Internet Applications in .NET

Generator QR Code 2d barcode in .NET Internet Applications

This is a helper routine that moves data from one stream to another. Private Sub CopyStream(ByVal source As Stream, ByVal dest As Stream) Dim sr As New StreamReader(source) Dim sw As New StreamWriter(dest) sw.WriteLine(sr.ReadToEnd) sw.Flush() End Sub

The EvalSubscriptionLevel is a private function that analyzes all the headers of the SoapMessage object and looks for an AccountInfoHeader object. If such a header is found, the function can determine whether the client s username and password are valid and returns the client s subscription level:

Private Function EvalSubscriptionLevel(ByVal message As SoapMessage) _ As Integer Check whether there is a header of type AccountInfoHeader. For Each header As SoapHeader In message.Headers If TypeOf header Is AccountInfoHeader Then Cast to the proper type. Dim accountInfo As AccountInfoHeader = _ DirectCast(header, AccountInfoHeader) Check user credentials and return subscription level. Return GetUserSubscriptionLevel(accountInfo.UserName, _ accountInfo.Password) End If Next If we get here, credentials were missing or invalid. Return -1 End Function

(I omitted the source code for the GetUserSubscriptionLevel class because it is the same as the class illustrated in the section Custom Authentication, earlier in this chap ter.) Here s the client-side code that invokes a method protected with a SoapCustomAu thentication attribute:

Dim accountInfo As New localhost.AccountInfoHeader()

accountInfo.UserName = JoeDoe"

accountInfo.Password = jdpwd"

Dim service As New localhost.SampleService()

Try This call succeeds only if user JoeDoe has a subscription level of 2 or higher. Dim res As Boolean = service.YetAnotherProtectedMethod() Catch ex As Exception MsgBox(ex.Message, MsgBoxStyle.Critical) End Try

29:

So far, I ve described what are called server-side SOAP extensions, which are by far the most common types of SOAP extensions. However, you can also implement client-side SOAP extensions. For example, a client-side SOAP extension might be necessary to decrypt the XML sent by a Web service and encrypted by a server-side SOAP extension. You can activate a client-side SOAP extension via custom attributes, exactly as you do for server-side extensions, except the custom attribute is applied to the methods in the proxy class. A client-side SOAP extension goes through the same four stages that server-side exten sions do, but their order is different: BeforeSerialize and AfterSerialize when the SOAP message is being sent to the Web service; BeforeDeserialize and AfterDeserialize when the result XML is being received from the Web service. (See Figure 29-9.)

Web Service Extensions (WSE)

The Web services story doesn t end with the techniques I have illustrated in this chap ter. Instead, I d dare to say that this is just the beginning of a saga that will keep devel opers occupied for many years to come. If you are serious about lear ning Web services, you should visit http:// www.msdn.microsoft.com/webservices and download the most recent version of the Web Services Enhancement (WSE) library, which implements great features such as authentication, encryption, and binary attachments. As of this writing, the Technology Preview version of WSE 2.0 is available, which adds many other useful characteristics, including role-based security and transactions. These features are implemented as SOAP extensions, so you can leverage what you ve learned in this chapter. When I began to write the second edition of this book, I was determined to add one chapter on WSE, but the fast pace at which Web services technology is evolving would have made that information stale after a few months (or even weeks). Instead of chas ing this new and exciting technology, I decided to devote the new chapters of this edi tion to other portions of the .NET Framework that are quite stable and that aren t going to change remarkably in the short run, starting with PInvoke and COM Interop.