Express app.all declaring req/res vs not

Express app.all declaring req/res vs not - javascript

In express, everything else held constant, is there a difference between:
app.all('/', mongoProxy(config.mongo.dbUrl, config.mongo.apiKey));
and
app.all('/', function (req, res) {
mongoProxy(config.mongo.dbUrl, config.mongo.apiKey);
});
The former is able to return the return value from mongoProxy while the latter is not, where mongoProxy looks something like this:
module.exports = function(basePath, apiKey) {
basePath = url.parse(basePath);
// Map the request url to the mongolab url
// #Returns a parsed Url object
var mapUrl = module.exports.mapUrl = function(reqUrlString) {
//use the basePath to Parse the URL
return newUrl;
};
var mapRequest = module.exports.mapRequest = function(req) {
var newReq = mapUrl(req.url);
// Make a new request and return it..
return newReq;
};
var proxy = function(req, res, next) {
try {
var options = mapRequest(req);
// Create the request to the db
var dbReq = https.request(options, function(dbRes) {
// Save result
});
// { send result }
res.send(data);
res.end();
});
});
// send request
dbReq.end(JSON.stringify(req.body));
} catch (error) {
//..
}
};
return proxy;
};
The documentation is not clear on explaining the conceptual difference between the two; in the examples I've seen, the former function
app.all('/', mongoProxy(config.mongo.dbUrl, config.mongo.apiKey));
is able to access the req and res object without having it actually passed in as done in the latter, function (req, res).
What is the difference between the two, and is one preferable?

tl;dr
Yes, there is a difference: the first will work, whereas the second will hang (you don't invoke the anonymous function returned by mongoProxy). The first is preferable because it is more idiomatic to express (you're using middleware).
First, note how in mongoProxy, you return proxy, an anonymous function:
module.exports = function(basePath, apiKey) {
/* snip */
var proxy = function(req, res, next) { // <-- here
/* snip */
};
return proxy; // <-- and here
};
Let's break it down:
var proxy = mongoProxy(config.mongo.dbUrl, config.mongo.apiKey)
// proxy is an anonymous function which accepts: (req, res, next)
app.all('/', proxy);
// express will use proxy as the callback (middleware), which means this is the same as:
app.all('/', function (req, res, next) {
proxy(req, res, next)
})
Let's rewrite the second example—which should make clear why it doesn't work:
var proxy = mongoProxy(config.mongo.dbUrl, config.mongo.apiKey)
app.all('/', function (req, res) {
proxy // nothing happens because you don't invoke the function
});
If you want to use the second example, you could invoke proxy with proxy(req, res, next), but this is not idiomatic (in general and especially for express). Express is all about middleware, so use the first example.
Here's another example, which uses a closure (much like your mongoProxy function):
function getPermissionLevelMiddleware (level) {
// returns an anonymous function which verifies users based on `level`
return function (req, res, next) {
if (req.isAuthenticated() && req.user.permission.level > level)
return next()
return res.redirect('/no/permission')
}
}
var isAdmin = getPermissionLevelMiddleware(9000)
// `isAdmin` only allows users with more than 9000 `user.permission.level`
var isPleb = getPermissionLevelMiddleware(1)
// `isPleb` allows users with more than 1 `user.permission.level`
app.get('/admin', isAdmin, function (req, res) {
res.render('admin.jade')
})

Obviously the first one will return result because req and res objects are accessible to it, where as second case you need to send req and res in the method params of mongoProxy. If you won't send, req and res won't be accessible to it. So, for second scenario to work, the method signature need to be changed to :
module.exports = function(basePath, apiKey, req, res) {
I have done

Related

How to display data as JSON using Routes and Controller?

I want to keep routes separate from controller.
My route is:
'use strict';
module.exports = function(app) {
var controller = require('../controllers/controller');
app.route('/').get(controller.index);
};
And controller is:
exports.index = function() {
request = new Request(
"MYQUERY",
function(err, rowCount) {
if (err) {
console.log(err);
} else {
console.log(rowCount + ' rows');
}
connection.close();
}
);
request.on('row', function(columns) {
columns.forEach(function(column) {
if (column.value === null) {
console.log('NULL');
} else {
console.log(column.value);
}
});
});
connection.execSql(request);
};
I am able to see the result in the terminal console but I want to return it as JSON to http. I can use the following if I am using controller and routes all together:
router.get('/about', function (req, res) {
res.send('About this wiki');
})

The callback function to .get (or any router request handler) takes at least two arguments: request and response. You can see this with your example:
router.get('/about', function (req, res) {
res.send('About this wiki');
})
You could rewrite this to make the callback a named function rather than an anonymous function:
const aboutHandler = function (req, res) {
res.send('About this wiki');
});
router.get('/about', aboutHandler);
Your controller.index is the same kind of function, so it will take those two arguments. You just have to change your function to take them:
exports.index = function (req, res) {
This will give you access to res, and you can use it as you need to do send the response via res.send or res.json if you build a JSON object by accumulating the row results. You can use request.on('end' ... to know when the query has emitted all its results.

