Bad attempt at using @fieldParentPtr

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

src/Client.zig

@@ -1,6 +1,3 @@
-const base64Enc = std.base64.Base64Encoder.init(std.base64.standard_alphabet_chars, '=');
-const base64Dec = std.base64.Base64Decoder.init(std.base64.standard_alphabet_chars, '=');
-
 var rand: ?Random = null;
 
 pub fn init() !void {
@@ -17,14 +14,9 @@ pub fn deinit() void {
     network.deinit();
 }
 
-fn broadcastSaprusMessage(msg: *SaprusMessage, udp_port: u16) !void {
-    if (false) {
-        var foo: gcat.nic.RawSocket = try .init("enp7s0"); // /proc/net/dev
-        defer foo.deinit();
-    }
-    const msg_bytes = msg.asBytes();
-    try msg.networkFromNativeEndian();
-    defer msg.nativeFromNetworkEndian() catch unreachable;
+fn broadcastSaprusMessage(msg: SaprusMessage, udp_port: u16, allocator: Allocator) !void {
+    const msg_bytes = try msg.toBytes(allocator);
+    defer allocator.free(msg_bytes);
 
     var sock = try network.Socket.create(.ipv4, .udp);
     defer sock.close();
@@ -48,22 +40,14 @@ fn broadcastSaprusMessage(msg: *SaprusMessage, udp_port: u16) !void {
 }
 
 pub fn sendRelay(payload: []const u8, dest: [4]u8, allocator: Allocator) !void {
-    const msg_bytes = try allocator.alignedAlloc(
-        u8,
-        @alignOf(SaprusMessage),
-        try SaprusMessage.lengthForPayloadLength(
-            .relay,
-            base64Enc.calcSize(payload.len),
-        ),
-    );
-    defer allocator.free(msg_bytes);
-    const msg: *SaprusMessage = .init(.relay, msg_bytes);
+    const msg = SaprusMessage{
+        .relay = .{
+            .header = .{ .dest = dest },
+            .payload = payload,
+        },
+    };
 
-    const relay = (try msg.getSaprusTypePayload()).relay;
-    relay.dest = dest;
-    _ = base64Enc.encode(relay.getPayload(), payload);
-
-    try broadcastSaprusMessage(msg, 8888);
+    try broadcastSaprusMessage(msg, 8888, allocator);
 }
 
 fn randomPort() u16 {
@@ -75,36 +59,34 @@ fn randomPort() u16 {
     return p;
 }
 
-pub fn sendInitialConnection(payload: []const u8, initial_port: u16, allocator: Allocator) !*SaprusMessage {
+pub fn sendInitialConnection(payload: []const u8, initial_port: u16, allocator: Allocator) !SaprusMessage {
     const dest_port = randomPort();
-    const msg_bytes = try allocator.alignedAlloc(
-        u8,
-        @alignOf(SaprusMessage),
-        try SaprusMessage.lengthForPayloadLength(
-            .connection,
-            base64Enc.calcSize(payload.len),
-        ),
-    );
+    const msg = SaprusMessage{
+        .connection = .{
+            .header = .{
+                .src_port = initial_port,
+                .dest_port = dest_port,
+            },
+            .payload = payload,
+        },
+    };
 
-    const msg: *SaprusMessage = .init(.connection, msg_bytes);
-
-    const connection = (try msg.getSaprusTypePayload()).connection;
-    connection.src_port = initial_port;
-    connection.dest_port = dest_port;
-    _ = base64Enc.encode(connection.getPayload(), payload);
-
-    try broadcastSaprusMessage(msg, 8888);
+    try broadcastSaprusMessage(msg, 8888, allocator);
 
     return msg;
 }
 
 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);
     } else unreachable;
 
-    var initial_conn_res: ?*SaprusMessage = null;
+    var initial_conn_res: ?SaprusMessage = null;
+    errdefer if (initial_conn_res) |c| c.deinit(allocator);
 
     var sock = try network.Socket.create(.ipv4, .udp);
     defer sock.close();
@@ -120,17 +102,15 @@ pub fn connect(payload: []const u8, allocator: Allocator) !?SaprusConnection {
     try sock.bind(bind_addr);
 
     const msg = try sendInitialConnection(payload, initial_port, allocator);
-    defer allocator.free(msg.asBytes());
 
-    var response_buf: [4096]u8 align(@alignOf(SaprusMessage)) = undefined;
+    var response_buf: [4096]u8 = undefined;
     _ = try sock.receive(&response_buf); // Ignore message that I sent.
     const len = try sock.receive(&response_buf);
 
