Previous Question Paper MSc III Semister - 3B Internet Programming

7/30/2019 Previous Question Paper MSc III Semister - 3B Internet Programming

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Write brief answers to the following questions.

1. What are the different methods CGI uses for returning HTTP ? 3

CGI.pm has two methods for returning HTTP headers: header and redirect.

They correspond to the two ways you can return data from CGI scripts: you can return a document,

or you can redirect to another document.

2. Which are the file locks available in peri ? 3

A shared lock allows more than one program (or other process) to access the file at the same time.

A program should use a shared lock when reading from a file.

An exclusive lock allows only one program or process to access the file while the lock is held. A

program should use an exclusive lock when writing to a file.

File locking is accomplished in Perl using the Fcntl module, EG: use Fcntl qw(:flock);

3. How do you set the environmental variables manually? 3

4. What are the common errors in programming with Perl? 3

Problem Typical Error Message

Application permissions 403 Forbidden

The pound-bang line 403 Forbidden

Line endings 500 Internal Server ErrorMalformed header 500 Internal Server Error

5. What are the advantages of XML? 3

The real power of XML comes from the fact that with XML, not only can you define your own

set of tags, but the rules specified by those tags need not be limited to formatting rules. XML

allows you to define all sorts of tags with all sorts of rules, such as tags representing business

rules or tags representing data description or data relationships.

Some of the benefits are:

With XML, the GUI is extracted. Thus, changes to display do not require futzing

with the data. Instead, a separate style sheet will specify a table display or a list

display.


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Searching the data is easy and efficient. Search engines can simply parse the

description bearing tags rather than muddling in the data. Tags provide the

search engines with the intelligence they lack.

Complex relationships like trees and inheritance can be communicated.

The code is much more legible to a person coming into the environment with noprior knowledge.

In the above example, it is obvious that 002 represents an ID whereas

002 might not. XML is self-describing.

Data is provided in a way that makes it easily transportable via HTTP.

By and large, tags make up the majority of XML markup. A tag is pretty much

anything between angular brackets < >

6. Explain the syntax of HTML template. 4

Example 7-1. current_time.tmpl

Current Time

Current Time

Welcome. The current time is .

7. Explain the structure of CGI program. 3

Perl has three types of variables:

Scalars: Scalar variables are variables that can hold only one value at a time. A scalar variable is

defined in Perl by using $,

Arrays: An array stores a list of values. While a scalar variable can only store one value, an array can

store many. Perl array names are prefixed with an at-sign (@)


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Hashes:

A hash is a special kind of array - an associative array, or paired group of elements. Perl hash

names are prefixed with a percent sign (%), and consist of pairs of elements - a key and a data

value.

---------

1. What is CGI? Explain with a diagram. 5

Ans: The Common Gateway Interface, or CGI, is a standard for external gateway

programs to interface with information servers such as HTTP servers. A plain HTML

document that the Web daemon retrieves is static, which means it exists in a

constant state: a text file that doesn't change. A CGI program, on the other hand, is

executed in real-time, so that it can output dynamic information

. The interactions are illustrated in the followingdiagram:Web Web CGI Appl.Browser Internet Server Protocol Program

HTTP Env. Var.request stdin

Send --------------> Convert ----------> Process|

HTTP |response stdout V

Receive


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2. Mention the programming language that are used for CGI Programming

Ans: Many languages are available for CGI programming, although certain languages are more

suited for CGI programming than others, Some of the most popular languages for CGI

programming include AppleScript, C/C++, C Shell, Perl, Tcl, and Visual Basic.

Before choosing a language, one must consider the following features.

Ease of text manipulation.

Ability to interface with other software libraries and utilities.

Ability to access environment variables (in UNIX).

3. What is the Acronym XML & CSS stands for

a. Extensible Markup Language, Cascading Style sheet4. What are the methods used for sending Form data to the server

a. Get Method and Post Method5. State SSI (Server Side Includes) environment variables

Environment Variable Description

DATE_GMT Current date and time in GMT (Greenwich Mean

Time)

DATE_LOCAL Current date and time in the local time zone

DOCUMENT_NAME The current filename

DOCUMENT_URI Virtual path (relative to the document root) to the

file

LAST_MODIFIED Last modification date and time for current file

QUERY_STRING_UNESCAPED Un-decoded query string with all shell meta

characters escaped with a \.

