Perl – Burningbird

Originally published at Web Techniques

Microsoft’s Active Server Pages (ASP) technology has grown very popular as a Web server-side technique, combining HTML, embedded scripts, and external components to deliver dynamic content. One feature of ASP is that different languages can be used for its scripting portion, though the most widely used ASP scripting language is VBScript—a subset of Microsoft’s Visual Basic.

However, just because VBScript is the most popular language used by ASP developers doesn’t mean it’s the only one, or even the best one to use in a particular circumstance. For instance, Perl has long been synonymous with Web server development, beginning with the earliest uses of the language by CGI, and is still one of the most popular languages among Web developers. But there hasn’t been much discussion of using Perl with ASP.

If your organization has been working with Perl, and you’re interested in developing for the ASP environment, you don’t have to give up your favorite language (or your existing Perl code) to make the transition to the new technology—you can employ Perl for ASP scripting through the use of PerlScript.

A (Very) Brief Overview of ASP

Microsoft originally introduced ASP technology was with the company’s own Web server, Internet Information Server (IIS). However, ASP has now been ported to other Web servers through the use of software such as ChiliSoft’s platform-independent version of ASP. In addition, ASP was created originally to work in a Windows environment, but again thanks to ChiliSoft and other companies, ASP now runs in non-Windows environments such as UNIX and Linux.

Still, the most popular use of ASP is within the Windows environment, with pages hosted on IIS. This environment—specifically Windows NT/IIS 4.0—is the one I’ll discuss.

ASP pages have an .asp extension, and are a mix of HTML and embedded script. When a client requests the page, the embedded script is accessed and processed. The results generated by the script are embedded into the Web page, which is then returned to the client browser.

The Response object—along with the other built-in ASP objects Server, Session, Request, and Application—provides access to the ASP and application environment for the ASP developer. The Response object provides a way to send information back to the Web-page client; the Request object provides access to information sent from the client, such as form contents; the Application object contains information that persists for the lifetime of the ASP application; the Session object contains information that persists for the lifetime of the particular ASP user session; and the Server object, among other things, lets the ASP developer create external components.

ActivePerl and PerlScript

A company named ActiveState was formed in 1997 to provide Perl tools for developers for all platforms. Among some of ActiveState’s more popular products is ActivePerl, a port of Perl for the Win32 environment.

ActivePerl is a binary installation containing a set of core Perl modules, a Perl installer (Perl Package Manager), an IIS plug-in for use with Perl CGI applications, and PerlScript. What is PerlScript? PerlScript is Perl, but within an ASP environment—it’s a Perl implementation of the Microsoft Scripting Engine environment, which allows Perl within ASP pages.

ActivePerl can be downloaded for free from ActiveState’s Web site (see the ” Online Resources“). To try it for yourself, access the ActiveState Web site and find the ActivePerl product page.

The installation process requires very little user input. You’ll need to specify where you want to put the files, and be sure to select the option to install PerlScript.

Using PerlScript Within ASP Pages

By default in IIS, all ASP scripting is VBScript, but you can change this using one of three different techniques. First, you can change the default scripting language for the entire ASP application using the IIS Management Console, and accessing the Properties dialog box for the Virtual Directory or Site where the ASP application resides. Click on the Home Directory (or Virtual Directory) tab, and then click on the Configuration button on the page. From the dialog box that opens, select the App Options page. Change the default scripting language from “VBScript” to “PerlScript.”

A second technique is to specify the scripting language in the scripting block itself. With this technique you could actually choose more than one scripting language in the page:

A third technique is to specify the scripting language directly at the beginning of the Web page. This is the approach we’ll use for examples. Add the following line as the first line of the ASP page:

<%@ LANGUAGE = PerlScript %>

All scripting blocks contained in the page are now handled as PerlScript.

Accessing Built-In ASP Objects From PerlScript

To assist the developer, PerlScript provides access to several objects available only within the ASP environment. As mentioned earlier, these are the Application, Session, Response, Request, and Server objects.

The Application object is created when an ASP application first starts, and lasts for the lifetime of the application. The object has two COM collections, both of which can be accessed from script: the StaticObjects collection, with values set using the <OBJECT> tag within an application file called global.asa; and the Contents collection, which contains values set and retrieved at runtime. A COM collection is a group of similar objects treated as a whole, with associated features that let the developer access individual elements directly, or iterate through the entire collection.

In addition to the two collections, the Application object also has two methods, Lock and UnLock, which are used to protect the object against attempts by more than one application user at a time to change its values.

We’ll take a closer look at using the Lock and UnLock methods by setting a value in the Application’s collection in one ASP page, and then retrieving that same value from another page.

First, Listing 1 contains a page that sets a new value to Application Contents by first locking down the object, setting the value, and then unlocking the object. Notice that you don’t have to create the Application object—it’s created for you, and exists in the main namespace of the PerlScript within the ASP page (the same holds true for all of the ASP objects).

