A348 Active Server Pages

• Basics
• Exercise 1 - Basic HTML, ASP and .Net
• Request and Response Objects
• User Interaction
  • Exercise 2 - Get Method
  • Exercise 3 - Post Method
• Server Variables
• Hidden Variables to Maintain State
• Exercise 4 - State

Basics

Microsoft ASP technology is a server-side programming technology primarily used to generate HTML and access databases, files and any other server resource.  Programs consist of scripts executed by an interpreter (JavaScript, VBScript, PerlScript, etc.) within the server space. One advantage of ASP scripts is they are generally light-weight to execute assuming the script interpreter is re-entrant and can be managed by the server to limit resources allocated to the script. The scripting languages are simple to program but limited but can be extended via ActiveX objects. A key disadvantage is ASP is not a cross-platform standard across servers so moving applications from a Microsoft Web server may be painful.

ASP.Net attempts to separate implementation logic (i.e. programming) from the user interface; but it is more tightly integrated into Microsoft software and offers fewer industry standard choices of languages.

We will use ASP and JavaScript as these are most commonly available in some version or flavor on other servers.

Example - The following uses an ASP VBScript on the server to generate text for the current time on the server. The time.Asp file can be executed from a virtual directory by (assuming the time.Asp file is in virtual directory A348 on the localhost):

http://localhost/A348/Time.asp

VBScript time.Asp Time is <%=Time()%>.

HTML Generated Time is 7:24:07 PM.

Points of Note

• <%=Time()%> Outputs the value of the VBScript Time( ) function to the page being generated by the server to the client. Anything between <%= and %> is evaluated and output to the browser by VBScript.

Example - The following uses ASP JavaScript to display Hello World three times.

JavaScript HelloWorld.Asp <%@ LANGUAGE = JScript %> <% for(i=1;i<=3;i++) { %> Hello World <%=i%><br/> <% } %>

HTML Generated Hello World 1<br> Hello World 2<br> Hello World 3<br>

Example - The following uses an ASP VBScript (in bold) on the server to generate a combination of HTML and JavaScript for the client browser. Clicking 4Buttons.Asp executes directly from the IUS server or download to A348 virtual directory and execute from the local server by: 

http://localhost/A348/4Buttons.Asp

VBScript 4Buttons.Asp <%@ Language=VBScript%> <title>Buttons</title> <h1>Buttons</h1> <form> <%  For intCounter = 1 to 4 %>  <INPUT TYPE = button     VALUE = Button<%=intCounter%>     OnClick="Button<%=intCounter%>_Click()" > <%  Next %> </form> <Script Language="JavaScript"> <% For intCounter = 1 to 4 %>   function Button<%=intCounter%>_Click() {    alert("Clicked button <%=intCounter%>");  } <% Next %> </Script>

HTML and JavaScript Generated <title>Buttons</title> <h1>Buttons</h1> <form>   <INPUT TYPE = button       VALUE = Button1       OnClick = "Button1_Click()">   <INPUT TYPE = button       VALUE = Button2       OnClick = "Button2_Click()">   <INPUT TYPE = button       VALUE = Button3  OnClick = "Button3_Click()">   <INPUT TYPE = button       VALUE = Button4       OnClick = "Button4_Click()"> </form> <Script Language="JavaScript">   function Button1_Click() {    alert( "Clicked button 1");   }   function Button2_Click() {    alert( "Clicked button 2");   }   function Button3_Click() {    alert( "Clicked button 3");   }   function Button4_Click() {    alert( "Clicked button 4");   } </Script>

Points of note

• <%@ Language=VBScript%> Defines the scripting language, it is possible to have multiple scripting languages in the same file.
• <% %> Mark the beginning and end of VBScript/JavaScript/PerlScript. The default script is VBScript.

  Example: <% For i = 1 to 4 %>

• <%=variable%> Outputs the value of variable to the page being generated to the browser client.

Script file only

When a script will re-execute itself several times there may be no HTML file needed. For example, the ASP below re-executes itself each time the Again submit button is clicked.

JavaScript Again.Asp

<%@ LANGUAGE = JScript %> 

<FORM Method='GET' Action='Again.asp'> 
    <Input Type=Submit value="Again">
</FORM>

HTML Generated

<FORM Method='GET' Action='Again.asp'> 
    <Input Type=Submit value="Again">
</FORM>

Request and Response Objects

Request yields input from the browser GET or POST methods. The value of the form input variable named "BuyHigh" is given by:

• Request("BuyHigh")

Response outputs to the browser among other uses. To output the string <h1>Hello</h1> from JavaScript:

• Response.Write("<h1>Hello</1>");

User Interaction 

The main motivation for server-side programming is to interact with the Web client by getting input from the client and sending back HTML. There are three main HTML methods for the client to send data back to the server from HTML forms:

1. GET
2. POST
3. Send data as part of the URL, a ? is appended to the URL followed by data. This will be examined later in the course.

