Tag: node.js

Async waterfall example nodejs

Posted on by admin

To avoid callback hell , a very useful tool for structuring calls in a sequence and make sure the steps pass the data to the next step.

var async = require('async');

async.waterfall(
    [
        function(callback) {
            callback(null, 'Yes', 'it');
        },
        function(arg1, arg2, callback) {
            var caption = arg1 +' and '+ arg2;
            callback(null, caption);
        },
        function(caption, callback) {
            caption += ' works!';
            callback(null, caption);
        }
    ],
    function (err, caption) {
        console.log(caption);
        // Node.js and JavaScript Rock!
    }
);

nJoy 😉

Node.js Start script or run command and handoff to OS (no waiting)

Posted on by admin

Sometimes you want to run something in the OS from your node code but you do not want to follow it or have a callback posted on your stack. The default for child_process spawning is to hold on to a handle and park a callback on the stack. however there is an option which is called detached.

var spawn = require('child_process').spawn;
spawn('/usr/scripts/script.sh', ['param1'], {
    detached: true
});

You can even setup the environment of the call to add stdio and stderr pipes to the call and connect them to OS fs descriptors like this:

var fs = require('fs'),
    spawn = require('child_process').spawn,
    out = fs.openSync('./out.log', 'a'),
    err = fs.openSync('./err.log', 'a');

spawn('/usr/scripts/script.sh', ['param1'], {
    stdio: [ 'ignore', out, err ], // piping stdout and stderr to out.log
    detached: true
}).unref();

The unref disconnects the process. from the parent it equates to a disown in shell.

Thanks to O/P : https://stackoverflow.com/questions/25323703/nodejs-execute-command-in-background-and-forget

Also Ref: https://nodejs.org/api/child_process.html#child_process_child_process_spawn_command_args_options

and

https://github.com/nodejs/node-v0.x-archive/issues/9255

nJoy 😉

hex2bin in node.js

Posted on by admin

Basically it’s all over-engineered and does not work well.

responses are out of alignment and though text-wise they are the same bit wise everything is all over the place :

curl http://phpimpl.domain.com/testhex.php | xxd

00000000: de56 a735 4739 c01d f2dc e14b ba30 8af0 .Q.%G9.....;.0..

curl http://nodejs.domain.com/ | xxd

00000000: c39e 56c2 a725 4739 c380 c3ad c3b1 c39c ..Q..%G9........
 00000010: c3a1 37c2 6b30 c28f c3b0 ..;..0....

The proper way to implement this in node is :

function hex2bin(hex){
return new Buffer(hex,”hex”);
}

curl http://nodejs.domain.com/ | xxd

00000000: de56 a735 4739 c01d f2dc e14b ba30 8af0 .Q.%G9…..;.0..

nJoy 😉

Install node.js on Centos 6.8

Posted on by admin

Epel’s yum install does not cut it anymore at time of writing installing node.js causes a mass of 404s and file not found.

 

current best approach :

Enterprise Linux and Fedora

Including Red Hat® Enterprise Linux® / RHEL, CentOS and Fedora.

Node.js is available from the NodeSource Enterprise Linux and Fedora binary distributions repository. Support for this repository, along with its scripts, can be found on GitHub at nodesource/distributions.

Note that the Node.js packages for EL 5 (RHEL5 and CentOS 5) depend on the EPEL repository being available. The setup script will check and provide instructions if it is not installed.

Run as root on RHEL, CentOS or Fedora, for Node.js v4 LTS Argon:

curl --silent --location https://rpm.nodesource.com/setup_4.x | bash -

Alternatively for Node.js v5:

curl --silent --location https://rpm.nodesource.com/setup_5.x | bash -

Alternatively for Node.js 0.10:

curl --silent --location https://rpm.nodesource.com/setup | bash -

Then install, as root:

yum -y install nodejs

Optional: install build tools

To compile and install native addons from npm you may also need to install build tools:

yum install gcc-c++ make
# or: yum groupinstall 'Development Tools'

Available architectures:

  • i386 (32-bit, not available for EL7)
  • x86_64 (64-bit)

Supported Red Hat® Enterprise Linux® versions:

  • RHEL 5 (32-bit and 64-bit)
  • RHEL 6 (32-bit and 64-bit)
  • RHEL 7 (64-bit)

Supported CentOS versions:

  • CentOS 5 (32-bit and 64-bit)
  • CentOS 6 (32-bit and 64-bit)
  • CentOS 7 (64-bit)

Supported CloudLinux versions:

  • CloudLinux 6 (32-bit and 64-bit)

Supported Fedora versions:

  • Fedora 21 (Twenty One) (32-bit and 64-bit)
  • Fedora 20 (Heisenbug) (32-bit and 64-bit)
  • Fedora 19 (Schrödinger’s Cat) (32-bit and 64-bit)

Other distributions known to be supported:

  • Oracle Linux (mirrors RHEL very closely)
  • Amazon Linux (tested on 2014.03)

nJoy 😉

 

package.json sample

Posted on by admin

This is the basic structure for a node.js package file

{
"name": "Express-Basic",
"description": "Demonstrating Express",
"version": "0.0.1",
"private": true,
"dependencies": {
"express": "3.x"
}
}

nJoy 😉

Node.js and Express with HTTPS

Posted on by admin

Quoting from the doco + some missing stuff:

var express = require('express');
var https = require('https');
var http = require('http');
var app = express();
var fs = require('fs');

var options = {
key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem')
};

http.createServer(app).listen(80);
https.createServer(options, app).listen(443);

nJoy 😉

Node.js handling mysql disconnects.

Posted on by admin

You may lose the connection to a MySQL server due to network problems, the server timing you out, the server being restarted, or crashing. All of these events are considered fatal errors, and will have the err.code = 'PROTOCOL_CONNECTION_LOST'. See the Error Handling section for more information.

A good way to handle such unexpected disconnects is shown below:

 

var db_config = {
  host: 'localhost',
    user: 'root',
    password: '',
    database: 'example'
};

var connection;

function handleDisconnect() {
  connection = mysql.createConnection(db_config); // Recreate the connection, since
                                                  // the old one cannot be reused.

  connection.connect(function(err) {              // The server is either down
    if(err) {                                     // or restarting (takes a while sometimes).
      console.log('error when connecting to db:', err);
      setTimeout(handleDisconnect, 2000); // We introduce a delay before attempting to reconnect,
    }                                     // to avoid a hot loop, and to allow our node script to
  });                                     // process asynchronous requests in the meantime.
                                          // If you're also serving http, display a 503 error.
  connection.on('error', function(err) {
    console.log('db error', err);
    if(err.code === 'PROTOCOL_CONNECTION_LOST') { // Connection to the MySQL server is usually
      handleDisconnect();                         // lost due to either server restart, or a
    } else {                                      // connnection idle timeout (the wait_timeout
       throw err;                                 // server variable configures this)
    });
}

handleDisconnect();

As you can see in the example above, re-connecting a connection is done by establishing a new connection. Once terminated, an existing connection object cannot be re-connected by design.

With Pool, disconnected connections will be removed from the pool freeing up space for a new connection to be created on the next getConnection call.