Motivation:

I want to develop a mesh VPN. Since I love netty, I would love to use it for this project. Therefore I need a TUN-based Channel implementation.

Modifications:

- Added native methods to io.netty.channel.kqueue.BsdSocket and io.netty.channel.epoll.LinuxSocket, allowing the creation of TUN devices and setting/getting the network interface MTU on macOS and Linux.
- Implemented io.netty.channel.kqueue.KQueueTunChannel and io.netty.channel.epoll.EpollTunChannel, allowing the creation of TUN-based channels using epoll and kqueue.
- Defined and implemented io.netty.channel.socket.TunChannelConfig, allowing setting/getting the network interface MTU.
- Modified io.netty.channel.unix.Socket to avoid Socket#isIPv6(fd) call that is not supported on TUN sockets.
- Modified io.netty.channel.epoll.AbstractEpollChannel allowing to set AbstractEpollChannel#local in EpollTunChannel#doBind as io.netty.channel.kqueue.Native#epollCtlAdd must be called after TUN device has been bound.
- Renamed io.netty.channel.kqueue.AbstractKQueueDatagramChannel to io.netty.channel.kqueue.AbstractKQueueMessageChannel because KQueueTunChannel needs to implement this class but is not datagram related. As this rename may break the API, I re-added AbstractKQueueDatagramChannel for legacy reasons.
- Added io.netty.channel.socket.Tun4Packet and io.netty.channel.socket.Tun6Packet to help work with IPv4 and IPv6 packets.
- Added io.netty.example.tun.TunPingDevice example creating a TUN device that will reply to IPMC/IPv6-ICMP echo ping requests.
- Added io.netty.example.tun.TunEchoDevice example that echoes all received IP packets (e.g., suitable for performance tests).
- Added native dependencies to example/pom.xml (might require changes to your release workflow).
- Modified run-example.sh to activate platform-dependent native transport maven profile.

Result:

Support for TUN-based Channels on kqueue- and epoll-enabled platforms.

Co-authored-by: Kevin Röbert <dev@roebert.eu>

Co-authored-by: Kevin Röbert <dev@roebert.eu>

Co-authored-by: Kevin Röbert <dev@roebert.eu>

Co-authored-by: Kevin Röbert <dev@roebert.eu>

Co-authored-by: Kevin Röbert <dev@roebert.eu>

Co-authored-by: Kevin Röbert <dev@roebert.eu>

Co-authored-by: Kevin Röbert <dev@roebert.eu>

Co-authored-by: Kevin Röbert <dev@roebert.eu>

Co-authored-by: Kevin Röbert <dev@roebert.eu>

Co-authored-by: Kevin Röbert <dev@roebert.eu>

Co-authored-by: Kevin Röbert <dev@roebert.eu>