Web Clients. Chapter 2. Web Protocols and Practice. WEB CLIENTS. Topics. Web Protocols and Practice. WEB CLIENTS. Web Client Definition. Web Protocols and Practice. WEB CLIENTS. Web Client Definition. Web Protocols and Practice. WEB CLIENTS. Browser Functions.
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1 DNS query
2 TCP Connection
3 HTTP Request
4 HTTP Response
5 Optional parallel connections
Figure 2.1. Steps in a browser process
Figure 2.1 shows the various steps in the process involved in a Web request as processed by a typical browser. The selected URL is parsed to determine the Web server that must be contacted. A connection is set up with the server, and an HTTP request is sent with the URL to obtain the response.
Figure 2.2. Container document foo.html
1 HTTP request for foo.ra
2 (Location, protocol)
3 Audio protocol request
Figure 2.3. Listening to audio data
Figure 2.3: The user selects a resource http://www.bar.com/foo.ra, and the browser sends an HTTP request to the origin server www.bar.com for the resource foo.ca (step 1). The origin server sends back an HTTP response (step 2), but the content of the response is simply a pointer to the information. The response is meaningful only to an audio client rather than a Web browser. Typically, the response is a URL such as pnm://ra-ms.com/foo.ra, where pnm stands for "Progressive Network Media" and ra-ms is the media server on which the resource foo.ca resides. Because the browser has been configured to invoke the helper program based on the file type, it would invoke the real-audio client program, which would contact the media server ra-ms.com (step 3) and start downloading the audio content.
Figure 2.4. Client-server exchange of cookie information
Figure 2.4 shows a client sending a request to an origin server (step 1). The origin server in its response includes the header (Set-cookie) with the cookie value (XYZ) (step 2). In all future requests to the origin server A, the client includes the cookie (step3, sent with the request via the header cookie).