Developing Web Applications

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Lecture 8 More PHP
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• Review
• PHP Basics
• Variables and arrays
• Output
• Sequence, repetition and selection

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• This week
• Forms
• Email
• Functions
• Cookies
• Sessions

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PHP for Forms

• HTML Forms are used to select different kinds of
  user input.
• Make your form using your favourite tool
• Set the form action attribute to
• ltform action"lt?php echo PHP_SELF ?gt"
  method"post"gt - or
• ltform action"script.php" method"post"gt
• Any form element in an HTML page will
  automatically be available to your PHP scripts.
  Make sure that you name each form field that you
  want to process as these names will be available
  to the processing script as variables
• ltinput type"text" name"inputtext"gt
• inputtext will contain whatever is typed into
  the text field

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Form Validation

• User input should be validated whenever possible.
  
• Client side validation is faster, and will reduce
  server load.
• However, client side validation is not secure.
• Should use server side validation if the form
  accesses a database.
• Good server side form validation post the form
  to itself, not to a different page.
• The user will then get the error messages on the
  same page as the form. This makes it easier to
  discover the error.

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PHP for Forms

• When a form is submitted to a PHP script, any
  elements from that form will be automatically
  made available to the PHP script as variables.
• These variables will be located in the
  associative arrays HTTP_POST_VARS,
  HTTP_GET_VARS
• Example -- simple form variable
• ltform action"foo.php"
  method"post"gt
• Name ltinput
  type"text" name"username"gtltbrgt
• ltinput
  type"submit"gt
• lt/formgt
• When the above form is submitted, the value from
  the text input will be available in
  HTTP_POST_VARS'username.

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Form Example

• ltHTMLgt
• ltHEADgt
• ltTITLEgtForm example 1lt/TITLEgt
• lt/HEADgt
• ltBODYgt
• lt!-- File form1 --gt
• ltFORM METHOD"POST" ACTIONscript1.php"gt
• Enter a numeric value
• ltBRgtltINPUT TYPE"TEXT" NAME"number"gt
• lt/FORMgt
• lt/BODYgt
• lt/HTMLgt

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Form Example Processing

• ltHTMLgt
• ltHEADgt
• ltTITLEgtForm 1 processinglt/TITLEgt
• lt/HEADgt
• ltBODYgt
• lt! script1.php --gt
• lt?php
• number _POSTnumber
• echo "The number entered was number."
• if (number gt 10)
• echo "ltBRgtThat's a big number."
• ?gt
• lt/BODYgt
• lt/HTMLgt

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The _GET Variable

• The _GET variable is used to collect values from
  a form with method"get".
• This variable is an associative array of variable
  names and values sent by the HTTP GET method.
• Information sent from a form with the GET method
  is visible to everyone (it will be displayed in
  the browser's address bar) and it has limits on
  the amount of information to send (max. 100
  characters).
• So this method should not be used when sending
  passwords or other sensitive information!
• However, because the variables are displayed in
  the URL, it is possible to bookmark the page.
  This can be useful in some cases.

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Example

• ltform action"welcome.php" method"get"gt
• Name ltinput type"text" name"name" /gt
• Age ltinput type"text" name"age" /gt
• ltinput type"submit" /gt
• lt/formgt
• When the user clicks the "Submit" button, the URL
  sent could look something like this
• http//www.w3schools.com/welcome.php?namePeterag
  e37
• The "welcome.php" file can now use the _GET
  variable to catch the form data
• Welcome lt?php echo _GET"name" ?gt.ltbr /gt
• You are lt?php echo _GET"age" ?gt years old!

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The _REQUEST Variable

• The PHP _REQUEST variable contains the contents
  of _GET, _POST, and _COOKIE.
• The PHP _REQUEST variable can be used to get the
  result from form data sent with both the GET and
  POST methods.
• Example
• Welcome lt?php echo _REQUEST"name" ?gt.ltbr /gt
• You are lt?php echo _REQUEST"age" ?gt years old!

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The _POST Variable

• The _POST variable is used to collect values
  from a form with method"post".
• The _POST variable is an associative array of
  variable names and values sent by the HTTP POST
  method.
• Information sent from a form with the POST method
  is invisible to others and has no limits on the
  amount of information to send.
• However, because the variables are not displayed
  in the URL, it is not possible to bookmark the
  page.

