I'm trying to write a header of an MD5 hash token using crypto then return it back as a response. For some reason, it isn't actually running synchronously. I know JS is an asynchronous language, and that's really the only part I'm struggling with right now. Any help would be appreciated.
This is what I have so far:
const crypto = require('crypto');
const bodyParser = require('body-parser');
const formidable = require('formidable');
const async = require('async')
app.post('/pushurl/auth', (req, res) =>
var data = req.body.form1data1 + '§' + req.body.form1data2
async.waterfall([
function(callback) {
var token = crypto.createHash('md5').update(data).digest("hex");
callback(null, token);
},
function(token, callback) {
res.writeHead(301,
{Location: '/dashboard?token=' + token}
);
callback(null)
},
function(callback) {
res.end();
callback(null)
}
]);
}
});
Output:
Uncaught Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
<node_internals>/internal/errors.js:256
No debugger available, can not send 'variables'
Process exited with code 1
JavaScript is an asynchronous language, yes, but it can also do synchronous tasks very well. In your case, you don't need to do any async expect if you're dealing with promises.
If you write your code like in the example below it will just execute from top to bottom.
But the error (probably) occurred because you forgot to add an opening curly brace to your app.post callback, which results in the data var being immediately returned because of an implied return statement () => (implied), () => {} (explicit).
const crypto = require('crypto');
const bodyParser = require('body-parser');
const formidable = require('formidable');
app.post('/pushurl/auth', (req, res) => {
const data = req.body.form1data1 + '§' + req.body.form1data2;
const token = crypto.createHash('md5').update(data).digest("hex");
res.writeHead(301, {
Location: '/dashboard?token=' + token
});
res.end();
});
Related
I'm trying to get a client token from the BrainTree API. I can establish a connection normally but when the code is executed the client token is always null. I've tried multiple solutions including this one here, but no luck.
The code is deployed in an Azure Function.
My Server Side Code :
module.exports = async function (context, req) {
const express = require("express");
const router = express.Router();
var braintree = require("braintree");
var clientToken;
var gateway = new braintree.BraintreeGateway({
environment: braintree.Environment.Sandbox,
merchantId: 'xxxx',
publicKey: 'xxxx',
privateKey: 'xxx'
});
context.log('about to generate a client key');
var Ctk = await gateway.clientToken.generate({}, (err, response) => {
clientToken = response.clientToken
});
var responseC = "The Client token is +" +clientToken;
context.res = {
body: responseC
};
context.log('client key generated');
}
The await keyword only works with functions that return Promise objects. While the Braintree documentation isn't 100% crystal-clear on this, the implication that's raised by switching the sample code on the linked page from "callbacks" to "Promises" is that when you specify a callback function via the second positional parameter a Promise isn't returned, thus nuking the value of using await in the first place. In this scenario, it doesn't work as you expect it and will continue to process asynchronously via the callback, which is why your clientToken isn't getting set the way you think it should.
If you're invested in using Promises all the way through, consider chaining the callback within a .then() call as the documentation prescribes. You also don't need to capture the return value of the call to generate(), as you're storing it in clientToken and not using Ctk at all.
await gateway.clientToken.generate({}).then((err, response) => {
clientToken = response.clientToken
});
I have resolved this using the following code in the end.
It looks like braintree's functions are async and therefore we need to wait for them to complete. Promisify() did the job.
module.exports = async function (context, req) {
const express = require("express");
const router = express.Router();
var app = express();
var braintree = require("braintree");
var clientToken;
var gateway = new braintree.BraintreeGateway({
environment: braintree.Environment.Sandbox,
merchantId: 'xxx',
publicKey: 'xxx',
privateKey: 'xxx'
});
const util = require('util');
const sale = util.promisify(gateway.clientToken.generate);
result = await gateway.clientToken.generate({
}).then(response => {
// pass clientToken to your front-end
clientToken = response.clientToken
});
var cToken= "client token is : " +clientToken;
context.res = {
body: cToken
};
}
I am building out an API using Node for the first time but a little stuck on something.
I have the following files:
My routes, routes/index.js:
const express = require('express');
const router = express.Router();
const transactionsController = require('../controllers/transactionsController');
const ordersController = require('../controllers/ordersController');
const ordersCountController = require('../controllers/ordersCountController');
router.get('/transactions', transactionsController);
router.get('/orders', ordersController);
router.get('/orders_count', ordersCountController);
module.exports = router;
My controllers, controllers/ordersCountController.js:
const ordersCountService = require('../services/ordersCountService');
const ordersCountController = async () => {
try {
const data = await ordersCountService();
console.log(data);
return data;
} catch(err) {
console.log(err);
}
};
module.exports = ordersCountController;
My service to fetch from an external API, services/ordersCountService.js:
const fetch = require('node-fetch');
const ordersCountService = async () => {
const URL = ....;
const settings = { method: 'Get'};
const res = await fetch(URL, settings);
if (!res.ok) throw new Error('Unable to retrieve data');
return await res.json();
}
module.exports = ordersCountService;
How can I pass the JSON through to the browser?