If you’ve worked with VBScript you’ve probably noticed that you have to use a different technique to set the value in the Contents collection with PerlScript. VBScript allows direct setting of collection values and properties using a shorthand technique, similar to the following:

Application.Contents("test") + val

PerlScript, on the other hand, doesn’t support this shorthand technique. Instead, you have to use the SetProperty method to set the Contents item:

$Application->Contents->SetProperty('Item', 'test', $val);

Additionally, you have to use SetProperty to set ASP built-in object properties with PerlScript, or you can use the Perl hash dereference to set (and access) the value:

my $lcid = $Session->{codepage};

Listing 2 contains another ASP page that accesses the variable set in Listing 1, prints out the value, increments it, and resets it back to the Application object. It then accesses this value and prints it out one more time. Accessing this page from any number of browsers, and from any number of separate client sessions, increments the same Application item because all of the sessions that access the ASP application share the same Application object.

In addition to the Application object, there is also a Session object, which persists for the lifetime of a specific user session.

This object is created when the ASP application is accessed for the first time by a specific user, and lasts until the session is terminated or times out, or the user disconnects in some way from the application. It, too, has a StaticObjects and a Contents collection, but unlike the Application object, you don’t lock or unlock the Session object when setting a value in Contents. But you do access the Contents collection in the exact same manner, both when setting a value:$Session->Contents->SetProperty('Item', 'test', 0);

as well as when retrieving the value:

my $val = $Session->Contents('test');

Additional Choices

There are also other properties and methods available with Session, including the Timeout property, used to set the session’s timeout value, and the Abandon method, used to abandon the current session. Each session is given a unique identifier, SessionID, and this value can be accessed in a script. But use caution when accessing this value if you hope to identify a unique person—the value is only unique and meaningful for a specific session.

In support of internationalization, there are Session properties that control the character set used with the page, CodePage, and to specify the Locale Identifier, LCID. The Locale Identifier is an international abbreviation for system-defined locales, and controls such things as currency display (for instance, dollars versus pounds).

Listing 3 shows an ASP page that sets the Timeout property for the Session object, and accesses and prints out both the CodePage and the LCID values. Retrieving this ASP page in my own environment and with my own test setup, the value printed out for CodePage is 1252—the character mapping used with American English and many European languages. The value printed out for LCID is 2048—the identifier for the standard U.S. locale.

The Application and Session examples used a third ASP built-in object, the Response object. This object is responsible for all communication from the server application back to the client. This includes setting Web cookies on the client (with the Cookies collection), as well as controlling whether page contents are buffered before sending back to the client, or sent as they’re generated, through the use of the Buffer property:

$Response->{Buffer} = 1;

You can use the Buffer property in conjunction with the End, Flush, and Clear methods to control what is returned to the client. By setting Buffer to true (Perl value of 1), no page contents are returned until the ASP page is finished. If an error occurs in the page, calling Clear erases all buffered contents up to the point where the method was called. Calling the End method terminates the script processing at that point and returns the buffered content; calling the Flush method flushes (outputs) the buffered contents, and ends buffering.

Listing 4 shows an ASP page with buffering enabled. In the code, the Clear method is called just after the first Response Write method, but before the second. The page that’s returned will then show only the results of the second Write method call.

The Buffer property must be set before any HTML is returned to the client, and this restriction also applies to several other Response properties, such as the Charset property (alters the character setting within the page header); the ContentType property (alters the MIME type of the content being returned, such as “text/html”); the AddHeader method, which lets you specify any HTTP header value; and the Status property, which can be used to set the HTTP status to values such as “403 Forbidden” or “404 File not found”. For example:

$Response->{Status} = "403 Forbidden";

If buffering is enabled for a Web page, then properties such as Charset and ContentType, as well as the AddHeader method can be used anywhere within the ASP page.

You can redirect the Web page using the Redirect method call to specify a new URL. As with the other properties and methods just mentioned, Redirect must also occur before any HTML content:

$Response->Redirect("http://www.somesite.com");

In addition to manipulating HTTP headers, the Response object also generates output to the page using the Write method, as demonstrated in the previous examples. You can also return binary output to the client using BinaryWrite. You can override whether an ASP page is cached with proxy servers through the use of the CacheControl property, as well as set cache expiration for the page by setting the Expires or the ExpiresAbsolute properties:

$Response->{Expires} = 20 # expires in 20 minutes

You can test to see if the client is still connected to the setting with the IsClientConnected property. Communication doesn’t just flow just from the server to the client. The Request object handles all client-based communication in either direction. This object, as with Response, has several different methods, properties, and collections. The collections interest us the most.

You can read Web cookies using the Request Cookies collection. And it’s possible to set and get information about client certificates using the ClientCertificate collection.

You can also process information that’s been sent from a client page using an HTML form, or appended as a query string to the Web page’s URL:

The two collections that hold information passed to the ASP page from a form or a query string are: the QueryString collection, and the Form collection. Use QueryString when data is passed via the GET method, and use Form when data is passed via the POST method.

