Lecture 15 CGI Sessions Perl CPE 401

Lecture 15 CGI Sessions Perl CPE 401 / 601 Computer Network Systems slides are modified from Dave Hollinger and Shwen Ho

Sessions q Many web sites allow you to establish a session. v v you identify yourself to the system. now you can visit lots of pages, add stuff to shopping cart, establish preferences, etc. CGI Sessions 2

State Information q Remember that each HTTP request is unrelated to any other v as far as the Web server is concerned q Each new request to a CGI program starts up a brand new copy of the CGI program. q Providing sessions requires keeping state information. CGI Sessions 3

Session Conversation Client Hi! I'm Joe. Hi Joe (it's him again) Welcome Back. . . Server CGI 1 I wanna buy a cookie. CGI 2 OK Joe, it will be there tomorrow. CGI Sessions 4

Hidden Field Usage q One way to propagate state information is to use hidden fields. q User identifies themselves to a CGI program v fills out a form q CGI sends back a form that contains hidden fields that identify the user or session. CGI Sessions 5

Revised Conversation Initial form has field for user name. GET /cgi 1? name=joe HTTP/1. 0 CGI 1 creates order form with hidden field. GET/cgi 2? name=joe&order=cookie HTTP/1. 0 CGI Sessions 6

Session Keys q Many Web based systems use hidden fields that identify a session. q When the first request arrives, the system generates a unique session key and stores it in a database. q The session key can be included in all forms/links generated by the system v as a hidden field or embedded in a link CGI Sessions 7

Session Key Properties q Must be unique. q Should expire after a while. q Should be difficult to predict. v typically use a pseudo-random number generator seeded carefully. CGI Sessions 8

Pizza Server Session Keys q We define a server to use session keys: q A request to order a pizza might look like this v all on one line GET /pizza. cgi? sessionkey= Hungry. Student 971890237&pizza=cheese &size=large HTTP/1. 0 CGI Sessions 9

HTTP Cookies q A "cookie' is a name, value pair that a CGI program can ask the client to remember. q The client sends this name, value pair along with every request to the CGI. q We can also use "cookies" to propagate state information. CGI Sessions 10

Cookies are HTTP q Cookies are HTTP headers. q A server (CGI) can give the browser a cookie by sending a Set-Cookie header line with the response. q A client can send back a cookie by sending a Cookie header line with the request. CGI Sessions 11

Set-Cookie Header Options The general form of the Set-Cookie header is: Set-Cookie: name=value; options The options include: expires=. . . domain=. . . path=. . . CGI Sessions 12

Setting a cookie HTTP/1. 0 200 OK Content-Type: text/html Set-Cookie: customerid=0192825 Content-Length: 12345. . . CGI Sessions 13

expires Option q This tells the browser how long to hang on to the cookie. expires=Friday 29 -Feb-2000 00: 00 GMT q The time/date format is very specific! Weekday, Day-Month-Year Hour: Minute: Second GMT CGI Sessions 14

Default expiration q If there is no expires option on the Set- Cookie header line, v the browser does not save the cookie to disk. q In this case, when the browser is closed it will forget about the cookie. CGI Sessions 15

domain Option domain=. unr. edu q The domain option tells the browser the domain(s) to which it should send the cookie. q Domains as in DNS. q The domain must start with ". " and contain at least one additional ". " CGI Sessions 16

Domain option rules q The server that sends the Set-Cookie header must be in the domain specified. q If no domain option is in the header, the cookie will only be sent to the same server. lt u Defa avior Beh : CGI Sessions 17

path Option path=/ or path=/~mgunes/cpe 401 q The path option tells the browser what URLs the cookie should be sent to. CGI Sessions 18

path default q If no path is specified in the header, v the cookie is sent to only those URLs that have the same path as the URL that set the cookie. q A path is the leading part of the URL v does not include the filename CGI Sessions 19

Default Path Example If the cookie is sent from: /~mgunes/cpe 401/pizza. cgi it would also be sent to /~mgunes/cpe 401/pizza/blah. cgi but not to /~mgunes/cpe 401/soda/pizza. cgi CGI Sessions 20

