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When looking through customer logs, we see a lot of "Resolved best route outside of tunnel" messages. Those get logged every time we need to rerun our re-implementation of Windows' weighting algorithm as to which source interface / IP a packet should be sent from. Currently, this gets cached in every socket instance so for the peer-to-peer socket, this is only computed once per destination IP. However, for DNS queries, we make a new socket for every query. Using a new source port DNS queries is recommended to avoid fingerprinting of DNS queries. Using a new socket also means that we need to re-run this algorithm every time we make a DNS query which is why we see this log so often. To fix this, we need to share this cache across all UDP sockets. Cache invalidation is one of the hardest problems in computer science and this instance is no different. This cache needs to be reset every time we roam as that changes the weighting of which source interface to use. To achieve this, we extend the `SocketFactory` trait with a `reset` method. This method is called whenever we roam and can then reset a shared cache inside the `UdpSocketFactory`. The "source IP resolver" function that is passed to the UDP socket now simply accesses this shared cache and inserts a new entry when it needs to resolve the IP. As an added benefit, this may speed up DNS queries on Windows a bit (although I haven't benchmarked it). It should certainly drastically reduce the amount of syscalls we make on Windows.
Connlib
Firezone's connectivity library shared by all clients.
Building Connlib
You shouldn't need to build connlib directly; it's typically built as a dependency of one of the other Firezone components. See READMEs in those directories for relevant instructions.