Active Server Pages

Here are my notes and resources I have found useful when doing ASP programming. Let me know what you find helpful or missing.

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History of Active Server Pages (ASP's)

ASP was first announced by Microsoft in November, 1996 (code named "Denali") and introduced March 97 to manage HTTP 1.0 as a part of Microsoft's Internet Information Server version 3 (code name “Gibraltar”).

ASP 2.0 came with IIS 4.0 installed from the NT4 Option Pack as Personal Web Server (PWS) and also on CD 2 of Visual Studio 6. PWS can also be installed on Windows 95 from the setup.exe in Add-ons\pws folder from the Win 98 CD after the 986KB Feb 98 WinSock2 Upgrade for Windows 95.

ASP 3.0 comes with IIS 5.0 shipped with Windows 2000. It introduces the Server.Transfer method (which redirects without a trip back to the client) and the Server.Execute method (which, unlike includes, parses code conditionally).

IIS 5.1 is installed with Windows XP Professional (not the XP Home version).

ASP.NET (pronounced "dot net") has a whole new architecture — the .NET Framework which references "code behind" program logic written in C Sharp or other language that compiles into MSIL. Because each file of a particular language is handled by that language's compiler, unlike ASP, languages cannot intermix in a single program file. This also requires ASP.NET to run on IIS server, and not under PWS.

ASP.NET 2.0, released with Visual Studion 2005, introduces controls such as <asp:Login

ASP.NET 3.5 was released with Visual Studio 2008.

Microsoft's ASP.NET 4.0 preview contains the AJAX Template Library and the AJAX Client Library for ADO.NET Data Services.

Sites where ASP is known to add interactivity to web pages:
• Dell.com sells $10 million of computers PER DAY.
• BarnesAndNoble.com (bn.com) booksellers.
• NASDAQ.
• Nordstrom
• Merrill-Lynch

  The Microsoft Solution for Windows-based Hosting

ASP Coding

When a client's Web/Internet browser clients requests a URL with an .asp file instead of an .htm, the ASP Interpreter (ASP.DLL) is invoked. MS .NET services also recognize .aspx files for processing only by ASP.NET servers. Unlike .htm files, the full http:// reference must be used to invoke ASP files through a web application server because the whole point of using ASP files is to dynamically generate Javascript and HTML code rather than serving up static .htm files.

The ASP interpreter acts on blocks of code between delimiter tags <% and %>

The first line of an ASP file specifies the syntax to be expected by the interpreter:

<%@Language=VBScript%>
This is the default. Specify Language=JScript to use Javascript syntax between delimiter tags <% and %>
<%@Language=Javascript runat="server"%>

Non-default code scripts (such as JScript within VBScript file) run on the server are (on IIS 4.0) executed before default script code.

An example of how an ASP.NET page begins:

<%@ Page Language="vb" AutoEventWireup="false" Codebehind="Webform1.aspx.vb" Inherits="MyApp.WebForm1" %>

The Page Language must be "vb" because to create this, in Microsoft Visual Studio 2004, open a new Visual Basic Project and select template ASP.NET Web Application. Resources for several projects are grouped into a Visual Studio Solution.

ASP.NET header <% Explicit="true" takes the place of <% Option Explicit %>

My sample "MySolution" has these resources:

• References
• AssemblyInfo.vb
• Global.asax
• Styles.css
• Web.config

• MyProj.vsdisco
• WebForm1.aspx

Data Flow

IIS returns to the calling client browser variables from Intrinsic Objects such as the user's browser type, URL, screen resolution, etc. ASP Server Variables for this machine/session

Instead of Response.Write use this shortcut with the equal sign:

<%=oRS("PeopleNameLast") %>

Instead of specifying just the variable name, professional ASP programmers usually encase the field in a function to format the field's values, such as using the oRS() function to retrieve the value of a database field or the ToCurrency() function to format numbers using the client's local currency symbols and separators.

In contrast, JSP pages

<% if( request.getMethod().equalsIgnoreCase("POST"))
{%>
User id:<%=request.getParameter("frmField1")%>
<%}%>

String Handling

James Musson's MSDN article notes that with ASP, the performance of issuing several Response.Writes (the quickest) is slower than string concantenation (the slowest). He also proposes an efficient StringBuilder method.

HTML FORM ACTION GET vs. PUT

To retrieve a variable named "X" in a form sent with METHOD="GET", use QueryString("X"). This variable name appears after the http: URL after ?. Each variable is separated by an ampersand (&).

