for data that only needs to be available during an individual request, where should it be stored?
i am creating new properties on the req and res objects so i dont have to pass that data from function to function.
req.myNewValue = 'just for this request'
is the process object an option? or is it shared globally across all requests?
In Express 4, the best practice is to store request level variables on res.locals.
An object that contains response local variables scoped to the
request, and therefore available only to the view(s) rendered during
that request / response cycle (if any). Otherwise, this property is
identical to app.locals.
This property is useful for exposing request-level information such as
the request path name, authenticated user, user settings, and so on.
app.use(function(req, res, next){
res.locals.user = req.user;
res.locals.authenticated = ! req.user.anonymous;
next();
});
The process object is shared by all requests and should not be used per request.
If you are talking about the variable passed like here:
http.createServer(function (req, res) {
req.myNewValue = 'just for this request';
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('Hello World\n');
}).listen(1337, '127.0.0.1');
then it is perfectly fine what you are doing. req stores the request data, you can modify it as you want. If you are using some framework like Express, then it should be fine as well (keep in mind that you may overwrite some built-in properties of req object).
If by "process object" you are refering to the global variable process, then absolutely not. The data here is global and shouldn't be modified at all.
If you want to preserve the data across the async callback and there could be scenarios, where request and response objects are not available. So in that case continuation-local-storage package, is helpful.
It is used to access the data or the current express request/response from a point where that is not readily accessible. It use the concept of namespace.
Here is how I set up this
Install the continuation-local-storage package
npm install continuation-local-storage --save
Create namespace
let app = express();
let cls = require('continuation-local-storage');
let namespace = cls.createNamespace('com.domain');
then middleware
app.use((req, res, next) => {
var namespace = cls.getNamespace('com.domain');
// wrap the events from request and response
namespace.bindEmitter(req);
namespace.bindEmitter(res);
// run following middleware in the scope of the namespace we created
namespace.run(function () {
// set data on the namespace, makes it available for all continuations
namespace.set('data', "any_data");
next();
});
})
Now in any file or function you can get this namespace and use the saved data in it
//logger.ts
var getNamespace = require("continuation-local-storage").getNamespace;
let namespace = getNamespace("com.domain");
let data = namespace.get("data");
console.log("data : ", data);
No, it isn't shared along with all requests, it only persists for that request long.
Related
In my express application I have a module called helpers thats is required in almost all my routes and modules. This module has a logger method that logs to fluentd (but that's unimportant). While building the data to log I'd like to add a unique identifier of the request, so that all the logs written for the same request have the same unique ID. Using a global var in the app entry point app.use doesn't work because this var would be overwritten every time a new request hits, so the global uuid will change would obviously change in case of high load or long running tasks. The res.locals is not available outside routing, so I can't use it for this matter. Is there a way to create a var that would be unique per request and available in every module or maybe a way to access the res.locals data outside routing? Thank you
EDIT
Maybe an example will help understand better the question.
Suppose I have a module called helpers.js like this:
let helpers = {};
helpers.log = (logData, logName) => {
fluentLogger.emit('', {
name: logName,
//uuid: the needed uuid,
message: logData
});
}
module.exports = helpers;
Now obviously I can do this in my app.js entry point:
app.use(function (req, res, next) {
res.locals.uuid = uuid.v4();
next();
});
and then in every loaded middleware module that requires helpers(adding a new param to the helpers.log method):
const helpers = require('helpers');
router.post('/', (req, res, next) => {
helpers.log('my log message', 'myLogName', res.locals.uuid);
next();
});
and this will normally work. But suppose a big or middle size project where there are hundreds of custom modules and models (not middlewares) and a module may require other modules that require other modules that require finally the helpers module. In this case I should pass the res.locals.uuid as a parameter to every method of every method so that I have it available in the logger method. Not a very good idea. Suppose I have a new module called dbmodel.js that is required in a middleware function:
const helpers = require('helpers');
let dbmodel = {};
dbmodel.getSomeData = (someParam) => {
//some logic
helpers.log('my log message', 'myLogName');
}
module.exports = dbmodel;
The dbmodel has no idea about the res.locals data if I don't pass it from the middleware, so the helpers.log method will also have no idea about this.
