Truncate source and dest interface at the beginning

[ak-1]

Truncate source and dest interface at the beginning to make name clashes less likely.
This solves an issue where different vpn configurations result in the same device name.

[jamesmcm]

Thanks, it looks good!

It could even be worth calculating a checksum here if this is such an issue (like we do for custom VPN provider files), since it's no longer going to be easy to read or understand the substring anyway.

[alexmo1997]

This change is a bit problematic for me. In my firewall (nftables) configuration, I disallow forwards by default and used to allow accept vopono* interfaces, but that is now not possible anymore.

[ak-1]

Maybe we could define a two or three letter code for everything. That could be enough to not exceed the name length limit and still have some legibility and names that can still be useful for firewall rules and such

[jamesmcm]

Yeah, that seems like a good trade-off.

[ak-1]

So there are 15 ascii chars available for the interface names.
Here is one way to allocate those chars:

123456789012345
vo_PN_CNFNAME_D

• vo_ would be a fixed prefix for all interfaces created by vopono.
• PN would be a two character code for the provider.
• CNFNAME are seven chars available for the config/server name.
• D is s or d for source and destination of the veth pair.

For config names longer than seven chars we could still use a seven char checksum instead.