Javascript OOP

Javascript is a prototypical langaage. Its OOP is achieved by prototype instead of class. Prototype is kind of like decorator patten, that decorates a initially bare object with more functionalities.

Some links to Javascript OOP:

• [1] Introduction to Object-Oriented JavaScript
• [2] JavaScript Classical Inheritance
• [3] JavaScript Private Members
• [4] Class-Based vs. Prototype-Based Languages
• [5] 3 ways to define a JavaScript class
• [6] Javascript - create object - with some depth

The most common syntax for defining a class is [3]:

if (typeof (classA == "undefined")) {

    // Another short-hand way of defining this class:  function classA() { ... }
    var classA = function() {
        this.property1 = 1;  // A public variable. Defined with "this.". To access, use "this.".
        var secret = 2;  // A private variable. Defined with "var". To access, don't use "this.".

        // A private method.
        // Another short-hand way of defining this:  function dec () { ... }
        var dec = function() {
             if (secret > 0) {
                secret -= 1;
            }
        }
       
        // A privileged method. Can access private variables and methods. Accessible to outside.
        // Defined with "this.".
        // Another way of defining this:  function getInfo() { ... }
        this.getInfo = function() {
            return secret + this.property1;
        }     
    }

    // A public method.
    classA.prototype.getColor = function() { return 'green'; }
}

To create an instance you do:

var objectA = new classA();

To inherit from classA you do something like this [2]:

function classB() {
    this.setValue(value);
} 
classB.inherits(classA);

Promiscuous multiple inheritance is possible but hard and may suffer from name collision.

Other related concepts include swiss inheritance, parasitic inheritance etc.

NMap - network scanning tool

The Official Nmap Project Guide to Network Discovery and Security Scanning

Nmap参考指南(Man Page)

Shell scripts to start and stop a server

Now I have a working Python|Authbahn websocket server. To start and stop both there are several steps to do.  The scripts here help to simplify the job.


== start_server.sh ==

export PYTHONPATH=.
export DJANGO_SETTINGS_MODULE=my_project.settings
daemonize  -c /django_projects/my_project  /django_projects/my_project/server/my_server.py

#
# Note here there is a need to setup PYTHONPATH and django project setting, since we have
# customized modules to use in the server.
# After setting up the path, when use daemonize then you need to specify
# the working directory with -c.
#

== stop_server.sh ==

output=`ps ax|grep my_server.py | grep -v grep`
echo killing process my_server.py
if [[ -z $output ]]; then
    echo 'this process doe not exist'
    exit 0
fi

set -- $output
pid=$1

echo killing proces $pid
kill -9 $pid
#sleep 2
#kill -9 $pid >/dev/null 2>&1


#
# Reference:
# [1]
# http://stackoverflow.com/questions/6437602/shell-script-to-get-the-process-id-on-linux
# The backticks allow you to capture the output of a comand in a shell variable.
# The set -- parses the ps output into words, and $2 is the second word on the
# line which happens to be the pid. Then you send a TERM signal, wait a couple
# of seconds for ruby to to shut itself down, then kill it mercilessly if it
# still exists, but throw away any output because most of the time kill -9 will
# complain that the process is already dead.
#
# [2]
# http://www.cyberciti.biz/tips/grepping-ps-output-without-getting-grep.html
# when ps aux | grep something, to avoid getting the line of grep, do either of
# 1) ps aux | grep something | grep -v grep
# 2) ps aux | grep [s]omething
# 3) ps aux | grep '[s]omething'
# for 2) and 3), it's actually a regular expression, [s] matches to s.
#

How to Install and Use Screen on an Ubuntu Cloud Server

Screen is a console application that allows you to use multiple terminal sessions within one window. The program operates within a shell session and acts as a container and manager for other terminal sessions, similar to how a window manager manages windows.

This is like the console version of Mac and Linux's multiple desktops. Very handy.

To run a program (say a server) in a screen session, detach it without killing the session:
     screen -d -m python server/server.py 80

This is like running the "daemonize" command, can make the program an independent daemon process.

[1] How to Install and Use Screen on an Ubuntu Cloud Server

Websocket

Websocket can be used to create real time chat and game services.

Autobahn|Python [3] is a WebSocket / WAMP library for Python 2 (using Twisted) and 3 (using asyncio). It's easy to setup and use.

