~~SLIDESHOW~~ ====== PHP for Web Applications ====== **Supplementary Material** Provided for Reference. This material is no longer taught on this module. **Lecturer**: [[C.P.Jobling@Swansea.ac.uk|Dr Chris P. Jobling]]. Using PHP for web applications development. ===== PHP for Web Applications ===== We conclude our review of the Basics of PHP with a discussion of its use in creating web applications. ---- Based on Chapter 12 of Robert W. Sebasta, //Programming the World-Wide Web//, 3rd Edition, Addison Wesley, 2006. and Chapter 12 of Chris Bates, //Web Programming: Building Internet Applications//, 3rd Edition, John Wiley, 2006. ===== Contents of this Lecture ===== //PHP for web applications with examples// * [[eg-259:lecture18#queries_and_query_strings|Queries and Query Strings]] * [[eg-259:lecture18#form_handling|Form Handling]] * [[eg-259:lecture18#files|Files]] * [[eg-259:lecture18#storing_information_about_client_state|Storing Information about Client State]] * [[eg-259:lecture18#session_tracking|Session Tracking]] The [[eg-259:examples:php1#example_from_lecture_18|Examples for PHP for Web Applications]]. ===== Learning Outcomes ==== //At the end of this lecture you should be able to answer these questions//: - How can the value of a form element be accessed by a PHP script? - What is a file variable? - What is a file pointer? - What does an ''fopen'' function return if it fails? - Explain the parameters and actions of the ''fread'' function. ===== Learning Outcomes (continued) ===== //At the end of this lecture you should be able to answer these questions//: - What is returned by the ''fwrite'' function? - How can a cookie be created in a PHP script? - How can a script determine whether a particular cookie exists? - How can a variable be saved in a session? ===== Queries and Query Strings ===== * Parameters sent to a Web Application from a web browser take the form of a //query string// * The //query string// is either appended to the URI in a GET request as in: GET /webapp.cgi?query_string HTTP/1.1 Host: some.host.com : * or is carried in the payload of a POST request as in: POST /webapp.cgi HTTP/1.1 Host: some.host.com : query_string ===== Processing GET rquests ===== * Web server passes two environment variables to helper application * ''$REQUEST_METHOD=GET'' and ''$QUERY_STRING=query_string'' * The query string will be content of ''$QUERY_STRING'' (everything in resource name after query marker ''?'') ===== A Real GET request ===== * //From [[http://localhost/beer_get.html|beer example]]// GET /cgi-bin/echo_params.cgi?colour=light&taste=malty HTTP/1.1 Host: localhost User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-GB; rv:1.8.1.9) Gecko/20071025 Firefox/2.0.0.9 Creative ZENcast v2.00.14 Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 Accept-Language: en-gb,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Referer: http://localhost/beer_get.html ---- * Web application is ''/cgi-bin/echo_params.cgi'' * Host is ''localhost'' * Query string is ''colour=light&taste=malty'' * Although data comes from a form (//referer// is http://localhost/beer_get.html), request is equivalent to and indistinguishable from URI: http://localhost/cgi-bin/echo_params.cgi?colour=light&taste=malty. ===== Processing POST requests ===== * Data passed to helper application in //environment variables// and //standard input// * ''$REQUEST_METHOD=POST'' * ''$CONTENT_LENGTH'' gives size of payload * ''$CONTENT_TYPE'' is type of data: usually ''application/x-www-form-urlencoded'' * Query string is ''$CONTENT_LENGTH'' bytes read from //standard input// ===== A Real POST request ===== * //Also from [[http://localhost/beer_post.html|beer example]]// POST /cgi-bin/echo_params.cgi HTTP/1.1 Host: localhost User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-GB; rv:1.8.1.9) Gecko/20071025 Firefox/2.0.0.9 Creative ZENcast v2.00.14 Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 Accept-Language: en-gb,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Referer: http://localhost/beer_post.html Content-Type: application/x-www-form-urlencoded Content-Length: 24 colour=light&taste=malty ---- * Web application is ''/cgi-bin/echo_params.cgi'' * ''Host'' is ''localhost'' * ''Content-Type'' is ''application/x-www-form-urlencoded'' * ''Content-Length'' is 24 bytes * Query string is ''colour=light&taste=malty'' (is ASCII 24 bytes in length) ===== Query String Format ===== * A query string includes names and values of HTML form elements (widgets) * Widget values are always coded as strings * The form of a name/value pair in a query string is: name=value * If the form has more than one widget, their values are separated with ampersands: milk=2&payment=visa ===== URL Specification ===== * The specification for URLs ([[http://www.rfc-editor.org/rfc/rfc1738.txt|RFC 1738]], Dec. '94) limits the use of allowed characters in URLs to only a limited subset of the US-ASCII character set: > "...Only alphanumerics ''[0-9a-zA-Z]'', the special characters "''$-_.+!*'(),''" , and reserved characters used for their reserved purposes may be used unencoded within a URL." * Any source of general text that appears in an HTML page that may be represented in a URL has to be encoded to ensure that illegal characters do not appear. * This includes widget names, and widget values. ===== URL Encoding ===== * Performed automatically by Browser on form submission * Each special character is encoded as a percent sign and a two-character hexadecimal number (the ASCII code for the character) * Some browsers code spaces as plus signs, rather than as ''%20'' * You should URL encode any text that will be sent to the browser in a form widget, or in the ''action'', ''src'', ''href'', etc. ---- For more more information on URL encoding see ((Brian Wilson, URL Encoding (or: 'What are the "%20" codes in URLs?'), Index DOT Html, URL: http://www.blooberry.com/indexdot/html/topics/urlencoding.htm)) ===== URL Encoding – Examples ===== * URL encode general text (e.g. from file input or results of a previous form submission) '; ?> * URL encode user input, then convert results into valid HTML (e.g. & -> &) '; ?> ===== PHP and Query Data ===== * PHP takes care of extracting the query parameters for you * It maps the HTTP request fields into PHP variables * It extracts the query string from the HTTP request, extracts the name/value pairs and places them into an array. * Array ''$_GET'' will contain data for GET method and ''$_POST'' will contain data passed by the POST method * value subscripts are the widget names * This is transparent and it does not matter whether GET or POST method is used to transmit the form data ===== Query parameters ===== * If the query string has ''colour=light&taste=malty'' * ''$_POST["colour"]'' will return ''"light"'' and ''$_POST["taste"]'' will return ''"malty"'' * Query matching will also turn check box group ''colour=red&colour=blue'' to an array so that ''$_POST["colour"]'' returns the right thing. ===== Form Handling ===== * Simple in PHP * Forms could be handled by the same document that creates the form, but that may be confusing * Better to separate "view" from data handling ===== Example – Popcorn Sales ===== * //The Form Page (just HTML)// : [[/~eechris/eg-259/examples/lecture18/popcorn3.html|popcorn3.html]] ( [[http://localhost/eg-259/examples/lecture18/popcorn3.html|popcorn3.html @ localhost]] )

