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Pull coding orclient pull is a style ofnetwork communication, where the initialrequest for data originates from theclient, and then is responded to by theserver. The reverse is known aspush technology, where the serverpushes data to clients.
Pull requests form the foundation of network computing, where many clients request data from centralized servers. Pull is used extensively on theInternet forHTTP page requests fromwebsites.
Apush can also be simulated using multiplepulls within a short amount of time. For example, when pullingPOP3 email messages from a server, a client can make regular pull requests, every few minutes. To the user, the email then appears to be pushed, as emails appear to arrive close to real-time. A trade-off of this system is that it places a heavier load on both the server and network to function correctly.
Manyweb feeds, such asRSS are technically pulled by the client. With RSS, the user'sRSS reader polls the server periodically for new content; the server does not send information to the client unrequested. This continual polling is inefficient and has contributed to the shutdown or reduction of several popular RSS feeds that could not handle the bandwidth.[1][2] For solving this problem, theWebSub protocol, as another example of a push code, was devised.
Podcasting is specifically a pull technology. When a new podcast episode is published to an RSS feed, it sits on the server until it is requested by a feed reader, mobile podcasting app, or directory. Directories such asApple Podcasts (iTunes), The Blubrry Directory, and many apps' directories request the RSS feed periodically to update the Podcast's listing on those platforms. Subscribers to those RSS feeds via app or reader will get the episodes when they request the RSS feed next time, independent of when the directory listing updates.
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