Applied XML Programming for Microsoft .NET.pdf - Csbdu.in

To avoid threading risks, be aware that loading a style sheet is an unprotectedoperation. Either lock the operation yourself, or avoid spawning concurrent threads thatperform style sheet loading on the same processor.Security ConsiderationsThe XslTransform class has a link demand permission set attached. A link demandspecifies which permissions direct callers must have to run the code, as shown in thefollowing example. Callers' rights are checked during just-in-time compilation.[PermissionSet(SecurityAction.LinkDemand, Name="FullTrust")]public sealed class XslTransform{}⋮The permission set attribute for the XslTransform class is expressed by name andpoints to one of the built-in permission sets— FullTrust. What does this mean to you?Only callers (direct callers are involved with the check, not caller's callers) with fullytrusted access to all the local resources can safely call into the XSLT processor.Try running the XSLT Quick Security Tester sample application over a network.Because of the class security settings, a security exception is thrown. Figure 7-5 showsthe security exception dialog box.Figure 7-5: The XSLT processor class works only if called by locally trusted callers. AnXSLT application can work well as long as you invoke it locally, but it will raise a securityexception if you run it over a network share.Under the Hood of the XSLT ProcessorIn the overall behavior of the .NET Framework XSLT processor, three phases can beclearly identified: loading the style sheet document, setting up the internal state, andperforming the transformations. Although you see, and interact with, only a single class(XslTransform), a lot of internal classes are involved in the process.The first two phases occur within the context of the Load method. Of course, you can'tcall the Transform method before a previous call to Load has successfully terminated. Ifyou do, you will experience an XsltException exception on the Transform method.254