• Choose a category
• All
• Classic-Fiction

By Root 352 0

that make the request and receive the data. In contrast to XML, where the client needs to make a fetch and parse the results, SOAP facilitates functions that (appear to) directly execute functions on remote services, which return data in easy-to-use variables. An example of a SOAP call is shown in Listing 26-13.

In typical SOAP calls, the SOAP interface and client are created and the parameters describing requested web services are passed in an array. With SOAP, using a web service is much like calling a local function.

If you'd like to experiment with SOAP, consider creating a free account at Amazon Web Services. Amazon provides SOAP interfaces that allow you to access large volumes of data at both Amazon and Alexa, a web-monitoring service (http://www.alexa.com). Along with Amazon Web Services, you should also review the PHP-specific Amazon SOAP tutorial at Dev Shed, a PHP developers' site (http://www.devshed.com).

PHP 5 has built-in support for SOAP. If you're using PHP 4, however, you will need to use the appropriate PHP Extension and Application Repository (PEAR, http://www.pear.php.net) libraries, included in most PHP distributions. The PHP 5 SOAP client is faster than the PEAR libraries, because SOAP support in PHP 5 is compiled into the language; otherwise both versions are identical.

include("inc/PEAR/SOAP"); // Import SOAP client

# Define the request

$params = array(

'manufacturer' => "XYZ CORP",

'mode' => 'development',

'sort' => '+product',

'type' => 'heavy',

'userkey' => $ACCESS_KEY

)

# Create the SOAP object

$WSDL = new SOAP_WSDL($ADDRESS_OF_SOAP_INTERFACE);

# Instantiate the SOAP client

$client = $WSDL->getProxy();

# Make the request

$result_array = $client->SomeGenericSOAPRequest($params);

Listing 26-13: A SOAP call

Advantages of SOAP

SOAP interfaces to web services provide a common protocol for requesting and receiving data. This means that web services running on one operating system can communicate with a variety of computers, PDAs, or cell phones using any operating system, as long as they have a SOAP client.

Disadvantages of SOAP

SOAP is a very heavy interface. Unlike the interfaces explored earlier, SOAP requires many layers of protocols. In traffic-heavy applications, all this overhead can result in sluggish performance. SOAP applications can also suffer from a steep learning curve, especially for developers accustomed to lighter data interfaces. That being said, SOAP and web services are the standard for exchanging online data, and SOAP instructions are something all webbot developers should know how to use. The best way to learn SOAP is to use it. In that respect, if you'd like to explore SOAP further, you should read the previously mentioned Dev Shed tutorial on using PHP to access the Amazon SOAP interface. This will provide a gradual introduction that should make complex interfaces (like eBay's SOAP API) easier to understand.

Chapter 27. KILLING SPIDERS

Thus far, we have talked about how to create effective, stealthy, and smart webbots. However, there is also a market for developers who create countermeasures that defend websites from webbots and spiders. These opportunities exist because sometimes website owners want to shield their sites from webbots and spiders for these purposes:

Protect intellectual property

Shield email addresses from spammers

Regulate how often the website is used

Create a level playing field for all users

The first three items in this list are fairly obvious, but the fourth is more complicated. Believe it or not, creating a level playing field is one of the main reasons web developers cite for attempting to ban webbots from their sites. Online companies often try to be as impartial as possible when wholesaling items to resellers or awarding contracts to vendors. At other times, websites deny access to all webbots to create an assumption of fairness or parity, as is the case with MySpace. This is where the conflict exists. Businesses that seek to use the Internet to gain competitive advantages are not interested in parity.