chore: exclude devices that don't support ARP

[weskoerber]

Closes #9 closes #12

TODOs:

• [ ] Implement for Windows
  • Windows has IfType in the IP_ADAPTER_ADDRESSES_LH structure; one of these values might indicate a layer 3+ device.

[weskoerber]

Windows has IfType in the IP_ADAPTER_ADDRESSES_LH structure; one of these values might indicate a layer 3+ device

The full IfType specification can be found in ipifcons.h (permalink).

The IfType value of my Tailscale device on my Windows 11 machine reports a value of 53:

#define IF_TYPE_PROP_VIRTUAL            53  // Proprietary virtual/internal

[weskoerber]

It seems that we'll have to get the ARP table and iterate each entry in the table, comparing it against the interface. Rough steps to make this work:

• GetAdaptersAddresses to get a list of adapters
• GetIpNetTable to get the ARP table
  • Iterate each row in table
  • If dwPhysAddrLen field in the table entry is 0, it means the interface identified by dwIndex is not attached to a physical address; filter it out

In one (confusing) sentence: Filter addresses returned from GetAdaptersAddresses having IfIndex that matches dwIndex in table returned from GetIpNetTable.

• https://learn.microsoft.com/en-us/windows/win32/api/iphlpapi/nf-iphlpapi-getipnettable
• https://learn.microsoft.com/en-us/windows/win32/api/ipmib/ns-ipmib-mib_ipnettable
• https://learn.microsoft.com/en-us/windows/win32/api/ipmib/ns-ipmib-mib_ipnetrow_lh