Bad attempt at using @fieldParentPtr

https://kagi.com/assistant/a8f0a9ac-a11a-472e-af38-98d7e877e293

build.zig

@@ -33,6 +33,7 @@ pub fn build(b: *std.Build) void {
     });
 
     lib_mod.addImport("network", b.dependency("network", .{}).module("network"));
+    lib_mod.addImport("gatorcat", b.dependency("gatorcat", .{}).module("gatorcat"));
 
     exe_mod.addImport("zaprus", lib_mod);
     exe_mod.addImport("clap", b.dependency("clap", .{}).module("clap"));

build.zig.zon

@@ -44,6 +44,10 @@
             .url = "git+https://github.com/Hejsil/zig-clap?ref=0.10.0#e47028deaefc2fb396d3d9e9f7bd776ae0b2a43a",
             .hash = "clap-0.10.0-oBajB434AQBDh-Ei3YtoKIRxZacVPF1iSwp3IX_ZB8f0",
         },
+        .gatorcat = .{
+            .url = "git+https://github.com/kj4tmp/gatorcat#bb1847f6c95852e7a0ec8c07870a948c171d5f98",
+            .hash = "gatorcat-0.3.2-WcrpTf1mBwDrmPaIhKCfLJO064v8Sjjn7DBq4CKZSgHH",
+        },
     },
     .paths = .{
         "build.zig",

src/Client.zig

@@ -76,7 +76,10 @@ pub fn sendInitialConnection(payload: []const u8, initial_port: u16, allocator:
     return msg;
 }
 
-pub fn connect(payload: []const u8, allocator: Allocator) !?SaprusMessage {
+pub fn connect(payload: []const u8, allocator: Allocator) !?SaprusConnection {
+    var foo: gcat.nic.RawSocket = try .init("enp7s0"); // /proc/net/dev
+    defer foo.deinit();
+
     var initial_port: u16 = 0;
     if (rand) |r| {
         initial_port = r.intRangeAtMost(u16, 1024, 65000);
@@ -109,10 +112,14 @@ pub fn connect(payload: []const u8, allocator: Allocator) !?SaprusMessage {
     // Complete handshake after awaiting response
     try broadcastSaprusMessage(msg, randomPort(), allocator);
 
-    return initial_conn_res;
+    if (false) {
+        return initial_conn_res.?;
+    }
+    return null;
 }
 
 const SaprusMessage = @import("message.zig").Message;
+const SaprusConnection = @import("Connection.zig");
 
 const std = @import("std");
 const Random = std.Random;
@@ -120,5 +127,6 @@ const posix = std.posix;
 const mem = std.mem;
 
 const network = @import("network");
+const gcat = @import("gatorcat");
 
 const Allocator = mem.Allocator;

src/main.zig

@@ -50,7 +50,7 @@ pub fn main() !void {
     }
 
     if (res.args.relay) |r| {
-        const dest = parseDest(res.args.dest) catch .{ 70, 70, 70, 70 };
+        const dest = parseDest(res.args.dest);
         try SaprusClient.sendRelay(
             if (r.len > 0) r else "Hello darkness my old friend",
             dest,
@@ -59,17 +59,10 @@ pub fn main() !void {
         // std.debug.print("Sent: {s}\n", .{r});
         return;
     } else if (res.args.connect) |c| {
-        const conn_res: ?SaprusMessage = SaprusClient.connect(if (c.len > 0) c else "Hello darkness my old friend", gpa) catch |err| switch (err) {
+        _ = SaprusClient.connect(if (c.len > 0) c else "Hello darkness my old friend", gpa) catch |err| switch (err) {
             error.WouldBlock => null,
             else => return err,
         };
-        defer if (conn_res) |r| r.deinit(gpa);
-        if (conn_res) |r| {
-            std.debug.print("{s}\n", .{r.connection.payload});
-        } else {
-            std.debug.print("No response from connection request\n", .{});
-        }
-        return;
     }
 
     return clap.help(std.io.getStdErr().writer(), clap.Help, &params, .{});
@@ -86,7 +79,7 @@ fn parseDest(in: ?[]const u8) [4]u8 {
         const addr = std.net.Ip4Address.parse(dest, 0) catch return "FAIL".*;
         return @bitCast(addr.sa.addr);
     }
-    return "zap".*;
+    return "zap\x00".*;
 }
 
 const builtin = @import("builtin");

src/message.zig

@@ -26,8 +26,207 @@ pub const ConnectionOptions = packed struct(u8) {
 pub const Error = error{
     NotImplementedSaprusType,
     UnknownSaprusType,
+    InvalidMessage,
 };
 
