Announcements Overview
Announcements are content or references to content that communicate new user activity to the rest of the network. Announcements are associated with an Identifier that can be validated as the creator of the Announcement. Depending on the implementation, Announcements may be published directly to the network, included in Batch Publication Files, or some combination of those two.
Announcement Types
Each Announcement has an enumerated type for use when separating out a stream of Announcements.
| Value | Name | Description | DSNP Content URI | Tombstone Allowed |
|---|---|---|---|---|
| 0 | Tombstone | an invalidation of previously announced content | no | no |
| 1 | ||||
| 2 | Broadcast | a public post | YES | YES |
| 3 | Reply | a public response to a Broadcast | YES | YES |
| 4 | Reaction | a public visual reply to a Broadcast | no | no |
| 5 | ||||
| 6 | Update | an update to content | YES | no |
| 7 | ||||
| 8 | User Attribute Set | an attribute set for a DSNP User | YES | YES |
| 9 | DSNP Content Attribute Set | an attribute set for a DSNP content item | YES | YES |
| 10 | External Content Attribute Set | an attribute set for a non-DSNP content item | YES | YES |
a Since DSNP version 1.2, social graph changes use User Data operations as described in the Graph section.
b Since DSNP version 1.3, public keys use User Data operations.
c Since DSNP version 1.3, profile changes use User Data operations.
Announcement Validation
There is no guarantee that, at time of creation, a given Announcement will be from the fromId claimed in the Announcement.
The reader MUST perform a validation of the Announcement at read time to ensure authenticity.
Implementations MUST provide a way to validate that the identifier associated with a given Announcement is authentic.
External Content URLs and Hashes
Where Announcements refer to external documents (such as Activity Content documents), these are referenced by both a URL and a DSNP Content Hash. The content hash MUST be generated by applying a Supported Hashing Algorithm to the full, unaltered contents of the document.
The URL associated with a content hash should be construed as a hint to initially locate a document matching the content hash, but is in no way meant to be the only way to locate the indicated document. Over time, a URL may cease to reference the specified document, or might have its contents altered; therefore, the content hash should be considered the authoritative value and the URL only one of many possible ways of locating a document. For example, services may cache documents or retrieve them from a content-addressed file system by applying the content hash (or a value derived from the content hash, such as a CID). When readers retrieve content referenced in an Announcement, they can validate the authenticity of the content, regardless of where it is hosted, by regenerating the hash output and comparing it with the content hash recorded in the Announcement.
Duplicate Handling
Due to the nature of asynchronous communication, duplicate Announcements may occur. In the case of duplicates, the first Announcement should be considered the ONLY valid Announcement. Additional duplicate Announcements MUST be rejected or ignored.
Ordering Announcements
- Order Batch Publications by implementation order.
- Order Announcements in a Batch Publication File by row appearance order.
Reverting an Announcement
Announcements may not be deleted, but may be marked invalid by using a Tombstone Announcement, or updated by using an Update Announcement. For example, if a user creates a Reaction Announcement, they may remove that reaction by creating a Tombstone Announcement.
Related Operations
Non-Normative
Duplicate Announcements
Due to the distributed nature of DSNP, duplicate Announcements are possible from time to time. These should be discarded and ignored.
Replay Attacks
Implementations typically restrict replay attacks by testing that the chain transaction sender is authorized (often via delegation) to publish an Announcement.
Announcement Ordering and Activity Content Published Timestamp
Activity Content has a published field that contains a user-generated timestamp. User-generated timestamps cannot be validated, but may be used to indicate ordering other than the network order for Announcements (which are not time dependent.)
Announcement Reference Ordering
Some Announcements contain references to other Announcements via the inReplyTo field.
Due to the distributed nature of DSNP, the canonical order can have an Announcement that refers to another Announcement appearing later in the network order.
For display purposes, these messages should be considered to have occurred after the reference.
DSNP v1.0 Announcement Signatures
In DSNP v1.0, Announcements had individual signatures, producing Batch Publications that were generic and disconnected from the user. Announcements could be submitted to the chain via anyone—not just delegates or users.
In DSNP v1.1, Announcement signatures were removed in favor of the implementation being responsible for the connection between the on-chain signature and the user. Implementations require that the transaction that produces a Batch be performed by the user or delegate directly. This creates batches that are delegate specific, but allows for faster testing of the validity of individual Announcements in a Batch.
For more information see DIP-145.