-    std.debug.print("response bytes: {x}\n", .{response_buf[0..len]});
-    initial_conn_res = SaprusMessage.init(.connection, response_buf[0..len]);
+    initial_conn_res = try SaprusMessage.fromBytes(response_buf[0..len], allocator);
 
     // Complete handshake after awaiting response
-    try broadcastSaprusMessage(msg, randomPort());
+    try broadcastSaprusMessage(msg, randomPort(), allocator);
 
     if (false) {
         return initial_conn_res.?;

src/main.zig

@@ -63,7 +63,6 @@ pub fn main() !void {
             error.WouldBlock => null,
             else => return err,
         };
-        return;
     }
 
     return clap.help(std.io.getStdErr().writer(), clap.Help, &params, .{});

src/message.zig

@@ -1,3 +1,6 @@
+const base64Enc = std.base64.Base64Encoder.init(std.base64.standard_alphabet_chars, '=');
+const base64Dec = std.base64.Base64Decoder.init(std.base64.standard_alphabet_chars, '=');
+
 /// Type tag for Message union.
 /// This is the first value in the actual packet sent over the network.
 pub const PacketType = enum(u16) {
@@ -20,25 +23,43 @@ pub const ConnectionOptions = packed struct(u8) {
     opt8: bool = false,
 };
 
-pub const MessageTypeError = error{
+pub const Error = error{
     NotImplementedSaprusType,
     UnknownSaprusType,
-};
-pub const MessageParseError = MessageTypeError || error{
     InvalidMessage,
 };
 
 // ZERO COPY STUFF
 // &payload could be a void value that is treated as a pointer to a [*]u8
-/// All Saprus messages
-pub const Message = packed struct {
+pub const ZeroCopyMessage = packed struct {
     const Relay = packed struct {
         dest: @Vector(4, u8),
         payload: void,
 
-        pub fn getPayload(self: *align(1) Relay) []u8 {
-            const len: *u16 = @ptrFromInt(@intFromPtr(self) - @sizeOf(u16));
-            return @as([*]u8, @ptrCast(&self.payload))[0 .. len.* - @sizeOf(Relay)];
+        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 {
@@ -55,14 +76,14 @@ pub const Message = packed struct {
             return @as([*]u8, @ptrCast(&self.payload))[0 .. len.* - @sizeOf(Connection)];
         }
 
-        fn nativeFromNetworkEndian(self: *align(1) Connection) void {
+        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) void {
+        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);
@@ -71,82 +92,70 @@ pub const Message = packed struct {
     };
 
     const Self = @This();
-    const SelfBytes = []align(@alignOf(Self)) u8;
 
     type: PacketType,
     length: u16,
     bytes: void = {},
 
-    /// Takes a byte slice, and returns a Message struct backed by the slice.
-    /// This properly initializes the top level headers within the slice.
-    pub fn init(@"type": PacketType, bytes: []align(@alignOf(Self)) u8) *Self {
-        std.debug.assert(bytes.len >= @sizeOf(Self));
-        const res: *Self = @ptrCast(bytes.ptr);
-        res.type = @"type";
-        res.length = @intCast(bytes.len - @sizeOf(Self));
-        return res;
-    }
-
-    pub fn lengthForPayloadLength(comptime @"type": PacketType, payload_len: usize) MessageTypeError!u16 {
-        std.debug.assert(payload_len < std.math.maxInt(u16));
+    pub fn init(allocator: Allocator, comptime @"type": PacketType, payload_len: u16) !*Self {
         const header_size = @sizeOf(switch (@"type") {
             .relay => Relay,
             .connection => Connection,
-            .file_transfer => return MessageTypeError.NotImplementedSaprusType,
-            else => return MessageTypeError.UnknownSaprusType,
+            else => return error.Bad,
         });
-        return @intCast(payload_len + @sizeOf(Self) + header_size);
+        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;
     }
 
-    fn getRelay(self: *Self) *align(1) Relay {
+    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(1) Connection {
+    fn getConnection(self: *Self) *align(@alignOf(Self)) Connection {
         return std.mem.bytesAsValue(Connection, &self.bytes);
     }
 
