WebSub (formerly PubSubHubbub) is an open protocol for distributed publish–subscribe communication on the

Internet The Internet (or internet) is the Global network, global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a internetworking, network of networks ...

. Initially designed to extend the

Atom Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...

(and

RSS RSS ( RDF Site Summary or Really Simple Syndication) is a web feed that allows users and applications to access updates to websites in a standardized, computer-readable format. Subscribing to RSS feeds can allow a user to keep track of many ...

) protocols for data feeds, the protocol can be applied to any data type (e.g.

HTML Hypertext Markup Language (HTML) is the standard markup language for documents designed to be displayed in a web browser. It defines the content and structure of web content. It is often assisted by technologies such as Cascading Style Sheets ( ...

, text, pictures, audio, video) as long as it is accessible via HTTP. Its main purpose is to provide real-time notifications of changes, which improves upon the typical situation where a client periodically polls the feed server at some arbitrary interval. In this way, WebSub provides pushed HTTP notifications without requiring clients to spend resources on polling for changes. In October 2017, PubSubHubbub was renamed to WebSub for simplicity and clarity. , the WebSub protocol has been adopted by the

W3C The World Wide Web Consortium (W3C) is the main international standards organization for the World Wide Web. Founded in 1994 by Tim Berners-Lee, the consortium is made up of member organizations that maintain full-time staff working together in ...

as a Recommendation.

Protocol

Under WebSub, there is an ecosystem of publishers, subscribers, and hubs. A subscriber first retrieves content from an HTTP resource (

URL A uniform resource locator (URL), colloquially known as an address on the Web, is a reference to a resource that specifies its location on a computer network and a mechanism for retrieving it. A URL is a specific type of Uniform Resource Identi ...

) by requesting it from the webserver. The subscriber then inspects the contents of the response, and if it references a hub, the subscriber can subscribe to that resource's URL (it's called a 'topic' by the spec) on that hub. The subscriber needs to run a web accessible server so that hubs can directly notify it when any of its subscribed topics have updated, using a webhook mechanism. Publishers expose their content with the inclusion of hub references in the HTTP headers. They post notifications to those referenced hubs whenever they publish something. Thus, when a publication event occurs, the publisher calls its hubs and the hubs call their subscribers. WebSub includes a simple verification of intent mechanism in order to prevent abusive subscriptions, and a validation mechanism allows for subscriptions to private or protected web resources. When the subscriber sends the subscription request to the hub, the subscriber address and a code needs to be included. The hub immediately sends a verification message to the subscriber with the URL of the topic and the above code. The subscription request will only be accepted if the subscriber sends a positive response to the verification request of the hub. In order to provide a secure chain, subscribers should share a secret with the hub, which will be used by the hub to compute an

HMAC In cryptography, an HMAC (sometimes expanded as either keyed-hash message authentication code or hash-based message authentication code) is a specific type of message authentication code (MAC) involving a cryptographic hash function and a se ...

key that will be sent to the subscriber. The latter can then easily verify the origin by comparing the supplied

signature A signature (; from , "to sign") is a depiction of someone's name, nickname, or even a simple "X" or other mark that a person writes on documents as a proof of identity and intent. Signatures are often, but not always, Handwriting, handwritt ...

with a similarly computed signature on their end.

Usage

WebSub is used to push content by many websites, including all

blog A blog (a Clipping (morphology), truncation of "weblog") is an informational website consisting of discrete, often informal diary-style text entries also known as posts. Posts are typically displayed in Reverse chronology, reverse chronologic ...

s served by

Blogger A blog (a Clipping (morphology), truncation of "weblog") is an informational website consisting of discrete, often informal diary-style text entries also known as posts. Posts are typically displayed in Reverse chronology, reverse chronologic ...

and WordPress.com, news sites including

CNN Cable News Network (CNN) is a multinational news organization operating, most notably, a website and a TV channel headquartered in Atlanta. Founded in 1980 by American media proprietor Ted Turner and Reese Schonfeld as a 24-hour cable ne ...

and

Fox News The Fox News Channel (FNC), commonly known as Fox News, is an American Multinational corporation, multinational Conservatism in the United States, conservative List of news television channels, news and political commentary Television stati ...

, and social networks like diaspora*,

Mastodon A mastodon, from Ancient Greek μαστός (''mastós''), meaning "breast", and ὀδούς (''odoús'') "tooth", is a member of the genus ''Mammut'' (German for 'mammoth'), which was endemic to North America and lived from the late Miocene to ...

MySpace Myspace (formerly stylized as MySpace, currently myspace; and sometimes my␣, with an elongated Whitespace character#Substitute images, open box symbol) is a social networking service based in the United States. Launched on August 1, 2003, it w ...

or Medium.com. Subscribing services (“feed readers”) include Flipboard, Feedly, NewsBlur, among other popular options. Community Hosted hub providers include pubsubhubbub.appspot.com (operated by

Google Google LLC (, ) is an American multinational corporation and technology company focusing on online advertising, search engine technology, cloud computing, computer software, quantum computing, e-commerce, consumer electronics, and artificial ...

), pubsubhubbub.superfeedr.com (operated by Superfeedr), and websubhub.com. Superfeedr provides a detailed PubSubHubbub guide for implementation.

References

{{W3C standards

RSS (file format) RSS (Resource Description Framework, RDF Site Summary or Really Simple Syndication) is a web feed that allows users and applications to access updates to websites in a standardized, computer-readable format. Subscribing to RSS feeds can allow ...

Web syndication formats XML-based standards Computer file formats World Wide Web Consortium standards

Protocol

Usage

See also

References