Need to build a back-end service using node-js which does the following.
Accepts file-upload from client (browser)
Save the file on disk and update DB (mongodb) with new filename and status as saved
Starts an long running process to parse the file ( written in python) and get feedback ( progress, error, success) , update DB with status feedback
How do we call # 3 from node.js - it could be system call like python parse_file.py filename
app.post('/upload',function(req,res, next){
// what should go here to call the process
res.writeHead(201, {'Content-type': 'text/plain'});
res.end("File uploaded.");
}
});
You can use require('child_process').spawn() or require('child_process').exec() to spawn a child process. The docs for those can be found at https://nodejs.org/dist/latest-v6.x/docs/api/child_process.html#child_process_child_process_spawn_command_args_options
Related
I am a beginner in node js and have a couple of months experience with javascript, have finished codecademy js and jquery introductory courses and learned more about js in the internet and have an understanding of html and css in intermediate level or near to intermediate level. I am a complete noob in getting the js and node js to run alltogether. Using VS code for text editor. Node.js is installed from their original homepage, using node.js APP. File named global js.is sticked to 2 folders: the same with node.js and desktop folder for vs code files( the ones I create in VS code as projects or just simple files). The darn thing just doesn't make sense to me and I dont get this mess to work either. To be more specific, then:
I have 2 issues:
Firstly, did an install: npm install javascript bla bla. It was a sucsess, mkdir and cd were successful. NUL >introduction.js says access denied.
Alos I have a file named global.js. It is sitting in the same foler as node.js + the original version of this fie is in the same folder of desktop vs code's excercises. I can't make my node.js open this global.js file.
How do I overcome of these issues?
I tried to use this as a guide line: How to run a hello.js file in Node.js on windows?.
Did following parts of that above: changed account type to ADMINISTRATOR via appwize smth from run. Called cmd from run after having given myself and admin status permanently and windows logged me off and back on again. Tried to run the file from command prompt, declaring the exact path to file in cmd. It reached to the path, showed no error, went to the file from there. No errors, NOTHING didn't happen... Tried the global install whatever faced an issue in there and got stuck with it.
I need some help in here! Would be nice if someone could explain to me what is wrong and what's the basic concept of using node.js or what are the alternative ways to programmetely launch it?
Do I need to use the node.js console or node.js app?
CODE IN main. js :
var http = require("http");
var path= require ("path");
http.createServer(function (request, response) {
// Send the HTTP header
// HTTP Status: 200 : OK
// Content Type: text/plain
response.writeHead(200, {'Content-Type': 'text/plain'});
// Send the response body as "Hello World"
response.end('Hello World\n');
}).listen(8081);
// Console will print the message
console.log('Server running at http://127.0.0.1:8081/');
console.log (`Rock on World from ${path.basename(__filename)}`);
var http = require("http");
http.createServer(function (request, response) {
// Send the HTTP header
// HTTP Status: 200 : OK
// Content Type: text/plain
response.writeHead(200, {'Content-Type': 'text/plain'});
// Send the response body as "Hello World"
response.end('Hello World\n');
}).listen(8081);
// Console will print the message
console.log('Server running at http://127.0.0.1:8081/');
No need to use any special console, on windows, standard cmd is enough.
Check if node is installed properly first. Run node -v and see if it prints its version.
Create a folder for your project and make sure your are in it before executing node or npm. Node.exe doesn't have to be in the project folder as long as it is in the path (by default it is)
Make sure your source files in that project folder. (test.js, introduction.js .. whatever you will run)
I have some data that I want to store locally and to be able to pull it dynamically, maybe in another session or after the browser was closed and all browser data was cleared.
I run the site with http-server CLI command and navigate to localhost to access it from the browser.
How can I send data to the server side so the server side will save the data as a file?
I tried to do an ajax post request to see if something happens in the console, but it just returned 404 and nothing came up in the console.
The docs don't mention anything about post requests: https://www.npmjs.com/package/http-server
PS: I have to run this with http-server, this is an offline project.
You will not be able to do this with http-server alone, because http-server can only serve static content and cannot be used to run any code on the server side.
You will have to write a backend yourself, possibly using a framework like Express, Hapi, Restify, Loopback etc. and serve your static files that you need with your new backend, or keep it served as you do now but then you will probably need to take CORS into account if you use different ports for your data saving/retrieving endpoints and your static content - unless you run a reverse proxy that makes it all appear on the same host name and port.
