06 server-side cgi - cs.uml.edu

I VPR 1© Copyright 2007 Haim Levkowitz

Server-side computing

• Why server-side?

• Approaches


• Markup languages cannot• Specify

• Computations• Interactions with users

• Provide access to• Server-side resources

• Databases• Programs• Services

Why server-side?


Approaches

• “programmer centered”

• “designer centered”


“programmer centered”

• Document generation insidecomputation code

• CGI• Java servlets


“designer centered”

• Computation code insidedocument template

• PHP• ASP

• JSP


• Let browsers request server-sideexecution

• Open source• “LAMP”

• Linux, Apache, MySQL, Px• Px

• Perl, PHP, Python

CGI: the CommonGateway Intefrace


ASP or ASP.NET: ActiveServer Pages

• Microsoft


JSP: Java Server Pages

• Similar to ASP and ASP.NET

• Java-based

• Sun Microsystems


CGI

• Interface between browser and server

• HTTP request ==>

• Program instead of document

• Server recognizes by file

• Location

• Special directories

• Extension


CGI program

• Often stored in cgi-bin directory

• Produce

• complete HTTP response, or• just URL of existing doc


CGI linkage

• Some CGI programs in machine code• Perl programs usually kept in source form

• ==> must be run perl on them


• source file can be made “executable”

• add line at beginning

• specifies language processing

• run first


For Perl programs

if perl in /usr/local/bin/perl

often in UNIX==> #!/usr/local/bin/perl -w


for Perl CGI programs

sometimes use file extension .cgi

e.g., for the CGI Wrap system


HTML document specifies CGI programwith hypertext reference attribute

href, of anchor tag, <a>

as in

<a href = “./cgi-bin/reply.cgi>" Click here to run the CGI program, reply.pl </a>


Communications andcomputation using CGI


Model ...

• Browser server application

CGI

Form

CGI program's

responseCGI program's

response

Submit completed form

Call CGI


<html><head><title> HTML to call the CGI-Perl programreply.cgi</title></head><body>This is our first CGI-Perl example<a href = "./cgi-bin/reply.cgi">Click here to run the CGI program,reply.cgi</a></body></html>


CGI --> browser

• connection from CGI program back to requestingbrowser• Through STDOUT• Through server

• HTTP header needs only content type• followed by blank line• print "Content-type: text/html\n\n";

• SHOW reply.cgi


Query string

• names and values of widgets• values always coded as strings• format of name/value pair

• name=value• If form has more than one widget

• ==> values separated with ampersands• milk=2&payment=visa

• special characters coded• percent sign + two-character hexadecimal number

• = ASCII code of character• Some browsers code spaces

• as + signs• rather than as %20

• get versus post HTTP methods


GET vs. POST ...

• GET

• + Access CGI prog. w/ query without a form

• Pass parameters to program ...

• Can send extra path info ...

• – Query might get truncated• Post

• + Unlimited query length

• – No “canned” queries (hard-coded url)


- A Perl module serves as a library

- Can be used as a function library or a class library

- Get info about by typing perldoc CGI

- The Perl use declaration is used to make a module available to a program

- To make only part of a module available, specify the part name after a colon

(For our purposes, only the standard part of the CGI module is needed)

use CGI ":standard";

- Common CGI.pm Functions

- “Shortcut” functions produce tags, using their parameters as attribute values

br;

returns

"<br/>"

The CGI.pm Module


The CGI.pm Module

Perl module serves as libraryCan be used as

function library orclass library

Info: perldoc CGI


Perl use declarationmake module available to program

to make only part of module availablespecify part name after colon

For our purposesonly need standard part of CGI module

use CGI ":standard";


Common CGI.pmFunctions“Shortcut” functions produce tags

using their parameters as attribute values

br;

returns

"<br/>"


e.g., h2("Very easy!");returns <h2> Very easy! </h2>

parameter to function h2used as content of <h2> tag


function output toreturn doccall must be parameter to print

print h2("Very easy!");


Tags can have bothcontent and attributes

Each attribute passed as name/value pair just as in hash literal

Attribute names passed with preceding dash


textarea(-name => "Description", -rows => "2",

-cols => "35");

Produces:

<textarea name ="Description" rows=2 cols=35> </textarea>


If both content and attributes passed to functionattributes specified in hash literal

as first parameter

a({-href => "fruit.html"}, "Press here for fruitdescriptions");

Output:<a href="fruit.html"> Press here for fruitdescriptions</a>


Tags and their attributesdistributed over parameters of function

ol(li({-type => "square"}, ["milk", "bread","cheese"]));

Output:<ol> <li type="square”>milk</li> <li type="square”>bread</li> <li type="square”>cheese</li>

</ol>


CGI.pm also includesnon-shortcut functionsproduce output for return to user

call to header() produces:

