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standards/core/sync.md
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@ -30,8 +30,17 @@ The protocol finds differences between 2 peers by
comparing _fingerprints_ of _ranges_ of message _IDs_.
_Ranges_ are encoded into payloads, exchanged between the peers and when the range _fingerprints_ are different, splitted into smaller ones.
This process repeats until _ranges_ include a small number of messages
at this point _IDs_ are sent instead of _fingerprints_.
When received, _IDs_ are individually compared for differences.
at this point _IDs_ are sent for comparison instead of _fingerprints_.
#### Overview
1. The requestor choose a time range to sync.
2. The range is encoded into a payload and sent.
3. The requestee receive the payload and decode it.
4. The range is processed and more ranges produced.
5. The new ranges are encoded and sent.
6. Payloads are repeatedly exchanged and differences between the peers are discovered.
7. The synchronization is done when no ranges are left to process.
#### Message Ids
Message _IDs_ MUST be composed of the timestamp and the hash of the [`14/WAKU2-MESSAGE`](https://rfc.vac.dev/waku/standards/core/14/message).
@ -60,17 +69,19 @@ Every _range_ MUST have one of the following types; _fingerprint_, _skip_ or _it
- _Fingerprint_ type contains a _fingerprint_.
- _Skip_ type contains nothing and is used to signal already processed _ranges_.
- _Item set_ type contains message _Ids_ and a _resolved_ boolean.
> _Item sets_ are an optimization, stopping the recursion early can
save network roundtrips.
> _Item sets_ are an optimization, sending multiple _IDs_ instead of
recursing further reduce the number of round-trips.
#### Range Processing
_Ranges_ have to be processed differently according to their types and sent back.
_Ranges_ have to be processed differently according to their types.
- _Skip_ ranges MUST be merged with other consecutive _skip ranges_.
- **Equal** _fingerprint ranges_ MUST become _skip ranges_.
- **Unequal** _fingerprint ranges_ MUST be splitted into smaller ranges. The new type MAY be either _fingerprint_ or _item set_.
- **Unresolved** _item set_ ranges MUST be checked for differences and marked resolved.
- **Resolved** _item set_ ranges MUST be checked for differences and become skip ranges.
- _Skip_ ranges MUST be merged with other consecutive _skip ranges_.
In the case where only skip ranges remains, the synchronization is done.
### Delta Encoding
Payloads MUST be delta encoded as follows for efficient transmission of _IDs_ and _ranges_.