+// ZERO COPY STUFF
+// &payload could be a void value that is treated as a pointer to a [*]u8
+pub const ZeroCopyMessage = packed struct {
+    const Relay = packed struct {
+        dest: @Vector(4, u8),
+        payload: void,
+
+        pub fn getPayload(self: *align(@alignOf(ZeroCopyMessage)) Relay) []u8 {
+            // Cast the 'self' pointer (which points to the Relay header,
+            // located at the same memory as the parent's 'bytes' field)
+            // to a pointer to void, as required by @fieldParentPtr for a void field.
+            // Preserve the known alignment.
+            const self_as_void_ptr: *align(@alignOf(ZeroCopyMessage)) void = @ptrCast(self);
+
+            // Cast the resulting *void pointer to the parent type *ZeroCopyMessage.
+            // This cast performs the necessary alignment check.
+            const parent: *ZeroCopyMessage = @alignCast(@fieldParentPtr("bytes", self_as_void_ptr));
+
+            // The 'length' field in the parent ZeroCopyMessage contains
+            // the size of the header (Relay) + payload length.
+            const total_len = parent.length;
+
+            // Payload length = total_len - size of the Relay header
+            const payload_len = total_len - @sizeOf(Relay);
+
+            // The payload starts immediately after the fixed fields of the Relay struct.
+            // The address of the 'payload' field represents this starting point.
+            const payload_start_ptr: [*]u8 = @ptrCast(&self.payload);
+
+            // Return a slice from the payload start address with the calculated length.
+            return payload_start_ptr[0..payload_len];
+        }
+    };
+    const Connection = packed struct {
+        src_port: u16, // random number > 1024
+        dest_port: u16, // random number > 1024
+        seq_num: u32 = 0,
+        msg_id: u32 = 0,
+        reserved: u8 = 0,
+        options: ConnectionOptions = .{},
+        payload: void,
+
+        pub fn getPayload(self: *align(1) Connection) []u8 {
+            const len: *u16 = @ptrFromInt(@intFromPtr(self) - @sizeOf(u16));
+            return @as([*]u8, @ptrCast(&self.payload))[0 .. len.* - @sizeOf(Connection)];
+        }
+
+        fn nativeFromNetworkEndian(self: *align(1) Connection) Error!void {
+            self.src_port = bigToNative(@TypeOf(self.src_port), self.src_port);
+            self.dest_port = bigToNative(@TypeOf(self.dest_port), self.dest_port);
+            self.seq_num = bigToNative(@TypeOf(self.seq_num), self.seq_num);
+            self.msg_id = bigToNative(@TypeOf(self.msg_id), self.msg_id);
+        }
+
+        fn networkFromNativeEndian(self: *align(1) Connection) Error!void {
+            self.src_port = nativeToBig(@TypeOf(self.src_port), self.src_port);
+            self.dest_port = nativeToBig(@TypeOf(self.dest_port), self.dest_port);
+            self.seq_num = nativeToBig(@TypeOf(self.seq_num), self.seq_num);
+            self.msg_id = nativeToBig(@TypeOf(self.msg_id), self.msg_id);
+        }
+    };
+
+    const Self = @This();
+
+    type: PacketType,
+    length: u16,
+    bytes: void = {},
+
+    pub fn init(allocator: Allocator, comptime @"type": PacketType, payload_len: u16) !*Self {
+        const header_size = @sizeOf(switch (@"type") {
+            .relay => Relay,
+            .connection => Connection,
+            else => return error.Bad,
+        });
+        const size = payload_len + @sizeOf(Self) + header_size;
+        const bytes = try allocator.alignedAlloc(u8, @alignOf(Self), size);
+        const res: *Self = @ptrCast(bytes.ptr);
+        res.type = @"type";
+        res.length = payload_len + header_size;
+        return res;
+    }
+
+    pub fn deinit(self: *Self, allocator: Allocator) void {
+        allocator.free(self.asBytes());
+    }
+
+    fn getRelay(self: *Self) *align(@alignOf(Self)) Relay {
+        return std.mem.bytesAsValue(Relay, &self.bytes);
+    }
+    fn getConnection(self: *Self) *align(@alignOf(Self)) Connection {
+        return std.mem.bytesAsValue(Connection, &self.bytes);
+    }
+
+    pub fn getSaprusTypePayload(self: *Self) Error!(union(PacketType) {
+        relay: *align(@alignOf(Self)) Relay,
+        file_transfer: void,
+        connection: *align(@alignOf(Self)) Connection,
+    }) {
+        return switch (self.type) {
+            .relay => .{ .relay = self.getRelay() },
