe640f6e4w","03g5er4g65erg","g0er1g654er65g4er","0g4er4g654reg654re"] //simulate idFiles array from view
}
//STEP (2)
//your upload files api
app.post('/upload', function(req, res) {
//Express headers, no important in this code
res.header("Access-Control-Allow-Origin", "*");
res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
let arrayIdFiles = req.body.arrayidFileExample; //create arrayIdFiles
let isBlock = false; //flag to block call loop to api
let countIndex = 0;
let currentIndex = 0;
//STEP (3)
//If "arrayIdFiles" index is not exist, set isBlock to true. Remeber flag to block call loop to api
for(let count in arrayIdFiles) {
if(req.body.idFile == arrayIdFiles[count]) {
console.log("current index --> ", countIndex)
countIndex++;
console.log("next index --> ", countIndex)
if(arrayIdFiles[countIndex] == undefined) {
isBlock = true;
}
break;
}
countIndex++;
currentIndex++;
}
//STEP (4)
//If isBlock is equal false, call get upload api with next idFile. this is simulate "recursive api loop"
if(isBlock == false) {
postUploadFile(
'http://localhost:3500/upload',
{
"idFile":arrayIdFiles[currentIndex + 1], //send next idFile from arrayIdFiles
"arrayidFileExample": arrayIdFiles //initial arrayIdFiles
});
}
//STEP (6)
//response json example
const json = JSON.stringify({
error:false,
statusCode: 200,
body:{
message:'current id file '+req.body.idFile,
}
});
res.write(json);
return res.end();
});
//STEP (5)
//call "/upload" api post
const postUploadFile = (url = '', body = {}) => {
return new Promise((resolve, reject)=>{
axios.post(url, body).then(response => {
return resolve(response.data);
}).catch(error => {});
});
};
//server listen instance
server.listen(3500,() => {
});

Node HTTP request hangs forever

We've got a Node.js script that is run once a minute to check the status of our apps. Usually, it works just fine. If the service is up, it exits with 0. If it's down, it exits with 1. All is well.
But every once in a while, it just kinda stops. The console reports "Calling status API..." and stops there indefinitely. It doesn't even timeout at Node's built-in two-minute timeout. No errors, nothing. It just sits there, waiting, forever. This is a problem, because it blocks following status check jobs from running.
At this point, my whole team has looked at it and none of us can figure out what circumstance could make it hang. We've built in a start-to-finish timeout, so that we can move on to the next job, but that essentially skips a status check and creates blind spots. So, I open the question to you fine folks.
Here's the script (with names/urls removed):
#!/usr/bin/env node
// SETTINGS: -------------------------------------------------------------------------------------------------
/** URL to contact for status information. */
const STATUS_API = process.env.STATUS_API;
/** Number of attempts to make before reporting as a failure. */
const ATTEMPT_LIMIT = 3;
/** Amount of time to wait before starting another attempt, in milliseconds. */
const ATTEMPT_DELAY = 5000;
// RUNTIME: --------------------------------------------------------------------------------------------------
const URL = require('url');
const https = require('https');
// Make the first attempt.
make_attempt(1, STATUS_API);
// FUNCTIONS: ------------------------------------------------------------------------------------------------
function make_attempt(attempt_number, url) {
console.log('\n\nCONNECTION ATTEMPT:', attempt_number);
check_status(url, function (success) {
console.log('\nAttempt', success ? 'PASSED' : 'FAILED');
// If this attempt succeeded, report success.
if (success) {
console.log('\nSTATUS CHECK PASSED after', attempt_number, 'attempt(s).');
process.exit(0);
}
// Otherwise, if we have additional attempts, try again.
else if (attempt_number < ATTEMPT_LIMIT) {
setTimeout(make_attempt.bind(null, attempt_number + 1, url), ATTEMPT_DELAY);
}
// Otherwise, we're out of attempts. Report failure.
else {
console.log("\nSTATUS CHECK FAILED");
process.exit(1);
}
})
}
function check_status(url, callback) {
var handle_error = function (error) {
console.log("\tFailed.\n");
console.log('\t' + error.toString().replace(/\n\r?/g, '\n\t'));
callback(false);
};
console.log("\tCalling status API...");
try {
var options = URL.parse(url);
options.timeout = 20000;
https.get(options, function (response) {
var body = '';
response.setEncoding('utf8');
response.on('data', function (data) {body += data;});
response.on('end', function () {
console.log("\tConnected.\n");
try {
var parsed = JSON.parse(body);
if ((!parsed.started || !parsed.uptime)) {
console.log('\tReceived unexpected JSON response:');
console.log('\t\t' + JSON.stringify(parsed, null, 1).replace(/\n\r?/g, '\n\t\t'));
callback(false);
}
else {
console.log('\tReceived status details from API:');
console.log('\t\tServer started:', parsed.started);
console.log('\t\tServer uptime:', parsed.uptime);
callback(true);
}
}
catch (error) {
console.log('\tReceived unexpected non-JSON response:');
console.log('\t\t' + body.trim().replace(/\n\r?/g, '\n\t\t'));
callback(false);
}
});
}).on('error', handle_error);
}
catch (error) {
handle_error(error);
}
}
If any of you can see any places where this could possibly hang without output or timeout, that'd be very helpful!
Thank you,
James Tanner
EDIT: p.s. We use https directly, instead of request so that we don't need to do any installation when the script runs. This is because the script can run on any build machine assigned to Jenkins without a custom installation.