Welcome to Millennium Gymnastics Booster Club Popcorn Sales

Buyer's Name:
Street Address:
City, State, Zip:

Product Price Quantity
Unpopped Popcorn (1 lb.) $3.00
Caramel Popcorn (2 lb. canister) $3.50
Caramel Nut Popcorn (2 lb. canister) $4.50
Toffey Nut Popcorn (2 lb. canister) $5.00

Payment Method

Visa
Master Card
Discover
Check

---- Popcorn Sales - for PHP handling

Welcome to Millennium Gymnastics Booster Club Popcorn Sales

Buyer's Name:
Street Address:
City, State, Zip:

Product Price Quantity
Unpopped Popcorn (1 lb.) $3.00
Caramel Popcorn (2 lb. canister) $3.50
Caramel Nut Popcorn (2 lb. canister) $4.50
Toffey Nut Popcorn (2 lb. canister) $5.00

Payment Method

Visa
Master Card
Discover
Check

===== Example – Popcorn Sales Receipt ===== * //The results page -- HTML with embedded PHP//: popcorn3.php ---- Process the popcorn3.html form

Customer:

$street
$city
"); ?>

Order Information
Product Unit Price Quantity Ordered Item Cost
Unpopped Popcorn $3.00
Caramel Popcorn $3.50
Caramel Nut Popcorn $4.50
Toffey Nut Popcorn $5.00

"); printf("Your total bill is: $ %5.2f
",$total_price); print("Your chosen method of payment is: $payment
"); ?> * Output

Customer:




Order Information
Product Unit Price Quantity Ordered Item Cost
Unpopped Popcorn $3.00 0 $ 0.00
Caramel Popcorn $3.50 0 $ 0.00
Caramel Nut Popcorn $4.50 0 $ 0.00
Toffey Nut Popcorn $5.00 0 $ 0.00

