# SLAP Topic Manager

**Protocol Name**: SLAP (Service Lookup Availability Protocol)  
**Manager Name**: `SLAPTopicManager`  

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## Overview

The SLAP Topic Manager is responsible for identifying valid SLAP outputs in transactions. These outputs advertise the availability of a **lookup service** that can be accessed within an overlay network. By publishing a SLAP token, a node declares it is providing a specific service, prefixed `ls_`.

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## Purpose

- **Announce**: Declare that the identity key provides a certain lookup service, such as `ls_example` or other overlay lookups.
- **Availability**: Indicate that the node or service is currently active and can be queried via the provided URI.

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## Requirements for a Valid SLAP Output

Similar to SHIP, SLAP tokens must follow a specific 5-field structure in a [PushDrop](https://www.npmjs.com/package/@bsv/sdk#pushdrop) script:

1. `"SLAP"` — The literal string indicating SLAP protocol.
2. `identityKey` — The public key that claims ownership of this advertisement.
3. `advertisedURI` — A valid URI, aligning with what is contemplated in BRC-101.
4. `service` — The name of the service. Must:
   - Pass the BRC-87 checks.
   - Start with `ls_`.
5. `signature` — The ECDSA signature from `identityKey` covering the above 4 fields.

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## Signature and Locking Key

The final field is a signature that **must** link back to the identity key. The `SLAPTopicManager` uses the `isTokenSignatureCorrectlyLinked` code to confirm:

- The signature is valid for the data in the first four fields.
- The `lockingPublicKey` of the UTXO matches the derived key from the identity key used to sign.

If any step fails, the SLAP output is rejected.

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## Data Format and Validation

1. **Exact 5 PushDrop Fields**:
   - If fewer or more than 5 fields are found, the SLAP manager will skip the output.
2. **Valid `service`**:
   - Must begin with `ls_`.
   - Only letters (lowercase) and underscores are allowed, per `isValidTopicOrServiceName` (BRC-87).
3. **Advertised URI**:
   - Must not be `localhost`.
   - Must use a recognized scheme (`https://`, `wss://`, or specialized custom `https+bsvauth...` forms).
4. **Signature**:
   - Must be in DER format.
   - Must match the identity key.

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## Further Reading

- **SLAPLookupService**: For how to query these records afterward.
- **SHIP**: The complementary protocol for advertising "host-based" topics (`tm_`).