I might be misunderstanding your question, but do you mean res.json(...);?

How to create a reusable function in Node without writing boilerplate code

I am using Express.js as http server. Defined all my routes.
Most endpoints need to verify session before returning a response. E.g. below code serves users in the system and list of services respectively:
function getUsers(req, res, next) {
verifyUser(req, res, next, function () {
//serve users
});
}
function getServices(req, res, next) {
verifyUser(req, res, next, function () {
//serve services
});
}
You probably noticed there is a verifyUser function which validates the session. Which is as below.
function verifyUser(req, res, next, callback) {
var sessionKey = req.cookies.sessionKey;
var user = users.userBySession(sessionKey);
if (user) {
callback(req, res, next, user);
} else {
res.status(401).send({
message: 'Unauthorized'
});
}
}
As you can see I keep passing in req, res and next parameters along with a callback whenever I use this function.
I tried to use apply function to make it easier. Changed my getUsers function like this:
function getUsers(req, res, next) {
verifyUser
.apply(null, arguments, function () {
//serve users
});
}
The problem with this approach is callback is not passed into verifyUser function. And I don't really like passing null as scope with each call.
How can I achieve this by writing less and better code ? Any ideas?

You could use bind to create a 'partial function':
// create bound responseHelper object
var responseHelper = verifyUser.bind(null, req, res, next);
// usage
responseHelper(getUsersCallback); // same as verifyUser(req, res, next, getusersCallBack);

I think you're looking to turn verifyUser into a middleware function.
function verifyUser (req, res, next) {
var user = // yadda yadda session stuff
if (user) {
req.user = user; // [1] what you do to the req object here...
} else {
return res.status(401).send({ message: "No way Smokey Joe"});
/**
* alternatively, do something like
* var err = new Error("Not authorized");
* err.statusCode = 401;
* return next(err);
*
* this will kick off Express' error handling mechanism,
* which you should read about in the docs (see the link below)
*/
}
next();
// very important to call next after this verifyUser has done its job
// if you don't, the next middleware won't go off,
// and the request will just hang
}
function getUsers (req, res, next) {
// [2] will show up on the req object here, assuming you chain these
// two functions together as middleware
}
app.get("/users", verifyUser, getUsers);
app.get("/services", verifyUser, getServices);
// here's a route that needs no session auth, so no need to verifyUser
app.get("/latest-posts", getLatestPosts);
When you tell Express to use a function or attach a function to a route path via get('/my/route', hanlderFun) or some such, you've basically turned handlerFun into a middleware.
You can define however many middleware as handlers on a route as you like, and they'll all execute in turn as long as you keep calling next.
app.post("/checkout", verifyUser, tallyCart, checkInventory, doPayment, sendInvoice);
The job of next is to pass control from the current middelware to the next one. It's an object
You can do other stuff with next, too, which you should read up on in the docs.
http://expressjs.com/en/guide/writing-middleware.html
http://expressjs.com/en/guide/using-middleware.html
The docs on routing have good info on middleware as well:
http://expressjs.com/en/guide/routing.html
For extra credit, check out error handling middleware, too:
http://expressjs.com/en/guide/error-handling.html

Decorate restify render

I am trying to decorate render function in restify's router with this code...
decorate.js
module.exports = function (server) {
return function (req, res, next) {
function newRender(orig) {
return function(path, params, query) {
return "http://localhost:3000" + orig(path, params, query);
}
}
server.router.render = newRender(server.router.render);
next();
}
}
and in my server.js
var restify = require("restify");
var decorate = require("./decorate");
var server = restify.createServer();
server.pre(decorate(server));
server.get({name: "get_user", path: "/users/:id"}, function(req, res){
res.send(req.params.id);
});
server.get("/decorate", function(req, res){
res.send({data: server.router.render("get_user", {id: 2})});
});
server.listen(3000);
but I only get this error. Please help.
{"code":"InternalError","message":"Cannot read property 'get_user' of undefined"}

You are passing the original render method with global this as context. Just bind the server.router as context when passing it:
original_render = server.router.render;
function decorate(){
...
server.router.render = newRender(original_render.bind(server.router));
...
}
Update: You keep the reference of original render method outside the middleware function. Otherwise there will be a stack of newRender calls with increasing requests.

