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142 lines
3.6 KiB
Markdown
142 lines
3.6 KiB
Markdown
NIP-xx
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======
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References to previous events
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-----------------------------
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`draft` `optional` `author:milahu`
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Events can contain references to previous events.
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Implementation
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--------------
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Each reference to a previous events consists of
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- the distance between this event and the previous event, as an integer number, greater-or-equal than 1
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- the ID of the previous event
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- optional: relay URL
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The choice of distances is arbitrary.
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Some choices:
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- exponentially increasing distances, for example: 1, 10, 100, 1000, 10000, ...
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- linearly increasing distances, for example: 1, 10, 20, 30, 40, 50, ...
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- random distances, for example: 1, 15, 32, 58, 93, 139, 185, ...
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```json
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{
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"id": ...,
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"kind": ...,
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...,
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...,
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"e_prev": [
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[<previous event distance>, <previous event ID>],
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[<previous event distance>, <previous event ID>],
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[<previous event distance>, <previous event ID>, <previous event relay URL>],
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...
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]
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}
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```
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Soft chain of events
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--------------------
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This is useful to build a "soft chain" of events, so the recipient can detect missing events.
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Events can go missing because of
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- political reasons (censorship)
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- technical reasons (data loss)
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Redundancy
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----------
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Each event can contain multiple references to previous events.
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The next-previous event (distance 1) SHOULD always be referenced.
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The number of referenced previous events is arbitrary.
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It can be as low as one previous event, or as high as all previous events.
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This gives a tolerance for missing events:
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When a previous event is missing, the recipient can seek back to another previous event.
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Forward search for missing events
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---------------------------------
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When an event is missing, and cannot be found on any other relay, the recipient will want to "seek forward" from another previous event.
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Example:
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The last received event `E0` contains references to previous events `[E1, E3, E7]` with the distances `[1, 3, 7]`.
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`E1` is missing (cannot be found on any relay).
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`E3` is found and received.
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Problem:
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How can we find `E2`?
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We only know the distance `2` relative to `E0`, but not the event ID of `E2`.
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Usually we would use the previous-event-reference with distance `1` relative to `E1`, but we dont have `E1`.
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Solution:
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We ask relays for events with references to `E3` or `E7` (or any other previous event in this chain).
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So relays SHOULD implement a "lookup of events by reference-to-previous-events".
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Limitations
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-----------
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Missing events can be detected only for past events, relative to a received event.
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Adoption
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--------
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Events created before the adoption of this NIP can be referenced in future events.
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To improve space-efficiency, it can make sense to distribute these back-references across multiple events ("sparse chains", "fragmented chains").
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Inconsistencies
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---------------
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There is no guarantee that the merging of multiple previous-events-lists produces a consistent chain of events.
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Eventual inconsistencies can be resolved by sorting events by time or event ID.
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(Multiple diverging chains can be merged by sorting events by time or event ID.)
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Such inconsistencies allow modification of the chain (insertion or deletion of previous events), so the chain is mutable.
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Visualization
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-------------
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Clients should visualize:
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- the reference to the first previous event
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- missing previous events
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If there are many missing previous events, these can be collapsed to a "N missing events" block.
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TODO: rename key
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----------------
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```json
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{
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...,
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"e_prev": [
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...
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]
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}
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```
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Rename the key to ...
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- previous_events
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- e_prev
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- prevs
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- history
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- soft_chain
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- chain
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Keywords
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--------
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- blockchain
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- censorship-resistance
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- tamper-proof
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- append-only
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