You can use the file system to save the data or you can use a database - either a standalone database like Mongo or Postgres or an embedded database like SQLite or Loki.
For examples on how to serve static content in your own backend see:
How to serve an image using nodejs
You should use express for this kind of stuff. You can easily make methods that handle certain requests.
Here is an exmaple on how to handle a get request by just sending some data
var express = require('express')
var app = express()
app.get('/', function (req, res) {
res.send('Hello World')
})
app.listen(3000)
And you can use the fs api from node itself to write data.
var fs = require('fs')
fs.writeFile('message.txt', 'Hello Node.js', (err) => {
if (err) throw err;
console.log('It\'s saved!');
});
Note: the fs example uses arrow functions. You can find more information here
So, I am wondering if there is a way to connect to the mongoDB I have setup in my Cloud9 from an html. I mean, I have already connected to the db from the terminal and everything is working like a charm but I need to do some stuff inside my script in an html document and when I try calling the function which contains this code it does nothing
var MongoClient = require('mongodb').MongoClient
, format = require('util').format;
MongoClient.connect('mongodb://127.0.0.1:27017/ingesoft', function (err, db) {
if (err) {
throw err;
} else {
console.log("successfully connected to the database");
}
db.close();
});
I have saved the same code into a "file.js" and ran it from console using node file.js and it outputs into the console log "successfully connected to the database", plus the terminal which is running mongo's connection shows me one more connection to the db. The thing is, when I try to run that code inside my script it doesn't work. Sorry for my ignorance I am new to mongo.
Any help would be much appreciated
To simplify your question, here's what's going on:
node file.js containing the code in your question is working
pasting the same code to your html file is not
So, getting to the bottom of the issue, let's ask first: what's the difference between running node file.js and putting the code in html?
The difference is that node ... is running on your Cloud9 workspace (let's call it the server machine).
Your MongoDB server is also running on that server machine
The mongodb npm package you installed is also present on the server machine
The url: mongodb://127.0.0.1:27017/ingesoft references 127.0.0.1 which is the localhost for your server
whereas with the code on your browser:
The code is being run on your customer's machine
That machine doesn't have your Mongodb server
Browser's usually don't support require
You can do requires if you bundle code and use something like webpack or browserify. Did you perhaps do that?
If you did indeed package everything, was the mongodb package that you're requiring packaged?
Can the mongodb package be run from the client side?
The url: mongodb://127.0.0.1:27017/ingesoft references 127.0.0.1 which is the localhost for your customer's machine
Basically, as you can see from the above, the two are very different.
If you want to talk to your db, a lot of people go the following route:
Make a server application that implements some form of REST API
That REST API talks to your DB
Your client code knows how to talk to the REST API and get the required data
That way, you only talk to your MongoDB using your server, and the client can talk to your server via the internet.
This is, of course, an oversimplification, but I hope this resolves your confusion.
So i have been looking at how to use mongodb from this tutorial: http://doduck.com/node-js-mongodb-hello-world-example/
I have installed mongodb locally within my project folder that contains my html css and js, i run npm list mongodb within the project folder and i get the mongodb version. I haven't installed it globablly, but as far as i know that is ok right?
Anyways, i tried adding the example from the tutorial to test connect to a mongodb database. I just created a function and called it as soon as my page loads:
function connectMongo(){
alert("test1");
var MongoClient = require('mongodb').MongoClient;
alert("test2");
var myCollection;
var db = MongoClient.connect('mongodb://127.0.0.1:27017/test', function(err, db) {
if(err){
throw err;
alert("mongoerror");
}
alert("connected to the mongoDB !");
// myCollection = db.collection('test_collection');
});
}
The first test alert works, but the second test does not appear. However, the rest of the code on the page still runs, so i dont think there is a syntax error. I have no idea how exactly im meant to run this example, can anyone tell me why my function is exiting after the line
var MongoClient = require('mongodb').MongoClient;
I also have mongoose installed, even though im not quite sure if im even using it in my example here
Sorry if my question is kind of vague, i have honestly no idea what im doing here
First although Nodejs is written in Javascript, you must clearly distinguish between client and server functions. Javascript's alert() is useful to pop messages on your browser. This is isn't something Nodejs does as it is a server app.