Set-Cookie Fields q Many options can be specified. q Things are separated by "; " Set-Cookie: a=blah; path=/; domain=. cse. unrr. edu; expires=Thursday, 21 -Feb-2002 12: 41: 07 2002 ust on e ne o ! ne li b ll m A CGI Sessions 21

CGI cookie creation q A CGI program can send back any number of HTTP headers. v can set multiple cookies q Content-Type is required! q Blank line ends the headers! CGI Sessions 22

C Example printf("Content-Type: text/htmlrn"); printf("Set-Cookie: prefs=nofrmsrn"); printf("Set-Cookie: Java=yesrn"); printf("rn"); … now sends document content CGI Sessions 23

Getting HTTP Cookies q The browser sends each cookie as a header: Cookie: prefs=nofrms Cookie: Java=OK q The Web server gives the cookies to the CGI program via an environment variable. CGI Sessions 24

Multiple Cookies q There can be more than one cookie. q The Web Server puts them all together like this: prefs=nofrms; Java=OK and puts this string in the environment variable: HTTP_COOKIE CGI Sessions 25

Cookie Limits q Each cookie can be up to 4 k bytes. q One "site" can store up to 20 cookies on a user's machine. CGI Sessions 26

Cookie Usage q Create a session. q Track user browsing behavior. q Keep track of user preferences. q Avoid logins. CGI Sessions 27

Cookies and Privacy q Cookies can't be used to: v send personal information to a web server without the user knowing about it. v be used to send viruses to a browser. v find out what other web sites a user has visited. * v access a user's hard disk * although they can come pretty close to this one! CGI Sessions 28

Some Issues q Persistent cookies take up space on user's hard disk. q Can be used to track your behavior within a web site. v This information can be sold or shared. q Cookies can be shared by cooperating sites v advertising agencies do this. CGI Sessions 29

Perl q Practical Extration and Reporting Language v a high-level programming language • whose semantics are largely based on C q Designed for text manipulation v Very fast to implement v particularly strong at process, file and text manipulation q Runs on many different platform v Windows, Mac, Unix, Linux, Dos, etc Perl 31

Running Perl q Perl scripts do not need to be compiled v interpreted at the point of execution v do not necessarily have a particular file extension • “. pl” is used commonly q Executing it via the command line> perl script. pl arg 1 arg 2. . . q Or add the line "#!/usr/bin/perl" to the start of the script if you are using unix/linux. /perlscript. pl • Remember to set the correct file execution permissions before running it Perl 32

Beginning Perl q Every statement end with a semi colon "; " q Comments are prefixed at the start of the line with a hash "#" q Variables are assigned a value using the "=" q Variables are not statically typed, v No need to declare what kind of data you want to hold in them. q Variables are declared the first time you initialize them and they can be anywhere in the program. Perl 33

Scalar Variables q Contains single piece of data q '$' character shows that a variable is scalar q Scalar variables can store v number v string • a chunk of text surrounded by quotes $name = "paul"; $year = 1980; print "$name is born in $year"; output: paul is born in 1980 Perl 34

Arrays Variables (List) q Ordered list of data, separated by commas q '@' character shows that a variable is an array Array of numbers @year_of_birth = (1980, 1975, 1999); Array of string @name = ("Paul", "Jake", "Tom"); Array of both string and numbers @paul_address = (14, "Cleveland St", "NSW", 2030); Perl 35

Retrieving data from Arrays q Printing Arrays @name = ("Paul", "Jake", "Tom"); print "@name"; q Accessing individual elements in an array @name = ("Paul", "Jake", "Tom"); print "$name[1]"; q What has changed? v @name to $name To access individual elements use the syntax $array[index] q Why did $name[1] print the second element? v index 0 represents the first element. Perl 36

Arrays … @name = ("Paul", "Jake", "Tom"); print "@name"; Paul Jake Tom print @name; Paul. Jake. Tom $count=@name; $count = 3 @name. R=reverse(@name); @name. R=("Tom", "Jake", "Paul") @name. S=sort(@name); @name. S=("Jake", "Paul", "Tom") Perl 37

Basic Arithmetic Operators + * / ++ -$a += 2 $b *= 3 Addition Subtraction multiplication division adding one to the variable subtracting one from the variable incrementing variable by 2 tripling the value of the variable Perl 38

