Definition
Client-Pull refers to a technique that enables a browser/client to request (or “pull”) data from the server automatically without the user-intervention.
The key property here is “without user-intervention.” If not for this attribute, then the term is meaningless because it will be no different than when an user enters an URL to request a page.
With this capability, it is possible to have a web page that refreshes/reload itself; or even a web page that loads another page, without the user doing anything.
How To
Client pull can be done via cgi, by outputting this http header
Refresh: numOfsecond; URL=someURL
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But the good news is that it can also be accomplished by using META tag within a html page. The syntax is as follows:
<META HTTP-EQUIV="Refresh"
CONTENT="X[; URL=http://whatever.com/something.html]">
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where:
- X is the number of seconds before the reload/refresh; and
- URL is the URL of the page to be loaded. Note that according to Netscape, this should be a fully qualified URL (complete with the site’s domain name); although I’ve seen it work with relative URL. Also, this doesn’t actually have to be a html page, it can be an image, or whatever.
Note that the URL field is optional.
Example 1:
This html code below will cause the current page to reload itself after 10 seconds. It reload itself because no URL is specified.
<HEAD>
<META HTTP-EQUIV="Refresh" CONTENT="2">
<TITLE>Page</TITLE>
</HEAD>
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Example 2:
This html code below will cause page2.html to be loaded after 2 seconds. Note that there are only 2 quote signs in
CONTENT=”2; URL=http://whatever.com/something.html”
This is not a typo. It’s the way it is specified in the http specification.
<HEAD>
<META HTTP-EQUIV="Refresh"
CONTENT="2; URL=https://www.permadi.com/page2.html">
<TITLE>Page</TITLE>
</HEAD>
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Example 3:
In the following concrete example, client-pull is used to create splash screens effect. Three html pages will be loaded subsequently after 2 second.
Why would anyone want to use this?
At the present time, client pull has been supplanted by newer and more powerful technologies such as “animated-gifs,” Flash, or “dynamic html.” However, on its days, it has been used for:
- Web-cam applications, such as web page that shows a real time image every some minutes. (This is perhaps one client-pull application that is still relevant today.)
- Automatic slideshows
- Splash pages
- Gimmick, novelty
For further reference, consult Netscape documentation athttp://home.netscape.com/assist/net_sites/pushpull.html