Aren't you missing the .end()?
http.request(options, callback).end()
Something like explained here.

Inside your response callback your not checking the status..
The .on('error', handle_error); is for errors that occur connecting to the server, status code errors are those that the server responds with after a successful connection.
Normally a 200 status response is what you would expect from a successful request..
So a small mod to your http.get to handle this should do..
eg.
https.get(options, function (response) {
if (response.statusCode != 200) {
console.log('\tHTTP statusCode not 200:');
callback(false);
return; //no point going any further
}
....

Increase of parallel requests form node.js to external system takes more time to respond

I have a simple case where I'm requesting a different upstream proxy server from my node.js server. With the increase in load I see the request takes lot of time to execute(though time taken to respond from my upstream proxy server is constant across the requests). To demonstrate the issue i've written a sample program as below. When I execute the below program, the first request takes 118ms to execute and the last one takes 10970ms depending on the website you hit (I've changed the url to google, Try it out with your favourite website). If you observe i'm using async to parallelize my requests.
The question is, what is the reason node.js takes this much time to execute a request when run in parallel. To give some more context on the infra settings(centos 6.5) I have opened up my port range from 1024 to 65535, change the fin_timeout to 15 seconds and enable tw_reuse =1 for sockets in sysctl.conf
var http = require('http');
var uuid = require('node-uuid');
var async = require('async');
function callExternalUrl(){
var uniqueId = uuid.v4();
console.time(uniqueId);
var options = {
host: 'google.com',
port: '80',
path: '/',
method: 'GET'
};
var req = http.request(options, function(res) {
var msg = '';
res.setEncoding('utf8');
res.on('data', function(chunk) {
msg += chunk;
console.timeEnd(uniqueId);
});
res.on('end', function() {
});
});
req.end();
}
function iterateAsync(callback){
var iter = [];
for(var i=0; i<1000; i++){
iter[i] = i;
}
async.each(iter,
function(item, callback) {
callExternalUrl();
},
function(err) {
callback(err);
}
);
}
iterateAsync(function(){console.log('done');});
To give more context below is the code in ruby to do the same. I understand i can't compare these two languages as in apples to apples. But the idea is to show the time it takes to execute the same requests in sequence using ruby. I don't see any increase in the response times for each request going out in sequence. So, I doubt the parallel requests using node is taking more time for the request to respond(and the issue is not from the server to respond but its from sending out the request from the machine itself)
require 'rest_client'
1000.times do |number|
beginning = Time.now
response = RestClient.get 'http://google.com'
puts "Time elapsed #{Time.now - beginning} seconds"
end

For one, you're not calling the async iterator callback function:
function callExternalUrl(asyncCallback) {
...
res.on('end', function() {
asyncCallback();
});
...
}
function iterateAsync(callback) {
var iter = [];
for(var i=0; i<1000; i++){
iter[i] = i;
}
async.each(iter,
function(item, asyncCallback) { // <-- HERE
callExternalUrl(asyncCallback);
},
function(err) {
callback(err);
}
);
}
Also, depending on the Node version you're using, the http module may limit the number of parallel requests being made to a particular hostname:
$ node -pe 'require("http").globalAgent.maxSockets'
On Node 0.10, the default is 5; on Node 0.12, the default is Infinity ("unlimited"). So if you're not on Node 0.12, you should increase that value in your code:
var http = require('http');
http.globalAgent.maxSockets = Infinity;
...

