What is FTP? And what is used for?

FTP is the abbreviation of File Transfer Protocol which is a protocol from application layer of the TCP/IP networking protocol. FTP works on top of TCP layer to provide a standard and uniform way of exchanging files remotely.

Because FTP works on top of TCP, it is connection oriented which means before file operation, a connection establishing is required and after completing the file operation a connection release is performed.

Differences from HTTP

Alike HTTP, FTP is composed from several text commands. HTTP instruction are done on a resource which can be static file, dynamic file or even virtual object. On the other side in the case of FTP, the commands are tightly related to a single file operation. For example there is instruction for file list, file upload, file download and so on. FTP is considered faster than HTTP in terms of file transfer because it is optimized for big files transfers and there is no much headers overhead comparing to HTTP.

Common FTP commands list

The following are list of the common FTP commands found in the standard FTP client.

Anonymous FTP

Anonymous FTP is a feature or implementation of FTP server to allow any one to login into the FTP client with a public user name (any arbitrary email address) and with no password. Usually anonymous FTP is offered on public networks and universities to allow download of open source software using anonymous FTP.

ASCII mode vs BINARY mode

ASCII mode is a mode to allow transfer of readable roman letters text. With ASCII mode enabled the transfer of any binary or compressed files will just transfer a corrupted copy of the files. So the usage of this mode should be done with caution to make sure no binary files are transferred.
On the contrary a binary mode allows the transfer of binary files (i.e. executable files, images or zip files)

FTP PASV mode vs ACTIVE mode

ACTIVE MODE
Active modes is a transfer mode on which when a file transfer command requested by the client, the client should listen to a different non standard port and send the port number to the server in the request. Then the server will connect to this new port to start the data transfer. This method obviously will not work if the client machine is limited on ports or if there is a firewall on the client machine that prevent listening on non standard ports which is very common practice by security softwares. So as a resolution, PASSIVE mode was developed.

PASSIVE MODE
On PASSIVE mode the FTP server will start listening on a non standard port after it receives a file transfer request from the client (provided that PASV mode is enabled) then it will send the port number to the client in the response to the transfer request. After that the client should connect to this new port numeber and the transfer begines.

Popular FTP clients

• File Zilla: A windows based FTP client software that is open source.
• FireFTP: A Firefox addon that is open source and free ware.

Popular FTP Servers

FTP Servers With GUI / Windows based

• File Zilla: An open source FTP server software that works on windows.
• WS FTP: Stands for WinSock File Transfer Protocol. It is non free windows based software.

Command Line Based FTP Servers / Linux based

• vsftpd(Very Secure FTP Daemon): An open source software available on linux that support FTP and SFTP.
• Pure-FTPd: Another open source software available on linux and BSD.

What is SFTP?

SFTP is a secure protocol which works on top of SSH protocol. It provides a similar sets of FTP commands but commands and data are encrypted preventing intruders from stealing sensitive data or password information. A FTP software alone can not interpolate with SFTP, it must support SFTP protocol explicitly to be able to connect to SSH server.

FTP alternatives

• Web based file manager
  Some web hosting providers do not provide FTP access especially free hosting in this case there will be usually web based file manager provided which provide access to basic file operations like file upload, download, files list, delete, edit and some file managers provide some more advanced operations like file move, copy, zip extraction and zip creation. One of the popular file manager software is the one provided as a part of cPanel.
  

What is Regular Expressions?

Regular expressions is a technique or a language for telling a programming language or text editor how to parse a text. In a little bit more detail, it is used to represent a pattern using some special characters then this pattern is searched through given text and the matched text is extracted or undergone some operation i.e update, replace, delete.

Here are the most common regular expressions build blocks:-

The expressions above can be combined to form a pattern that validates any pattern. i.e. email, zip code, telephone number or credit cards.

The regular expression for validating an e-mail:-

The regular expression for validating a url :-

The regular expression for validating a telephone number:-

The regular expression for validating a visa credit card number:-

The regular expression for validating a master card number:-

The regular expression for validating US zip codes:-

The regular expression for matching IP address:-

The regular expression for matching a date in the format dd/mm/yyyy:-

What is HTTP? And what is it used for?

HTTP is the abbreviation for Hyper Text Transfer Protocol. Hyper Text means HTML pages. The protocol is one of the protocols included in the application layer of TCP/IP which works on top of TCP (Transmission Control Protocol) that provides a connection oriented reliable bytes stream connection. In easier way to say, HTTP works like there is already connection between source and destination that accepts text data. The protocol is composed from HTTP Request and HTTP Response each of them has certain keywords to distinguish type or request or response status.