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PHP Predefined variables

• PHP has a range of predefined variables available
  - for example Apache variables, environment
  variables and PHP-specific variables
• PHP_SELF - the filename of the currently
  executing script
• HTTP_POST_VARS - an associative array of
  variables passed to the current script via the
  HTTP POST method.
• HTTP_GET_VARS - an associative array of
  variables passed to the current script via the
  HTTP GET method.
• HTTP_ENV_VARS - an associative array of
  variables passed to the current script via the
  parent environment.
• SERVER_NAME - the name of the server host under
  which the current script is executing.
• DOCUMENT_ROOT - the document root directory
  under which the current script is executing, as
  defined in the server's configuration file.
• HTTP_REFERER - the address of the page (if any)
  which referred the browser to the current page.
• REMOTE_ADDR - IP address of the client
• REMOTE_HOST - Host name of the client

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Sending email by PHP

• PHP allows you to send e-mails directly from a
  script.
• The PHP mail() function is used to send emails
  from inside a script.
• Syntax
• mail(to,subject,message,headers,parameters)

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• Sending an email
• //recipient's email address
• to EMAIL
• //subject of the message
• re COURSE_TITLE." Submission"
• //message from the feedback form
• comments "Hello student, your submission for
  ".COURSE_TITLE." course work has been
  successful\n\n"
• msg comments."\n\nFile file_name\n
  Assignment ass\n Size file_size bytes\n Type
  file_type\n Receipt Code part_code\n\n!Remember
  to keep a copy of this work!\n"
• //set the From header
• headers "From ".COURSE_EMAIL
• //send the email now...
• mail(to,re,msg, headers)

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PHP Mail Form
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PHP cookies

• A cookie is often used to identify a user.
• A cookie is a small file that the server embeds
  on the user's computer.
• Each time the same computer requests a page with
  a browser, it will send the cookie too.
• With PHP, you can both create and retrieve cookie
  values.
• Problems
• User can disable cookies in the browser
• Cookies may be viewed by other users
• Can only store 20 cookies max 4KB.

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How to Create a Cookie?

• The setcookie() function is used to set or create
  a cookie.
• Note The setcookie() function must appear BEFORE
  the lthtmlgt tag.
• Syntax setcookie(name, value, expire, path,
  domain)
• Example 1
• lt?php setcookie("user", "Alex Porter",
  time()3600) ?gt
• lthtmlgt .....
• Example 2
• lt?php expiretime()60602430
• setcookie("user", "Alex Porter", expire) ?gt
• lthtmlgt .....
• Note The value of the cookie is automatically
  URLencoded when sending the cookie, and
  automatically decoded when received (to prevent
  URLencoding, use setrawcookie() instead).

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How to Retrieve a Cookie Value?

• The PHP _COOKIE variable is used to retrieve a
  cookie value.
• Example
• lt?php// Print a cookieecho _COOKIE"user"
• // A way to view all cookies
• print_r(_COOKIE)
• ?gt

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How to Retrieve a Cookie Value?

• lthtmlgt ltbodygt
• lt?php
• if (isset(_COOKIE"user"))
• echo "Welcome " . _COOKIE"user" . "!ltbr /gt"
  
• else
• echo "Welcome guest!ltbr /gt"
• ?gt
• lt/bodygt lt/htmlgt

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Deleting a Cookie

• Automatically deleted after expiration time
• Can manually delete by setting negative time
• setcookie(username,,time()-3600)

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Sessions

• Application and session When you are working
  with an application, you open it, do some changes
  and then you close it. This is much like a
  Session. The computer knows who you are. It knows
  when you start the application and when you end.
  But on the internet there is one problem the web
  server does not know who you are and what you do
  because the HTTP address doesn't maintain state.
• A PHP session solves this problem by allowing you
  to store user information on the server for later
  use (i.e. username, shopping items, etc).
• However, session information is temporary and
  will be deleted after the user has left the
  website. If you need a permanent storage you may
  want to store the data in a database.
• Sessions work by creating a unique id (UID) for
  each visitor and store information about the
  visitor based on this UID. The UID is either
  stored in a cookie or is propagated via URL
  between different pages.

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Sessions

• UID and related information can be stored as
  cookies, but cookies can be disabled by a
  browser.
• Need to store on the server, through the use of
  session variables.
• A session variable is used to store information
  about a user session, and is available to all
  pages in one application.
• Built-in SESSION associative array variable
• User-defined must be registered.
• Session variables can be deleted after use.

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Start a PHP Session

• Before you can store user information in your PHP
  session, you must first start up the session by
  the session_start() function.
• This function must appear BEFORE lthtmlgt
• lt?php session_start() ?gt
• lthtmlgt ltbodygt lt/bodygt lt/htmlgt
• The code above will register the user's session
  with the server, allow you to start saving user
  information, and assign a UID for that user's
  session.

