Not just HTTP in Visual Studio .NET

Painting UPC-A in Visual Studio .NET Not just HTTP

Your Web service operates over the Internet using the common HTTP protocol However, it could travel in several other ways For example, if you had an FTP server, the client could drop requests there and pick up the answers Your software could accept e-mail messages from clients with SOAP packages included as attachments The software would pull out the bundled request, and submit it for processing An e-mail server that supports the Simple Mail Transport Protocol (SMTP) would e-mail back the answer automatically If the expanding supercomputation business threatened to steal too many cycles from your chess program, you could put requests in a queue When the chess program is waiting for your move, the supercomputer could pick a couple of items out of the queue and crunch away on them When finished, it would return the answers to a pickup directory for forwarding Maybe you d charge less for delayed results, or perhaps the system could offer a secondary Web service that clients could poll for the estimated wait time

Sometimes sidelines and hobbies become a person s main business Some of the clients are getting more demanding They want you to offer enhanced privacy for their messages, encryption, a guarantee that requests and responses will be delivered, and a way to route a request to somewhere else if your system can t process the computation right away

You can build everything that you ve read in the preceding scenarios with existing tools and technologies Some aspects, like security, require add-ons to the basic SOAP protocol You d certainly need more servers and software, but it can be done without a lot of grief Given that you already have the supercomputer to crunch the data lucky you! the rest is relatively cheap Now that you understand what a Web service is or can be, we can launch into building one with Visual Web Developer Express (VWDE) No, we won t be hooking it up to the supercomputer our computation needs aren t that extreme

Creating a Web service using Visual Web Developer Express is easier than creating a Web page because there s only half as much to do Unlike a Web page, a Web service has no user interface There are no buttons or boxes to design (Actually, that s not quite true because ASPNET automatically builds some user interface elements for testing the Web service We dig into that in the section Providing information to clients, later in this chapter

Our first Web service is a converter from Arabic numbers to Roman numerals There s strong demand for this service in Hollywood where the artists who create the credits for films use Roman numerals for the copyright date To get started, you should have an ASPNET Web project open We re coding the Web services in Visual Basic (VB)

1 In Solution Explorer, right-click the project name and, from the context menu, click Add New Item The Add New Item dialog box opens

romannumeralsasmx, as shown in Figure 6-1

Hey, did you notice the new extension, asmx there Microsoft reserves the extension asmx for Web services The asmx extension ensures that the Web server produces XML output rather than HTML (or XHTML) A regular aspx page is intended for browsing while a asmx file is for data exchange

File check box, and click Add Visual Web Developer adds two files to your project: an asmx file and a vb file Then, it opens the vb file in the editor, as shown in Figure 6-2

At this point, you have a somewhat usable Hello World Web service because Microsoft inserts the skeleton code as an example

Analyze this!

Notice that there s no Design mode choice for a Web service As previously mentioned, a Web service is all code, all the time Here s the complete starter code for the Web service:

<%@ WebService Language= VB Class= romannumerals %> Imports SystemWeb Imports SystemWebServices Imports SystemWebServicesProtocols <WebService(Namespace := http://tempuriorg/ )> _ <WebServiceBinding(ConformsTo:=WsiProfilesBasicProfile1_1)>_ Public Class romannumerals Inherits SystemWebServicesWebService <WebMethod()> _ Public Function HelloWorld() As String Return Hello World End Function End Class

Let s look at what goes into the default code before we start changing it to implement our own service