[FR] Support NIP-09 Event Deletion

[UTXOnly]

Background

NIP-09 Allows clients to send a kind 5 event to delete events from storage within the relay.

Example kind 5 event:

{
  "kind": 5,
  "pubkey": <32-bytes hex-encoded public key of the event creator>,
  "tags": [
    ["e", "dcd59..464a2"],
    ["e", "968c5..ad7a4"],
    ["a", "<kind>:<pubkey>:<d-identifier>"]
  ],
  "content": "these posts were published by accident",
  ...other fields
}

User Story

As any user I want to send a kind 5 event to a relay and have that event deleted from the relay's database. The relay should also store the kind 5 event for future reference

Considerations

Although the spec only indicated that the pubkey from the kind 5 event should match the pubkey for the events to be deleted, I would like to actually verify the validity of the event using a method like below:

• Was previously implemented in Nostpy for all events added link

async def verify_signature(event_id: str, pubkey: str, sig: str) -> bool:
    try:
        pub_key: secp256k1.PublicKey = secp256k1.PublicKey(bytes.fromhex("02" + pubkey), True)
        result: bool = pub_key.schnorr_verify(bytes.fromhex(event_id), bytes.fromhex(sig), None, raw=True)
        if result:
            logger.info(f"Verification successful for event: {event_id}")
        else:
            logger.error(f"Verification failed for event: {event_id}")
        return result
    except (ValueError, TypeError, secp256k1.Error) as e:
        logger.error(f"Error verifying signature for event {event_id}: {e}")
        return False

TO DO

• Update event_handler service dependencies to include secp256k1
• Update handle_new_event to check for kind 5
• Update Event class to include method/s that:
  • Validates kind 5 event
  • Constructs DELETE statement
  • Executes DELETE statement
  • Replies to client with OK message indicating if the request was successful:
    • Ex ["OK", "b1a649ebe8...", true, ""]