Types of HTTP Requests

• The first HTTP request type is GET request, its syntax is as following:-

  GET /index.html HTTP/1.0

  1	GET /index.html HTTP/1.0

  GET means a get request that is asks for a resource located at the server. The resource location in the example is /index.html which refers to the file index.html located at the root directory. Also index.html can be omitted and replaced with just /
  HTTP/1.0 is the protocol version used.

• The second HTTP request type is POST request, its syntax is as following:-

  POST /path/to/script.php HTTP/1.0 User-Agent: Mozilla/1.0 Content-Type: application/x-www-form-urlencoded Content-Length: 23 var1=value&var2=value2

  1 2 3 4 5 6

  POST /path/to/script.php HTTP/1.0 User-Agent: Mozilla/1.0 Content-Type: application/x-www-form-urlencoded Content-Length: 23   var1=value&var2=value2

  POST means a posting data to some script located at the server. The script location in the example is /path/to/script.php. The data posted is var1=value and var2=value2 here, two variable posted to the script. It is the responsibility of the script to fetch and interpret those values.
  HTTP/1.0 is the protocol version used.

• The third HTTP request type is PUT Request:-

  PUT /path/to/script.php HTTP/1.0 User-Agent: Mozilla/1.0 Content-Type: application/x-www-form-urlencoded Content-Length: 23 var1=value&var2=value2

  1 2 3 4 5 6

  PUT /path/to/script.php HTTP/1.0 User-Agent: Mozilla/1.0 Content-Type: application/x-www-form-urlencoded Content-Length: 23   var1=value&var2=value2

  From the example above, a PUT request is pretty much the same as POST request the main difference is that PUT request usually used to either create new resource or replace existing resource. While POST is historically used to create new resource only. Of course this is up to the handler script and not part of the protocol itself.

• The last HTTP request type is DELETE request:-

  The server is requested to delete the indicated resource or move it to inaccessible location.

HTTP Response Codes

• 200

  Status: 200 OK

  1	Status: 200 OK

  Means success or resource found.

• 400

  Status: 400 Bad Request

  1	Status: 400 Bad Request

  Means the request is malformed or not supported by the server.

• 401

  Status: 401 Unauthorized

  1	Status: 401 Unauthorized

  Means to access the required resource an authorization headers required.

• 403

  Status: 403 Forbidden

  1	Status: 403 Forbidden

  Means the requested resource is forbidden. An authorization will not help.

• 404

  Status: 404 Not Found

  1	Status: 404 Not Found

  Means the requested resource or file not found.

• 500

  Status: 500 Internal Error

  1	Status: 500 Internal Error

  The server encountered a fatal condition which prevented it from responding to the request.

• 301

  Status: 301 Moved URI: http://new-url/path/to

  1 2	Status: 301 Moved URI: http://new-url/path/to

  Means the requested resource moved to the indicated location permanently.

• 302

  Status: 302 Found URI: http://new-url/path/to

  1 2	Status: 302 Found URI: http://new-url/path/to

  Means the requested resource moved to the indicated location temporarily
  .

• 304

  Status: 304 Not Modified

  1	Status: 304 Not Modified

  Means the requested resource found but has not been modified since last cached version.

Finally, the following figure depict a real HTTP request and response and shows some of the most commonly used headers.

Why Dynamic IP is made?

Dynamic IP means dynamically assigning a new IP each time a machine is connected to the internet or to a router. Dynamic IP mechanism existent simply to be able to reuse the allocated IP with another machine when the connected machine is shutdown.

IPv4 and its limitation

IPv4 consists of 32 bits divided into four parts each part is 8 bits and is written in decimal form and all parts separated by a dot (.)

By simple calculations one would conclude that all combinations from 0.0.0.0 until 255.255.255.255 forms roughly 4 Billions of addresses. Looking at nowadays internet, there are many servers and users connected to the internet and usable address space is becoming overwhelmingly limited.

DHCP Servers

Due to this reason when a machine is disconnected from internet (user shutdowns his PC) there is a need to free up the allocated IP to use it with another machine.
This need is covered by dynamic IP allocation which means a machine will get a new IP each time it connects to the internet. The server responsible on this process is called DHCP Server (Dynamic Host Control Protocol) and it is available as a builtin software in all routers.

IPv6

IPv6 is the new age of internet addresses. It is a huge address space with 128 bits divided into 8 parts each is 16 bits written into hexadecimal and separated by colons (:)

By simple calculations, this new space provides a range of up to 3 x 10 power 38 or three hundreds trillions trillions trillions addresses. It is said that with IPv6, there will be assignable address for each molecule on earth.

What is HTML? What is CSS? What are JavaScript, PHP and MySQL?