-    pub fn getSaprusTypePayload(self: *Self) MessageTypeError!(union(PacketType) {
-        relay: *align(1) Relay,
+    pub fn getSaprusTypePayload(self: *Self) Error!(union(PacketType) {
+        relay: *align(@alignOf(Self)) Relay,
         file_transfer: void,
-        connection: *align(1) Connection,
+        connection: *align(@alignOf(Self)) Connection,
     }) {
         return switch (self.type) {
             .relay => .{ .relay = self.getRelay() },
             .connection => .{ .connection = self.getConnection() },
-            .file_transfer => MessageTypeError.NotImplementedSaprusType,
-            else => MessageTypeError.UnknownSaprusType,
+            .file_transfer => Error.NotImplementedSaprusType,
+            else => Error.UnknownSaprusType,
         };
     }
 
-    pub fn nativeFromNetworkEndian(self: *Self) MessageTypeError!void {
+    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);
-        errdefer {
-            // If the payload specific headers fail, revert the top level header values
-            self.type = @enumFromInt(nativeToBig(
-                @typeInfo(@TypeOf(self.type)).@"enum".tag_type,
-                @intFromEnum(self.type),
-            ));
-            self.length = nativeToBig(@TypeOf(self.length), self.length);
-        }
         switch (try self.getSaprusTypePayload()) {
             .relay => {},
-            .connection => |*con| con.*.nativeFromNetworkEndian(),
+            .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) MessageTypeError!void {
+    pub fn networkFromNativeEndian(self: *Self) Error!void {
         try switch (try self.getSaprusTypePayload()) {
             .relay => {},
             .connection => |*con| con.*.networkFromNativeEndian(),
-            .file_transfer => MessageTypeError.NotImplementedSaprusType,
-            else => MessageTypeError.UnknownSaprusType,
+            .file_transfer => Error.NotImplementedSaprusType,
+            else => Error.UnknownSaprusType,
         };
         self.type = @enumFromInt(nativeToBig(
             @typeInfo(@TypeOf(self.type)).@"enum".tag_type,
@@ -155,9 +164,23 @@ pub const Message = packed struct {
         self.length = nativeToBig(@TypeOf(self.length), self.length);
     }
 
-    /// Deprecated.
-    /// If I need the bytes, I should just pass around the slice that is backing this to begin with.
-    pub fn asBytes(self: *Self) SelfBytes {
+    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];
     }
@@ -167,42 +190,180 @@ 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 Message
-    const msg: *Message = try .init(gpa, .relay, payload.len);
-    defer msg.deinit(gpa);
+    // 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.
-            // msg.type = .relay;
-            // msg.length = payload_len;
+            // zcm.type = .relay;
+            // zcm.length = payload_len;
         }
-        const relay = (try msg.getSaprusTypePayload()).relay;
+        const relay = (try zcm.getSaprusTypePayload()).relay;
         relay.dest = .{ 1, 2, 3, 4 };
         @memcpy(relay.getPayload(), payload);
     }
 
     {
-        const bytes = msg.asBytes();
+        const bytes = zcm.asBytes();
 
         // Print the message as hex using the network byte order
-        try msg.networkFromNativeEndian();
+        try zcm.networkFromNativeEndian();
         // We know the error from nativeFromNetworkEndian is unreachable because
         // it would have returned an error from networkFromNativeEndian.
-        defer msg.nativeFromNetworkEndian() catch unreachable;
+        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 msg.getSaprusTypePayload()).connection});
+        std.debug.print("{any}\n", .{(try zcm.getSaprusTypePayload()).connection});
     }
 
-    try std.testing.expectEqualDeep(msg, try Message.bytesAsValue(msg.asBytes()));
+    try std.testing.expectEqualDeep(zcm, try ZeroCopyMessage.bytesAsValue(zcm.asBytes()));
 }
 
