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fep-a1d1: ActivityPub Patch (#795)
Co-authored-by: Steve Bate <svc-github@stevebate.net> Reviewed-on: https://codeberg.org/fediverse/fep/pulls/795 Co-authored-by: Steve Bate <steve-bate@noreply.codeberg.org> Co-committed-by: Steve Bate <steve-bate@noreply.codeberg.org>
This commit is contained in:
Steve Bate
silverpill
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{
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"@context": [
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{
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"@version": 1.1,
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"fep-a1d1": "https://w3id.org/fep/a1d1#",
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"Patch": "fep-a1d1:Patch",
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"PatchOperations": {
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"@id": "fep-a1d1:PatchOperations",
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"@context": {
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"operations": {
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"@id": "fep-a1d1:operations",
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"@container": "@list",
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"@context": {
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"op": "fep-a1d1:op",
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"path": "fep-a1d1:path",
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"value": {
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"@id": "fep-a1d1:value",
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"@type": "@json"
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},
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"from": "fep-a1d1:from",
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"add": "fep-a1d1:add",
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"remove": "fep-a1d1:remove",
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"replace": "fep-a1d1:replace",
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"move": "fep-a1d1:move",
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"copy": "fep-a1d1:copy",
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"test": "fep-a1d1:test"
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}
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}
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}
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}
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}
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]
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}
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---
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slug: "a1d1"
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type: implementation
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authors: Steve Bate <svc-fep@stevebate.net>
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status: DRAFT
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discussionsTo: https://codeberg.org/steve-bate/fep/issues
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dateReceived: 2026-03-19
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---
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# FEP-a1d1: ActivityPub Patch
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## Summary
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[ActivityPub] Client-to-Server (C2S) Partial Update relies on shallow top-level replacement and uses JSON `null` to signal property removal, but in compacted JSON-LD `null` is elided, so deletions can be lost in transit. This FEP introduces a `Patch` activity (based on [JSON Patch][RFC6902]) that cleanly separates patch operations from the target object and supports nested property updates via JSON Pointer ([RFC6901](https://www.rfc-editor.org/rfc/rfc6901)).
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## Motivation
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ActivityPub client-to-server updates are currently defined as shallow partial replacements of top-level properties, with a special rule that a property set to JSON `null` is removed from the stored object. In practice, that removal rule is not compatible with ActivityPub's JSON-LD serialization model.
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In compacted JSON-LD, `null` values are removed and treated as if the property wasn't specified, so a server may never receive the signal that a property is meant to be deleted. This issue has been recorded in the [ActivityPub errata], and related discussion in the W3C ActivityPub issue tracker (Issues #[396](https://github.com/w3c/activitypub/issues/396) and #[477](https://github.com/w3c/activitypub/issues/477)).
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The semantics of the C2S Partial Update is also incorrect. The update is specified in the `object` property with an `id`. However, the `id` is the URI of the target object rather than the update object. In other words, the `id` is not being used to specify the identity of the `Update` `object`, but rather a completely different target object. The `Patch` operation separates the patch operations from the `target` object that will be patched.
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The C2S Partial Update can only modify top-level properties. The `Patch` activity can modify nested properties (using JSON Pointer [RFC6901](https://www.rfc-editor.org/rfc/rfc6901) ).
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Ideally, the `Patch` activity will replace partial `Update` activities in the C2S specification. For complete object replacement, the C2S `Update` activity can continue to be used in a consistent manner as for the Server-to-Server (S2S) `Update`.
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## Patch
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Based on [JSON Patch](https://datatracker.ietf.org/doc/html/rfc6902/), a `Patch` `object` refers to a `PatchOperations` object. This object has an `operations` property containing an ordered list of operations.
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**Example**
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```json
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{
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"@context": [
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"https://w3id.org/fep/a1d1",
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"https://www.w3.org/ns/activitystreams"
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],
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"id": "https://server.example/patch/1",
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"type": "Patch",
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"object": {
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"type": "PatchOperations",
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"operations": [
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{
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"op": "add",
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"path": "/name",
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"value": "Daily post"
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},
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{
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"op": "remove",
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"path": "/summary",
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},
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{
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"value": "Some new content...",
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"path": "/content",
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"op": "replace"
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},
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{
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"value": "Du nouveau contenu...",
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"path": "/contentMap/fr",
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"op": "replace"
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},
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]
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},
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"target": "http://object-to-update"
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}
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```
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The `operations` are standard JSON Patch operations so they will not be covered in detail in this FEP. The operations include:
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* `add`
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* `remove`
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* `replace`
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* `move`
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* `copy`
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* `test`
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[RFC6902] contains numerous examples that describe the semantics of these operations. This FEP defines a JSON-LD context for the `Patch` activity and the JSON Patch language.
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## Side-Effects
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When a `Patch` activity is posted to the outbox, the server MUST apply authorized operations to the target object. After the update is complete, the server SHOULD send an `Update` notification (with the full, updated object) notification, on behalf of the `Patch` actor, to any specified recipients.
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## JSON-LD Context
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```json
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{
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"@context": [
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{
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"@version": 1.1,
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"fep-a1d1": "https://w3id.org/fep/a1d1#",
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"Patch": "fep-a1d1:Patch",
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"PatchOperations": {
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"@id": "fep-a1d1:PatchOperations",
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"@context": {
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"operations": {
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"@id": "fep-a1d1:operations",
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"@container": "@list",
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"@context": {
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"op": "fep-a1d1:op",
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"path": "fep-a1d1:path",
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"value": {
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"@id": "fep-a1d1:value",
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"@type": "@json"
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},
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"from": "fep-a1d1:from",
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"add": "fep-a1d1:add",
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"remove": "fep-a1d1:remove",
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"replace": "fep-a1d1:replace",
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"move": "fep-a1d1:move",
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"copy": "fep-a1d1:copy",
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"test": "fep-a1d1:test"
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}
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}
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}
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}
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}
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]
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}
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```
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> **NOTE:** The `fep-a1d1:value` term is defined as a JSON-LD `@json` type. For JSON consumers, this will not make a difference but it tells JSON-LD consumers
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that the content is a serialized JSON string (which may itself be JSON-LD). Linked Data applications will typically need to parse this string to retrieve the original JSON content.
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## Implementations
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- [FIRM](https://github.com/steve-bate/firm)
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## Copyright
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CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
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To the extent possible under law, the authors of this Fediverse Enhancement
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Proposal have waived all copyright and related or neighboring rights to this work.
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[ActivityPub]: https://www.w3.org/TR/activitypub/ "ActivityPub is a decentralized social networking protocol based upon the ActivityStreams 2.0 data format."
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[ActivityPub errata]: https://www.w3.org/wiki/ActivityPub_errata
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[ActivityStreams]: https://www.w3.org/TR/activitystreams-vocabulary/
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[RFC6902]: https://datatracker.ietf.org/doc/html/rfc6902/
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