CSCI A348/548 Lecture Notes Sixteen Spring 2001 (Second semester 2000-2001)

Please write your name or username here:

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Correct answers appear written in blue.

to display HTML documents
to process HTTP requests
to run CGI scripts
all of the above
none of the above

The primary function of an HTTP server is to service client requests for documents. It waits for HTTP requests and then returns data for each one. An HTTP daemon provides an HTTP service. It allows a server to support client requests for documents. It generates errors when invalid requests are received or when a document cannot be found. The Web server process also generates log files of requests, errors, and other information.

to send e-mail
to read news
to display HTML documents
all of the above
to run CGI scripts
none of the above

The primary function of a Web browser is to display HTML documents. Although it can be used to view local documents on a hard drive, it is normally used as a client to retrieve documents from an HTTP server. Although browser software has expanded over the past few years to include such services as e-mail and news, its primary function is to format HTML documents for display.

software hardware both

Technically, a Web server consists of two pieces: the hardware and the software. The machine itself is often called a Web server, and the HTTP daemon is also known as a Web server. Still you can have 'your web server' running on the same machine as 'my server' thus sharing the hardware resources but not the programs. Choosing the first answer without any qualifications or notes, should give you most of the credit, and you should get full credit if you mentioned that "it needs hardware, just not dedicated hardware" or something to this effect. ,

true false

Although you probably wouldn't want to run your corporate Web site from a server the size of a matchbook, it is possible to run a Web server on even the smallest computers. Even relatively old and slow computers can do a good job of serving Web pages for a small site.

A network A Web server A phone line HTTP

The browser only deals with HTTP directly, so that's the main emphasis of this question. It does use a network and talks to a Web server (indirectly). A phone line is not a necessity to use with a browser, but it may be needed to connect to your ISP.

a) You don't have access to port 80 (since you are not root).
b) You are running multiple Web servers on the same machine.
c) You don't have enough memory.
d) Both a) and b).
e) All of the above.

The amount of memory has nothing to do with ports.

true false

The server machine that runs a Web server might also be used by users to browse the Web, for example. But that only means we can run clients on any hardware. More specifically, your web server could start a CGI script that retrieves some data over the network from another (database) server. Then it produces the output. The result is passed to the Web server which sends it back to the client. Through the CGI script the Web server acted as a client to a third-tier (back-end) server.

Text Images Both text and images Binary data

An HTML file only contains text; images are not part of the document. The HTML contains tags that reference images (which are subsequently being retrieved by the browser).

A simple text editor
A word processing program
An automatic HTML generator
A graphics utility
All of these are capable of creating hypertext documents

Most graphics (drawing) programs will not output HTML; they only create graphics images. Those images can be used from a hypertext document, however.

They allow the browser and server to communicate
They tell applications what kinds of documents are being sent
They speed the transmission of binary files
FTP uses them to determine how to transfer files
MIME types are really used only to allow applications to determine the type of document they are dealing with.

html/text
HTML
text/html
text/plain
none of the above

The media type is text, the subtype is html.

It generates plain text files with no special characters
Text editors are generally available on all platforms
In many cases it's quicker than using a large application
All of the above
A simple text editor is not useful to a webmaster

A request or response line, a header section, and an entity body.

A request line is sent as the first line of all HTTP requests. The browser then sends any relevant headers. An entity body is sent only when data other than the headers needs to be sent to the server. A GET method does not usually contain an entity body, but a POST or PUT method usually does.

A response line is sent as the first line of all HTTP responses. The server then sends any relevant headers and the entity body. The entity body is usually the document requested, but it could also be error information if an error occured while trying to retrieve the document.

14. Name the three most widely used request methods.

GET, POST, and HEAD.

Currently, these are the most widely used request methods. As new features are added to the HTTP specification, other methods may become more widely used.

15. What is the difference between a HEAD and a GET?

The HEAD method is used to return the header section for a specific document; it does not return the document itself.

16. What header is sent by the server so that the browser can determine what type of content is being returned?

The Content-type: header indicates the media type of the data contained in the entity body. The server determines the type of data by looking at the file extension and referencing the MIME types file. Server scripts are responsible for properly labelling their output themselves.

17. What is the first thing that is passed to the server when an HTTP transaction begins?

The request line
The response line
The entity body
The transaction line
All of the above could be sent first
None of the above could be sent first

The request line is sent first, containing

1. the request method,
2. the requested resource, and
3. the protocol version.

true false

The HEAD method is also used to retrieve information from the server, although it doesn't return an entire document, only information about the document.

true false

You will normally require some type of login and password to be able to put files on the Web server machine. You can get credit for choosing the other answer if you clearly identify under what realistic circumstances you can publish without logging in.

true false

Users can give other people permission to modify their files. Be careful.

