Detect interface and use real mac

src/main.zig

@@ -147,13 +147,16 @@ pub fn main(init: std.process.Init) !void {
         }
 
         fn setPayloadLen(self: *@This(), len: usize) void {
-            self.ip.len = @intCast(len + @sizeOf(@TypeOf(self.udp)) + @sizeOf(@TypeOf(self.ip)));
-            self.udp.len = @intCast(len + @sizeOf(@TypeOf(self.udp)));
+            self.ip.len = @intCast(len + (@bitSizeOf(@TypeOf(self.udp)) / 8) + (@bitSizeOf(@TypeOf(self.ip)) / 8));
+            self.udp.len = @intCast(len + (@bitSizeOf(@TypeOf(self.udp)) / 8));
         }
     };
 
+    var socket: RawSocket = try .init();
+    defer socket.deinit();
+
     var headers: EthIpUdp = .{
-        .src_mac = undefined, // TODO: REAL MAC
+        .src_mac = socket.mac,
         .ip = .{
             .id = 0,
             .src_addr = rand.int(u32),
@@ -191,8 +194,6 @@ pub fn main(init: std.process.Init) !void {
 
         std.debug.print("full message = {any}\n", .{full_msg});
 
-        var socket: RawSocket = try .init("enp7s0");
-        defer socket.deinit();
         try socket.send(full_msg);
         return;
     }
@@ -229,8 +230,6 @@ pub fn main(init: std.process.Init) !void {
 
         std.debug.print("full message = {any}\n", .{full_msg});
 
-        var socket: RawSocket = try .init("enp7s0");
-        defer socket.deinit();
         try socket.send(full_msg);
         return;
     }
@@ -268,47 +267,90 @@ const SOCK = std.os.linux.SOCK;
 const RawSocket = struct {
     fd: i32,
     sockaddr_ll: std.posix.sockaddr.ll,
+    mac: [6]u8,
 
-    fn init(ifname: []const u8) !RawSocket {
-        const socket: i32 = @intCast(std.os.linux.socket(AF.PACKET, SOCK.RAW, 0));
+    const IFF_LOOPBACK = 0x8;
 
-        var ifr: std.posix.ifreq = std.mem.zeroInit(std.posix.ifreq, .{});
-        @memcpy(ifr.ifrn.name[0..ifname.len], ifname);
-        ifr.ifrn.name[ifname.len] = 0;
-        try std.posix.ioctl_SIOCGIFINDEX(socket, &ifr);
+    const ifconf = extern struct {
+        ifc_len: i32,
+        ifc_ifcu: extern union {
+            ifcu_buf: ?[*]u8,
+            ifcu_req: ?[*]std.os.linux.ifreq,
+        },
+    };
+
+    fn init() !RawSocket {
+        const socket: i32 = @intCast(std.os.linux.socket(std.posix.AF.PACKET, std.posix.SOCK.RAW, 0));
+        if (socket < 0) return error.SocketError;
+
+        // 1. Enumerate interfaces
+        var ifreq_storage: [16]std.os.linux.ifreq = undefined;
+        var ifc = ifconf{
+            .ifc_len = @sizeOf(@TypeOf(ifreq_storage)),
+            .ifc_ifcu = .{ .ifcu_req = &ifreq_storage },
+        };
+
+        if (std.os.linux.ioctl(socket, std.os.linux.SIOCGIFCONF, @intFromPtr(&ifc)) != 0) {
+            return error.NicError;
+        }
+
+        const count = @divExact(ifc.ifc_len, @sizeOf(std.os.linux.ifreq));
+        var target_ifr: ?std.os.linux.ifreq = null;
+
+        for (ifreq_storage[0..@intCast(count)]) |ifr| {
+            var temp_ifr = ifr;
+            if (std.os.linux.ioctl(socket, std.os.linux.SIOCGIFFLAGS, @intFromPtr(&temp_ifr)) == 0) {
+                // Cast the packed flags to u16 to match the kernel's ifr_flags size
+                const flags: u16 = @bitCast(temp_ifr.ifru.flags);
+                if (flags & IFF_LOOPBACK != 0) continue;
+
+                target_ifr = ifr;
+                break;
+            }
+        }
+
+        var ifr = target_ifr orelse return error.NoInterfaceFound;
+
+        // 2. Get Interface Index
+        if (std.os.linux.ioctl(socket, std.os.linux.SIOCGIFINDEX, @intFromPtr(&ifr)) != 0) {
+            return error.NicError;
+        }
         const ifindex: i32 = ifr.ifru.ivalue;
 
-        var rval = std.posix.errno(std.os.linux.ioctl(socket, std.os.linux.SIOCGIFFLAGS, @intFromPtr(&ifr)));
-        switch (rval) {
-            .SUCCESS => {},
-            else => {
+        // 3. Get Real MAC Address
+        if (std.os.linux.ioctl(socket, std.os.linux.SIOCGIFHWADDR, @intFromPtr(&ifr)) != 0) {
+            return error.NicError;
+        }
+        var mac: [6]u8 = ifr.ifru.hwaddr.data[0..6].*;
+        std.mem.reverse(u8, &mac);
+
+        // 4. Set Flags (Promiscuous/Broadcast)
+        if (std.os.linux.ioctl(socket, std.os.linux.SIOCGIFFLAGS, @intFromPtr(&ifr)) != 0) {
             return error.NicError;
-            },
         }
         ifr.ifru.flags.BROADCAST = true;
         ifr.ifru.flags.PROMISC = true;
-        rval = std.posix.errno(std.os.linux.ioctl(socket, std.os.linux.SIOCSIFFLAGS, @intFromPtr(&ifr)));
-        switch (rval) {
-            .SUCCESS => {},
-            else => {
+        if (std.os.linux.ioctl(socket, std.os.linux.SIOCSIFFLAGS, @intFromPtr(&ifr)) != 0) {
             return error.NicError;
-            },
         }
-        std.debug.print("ifindex: {}\n", .{ifindex});
+
         const sockaddr_ll = std.posix.sockaddr.ll{
             .family = std.posix.AF.PACKET,
             .ifindex = ifindex,
             .protocol = std.mem.nativeToBig(u16, @as(u16, std.os.linux.ETH.P.IP)),
-            .halen = 0, //not used
-            .addr = .{ 0, 0, 0, 0, 0, 0, 0, 0 }, //not used
-            .pkttype = 0, //not used
-            .hatype = 0, //not used
+            .halen = 0,
+            .addr = .{ 0, 0, 0, 0, 0, 0, 0, 0 },
+            .pkttype = 0,
+            .hatype = 0,
         };
-        _ = std.os.linux.bind(socket, @ptrCast(&sockaddr_ll), @sizeOf(@TypeOf(sockaddr_ll)));
+
+        const bind_ret = std.os.linux.bind(socket, @ptrCast(&sockaddr_ll), @sizeOf(@TypeOf(sockaddr_ll)));
+        if (bind_ret != 0) return error.BindError;
 
         return .{
             .fd = socket,
             .sockaddr_ll = sockaddr_ll,
+            .mac = mac,
         };
     }
 
@@ -333,7 +375,7 @@ const RawSocket = struct {
             self.fd,
             buf.ptr,
             buf.len,
-            0, // flags
+            0,
             null,
             null,
         );