ASP: Course 2

1
ASP Course 2

• An Introduction to Server-side Scripting
  Continued...

2
ASP References

• ASP
• http//www.aspalliance.com
• http//www.activeserverpages.com
• http//www.15seconds.com
• http//www.asphole.com
• VBScript
• http//msdn.microsoft.com/scripting/vbscript/doc/v
  bstoc.htm

3
Overview
Client
Response
Server Object
Application Object
Request
Session Object
ObjectContext
From Prof. Server Pages (WROX) p. 83
4
Response Object

• .Write( ) is used to send text back to the
  client. If the text contains markup information
  (Elements) those are sent and interpreted by the
  browser. Compose strings using the cStr() and
  vbScript Commands.
• The operator by alone equivalent to
  response.write() lt var gt
• .Redirect() sends the user to another page. Must
  use .buffer/.flush OR use before ltHTMLgt element.
  Can be used in combination with Browser
  Capabilities Component to direct users to a
  different page.
• .Clear, .Buffer, .Flush manages how the client
  receives the stream (default is line by line,
  buffered is at end of page or on .Flush.)
• .Expires or .ExpiresAbsolute properties sets how
  long the browser should cache the page, for most
  ASP pages this should be very small.
• .AppendToLog() is very useful for recording
  things to the log.
• The cookies() collection is used to write cookies
  TO the browser.

5
Request Object

• .Cookies() collection is the cookies fetched from
  the client.
• .ServerVariables() collection allows the
  programmer to get at environment variables and
  HTTP header information.
• The Request object contains the information from
  Forms and CGI style queries (from last time).
• Two Collections
• .QueryString() for command line parameters
  (?A1v1A2v2) and GET action calls.
• Form() for POST action calls.
• BOTH may be used. In fact using both is the best
  and trickiest trick of all. (More about this next
  time!)

6
Request Object and Forms

• The request objects two collections QueryString()
  and Forms() "front" for the command line
  parameters and STDIN data (from CGI) giving ASP
  programmers a leg up on coping with forms.
• (ltform action'get' gt) The QueryString()
  collection parses
• ?arg1v1arg2v2
• v1 request.QueryString("arg1") , v2
  request.QueryString("arg2")
• (ltform action'post' gt) The forms collection
  parses the STDIN stream (in the http header) into
  control name, value pairs
• ltinput type'text' name'txtX'gt
• v1request.forms("txtX")

7
ASP and Forms
For forms whose action property is 'GET' the form
elements are sent as parameters after the ?
Separated by For forms whose action property
is 'POST' the form elements are sent as part of
the message header to the server.
ltform method'___' action'http//myServer/xyz.asp
gt lt/formgt
1
2
Xyz.ASP
myServer
Explicit Parameters or GET form fields --gt
Request.QueryString()
Submit
http//myServer/xyz.asp?Arg1XArg2Y
Page on Client
3
Response Returned as HTML to Caller
8
Application Object

• Object contains two important events OnStart()
  events launch with the first invocation of the
  page. OnEnd() events occur during an orderly
  shutdown of webserver. These events can be used
  to create a single instance of an object to be
  used across all sessions (e.g., some business
  logic components or a helper object like a
  discussion web engine)
• Can provide coordination across all instances of
  a page by use of application collections contents
  and staticobjects, the semaphore methods lock and
  unlock being used to control access to the
  critical sections.
• Application.Lock 'Prevent other
  sessions from accessing the contents collection
• Application("myAppVar") 37 'set a value
• Application.Unlock 'Clear locks

9
Session Object

• A session is a series of visits by the same
  person to an ASP application in a defined time
  period (default timeout is 30 minutes).
• A session starts when the user hits a page with
  sessions enabled for the first time (i.e., the
  global.asa file contains the session_onstart()
  event or when the session object is referenced).
• A session ends when either the abandon method is
  called or when no response from the client occurs
  within the timeout period thus firing the
  session_onend() event.
• Like the application object, the collections
  contents and staticobjects are used to reference
  variables and objects created in the scope of the
  session.
• Sessions depend on cookies! Test for browser
  having cookies enabled by sending and receiving a
  cookie.

10
Server Object

• The .CreateObject() function is most commonly
  used method. It is used to create instances of
  createable objects such as
• Filesystem (Represents files and file operations)
• TextStream (used for i/o to files)
• ADODB (the most common type of database
  connection and recordset library)
• Browser Capabilities Component

11
ObjectContext Object

• Used for making transaction based applications
  using Microsoft Transaction Server (IIS 4 runs
  on top of it!)
• It provides the handle to the specific
  transaction objects and its methods control the
  successful completion of the transactions
  themselves (or not as the case may be.)
• This allows building web apps that can cooperate
  in n-Phase commitment following the ACID (Atomic,
  Consistent, Isolated, and Durable) rules.
• The typical example would be pages that allow
  people to do web banking or stock trading.

12
ASP and Cookies
Client Browser
1
Xyz.ASP
myServer
Response.Cookies() sent to browser
Request.Cookies() gets them back
2
13
Sending Cookies.

• A cookie is a small piece of information that is
  sent back with the response page that contains
  programmer defined strings.
• In practice any type of information can be sent
  once it is converted to string with the cStr().
• Cookies can contain arrays of data. The elements
  are called Keys. (More about this on the Request
  object.)
• The properties
• .Expires (For cookies that are of limited
  duration)
• .Domain (So that the cookie is specific to a
  site)
• .Path (rarely used, specifies a particular
  location on a site)
• .Secure (Specifies that the cookie should be
  transmitted using https//)
• Cookies are good. Some people are misinformed
  about cookies and their dangers. ASP Applications
  (using sessions) require cookies.

14
Small Cookies Example
'This sends a cookie with a single value to the
client ' which expires 5/2/2023. Response.cookies
("mySiteCookie") "Moo Cows are
Fun" Response.cookies("mySiteCookie").expires
5/2/2023 Response.cookies("mySiteCookie").domain
'/www.moo.cows/'
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Getting Cookies from the Client
'Use for each to iterate cookies collection 'From
Wrox Prof ASP Book pg. 109 dim item dim
itemkey for each item in request.cookies if
request.cookies(item).HasKeys then for each
itemkey in request.cookies(item) ...
request.cookies(item)(itemkey) next else ...
request.cookies(item) end if next 'Get the
cookie we sent several slides ago item
request.cookie("mySiteCookie")