<!--
{
  "availability" : [
    "iOS: 12.0.0 -",
    "iPadOS: 12.0.0 -",
    "macCatalyst: 12.0.0 -",
    "macOS: 10.14.0 -",
    "tvOS: 12.0.0 -",
    "visionOS: 1.0.0 -",
    "watchOS: 5.0.0 -"
  ],
  "documentType" : "symbol",
  "framework" : "Network",
  "identifier" : "/documentation/Network/NWParameters/allowFastOpen",
  "metadataVersion" : "0.1.0",
  "role" : "Instance Property",
  "symbol" : {
    "kind" : "Instance Property",
    "modules" : [
      "Network"
    ],
    "preciseIdentifier" : "s:7Network12NWParametersC13allowFastOpenSbvp"
  },
  "title" : "allowFastOpen"
}
-->

# allowFastOpen

A Boolean that enables sending application data with protocol handshakes.

```
final var allowFastOpen: Bool { get set }
```

## Discussion

When fast open is enabled on a connection, the application is expected to send its early data to be included with the handshake as idempotent data. This data can be sent before or after calling start.

## See Also

[`case idempotent`](/documentation/Network/NWConnection/SendCompletion/idempotent)

Mark the sent data as idempotent—data that can be sent multiple times.


---

Copyright &copy; 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)