---
title: NWProtocolWebSocket.CloseCode.Defined.mandatoryExtension
framework: network
role: symbol
role_heading: Case
path: network/nwprotocolwebsocket/closecode/defined/mandatoryextension
---

# NWProtocolWebSocket.CloseCode.Defined.mandatoryExtension

The WebSocket client expected the server to negotiate one or more extensions that were not negotiated.

## Declaration

```swift
case mandatoryExtension
```

## See Also

### Defined Close Codes

- [NWProtocolWebSocket.CloseCode.Defined.normalClosure](network/nwprotocolwebsocket/closecode/defined/normalclosure.md)
- [NWProtocolWebSocket.CloseCode.Defined.goingAway](network/nwprotocolwebsocket/closecode/defined/goingaway.md)
- [NWProtocolWebSocket.CloseCode.Defined.protocolError](network/nwprotocolwebsocket/closecode/defined/protocolerror.md)
- [NWProtocolWebSocket.CloseCode.Defined.unsupportedData](network/nwprotocolwebsocket/closecode/defined/unsupporteddata.md)
- [NWProtocolWebSocket.CloseCode.Defined.noStatusReceived](network/nwprotocolwebsocket/closecode/defined/nostatusreceived.md)
- [NWProtocolWebSocket.CloseCode.Defined.abnormalClosure](network/nwprotocolwebsocket/closecode/defined/abnormalclosure.md)
- [NWProtocolWebSocket.CloseCode.Defined.invalidFramePayloadData](network/nwprotocolwebsocket/closecode/defined/invalidframepayloaddata.md)
- [NWProtocolWebSocket.CloseCode.Defined.policyViolation](network/nwprotocolwebsocket/closecode/defined/policyviolation.md)
- [NWProtocolWebSocket.CloseCode.Defined.messageTooBig](network/nwprotocolwebsocket/closecode/defined/messagetoobig.md)
- [NWProtocolWebSocket.CloseCode.Defined.internalServerError](network/nwprotocolwebsocket/closecode/defined/internalservererror.md)
- [NWProtocolWebSocket.CloseCode.Defined.tlsHandshake](network/nwprotocolwebsocket/closecode/defined/tlshandshake.md)