HTML <FORM> 

Sending parameters to a server program from a HTML input form uses the GET or POST method. The main difference is that the GET passes parameters in the URL or address so is limited to how much data can be passed. The POST method passes parameters back to the server through standard input so is effectively unlimited in the amount of data that can be returned. 

The following uses named parameters in HTML form as program arguments. The <Input Type='Text' name="myname"> defines a text box for input and the parameter of myname.

Form GET Method 

The GET method passes user data from the browser to the server as part of the URL. The Get method and form to input from a Text box is:

GetName.htm

<FORM Method='GET' Action='http://localhost/A348/GetName.asp'>             Enter your name: <Input Type='Text' name="myname"><br> </FORM>

GET - Form data is passed to server appended to the URL.   Action - The URL when user presses the Enter key. Text - The browser renders a text box for user input. myname - The name of the text box. Suppose that ABC is entered into the text box. Browser will send myname=ABC for the myname text box value.

The browser passes the parameters to the server appended to the URL, the server passes the parameters to the ASP program in a Request variable. The GetName.asp program reads the variable and parses out the "myname=" string and assigns whatever string follows to the character array myname. The steps followed are roughly:

1. Load the GetName.htm file into the browser, enter Ray, and press Enter.
2. The form instructs the browser to send request http://localhost/A348/GetName.asp?myname=Ray which executes the GetName.asp program with parameter data myname=Ray.
3. The GetName.asp program requests the value of myname  giving the response output of:

   <H1>Hello Ray</H1>

4. The output of <H1>Hello Ray</H1> is passed back from the server to the browser which renders the HTML.

<FORM Method='GET'>

GetName.htm <FORM Method='GET'               Action='http://localhost/A348/GetName.asp'> Enter your name: <Input Type='Text' name="myname"> </FORM>   GetName.asp <H1> Hello <%= Request("myname") %> </H1> URL generated on browser for form http://localhost/A348/GetName.asp?myname=Ray

Output <H1>Hello Ray</H1>

Points of note:

• Request("myname") - Returns the string "Ray".

Form POST Method

The POST method differs from the GET by sending user data to the server, not appended to the URL, but as an input stream. The server passes the data stream to the ASP program on standard input so essentially the amount of data sent from the browser client is unlimited. 

In ASP, the Request object handles GET and POST identically.

<FORM Method='POST'>

Post.htm <FORM Method='POST'               Action='http://localhost/A348/Post.asp'> Enter your name: <Input Type='Text' name="myname"> </FORM>   Post.asp <H1> Hello <%= Request("myname") %> </H1> URL generated on browser for form http://localhost/A348/Post.asp Standard input passed to ASP program myname=Ray

Output <H1>Hello Ray</H1>

Server variables

The operating system maintains state in part through the use of global variables. At the Command prompt these variable can be displayed by the SET command.

SET COMPUTERNAME=RAY ComSpec=C:\WINDOWS\system32\cmd.exe HOMEDRIVE=C: NUMBER_OF_PROCESSORS=2 OS=Windows_NT Path=c:\apps\imagemagick-6.2.1-q16;C:\apps\ PROCESSOR_ARCHITECTURE=x86 PROCESSOR_IDENTIFIER=x86 Family 15 Model 2 PROMPT=$P$G SystemRoot=C:\WINDOWS USERNAME=ray

The server and operating system maintain a large number of server variables that can be examined by an ASP program. The following prints all server variables back to the browser. Note that the browser output has been edited to reduce size.

The ServerVariables collection has the following properties:

• Item - The value of a specific item by name. For example, the following are equivalent, returning the value of SERVER_PORT, normally 80: 
  • Request.ServerVariables.Item("SERVER_PORT")
  • Request("SERVER_PORT")
• Key - Returns the name of a specific in the collection. The following returns the string "SERVER_PORT":
  • Request.ServerVariables.Key(38)
• Count - The number of ServerVariables in the collection. Example:
  • Request.ServerVariables.Count()

The server variable QUERY_STRING contains any form variables returned by the GET method.