How to make dynamic chain of middleware in express.js

I am currently working on a project to develop an API manager to control an existing API.
It contains a list of "before" and "after" middlewares, which are used to do things like security checking and logging. And a "service" middleware to do http request to the existing API. But the problem is that I want to make the order the middleware being executed to be dynamic, meaning that I could load some configuration file to change the order the middleaware get executed every time the request comes in.
here is my previous code:
'use strict';
// Loading the express library
var express = require('express');
var app = express();
var service = require('./routes/index');
// Testing configurable middleware
var confirguration = {
before1: {
priority: 100,
enable: true
},
before2: {
priority: 80,
enable: true
},
service: {
priority: 50,
enable: true
},
after1: {
priority: 30,
enable: true
},
after2: {
priority: 10,
enable: true
}
}
var before1 = require('./example_middleware/before1');
var before2 = require('./example_middleware/before2');
var after1 = require('./example_middleware/after1');
var after2 = require('./example_middleware/after2');
// Fake request to simulate the /service
var fakeRequest = require('./example_middleware/fake_request');
// Function to sort the order of the middleware to be executed
var sortConfig = function(confirguration){
var sortable = [];
for (var middleware in confirguration)
// To make middlewares configurable
if (confirguration[middleware]['enable'] == true){
sortable.push([middleware, confirguration[middleware]['priority']]);
}
sortable.sort(function(a, b) {return b[1] - a[1]});
return sortable;
}
// var sortedConfig = [];
var middlewareSet = new Array();
app.use('/test', function(request, response, next){
var middleware;
var sortedConfig = sortConfig(confirguration);
for (var i in sortedConfig){
switch(sortedConfig[i][0]){
case 'before1':
middleware = before1;
break;
case 'before2':
middleware = before2;
break;
case 'service':
middleware = fakeRequest;
break;
case 'after1':
middleware = after1;
break;
case 'after2':
middleware = after2;
break;
}
// console.log(sortedConfig[i][0]);
// Execute the middleware in expected order
middlewareSet.push(middleware);
}
// request.sortedConfig = sortedConfig;
console.log(middlewareSet);
console.log('middleware list sorted');
next();
});
app.use('/test', middlewareSet);
But I keep getting the same error message coming from the app.use() at the last line:
app.use() requires middleware functions
It works if I use:
app.use('/test', [before1, before2, fakeRequest, after1, after2]);
But it's not dynamic though, what did I misunderstand? There must be a way to do this in express.js.
Thanks in advance.
EDIT:
I modified my code according to Ryan's answer, here is the code:
var async = require('async');
app.use('/test', configurableMiddleWare);
function configurableMiddleWare(req, res, next) {
var operations = [];
var middleware;
var sortedConfig = sortConfig(confirguration);
// push each middleware you want to run
sortedConfig.forEach(function(fn) {
switch(fn[0]){
case 'before1':
middleware = before1;
break;
case 'before2':
middleware = before2;
break;
case 'service':
middleware = fakeRequest;
break;
case 'after1':
middleware = after1;
break;
case 'after2':
middleware = after2;
break;
}
operations.push(middleware); // could use fn.bind(null, req, res) to pass in vars
});
console.log('middleware list sorted');
// now actually invoke the middleware in series
async.series(operations, function(err) {
if(err) {
// one of the functions passed back an error so handle it here
return next(err);
}
// no errors so pass control back to express
next();
});
}
Just to make sure I haven't made any mistakes in my test middleware, here is an example of one of them:
'use strict';
var express = require('express');
var router = express.Router();
router.route('/')
.all(function(request, response, next){
console.log('This is middleware BEFORE1');
next();
});
module.exports = router;
Now, when I run my application, I got the following error from npm:
TypeError: Cannot call method 'indexOf' of undefined
at Function.proto.handle (/Users/jialunliu/Documents/SOA_project/FAT-LADY/node_modules/express/lib/router/index.js:130:28)
at router (/Users/jialunliu/Documents/SOA_project/FAT-LADY/node_modules/express/lib/router/index.js:35:12)
at /Users/jialunliu/Documents/SOA_project/FAT-LADY/node_modules/async/lib/async.js:610:21
at /Users/jialunliu/Documents/SOA_project/FAT-LADY/node_modules/async/lib/async.js:249:17
at iterate (/Users/jialunliu/Documents/SOA_project/FAT-LADY/node_modules/async/lib/async.js:149:13)
at async.eachSeries (/Users/jialunliu/Documents/SOA_project/FAT-LADY/node_modules/async/lib/async.js:165:9)
at _asyncMap (/Users/jialunliu/Documents/SOA_project/FAT-LADY/node_modules/async/lib/async.js:248:13)
at Object.mapSeries (/Users/jialunliu/Documents/SOA_project/FAT-LADY/node_modules/async/lib/async.js:231:23)
at Object.async.series (/Users/jialunliu/Documents/SOA_project/FAT-LADY/node_modules/async/lib/async.js:608:19)
at configurableMiddleWare (/Users/jialunliu/Documents/SOA_project/FAT-LADY/app.js:135:11)
Which is coming from the line
async.series(operations, function(err){})
I am keep getting this kind of error message, saying the function could not read from this array of functions "operations"....