Relational Operators Comparison Equals Not equal Less than Greater than Less than or equal Greater than or equal Comparison Numeric String == != < > <= >= <=> eq ne lt gt le gt cmp Perl 39

Control Operators - If if ( expression 1) {. . . } elsif (expression 2) {. . . } else {. . . } Perl 40

Iteration Structures q while (CONDITION) { BLOCK } q until (CONDITION) {BLOCK} q do {BLOCK} while (CONDITION) q for (INITIALIZATION ; CONDITION ; Re-INITIALIZATION) {BLOCK} q foreach VAR (LIST) {BLOCK} v for VAR (LIST) {BLOCK} Perl 41

Iteration Structures $i = 1; while($i <= 5){ print "$in"; $i++; } for($x=1; $x <=5; $x++) { print "$xn"; } @array = [1, 2, 3, 4, 5]; foreach $number (@array){ print "$numbern"; } Perl 42

String Operations q Strings can be concatenated with the dot operator $lastname = "Harrison"; $firstname = "Paul"; $name = $firstname. $lastname; $name = "$firstname$lastname"; q Comparison can be done with the relational operator $string 1 = "hello"; $string 2 = "hello"; if ($string 1 eq $string 2) { print "they are equal"; } else { print "they are different"; } Perl 43

String comparison using patterns q The ‘=~ ’ operator return true if the pattern within the ‘/’ quotes are found. $string 1 = "HELLO"; $string 2 = "Hi there"; # test if the string contains the pattern EL if ($string 1 =~ /EL/) { print "This string contains the pattern"; } else { print "No pattern found"; } Perl 44

Functions in Perl q No strict variable type restriction during function call q Perl has provided lots of useful functions chop - remove the first character of a string v chomp - remove the carriage return character from the end of a string v push - append one or more element into an array v pop - remove the last element of an array and return it v shift - remove the first element of an array and return it vs - replace a pattern with a string v Perl 45

Functions in Perl q The "split" function breaks a given string into individual segments given a delimiter q split( /pattern/, string) returns a list @output = split (/s/, $string); # breaks the sentence into words @output = split (//, $string); # breaks the sentence into single characters @output = split (/, /, $string); # breaks the sentence into chunks separated by a comma. § join ( /delimiter/, array) returns a string Perl 46

Functions in Perl A simple perl function sub say. Hello { print "Hello!!n"; } say. Hello(); Perl 47

Executing functions in Perl q Function arguments are stored automatically in a temporary array called @_ sub say. Helloto { @name = @_; $count = @_; foreach $person (@name){ print "Hello $personn"; } return $count; } @array = ("Paul", "Jake", "Tom"); say. Helloto(@array); say. Helloto("Mary", "Jane", "Tylor", 1, 2, 3); Perl 48

Input / Output q Perl allows you to read in any input that is automatically sent to your program via standard input by using the handle . q Other I/O topics include reading and writing to files, Standard Error (STDERR) and Standard Output (STDOUT). q One way of handling inputs via is to use a loop to process every line of input Perl 49

Input / Output q Count the number of lines from standard input and q print the line number together with the 1 st word of each line. $count = 1; foreach $line (){ @array = split(/s/, $line); print "$count $array[0]n"; $count++; } Perl 50

Regular Expression q Regular expression is a set of characters that specify a pattern. q Used for locating piece of text in a file. q Regular expression syntax allows the user to do a "wildcard" type search without necessarily specifying the character literally q Available across OS platform and programming language. Perl 51

Simple Regular Expression q A simple regular expression contains the exact string to match $string = "aaaabbbbccc"; if($string =~ /bc/){ print "found patternn"; } output: found pattern Perl 52

Simple Regular Expression q The variable ‘$& ’ is automatically set to the matched pattern $string = "aaaabbbbccc"; if($string =~ /bc/){ print "found pattern : $&n"; } output: found pattern bc Perl 53

Simple Regular Expression q What happen when you want to match a generalised pattern v like an "a" followed by some "b"s and a single "c" $string = "aaaabbbbccc"; if($string =~ /abbc/){ print "found pattern : $&n"; } else {print "nothing foundn"; } output: nothing found Perl 54

Regular Expression - Quantifiers q We can specify the number of times we want to see a specific character in a regular expression by adding operators behind the character. q ‘ * ’ (asterisk) v matches zero or more copies of a specific character q ‘ + ’ (plus) v matches one or more copies of a specific character Perl 55

