# findPieceIdsByCid

> **findPieceIdsByCid**(`client`, `options`): [`Promise`](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Promise)\<[`OutputType`](/reference/filoz/synapse-core/pdp-verifier/namespaces/findpieceidsbycid/type-aliases/outputtype/)\>

Defined in: [packages/synapse-core/src/pdp-verifier/find-piece-ids-by-cid.ts:89](https://github.com/FilOzone/synapse-sdk/blob/aaa98045b003ec23f4318ba9a3032a434e5a20c9/packages/synapse-core/src/pdp-verifier/find-piece-ids-by-cid.ts#L89)

Find one bounded page of piece IDs matching a PieceCID in a data set.

Uses the on-chain `findPieceIdsByCid` function for efficient CID-to-ID
lookup. Pass `nextCursor` back unchanged; use [paginate](/reference/filoz/synapse-core/core/functions/paginate/) to collect
every match. The default page size is one match.

## Parameters

| Parameter | Type | Description |
| ------ | ------ | ------ |
| `client` | `Client`\<`Transport`, `Chain`\> | The client to use to find piece IDs. |
| `options` | [`OptionsType`](/reference/filoz/synapse-core/pdp-verifier/namespaces/findpieceidsbycid/type-aliases/optionstype/) | [findPieceIdsByCid.OptionsType](/reference/filoz/synapse-core/pdp-verifier/namespaces/findpieceidsbycid/type-aliases/optionstype/) |

## Returns

[`Promise`](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Promise)\<[`OutputType`](/reference/filoz/synapse-core/pdp-verifier/namespaces/findpieceidsbycid/type-aliases/outputtype/)\>

A page of piece IDs matching the CID [findPieceIdsByCid.OutputType](/reference/filoz/synapse-core/pdp-verifier/namespaces/findpieceidsbycid/type-aliases/outputtype/)

## Examples

**Read the first page**

```ts
import { findPieceIdsByCid } from '@filoz/synapse-core/pdp-verifier'
import { calibration } from '@filoz/synapse-core/chains'
import { createPublicClient, http } from 'viem'
import * as Piece from '@filoz/synapse-core/piece'

const client = createPublicClient({
  chain: calibration,
  transport: http(),
})

const pieceCid = Piece.from('bafkzcibcd4bdomn3tgwgrh3g532zopskstnbrd2n3sxfqbze7rxt7vqn7veigmy')
const page = await findPieceIdsByCid(client, { dataSetId: 1n, pieceCid })
console.log(page.items, page.nextCursor)
```

**Iterate over every page**

```ts
import { paginate } from '@filoz/synapse-core'
import { findPieceIdsByCid } from '@filoz/synapse-core/pdp-verifier'

for await (const pieceId of paginate(({ cursor }) =>
  findPieceIdsByCid(client, { dataSetId: 1n, pieceCid, cursor })
)) {
  console.log(pieceId)
}
```

## Throws

Errors [findPieceIdsByCid.ErrorType](/reference/filoz/synapse-core/pdp-verifier/namespaces/findpieceidsbycid/type-aliases/errortype/)