I think you are on the right track, you will just need to tweak a few things. I would register one top level function with app.use() and then do all of your dynamic stuff within that function. Updating my answer to a working example. Be sure to install async first npm install --save async
// define all middleware functions
var middleware = {
mw1: function(req, res, next) {
console.log('mw 1');
next();
},
mw2: function(req, res, next) {
console.log('mw 2');
next();
},
mw3: function(req, res, next) {
console.log('mw 3');
next();
},
mw4: function(req, res, next) {
console.log('mw 4');
next();
}
};
// register our "top level function"
app.use(configurableMiddleware);
var requestCount = 1; // this is just for the working example
function configurableMiddleware(req, res, next) {
var isEvenRequest = requestCount++ % 2 === 0; // simple logic to alternate which "configurable" middleware to use
var operations; // in the real world you could build this array dynamically, for now we just hardcode two scenarios as an example
// Each request to http://localhost:3000 will alternate which middleware is used, so you will see a different log each time
if(isEvenRequest) {
console.log('Even request should log mw2 and mw4');
// .bind(null, req, res) makes sure that the middleware gets the request and response objects when they are invoked,
// as of this point they still haven't been invoked...
operations = [middleware.mw2.bind(null, req, res), middleware.mw4.bind(null, req, res)];
}
else {
console.log('Odd request should log mw1 and mw3');
operations = [middleware.mw1.bind(null, req, res), middleware.mw3.bind(null, req, res)];
}
// invoke each middleware in series - you could also do async.parallel if the order of middleware doesn't matter
// using the async module: https://github.com/caolan/async
async.series(operations, function(err) {
if(err) {
console.log('There was a problem running the middleware!');
return next(err);
}
// all middleware has been run
next();
});
}
For more info on .bind() see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind

connect-sequence: a dedicated node module for that specific purpose:
You can just use the module connect-sequence which is designed for that purpose:
npm install --save connect-sequence
see:
the npmjs page: https://www.npmjs.com/package/connect-sequence
or the github project: https://github.com/sirap-group/connect-sequence
and then, here an example of usage:
/**
* Product API
* #module
*/
var ConnectSequence = require('connect-sequence')
var productsController = require('./products.controller')
module.exports = productRouter
function productRouter (app) {
app.route('/api/products/:productId')
.get(function (req, res, next) {
// Create a ConnectSequence instance and setup it with the current `req`,
// `res` objects and the `next` callback
var seq = new ConnectSequence(req, res, next)
// build the desired middlewares sequence thanks to:
// - ConnectSequence#append(mid0, ..., mid1),
// - ConnectSequence#appendList([mid0, ..., mid1])
// - and ConnectSequence#appendIf(condition, mid)
if (req.query.filter) {
seq.append(productsController.filter)
}
if (req.query.format) {
seq.append(
productsController.validateFormat,
productsController.beforeFormat,
productsController.format,
productsController.afterFormat
)
}
// append the productsController.prepareResponse middleware to the sequence
// only if the condition `req.query.format && req.formatedProduct` is true
// at the moment where the middleware would be called.
// So the condition is tested after the previous middleware is called and thus
// if the previous modifies the `req` object, we can test it.
seq.appendIf(isProductFormatted, productsController.prepareResponse)
seq.append(productsController.sendResponse)
// run the sequence
seq.run()
})
app.param('productId', function (req, res, next, id) {
// ... yield the product by ID and bind it to the req object
})
function isProductFormatted (req) {
return Boolean(req.formatedProduct)
}
}
This is open source, PR are welcome!
If you like and use connect-sequence, but if you find bug or need some new features, feel free to post issues or submit pull requests!