Server Variables

Browser Output 4 APPL_PHYSICAL_PATH=C:\A348\ 29 PATH_INFO=/A348/ServerVariables.asp 31 QUERY_STRING=myname=Ray 35 REQUEST_METHOD=GET 36 SCRIPT_NAME=/A348/ServerVariables.asp 37 SERVER_NAME=localhost 38 SERVER_PORT=80 39 SERVER_PORT_SECURE=0 40 SERVER_PROTOCOL=HTTP/1.1 41 SERVER_SOFTWARE=Microsoft-IIS/5.0 42 URL=/A348/ServerVariables.asp

URL http://localhost/A348/ServerVariables.asp?myname=Ray ServerVariables.asp <%@ Language=JavaScript%> <% for(i=1; i<=Request.ServerVariables.Count(); i++) { strKeyName = Request.ServerVariables.Key(i); strKeyValue = Request.ServerVariables.Item(strKeyName); Response.Write( i + " " + strKeyName + "=" + strKeyValue + "<br>"); } %>

 

Hidden Variables to Maintain State

Maintaining state is critical for user interaction such as games, shopping carts, etc. but somewhat challenging given that the HTTP protocol of the Web is a stateless protocol, the server does not automatically maintain user state. We've examined several ways to maintain state on the client such as client scripts (e.g. JavaScript). Hidden form variables represent yet another way to maintain state on the client but pass the state information to the server. Hidden variable are simply HTML form variables that are declared as hidden, that is there is no visible text box, check box, etc.

Example - Simple Counter

The following is an example in ASP that maintains a counter using hidden form variable formCounter. The basic concept is that the server program has two separate executions:

1. an initial execution where no data supplied, triggering the generation of the initial HTML form that contains the hidden variable. 
2. subsequent executions are supplied counter data, which is incremented and returned to the browser as a hidden variable. 

The hidden variable maintains state, the state is the number of times the program has been executed by a specific browser. 

The communication between the browser and server is in two parts.

1. Browser sends request without any data to the server: http://localhost/A348/counter.asp
   • The server executes counter.asp, checks if the formCount form variable is defined (i.e. Request("formCount").count == 0 implies undefined). If formCount is undefined, indicating the first execution of the program, set ASP variable aspCOUNT = 0.
   • The browser receives the <FORM> with the hidden variable formCount=0.
   • The initial <FORM> with no data is: 

     Count is: 0 <br> <FORM Name="CounterForm" Method='GET'  Action='http://localhost/A348/counter.asp'>  <Input Type='hidden' name='formCount' value='0'><br>  <Input Type=Submit> </FORM>

2. Browser sends request with data to the server: http://localhost/A348/counter.asp?formCount=0
   • The server checks if the formCount form variable has a value, assign aspCOUNT = 0.
   • Increment aspCOUNT=parseInt(Request("formCount"))+1.
   • Server generated HTML form is returned to the browser with the hidden variable counter value of COUNT in the ASP script. The value of formCount form variable is incremented with each execution. The following would be generated for a aspCOUNT = 1.

Count is: 1 <br> <FORM Name="CounterForm" Method='GET'  Action='http://localhost/A348/counter.asp'>  <Input Type='hidden' name='formCount' value='1'><br>  <Input Type=Submit> </FORM>

      

Maintaining State of a Counter with a Hidden Variable

counter.asp - Execute when in virtual A348 directory by:  http://localhost/A348/counter.asp <%@ LANGUAGE = JScript %> <% if (Request("formCount").count == 0) aspCOUNT = 0; else aspCOUNT = parseInt(Request("formCount")) + 1; %> Count is: <%= aspCOUNT %> <br> <FORM Name="CounterForm" Method='GET'  Action='counter.asp'>  <Input Type='hidden' name='formCount' value='<%= aspCOUNT %> '> <br>  <Input Type=Submit> </FORM>

HTML generated by counter.asp execution Count is: 3 <br>   <FORM Name="CounterForm" Method='GET'                Action='counter.asp'>     <Input Type='hidden' name='formCount'               value='3'>               <br>     <Input Type=Submit>   </FORM>  URL generated by Submit when formCount=2 http://localhost/A348/counter.asp?formCount=2 Browser output

Notes

• Request("QUERY_STRING") == "" is true when no GET data has been sent, in the case when invoked by: 

http://localhost/A348/count.asp

To test that the individual form variable is undefined even though other variables may be defined by:

Request("formCount").count == 0

• parseInt(Request("formCount")) converts the string value of formCount to an integer, otherwise concatenation is performed by the + operator rather than addition.

  parseInt("4") + 1 is 5
  "4" + 1 is "41"

• The action of the form does not need to specify the complete URL since the ASP file is in the same directory as the previous invocation.

  Action='counter.asp'