I have been trying a few things - you'll notice the return data; - but I can't figure out how to return the JSON so that it's displayed in the browser when someone visits ourdomain.com/api/orders_count.
Any suggestions as to what I am doing wrong here? I am still new to JS so sorry if I am missing something completely obvious here.
Thank you all for your time. If there is anything I can add for clarity, please don't hesitate to ask.
In your controller, ordersCountService should have 2 parameters: req and res:
The req object represents the HTTP request and has properties for the request query string, parameters, body, and HTTP headers.
The res object represents the HTTP response that an Express app sends when it gets an HTTP request.
In this case, your controller should be:
const ordersCountController = async (req, res) => {
try {
const data = await ordersCountService();
console.log(data);
res.json({data})
} catch(err) {
console.log(err);
}
};
Save it, and open the express server, and type the route url in the browser, you would see the json format.
You could find more information about Express in this article.
Express Explained with Examples - Installation, Routing, Middleware, and More
I'm using n-readline npm package to read text files from the server.
I have a use case, where I had to read at least 300MB of data from those text files and will be using Redis or Mongoose to save around 40mb of data to be transferred to the browser where I use vue to process that or load data whenever needed.
Now I'm running into a problem where I'm unable to get the results when I call that function for the first time, if I call that again, the function provides me with results.
const express = require('express');
const multer = require('multer');
const fs = require('fs');
const NreadLine = require('n-readline');
const app = express();
var asyncres = [];
var lines = []
const upload = multer({ storage });
async function nreadline(){
let linenumbers = [];
var rl = new NreadLine({
filepath: './uploads/6789765/serverout1.txt',
limit: 50
});
await rl.start();
await rl.on('line', (line, linenumer) => {
linenumbers.push(linenumer);
});
await rl.on('end', () => {
console.log('done');
asyncres = [...linenumbers];
});
//This is where I'm expecting the results to be returned
return asyncres;
}
function getresults() {
let ress = nreadline();
console.log(ress);
return ress;
}
// Express APIs defined below
app.post('/upload', upload.single('file'), (req, res) => {
res.json({ "status": "success", file: req.file });
});
// API for multiple form upload
app.post('/multiple', upload.array('files'), (req, res) => {
// ticket = req.body.ticket
res.json({ "status": "success", files: req.files });
});
//Get Request for reading the files
app.get('/reader', (req, res) => {
let results = getresults();
res.json({ "status": results });
});
app.listen(port, () => {
console.log("running on 3344 port");
});
Please Help. I am not sure what I'm doing wrong.
To answer my own question, I found another npm package, that kinda solves my problem.
The package name is n-readlines and below the code that I modified.
const lineByLine = require('n-readlines');
function nreadline(filePath){
let logs = [];
try{
let rl = new lineByLine('./uploads/6789765/serverout0.txt');
let line;
while(line=rl.next()){
logs.push(line.toString('utf8'));
}
return logs;
}catch(err){
}
I'm kinda new to module creation and was wondering about module.exports and waiting for async functions (like a mongo connect function for example) to complete and exporting the result. The variables get properly defined using async/await in the module, but when trying to log them by requiring the module, they show up as undefined. If someone could point me in the right direction, that'd be great. Here's the code I've got so far:
// module.js
const MongoClient = require('mongodb').MongoClient
const mongo_host = '127.0.0.1'
const mongo_db = 'test'
const mongo_port = '27017';
(async module => {
var client, db
var url = `mongodb://${mongo_host}:${mongo_port}/${mongo_db}`
try {
// Use connect method to connect to the Server
client = await MongoClient.connect(url, {
useNewUrlParser: true
})
db = client.db(mongo_db)
} catch (err) {
console.error(err)
} finally {
// Exporting mongo just to test things
console.log(client) // Just to test things I tried logging the client here and it works. It doesn't show 'undefined' like test.js does when trying to console.log it from there
module.exports = {
client,
db
}
}
})(module)
And here's the js that requires the module
// test.js
const {client} = require('./module')
console.log(client) // Logs 'undefined'
I'm fairly familiar with js and am still actively learning and looking into things like async/await and like features, but yeah... I can't really figure that one out
You have to export synchronously, so its impossible to export client and db directly. However you could export a Promise that resolves to client and db:
module.exports = (async function() {
const client = await MongoClient.connect(url, {
useNewUrlParser: true
});
const db = client.db(mongo_db);
return { client, db };
})();
So then you can import it as:
const {client, db} = await require("yourmodule");
(that has to be in an async function itself)
PS: console.error(err) is not a proper error handler, if you cant handle the error just crash
the solution provided above by #Jonas Wilms is working but requires to call requires in an async function each time we want to reuse the connection. an alternative way is to use a callback function to return the mongoDB client object.
mongo.js:
const MongoClient = require('mongodb').MongoClient;
const uri = "mongodb+srv://<user>:<pwd>#<host and port>?retryWrites=true";
const mongoClient = async function(cb) {
const client = await MongoClient.connect(uri, {
useNewUrlParser: true
});
cb(client);
};
module.exports = {mongoClient}
then we can use mongoClient method in a diffrent file(express route or any other js file).
app.js:
var client;
const mongo = require('path to mongo.js');
mongo.mongoClient((connection) => {
client = connection;
});
//declare express app and listen....
