fix use after free

For some reason I am still getting this:

2025/05/10 16:37:06 Error decoding message: SGVsbG8gZGFya25lc3MgbXkgb2xkIGZyaWVuZA==::53475673624738675a4746796132356c63334d6762586b676232786b49475a79615756755a413d3daaaa

src/Client.zig

@@ -48,15 +48,22 @@ fn broadcastSaprusMessage(msg: *SaprusMessage, udp_port: u16) !void {
 }
 
 pub fn sendRelay(payload: []const u8, dest: [4]u8, allocator: Allocator) !void {
-    const msg: *SaprusMessageNew(.relay) = try .init(
-        allocator,
-        @intCast(base64Enc.calcSize(payload.len)),
+    const msg_bytes = try allocator.alignedAlloc(
+        u8,
+        @alignOf(SaprusMessage),
+        try SaprusMessage.lengthForPayloadLength(
+            .relay,
+            base64Enc.calcSize(payload.len),
+        ),
     );
-    defer msg.deinit(allocator);
-    msg.dest = dest;
-    _ = base64Enc.encode(msg.getPayload(), payload);
+    defer allocator.free(msg_bytes);
+    const msg: *SaprusMessage = .init(.relay, msg_bytes);
 
-    try broadcastSaprusMessage(try SaprusMessage.bytesAsValue(msg.asBytes()), 8888);
+    const relay = (try msg.getSaprusTypePayload()).relay;
+    relay.dest = dest;
+    _ = base64Enc.encode(relay.getPayload(), payload);
+
+    try broadcastSaprusMessage(msg, 8888);
 }
 
 fn randomPort() u16 {
@@ -70,12 +77,21 @@ fn randomPort() u16 {
 
 pub fn sendInitialConnection(payload: []const u8, initial_port: u16, allocator: Allocator) !*SaprusMessage {
     const dest_port = randomPort();
-    const msg: *SaprusMessage = try .init(allocator, .connection, @intCast(payload.len));
-    defer msg.deinit(allocator);
+    const msg_bytes = try allocator.alignedAlloc(
+        u8,
+        @alignOf(SaprusMessage),
+        try SaprusMessage.lengthForPayloadLength(
+            .connection,
+            base64Enc.calcSize(payload.len),
+        ),
+    );
+
+    const msg: *SaprusMessage = .init(.connection, msg_bytes);
+
     const connection = (try msg.getSaprusTypePayload()).connection;
     connection.src_port = initial_port;
     connection.dest_port = dest_port;
-    @memcpy(connection.getPayload(), payload);
+    _ = base64Enc.encode(connection.getPayload(), payload);
 
     try broadcastSaprusMessage(msg, 8888);
 
@@ -88,8 +104,7 @@ pub fn connect(payload: []const u8, allocator: Allocator) !?SaprusConnection {
         initial_port = r.intRangeAtMost(u16, 1024, 65000);
     } else unreachable;
 
-    var initial_conn_res: ?SaprusMessage = null;
-    errdefer if (initial_conn_res) |*c| c.deinit(allocator);
+    var initial_conn_res: ?*SaprusMessage = null;
 
     var sock = try network.Socket.create(.ipv4, .udp);
     defer sock.close();
@@ -105,13 +120,14 @@ 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(4) = @splat(0);
+    var response_buf: [4096]u8 align(@alignOf(SaprusMessage)) = 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});
-    initial_conn_res = (try SaprusMessage.bytesAsValue(response_buf[0..len])).*;
+    std.debug.print("response bytes: {x}\n", .{response_buf[0..len]});
+    initial_conn_res = SaprusMessage.init(.connection, response_buf[0..len]);
 
     // Complete handshake after awaiting response
     try broadcastSaprusMessage(msg, randomPort());
@@ -123,7 +139,6 @@ pub fn connect(payload: []const u8, allocator: Allocator) !?SaprusConnection {
 }
 
 const SaprusMessage = @import("message.zig").Message;
-const SaprusMessageNew = @import("message.zig").MessageNew;
 const SaprusConnection = @import("Connection.zig");
 
 const std = @import("std");

src/message.zig

@@ -20,130 +20,14 @@ pub const ConnectionOptions = packed struct(u8) {
     opt8: bool = false,
 };
 
-pub const Error = error{
+pub const MessageTypeError = error{
     NotImplementedSaprusType,
     UnknownSaprusType,
+};
+pub const MessageParseError = MessageTypeError || error{
     InvalidMessage,
 };
 
