# SLAP Lookup Service

**Protocol Name**: SLAP (Service Lookup Availability Protocol)  
**Lookup Service Name**: `SLAPLookupService`

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## Overview

The SLAP Lookup Service is an overlay component that answers queries about SLAP advertisements. A SLAP advertisement states that an identity key offers a service (prefixed `ls_`) at a given URI. By querying this service, you can find all known SLAP records that match your criteria.

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## Purpose

- **Discovery**: Find all services that have been advertised with the `SLAP` protocol.
- **Filtering**: Narrow results by domain or by the `ls_` service name.

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## How to Query the SLAP Lookup Service

You will typically provide a [LookupQuestion](https://www.npmjs.com/package/@bsv/overlay#lookupservice) object to the `lookup` method with:
- `question.service = 'ls_slap'`
- `question.query` describing the domain and/or service name you want.

### `question.query` Options

1. **`"findAll"`** (string literal): Returns every SLAP record in the database.
2. **`SLAPQuery` object**:
   ```ts
   interface SLAPQuery {
     domain?: string
     service?: string
   }
   ```
   - `domain`: Optional. If provided, only returns records whose `advertisedURI` matches this domain.
   - `service`: Optional. Must be a string starting with `ls_`.

### Example Usages

1. **Find all**:
   ```js
   const question = {
     service: 'ls_slap',
     query: 'findAll'
   }
   const answers = await overlayClient.lookup(question)
   ```

2. **Find by domain**:
   ```js
   const question = {
     service: 'ls_slap',
     query: { domain: 'https://mylookup.example' }
   }
   const answers = await overlayClient.lookup(question)
   ```

3. **Find by service (most common)**:
   ```js
   const question = {
     service: 'ls_slap',
     query: { service: 'ls_treasury' }
   }
   const answers = await overlayClient.lookup(question)
   ```

4. **Find by domain & service**:
   ```js
   const question = {
     service: 'ls_slap',
     query: {
       domain: 'https://mylookup.example',
       service: 'ls_treasury'
     }
   }
   const answers = await overlayClient.lookup(question)
   ```

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## Gotchas

- **Strict Matching**: Domain matching requires an exact string match. If you have a different protocol (https vs https+bsvauth vs https+bsvauth+smf), be sure to store/lookup accordingly.
- **Must Start with `ls_`**: The `service` field in the original SLAP advertisement must begin with `ls_`. If you query for something that doesn't match exactly, you may get zero results.

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## Further Reading

- **SLAPTopicManager**: Learn how SLAP outputs are detected and admitted.
- **BRC-101 Overlays**: The higher-level specification for modular overlay availability schemes.