//simple post reuest to store a student..
app.post('/', async (req, res, next) => {
const newStudent = {
name: req.body.name,
description: req.body.description,
studentId: req.body.studetId,
image: req.body.image
};
try
{
await client.db('university').collection('students').insertOne({newStudent});
}
catch(err)
{
console.log(err);
return res.status(500).json({ error: err});
}
return res.status(201).json({ message: 'Student added'});
};
I have an http-proxy to proxy any website and inject some custom JS file before to serve the HTML back to the client. Whenever I try to access the proxied website, it will hang up or the browser seems to load indeterminately. But when I check the HTML source, I successfully managed to inject my custom JavaScript file. Here is the code:
const cheerio = require('cheerio');
const http = require('http');
const httpProxy = require('http-proxy');
const { ungzip } = require('node-gzip');
_initProxy(host: string) {
let proxy = httpProxy.createProxyServer({});
let option = {
target: host,
selfHandleResponse: true
};
proxy.on('proxyRes', function (proxyRes, req, res) {
let body = [];
proxyRes.on('data', function (chunk) {
body.push(chunk);
});
proxyRes.on('end', async function () {
let buffer = Buffer.concat(body);
if (proxyRes.headers['content-encoding'] === 'gzip') {
try {
let $ = null;
const decompressed = await ungzip(buffer);
const scriptTag = '<script src="my-customjs.js"></script>';
$ = await cheerio.load(decompressed.toString());
await $('body').append(scriptTag);
res.end($.html());
} catch (e) {
console.log(e);
}
}
});
});
let server = http.createServer(function (req, res) {
proxy.web(req, res, option, function (e) {
console.log(e);
});
});
console.log("listening on port 5051");
server.listen(5051);
}
Can someone please tell me if I am doing anything wrong, it looks like node-http-proxy is dying a lot and can't rely much on it since the proxy can work sometimes and die at the next run, depending on how many times I ran the server.
Your code looked fine so I was curious and tried it.
Although you do log a few errors, you don't handle several cases:
The server returns a body with no response (cheerio will generate an empty HTML body when this happens)
The server returns a response that is not gzipped (your code will silently discard the response)
I made a few modifications to your code.
Change initial options
let proxy = httpProxy.createProxyServer({
secure: false,
changeOrigin: true
});
Don't verify TLS certificates secure: false
Send the correct Host header changeOrigin: true
Remove the if statement and replace it with a ternary
const isCompressed = proxyRes.headers['content-encoding'] === 'gzip';
const decompressed = isCompressed ? await ungzip(buffer) : buffer;
You can also remove the 2 await on cheerio, Cheerio is not async and doesn't return an awaitable.
Final code
Here's the final code, which works. You mentioned that "it looks like node-http-proxy is dying a lot [...] depending on how many times I ran the server." I experienced no such stability issues, so your problems may lie elsewhere if that is happening (bad ram?)
const cheerio = require('cheerio');
const http = require('http');
const httpProxy = require('http-proxy');
const { ungzip } = require('node-gzip');
const host = 'https://github.com';
let proxy = httpProxy.createProxyServer({
secure: false,
changeOrigin: true
});
let option = {
target: host,
selfHandleResponse: true
};
proxy.on('proxyRes', function (proxyRes, req, res) {
console.log(`Proxy response with status code: ${proxyRes.statusCode} to url ${req.url}`);
if (proxyRes.statusCode == 301) {
throw new Error('You should probably do something here, I think there may be an httpProxy option to handle redirects');
}
let body = [];
proxyRes.on('data', function (chunk) {
body.push(chunk);
});
proxyRes.on('end', async function () {
let buffer = Buffer.concat(body);
try {
let $ = null;
const isCompressed = proxyRes.headers['content-encoding'] === 'gzip';
const decompressed = isCompressed ? await ungzip(buffer) : buffer;
const scriptTag = '<script src="my-customjs.js"></script>';
$ = cheerio.load(decompressed.toString());
$('body').append(scriptTag);
res.end($.html());
} catch (e) {
console.log(e);
}
});
});
let server = http.createServer(function (req, res) {
proxy.web(req, res, option, function (e) {
console.log(e);
});
});
console.log("listening on port 5051");
server.listen(5051);
I ended up writing a small Python Server using CherryPy and proxied the web app with mitmproxy. Everything is now working smoothly. Maybe I was doing it wrong with node-http-proxy but I also became sceptic about using it in a production environment.