Websocket and browser support [1]:

WebSocket is a protocol providing full-duplex communications channels over a single TCP connection. The WebSocket protocol was standardized by the IETF as RFC 6455 in 2011, and the WebSocket API in Web IDL is being standardized by the W3C.

WebSocket is designed to be implemented in web browsers and web servers, but it can be used by any client or server application. The WebSocket Protocol is an independent TCP-based protocol. Its only relationship to HTTP is that its handshake is interpreted by HTTP servers as an Upgrade request.[1] The WebSocket protocol makes more interaction between a browser and a website possible, facilitating live content and the creation of real-time games. This is made possible by providing a standardized way for the server to send content to the browser without being solicited by the client, and allowing for messages to be passed back and forth while keeping the connection open. In this way a two-way (bi-directional) ongoing conversation can take place between a browser and the server. A similar effect has been achieved in non-standardized ways using stop-gap technologies such as Comet.

In addition, the communications are done over TCP port number 80, which is of benefit for those environments which block non-web Internet connections using a firewall. The WebSocket protocol is currently supported in most major browsers including Google Chrome, Internet Explorer, Firefox, Safari and Opera. WebSocket also requires web applications on the server to support it.


Turn on websockets in firefox [2]:

1. Type about:config in address bar, and continue by clicking “I’ll be careful, I promise”
2. Set network.websocket.enabled  value to ‘true’ and set network.websocket.override-security-block preferences to ‘true’.
3. Restart Firefox browser.

== Change a websocker server to daemon ==

Each time you can run this to start a websocket server: python ./server.py

To change it to a daemon you can do this:
- add "#!/usr/bin/python" to top of server.py
- install daemonize [4]
- use absolute path of server.py, run this: daemonize /../server.py

Now server.py is started as a daemon. To find out which process it's running as and to shut it down, do:

- ps -aux | grep server.py

This will (usually, if you don't have other process with the name "server") find 2 entries, one for the server.py process, one for the grep command. Pick the former, you can watch its activity by:

- top -p [pid]

To kill it:

- kill -9 [pid]


[1] http://en.wikipedia.org/wiki/WebSocket
[2] http://techdows.com/2010/12/turn-on-websockets-in-firefox-4.html
[3] http://autobahn.ws/
[4] http://software.clapper.org/daemonize/ 
[5] websocket browser support

Monitor Linux (Ubuntu) network traffic in real time

== Monitor incoming network traffic in real time:
[http://manpages.ubuntu.com/manpages/lucid/man1/tcptrack.1.html]

ifstat
iftop
iptraf
tcptrack

== Commands to verify ports:
[https://www.serverpronto.com/accounts/knowledgebase.php?action=displayarticle&id=11]

nmap IP#
nmap localhost
netstat –ntulp

== to verify single port

netstat -nap | grep 

== to list all current rules in iptables

iptables -L

== For opening a TCP port:

iptables -A INPUT  -p tcp –dport -j ACCEPT

== For opening a UDP port:

iptables -A INPUT -p udp –sport   -j ACCEPT

== Save changes:

iptables-save > /etc/iptables.rules

== If you need to disable the firewall temporarily, you can flush all the rules using:

iptables -F

Sqlite3

Sqlite3 is a light-weighted database server. It comes directly with Django.

Here is an introduction to its use: http://www.sqlite.org/sessions/sqlite.html

Some common commands:

- to enter sqlite3 shell: sqlite3 [sqlite3 db filename]
- show all databases: .databases
- show all tables: .tables
- query a table: select * from sqlite_master;
- show all table schema: .schema
- backup database to another file: .backup another_db.db
- exit shell: .q, or .exit

Note that there is only 1 database per database file in Sqlite3. So there is no command like "use database1".

Some notes:

- For sqlite3 database to be writable, it should be writable by the web account, its containing folder should also be writable by the web account.

- If a column in missing in a table, you can do this to add it:
sqlite3 yourdb.db
> drop table bookmarks_bookmark;
> .quit
cd yourpythonproj
python manage.py syncdb
python manage.py runserver

Basically, syncdb cannot change integrate schema once the tables are created. You have to drop that table first (or maybe need to remove the database totally, which can be done by mv the current db.sqlite3 to db.sqlite3.bak and do syncdb).

shell script to concat all files

This shell script runs on *nix and concatenates all files into a single one, including file name before file content. This is useful, for example, when you want to print out all files to read.

