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

@@ -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, '=');
+
 var rand: ?Random = null;
 
 pub fn init() !void {
@@ -14,9 +17,14 @@ pub fn deinit() void {
     network.deinit();
 }
 
-fn broadcastSaprusMessage(msg: SaprusMessage, udp_port: u16, allocator: Allocator) !void {
-    const msg_bytes = try msg.toBytes(allocator);
-    defer allocator.free(msg_bytes);
+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;
 
     var sock = try network.Socket.create(.ipv4, .udp);
     defer sock.close();
@@ -40,14 +48,22 @@ fn broadcastSaprusMessage(msg: SaprusMessage, udp_port: u16, allocator: Allocato
 }
 
 pub fn sendRelay(payload: []const u8, dest: [4]u8, allocator: Allocator) !void {
-    const msg = SaprusMessage{
-        .relay = .{
-            .header = .{ .dest = dest },
-            .payload = payload,
-        },
-    };
+    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);
 
-    try broadcastSaprusMessage(msg, 8888, allocator);
+    const relay = (try msg.getSaprusTypePayload()).relay;
+    relay.dest = dest;
+    _ = base64Enc.encode(relay.getPayload(), payload);
+
+    try broadcastSaprusMessage(msg, 8888);
 }
 
 fn randomPort() u16 {
@@ -59,34 +75,36 @@ 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 = SaprusMessage{
-        .connection = .{
-            .header = .{
-                .src_port = initial_port,
-                .dest_port = dest_port,
-            },
-            .payload = payload,
-        },
-    };
+    const msg_bytes = try allocator.alignedAlloc(
+        u8,
+        @alignOf(SaprusMessage),
+        try SaprusMessage.lengthForPayloadLength(
+            .connection,
+            base64Enc.calcSize(payload.len),
+        ),
+    );
 
-    try broadcastSaprusMessage(msg, 8888, allocator);
+    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);
 
     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;
-    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();
@@ -102,15 +120,17 @@ 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 = undefined;
+    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);
 
-    initial_conn_res = try SaprusMessage.fromBytes(response_buf[0..len], allocator);
+    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(), allocator);
+    try broadcastSaprusMessage(msg, randomPort());
 
     if (false) {
         return initial_conn_res.?;

src/main.zig

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

src/message.zig

@@ -1,6 +1,3 @@
-const base64Enc = std.base64.Base64Encoder.init(std.base64.standard_alphabet_chars, '=');
-const base64Dec = std.base64.Base64Decoder.init(std.base64.standard_alphabet_chars, '=');
-
 /// Type tag for Message union.
 /// This is the first value in the actual packet sent over the network.
 pub const PacketType = enum(u16) {
@@ -23,43 +20,25 @@ 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,
 };
 
 // ZERO COPY STUFF
 // &payload could be a void value that is treated as a pointer to a [*]u8
-pub const ZeroCopyMessage = packed struct {
+/// All Saprus messages
+pub const Message = 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];
+        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)];
         }
     };
     const Connection = packed struct {
@@ -76,14 +55,14 @@ pub const ZeroCopyMessage = packed struct {
             return @as([*]u8, @ptrCast(&self.payload))[0 .. len.* - @sizeOf(Connection)];
         }
 
-        fn nativeFromNetworkEndian(self: *align(1) Connection) Error!void {
+        fn nativeFromNetworkEndian(self: *align(1) Connection) 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 {
+        fn networkFromNativeEndian(self: *align(1) Connection) 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);
@@ -92,70 +71,82 @@ pub const ZeroCopyMessage = packed struct {
     };
 
     const Self = @This();
+    const SelfBytes = []align(@alignOf(Self)) u8;
 
     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);
+    /// 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(@alignOf(Self)) Relay {
+    fn getRelay(self: *Self) *align(1) Relay {
         return std.mem.bytesAsValue(Relay, &self.bytes);
     }
-    fn getConnection(self: *Self) *align(@alignOf(Self)) Connection {
+    fn getConnection(self: *Self) *align(1) Connection {
         return std.mem.bytesAsValue(Connection, &self.bytes);
     }
 
-    pub fn getSaprusTypePayload(self: *Self) Error!(union(PacketType) {
-        relay: *align(@alignOf(Self)) Relay,
+    pub fn getSaprusTypePayload(self: *Self) MessageTypeError!(union(PacketType) {
+        relay: *align(1) Relay,
         file_transfer: void,
-        connection: *align(@alignOf(Self)) Connection,
+        connection: *align(1) Connection,
     }) {
         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),
         ));
         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| try con.*.nativeFromNetworkEndian(),
+            .connection => |*con| 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 {
+    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,
@@ -164,23 +155,9 @@ pub const ZeroCopyMessage = packed struct {
         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 {
+    /// 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];
     }
@@ -190,180 +167,42 @@ 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});
+    // Create a view of the byte slice as a Message
+    const msg: *Message = try .init(gpa, .relay, payload.len);
+    defer msg.deinit(gpa);
 
     {
         // Set the message values
         {
             // These are both set by the init call.
-            // zcm.type = .relay;
-            // zcm.length = payload_len;
+            // msg.type = .relay;
+            // msg.length = payload_len;
         }
-        const relay = (try zcm.getSaprusTypePayload()).relay;
+        const relay = (try msg.getSaprusTypePayload()).relay;
         relay.dest = .{ 1, 2, 3, 4 };
         @memcpy(relay.getPayload(), payload);
     }
 
     {
-        const bytes = zcm.asBytes();
+        const bytes = msg.asBytes();
 
         // Print the message as hex using the network byte order
-        try zcm.networkFromNativeEndian();
+        try msg.networkFromNativeEndian();
         // We know the error from nativeFromNetworkEndian is unreachable because
         // it would have returned an error from networkFromNativeEndian.
-        defer zcm.nativeFromNetworkEndian() catch unreachable;
+        defer msg.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});
+        std.debug.print("{any}\n", .{(try msg.getSaprusTypePayload()).connection});
     }
 
-    try std.testing.expectEqualDeep(zcm, try ZeroCopyMessage.bytesAsValue(zcm.asBytes()));
+    try std.testing.expectEqualDeep(msg, try Message.bytesAsValue(msg.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;