Remote Processing

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ITC125 The Information Superhighway

• Remote Processing

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Remote processing Objectives

• After completing the work for this week, you
  should be able to
• Explain what remote processing is
• Understand the function and operation of the
  Common Gateway Interface (CGI)
• Understand how forms are created and processed

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In previous times ..

• WWW was made of static documents
• Each URL represented a single file that did not
  change over time
• Today documents are created on the WWW as
  required
• in real time
• dynamic

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How do we retrieve dynamic information on the WWW?

• A web client (you) requests information from a
  server you send this to a server.
• The web server listens for such requests from
  browsers and then runs a script (or small
  program).
• Such scripts reside in a special area on the
  server these instructions tell the server what
  to do typically to access a database.
• The database provides the required information.
• The script obtains the information and then
  creates a web page contained that information
  displays it.

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Client Server Model

• Basically we have a script (program) on one
  computer that has rights to access the data in a
  database and provide that data to a client.

Intermediary Computer
Client Computer
Server
Issues URL requests
Database
Specialisedsoftware to process
requests
Request
Results
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Another diagram to show this
Process.html
HTTP SERVER
WWW client
Hypertext link
Internet
CGI script
Database/s
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Web Servers

• First web servers were developed for UNIX.
• They are the gateways between you and Internet
• Generally web server software is free - HTTP
  servers available from CERN, NCSA.
• Basically they are computer program that listens
  for requests (using the HTTP protocol) from
  browsers.
• HTTPd (ddaemon) listens on the server for
  requests from the client

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daemons

• Different daemons are located on web servers
• HTTPd HTTP daemon which waits for web browser
  requests in the form of http//
• Telnetd Telnet daemon waits for a user to
  logon to the system using the telnet protocol
• FTPd FTP daemon again software that waits for
  a FTP request from a client

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What happens when a request is sent to a Web
server?

• http//csusap.csu.edu.au/jatkinso/index.html
• Request sent to csusap server
• httpd daemon locates the document index.html
• The daemon will carry out the requirements
  defined in index.html and return it to the
  browser
• http//csusap.csu.edu.au/cgi-bin/assign.cgi?namej
  ohn
• Request sent to csusap server with data
• Server runs the script assign.cgi with the data
  and returns the information associated with this
  script

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Remote Processing - definitions

• Remote processingis based on CGI programming.
• CGIthe Common Gateway Interface is not a
  programming language rather it is an agreed
  standard that allows you (through your web
  browser) to exchange data with computer programs
  that are located on a web server.
• ExampleWhen you send your personal details to a
  server, the CGI ensures that it is sent and
  received in an agreed format.

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Common Gateway Interface

• Common platform independent
• Gateway CGI scripts run on a server they are
  basically the programs that process the data
  received from a clients browser.
• Interface CGI scripts can act as a communication
  channel between your customers and your server.

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More on CGI .

• CGI scripts
• the most common use of CGI is to handle the
  results of forms and query submissions.
• It is the method by which a web server can obtain
  data from (or send data to) databases, documents
  and other programs, and presents that data to
  viewers on the web
• It is not a programming language it is a script
  that communicates between Web server and you (the
  client)

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So CGI is not a programming language?

• No . It is not programming language.
• Rather it is a protocol (or specification) for
  running programs on a Web server to enable
• a web client to request from a web server
• to run a particular program for the requesting
  client.
• It is a series of simple rules that programs have
  to follow to allow the above to occur
  (interpreted not executed).

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Security

• it is basically the equivalent of letting the
  world run a program on your system.
• you open a window into your local network that
  the entire Internet can peer through
• CGI programs must reside in a special directory
  (/cgi-bin) under control of the webmaster
• Hackers will attempt to get to this directory to
  perhaps steal database files or change web pages

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Means to increase security

• Aim of network security is to keep strangers out
  of a web site
• Problem
• Web site provide the world with controlled access
  to your network where CGI scripts are executed in
  response to your remote requests.
• Firewalls are security walls that protect part of
  a computer system password protected.

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More on CGI ..

• Why use remote processing?
• ideal method for feedback
• great opportunities for marketing
• beware of the concerns .....
• What do you need?
• authority to configure the server to deal with
  resulting incoming data

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What does the CGI programs do?

• There are actually three steps to a CGI script
• Checks, receives and parses the values from the
  client to the CGI script.
• Decodes the values and extracts them and then
  acts upon them.
• Prepares the output generated as a result of the
  parsed values to a Web server.
• The output may be a Web page, a file, an image,
  audio clip or any other applicable MIME type.

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Similar diagram to before ..
form.html
HTTP SERVER
WWW client
Hypertext link
Internet
CGI program
Database/s
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Remote processing steps
Web Client
Web Server
CGI program
Database
Send URL and data
Pass data to CGI program
Store and retrieve data from database
Construct HTML page using data from input and
database
Send HTML to user
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Yet another View of the Remote Processing Process.
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CGI scripts

• PERL
• C / C
• shell script
• Visual Basic
• JAVA
• Applescript

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Time for an example ..

• Basically
• Use HTML forms to collect data from the client
• JavaScript can be used to validate the users
  input.
• A submit button (on a Web browser) is used to
  pass the data from the client to the server.
• In such cases the Web browser makes a request to
  run a CGI program.
• The Web server checks to make sure the CGI
  program exists
• If it does the CGI program is executed
• Output from the CGI program is returned to the
  Web browser
• The Web browser displays the output.