-pub fn MessageNew(comptime packet_type: PacketType) type {
-    comptime {
-        if (packet_type == .file_transfer)
-            @compileError("File transfer not implemented");
-        if (packet_type != .relay and packet_type != .connection)
-            @compileError("Unkown message type");
-    }
-
-    return packed struct {
-        const Self = @This();
-        const SelfBytes = []align(@alignOf(Self)) u8;
-
-        const Relay = struct {
-            pub fn getPayload(self: *Self) []u8 {
-                return @as([*]align(@alignOf(Self)) u8, @ptrCast(&self.payload))[0 .. self.length - 4];
-            }
-        };
-        const Connection = packed struct {
-            pub fn getPayload(self: Self) []u8 {
-                return @as([*]u8, &self.payload)[0 .. self.length - 4];
-            }
-        };
-
-        type: PacketType = packet_type,
-        length: u16,
-
-        // Relay
-        dest: if (packet_type == .relay) @Vector(4, u8) else void,
-
-        // Connection
-        src_port: if (packet_type == .connection) u16 else void, // random number > 1024
-        dest_port: if (packet_type == .connection) u16 else void, // random number > 1024
-        seq_num: if (packet_type == .connection) u32 else void,
-        msg_id: if (packet_type == .connection) u32 else void,
-        reserved: if (packet_type == .connection) u8 else void,
-        options: if (packet_type == .connection) ConnectionOptions else void = if (packet_type == .connection) .{} else {},
-
-        // Relay or Connection
-        payload: switch (packet_type) {
-            .relay, .connection => void,
-            else => noreturn,
-        },
-
-        pub usingnamespace switch (packet_type) {
-            .relay => Relay,
-            .connection => Connection,
-            .file_transfer => @compileError("File Transfer message type not implemented"),
-            else => @compileError("Unknown message type"),
-        };
-
-        pub fn init(allocator: Allocator, payload_len: u16) !*Self {
-            const size = payload_len + @sizeOf(Self);
-            const bytes = try allocator.alignedAlloc(u8, @alignOf(Self), size);
-            const res: *Self = @ptrCast(bytes.ptr);
-            res.type = packet_type;
-            res.length = payload_len;
-            return res;
-        }
-
-        pub fn deinit(self: *Self, allocator: Allocator) void {
-            allocator.free(self.asBytes());
-        }
-
-        pub fn nativeFromNetworkEndian(self: *Self) void {
-            self.type = @enumFromInt(bigToNative(
-                @typeInfo(@TypeOf(self.type)).@"enum".tag_type,
-                @intFromEnum(self.type),
-            ));
-            self.length = bigToNative(@TypeOf(self.length), self.length);
-
-            if (packet_type == .connection) {
-                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);
-            }
-        }
-
-        pub fn networkFromNativeEndian(self: *Self) void {
-            self.type = @enumFromInt(bigToNative(
-                @typeInfo(@TypeOf(self.type)).@"enum".tag_type,
-                @intFromEnum(self.type),
-            ));
-            self.length = bigToNative(@TypeOf(self.length), self.length);
-
-            if (packet_type == .connection) {
-                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);
-            }
-        }
-
-        pub fn asBytes(self: *Self) SelfBytes {
-            const size = @sizeOf(Self) + self.length;
-            return @as([*]align(@alignOf(Self)) u8, @ptrCast(self))[0..size];
-        }
-    };
-}
-
-test MessageNew {
-    comptime for (@typeInfo(MessageNew(.connection)).@"struct".decls) |field| {
-        @compileLog(field);
-    };
-}
-
-// pub fn bytesAsMessage(bytes: []const u8) !*Self {
-//     const res = std.mem.bytesAsValue(Self, 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,
-//     };
-// }
-
 // ZERO COPY STUFF
 // &payload could be a void value that is treated as a pointer to a [*]u8
 /// All Saprus messages
@@ -193,23 +77,25 @@ pub const Message = packed struct {
     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,
-            .file_transfer => return Error.NotImplementedSaprusType,
-            else => return Error.UnknownSaprusType,
-        });
-        const size = payload_len + @sizeOf(Self) + header_size;
-        const bytes = try allocator.alignedAlloc(u8, @alignOf(Self), size);
+    /// 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 = payload_len + header_size;
+        res.length = @intCast(bytes.len - @sizeOf(Self));
         return res;
     }
 