What is HTML?

HTML is a static language for text formatting for web pages use. All web pages on the web consists of HTML which is sent to the browser for rendering. Browser interpret the HTML and convert it into colors, fonts and design. HTML is the abbreviation of Hyper Text Markup Language which means a language for writing text contents with non text contents i.e. list, table, alignment etc…
HTML mainly consists from TAGS with some contents inside. i.e. <p>Hello World</p> this tells the browser that there is a paragraph with the sentence “Hello World” inside. Similarly <img src=”http://path/to” /> tells the browser to display an image located at the url http://path/to
HTML has many versions starting from HTML 4.0 which issued at late 1997 until the most recent HTML5.
HTML5 has incorporated many new TAGS and supports a wide range of contents other than images like video and audio.

What is CSS?

CSS is the abbreviation of “Cascaded Style Sheets” and it is a coding method to let the browser knows the design of the HTML contents rendered. The word design here means colors, alignment, spacing, borders, backgrounds, font, width, height, etc… Because there is no code running here, CSS is considered a static language “Not a programming language”.

There are three different ways to embed a style sheet it can be either embedded into the tag, in a separate block in the page or in a separate file.
The syntax for embedding into a tag is as following:-

While the syntax for writing the style sheet into a separate block is just writing all styling enclosed into a style tag.

Last way of writing style sheets is by writing the styles into a separate file with the extension .css then adding the following tag into the head section.

The following image depicts a styling for h1 and body elements. With this style sheet any h1 in the web page will be colored white with orange background.

What is Javascript?

Javascript is a programming language that can be embedded or loaded alongside the web page. The code is downloaded and run by the browser. With javascript you can do any processing, do calculations or access cookies. However you can not access user data or files located on his PC. Also access to network is limited i.e. you can not run a server on the user machine.
With web being evolved to Web 2.0 more dynamic contents are incorporated into web pages. Starting from drop down menus, sliders, image galleries and more… Every thing here make use of javascript to provide the dynamics of the web page. Since both HTML and CSS are just static languages, here JavaScript comes into use. With Javascript you can load contents dynamically, do some calculations and change existing text and more…
Javascript alike CSS can either be embedded into the same page or included from external file.

What is PHP?

With javascript you can create dynamic contents, but it will lacks persistency and security. With javascript you can store data only in cookies which can be wiped out either when expired or by the user. Also cookies can be accessed by any application running on the user side which is considered insecure. So to store persistent data securely like user information another medium is required. Here PHP comes into play. PHP is one of many “Server Side” programming languages however it is the most popular one. A server side means the code run on the server side before sending the page contents to the user browser. With PHP you can run code that no one can access or inspect (Javascript code can be viewed or tempered by the user) because PHP code itself is not sent to the browser but it is run instead and its output is sent to the browser.

What is MySQL?

While you can use files to store your data but it is not good idea especially if you want functionalities like user search or reordering. Here a DBMS (Database Management Systems) comes into hand. With MySQL which is a freely distributed open source DBMS you can insert, update or query data using the standard SQL statements.

The following image is an example ER diagram which depicts a sample database with multiple tables liked together.

Check Database Explanation to know more info.

What is MySQL? What is a Database? What is SQL?

What is MySQL

MySQL is free and open source Relational Database Management System (RDBMS) that uses Structured Query Language (SQL). MySQL was owned by Sun Micro Systems but currently owned by Oracle. It can be installed on the majority of available operating systems like Windows, CentOS, Ubuntu, Depian, etc…
With MySQL you can create and manage databases using SQL. MySQL is just one for many RDBMS available. Other examples are Microsoft SQL Server, Oracle and PostgreSQL. However MySQL is quite popular among web applications.

What is a Database

Database from its name means a center or base to store data in a structured way to be able to query and manipulate it in a speedy manner. Database consist of tables, tables is composed of columns and rows. Each row consist of fields corresponding to those columns. A database is mostly a relational database which means it is composed of tables related or linked together using “Primary keys” and “foreign keys”. Speaking in a little bit more detail, a primary key is a unique number (i.e. serial number) stored in a column in a table and optimized for high speed lookup. A foreign key is another number in a different table that each one of it matches a number from primary keys list mentioned earlier. This way a database engine can combine a table containing primary key and table containing foreign key by matching those keys together, which is called JOIN process. Speaking in terms on speed when correctly configured, a good database engine can combine a tables of millions of records in just a matter of few seconds.

What is SQL

SQL is a short for Structured Query Language which is according to ANSI (American National Standards Institute), it is the standard language for relational database management systems to to search, update, delete and insert data into a database in a highly optimized speed.