Tips and Tricks

Client Pull/Server Push

Client Pull and Server Push are two recent additions to the HTML and CGI standards. With these two methods, you can extend the capabilities of both Web browsers and Web servers.

Client Pull sends information to the Web browser via the <META> tags in an HTML file and allows it to perform additional functions. Server Push similarly sends special information to the browser in an HTML file but relies on the server, rather than the browser, to send additional data as specified in the HTML document.

The functionality of these two features depends on the MIME standard and the HTTP response header.

Client Pull

Client Pull is a method used to give additional instructions to a Web browser that would not have been sent by the server it is currently browsing. Client Pull is not a language, although it is usually implemented using HTML. You probably have seen Client Pull-in action but did not recognize it. A common implementation of Client Pull is to have the browser automatically move to a different page without the user clicking a hyperlink. For example, sites that have changed their URL might use Client Pull to tell a browser to automatically load the new URL. You could also specify the browser to load the new URL after a time frame has expired. How exactly is this done? To understand what goes on in the background of Client Pull, you need to know about HTTP response headers and the <META> tags.

Server Push

Server Push is similar to Client Pull in that it also includes extra information within the HTML document. Server Push does not rely on the browser to act on the information included in the document but, instead, relies on the server to push the additional information as scheduled. To understand how Server Push works, we must take a more in-depth look into the MIME standard and specifically the MIME content-type multipart/mixed.

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