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src/main.zig

@@ -99,12 +99,15 @@ pub fn main(init: std.process.Init) !void {
     // std.debug.print("Interface: {s}\n", .{(try net_interface.name(init.io)).toSlice()});
     const EthIpUdp = packed struct(u336) { // 42 bytes * 8 bits = 336
         // --- UDP (Last in memory, defined first for LSB->MSB) ---
+        udp: packed struct {
             checksum: u16 = 0,
-        udp_len: u16,
+            len: u16,
             dst_port: u16,
             src_port: u16,
+        },
 
         // --- IP ---
+        ip: packed struct {
             dst_addr: u32,
             src_addr: u32,
             header_checksum: u16 = 0,
@@ -122,13 +125,14 @@ pub fn main(init: std.process.Init) !void {
             } = .{},
 
             id: u16,
-        total_length: u16,
+            len: u16,
             tos: u8 = undefined,
 
             // ip_version (4 bits) + ihl (4 bits) = 8 bits
             // To have version appear first (high nibble), define it last.
             ihl: u4 = 5,
             ip_version: u4 = 4,
+        },
 
         // --- Ethernet ---
         eth_type: u16 = std.os.linux.ETH.P.IP,
@@ -141,18 +145,26 @@ pub fn main(init: std.process.Init) !void {
             w.writeStruct(self, .big) catch unreachable;
             return res;
         }
+
+        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)));
+        }
     };
 
-    const headers: EthIpUdp = .{
+    var headers: EthIpUdp = .{
         .src_mac = @splat(0x0e),
+        .ip = .{
             .id = 0,
             .src_addr = 0,
             .dst_addr = @bitCast([_]u8{ 255, 255, 255, 255 }),
+            .len = undefined,
+        },
+        .udp = .{
             .src_port = undefined, // TODO: change this?
             .dst_port = 8888,
-
+            .len = undefined,
-        .total_length = undefined,
+        },
-        .udp_len = undefined,
     };
     std.debug.print("headers: {any}\n", .{&headers.toBytes()});
 
@@ -163,8 +175,20 @@ pub fn main(init: std.process.Init) !void {
         },
     };
 
-    var relay_bytes: [2048]u8 = undefined;
+    var relay_buf: [2048]u8 = undefined;
-    std.debug.print("payload: {any}\n", .{relay.toBytes(&relay_bytes)});
+    const relay_bytes = relay.toBytes(&relay_buf);
+    std.debug.print("payload: {any}\n", .{relay_bytes});
+    headers.setPayloadLen(relay_bytes.len);
+
+    const full_msg = blk: {
+        var msg_buf: [2048]u8 = undefined;
+        var msg_w: Writer = .fixed(&msg_buf);
+        msg_w.writeAll(&headers.toBytes()) catch unreachable;
+        msg_w.writeAll(relay_bytes) catch unreachable;
+        break :blk msg_w.buffered();
+    };
+
+    std.debug.print("full message = {any}\n", .{full_msg});
 }
 
 fn parseDest(in: ?[]const u8) [4]u8 {