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Once you ve selected your service and placed it on either the file system or your local IIS, Visual Studio will create the project files and open the editor. You ll notice a new file type, with the .svc extension. As you can probably guess, this is a service. The SVC file structure is a lot like the base ASMX file that we saw earlier. It simply defines the language, the debug mode, the service class, and the location of the code-behind. Here s an example:

This private method determines the robots.txt file that governs access to the host on which the link resides, parses, and then disallows access to links as required by the robots specification; however, we re polite and assume that any link that s disallowed to anybody must be forbidden to us. This makes the logic slightly simpler but would not normally be done in a production system. The robots.txt information is cached with the host as the key, so we look it up only when we encounter the first link from a site:

Figure 13-16. Application that validates XDocument against an XSD schema The application consists of two text boxes and one button. The text boxes accept a path to the XML document that is to be validated and a path to the XSD schema file. Clicking the Validate button loads the XML document in an XDocument instance and validates the document against the supplied schema. Errors during validation (if any) are reported to the user. In this example, we will use the Employees.xsd schema file that we developed in 5 to validate the Employees.xml file. Just to give you a quick recap of the structure of the XSD schema file, Listing 13-24 shows a part of it. Listing 13-24. Partial Markup from Employees.xsd < xml version="1.0" encoding="utf-8" > <xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified"

The code-behind is a standard C# class, but there are some new attributes on the code that WCF uses to determine contracts and binding. The basic service created by the IDE will look like this:

private void processRobots(URL link) {

xmlns:xs="http://www.w3.org/2001/XMLSchema"> <xs:element name="employees"> <xs:complexType> <xs:sequence> <xs:element name="employee" type="EmployeeType" minOccurs="0" maxOccurs="unbounded" /> </xs:sequence> </xs:complexType> </xs:element> <xs:complexType name="EmployeeType"> <xs:all> <xs:element name="firstname" type="NameSimpleType" /> <xs:element name="notes" type="NotesSimpleType" /> <xs:element name="lastname" type="NameSimpleType" /> <xs:element name="homephone" type="PhoneSimpleType" /> </xs:all> ... The Click event handler of the Validate button is shown in Listing 13-25. Listing 13-25. Validating Against the XSD Schema private void button1_Click(object sender, EventArgs e) { XDocument doc = XDocument.Load(textBox1.Text); XmlSchemaSet schema=new XmlSchemaSet(); schema.Add(null,textBox2.Text); ValidationEventHandler handler = new ValidationEventHandler(MyHandler); doc.Validate(schema, handler); } public void MyHandler(object sender, ValidationEventArgs e) { MessageBox.Show(e.Message); } The code loads the source XML document in an instance of the XDocument class. It then creates an XmlSchemaSet and adds the specified XSD schema to it using the Add() method. The Validate() extension method of the XDocument class accepts two parameters: XmlSchemaSet and an event handler that gets called if validation fails. The event handler is of type ValidationEventHandler. The MyHandler() method acts as the event handler in our example. The validation is triggered by calling the Validate() method. If there are any validation errors, the MyHandler() event handler gets invoked. The MyHandler() event handler receives a parameter of type ValidationEventArgs. The Message property of the ValidationEventArgs class provides information about the validation errors. In order to test the code, remove the employeeid attribute from the first <employee> element of the Employees.xml file and run the application. Figure 13-17 shows a validation error message after a sample run.

using System; using System.ServiceModel; using System.Runtime.Serialization; // // // // // A WCF service consists of a contract (defined below as IMyService, DataContract1), a class that implements that interface (see MyService), and configuration entries that specify behaviors associated with that implementation (see <system.serviceModel> in web.config)

If the host has been visited before, we re not obliged to reread the robots.txt file. If this is the first visit, however, we need to determine which paths to discard:

HttpURLConnection connection = null; try { if( !visitedHosts.contains(link.getHost()) ) {

In 6, we discussed how to transform XML data using XSLT style sheets. Though that approach still remains valid, LINQ to XML provides a new handy way of transforming XML data. Using this new approach, you can transform XML from one shape to another without knowing anything about XSLT.