-    pub fn deinit(self: *Self, allocator: Allocator) void {
-        allocator.free(self.asBytes());
+    pub fn lengthForPayloadLength(comptime @"type": PacketType, payload_len: usize) MessageTypeError!u16 {
+        std.debug.assert(payload_len < std.math.maxInt(u16));
+        const header_size = @sizeOf(switch (@"type") {
+            .relay => Relay,
+            .connection => Connection,
+            .file_transfer => return MessageTypeError.NotImplementedSaprusType,
+            else => return MessageTypeError.UnknownSaprusType,
+        });
+        return @intCast(payload_len + @sizeOf(Self) + header_size);
     }
 
     fn getRelay(self: *Self) *align(1) Relay {
@@ -219,7 +105,7 @@ pub const Message = packed struct {
         return std.mem.bytesAsValue(Connection, &self.bytes);
     }
 
-    pub fn getSaprusTypePayload(self: *Self) Error!(union(PacketType) {
+    pub fn getSaprusTypePayload(self: *Self) MessageTypeError!(union(PacketType) {
         relay: *align(1) Relay,
         file_transfer: void,
         connection: *align(1) Connection,
@@ -227,12 +113,12 @@ pub const Message = packed struct {
         return switch (self.type) {
             .relay => .{ .relay = self.getRelay() },
             .connection => .{ .connection = self.getConnection() },
-            .file_transfer => Error.NotImplementedSaprusType,
-            else => Error.UnknownSaprusType,
+            .file_transfer => MessageTypeError.NotImplementedSaprusType,
+            else => MessageTypeError.UnknownSaprusType,
         };
     }
 
-    pub fn nativeFromNetworkEndian(self: *Self) Error!void {
+    pub fn nativeFromNetworkEndian(self: *Self) MessageTypeError!void {
         self.type = @enumFromInt(bigToNative(
             @typeInfo(@TypeOf(self.type)).@"enum".tag_type,
             @intFromEnum(self.type),
@@ -255,12 +141,12 @@ pub const Message = packed struct {
         }
     }
 
-    pub fn networkFromNativeEndian(self: *Self) Error!void {
+    pub fn networkFromNativeEndian(self: *Self) MessageTypeError!void {
         try switch (try self.getSaprusTypePayload()) {
             .relay => {},
             .connection => |*con| con.*.networkFromNativeEndian(),
-            .file_transfer => Error.NotImplementedSaprusType,
-            else => Error.UnknownSaprusType,
+            .file_transfer => MessageTypeError.NotImplementedSaprusType,
+            else => MessageTypeError.UnknownSaprusType,
         };
         self.type = @enumFromInt(nativeToBig(
             @typeInfo(@TypeOf(self.type)).@"enum".tag_type,
@@ -269,18 +155,8 @@ pub const Message = packed struct {
         self.length = nativeToBig(@TypeOf(self.length), self.length);
     }
 
-    pub fn bytesAsValue(bytes: SelfBytes) !*Self {
-        const res = std.mem.bytesAsValue(Self, 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,
-        };
-    }
-
+    /// 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 {
         const size = @sizeOf(Self) + self.length;
         return @as([*]align(@alignOf(Self)) u8, @ptrCast(self))[0..size];
@@ -334,6 +210,45 @@ 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;
+    const msg = Message{
+        .relay = .{
+            .header = .{ .dest = .{ 255, 255, 255, 255 } },
+            .payload = "Hello darkness my old friend",
+        },
+    };
+
+    const to_bytes = try msg.toBytes(gpa);
+    defer gpa.free(to_bytes);
+
+    const from_bytes = try Message.fromBytes(to_bytes, gpa);
+    defer from_bytes.deinit(gpa);
+
+    try std.testing.expectEqualDeep(msg, from_bytes);
+}
+
+test "Round trip Connection toBytes and fromBytes" {
+    const gpa = std.testing.allocator;
+    const msg = Message{
+        .connection = .{
+            .header = .{
+                .src_port = 0,
+                .dest_port = 0,
+            },
+            .payload = "Hello darkness my old friend",
+        },
+    };
+
+    const to_bytes = try msg.toBytes(gpa);
+    defer gpa.free(to_bytes);
+
+    const from_bytes = try Message.fromBytes(to_bytes, gpa);
+    defer from_bytes.deinit(gpa);
+
+    try std.testing.expectEqualDeep(msg, from_bytes);
+}
+
 test {
     std.testing.refAllDeclsRecursive(@This());
 }