LocalIP (macOS): detect default route

src/detection/localip/localip_linux.c

@@ -11,11 +11,14 @@
 
 #if defined(__FreeBSD__) || defined(__APPLE__)
 #include <net/if_dl.h>
+#include <net/route.h>
+#include <sys/socket.h>
 #else
 #include <netpacket/packet.h>
 #endif
 
-static bool getDefaultRoute(char iface[16 /*IF_NAMESIZE*/ + 1])
+#ifdef __linux__
+static bool getDefaultRoute(char iface[IF_NAMESIZE + 1])
 {
     FILE* FF_AUTO_CLOSE_FILE netRoute = fopen("/proc/net/route", "r");
     // skip first line
@@ -24,6 +27,7 @@ static bool getDefaultRoute(char iface[16 /*IF_NAMESIZE*/ + 1])
     funlockfile(netRoute);
     unsigned long long destination; //, gateway, flags, refCount, use, metric, mask, mtu,
 
+    static_assert(IF_NAMESIZE >= 16, "IF_NAMESIZE is too small");
     while (fscanf(netRoute, "%16s%llx%*[^\n]", iface, &destination) == 2)
     {
         if (destination == 0)
@@ -31,6 +35,96 @@ static bool getDefaultRoute(char iface[16 /*IF_NAMESIZE*/ + 1])
     }
     return false;
 }
+#elif defined(__FreeBSD__) || defined(__APPLE__)
+
+#define ROUNDUP2(a, n)       ((a) > 0 ? (1 + (((a) - 1U) | ((n) - 1))) : (n))
+
+#if defined(__APPLE__)
+# define ROUNDUP(a)           ROUNDUP2((a), sizeof(int))
+#elif defined(__NetBSD__)
+# define ROUNDUP(a)           ROUNDUP2((a), sizeof(uint64_t))
+#elif defined(__FreeBSD__)
+# define ROUNDUP(a)           ROUNDUP2((a), sizeof(int))
+#elif defined(__OpenBSD__)
+# define ROUNDUP(a)           ROUNDUP2((a), sizeof(int))
+#else
+# error unknown platform
+#endif
+
+static struct sockaddr *
+get_rt_address(struct rt_msghdr *rtm, int desired)
+{
+    struct sockaddr *sa = (struct sockaddr *)(rtm + 1);
+
+    for (int i = 0; i < RTAX_MAX; i++)
+    {
+        if (rtm->rtm_addrs & (1 << i))
+        {
+            if ((1 <<i ) == desired)
+                return sa;
+            sa = (struct sockaddr *)(ROUNDUP(sa->sa_len) + (char *)sa);
+        }
+    }
+    return NULL;
+}
+
+static bool getDefaultRoute(char iface[IF_NAMESIZE + 1])
+{
+    //https://github.com/hashPirate/copenheimer-masscan-fork/blob/36f1ed9f7b751a7dccd5ed27874e2e703db7d481/src/rawsock-getif.c#L104
+
+    FF_AUTO_CLOSE_FD int pfRoute = socket(PF_ROUTE, SOCK_RAW, AF_INET);
+    if (pfRoute < 0)
+        return false;
+
+    {
+        struct timeval timeout = {1, 0};
+        setsockopt(pfRoute, SOL_SOCKET, SO_RCVTIMEO, (char *)&timeout, sizeof(timeout));
+        setsockopt(pfRoute, SOL_SOCKET, SO_SNDTIMEO, (char *)&timeout, sizeof(timeout));
+    }
+
+    int pid = getpid();
+
+    struct {
+        struct rt_msghdr hdr;
+        struct sockaddr_in dst;
+        uint8_t data[512];
+    } rtmsg = {
+        .hdr = {
+            .rtm_type = RTM_GET,
+            .rtm_flags = RTF_UP | RTF_GATEWAY,
+            .rtm_version = RTM_VERSION,
+            .rtm_addrs = RTA_DST | RTA_IFP,
+            .rtm_msglen = sizeof(rtmsg.hdr) + sizeof(rtmsg.dst),
+            .rtm_pid = pid,
+            .rtm_seq = 1,
+        },
+        .dst = {
+            .sin_family = AF_INET,
+            .sin_len = sizeof(rtmsg.dst),
+        },
+    };
+
+    if (write(pfRoute, &rtmsg, rtmsg.hdr.rtm_msglen) != rtmsg.hdr.rtm_msglen)
+        return false;
+
+    while (read(pfRoute, &rtmsg, sizeof(rtmsg)) > 0)
+    {
+        if (rtmsg.hdr.rtm_seq == 1 && rtmsg.hdr.rtm_pid == pid)
+        {
+            struct sockaddr_dl* sdl = (struct sockaddr_dl *)get_rt_address(&rtmsg.hdr, RTA_IFP);
+            if (sdl)
+            {
+                assert(sdl->sdl_nlen <= IF_NAMESIZE);
+                memcpy(iface, sdl->sdl_data, sdl->sdl_nlen);
+                iface[sdl->sdl_nlen] = 0;
+                return true;
+            }
+            return false;
+        }
+    }
+    return false;
+}
+#endif
 
 static void addNewIp(FFlist* list, const char* name, const char* addr, int type)
 {