6. Mention any 2 image formats used on line

Ans: GIF and JPEG

7. Give basis of CGI Program

8. Java Script is a Scripting Language

9. CGI.PM module has become standard tool for creating CGI scripts in Perl

10.To execute the external program SSI directive is used

11.TextArea tag is used to enter multiple lines of text

12.Hash is also called as Associative array

13.CGI Script is the module used for producing graphs

1. The common applications that are designed using CGI are Forms, gateways and virtual

documents

2. Status code 200 indicates that the request is processed successfully and response is

included in the content. 1


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Perl allows rapid development because it is interpreted; the source code does not need

to be compiled before execution.

Perl is easily portable and available on many platforms.

Perl contains extremely powerful string manipulation operators, with regular expression

matching and substitution built right into the language. Perl handles and manipulates binary data just as easily as it handles text.

Perl does not require strict variable types; numbers, strings, and Booleans are simply

scalars.

Perl interfaces with external applications very easily and provides its own file system

functions.

2. What is meant by status code? List any four status code 8

The Status header consists of a three-digit numerical status code, indicating

the status of the initiated operation, return status code helps the programmerto handle the situation accordingly

Status Code Message

200 Success

204 No Response

301Document

Moved

401 Unauthorized

403 Forbidden

404 Not Found

500Internal Server

Error

501 Not Implemented

b) How form data is sent to servers? 7

There are two methods for sending form data: GET and POST. These methods determine howthe form data is sent to the server. In the GET method, the input values from the form are sent

as part of the URL, and saved in the QUERY_STRING environment variable. With POST, data is

sent as an input stream to the program.

If the GET method is used, the input values are simply appended to the URL of the program

when the client issues the request to the server.


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The query string is appended to the URL after the ? character. The server then takes this

string and assigns it to the environment variable QUERY_STRING.

The GET method has both advantages and disadvantages. The main advantage is that the CGI

program can be accessed with a query without using a form. Basically, just passing the

parameters to the program

POST is more secure than GET, since the data isnt sent as part of the URL, and more data can

be sent with POST. Also, browser, web server, or proxy server may cache GET queries, but

posted data is resent each time. Web browser, when sending forms data, encodes the data

being sent. Alphanumeric characters are sent as themselves; spaces are converted to plus signs

(+); other characters like tabs, quotes, etc. are converted to %HH a percent sign and

two hexadecimal digits representing the ASCII code of the character. This is called URL

encoding.

6. a) What are the forms used for in CGI applications ? 8

HTML forms are the user interface that provides input to the CGI scripts. They are primarily

used for two purposes: collecting data and accepting commands. Examples of data that may be

collected are registration information, payment information, and online surveys. The

commands that can be accepted via forms are using checkboxes, lists, and buttons to control

various aspects of CGI application.

Thus forms basic functions are data collection and interactive communication.

The great advantage of HTML form is that user can use them to create a front end fornumerous gateways (such as databases or other information servers) that can be accessed by

any client without worrying about platform dependency.

In order to process data from an HTML form, the browser must send the data via an HTTP

request.

A CGI script cannot check user input on the client side; the user must press the submit button

and the input can only be validated once it has travelled to the server. JavaScript, on the other

hand, can perform action in the browser. It can be used in conjunction with CGI script to

provide a more responsive user interface.

A form is simply an area that can contain form fields for example text boxes, drop-down menus or

radio buttons. When the visitor clicks a submit button, the content of the form is usually sent to a

program that runs on the server

.

.


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The attributes of the tag are:

METHOD

METHOD specifies the HTTP request method used when calling the CGI script. The options are

GET and POST,

ACTION

ACTION specifies the URL of the CGI script that should receive the HTTP request made by the CGI

script. By default, it is the same URL from which the browser retrieved the form.

ENCTYPE

ENCTYPE specifies the media type used to encode the content of the HTTP request. Because GET

requests do not have a body, this attribute is only meaningful if the form has POST as its method.

This attribute is rarely included. The only reason to specify another media type is when creating a

form that accepts file uploads. File uploads must use multipart/form-data instead.

b) What does SSI mean? Explain with a neat diagram the working of SSI. 7

Server Side Includes (SSI) is a simple interpreted server-side scripting language used almost

exclusively for the Web, SSI has a simple syntax: . Directives are placed in HTML comments so that if SSI is not enabled,

users will not see the SSI directives on the page

Refer to 5.3.1

7. a) Write a note on Perl taint mode. 8

The purpose of taint mode is (to stop) / not to allow any outside application data affect theapplication in ay manner. Thus perl will not allow user inputted values to be used in an eval,

passed through a shell or used in any of the Perl commands that affect files and process. It was

created for situations when security is important such as writing perl programs that run as root

or CGI scripts. You should always use taint mode in your CGI scripts.