To retrieve a variable named "X" in a form sent with METHOD="PUT", use Request.Form("X"). For example, the code to redisplay a radio button variable by an ASP program that sends to itself:

<% if Request.Form("X") = "on" then "selected" %>

Instead of these native commands, professional ASP programmers use a custom function (typically from a common library) to consistently process values. For example, I run data to be stored in SQL databases through the ToSQL() function, which converts single quotes into double quotes. I use the ToHTML() function to format special characters to HTML encoding.

NOTE: In the Ruby language, this information is obtained by coding params[:id].

ASP Document Object Model

• The Request object supplies information from a client visitor (Form, QueryString, ServerVariables, Cookies, ClientCertificate). Its TotalBytes property provides how much data is transferred each time.
• The Response object contains methods for building a response to the client (End, Redirect, AddHeader, Write, BinaryWrite, Clear, Flush) and the Cookies collection. Its properties are Buffer, Charset, Expires, ExpiresAbsolute, CacheControl, ContentType, Pics rating, Status line text. IIS5 added AppendToLog.
• ObjectContext method SetAbort triggers the OnTransactionAbort event. SetComplete transactions triggers the OnTransactionCommit event.
• The ASPError object (new since IIS5) exposes properties of the last error when Server.GetLastError is called, such as the Category and shorter Description or longer ASPDescription of the error Source and which Line and Column in the File causing the error.
• The Server object also has methods to do HTMLEncode, URLEncode, and MapPath. Its ScriptTimeout property manages its lifetime.
• Application methods Lock and UnLock control availability of objects in its Contents and StaticObjects collections. Variables available to all users are defined with Application_OnStart and _OnEnd events.
• The Session object holds the CodePage, LCID, SessionId, and Timeout properties pertaining to a particular visitor. Like the Application object, Contents and StaticObjects collections for each user session are managed with Abandon and Contents.Remove methods.

Web Environment Variables

Variables available to each session object is defined with Session_OnStart and _OnEnd events.

objRecordset.Fields("DATE") = Now()
objRecordset.Fields("HTTP_USER_AGENT") = Request.ServerVariables("HTTP_USER_AGENT")
objRecordset.Fields("HTTP_REFERER") = Request.ServerVariables("HTTP_REFERER")
objRecordset.Fields("QUERY_STRING") = Request.ServerVariables("QUERY_STRING")
objRecordset.Fields("REMOTE_ADDR") = Request.ServerVariables("REMOTE_ADDR")
objRecordset.Fields("REMOTE_HOST") = Request.ServerVariables("REMOTE_HOST")
objRecordset.Fields("SERVER_PORT") = Request.ServerVariables("SERVER_PORT")
objRecordset.Fields("URL") = Request.ServerVariables("URL")

CGI coding

print "QUERY_STRING ", $ENV{'REMOTE_ADDR'}, "\n";

These variables maintained internally by web application programs such as CGI, ASP, and JSP.

Environment Variable	Description
AUTH_TYPE	The authentication method used to validate a user.
DOCUMENT_ROOT	The directory from which Web documents are served.
CONTENT_TYPE	The MIME type of the query data, such as "text/html".
CONTENT_LENGTH	The length of the data in bytes passed to the CGI program through standard input
GATEWAY_INTERFACE	The revision of the Common Gateway Interface that the server uses
HTTP_ACCEPT	A list of the MIME types that the client can accept.
HTTP_FROM	The email address of the user making the request. Most browsers do not support this variable.
HTTP_USER_AGENT	The browser the client is using to issue the request.
HTTP_REFERER	The URL of the document that the client points to before accessing the CGI program.
PATH_INFO	Extra path information passed to a CGI program.
PATH_INTERFACE	The translated version of the path given by the variable PATH_INFO.
QUERY_STRING	The query information passed to the program. It is appended to the URL with a "?".
REQUEST_METHOD	The method with which the information request was issued.
REMOTE_HOST	The remote hostname of the user making the request.
REMOTE_ADDR	The remote IP address of the user making the request
REMOTE_USER	The authenticated name of the user.
REMOTE_IDENT	The user making the request. This variable will only be set if the NCSA IdentityCheck flag is enabled, and the client machine supports the RFC 931 identification scheme (ident daemon).
SCRIPT_NAME	The virtual path (e.g. /cgi-bin/program.pl) of the script being executed.
SERVER_NAME	The serevr's hostname or IP address.
SERVER_SOFTWARE	The name and version of the server software that is answering the client request.
SERVER_PROTOCOL	The name and revision of the information protocol the request came in with.
SERVER_PORT	The port number of the host on which the server is running.

