ActivityPub

Last updated

ActivityPub
Communication protocol
ActivityPub-logo.svg
ActivityPub-tutorial-image.svg
An infographic of the core functionality of ActivityPub
AbbreviationAP
Purpose Decentralized social networking
Developer(s) World Wide Web Consortium and
IntroductionJanuary 23, 2018;7 years ago (2018-01-23)
Based on ActivityStreams, JSON-LD
Influenced AT Protocol [1]
Website activitypub.rocks OOjs UI icon edit-ltr-progressive.svg

ActivityPub is a protocol and open standard for decentralized social networking. It provides a client-to-server (C2S) API for creating and modifying content, as well as a federated server-to-server (S2S) protocol for delivering notifications and content to other servers. [2] ActivityPub has become the main standard used in the fediverse, a popular network used for social networking that consists of software such as Mastodon, Pixelfed and PeerTube. [3]

Contents

ActivityPub is considered to be an update to the ActivityPump protocol used in pump.io, and the official W3C repository for ActivityPub is identified as a fork of ActivityPump. [4] [5] The creation of a new standard for decentralized social networking was prompted by the complexity of OStatus, the most commonly used protocol at the time. OStatus was built using a multitude of technologies (such as Atom, Salmon, WebSub and WebFinger), a product of the infrastructure used in GNU social (the originator and largest user of the OStatus protocol), which made it difficult to implement the protocol into new software. OStatus was also only designed to work with microblogging services, with little flexibility to the types of data that it could hold.

The standard was first published by the World Wide Web Consortium (W3C) as a W3C Recommendation in January 2018 by the Social Web Working Group (SocialWG), a working group chartered to build the protocols and vocabularies needed to create a standard for social functionality. [6] Shortly after, further development was moved to the Social Web Community Group (SocialCG), the successor to the SocialWG.

Design

ActivityPub uses the ActivityStreams 2.0 format for building its content, which itself uses JSON-LD. The three main data types used in ActivityPub are Objects, Activities and Actors. Objects are the most common data type, and can be images, videos, or more abstract items such as locations or events. Activities are actions that create and modify objects, for example a Create activity creates an object. Actors are representative of an individual, a group, an application or a service, and are the owners of objects.

Every actor type contains an inbox and outbox stream, which sends and receives activities for a user. In order to publish data (for example liking an article), a user creates an activity that declares that they liked an Article object and publishes it to their outbox, where it is then delivered by the ActivityPub server via a POST request to the inboxes listed in the activity's to, bto, cc and bcc fields. The receiving servers then account for the newly received activity and update the article by adding the like action to it.

Example data

An example actor object that represents a user account: [7] 

{"@context":["https://www.w3.org/ns/activitystreams",{"@language":"ja"}],"type":"Person","id":"https://kenzoishii.example.com/","following":"https://kenzoishii.example.com/following.json","followers":"https://kenzoishii.example.com/followers.json","liked":"https://kenzoishii.example.com/liked.json","inbox":"https://kenzoishii.example.com/inbox.json","outbox":"https://kenzoishii.example.com/feed.json","preferredUsername":"kenzoishii","name":"石井健蔵","summary":"この方はただの例です","icon":["https://kenzoishii.example.com/image/165987aklre4"]}

An example activity that likes an article object:

{"@context":["https://www.w3.org/ns/activitystreams",{"@language":"en"}],"type":"Like","actor":"https://dustycloud.org/christine/","summary":"Christine liked 'Minimal ActivityPub update client'","object":"https://rhiaro.co.uk/2016/05/minimal-activitypub","to":["https://rhiaro.co.uk/#amy","https://dustycloud.org/followers","https://rhiaro.co.uk/followers/"],"cc":"https://e14n.com/evan"}

An example article object:

{"@context":["https://www.w3.org/ns/activitystreams",{"@language":"en-GB"}],"id":"https://rhiaro.co.uk/2016/05/minimal-activitypub","type":"Article","name":"Minimal ActivityPub update client","content":"Today I finished morph, a client for posting ActivityStreams2...","attributedTo":"https://rhiaro.co.uk/#amy","to":"https://rhiaro.co.uk/followers/","cc":"https://e14n.com/evan"}

Project status

The SocialCG previously organized a yearly free conference called ActivityPub Conf about the future of ActivityPub. [8] [9] Triages are held regularly to review issues pertaining to the ActivityPub and ActivityStreams 2.0 specifications as part of the SocialCG. [10]

In 2023, Germany's Sovereign Tech Fund donated €152,000 to socialweb.coop with the goal of building a new suite for testing various ActivityPub implementations and their compliance with the specification. [11]

Adoption

The initial wave of adoption for ActivityPub (circa 2016-2018) came from software that was already using OStatus as their federation protocol, such as Mastodon, GNU social and Pleroma. [12] Following the acquisition of Twitter by Elon Musk in 2022, many groups of users that were critical of the acquisition migrated to Mastodon, bringing new attention to the ActivityPub protocol with it. [13] Various major social media platforms and corporations have since pledged to implement ActivityPub support, including Tumblr, [14] Flipboard [15] and Meta Platforms' Threads. [16] Threads introduced crossposting to ActivityPub in 2024 for users outside of the European Economic Area, [17] however full 2-way compatibility remains incomplete as of 2025. [18]

