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

The VaryByHeaders property enables you to cache multiple versions of a page,depending on the value of the HTTP header (or headers) you specify—in this example,the header value is SOAPAction. The VaryByParams property, on the other hand, letsyou maintain different caches for each set of distinct values of the specified parameters.In this case, using the asterisk (*) indicates that all parameters must be consideredwhen caching a page.NoteUnder certain conditions, the CacheDurationattribute can constitutea significant improvement for your Web services. Ideally, you mightwant to set this attribute when your method returns a large amountof data (for example, a DataSet object) but receives quite a fewrequests distributed throughout the day. The caching mechanism—the same mechanism available to all ASP.NET applications—letsyou distinguish cached copies of the output that are also based onparameters. Under these circumstances, generating a new data setevery time the method is called isn't efficient—unless, of course,user requirements mandate that you return fresh data. Theadvantage in performance can be relevant and significant. In myexperimentation, I was able to get response times up to 8 timesfaster, with 2 or 3 times faster being the average.The Role of the XML SerializerAs shown in Figure 13-5, the return value of the method call is packed as XML usingthe XML serializer that we saw in action in Chapter 11. The following script representsthe pseudocode that creates the response for a Web service method:Response.ContentType = ContentType.Compose("text/xml",Encoding.UTF8Encoding);ser.Serialize(outputStream, returnValue);The XML serializer can't process all .NET Framework types. Remember, the XMLserializer doesn't work with types that have circular references and only packs publicand read/write members. The XML serializer doesn't ensure type fidelity but simply aneffective XSD (or SOAP-encoded) representation of the data.NoteA Web service can't return an ADO.NET object other than theDataSet object for the simple reason that the XmlSerializer classdoesn't know how to handle them. On the other hand, XmlSerializercan normally handle arrays of primitive objects, and this can helpwhen you're creating workarounds for returning complex data likethat stored in many ADO.NET objects.Disabling HTTP-POST and HTTP-GETAs we'll see in more detail in the section "Invoking a Web Service Through Script," onpage 586, you can invoke a Web service method using a SOAP message as well as aplain HTTP-POST or HTTP-GET command. The latter two protocols have beenintroduced to make accessing a Web service easier than ever. However, leaving theWeb service door open to HTTP packets can constitute a potential security hole.If you want to disable the HTTP-POST and HTTP-GET support on a machine-widebasis, do as follows. First locate the machine.config file (more on configuration files inChapter 15) in the local system. The file is normally located in the config subdirectory ofthe .NET Framework installation path. A typical path is shown here:c:\winnt\microsoft.net\framework\v1.0.3705\config\machine.config469