ASP Object Model

The global.asa file contains initialization code for the user's session and the application.

Includes

Use "include" preprocessor directives to dynamically add code from another file whenever it's invoked. The adovbs.inc is in most ASP pages to define common literals.

Including other files makes it easier to keep common elements such as menu bars, copyright statements, etc. consistent across in all pages of a website by using a single source file for the contents. This is typically used to enforce login before users can access a page:

<!--#includesecuritylevel1required.asp"-->
' Define VBScript Constants:
<!-- #include file="common.asp" -->

If the file is not in the folder, specify instead

<!-- #include virtual="../lib/edits.asp" -->
• server.execute conditionally executes a dynamically generated string naming an asp script to be executed. Control is returned after that is executed.
  Server.Execute("Lookup.asp")

• To abort ASP processing and send the page to the client:
  Response.End

• To ...
  Response.Flush

• To forward user to another URL:
  Response.Redirect "http://www.dilbert.com"

  A common mistake is to leave out "http://".

  server.transfer new to Windows 2000 unlike redirect, does not return to the browser but switches to a different page/site.

• Active Server Pages.com offers code "Toolbelt"
• asp101.com
• ultimateasp.com
• webwizguide.com/asp
• asptoday.com
• Download NT4 Option Pack from Microsoft
• What's new in Microsoft Web Services.
• ASP Resource Index
• ASPHole
• 15 Seconds is the largest free independent resource for Active Server.
• ChiliASP has an ASP tutorial.
• ActiveX and HTML together
• Ruleweb
• 4guysfromrolla.com
• W3schools.com is for the beginner wanting all the basics.
• Newsgroup alt.activeserverpages

  Take the Brainbench certification test on Active Server Pages or ASP.NET

Error Handling

Click to create ASP error

Click "Submit" without entering any data on and see a sample error page:

Microsoft OLE DB Provider for ODBC Drivers error '80004005'

[Microsoft][ODBC Microsoft Access Driver] Field 'tblAdoAdd.FirstName' cannot be a zero-length string.

Add this under the </HTML> in ASP pages to trap time-outs:

<%
Sub OnTranactionAbort()
    response.clear
    Response.Write "Script timed out."
end sub
%>

ASP for dummies.com by Bill Hatfield at edgequest.com

Flow Control

Sample classic ASP script to read an MS-Access database
Download the source code

Flat File Operations

To operate on individual files (such as .mdb), ADO uses built-in methods of the File System Object of the ADO (Active Database Objects) interface.

To create (instantiate) a object called objFSO

Dim objFSO
set objFSO=Server.CreateObject("Scripting.FileSystemObject")
	

To delete prior output file (if one exists):

If objFSO.FileExists(Server.MapPath("myfile")) Then
   objFSO.DeleteFile Server.MapPath("myfile")
End IF
Set objFSO = Nothing
	

How To Manipulate Text Files in an ASP Page

FileSystemObject Basics

Programming the FileSystemObject

Opening and Closing Databases

1. Create (instantiate) an ADO Connection (cnn) object:

Dim cnnXXX
set cnnXXX=Server.CreateObject("ADODB.Connection")
2. Open a database using a Connection String
cnnXXX.ConnectionString = strConn
cnnXXX.Open

3. Create (instantiate) a Recordset (rst) to hold the output:

Dim rstXXX
Set rstXXX = Server.CreateObject("ADODB.Recordset")
rstXXX.CursorLocation=3
rstXXX.CacheSize=10

4. Define a SQL dynamic query string, (which ends with a semicolon):

Dim strSQL
strSQL = "SELECT * FROM People;"

5. Execute the SQL query through the connection and into the recordset:

Set rstXXX = cnnXXX.Execute( strSQL )

6. Do stuff with the data

7. Finally, close the object and set it to nothing:

cmmXXX.Close
set cnnXXX=Nothing

The ConnectionString property identifies the data source to be used for retrieving and storing the information manipulated by the data control. It includes information OLE DB provider used to communicate with the data source.

The RecordSource property identifies the information managed by the data control. This could relate to all of the information in a single table, some of the information from a single table, or information stored in multiple tables in the data source.

Young Alex Haneng offers clear explanations

Doing Stuff With a Recordset

You can perform insert, update, delete, or selection of data on a database.