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Use Built-in Session Variable

• lt?php session_start()
• _SESSION'views'1 // store session data
• ?gt
• lthtmlgt ltbodygt
• lt?php
• echo "Pageviews". _SESSION'views'
  //retrieve session data
• ?gt
• lt/bodygt lt/htmlgt
• Output
• Pageviews1

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An example page-views counter

• The isset() function checks if the "views"
  variable has already been set. If "views" has
  been set, we can increment our counter. If
  "views" doesn't exist, we create a "views"
  variable, and set it to 1
• lt?phpsession_start()
• if(isset(_SESSION'views')) _SESSION'views'
  _SESSION'views'1else _SESSION'views'1
  echo "Views". _SESSION'views' ?gt

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Register user-defined session variables

• To register a session variable, call
• session_register("variable_name").
• On all subsequent pages that uses sessions (by
  calling session_start()), the variable
  variable_name will become available.
• Store and retrieve values through this variable.

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count.php

• lt?php
• session_start()
• session_register("count")
• count
• msg"You have visited the page count times in
  this session"
• ?gt
• lthtmlgtltheadgtlttitlegtCount visitslt/titlegtlt/headgt
• ltbodygt
• lt?php echo( msg ) ?gt
• lt/bodygtlt/htmlgt

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Destroy a Session

• To delete some session data
• unset() delete a session variable free up
  space
• session_destroy() delete a whole session and you
  lose all stored session data
• lt?php unset(_SESSION'views') ?gt
• lt?php session_destroy() ?gt

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• Using session variables for authentication in
  conjunction with a database . Create a login-page
  gives the user a userid and password form and
  posts to another PHP page (this example uses
  mysql)  
• lt?php
• session_start()
• if (userid password)
• res mysql_query("SELECT userid FROM users
  WHERE userid'userid' AND password'password'")
  
• if(mysql_num_rows(res) ! 0)
• verified_user userid
• session_register("verified_user")
• Header("Location your_main_page.php")
• ?gt  
• Now, on 'your_main_page.php', you call
  session_start() and then you can check the
  verified_user variable to see if the user has
  been authenticated (and who he is). Other uses
  for session variables, easing database load by
  caching certain values in the session rather than
  reading them from the database on each page
  access.

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Session Functions

• session_start -- Initialise session data
• session_destroy -- Destroys all data registered
  to a session
• session_name -- Get and/or set the current
  session name
• session_module_name -- Get and/or set the current
  session module
• session_save_path -- Get and/or set the current
  session save path
• session_id -- Get and/or set the current session
  id
• session_register -- Register one or more
  variables with the current session
• session_unregister -- Unregister a variable from
  the current session
• session_unset -- Free all session variables
• session_is_registered -- Find out if a variable
  is registered in a session
• session_get_cookie_params -- Get the session
  cookie parameters
• session_set_cookie_params -- Set the session
  cookie parameters
• session_decode -- Decodes session data from a
  string
• session_encode -- Encodes the current session
  data as a string
• session_set_save_handler -- Sets user-level
  session storage functions
• session_cache_limiter -- Get and/or set the
  current cache limiter
• session_cache_expire -- Return current cache
  expire
• session_write_close -- Write session data and end
  session

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Redirection

• Once login data is captured/validated then want
  to go to a new page.
• Header(Location URL)
• header("Location http//ralph-moseley.co.uk/cmt3
  092/lab7.html")
• General technique
• Site start page login page
• Login page validates user and set cookies
• Redirect to new page
• New page uses cookie data to access DB info

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Using Custom Functions

• If you have some things that you do in a number
  of different scripts, you might consider putting
  them into custom functions. You could collect
  them into a file called functions.php and include
  them in all your scripts, or you could name them
  individually and include them only as needed.
  For example, you might want to make your own mail
  function which includes some default values. To
  make it flexible, you will want to pass it
  information (arguments) to use in different
  circumstances.

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• You could use the previous email example as a
  function and turn it into one with the header
• my_mail("My sample subject", msg, email)
• You could then include it in all your scripts as
• require (functions.php)

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Functions

• Another example of a function
• function compute_area(height, width)
• return heightwidth
• Function names are not case sensitive
• Return statement terminates function
• Exit() terminates script
• If no return statement NULL is returned

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Default Arguments

• Eg. function gst(amount, rate0.12)
• Return amountrate
• May be called using to override rate
• tax gst(purchase, 0.08)
• Or to use default rate
• tax gst(purchase)

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Today

• Forms
• Email
• Functions
• Cookies
• Sessions

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Next Week

• Databases SQL