#!/bin/bash

#
# Dump multiple files to one text file.
# By: HomeTom. 3/11/2015
#

cd my_dir;  # go to the target file directory.

ct=0;  # keep a counter of file.

for i in README.md manage.py my_dir/*.py;
do
    ct=$(($ct + 1));
    echo;
    echo == File $ct: "$i" ==;  # print file name and its counter.
    echo;
    cat "$i";
done

This second shell script is improved from the above, by adding a table of contents (a list of all files) to the beginning of output.

#!/bin/bash

#
# Dump multiple files to one text file.
# By: HomeTom. 3/11/2015
#

cd my_dir;  # go to target file directory.

# define file list.
arr=(README.md manage.py my_dir/*.py);

# 1) get table of contents.
echo Table of Contents;
echo;
ct=0;  # keep a counter of file.
for i in ${arr[@]};
do
    ct=$(($ct + 1));
    echo == File $ct: "$i";  # print file name and its counter.
done

# 2) get file content.
ct=0;  # keep a counter of file.
for i in ${arr[@]};
do
    ct=$(($ct + 1));
    echo;
    echo == File $ct: "$i" ==;  # print file name and its counter.
    echo;
    cat "$i";
done

Django framework

To tell if you have Django installed with Python:
$ python -c "import django; print(django.get_version())"

Setup Django on bluehost:

[1] Python 2.7 + Django 1.4 on Bluehost
[2] Django on Bluehost in Five Minutes
[3] Django documentation
[4] Django documentation - tutorial

To access database using Django, see:
[5] Writing your first Django app, part 1 - create project and model (database)
[6] Writing your first Django app, part 2 - create admin site superuser
      basically it's by command: $ python manage.py createsuperuser

== Appendix 1. Python 2.7 + Django 1.4 on Bluehost ==

To avoid loss of previous web page, the basic process [1] is copied here:
Monday, April 30, 2012
Python 2.7 + Django 1.4 on Bluehost

Bluehost is a cheap shared hosting provider, that allows to run applications using fastCGI, among others, webapps created with django - python web framework. In this post you will find information how to install the newest (in April 2012) versions of python and django and how to configure them for  bluehost.

First you need to enable ssh access to your bluehost account. Sign in to their control panel, enter Security > SSH/Shell Access and click Manage SSH Access button. Select SSH Access enabled and submit. Now connect via ssh to your bluehost account.

Python
Download, extract and install python 2.7 in your home directory:
mkdir python27
wget http://www.python.org/ftp/python/2.7.2/Python-2.7.2.tgz
tar xzvf Python-2.7.2.tgz
cd Python-2.7.2
./configure -prefix=/homeX/your_username/python27 --enable-unicode=ucs4
make
make install

Rename the python binary (to avoid overriding current system python version - if you're not using default bluehost python for anything else you can skip this step):
mv ~/python27/bin/python ~/python27/bin/python27
Add new python directory with binaries to your PATH environment variable. To do this edit .bashrc file in your HOME directory, for example with vim:
vim ~/.bashrc
and add the line at the end of the .bashrc file:
PATH=/homeX/your_username/python27/bin:$PATH
load the new settings:
source .bashrc
and then test it:
python27
You should see something similar to:
Python 2.7.2 (default, Apr 11 2012, 01:29:09)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-52)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>

New python is available for you. Remember to use command python27 instead of python from now on.

Pip
We're going to use pip here - easy to use python package manager. It requires setuptools before it can be installed:

wget http://pypi.python.org/packages/source/s/setuptools/setuptools-0.6c11.tar.gz
tar xzvf setuptools-0.6c11.tar.gz
cd setuptools-0.6c11
python27 setup.py install
cd
wget http://pypi.python.org/packages/source/p/pip/pip-1.1.tar.gz
tar xzvf pip-1.1.tar.gz
cd pip-1.1
python27 setup.py install

Now thanks to our earlier PATH settings pip is available from command line.