I've tried to run your scenario by using JXcore (fork of Node.JS, and an open source project now on github), which offers multitasking (among many other new features).
var task = function (item) {
var http = require('http');
var uuid = require('node-uuid');
var uniqueId = uuid.v4() + "-" + process.threadId;
console.time(uniqueId);
var options = {
host: 'google.com',
port: '80',
path: '/',
method: 'GET'
};
var req = http.request(options, function (res) {
var msg = '';
res.setEncoding('utf8');
res.on('data', function (chunk) {
msg += chunk;
console.timeEnd(uniqueId);
});
res.on('end', function () {
process.release();
});
});
req.end();
process.keepAlive();
};
jxcore.tasks.setThreadCount(4);
console.time("total");
process.on('exit', function () {
console.timeEnd("total");
});
for (var i = 0; i < 1000; i++)
jxcore.tasks.addTask(task, i);
The sample is not really optimized, but still the total 1000 requests runs with JXcore a little bit faster for me (I was able to measure up to 20% gain on my platform). That may vary depending on the machine, since multitasking is using different threads/instances within one single process (no need for clustering any more). My machine has just 4 threads, that's why I used jxcore.tasks.setThreadCount(4);. You can try with your 32 :)
The way of handling each single request is not significantly different, so I'm not saying that each request takes less time, but the key might be hidden in different queuing mechanism as opposite to "async" module. And of course thanks to multitasking.

How to detect client disconnection from node.js server

I am new to node.js. How to detect client is disconnected from node.js server .
Here is my code:
var net = require('net');
var http = require('http');
var host = '192.168.1.77';
var port = 12345;//
var server = net.createServer(function (stream) {
stream.setEncoding('utf8');
stream.on('data', function (data) {
var comm = JSON.parse(data);
if (comm.action == "Join_Request" && comm.gameId =="game1") // join request getting from client
{
var reply0 = new Object();
reply0.message = "WaitRoom";
stream.write(JSON.stringify(reply0) + "\0");
}
});
stream.on('disconnect', function() {
});
stream.on('close', function () {
console.log("Close");
});
stream.on('error', function () {
console.log("Error");
});
});
server.listen(port,host);
How to know client side internet disconnection.

The best way to detect "dead sockets" is to send periodic application-level ping/keepalive messages. What that message looks like depends on the protocol you're using for communicating over the socket. Then it's just a matter of using a timer or other means of checking if you've received a "ping response" within a certain period of time after you sent the ping/keepalive message to the client.
On a semi-related note, it looks like you're using JSON messages for communication, but you're assuming a complete JSON string on every data event which is a bad assumption. Try using a delimiter (a newline is pretty common for something like this, and it makes debugging the communication more human-readable) instead.
Here is a simple example of how to achieve this:
var PING_TIMEOUT = 5000, // how long to wait for client to respond
WAIT_TIMEOUT = 5000; // duration of "silence" from client until a ping is sent
var server = net.createServer(function(stream) {
stream.setEncoding('utf8');
var buffer = '',
pingTimeout,
waitTimeout;
function send(obj) {
stream.write(JSON.stringify(obj) + '\n');
}
stream.on('data', function(data) {
// stop our timers if we've gotten any kind of data
// from the client, whether it's a ping response or
// not, we know their connection is still good.
clearTimeout(waitTimeout);
clearTimeout(pingTimeout);
buffer += data;
var idx;
// because `data` can be a chunk of any size, we could
// have multiple messages in our buffer, so we check
// for that here ...
while (~(idx = buffer.indexOf('\n'))) {
try {
var comm = JSON.parse(buffer.substring(0, idx));
// join request getting from client
if (comm.action === "Join_Request" && comm.gameId === "game1") {
send({ message: 'WaitRoom' });
}
} catch (ex) {
// some error occurred, probably from trying to parse invalid JSON
}
// update our buffer
buffer = buffer.substring(idx + 1);
}
// we wait for more data, if we don't see anything in
// WAIT_TIMEOUT milliseconds, we send a ping message
waitTimeout = setTimeout(function() {
send({ message: 'Ping' });
// we sent a ping, now we wait for a ping response
pingTimeout = setTimeout(function() {
// if we've gotten here, we are assuming the
// connection is dead because the client did not
// at least respond to our ping message
stream.destroy(); // or stream.end();
}, PING_TIMEOUT);
}, WAIT_TIMEOUT);
});
// other event handlers and logic ...
});
You could also just have one interval instead of two timers that checks a "last data received" timestamp against the current timestamp and if it exceeds some length of time and we have sent a ping message recently, then you assume the socket/connection is dead. You could also instead send more than one ping message and if after n ping messages are sent and no response is received, close the connection at that point (this is basically what OpenSSH does).
There are many ways to go about it. However you may also think about doing the same on the client side, so that you know the server didn't lose its connection either.

