ifaddrs FFI

gistfile1.lua

ffi.cdef([[
struct ifaddrs {
   struct ifaddrs  *ifa_next;    /* Next item in list */
   char            *ifa_name;    /* Name of interface */
   unsigned int     ifa_flags;   /* Flags from SIOCGIFFLAGS */
   struct sockaddr *ifa_addr;    /* Address of interface */
   struct sockaddr *ifa_netmask; /* Netmask of interface */
   union {
       struct sockaddr *ifu_broadaddr;  /* Broadcast address of interface */
       struct sockaddr *ifu_dstaddr;    /* Point-to-point destination address */
   } ifa_ifu;
   void            *ifa_data;    /* Address-specific data */
};
// the union will be populated based on the following ifa_flags:
enum { 
    IFF_BROADCAST   = 0x2,  /* broadcast address valid      */
    IFF_POINTOPOINT = 0x10  /* interface is has p-p link    */
};

int getifaddrs(struct ifaddrs **ifap);
void freeifaddrs(struct ifaddrs *ifa);

]])

-- Returns a Lua array of interfaces retrieved via C.getifaddrs
-- The original ifaddrs linked list is stored in ret.ifaddrs and is freed upon GC of ret
local function getifaddrs()
    local ifaddrs_root = ffi.new("struct ifaddrs *[1]")
    local res = C.getifaddrs( ifaddrs_root )
    assert( res == 0, ffi.errno() )

    -- convert linked list to Lua array for convenience
    local tret = {}
    local iter = ifaddrs_root[0]
    while iter ~= nil do
        tret[#tret + 1] = iter
        iter = iter.ifa_next
    end

    -- free ifaddrs when tret is gc'd
    tret.ifaddrs = ifaddrs_root
    ffi.gc( ifaddrs_root, function(t) C.freeifaddrs(t[0]) end )
    return tret
end