+            .connection => .{ .connection = self.getConnection() },
+            .file_transfer => Error.NotImplementedSaprusType,
+            else => Error.UnknownSaprusType,
+        };
+    }
+
+    pub fn nativeFromNetworkEndian(self: *Self) Error!void {
+        self.type = @enumFromInt(bigToNative(
+            @typeInfo(@TypeOf(self.type)).@"enum".tag_type,
+            @intFromEnum(self.type),
+        ));
+        self.length = bigToNative(@TypeOf(self.length), self.length);
+        switch (try self.getSaprusTypePayload()) {
+            .relay => {},
+            .connection => |*con| try con.*.nativeFromNetworkEndian(),
+            // We know other values are unreachable,
+            // because they would have returned an error from the switch condition.
+            else => unreachable,
+        }
+    }
+
+    pub fn networkFromNativeEndian(self: *Self) Error!void {
+        try switch (try self.getSaprusTypePayload()) {
+            .relay => {},
+            .connection => |*con| con.*.networkFromNativeEndian(),
+            .file_transfer => Error.NotImplementedSaprusType,
+            else => Error.UnknownSaprusType,
+        };
+        self.type = @enumFromInt(nativeToBig(
+            @typeInfo(@TypeOf(self.type)).@"enum".tag_type,
+            @intFromEnum(self.type),
+        ));
+        self.length = nativeToBig(@TypeOf(self.length), self.length);
+    }
+
+    pub fn bytesAsValueUnchecked(bytes: []align(@alignOf(Self)) u8) *Self {
+        return std.mem.bytesAsValue(Self, bytes);
+    }
+
+    pub fn bytesAsValue(bytes: []align(@alignOf(Self)) u8) !*Self {
+        const res = bytesAsValueUnchecked(bytes);
+        return switch (res.type) {
+            .relay, .connection => if (bytes.len == res.length + @sizeOf(Self))
+                res
+            else
+                Error.InvalidMessage,
+            .file_transfer => Error.NotImplementedSaprusType,
+            else => Error.UnknownSaprusType,
+        };
+    }
+
+    pub fn asBytes(self: *Self) []align(@alignOf(Self)) u8 {
+        const size = @sizeOf(Self) + self.length;
+        return @as([*]align(@alignOf(Self)) u8, @ptrCast(self))[0..size];
+    }
+};
+
+test "testing variable length zero copy struct" {
+    const gpa = std.testing.allocator;
+    const payload = "Hello darkness my old friend";
+
+    // Create a view of the byte slice as a ZeroCopyMessage
+    const zcm: *ZeroCopyMessage = try .init(gpa, .relay, payload.len);
+    defer zcm.deinit(gpa);
+    std.debug.print("outer: {*}\n", .{zcm});
+
+    {
+        // Set the message values
+        {
+            // These are both set by the init call.
+            // zcm.type = .relay;
+            // zcm.length = payload_len;
+        }
+        const relay = (try zcm.getSaprusTypePayload()).relay;
+        relay.dest = .{ 1, 2, 3, 4 };
+        @memcpy(relay.getPayload(), payload);
+    }
+
+    {
+        const bytes = zcm.asBytes();
+
+        // Print the message as hex using the network byte order
+        try zcm.networkFromNativeEndian();
+        // We know the error from nativeFromNetworkEndian is unreachable because
+        // it would have returned an error from networkFromNativeEndian.
+        defer zcm.nativeFromNetworkEndian() catch unreachable;
+        std.debug.print("network bytes: {x}\n", .{bytes});
+        std.debug.print("bytes len: {d}\n", .{bytes.len});
+    }
+
+    if (false) {
+        // Illegal behavior
+        std.debug.print("{any}\n", .{(try zcm.getSaprusTypePayload()).connection});
+    }
+
+    try std.testing.expectEqualDeep(zcm, try ZeroCopyMessage.bytesAsValue(zcm.asBytes()));
+}
+
 /// All Saprus messages
 pub const Message = union(PacketType) {
     pub const Relay = struct {
@@ -170,6 +369,7 @@ const Allocator = std.mem.Allocator;
 
 const asBytes = std.mem.asBytes;
 const nativeToBig = std.mem.nativeToBig;
+const bigToNative = std.mem.bigToNative;
 
 test "Round trip Relay toBytes and fromBytes" {
     const gpa = std.testing.allocator;
@@ -209,3 +409,7 @@ test "Round trip Connection toBytes and fromBytes" {
 
     try std.testing.expectEqualDeep(msg, from_bytes);
 }
+
+test {
+    std.testing.refAllDeclsRecursive(@This());
+}

src/root.zig

@@ -1,2 +1,4 @@
 pub const Client = @import("Client.zig");
+pub const Connection = @import("Connection.zig");
+
 pub usingnamespace @import("message.zig");