In PHP one would normally write a GLOBAL var in the application's entry point so a hypothetical logger function would have access to this global on every method request from whichever class of the application.
Hope this explanation will help :) Thank you
EDIT 2
The solution for this kind of problems is CLS. Thanks to #robertklep for the hint. A good slideshare explaining exactly the same problem (logger with unique ID) and explaining the CLS solutions can be found here: https://www.slideshare.net/isharabash/cls-and-asynclistener
I answered a very similar question here which will solve this problem.
I used to solve the problem the libraries node-uuid and continuation-local-storage. Take a look to the answer of this question and see if it helps:
NodeJS Express - Global Unique Request Id
And you want a bigger explanation, take a look here:
Express.js: Logging info with global unique request ID – Node.js
Yes you can do so by one method .
Every request comes to his routes pass that request inside the middleware.
Suppose you have
app.get('/', function(req, res) {
res.sendFile(path.join(public + "index.html"));
});
a request.
Place Middleware in it .and edit req field coming , in this way you will get the unique variable values for each request
check out this .
https://expressjs.com/en/guide/writing-middleware.html
Like this
var requestTime = function (req, res, next) {
req.requestTime = Date.now()
next()
}
app.use(requestTime)
app.get('/', function (req, res) {
var responseText = 'Hello World!<br>'
responseText += '<small>Requested at: ' + req.requestTime + '</small>'
res.send(responseText)
})
Here req.requestTime is unique for each request.
I have multiple routes, split into different files (my app consists of different "modules", which I maintain in separate folders. For each folder, there is an index.js file in which I manage the routes per module, and I require these in the app.js file).
For every route, I will require to check the auth, and pass the loggedIn status to the header of every page:
//Default variables for the ejs template
var options = {
loggedIn: true
};
res.render("home/home", options);
If the logged in status is true, then the user's name will be displayed. If not, the login / signup labels are displayed.
What is the best way to centralise this, so that I don't need to require the auth script in every of these index.js (route) files?
I need to be able to pass the auth status to the view via the options object (see example).
In your auth, module, use a middleware function. That function can check and store res.locals.loggedIn which will be available for any view that will eventually be rendered. Just make sure the app.use call executes prior to your other routes and it will work properly.
app.use(function auth(req, res, next) {
res.locals.loggedIn = true; // compute proper value here
next();
});
From what I understand you need to do this for every request.One common thing is adding this as middleware so that all the request gets this .
For Example :
var http = require('http');
var connect = require('connect');
var app = connect();
app.use(function(req, res) {
res.end('Hello!');
});
http.createServer(app).listen(3000)
Now for every request , Hello is printed . You could extract this as a module and reuse it across projects. Check here for more details
I am very new to Node.js, and I was wondering if that, except for session(), I could use a "storage" to store variables for the current request?
I have an API which is based on an Authorization header, and a pool of valid tokens stored in Redis.
Therefore I don't have a session and don't want to.
But I would like to store variables for further use during this request. For example, I would like to store the user_id corresponding to the token found in Redis, so that I can use it wherever I want.
If I do something like:
app = express();
app.user_id = 1;
Is it ok, or will my user_id become global to all requests handled by the app? (in short: is the app instanciated for each request handled by the server, or is it persistent?)
If this is not ok, how could I achieve something like this without sessions?
Thank you for any help :)
The app handles all requests, and would only be created once on startup, but req lives for only the lifetime of the request. Keep in mind that the req in Express is just an object, and as such, can be assigned values. So if you wanted to allow the controller to have access to some value (similar to sessions), you could do something like this:
var express = require('express');
var app = express();
// middleware that assigns a value '123' to 'req.user_id'
app.use(function(req, res, next) {
req.user_id = 123;
next();
});
// controller which responds with the 'req.user_id'
app.get('/hello', function(req, res){
res.send('req.user_id: ' + req.user_id); // responds with req.user_id: 123
});
app.listen(3000, function() {
console.log('Listening on port 3000');
});
In the above example, the middleware that I created assigns a value to the request, called user_id. This value lives for the life of the request. You could do a similar thing to assign a dynamic value to the req so that you can access it via your controllers.
