keepAlive not working with NIO

[mbarnach]

Context and Description

When building Kitura with NIO, the keepAlive option is causing a crash of the server.

Environment Details

Tried on MacOS 10.15.3, with Swift 5.1.3 using Kitura 2.9.1.

Steps to Reproduce

1. Create a Kitura server with NIO disabling the keepAlive option:

Kitura.addHTTPServer(onPort: 8080, with: router, keepAlive: .disabled)

2. Every attempt to connect to the server will lead to a crash on KeepAliveState.swift line 40

This issue can also be reproduced by setting the keepAlive to .limited(maxRequests: X) and trying to connect X+1 time to the server.

It worth noting that this issue doesn't affect the non NIO version of Kitura.

Expected vs. Actual Behaviour

• Not crashing and leaving the connection alive if possible.
• Crash!