Content-type: text/html;charset=ISO-8859-1

-- blank line --


The start_htmlfunctioncreate

head of return document<body> tag

parameter to start_htmlused as title of document

start_html("Bill’s Bags");


DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0 //EN" "http://www.w3.org/TR/xhtml-basic/ xhtml-basic10.dtd"><html xmlns= "http://www.w3.org/1999/xhtmllang="en-US">

<head><title>Bill’s Bags</title></head><body>


The param function

given a widget’s namereturns widget’s value

If, e.g., query string has name=Abraham in it,

param("name") will return "Abraham"


The end_html function

generates </body></html>

SHOW popcorn.html display popcorn.cgi


FIGURE 10.2 Display ofpopcorn.html


FIGURE 10.3 Display ofpopcorn.html, form filledout


FIGURE 10.4 Output ofpopcorn.cgi


A Survey Example

- Use form to collect survey data from users

- accumulate survey results,stored between form submissionsin file on server


concurrent use of file==> must be protected from corruption

block other accesses while being updated

Under UNIX, Perl functionflock


parameter values for flockdefined in Perl Fcntl module(write lock is LOCK_EX)

To update fileopen filelock with flockmodifyrewind with seekclose file

--> SHOW conelec.html + display


Two CGI programs used1. collect survey submissions and record new

data2. produce current totals

file formateight lineseach w/ 7 values first four for female responses last four for male responses


FIGURE 10.5 Display ofconelec.html


To collect and recordform data must:1. Get form values (with param)

2. Determine row of file to be modified

3. Open, lock, and read survey data file

4. Split affected data string into numbers + store them in array

…


5. Modify affected array element& join array back into string

(use gender to determine which half of dataaffected)

6. Rewind data file (with seek)

7. Rewrite and close survey data file

--> SHOW conelec1.pl


Tables easier to specifywith CGI.pm

- table created with table function

- border attribute specified as parameter

- table’s caption created with call to caption, as second parameter to table


- Each row of table is created with call to Tr

- heading row created with call to th

- Data cells created with calls to td

- calls to Tr, th, and td require references as parameters


- Suppose have three arrays of sales numbers- one for each of three salespersons- each array has one value for each day of work

week

- want to build table of this information- using CGI.pm


table({-border => "border"},caption("Sales Figures"),Tr(

[th(["Salesperson", "Mon", "Tues", "Wed", "Thu", "Fri"]),

th("Mary").td(\@marysales),th("Freddie").td(\@freddiesales),th("Spot").td(\@spotsales),

])

);


program that producescurrent results must:

1. Open file and read lines into array of strings

2. Split first four rows (responses from females)into arrays of votes for four age groups

3. Unshift row titles into vote rows(making them first elements)

4. Create column titles row with thput its address in array


5. Use td on each rows of votes

6. Push addresses of rows of votes onto rowaddress array

7. Create table using Tr on array of rowaddresses

8. Repeat Steps 2-7 for last four rows of data(responses from males)


--> SHOW conelec2.cgi--> SHOW Figure 10.7


FIGURE 10.7 Surveyresults page


10.6 Cookies

- session = time span during which browserinteracts with particular server

- HTTP protocol is stateless- But, several reasons why useful for server to

relate request to session- Shopping carts for many different simultaneous

customers- Customer profiling for advertising- Customized interfaces for specific clients


Approaches to storingclient information:

- Store on server- too much to store!

- Store on client machine- this works


cookie = small object ofinformationname and text value

created by some software system on server(maybe CGI program)

Every HTTP communication between browser and server includesinformation in header about message

when cookie createdgiven lifetime

Every time browser sends request to server that created cookie,while cookie is still alivecookie included


browser can be set to reject cookies

- CGI.pm includes support for cookies

cookie(-name => a_cookie_name, -value => a_value, -expires => a_time_value);

- name can be any string- value can be any scalar value- time is a number followed by a unit code (d, s, m, h, M, y)


Cookies must be placed inHTTP headerwhen header created

header(-cookie => $my_cookie);

To fetch cookies from HTTP requestcall cookie with no parametershash of all current cookies returned

To fetch value of one particular cookiesend cookie’s name to cookie function

$age = cookie(′age′);


Example:

cookie that tells customer time of last visit to thissite

Use Perl function, localtimeto get parts of time

($sec, $min, $hour, $mday, $mon, $year, $wday, $yday, $isdst) =localtime;

SHOW time_date.pl


CGI program to solve ourproblem:1. Get cookie named last_time

2. Get currentday of weekmonthday of month& put them in cookie

named last_time

3. Put cookie in header of return document


4. If no existing cookieproduce welcome message for first-time visitor

5. If there was cookieproduce welcome message

includes previousday of weekmonthday of month

SHOW day_cookie.pl

06 server-side cgi - cs.uml.edu

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