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Environment variables

• A keystones of CGI is a collection of data called
  environment variables
• These are set each time the browser sends
  information to the server and is the means to
  send your data to the server.
• Perhaps the most important for CGI is whether the
  data is sent to the server via GET or POST and
  how much was sent for POST, and what the data was
  for GET
• Other information sent includes IP address of the
  visitor, the browser being sent

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Examples of Environment Variables

• Remote_address where the form was filled in at
• Request_method defines how the data will be
  sent to the server (either POST or GET)
• Content_length contains the length of the data
  coming from the form using the POST method.
• Query_string only used with the GET method
  contains the data that is being sent. Note it
  will be empty for the POST method
• HTTP_USER_AGENT defines the visitors platform

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What are forms

• Forms can contain a wide range of HTML markup
  including (these examples are only specific to
  HTML)
• Single and multi-line text fields
• Radio button groups
• Checkboxes
• Menus
• Buttons (submit and reset)
• Password fields (non-display)

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HTML code to create form elements

• To create a form use
• ltformgt and lt/formgt tags
• Inside the form, use a series of INPUT fields
  plus ordinary HTML this involves
• via key value pairs for each input variable
• GET and POST used to pass these variables to CGI
  program

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Form code

• ltform ACTIONurl methodmethod
  enctypetypegt field definitions lt/FORMgt
• ACTION specifies a URL which is either used to
  post forms via email or used to invoke a server
  side forms handler via HTTP.
• METHOD - GET - appends key value pairs to
  the URL - ? separates the URL proper from the
  parameters which are extracted by the httpd
  server and passed to the CGI program -
  POST - sends the data as a separate stream
• ENCTYPE - specifies the encoding to be used

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ITC125 The Information Super Highway
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ITC125 The Information Super Highway
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Examples of GET and POST

• Method examples of the format
• a. GET
• data is encoded in the URL - actual data follows
  a ?
• b. POST
• data pasted in the body of the request to the
  server
• field values are sent as values/name pairs
• field11field2threeseparatewordsfield37e
• decoding of input

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Example of a form

• Example
• ltform actionmailtojatkinson_at_csu.edu.au
  methodpostgt
• ltfont size1gt19lt/fontgt I would recommend
  .... lt input typeradio nameq19
  valueSAgtStrongly Agree ltinput typeradio
  nameq19 valueAgtAgree
• ltPgt
• lt input typeradio nameq19
  valueDAgtDisagree ..
• lt/formgt

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Example of a comment box

• Example
• lth3gtCommentslt/h3gtltbgtComment on two
  ....lt/bgtlttextarea namepos rows6
  cols60gtlt/textareagt

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Example of submit / reset a form

• Exampleltinput type submit valueSubmit
  questionnairegt
• ltinput typereset value Clear formgt
• Submit defines a button that users can click to
  submit the forms content to the server. The
  button name is set.
• Reset defines a button that users can click to
  reset the form fields to their initial state when
  the document was first loaded. Reset button data
  is never sent as part of the forms contents

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Other references on forms

• Try this reference http//archive.ncsa.uiuc.edu/S
  DG/Software/Mosaic/Docs/fill-out-forms/example-1.h
  tmlThere are 13 examples of basic forms - a
  fantastic reference to copy material into your
  new forms.

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• action"mailtojsmit01_at_life.csu.edu.au" method
  "POST"
• Your Name ltinput name"ReaderName size 15gt
• Did you like my Homepage?ltBRgt
• ltinput typeradio" name"Page" value"Yes"gt Yes
  lt /brgt
• lt input type radio" name "Page" value "No"gtNo
• ltpgt lt input type checkbox" name"Flag"
  value"Like"gt lt/pgt
• Check the box if you think I did alright. ltPgt
• How Good did I do?
• ltselect name"PageJob"gt
• ltoptiongtExcellent ltoptiongtVery Good
  ltoptiongtGood
• ltoptiongtKeep Trying lt/selectgt
• ltPgt ltinput type"SUBMIT" value"Send your vote"gt
  lt/formgt

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Outputs from CGI programs

• referred to as dynamic documents these are
  documents that are created on-the-fly by a CGI
  program. This can be done by
• hard coding in the CGI program via a number of
  print statements or equivalent
• HTML template files residing on the server that
  substitute in the variables and writing it to
  STDOUT
• static HTML files read by the CGI program and
  written directly to STDOUT with no processing
• CGI specifications define how HTTP servers
  interact with external gateways

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JAVA script

• JAVA script basically a means to customise your
  web pages and process information
• Example of a very simple java script program
• ltscriptgt document.bgcolorgreenlt/scriptgt
• or
• ltscriptgt window.status"Welcome to my
  homepage"lt/scriptgt

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More little examples for your to try

• ltscriptgt alert("Welcome, my
  friend!")lt/scriptgt
• ltscriptgt var answerconfirm("Jump to CSU?")
  if (answer) window.location"http//www.csu.
  edu.au" lt/scriptgt
• ltscriptgt var answerprompt("Please enter your
  name") alert("Hello "answer)lt/scriptgt

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Electronic Commerce

• Electronic commerce (E-commerce) online selling
• E-Commerce differs from the traditional shop
  front for example
• Traditional Store E-Commerce store
• Physical space Web Space
• Aisles and shelves Searchable databases
• Cash register Electronic payment only
• Shopping trolleys Virtual shopping trolleys
• Cash-and-carry Shipped deliveries only
• Personalised service Impersonalised service

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Electronic Commerce

• Building your own E-Commerce site how can you
  do it?
• Off-the-shelf software
• Domain names
• Order processing how can they be received
• Payment details method and security
• Look and layout
• Security secure socket layer (SSL)