Django installation
With pip you can install latest stable Django (in my case 1.4) simply by entering:
pip install Django
Wait for download and installation process to complete. After that django is installed and command django-admin.py available. You will also probably need python driver for mysql database. Install it with pip:
pip install MySQL-python
If you're going to use PosgreSQL install psycopg2 library:
pip install psycopg2

Django configuration
Create django project:
django-admin.py startproject myproject

Decide what url should be used to access your django app. In my case it will be subdirectory:
http://somedomain.com/myproject

Prepare directory in bluehost public_html:
mkdir public_html/myproject
cd public_html/myproject


In this directory create fastcgi file (for example: mysite.fcgi) with content:
#!/homeX/your_username/python27/bin/python27
import sys, os

# Add a custom Python path.
sys.path.insert(0, "/homeX/your_username/python27")
sys.path.insert(13, "/homeX/your_username/myproject")

os.environ['DJANGO_SETTINGS_MODULE'] = 'myproject.settings'
from django.core.servers.fastcgi import runfastcgi
runfastcgi(method="threaded", daemonize="false")

Remember to change /homeX/your_username to your home directory path on bluehost. Change myproject.settings to correct project name. The first line contains path to your custom python binary.

Django fastcgi requires flup so install it with pip:
pip install flup
Also change file permissions to mysite.fcgi:
chmod 0755 mysite.fcgi

Now create .htaccess file in the public_html/myproject directory with content:
AddHandler fcgid-script .fcgi
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ mysite.fcgi/$1 [QSA,L]


That's all. You should see your django start page on: http://somedomain.com/myproject. You can start coding some real stuff in django now. Remember to install every python and django packages using pip - that way they will be available to your django app. Also keep in mind that every django commands like syncdb, collectstatic  etc. should be run using python27 for example:
python27 manage.py syncdb


== Appendix 2. Python/Django setup on Mac ==

-- Intall wget on Mac --

Note, on Mac, to install wget, you need to download from http://ftp.gnu.org/gnu/wget/, and then do:
./configure --with-ssl=openssl
make
make install

See:
[5] http://coolestguidesontheplanet.com/install-and-configure-wget-on-os-x/

-- Install setuptools --

For more recent version of setup tools, follow instruction at:
[6] https://pypi.python.org/pypi/setuptools

You may need superuser privilege:
wget https://bootstrap.pypa.io/ez_setup.py -O - | sudo python

-- Install mysql-python --

When install mysql-python, it may report "EnvironmentError: mysql_config not found". See
[7] http://stackoverflow.com/questions/25459386/mac-os-x-environmenterror-mysql-config-not-found
In that case, do:

> locate mysql_config
# this should report something like: /usr/local/mysql-5.5.18-osx10.6-x86_64/bin/mysql_config.
# then add it to current path:
> PATH=$PATH:/usr/local/mysql-5.5.18-osx10.6-x86_64/bin/
> mysql_config
# this should show that mysql_config is available. Finally:
> sudo pip install mysql-python

-- Install mod_fcgid --

On mac, you may need to install mod_fcgid. Without mod_fcgid, will get this error:
/mysite.fcgi/ was not found on this server.
E.g.: http://stackoverflow.com/questions/24446496/deploying-django-error-mysite-fcgi-was-not-found-on-this-server-in-shared

To install mod_fcgid, you need to install macport first. See:
[8] http://www.dionysopoulos.me/apache-mysql-php-server-on-mac-os-x-with-multiple-simultaneous-php-versions/

To install macport, go to: http://www.macports.org/install.php. Use "pkg" installer.
Then do:
sudo port selfupdate
sudo port install mod_fcgid
sudo cp /opt/local/apache2/modules/mod_fcgid.so /usr/libexec/apache2

Then: sudo vi /etc/apache2/httpd.conf

Find all the LoadModule lines. After the last one add:
LoadModule fcgid_module libexec/apache2/mod_fcgid.so

Then restart apache:
sudo apachectl restart


== Appendix 3. Use Python in the web ==

Use Python in the web: https://docs.python.org/2/howto/webservers.html

Save code below as a.fcgi. This can run as fastcgi.

#!/usr/bin/env python
# -*- coding: UTF-8 -*-

from cgi import escape
import sys, os
from flup.server.fcgi import WSGIServer

def app(environ, start_response):
    start_response('200 OK', [('Content-Type', 'text/html')])

    yield 'Use Python in the web: https://docs.python.org/2/howto/webservers.html'
    yield '<h1>FastCGI Environment</h1>'
    yield '<table>'
    for k, v in sorted(environ.items()):
         yield '<tr><th>%s</th><td>%s</td></tr>' % (escape(k), escape(v))
    yield '</table>'

WSGIServer(app).run()


== Appendix 4. Install rest_framework ==

sudo pip install djangorestframework

怎样尊重一个程序员

怎样尊重一个程序员 (from http://www.yinwang.org)

Why I left Google.