Based on the idea behind #Ryan's code I came up with this function. It executes a list of middleware in order binding the variables as needed, allowing everything to be executed by just executeMiddlewareList([middleware1, middleware2...], req, res, next);. For each middlewarereq, res is passed and the callback from async.eachSeries. This means when next() is called inside the middleware, then next one will be handled from the list. If middleware throws an error with next(err), execution will stop and you can manually handle this.
function executeMiddlewareList (middlewareList, req, res, next) {
async.eachSeries(middlewareList, function(middleware,callback) {
middleware.bind(null,req,res,callback)()
}, function(err) {
if (err) return res.status(500).json({error: err});
next();
})
}
function testMid (number) {
return function (req, res, next) {
log.debug('req.test from', req.test, " to ", number);
req.test=number;
next();
}
}
router.get('/test', function(req, res, next) {
m.executeMiddlewareList([test(1), test(2)], req, res, next);
//Output: req.test from undefined to 1
// req.test from 1 to 2
}, function (req,res) {
//Do stuff after the executeMiddlewareList, req.test = 2
})

Finally, I find the answer according the Ryan's, the code would look like this:
function configurableMiddleWare(req, res, next) {
var operations = [];
var middleware;
var sortedConfig = sortConfig(confirguration);
// push each middleware you want to run
sortedConfig.forEach(function(fn) {
switch(fn[0]){
case 'before1':
middleware = before1;
break;
case 'before2':
middleware = before2;
break;
case 'service':
middleware = fakeRequest;
break;
case 'after1':
middleware = after1;
break;
case 'after2':
middleware = after2;
break;
}
console.log(fn[0]);
console.log(middleware);
operations.push(middleware.bind(null, req, res)); // could use fn.bind(null, req, res) to pass in vars
});
console.log('middleware list sorted');
// now actually invoke the middleware in series
async.series(operations, function(err) {
if(err) {
// one of the functions passed back an error so handle it here
return next(err);
}
console.log('middleware get executed');
// no errors so pass control back to express
next();
});
}
app.use('/test', configurableMiddleWare);
The key step is indeed the operations.push(middleware.bind(null, req, res));
Which to be honest, I don't understand what does it mean exactly. I know this is passing "req" and "res" variable into the middleware, but I don't get what the point of the "null" in the front. Much appreciated if someone could help me clarify this.

How to scope data in express / node controller

I'm trying to avoid callback hell by breaking down my Express / Kraken.js controller into smaller callback functions.
I was processing a request and had about 6 levels of nested anonymous callback functions.
so now I have my main function that looks like this:
// ugh, I know this isn't right
var globalProducts = {};
module.exports = function (server) {
server.get('/project', function (req, res) {
var data = req.query;
globalData = data;
if(!data.projectId || !data.ruleSetId)
res.json({error: "Incomplete input data."});
// pass response to products call back
Project.findOne({ _id: mongoose.Types.ObjectId(data.projectId) }, setUpProducts);
});
};
function setUpProducts(err, project){
// get all products and pass them down the pipe
project.findAllChildren(setUpRules);
}
function setUpRules(err, products) {
// we need to access products in another function
globalProducts = products;
// find the rule set and build the rule Flow
RuleSet.findOne({ _id: mongoose.Types.ObjectId(globalData.ruleSetId) }, function(err, ruleSet) {
ruleSet.buildFlow(processFlow);
});
}
My question is what is the best way to pass around info between callbacks ? My solution was var globalProducts = {}; but to me, the controller contain any 'global state' .. whats the best way to handle this ?

Doing this is a bad idea. It will cause race condition type issue — basically it's the same as sharing data in multithreaded environment. Instead you can use req or res to store data. To do that you need them in scope, so you can define all functions inside route handler or make each function a middleware so it will have req and res as arguments. Here is an example of this approach:
function check (req, res, next) {
if(!req.query.projectId || !req.query.ruleSetId) return res.json({error: "Incomplete input data."});
next()
}
function findProject (req, res, next) {
Project.findOne({ _id: mongoose.Types.ObjectId(req.query.projectId) }, after);
function after (err, project) {
if (err) return next(err);
req.project = project;
next();
}
}
function findProducts (req, res, next) {
req.project.findAllChildren(after)
function after (err, products) {
if (err) return next(err);
req.products = products;
next();
}
}
function respond (req, res) {
res.render('view', {
products : req.products,
project : req.project
});
}
module.exports = function (server) {
server.get('/project', check, findProject, findProducts, respond);
};

Develop Reference

JavaScript is the programming language of the Web.

Express app.all declaring req/res vs not - javascript

Related

How to display data as JSON using Routes and Controller?

How to create a reusable function in Node without writing boilerplate code

Decorate restify render

How to make dynamic chain of middleware in express.js

How to scope data in express / node controller

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