Regardless of which technique you use to send the name/value pairs, accessing the information is similar. Listing 5 shows an ASP page that processes an HTML form that has been POSTed:

The example ASP page pulls out the values of three text fields in the form: lastname, firstname, and email. It then uses these to generate a greeting page, including adding a hypertext link for the email address. If the form had been sent using the GET method (where the form element name/value pairs get concatenated onto the form processing page’s URL), then the page contents would be accessed from QueryString:

my $firstname = $Request->QueryString('firstname')->item;In addition to the Form and QueryString collections, the Request object also has a ServerVariables collection, containing information about the server and client environment. The ServerVariables collection is comparable to accessing %ENV in CGI.

You can access individual elements in the Server Variables collection by specifying the exact variable name when accessing the collection:

my $val = $Request->ServerVariables('PATH_TRANSLATED')->item;Or you can iterate through the entire collection. To do this, you can use the Win32::OLE::Enum Perl module to help you with your efforts. The Enum class is one of the many modules installed with ActivePerl, and provides an enumerator created specifically to iterate through COM collections such as ServerVariables.

Listing 6 shows an ASP page that uses the Enum class to pull the elements of the ServerVariables collection into a Perl list. You can then use the Perl foreach statement to iterate through each ServerVariables element, printing out the element name and its associated value.

If an HTML form contains a File input element—used to upload a file with the form—you can use the Request BinaryRead method to process the form’s contents. The TotalBytes property provides information about the total number of bytes being uploaded.

Break Out with COM

All of the examples up to this point have used objects that are built in to the ASP environment. You can also create COM-based components within your ASP pages using the built-in Server object. The Server object has one property, ScriptTimeout, which can be used to determine how long a script will process—a handy property if you want to make sure scripting processes don’t take more than a certain length of time.

The Server object also has a couple of methods that can be used to provide encoding, such as HTML encoding, where all HTML-relevant characters (like the angle bracket) get converted to their display equivalents. MapPath maps server paths relative to their machine locations. URLEncode maps URL-specific characters into values that are interpreted literally rather than procedurally:my $strng = $Server->URLEncode("Hello World");The result of this method call is a string that looks like:

Hello+World%21Although these methods and the one property are handy, Server is known generally as the object used to instantiate external ASP components, through the use of the CreateObject method. This method takes as its parameter a valid PROGID for the ASP component. A PROGID is a way of identifying a specific COM object, using a combination of object.component (sometimes with an associated version number):

simpleobj.smplcmpntAs an example, I created a new Visual Basic ActiveX DLL, named the project simpleobj, and the associated class smplcmpnt. The component has one method, simpleTest, which takes two parameters and creates a return value from them, based on the data type of the second parameter. This component method, shown in Example 1, has a first parameter defined as a Visual Basic Long value (equivalent to a Perl integer), and a second parameter of type Variant, which means the parameter could be of any valid COM data type—Visual Basic functions are used to determine the data type of the value.

A new page uses the Server CreateObject method to create an instance of this ASP component, and tests are made of the component method. As shown in Listing 7, the first test passes two integers to the external VB component method. The component tests the second parameter as a Long value, adds the two parameters, and returns the sum.

The next test passes a string as the second parameter. The component tests this value, finds it is not a number, and concatenates the value onto the returned string.

The script for the final test creates a date variable using the Win32::OLE::Variant Perl module, included with ActivePerl. The standard localtime Perl method is used to create the actual date value, but if this value isn’t “wrapped” using the Variant module, the Visual Basic ASP component will receive the variable as a string parameter rather than as an actual date—PerlScript dates are treated as strings by ASP components.When the Visual Basic component receives the date as the second parameter, the component finds that it is not a number, and concatenates the value onto the string returned from the function. When displayed, the returned string looks similar to the following:

3/15/1905 100I could have passed the date value directly instead of using Variant, but as I mentioned, the COM-based VB component sees the Perl date as a string rather than as a true date type. The Variant Perl module provides techniques to ensure that the data types we create in PerlScript are processed in specific ways in ASP components.

Summary

Perl is a mature language that has been used for many years for Web development. As such, there is both expertise with, and a preference for, using this language for future development with the newer Web development techniques such as ASP.

ActivePerl and PerlScript are the key tools for using Perl within the ASP environment. Perl can be used for ASP scripting through PerlScript, but the Perl developer also has full access to the objects necessary to work within the ASP environment: namely the ASP built-in objects such as the Response and Request objects.

Additional modules to assist Perl developers—such as Win32::OLE::Enum and Win32::OLE::Variant—are included with the ActivePerl installation, and help make PerlScript as fully functional within the ASP scripting environment as VBScript.

Best of all, with ActivePerl and PerlScript you can develop within an ASP environment and still have access to all that made Perl popular in the first place: pattern matching and regular expressions, the Perl built-in functions, and a vast library of free or low-cost Perl modules to use in your code. Interest in ASP is growing, and with PerlScript you can work with this newer Web technology and still program in your favorite programming language.