Windows CE is often used on embedded systems, on which there are limited resources. Most of Windows CE devices don’t have disk drive, files are stored in memory, called object store. Improved networking ability on devices will save the memory space, achieve to access unlimited information through the global Internet, and realize a disk-free computing. In this project, we have tried to develop a networking application, and investigate the networking functions on Windows CE.

A Practice of Windows CE Networking

To design an Internet appliance on Windows CE, it follows above steps. At the highest level, WinInet functions are ready to use to implement FTP and HTTP-like applications, as we have practiced in the project. In reality, WinInet functions wrap WinSock functions. WinSock is a set of functions similar to UNIX BSD Socket. Socket functions help programmers saving the details of TCP/IP protocol stacks. Programmers can either use WinSock or WinInet functions for Internet applications, but they can’t directly use TCP/IP functions, such as routing and IP forwarding, because those functions work in OS kernel.

The MAC layer networking schemes are included in network device driver. In Windows CE, it is called NDIS(current version 4.0). Windows CE has a default network driver for NE2000 compliance. But, NDIS belongs to external driver model That allows third parties to develop their own drivers and add new networking features on Windows CE. 

(In above block diagram, the boxes in green are accessable)

Project Implementation 
 
 

Our project is trying to implement a HTTP client running on Windows CE. After setting up a connection, the client sends HTTP requests to web server, and retrieves the web page data, which later on is saved into a file for parsing. HTTP protocol is specifically for web browsing applications. At network and transportation layers, HTTP uses TCP/IP functions as it is connection-oriented. In Microsoft Win32, there are already a set of functions in WinInet just for HTTP and FTP Internet-based application protocols. By using WinInet, I can avoid the complexity inside the protocols.

This code (DoInet.cpp) is modified from a sample code (httpdumpce.cpp) at Microsoft Windows CE web site. It uses the OPENURL method by calling InternetOpenURL to send web requests. To do an Internet web request, the procedures are following:

1.Declare an Internet handler using InternetOpen();

2.Declare an Internet handler and bind the specific URL to this handler using InternetOpenURL(), this is because it may need multiple connections in one web page;

3.Get the HTTP query information to check the status usingHttpQueryInfo();

4.Retrieve HTTP header information also using HttpQueryInfo(), this tells the size of web page;

5.Use a while loop to receive the data of web page.

It also need to convert the data into Unicode on Windows CE, and send the data to callback function for Windows event dispatching.