# asLegacyPieceCID

> **asLegacyPieceCID**(`pieceCidInput`): `LegacyPieceLink` \| `null`

Defined in: [packages/synapse-core/src/piece.ts:149](https://github.com/FilOzone/synapse-sdk/blob/32f86959b0bf15557657ea412e31a0897440ca98/packages/synapse-core/src/piece.ts#L149)

Convert a LegacyPieceCID input (string or CID) to a validated CID
This function can be used to parse a LegacyPieceCID (CommPv1) or to downgrade a PieceCID
(CommPv2) to a LegacyPieceCID.

## Parameters

| Parameter | Type | Description |
| ------ | ------ | ------ |
| `pieceCidInput` | `string` \| `PieceLink` \| `LegacyPieceLink` \| `CID`\<`unknown`, `number`, `number`, `Version`\> \| `null` \| `undefined` | LegacyPieceCID as either a CID object or string |

## Returns

`LegacyPieceLink` \| `null`

The validated LegacyPieceCID CID or null if not a valid LegacyPieceCID