81 lines
4 KiB
Markdown
81 lines
4 KiB
Markdown
---
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title: Relayable
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---
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If a person participates on an entity, it needs to be relayed via the author of the root entity, because only the
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root author knows, to whom they shared the original entity.
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The root is the most top parent of the relayable: If the parent of a relayable is a relayable itself,
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the parent of that should be used, until it isn't a relayable anymore.
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For example, for both, a `Like` for a `Post` and a `Like` for a `Comment`, the author of the `Post` should be used.
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Such relayable entities are:
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* [Comment][comment]
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* [Like][like]
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* [PollParticipation][poll_participation]
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## Common Properties
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All relayables have the following properties:
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| Property | Type | Description |
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| ------------------------- | ---------------------------- | ------------------------------------------------- |
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| `author` | [diaspora\* ID][diaspora-id] | The diaspora\* ID of the author of the relayable. |
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| `guid` | [GUID][guid] | The GUID of the relayable. |
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| `parent_guid` | [GUID][guid] | The GUID of the parent entity. |
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| `author_signature` | [Signature][signature] | The signature from the author of the relayable. |
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## Relaying
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If the author is not the same as the root author, the author of the relayable sends the entity to the root author
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and the author must include the `author_signature`.
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The root author then must envelop it in a new [Magic Envelope][magicsig] and send the entity to all the recipients
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of the root entity. If the author and the root author are on the same server, the author must sign the
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`author_signature` and the root author needs to sign the Magic Envelope.
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If someone other then the root author receives a relayable without a valid Magic Envelope signed from
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the root author, it must be ignored. If the author is not the same as the root author and the `author_signature`
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is missing or invalid, it also must be ignored. If the author is the same as the root author, the `author_signature`
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can be missing, because a valid signature in the Magic Envelope from the author is enough in that case.
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## Signatures
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The string to sign is built with the content of all properties (except the `author_signature` itself),
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concatenated using `;` as separator in the same order as they appear in the XML. The order in the XML is not specified.
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This ensures that relayables even work, if the root author or another recipient does not know all properties of the
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relayable entity (e.g. older version of diaspora\*).
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This string is then signed with the private RSA key using the RSA-SHA256 algorithm and base64-encoded.
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The root author must use the same order as the relayable author. Unknown properties must be included again in the XML
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and the signature.
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To support fetching of the relayables, the root author should save the following information:
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* order of the received XML
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* additional (unknown) properties
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* `author_signature`
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## Retraction / Reject
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The root author is allowed to retract the entity, so there are no additional signatures required for the
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[Retraction][retraction] (only the [Salmon Magic Signature][magicsig]).
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If the author retracts the entity, they send a [Retraction][retraction] to the root author. The root author also
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must relay this retraction to all recipients of the root entity.
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If the root author wants to reject the entity (e.g. if they ignore the author of the relayable), they can simply send
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a [Retraction][retraction] for it back to the author.
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[diaspora-id]: {{ site.baseurl }}/federation/types.html#diaspora-id
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[guid]: {{ site.baseurl }}/federation/types.html#guid
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[signature]: {{ site.baseurl }}/federation/types.html#signature
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[comment]: {{ site.baseurl }}/entities/comment.html
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[like]: {{ site.baseurl }}/entities/like.html
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[poll_participation]: {{ site.baseurl }}/entities/poll_participation.html
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[retraction]: {{ site.baseurl }}/entities/retraction.html
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[magicsig]: {{ site.baseurl }}/federation/magicsig.html
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