To save the file to XML format:

rstXML.Save Server.MapPath("db_xml.xml"), adPersistXML

Using a Forward-Only Cursor on an ADO Database To use the oRS object's default method to return the value of a column named PeopleNameLast from the first row:

oRS.MoveFirst
Response.Write oRS("PeopleNameLast")

You can also use method MoveLast for the last row or MoveNext. Note that cursors to simple recordsets cannot move backward (using MovePrevious) through the database.

While Loop Programming

Enterprise Application Development

Data Management with MS-Access

Developing ASP Components by Shelley Powers (Beijing: Cambridge O'Reilly and Associates, 1999)

ASP in a Nutshell: A Desktop Quick Reference by Weissinger, A. Keyton (Sebastopol, Calif., 1999)

ASP Packages

I recommend these ASP code packages for

• DBAdmin and ASPRunner, which generates ASP code for managing MS-Access databases using an internet browser.

• Newsletters Manager for managing subscriptions and sending newsletters using different templates.

• Snitz for ASP Discussion Forums.
• Asp.Net Forum 2004 from ITCN
• Web message board that runs on Microsoft's ASP.NET

• Making Bar Charts using ASP
• $699 Dundas Chart, Guage, and Diagram for .NET

• Comersus for shopping carts, programmed using British spelling such as "colour". The current version uses Access 97 format (not Access 2000 or Access 2002) to store its "setting" table.

• Photo gallery I-Gallery from Blue Collar donationware

• adMentor.NET for rotating ad banners in specific zones.

• Hexillion for doing nslookup (to detect spammers via spamhaus.org) and other Windows COM functions.

• ASP classic scripts at hotscripts.com

• Phalanger enables PHP 5.0 programs to run within the ASP.NET platform by compiling PHP code into .NET Framework MSIL. With Phalanger, cross-platform extensions can be developed both ways. Objects in the PHP 5.0 object model can be combined with .NET objects. .NET classes (written in C# or Visual Basic .NET) can be loaded into PHP scripts provided that this class respects the PHP object model implemented in the Phalanger. PHP utilities such as Zend Optimizer have been tested with Phalanger.

dotnetnuke (DNN) is a one-stop shop for hosting of open-source collaboration suites. Some prefer the XMod module (particularly the Calendar widget). Add-on controls for it are from Infragistics.

Michael Washington's tutorials.

Beginning DotNetNuke 4.0 Website Creation in C# 2005 with Visual Web Developer 2005 Express: From Novice to Professionalby Nick Symmonds

Professional DotNetNuke 4: Open Source Web Application Framework for ASP.NET 2.0 (Programmer to Programmer) By the architects: Shaun Walker, Joe Brinkman, Bruce Hopkins, Scott McCulloch, Chris Paterra, Patrick J. Santry, Scott Willhite, Dan Caron

Professional DotNetNuke ASP.NET Portals by Shaun Walker

Beginning DotNetNuke Skinning and Design by Andrew Hay and Shaun Walker

ASP and Front Page Together

ASP takes Microsoft Front Page controls to another level of functionality.

• Each IS/IPA must install on their servers software to support Microsoft Front Page Extensions and Active Server Pages.

• Avoid using FrontPage 97 or FrontPage 98 when working with ASP files. The Personal Web Server which comes with FP does not run Active Server Pages. If you try to execute an ASP file with it installed, you will see your ASP code printed on the screen exactly as you typed it.

  During installation, FP muscles itself in as the default application to be invoked when you double-click on file names ending with ".asp". To change this in Windows Explorer, hold the shift key down while right clicking on an .asp file, then select Open With... and choose a new application, such as Wordpad, Notepad, or an HTML editor like Allaire's HomeSite that doesn't change coding.

• On a stand-alone PC, before installing FP, dial up your ISP to get TCP/IP in memory. FrontPage 98 and PWS98 (PWS4), need 32bit TCP/IP to be "running". To avoid a common annoyance of the computer dialing automatically whenever it starts, reconfigure Internet Explorer and go to View, Connect and choose "I connect to the Internet via the LAN" rather than "through a Modem". This satisfies PWS and you just have to make sure you actually DO connect to your ISP if you want to surf the web or check your email.

• When installing NTOP, if you choose to install the HTML Internet Manager, you will be able to create and manage virtual directories from a browser on another machine.

gotdotnet Workspaces is an online collaborative development environment where .NET developers can create, host and manage projects throughout the project lifecycle.

Resources

List of tools by scott.hanselman