# convertIPv4MappedIPv6ToIPv4

**Kind:** Function

**Source:** [`src/utils/ipaddr.ts`](https://github.com/honojs/hono/blob/main/src/utils/ipaddr.ts#L320)

**Part of:** [Utils](subsystem-src-utils)

Extract the IPv4 portion from an IPv4-mapped IPv6 address

`convertIPv4MappedIPv6ToIPv4` extracts the IPv4 address portion from an IPv4-mapped IPv6 address. It is intended for address-handling paths where network inputs may represent IPv4 clients in IPv6 notation.

## Signature

```ts
function convertIPv4MappedIPv6ToIPv4(ipv6binary: bigint): bigint
```

## Parameters

| Name | Type |
|---|---|
| `ipv6binary` | `bigint` |

**Returns:** `bigint`

## Diagram

```mermaid
graph LR
  A[Network address input] --> B[convertIPv4MappedIPv6ToIPv4]
  B --> C[IPv4 address portion]
```

## Usage

```ts
import { convertIPv4MappedIPv6ToIPv4 } from './utils/ipaddr';

const remoteAddress = request.socket.remoteAddress;

if (remoteAddress) {
  const clientAddress = convertIPv4MappedIPv6ToIPv4(remoteAddress);

  console.log(clientAddress);
}
```

## AI Coding Instructions

- Call this function when processing network addresses from sockets, proxies, or request metadata.
- Pass the raw address string into the function before comparing it with IPv4 allowlists or blocklists.
- Do not treat this function as a general IPv6 parser or formatter.
- Add tests for IPv4-mapped IPv6 inputs and address inputs that are not IPv4-mapped.

## Used by

1 reference from 1 file. Each is a place in this repository where the symbol is actually used — go read one rather than trusting an example.

### Imported by (1)

- `IPRestrictionRule` — `src/middleware/ip-restriction/index.ts`:38