An absolute pathname always starts with the root directory, in most cases a slash or the backslash. It specifies the exact location of a file in the file system. A relative pathname is used to specify a file with regard to the current directory. A relative pathname does not start with a slash; it can start with a directory name (including dot-dot) or a filename.

22. Which of the following are absolute paths? (Check all that apply).

/usr/local/apache/htdocs/
../support/vortex.html
moose.gif
/etc/passwd

/export/home/eric1
../images/backgrounds/water.gif
sales/
./sales/

c:\
c:\html_docs
/opt/apache/htdocs
It depends on how the web server is configured

Which of the following names have we used in this class for default documents?

index.html
default.html
welcome.html
All of the above

true false

true false

A+WeirD&Filename.html
A%2BWeirD%26Filename.html
None of the above
This file cannot be accessed over the web.

true false

Speed
Customization
Easy-to-use GUI configuration
Expensive

It currently uses text-based configuration files and it's free.

true false

true false

Apache is used on many large sites.

A programming language
An API (Application Programming Interface)
A method for a Web server to communicate with other programs
All of the above
None of the above

true false

true false

Client-side scripting languages such as JavaScript are tightly integrated into the browser. [...] A server-side program cannot do anything with the browser directly; [...]

If a JavaScript program is written to respond to user interaction, it can provide very quick responses. [...]

Although there is no limit to the size of JavaScript programs, it is usually a good idea to keep them short. A page with an excessive amount of JavaScript code may take longer to load. Maintaining pages of JavaScript code can become a nightmare; design your pages and write your code with maintenance in mind.

Consider the following JavaScript code:

function a(x, y) {
  return x + y;
}
function b(x, y) {
  return x * y;
}
// a = b;
document.write(a(a(3, 4), b(3, 4))); 

37. (2 points) What will the browser display when you load the page in it.

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38. How does the answer change if you uncomment the line currently commented?

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39. (2 points) Consider the following JavaScript code:

function a(x, y) {  
  return y(x, x);
} 
function b(x, y) {  
  return x - y;
} 
document.write(a(b(2, 4), b)); 

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40. (2 points) How do you find out if your server is running, from the Unix prompt?

ps -ef | grep username | grep httpd

Or something to that effect.

41. (2 points) What's in the httpd.pid file?

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42. (2 points) What's ENV and where did we use it? What does it contain?

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43. (8 points) Here's a form:

<html>
  <body bgcolor=white>
    <form method="POST" action="/cgi-bin/alpha">
      <input type=text name="a"> 
      <input type=text name="c"> 
      <input type="submit" value="Proceed">
    </form>
  </body>
</html>

if ($ENV{REQUEST_METHOD} eq 'GET') {

  $in = $ENV{QUERY_STRING};
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} else {
  read(STDIN, __$in___, $ENV{CONTENT_LENGTH});
}

print "Content-type: text/html\n\n";

@in = split(/&/, $in); 
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foreach $e (@in) {
  ($name, $value) = split(/=/, $e);

  $name =~ s/%(..)/chr(hex($1))/ge;
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  $value =~ s/%(..)/chr(hex($1))/ge;
  print $name, "=(", $value, ")";
}

The Internet is the global network allowing computers of all sizes, from many different computer vendors, running totally different operating systems, to communicate with each other. It operates using the TCP/IP protocol suite, which provides the transport and network layers of Internet operation.

The World Wide Web is the most popular Internet application, merging hypertext and internetworking paradigms to allow user access to multimedia data. It operates using the HTTP protocol, which is one of the many application layers of the Internet.

45. (2 points) Briefly explain the event handling mechanism in JavaScript.

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46. (2 points) What is the output of the following simple Perl program?

#!/usr/bin/perl
@a = (1, 2, 3, 4);
print $#a;

#!/usr/bin/perl
$a = "There's a tomato in every automaton.";
$a =~ s/tomato/**/g;
print $a;

#!/usr/bin/perl
$a = "My goodness!"; 
$a =~ s/(.)/($1)/;
print $a;     

#!/usr/bin/perl
$a = "My goodness!"; 
$a =~ s/(.)/($1)/g;
print $a;     

50. (2 points) What is the output of the following simple Perl program?

#!/usr/bin/perl
$a = "hOoB!y"; 
$a =~ s/(.)(.)/$2$1/g;
print $a;     

#!/usr/bin/perl
$a = "12345"; 
$a =~ s/(..)/$1+1/g;
print $a;     

#!/usr/bin/perl
$a = "12345"; 
$a =~ s/(..)/$1+1/ge;
print $a;     

For all the programming exercises you can obtain the answers by running the programs.