NIP-34 ====== Algorithmic Filter ------------------ `draft` `optional` `author:arthurfranca` According to [NIP-01](01.md), filters with `limit` attribute are replied with events sorted in **descending** order by the `created_at` event field (newest events first). For filters containing `limit` attribute, this NIP-34 adds `nip34` as a new filter attribute whose value indicates the algorithm the `client` wishes to use for sorting events. For instance, if a `client` sends the message `["REQ", , { kinds: [1], ..., limit: 5, nip34: 'a' }]`, it is asking the `relay` to sort five kind 1 events in **descending** order by the `nip34a` event field instead of by `created_at`. In the above example, `relays` that want to support the NIP-34a algorithm must add the `nip34a` event field to each event saved to their internal databases. The new field is populated following rules described at the NIP-34a NIP extension. Besides that, upon replying to such requests, the supporting `relay` MUST add `nip34: { score: '' }` field to each returned event JSON. It is a backward-compatible proposal because non-supporting `relays` ignore the `nip34` filter attribute and sort by `created_at`, as usual. `Relays` should advertise support using both [NIP-11](11.md) `supported_nips` and `supported_nip_extensions` fields. `Relays` should limit max daily user events, such as likes, reposts, zaps and comments, per IP to avoid bad actors gaming the algorithms. ## Motivation Different algorithms are required to support diverse apps' event sorting needs. However, they should be presented as optional and backward-compatible features that respect dumb `relays`/smart `clients` nostr philosophy so that any `relay` can easily adopt it. This NIP also takes into account the `relay` database software diversity, as explained ahead, so to not rule out as many `relays` as possible. Considering the request example above, we expect most `relays` to simply swap the `created_at` field on a regular query for the `nip34a` one. If a `relay` implementation uses a SQL DB, the above filter would turn this: `SELECT * FROM events WHERE kind in (1) ORDER BY created_at DESC LIMIT 5` Into this: `SELECT * FROM events WHERE kind in (1) ORDER BY nip34a DESC LIMIT 5` ## How Clients Make Custom Requests for a Specific User The algorithms are generic, meaning the "score" represented by the new event field does not differ for different users. However, smart `clients` may keep track of pubkeys from whom the user is consuming content, also hashtags, for instance, and use such pubkeys/hashtags as a way to tailor the query to that specific user. For example: `["REQ", , { kinds: [1], limit: 5, nip34: 'b', authors: ["pubkey1 user follows", "pubkey2 user has read content from recently", "pubkey3 that user has liked content recently"] }, { kinds: [1], limit: 5, nip34: 'b', '#t': ['cat', 'bitcoin'] }]` ## Rules for Submitting a NIP-34 Algorithm Each algorithm section describes **how** and **when** to compute the corresponding database field for each event. For example, [NIP-34asc](34asc.md) extension teaches `relays` the math used to update the `nip34asc` event field. The NIP extension MUST have atleast one example in any programming language, preferably with inline comments. All algorithms' field values MUST be **unique strings** for each event. This is needed to support the most rudimentary databases that `relays` may be using such as file DBs. The event id may be appended to the string to make it unique, similar to NIP-34asc solution. Bugfixes and small updates to embrace new event kinds may be submitted at any time by the algorithm author(s). ## Available Algorithms | Extension | Name | Description | Modification Date | | ------------------- | ----------| -------------------------------------------------- | ----------------- | | [34asc](34asc.md) | Ascending | Events with older `created_at` are retrieved first | 27 / jun / 2023 | | [34seen](34seen.md) | Seen At | Events are desc sorted by first seen at timestamp | 27 / jun / 2023 |