I want my session to be available in all views (*.ejs) without having to pass it on every single action. My code is shown below, but the req.session object is always null here, even though in my "controllers" I can access a session object after an user has authenticated, by specifying:
req.session.whatever
My initialization code (that is currently executed on every single request (I double checked with a debug breakpoint) is:
var appendLocalsToUseInViews = function(req, res, next)
{
//append request and session to use directly in views and avoid passing around needless stuff
res.locals.request = req;
if(req.session != null && req.session.user != null)
{
res.locals.user = req.session.user;
}
next(null, req, res);
};
I register this function in the app setup preamble:
app.use(appendLocalsToUseInViews);
I have seen people use app.use methods and dynamicHelpers. I am using express 3, and it seems they are gone, deprecated from Express 2... But that does not seem to be the point, as the function is being called correctly on every single request. How to I access the Express session in this sort of pre-controller code?
Thanks!
SOLUTION thanks Jani Hartikainen:
I moved the code to after the session middleware is loaded and its working!!! Here is the new code.
app.use(express.cookieParser(appSecret));
app.use(express.session({ secret: appSecret }));
---->>>app.use(appendLocalsToUseInViews);
This should work but make sure your app.use for this is only after you have initialized your session middleware. If you have this before the initialization for the session middleware, it will be ran before it in the chain, and thus the data will not be available.
Here's the basic setup. I'm trying to create a simple middleware component that would allow me to easily pass data from my route directly to my javascript in the client side. (Very similiar to the Gon gem in ruby). The way I'm doing it is by having a module that looks like this:
module.exports = function(){
return function(req,res,next){
var app = req.app;
if(typeof(app) == 'undefined'){
var err = new Error("The JShare module requires express");
next(err);
return;
}
res.jshare = {};
app.dynamicHelpers({
includeJShare: function(req,res){
if(typeof(res.jshare) === 'undefined'){
return "";
}
return function(){
return '<script type="text/javascript">window.jshare=' + JSON.stringify(res.jshare) + '</script>';
}
}
});
next();
};
}
Then, in my route I can do this:
exports.index = function(req, res){
res.jshare.person = {firstName : "Alex"};
res.render('index', { title: 'Express' })
};
Finally in the layout.jade:
!{includeJShare()}
What that does is in outputs a line of javascript on the client that creates the exact JSON object that was created server side.
Here's the question; it all works as expected, but being new to Express and Node.js in general, I was just curious if attaching properties onto the response object is OK, or is there something wrong with doing it that I'm simply overlooking? For some reason it doesn't pass my "smell test" but I'm not sure why.....
I know this is an old thread, but there is something else to add to this topic.
Express has a response.locals object which is meant for this purpose - extending the response from middleware to make it available to views.
You could add a property directly to the response object, and as #hasanyasin indicated, is how JavaScript is designed. But Express, more specifically, has a particular way they prefer we do it.
This may be new in express 3.x, not sure. Perhaps it didn't exist when this question was asked.
For details, see
http://expressjs.com/en/api.html#res.locals
There is also an app.locals for objects which don't vary from request to request (or response to response I suppose).
http://expressjs.com/en/api.html#app.locals
See also: req.locals vs. res.locals vs. res.data vs. req.data vs. app.locals in Express middleware
It is perfectly OK. It is how JavaScript is designed. Only thing you should be careful is to not accidentally overriding already existing properties or being overridden by others. To be safer, instead of adding everything directly to req/res objects, you might consider going a level deeper:
res.mydata={}
res.mydata.person= ...
Like that.
Use res.locals for including custom variables in your response object.