Criticism

Accidental denial-of-service attacks

Poorly optimized ActivityPub implementations can cause unintentional distributed denial-of-service (DDOS) attacks on other websites and servers, due to the decentralized nature of the network.[ citation needed ] An example would be Mastodon's implementation of OpenGraph link previews, wherein every instance that receives a post that contains a link with OpenGraph metadata will download the associated data, such as a thumbnail, in a very short timeframe, which can slow down or crash servers as a result of the sudden burst of requests. [19] [20]

Account migration

ActivityPub has been criticized for not natively supporting moving accounts from one server to another, forcing implementations to build their own solutions. [21] While there has been work on building a standardized system for migrating accounts using the Move activity via the Fediverse Enhancement Proposal organization, the current proposal only allows for basic follower migration, with all other data remaining linked to the original account. [22]

Missing content and data

ActivityPub implementations have been criticized for missing replies and parts of reply threads from remote posts, and presenting outdated statistics (e.g. likes and reposts) about remote posts. [23] [24] However, this isn't a problem with the ActivityPub protocol itself, but with implementations not refreshing their content for updated data when needed. [25] [26] [ citation needed ]

Software using ActivityPub

Software nameTotal users [27] [28] Initial ActivityPub-compatible releaseType of software Fork of
Akkoma 9,5302022 [29] Blogging Pleroma
BookWyrm [30] 49,6002021 [31] Book cataloging
Castopod818 podcasts [32] 2020 [33] Audio hosting
Discourse ?2025 [34] Internet forum
dokieli ?2018 [35] Authoring system, Blogging, Notification system, Semantic publishing, Web annotation
Epicyon32019 [36] Blogging
Firefish4,5602022 [37] BloggingMisskey
Flipboard [38] 145,000,000 [39] 2023 [40] [41] Social news
Friendica [42] 19,8002019 Blogging, event management, groups, image gallery
Funkwhale8,8502018 [43] Audio hosting
Gancio [44] 1,9002020 [45] Calendar, event planner
Ghost [46] [47] ?2025 (in beta) [48] Blogging
GNU social 932018 [49] Blogging
Guppe [50] not relevant2021 [51] Groups
GoToSocial382021 [52] Blogging
Hollo642024 [53] Blogging
Honk62019 [54] Blogging
Hubzilla [55] 6,7402017Blogging, event planner, file hosting, image gallery, wiki
Iceshrimp [56] ?2023BloggingFirefish
Iceshrimp.NET [57] ?2024Blogging
Inventaire.io [58] ?2021Book cataloging
kbin [59] 5072023Social news
Lemmy [60] 485,0002019Social news
Libervia [61] ?2022 (in beta)Blogging, event management, file sharing, instant messaging
lotide [62] 4622020 [63] Social news
Mastodon 7,960,0002017 [64] Blogging
Mobilizon 76,9002020Event management, groups
mbin [65] 6,9502023Social newskbin
Micro.blog 198,0002021 [66] Microblogging
microblog.pub392022 [67] Blogging
Misskey 1,052,5112018 [68] Blogging
Nextcloud Social50 (approx.)2018 [69] Blogging
NodeBB2,750,0002025 [70] Internet forum
Owncast [71] 1912022 Live streaming
PeerTube [72] 473,0002018 Video sharing
PieFed1,116 [73] 2023 [74] Social News
Pixelfed [75] 857,0002018 Image sharing
Pleroma 52,0002018 [76] Blogging
Plume [77] 24,4002018 [78] Blogging
Postmarks [79] 252023 [80] Social bookmarking
Sharkey [81] 23,1002023BloggingMisskey
Snac [82] 3,0702022 [83] Blogging
Socialhome3,0002016 [84] Blogging
Streams [85] ?2022 [86] Blogging, image sharing, wiki
Takahē3412022 [87] Blogging
Threads 130,000,000 [88] 2023 [89] Blogging
Wafrn [90] 2,4802023Blogging
WordPress [91] [92] 29,100 in 6,000+ blogs [93] 2023 [94] Blogging
WriteFreely73,2002018 [95] Blogging
Zap [96] 12019 [97] Blogging, file hosting, image gallery

Future implementations

Uncertain future implementations

See also

References

  1. ↑ "FAQ". AT Protocol. Retrieved June 20, 2024.
  2. ↑ "W3C Recommendation 23 January 2018".
  3. ↑ Pierce, David (February 7, 2024). "The fediverse, explained". The Verge. Retrieved June 20, 2024.
  4. ↑ w3c/activitypub, World Wide Web Consortium, June 20, 2024, retrieved June 22, 2024
  5. ↑ "Sandstorm and the Social Web". zenhack.net. May 29, 2016. Archived from the original on October 30, 2020. Retrieved September 23, 2017.
  6. ↑ "Social Web Working Group". W3C. Retrieved June 23, 2024.
  7. ↑ "ActivityPub Specification". W3C . January 23, 2018. Retrieved June 22, 2024.
  8. ↑ "ActivityPub Conf 2019". Archived from the original on March 8, 2021. Retrieved August 1, 2020.
  9. ↑ "ActivityPub Conf 2020". Archived from the original on June 2, 2021. Retrieved August 1, 2020.
  10. ↑ "W3C Social Web Incubator Community Group Mailing List" . Retrieved March 18, 2024.
  11. ↑ "ActivityPub Test Suite". Sovereign Tech Fund. Retrieved May 26, 2024.
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  15. ↑ McCue, Mike (December 18, 2023). "Flipboard Begins to Federate". Flipboard. Retrieved June 23, 2024.
  16. ↑ Guinness, Harry (July 12, 2023). "How ActivityPub is setting the stage to weave all your social media feeds together". Popular Science. Retrieved June 23, 2024.
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