When taint mode is enabled perl monitors every variable to see if it is tainted. Tainted data,

according to Perl, is any data that comes from outside your code. Because this includes anything

read from the STDIN (or any other file input) as well as all environment variables this covers

everything your CGI script receives from the user.

What is monitored by Taint Mode: The base rule as we have said, is that Perl considers any action

that could modify resources outside the script subject to enforcement. Thus you may open a file

using a tainted filename and read from it as long as you did so in read only mode. However if you

try to open the file to write to it, using a tainted filename Perl will abort with an error.

It is generally better to determine what characters to allow than to try determining what not to

allow. Build your untaint regular expressions with this in mind
http://en.wikipedia.org/wiki/Server-side_scriptinghttp://en.wikipedia.org/wiki/Server-side_scripting


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Explain the environment variable content length

One of the methods that the web server uses to pass information to a cgi script is through environmental

variables. These are created and assigned appropriate values within the environment that the server spawns

for the cgi script. They can be accessed as any other environmental variable

The length, in bytes, of the input stream is being passed through standard input. This is needed when a script

is processing input with the POST method, in order to read the correct number of bytes from the standard

input. Some servers end the input string with EOF, but this is not guaranteed behavior, so, in order to be sure

that you read the correct input length you can do something

like read(STDIN,$input,$ENV{CONTENT_LENGTH})

What is DHTML? Explain. 9

Ans: Dynamic HTML (DHTML) is a set of innovative features which enables authors to dynamically

change the rendering and content of a document. DHTML gives authors the ability to create visually

outstanding HTML documents that interact with the user, without the burden of relying on server-

side programs or complicated sets of HTML pages to achieve special effects.

With DHTML, you can easily add effects to your documents that previously were difficult to achieve.

For example, you can:

Hide text and images in your document and keep this content hidden until a given time

elapses or the user interacts with the page.

Animate text and images in your document, independently moving each element from any

starting point to any ending point, following a path that you choose or that you allow the

user choose.

Create a ticker that automatically refreshes its content with the latest news, stock quotes, or

other data.

Create a form and then instantly read, process, and respond to the data the user enters in

the form.

Explain CGI.PM, How is input handled in CGI.PM / Explain http, https, self-url.

CGI.pm primarily handles two separate tasks: it reads and parses input from the user,

and it provides a convenient way to return HTML output, inputs are accepted with

help of Environment variables, Most of these CGI.pm methods take no arguments and returnthat same value as the corresponding environment variable.

HTTP: If the http method is called without arguments, it returns the name of the

environment variables available that contain an HTTP_ prefix. If you call http with an

argument, then it will return the value of the corresponding HTTP_ environment

variable. When passing an argument to http, the HTTP_ prefix is optional,

capitalization does not matter, and hyphens and underscores are interpreted the

same


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HTTPS: The https method functions similarly to the http method when it is passed a

parameter. It returns the corresponding HTTPS_ environment variable. These

variables are set by your web server only if you are receiving a secure request via

SSL. When https is called without arguments, it returns the value of the HTTPS

environment variable, which indicates whether the connection is secure (its values

are server-dependent).

Self_URL: This method does not correspond to a standard CGI environment variable,

although you could manually construct it from other environment variables. It

provides you with a URL that can call your CGI with the same parameters. The path

information is maintained and the query string is set to the value of

the query_string method.

Your CGI script may have been called because of an internal redirection by the web

server. Also, because all of the parameters are moved to the query string, this new

URL is built to be used with a GET request, even if the current request was a POST

request.

What is CSS? How it works?

Cascading Style Sheets (CSS) are a collection of formatting rules that control the appearance of

content in a web page. They are very useful for maintaining a web site since its appearance

(controlled by properties of HTML tags) can be managed from just one file. CSS Styles also enhance

your sites look, accessibility and reduces file size. Another main advantage is reusability - instead ofdefining the properties of fonts, backgrounds, borders, bullets, uniform tags, etc. each time you use

them you can just assign the corresponding CSS style in the class property. You can store CSS styles

directly in each document or, for more control and flexibility, in an external style sheet.

There are 3 types of CSS Styles:

Custom CSS (Class) styles: create a customized style with the set attributes. These class

styles can be applied to any tag.

HTML Tag styles: redefine the formatting for a particular tag, such as . All text

formatted with the h1 tag is immediately updated.