Node.js / express: respond immediately to client request and continue tasks in nextTick

I would like to separate server high consuming CPU task from user experience:
./main.js:
var express = require('express');
var Test = require('./resources/test');
var http = require('http');
var main = express();
main.set('port', process.env.PORT || 3000);
main.set('views', __dirname + '/views');
main.use(express.logger('dev'));
main.use(express.bodyParser());
main.use(main.router);
main.get('/resources/test/async', Test.testAsync);
main.configure('development', function() {
main.use(express.errorHandler());
});
http.createServer(main).listen(main.get('port'), function(){
console.log('Express server app listening on port ' + main.get('port'));
});
./resources/test.js:
function Test() {}
module.exports = Test;
Test.testAsync = function(req, res) {
res.send(200, "Hello world, this should be sent inmediately");
process.nextTick(function() {
console.log("Simulating large task");
for (var j = 0; j < 1000000000; j++) {
// Simulate large loop
}
console.log("phhhew!! Finished!");
});
};
When requesting "localhost:3000/resources/test/async" I would expect the browser rendering "Hello world, this should be sent inmediately" really fast and node.js to continue processing, and after a while in console appearing "finished" message.
Instead, browser keeps waiting until node.js finishes large task and then renders the content. I've tried with res.set({ 'Connection': 'close' }); and also res.end(); but nothing works as expected. I've also googled with no luck.
How should it be to send the response to client immediately and server continue with tasks?
EDIT
posted fork method in solution

Try waiting instead of hogging the CPU:
res.send("Hello world, this should be sent inmediately");
console.log("Response sent.");
setTimeout(function() {
console.log("After-response code running!");
}, 3000);
node.js is single-threaded. If you lock up the CPU with a busy loop, the whole thing grinds to a halt until that is done.

Thakns for Peter Lyons help, finally the main problem was firefox buffer: response was not so long as to flush it (so firefox kept waiting).
Anyway, for hight CPU performing tasks, node would keep hanged until finishing, so will not be attending new requests. If someone needs it, it can be achieved by forking (with child_process, see sample in http://nodejs.org/api/child_process.html)
Have to say that change of context by forking could take longer than splitting the task in different ticks.
./resources/test.js:
var child = require('child_process');
function Test() {}
module.exports = Test;
Test.testAsync = function(req, res) {
res.send(200, "Hello world, this should be sent inmediately");
var childTask = child.fork('child.js');
childTask.send({ hello: 'world' });
};
./resources/child.js:
process.on('message', function(m) {
console.log('CHILD got message:', m);
});

A good solution is to use child_process.fork(): it allows you to execute another JavaScript file of your app in a different Node instance, and thus in a different event loop. Of course, you can still communicate between the two processes by sending messages: so, from your UI process, you can send a message to the forked process to ask it to execute something.
For example, in ui.js:
var ChildProcess = require('child_process');
var heavyTaskWorker = ChildProcess.fork('./heavyTaskWorker.js');
...
var message = {
operation: "longOperation1",
parameters: {
param1: "value1",
...
}
};
heavyTaskWorker.send(message);
And in heavyTaskWorker.js:
process.on('message', function (message) {
switch (message.operation) {
case 'longOperation1':
longOperation1.apply(null, message.parameters);
break;
...
}
});
Tested here, and it works fine!
Hope that helps!