Regular Expression - Quantifiers @array = ["ac", "abbc", "abb", "bbc", "bcf", "abbb", "c"]; foreach $string (@array){ if($string =~ /ab*c/){ print "$string "; } } output: ac abbc abbbc Perl 56

Regular Expression - Quantifiers @array = ["ac", "abbc", "abb", "bbc", "bcf", "abbb", "c"]; Regular Exp Matched pattern abc ab*c ac abbc abbbc ab+c abbc abbbc Perl 57

Regular Expression - Anchors q Anchor restrictions preceding and behind the pattern specify where along the string to match to. q ‘^’ indicates a beginning of a line restriction q ‘$’ indicates an end of line restriction Perl 58

Regular Expression - Anchors @array = ["ac", "abbc", "abb", "bbc", "bcf", "abbb", "c"]; Regular Exp Matched pattern ^bc bc ^b*c bbc bcf c ^b*c$ bbc c b*c$ ac abbc abbbc c Perl 59

Regular Expression - Range q […] is used to identify the exact characters you are searching for q [0123456789] will match a single numeric character q [0 -9] will also match a single numeric character q [A-Za-z] will match a single alphabet of any case Perl 60

Regular Expression - Range q Search for a word that v starts with the uppercase T v second letter is a lowercase alphabet v third letter is a lower case vowel v is 3 letters long followed by a space q Regular expression : "^T[a-z][aeiou] " q Note : [z-a] is backwards and does not work q Note : [A-z] does match upper and lowercase but also 6 additional characters between the upper and lower case letters in the ASCII chart: [ ] ^ _ ` Perl 61

Regular Expression - Others q Match a single character (non specific) with ". " (dot) a. c matches any string with "a" follow by one character and followed by "c" q Specifying number of repetition sets with "{" and "}“ [a-z]{4, 6} match four, five or six lower case alphabet q Remembering Patterns with "(, )" and "1" v Regular Exp allows you to remember and recall patterns Perl 62

Reg. Exp problem and strategies q You tend to match more lines than desired. A. *B matches AAB as well as AAAAAAACCCAABBBBAABBB q Knowing what you want to match q Knowing what you don’t want to match q Writing a pattern out to describe that you want to match q Testing the pattern Perl 63

Web Servers & CGI q Most web server are capable of running CGI programs. q The server must be able to determine whether a URI refers to: v Document • just send it back v CGI program • run it and send back the result. CGI … 65

CGI recognition q Some servers insist that CGI programs be in a special place v typically the URL path is one of: /CGI-BIN /cgi-bin /CGI /cgibin q Some servers look at the filename: v filename ends with. cgi q Some servers are given a list of URLS that are CGIs CGI … 66

User files and Web Servers On Unix based web servers, the URL /~username is typically mapped to the directory ~username/public. html -or~username/public_html CGI … 67

www. cse. unr. edu q On the CSE web server you should put your files in ~/public. html The URI http: //www. cse. unr. edu/~you is your home page where you is your CSE username. CGI … 68

Directories q Most web servers do the following when a URL maps to a directory: v if there is a file named index. html in the directory • it is sent back. v if there is no index. html, • an HTML formatted directory listing is sent back. CGI … 69

Debugging q It's hard to debug a CGI program! q Debugging print statements should generate HTML. q You can run the program from the Unix command line v you just need to set the environment variables right (use GET for this). CGI … 70

CGI script example Perl 71

HTML for Forms

This is a sample page to read two data items from the web page:

Perl - CGI script #!/usr/bin/perl print “Content-Type: text/htmlnn”; print “n”; print “n”; print “n”; print “

Query_string is $ENV{'QUERY_STRING'}n”; foreach ( split( /&/, $ENV{'QUERY_STRING'}) ) { ( $key, $val ) = split( /=/, $_, 2 ); $tmp{$key} = $val; } print “

First name is $tmp{'xfirst'}n”; print “

Last name is $tmp{'xlast'}n”; print “n” • Perl program first reads parameters as xfirst&zlast from $ENV (environment) into QUERY_STRING • Output of Perl is the syntax of an HTML page that is displayed Perl 73