Overview

1
Overview

• Internet
• Internet Protocols
• Fundamentals about HTTP Communication
• HTTP-Server, mode of operation
• Static/Dynamic Webpages
• HTML
• PHP programming

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Internet
Server
Text, Audio, Video and Graphics
Connectionvia TCP/IP-Protocol
Client
3
History

• The WWW is 18 years old
• On the 30th April 1993 the originator of the WWW
  Tim Berners-Lee declared Everyone is allowed to
  use the World Wide Web and all possibilities it
  offers without any licenses. Eine gute Idee.

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Internet Services

• E-Mail
• WWW
• Chat
• Internet News
• FTP
• Telnet
• Applications

5
Internet Protocols
Server

• HTTP
• HTTPS
• FTP
• SMTP
• NNTP

Data
Connection via Internet Protocol
Client
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Protocols
HTTP
FTP
SMTP
DNS
SNMP
RIP
Application
TCP
UDP
Transport
IP
Internet
Ethernet
Token-Ring
ATM
Phys. Network
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http (Hypertext Transfer Protocol)

• Two Types of http messages Request, Response
• Requests
• Request method i.e. Get, Post
• wanted URL
• HTTP-Protocol version (actual 1.1)
• Headerinfo i.e. which documents could be
  received by the client
• Responses
• Status messages i.e. 200 OK, 404 File Not
  Found
• Headerinfo i.e. Content-Length, Content-Type
  (Text, Html, etc.)
• The requested document

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http (Interaction)

• HTTP Interaction Principles
• Connection establishmentTCP-Connection from
  Client to Server (usually Port 80 on the Server)
• Request from Client to ServerMethod
  selectionadditional parameters for the method
• Response from Server to ClientResult as a status
  codeadditional parameters on the result
• Connection terminationusually ending the
  connectionnewer versions (newer then HTTP/1.1)
  can keep connection longer alive

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http (Methods)

• OPTIONS requests server features
• GET fetch a resource from server
• HEAD provides only meta information about a
  resource
• PUT saves a resource
• POST sends a data set to a resource (CGI-Script)
• DELETE deletes a resource
• TRACE allows tracking of the processing of
  requests

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https (1)

• Widely used security technology
• http-Server accepts ssl (secure socket-layer)
  connection
• Identification of secure connection
  viahttps//url
• SSL connection uses port 443
• Transmitted data are quasi tap-proof (key length)
• Higher working load on server, because encryption
  causes additional computing time

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https (2)

HTTPS
Application
SSL
Security
TCP
Transport
IP
Internet
Ethernet
Token Ring
ATM
Phys. Network
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Client Server Principle
Webserver
Client with Webbrowser
Request over
http request
Results
HTTP
http answer
IP-Adresse
TCP/IP
TCP/IP
Netzwerk
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URL

• URL unified resource locator
• The access to the server is done by the URL
• Formataccess_method//computerernameport/docume
  nt?querystring
• Examplehttp//www.uni-duisburg.de/netlab/student
  .php?matr123456
• access method http
• computer name fb9dv.uni-duisburg.de
• port standard port (80 for HTTP), here not
  specified
• document netlab/students.html (path/filename)
• Query string matr123456

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Domain names

• Domain name fb9dv.uni-duisburg.de
• de first layer name (top-level-domain)
• uni-duisburg second layer name
• fb9dv third layer name

iis.uni-duisburg.de
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Port communication

• communication via TCP/IP operates by IP-Addresses
  and Ports
• each IP-Adresse has 216 potential ports
• The ports below 1024 are standardized (standard
  ports), which are allocated to dedicated
  services, i.e.23 telnet25 smtp80 http443 http
  s

134.91.100.1
. . . . . . . .
23
25
80
30000
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Query GET/POST

• Data transfer to server
• Data are computed by the server and the resulted
  page is sent to the client
• Two procedures Get and Post method
• Get Query-String is specified within the url
  http//www.uni-duisburg.de/student.php?namepeter
  
• Post Data are transmitted in HTTP querys body
  (not in url)
• Example form data

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HTTP-Server (1)

• Document Root Folderroot directory where all
  files for the website are stored
• Documents are organized in directories
• Access rights are considered read, write,
  deletepublic accessed web pages have to be
  readable by everyone, in terms of access rights
• Definition of standard documents like index.html,
  start.htm
• Modular structured, additional services like
  php-Modul can be integrated
• Multiple configurations i.e. - directory level
  control- allow access only from specific
  IP-Addresses

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HTTP-Server (2)

• Apache-Server configuration is done using the
  file httpd.conf. This file is read in and
  evaluated when starting the servers
• Contains information about the Apache Web-Server
  itself, about logs and additional configuration
  files. Examples
• ServerRootThe statement ServerRoot defines the
  path to the top level directory, which includes
  configuration folders and files, log-files and
  documents.
• DocumentRootThe document folder is the
  directory, where the server tries to locate the
  file, in case no path was specified within the
  url. Only one DocumentRoot can be defined in the
  resource list of the Apache Web-Servers.
• UserDirUserDir makes it possible for the
  web-server to access documents out of the users
  home directory. Example http/server/username/d
  ocument.htm

