Presentation Layer: Three different approaches. Database Access Layer: same as above.

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1 Overview of web application development Overview of ASP HTTP request/response processing State management of the script logic Microsoft Scripting Runtime library Remote Scripting Ch 5 - ASP 1

2 Presentation Layer: Three different approaches ASP mostly COM-based DLL using ASP as the glue WebClass Business Logic Layer: COM-based DLL using ASP as the glue Run the DLL within MTS (Microsoft Transaction Server) Database Access Layer: same as above. Ch 5 - ASP 2

3 Accept input that the user has entered in HTML forms. Interpret its users' requests and run whatever commands are appropriate. Generate HTML that contains page content and layout details and send it back to the browser. Ch 5 - ASP 3

4 Puts all the presentation-tier code along with the layout details inside ASP. Upsides: Productivity is high due to WYSIWYG nature of the page editor (InterDev) It s fast and easy to change pages on a production site. Downside: Slow (interpretative mode) Code reuse made difficult (codes are stored as pages) Ch 5 - ASP 4

5 Uses ASP script as little as possible. Puts all presentation-tier code inside one or more COMbased DLLs. Generates all page content and layout details dynamically. Data-driven approach: DLLs using content and layout as input parameters. Upside: it avoids all downsides of ASP approach Downside: Compile-approach makes presentation coding tedious. Data-driven approach requires skilled programming Ch 5 - ASP 5

6 Uses the same approach as COM fanatic, but uses the WebClass framework as a starting point instead of starting from scratch. WebClasses represent a framework for data-driven approach built on top of ASP. Downsides: Your preferred approach may differ from that of the WebClass architects You must understand well the WebClass architecture. WebClasses does not understand MTS. Political risk (?) Ch 5 - ASP 6

7 Start with ASP to find out how others write codes to perform the presentation tasks. Graduating from ASP coding, pick up skill in data-driven approach by using WebClasses. As an experienced, career Web programmer, build your own framework using your own COM-based DLLs. Ch 5 - ASP 7

8 What is an ASP Page: A file with.asp suffix A combination of HTML statements and script logic for execution on the server side Script logic written as Jscript or Vbscript Access to Microsoft Scripting Runtime library Enclosed in <% %> for processing by ASP.DLL which results in HTML primitives. Programming Constructs: Intrinsic, pre-built and custom-built objects Global.asa Ch 5 - ASP 8

9 HTTP request/response processing State management of the script logic Transaction management Ch 5 - ASP 9

10 Client Request Object Response Object ObjectContext Object Server Object Server Application Object Sesson Object Ch 5 - ASP 10

11 Each Web Application has at most one file, Global.asa to store executable objects. The file is executed by IIS (not asp.dll) Contents of Global.asa: Scripts to process Application and Session events <OBJECT> declaration <object runat=server scope=session ID=abc>..</object> User Beware! Ch 5 - ASP 11

12 Much of the info is communicated to ASP by IIS through ServerVariables: e.g. Request.ServerVariables( http_user_agent ) Request.ServerVariable( last_modified ) Input values entered by the user are stored in Form and QueryString collections File posted by the user is read using BinaryRead method. Ch 5 - ASP 12

13 Caching directives: Response.CacheControl Response.Expire, Response.ExpireAbsolute Contents: Response.ContentType, Response.Charset Return-code Response.Status Re-direction: Response.redirect Output Response.write(firstname) Response.binarywrite mypicture Ch 5 - ASP 13

14 By default, ASP in IIS 4.0 does not buffer output info is sent as it is made available Consequence: all header info (e.g. cookie & redirection) must first be generated before the body. As an option, response.buffer may be set to true, which means more control how response is sent: clear (empty the content without sending) flush (send the current content in the buffer) end (stop response processing) Ch 5 - ASP 14

15 Send partial info early Avoid errors while using cookies and redirection. Trap errors which may cause modification of output Send dynamic contents by flushing the buffer regularly. Ch 5 - ASP 15

16 HTTP is a stateless protocol: each browser request to IIS is independent, and IIS retains no memory of browser s past request Client-server applications are inherently stateful, i.e. client and server enter into a dialogue containing multiple requests/responses. e.g. On-line shopping Being stateless is glorious! (if feasible) Ch 5 - ASP 16

17 Page-scope: information on the HTML page e.g. variable values. Session-scope: information needed to conduct a dialogue e.g. adding items to the shopping cart Application-scope: information that is global in nature and needs to be shared between all active sessions. e.g. Number of sales today Concurrency consideration (Application.Lock/.Unlock) External-scope: information managed by another application which does not depend on the web application. e.g. DBMS. Ch 5 - ASP 17

18 Pass-by-content: Move the state info back and forth on each request/response, using hidden HTML fields, HTTP cookies, or the (WebClass) URLData property. Pass-by-reference: Use objects on the server to store state information between client requests. objects: WebClass, ASP Session/Application Objects or VB COM objects (?!) Database may be used to store state information between requests. Ch 5 - ASP 18

19 <FORM NAME=frmEmployee METHOD=POST ACTION=process.asp> [...] <INPUT TYPE="Hidden" NAME="ExtraInfo"> </FORM> <SCRIPT Language="VBScript"> Function frmemployee_onsubmit document.frmemployee.extrainfo = time End Function </SCRIPT> Ch 5 - ASP 19

20 Originated by Netscape, the concept of cookie was formalized by the IETF standard RCF2109 (Feb. 1997) HTTP cookies provide the server with a mechanism to store and retrieve state information on the client application's system, e.g. client preference registration Ch 5 - ASP 20

21 A cookie has six attributes: Name Value Domain Path Expiry Time Security Cookie ID is a combination of Domain and Path Ch 5 - ASP 21

22 Creation by server: command on the set-cookie header: <name>=<value>, The client may reject the set-cookie header The client will send the stored cookie via a cookie header if the the incoming set-cookie header has the same cookie ID, and valid expiry time. The stored cookie with the client will be updated if set-cookie header is updated by the server. Ch 5 - ASP 22

23 Start of a session End of a session Use of cookie Maintenance of state of a session Ch 5 - ASP 23

24 Usual ways to begin a session: New user requests a URL that identifies an.asp file, and the Global.asa file for that application includes a Session_OnStart procedure Server receives a request that does not contain a valid SessionID cookie An event will be triggered, invoking the Session_OnStart procedure Ch 5 - ASP 24

25 Session timeout (20 minutes by default) Option: <% Session.Timeout = 5 %> Session abandoned by client or server <% Session.Abandon %> All variables remains until session_end event is processed. Ch 5 - ASP 25

26 SessionID is generated when the user request an.asp file for the first time. SessionID is sent to the user in the set-cookie header, with no expiry date. SessionID is sent to the server in the cookie header in subsequent requests in the same session. SessionID is used as a key to state information stored in the contents variables of sessionid or in the database. Ch 5 - ASP 26

27 ASP Session-Aware Load-Balancing In load-balancing (e.g. round-robin), the server may rotate within a session One solution: When the session is first created, the designated server runs a re-direct request to the specific server, e.g. <% Response.redirect( ) %> Use relative URL in subsequent requests. Ch 5 - ASP 27

28 ADO Ad Rotator Browser Capabilities Content Linking Content Rotator Page Counter Permission Checker Counters MyInfo Tools FileExists ProcessForm Random Ch 5 - ASP 28

29 It contains the following types of scripting objects: Directory objects system-managed hashed tables FileSystemObject objects file management functions TextStream objects text file management functions Err objects Ch 5 - ASP 29