Advanced CSS Selector styles: redefine the formatting for:

1. A particular combination of tags (for example, td h2 applies whenever an h2 header

appears inside a table cell) and pseudo-class styles (for example, a:link, a:hover,

a:visited)

2. A specific ID attribute (for example, #myStyle applies to all tags that contain the

attribute-value pair id=myStyle)


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Or

External style sheet, which you use when you want to apply the same styles consistently across all the

pages in your Web site that are linked to it. Also known as linked style sheet.

Embedded style sheet, which you use when you want to define styles for the current page

Inline style sheet, which you apply to individual elements on a page.

CSS styles are defined within the tag. If you define the styles embedded within your current

document you will find code similar to the following in your head content:

.bluetext ..

>

Explain the different applications of SSI

SSI (Server Side Includes) is directives that are placed in HTML pages, and evaluated

on the server while the pages are being served. They let you add dynamically

generated content to an existing HTML page, without having to serve the entire page

via a CGI program, or other dynamic technology.

SSI is certainly not a replacement for CGI, or other technologies used for generating

dynamic web pages. But it is a great way to add small amounts of dynamic content to

pages, without doing a lot of extra work

Basic SSI directives

Today's date

Today is

Modification date of the file

This document last modified

Including the results of a CGI program

This is one of the more common uses of SSI - to output the results of a CGI program,

such as everybody's favorite, a ``hit counter.''

Executing commands


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You can actually have SSI execute a command using the shell (/bin/sh, to be precise -

or the DOS shell, if you're on Win32). The following, for example, will give you a

directory listing.

1. Explain loops and conditionals in HTML:: Template

2. Explain the following SSI directives. 8

3. i) fsize ii) flastmod

The #flastmod and #fsize server-side includes provide important information on web pages

hosted by classic ASP web sites.

The #flastmod include prints the date when the file was last modified. The #fsize include

prints the size of the specified file.

When you apply these includes to a web site that allows users to download files, they allow usersto check and see whether a file is new, and also the size, so that the user can estimate how longthe download will take.

Also, these commands are dynamic. This means that if the file size changes or the last modifieddate changes, the files are updated automatically.

SSI Include

The file available for download isDownload.zip, its size is. The file was last updatedon

4. What are the different modules available for creating graphs?

5. Explain how to prevent catching of images

a. Expires HTTP header is one of the option however this is not supported by

many browsers

b. Alternately we can use generate the file name dynamically along with the

tag name as well in order not to have the same cached, this approach

needs to be used sparingly

my $time = time;print $q->img( { -src => /cgi/survey_graph.cgi/$time/survey.png } );

6. What are gateways


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Ans : Gateways, are programs or scripts used to access information that is not directly readableby the client, CGI provides solution to this in the form of a gateway. To read the informationcontained within the database, a language such asoraperlor a DBI extension to perl to form SQLqueries can be used. In these cases, the CGI program serves as a gateway to the database, asshown in Figure

7. b) What is the security threats associated with browser? 7

8. b) What do you mean by dynamic web pages? 7

9. a) Explain the internal working of CGI with architecture. 8

10. With a neat diagram, explain the steps involved in form interaction with CGI. 8

11.b) What are the benefits of server redirections? Explain with diagram. 7

12. What are environment variables? Explain any four with suitable example. 813.What programming language features are required for CGI programming? 5

14.Mention two coding techniques used in perl to develop stable applications, Explain one

of them. 5

15.Which are the applications that are designed in CGI

16.Explain any two control structures in Perl. 8

17.Explain the basic structure of Perl program 8

18. Explain the variable type hash with the functions to access the contents of the hash. 8

Ans: A hash is a special kind of array - an associative array, or paired group of elements. Perl

hash names are prefixed with a percent sign (%), and consist of pairs of elements - a key and adata value. Heres how to define a hash:

The exists function can be used to see if a particular key/value pair exists in the hash:exists $hashname{key}

To empty out the entire hash, do:%hashname = ();


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19.Explain the different image file formats. 7

20. What are the design goals of XML ? 8

21.Explain the added features of PNG over GIF. 7

22.Explain the importance of web security. 7

23.Explain the methods of developing scheme solution. 8

24.Write a perl program which does the same as the UNIX cat command on text file. 7

$file = /abcd; # Name the fileopen(INFO, $file); # Open the file

@lines = ; # Read it into an arrayclose(INFO); # Close the fileprint @lines; # Print the array

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