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HTTP-Server (3)
Configuration panel for IIS (Windows 2000)
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Static Internet Pages

• Pages (content) are already available before they
  are requested
• Pages are quickly available
• The Server does not need any additional services
  (applications) like Interpreter, Database.
• Interaction with Server is limited to links
• Pages can be computed, respectively displayed, on
  the client computer, without any additional
  procedures

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HTML (1)

• HTML (Hypertext Markup Language)
• Markup language it describes the logical part of
  a text oriented document.
• HTML offers the possibility to define typical
  elements of a text oriented document, like
  header, paragraphs, lists, tables or graphical
  references.
• Advantages
• HTML is a so called clear text format (can be
  edited with every text editor)
• Easy to learn
• Disadvantages
• No separation between form and content
• Design and Interaction possibilities are limited

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HTML (2)

lthtmlgt ltheadgt lttitlegtBeispiel
1lt/titlegt lt/headgt ltbodygt Textfeldltbrgt lt/bodygt lt/ht
mlgt
Browser
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Dynamic Internet Pages (Server1)

• Page content is generated (immediately) after
  request
• Access may be slower, due to the need of page
  generation
• System has to have adequate resources
• Optional applications possible
• Database access
• Graphics generation
• Access of processes (application), which offer
  interfaces
• General 2 methods
• GGI (Common Gateway Interface)i.e. perl, c
• As a modul (server extension)i.e. php

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Dynamic Internet Pages (Server2)
Server
Client
CGI
DB
Request
Generated HTML-File
Generated HTML-File
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Dynamic Internet Pages (Client)

• DHTML
• Browser can execute (interpret) scripts, which
  are included in HTML-Files.
• By the use of a script language a dynamic page
  can be created on the client.
• Example JavaScript (Browser independent)
  Alternatively JavaScript can be embedded in the
  HTML-File or it can be located in a separate
  file. JavaScript is interpreted by the web
  browser at runtime. Therefore modern web browser
  have an interpreter software integrated.Example

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Sessions

• HTTP is a stateless protocol
• After the request (and response) for a web page
  the connection between client and server is
  terminated
• Server do not have a history list or anything
  similar, which means that two consecutive
  requests from the same client are treated as two
  different independent requests
• How is this problem solved? i.e. online shops

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Sessions (2)

• Implementation of a mechanism, which generates
  (on the server) an unique session-ID at the first
  request. It will be sent with each further client
  request to the server.
• Session ID is transmitted
• Within the URL, which means each link, used
  within a session, includes the session-ID
• With use of cookiesmax 4 KB text files, which
  are initiated by the server and sent to the
  client. They can be used by the client on demand.

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Php

• PHP is an interpreted language
• Platform independent (Windows/UNIX)
• Easy Syntax (C-similar)
• Easy to integrate in http-Servers (Apache, IIS)
• Powerful functions (database access, graphical
  libraries, etc)
• Free Software (no license costs)
• Frequently used (as well by public providers)
• A lot of ready-to-use modules (forums, web pages,
  sample scripts)

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PHP Structure

• PHP can be embedded in HTML documents or used as
  pure PHP files.
• The PHP code is between two tags
• lt?php
• and
• ?gt
• The file name has in both cases the extension
  .php
• Each command ends in PHP by a semicolon or by
  the PHP end tag.
• Example

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PHP Comments

• Comments in PHP are characterized as follows
• By the symbol or // Denotes the following
  text, until the end of the line as a comment.
• by / / Hereby the enclosed text is denoted
  as a comment.

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PHP Variables

• PHP uses an automatic data type conversion (i.e.
  integer to string, etc.).
• Definition
• Variables
• variable_namevalue
• Arrays
• Array_name array
• value1,
• value2,

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PHP Control Structures

• IF (condition)
• instructions, if condition is true
• ELSEIF (further conditions)
• instructions, if the first condition was
  false and this condition is true
• ELSE
• instructions, if all conditions are false

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PHP Loops

• WHILE-loop
• WHILE (condition)
• instructions, execute while condition is true
• FOR-loop
• FOR (start value condition instruction)
• instructions

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PHP Functions

• FUNCTION function_name (variables as parameters)
  
• instructions
• optional RETURN (return value)

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PHP Text Output

• TEXT (HTML-Code) generation with PHP using the
  command PRINTcommands
• PRINT (output text)
• PRINT (variable)
• PRINT (variable.output text)

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PHP File Operations

• Open file for writing
• Save data in file
• Read data from fileImportant adequate file
  permissions are required!!!

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PHP hand over data

• The array HTTP_POST_VARS contains all the
  variables handed over via POST method. i.e. from
  a form via POST.
• The Array HTTP_GET_VARS contains all the
  variables handed over via GET method. i.e. from
  a form via GET.
• Example

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Sample Program
Source-Code of the example
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Links about PHP/HTML

• PHP developers homepagehttp//www.php.net
• selfhtml Excellent document (tutorial) about
  HTML and morehttp//selfaktuell.teamone.de/