You ordered 0 popcorn items
Your total bill is: $ 0.00
Your chosen method of payment is:
===== Files ===== * PHP can: * Deal with any files on the server * Deal with any files on the Internet, using either HTTP or FTP * Instead of filehandles, PHP associates a variable with a file, called the //file variable// (for program reference) * A file has a //file pointer// (where to read or write) ===== Opening a File ===== * Command to open a file and assign to a file variable: $fptr = fopen(filename, use_indicator) ===== File use indicators ===== ^ Indicator ^ Purpose ^ | ''r'' | read only, from the beginning | | ''r+'' | read and write, from the beginning | | ''w'' | write only, from the beginning (also creates the file, if necessary) | | ''w+'' | read and write, from the beginning (also creates the file, if necessary) | | ''a'' | write only, at the end, if it exists (creates the file, if necessary) | | ''a+'' | read and write, read at the beginning, write at the end | ===== File opening and closing ===== * Because //fopen// could fail, use it with die: $file_var = fopen("testdata.dat", "r") or die ("Error - testdata.dat cannot be opened"); * Use ''file_exists(filename)'' to determine whether file exists before trying to open it * Use ''fclose(file_var)'' to close a file ===== File use cases ===== - [[#read_all_or_part_of_the_file_into_a_string_variable|Read all or part of the file into a string variable]] - [[#read_the_lines_of_the_file_into_an_array|Read the lines of the file into an array]] - [[#read_one_line_from_the_file|Read one line from the file]] - [[#read_one_character_at_a_time|Read one character at a time]] ===== Read all or part of the file into a string variable ===== $str = fread(file_var, number_of_bytes) * To read the whole file, use ''filesize(file_name)'' as the second parameter ===== Read the lines of the file into an array ===== $file_lines = file(file_name) * Need not open or close the file ===== Read one line from the file ===== $line = fgets(file_var, number_of_bytes) * Reads characters until //eoln//, //eof//, or ''number_of_bytes'' characters have been read ===== Read one character at a time ===== $ch = fgetc(file_var) * Control reading lines or characters with //eof// detection using ''feof'' (''TRUE'' for ''eof''; ''FALSE'' otherwise): while( ! feof($file_var) ) { $ch = fgetc($file_var); } ===== Writing to files ===== * To write to a file use: $bytes_written = fwrite(file_var, string) * ''fwrite'' returns the number of bytes it wrote * Files can be locked (to avoid interference from concurrent accesses) with ''flock''((PHP Manual Page: [[http://uk3.php.net/flock|Flock]])) ===== Storing Information about Client State ===== * A session is the time span during which a browser interacts with a particular server * The HTTP protocol is stateless * But, there are several reasons why it is useful for the server to relate a request to a session * Shopping carts for many different simultaneous customers * Customer profiling for advertising * Customized interfaces for specific clients * Approaches to storing client information: * Store it on the server -- often too much to store! * Store it on the client machine -- this works ===== Session Tracking with Cookies ===== * A cookie is a small object of information consisting of a name and a textual value * Cookies are created by some software system on the server * Every HTTP communication between the browser and the server includes information in its header about the message * At the time a cookie is created, it is given a lifetime * Every time the browser sends a request to the server that created the cookie, while the cookie is still alive, the cookie is included * A browser can be set to reject all cookies ===== Baking Cookies ===== * Create a cookie with setcookie: setcookie(cookie_name, cookie_value, lifetime) * e.g.: setcookie("voted", "true", time() + 86400); * Cookies must be created before any other HTML is created by the script ---- //Lifetime// is measured in seconds. The value 86400 is 24 hours. The PHP function ''time()'' returns the number of seconds since the "//UNIX epoch date//" [Midnight GMT, 1st January 1970]. Thus the use of ''time() + 86400'' creates a cookie that expires 24 hours from the time it was set. ===== Consuming Cookies ===== * Cookies are obtained in a script the same way form values are obtained, using the ''$_COOKIES'' array ===== Session Tracking ===== * For session tracking, PHP creates and maintains a session tracking id * Create the id with a call to ''session_start'' with no parameters * Subsequent calls to ''session_start'' retrieves any session variables that were previously registered in the session ===== Session Tracking ===== * To create a session variable, use the global array ''$_SESSION'' ===== Session Tracking: Example ===== * To count number of pages visited in a web site, put the following code in all documents: : "); $_SESSION['page_number']++; ?> ===== Summary of this Lecture ===== //PHP for web applications with examples// * [[eg-259:lecture18#queries_and_query_strings|Queries and Query Strings]] * [[eg-259:lecture18#form_handling|Form Handling]] * [[eg-259:lecture18#files|Files]] * [[eg-259:lecture18#storing_information_about_client_state|Storing Information about Client State]] * [[eg-259:lecture18#session_tracking|Session Tracking]] The [[eg-259:examples:php1#examples_from_lecture_18|Examples for PHP for Web Applications]]. ===== Learning Outcomes ==== //At the end of this lecture you should be able to answer these questions//: - How can the value of a form element be accessed by a PHP script? - What is a file variable? - What is a file pointer? - What does an ''fopen'' function return if it fails? - Explain the parameters and actions of the ''fread'' function. ===== Learning Outcomes (continued) ===== //At the end of this lecture you should be able to answer these questions//: - What is returned by the ''fwrite'' function? - How can a cookie be created in a PHP script? - How can a script determine whether a particular cookie exists? - How can a variable be saved in a session? ===== Homework Exercise ===== Write, test, and debug (if necessary) a PHP script for the following function. Write functions and the code to test them. - //Parameter//: A file variable of a file of text, where the words are separated by spaces or colons. //Return value//: The word that appears most often in the file. There are more exercises [[eg-259:homework:18|here]] and in the [[eg-259:cw2|second coursework]]. ===== What's Next? ===== **Database Access through the Web** * [[eg-259:lecture19#relational_databases|Relational Databases]] * [[eg-259:extras:dbandsql|Introduction to SQL]] (not examined) * [[eg-259:lecture19#architectures_for_database_access|Architectures for Database Access]] * [[eg-259:lecture19#the_mysql_database_system|Introducing MySQL]] * [[eg-259:lecture19#database_access_with_php_mysql|Database Access with PHP and MySQL]] [[eg-259:lecture17|Previous Lecture]] | [[eg-259:home]] | [[eg-259:lecture19|Next Lecture]]