Forget about alert("message"); You want to use console.log("message"); to view log info on the server console.
Prerequisite
Let's quickly review Client-Server web interactions:
Server is up and running
Client Requests page via browser
Page shows up on the client's browser
Step 1
The missing step for you is (1), because the server is not up and running.
This is done by typing the following on your terminal:
$ node name_of_file_here.js
If there are errors in your syntax, or missing dependencies the console will log the errors. If none appear all should be well.
Step 2
Now at this point, you still can't expect to see anything "relevant" on the browser, because your server although it has setup a MongoDB instance, is still not listening to requests from clients.
Some code needs to be added:
'use strict';
var http = require('http');
var PORT=8009;
var MongoClient = require('mongodb').MongoClient;
// Connect to the db
var d = MongoClient.connect("mongodb://localhost:27017/exampleDb", function(err, db) {
if(!err) {
console.log("We are connected");
}
});
//Create a server
var server = http.createServer(function(request, response) {
console.log("received request");
// use MongoClient to get relevant data
// var relevant_data = ...;
// response.write(relevant_data);
response.write("hey there");
response.end();
});
server.listen(PORT, function(){
//Callback triggered when server is successfully listening. Hurray!
console.log("Server listening on: http://localhost:%s", PORT);
});
Final Note
I am in no way a MongoDB guru, but I believe a mongodb service (server) has to be running on your system for the MongoDB client to be able to create a connection.
It sounds like you are trying to run the mongo connection javascript in the browser. The mongodb connection runs on the server via the node executable. So this is javascript code in the web app running server side, rather than javascript delivered by the web app to a browser to run client side.
Create a file test.js
function connectMongo(){
var MongoClient = require('mongodb').MongoClient;
console.log('MongoClient is',typeof MongoClient)
var myCollection;
var url = 'mongodb://127.0.0.1:27017/test';
var db = MongoClient.connect(url, function(err, db) {
if(err){
console.log("mongoerror", err);
throw err;
}
console.log("connected to the mongoDB!");
myCollection = db.collection('test_collection');
});
}
connectMongo()
Then on your system, at a command or shell prompt, run
node test.js
It should print
$ node test.js
MongoClient is function
connected to the mongoDB!
^C
Once your server is connected to the database you can pass messages from your front end javascript to the backend server code. Normally this is done via an Ajax http request, so your javascript makes additional HTTP requests in the background. The JQuery client side library provides a simple cross browser API for this. You could also use Websockets to pass message back and forth from the server via SocketIO
For the basics of a Node/Express/MongoDB app try this: http://cwbuecheler.com/web/tutorials/2013/node-express-mongo/
I'm running node.js v0.11 on Android (via https://github.com/paddybyers/node). I attempted to try out the "Hello HTTP" example found here: http://howtonode.org/hello-node, however, I ran into problems.
The server starts fine, but as soon as I attempt to connect to the http server (by visiting http://localhost:8000/), I get this error:
net.js:1156
COUNTER_NET_SERVER_CONNECTION(socket);
^
ReferenceError: COUNTER_NET_SERVER_CONNECTION is not defined
at TCP.onconnection (net.js:1156:3)
My code is exactly the same as the Hello HTTP example:
//Load the http module to create an http server.
var http = require('http');
// Configure our HTTP server to respond with Hello World to all requests.
var server = http.createServer(function (request, response) {
response.writeHead(200, {"Content-Type": "text/plain"});
response.end("Hello World\n");
});
// Listen on port 8000, IP defaults to 127.0.0.1
server.listen(8000);
// Put a friendly message on the terminal
console.log("Server running at http://127.0.0.1:8000/");
How can I fix this?
Thanks!
Compile Node.js with the HAVE_PERFCTR option. (You Need to implement your own perfctrs for Android. See node_counters.cc line 130).
It should be also possible to define the missing functions in your script as empty functions.
PS.:
You also need DTRACE.
I simply commented out all COUNTER_NET_, COUNTER_HTTP_, DTRACE_NET_, and DTRACE_HTTP_ calls in the javascript files under lib/. This amounted to about 10 or so lines that I commented out of net.js and http.js.
I think that js2c.py is supposed to process src/macros.py and src/perfctr_macros.py to effectively do this 'commenting out' for you when it serializes the scripts under lib/ to C arrays in out/release/src/node_natives.h, but that doesn't seem to be happening.