+/// All Saprus messages
+pub const Message = union(PacketType) {
+    pub const Relay = struct {
+        pub const Header = packed struct {
+            dest: @Vector(4, u8),
+        };
+        header: Header,
+        payload: []const u8,
+    };
+    pub const Connection = struct {
+        pub const Header = 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 = .{},
+        };
+        header: Header,
+        payload: []const u8,
+    };
+    relay: Relay,
+    file_transfer: void, // unimplemented
+    connection: Connection,
+
+    /// Should be called for any Message that was declared using a function that you pass an allocator to.
+    pub fn deinit(self: Message, allocator: Allocator) void {
+        switch (self) {
+            .relay => |r| allocator.free(r.payload),
+            .connection => |c| allocator.free(c.payload),
+            else => unreachable,
+        }
+    }
+
+    fn toBytesAux(
+        header: anytype,
+        payload: []const u8,
+        buf: *std.ArrayList(u8),
+        allocator: Allocator,
+    ) !void {
+        const Header = @TypeOf(header);
+        // Create a growable string to store the base64 bytes in.
+        // Doing this first so I can use the length of the encoded bytes for the length field.
+        var payload_list = std.ArrayList(u8).init(allocator);
+        defer payload_list.deinit();
+        const buf_w = payload_list.writer();
+
+        // Write the payload bytes as base64 to the growable string.
+        try base64Enc.encodeWriter(buf_w, payload);
+
+        // At this point, payload_list contains the base64 encoded payload.
+
+        // Add the payload length to the output buf.
+        try buf.*.appendSlice(
+            asBytes(&nativeToBig(u16, @intCast(payload_list.items.len + @bitSizeOf(Header) / 8))),
+        );
+
+        // Add the header bytes to the output buf.
+        var header_buf: [@sizeOf(Header)]u8 = undefined;
+        var header_buf_stream = std.io.fixedBufferStream(&header_buf);
+        try header_buf_stream.writer().writeStructEndian(header, .big);
+        // Add the exact number of bits in the header without padding.
+        try buf.*.appendSlice(header_buf[0 .. @bitSizeOf(Header) / 8]);
+
+        try buf.*.appendSlice(payload_list.items);
+    }
+
+    /// Caller is responsible for freeing the returned bytes.
+    pub fn toBytes(self: Message, allocator: Allocator) ![]u8 {
+        // Create a growable list of bytes to store the output in.
+        var buf = std.ArrayList(u8).init(allocator);
+        errdefer buf.deinit();
+
+        // Start with writing the message type, which is the first 16 bits of every Saprus message.
+        try buf.appendSlice(asBytes(&nativeToBig(u16, @intFromEnum(self))));
+
+        // Write the proper header and payload for the given packet type.
+        switch (self) {
+            .relay => |r| try toBytesAux(r.header, r.payload, &buf, allocator),
+            .connection => |c| try toBytesAux(c.header, c.payload, &buf, allocator),
+            .file_transfer => return Error.NotImplementedSaprusType,
+        }
+
+        // Collect the growable list as a slice and return it.
+        return buf.toOwnedSlice();
+    }
+
+    fn fromBytesAux(
+        comptime packet: PacketType,
+        len: u16,
+        r: std.io.FixedBufferStream([]const u8).Reader,
+        allocator: Allocator,
+    ) !Message {
+        const Header = @field(@FieldType(Message, @tagName(packet)), "Header");
+
+        // Read the header for the current message type.
+        var header_bytes: [@sizeOf(Header)]u8 = undefined;
+        _ = try r.read(header_bytes[0 .. @bitSizeOf(Header) / 8]);
+        var header_stream = std.io.fixedBufferStream(&header_bytes);
+        const header = try header_stream.reader().readStructEndian(Header, .big);
+
+        // Read the base64 bytes into a list to be able to call the decoder on it.
+        const payload_buf = try allocator.alloc(u8, len - @bitSizeOf(Header) / 8);
+        defer allocator.free(payload_buf);
+        _ = try r.readAll(payload_buf);
+
+        // Create a buffer to store the payload in, and decode the base64 bytes into the payload field.
+        const payload = try allocator.alloc(u8, try base64Dec.calcSizeForSlice(payload_buf));
+        try base64Dec.decode(payload, payload_buf);
+
+        // Return the type of Message specified by the `packet` argument.
+        return @unionInit(Message, @tagName(packet), .{
+            .header = header,
+            .payload = payload,
+        });
+    }
+
+    /// Caller is responsible for calling .deinit on the returned value.
+    pub fn fromBytes(bytes: []const u8, allocator: Allocator) !Message {
+        var s = std.io.fixedBufferStream(bytes);
+        const r = s.reader();
+
+        // Read packet type
+        const packet_type = @as(PacketType, @enumFromInt(try r.readInt(u16, .big)));
+
+        // Read the length of the header + base64 encoded payload.
+        const len = try r.readInt(u16, .big);
+
+        switch (packet_type) {
+            .relay => return fromBytesAux(.relay, len, r, allocator),
+            .connection => return fromBytesAux(.connection, len, r, allocator),
+            .file_transfer => return Error.NotImplementedSaprusType,
+            else => return Error.UnknownSaprusType,
+        }
+    }
+};
+
 const std = @import("std");
 const Allocator = std.mem.Allocator;