fix use after free

For some reason I am still getting this:

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

build.zig

@@ -1,5 +1,4 @@
 const std = @import("std");
-const Step = std.Build.Step;
 
 // Although this function looks imperative, note that its job is to
 // declaratively construct a build graph that will be executed by an external
@@ -34,34 +33,18 @@ 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"));
 
-    const static_lib = b.addLibrary(.{
+    const lib = b.addLibrary(.{
         .linkage = .static,
         .name = "zaprus",
         .root_module = lib_mod,
     });
 
-    b.installArtifact(static_lib);
+    b.installArtifact(lib);
-
-    const dynamic_lib = b.addLibrary(.{
-        .linkage = .dynamic,
-        .name = "zaprus",
-        .root_module = lib_mod,
-    });
-
-    b.installArtifact(dynamic_lib);
-
-    // C Headers
-    const c_header = b.addInstallFileWithDir(
-        b.path("include/zaprus.h"),
-        .header,
-        "zaprus.h",
-    );
-
-    b.getInstallStep().dependOn(&c_header.step);
 
     // This creates another `std.Build.Step.Compile`, but this one builds an executable
     // rather than a static library.

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",

include/zaprus.h

@@ -1,24 +0,0 @@
-// client
-
-int zaprus_init(void);
-
-int zaprus_deinit(void);
-
-int zaprus_send_relay(const char* payload, usize len, char[4] dest);
-
-int zaprus_send_initial_connection(const char* payload, usize len, uint16_t initial_port);
-
-struct SaprusMessage* zaprus_connect(const char* payload, usize len);
-
-// message
-struct SaprusMessage {
-  
-};
-
-// ptr should be freed by the caller.
-int zaprus_message_to_bytes(struct SaprusMessage msg, char** ptr, usize* len);
-
-// Return value should be destroyed with zaprus_message_deinit.
-struct SaprusMessage* zaprus_message_from_bytes(const char* bytes, usize len);
-
-void zaprus_message_deinit(struct SaprusMessage* msg);

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 {
+fn broadcastSaprusMessage(msg: *SaprusMessage, udp_port: u16) !void {
-    const msg_bytes = try msg.toBytes(allocator);
+    if (false) {
-    defer allocator.free(msg_bytes);
+        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{
+    const msg_bytes = try allocator.alignedAlloc(
-        .relay = .{
+        u8,
-            .header = .{ .dest = dest },
+        @alignOf(SaprusMessage),
-            .payload = payload,
+        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 {
@@ -59,31 +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{
+    const msg_bytes = try allocator.alignedAlloc(
-        .connection = .{
+        u8,
-            .header = .{
+        @alignOf(SaprusMessage),
-                .src_port = initial_port,
+        try SaprusMessage.lengthForPayloadLength(
-                .dest_port = dest_port,
+            .connection,
-            },
+            base64Enc.calcSize(payload.len),
-            .payload = payload,
+        ),
-        },
+    );
-    };
 
-    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) !?SaprusMessage {
+pub fn connect(payload: []const u8, allocator: Allocator) !?SaprusConnection {
     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();
@@ -99,20 +120,26 @@ pub fn connect(payload: []const u8, allocator: Allocator) !?SaprusMessage {
     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());
 
-    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 +147,6 @@ const posix = std.posix;
 const mem = std.mem;
 
 const network = @import("network");
+const gcat = @import("gatorcat");
 
 const Allocator = mem.Allocator;

src/c_api.zig

@@ -1,56 +0,0 @@
-// client
-
-export fn zaprus_init() c_int {
-    SaprusClient.init() catch return 1;
-    return 0;
-}
-
-export fn zaprus_deinit() c_int {
-    SaprusClient.deinit();
-    return 0;
-}
-
-export fn zaprus_send_relay(payload: [*]const u8, len: usize, dest: [4]u8) c_int {
-    SaprusClient.sendRelay(payload[0..len], dest, allocator) catch return 1;
-    return 0;
-}
-
-export fn zaprus_send_initial_connection(payload: [*]const u8, len: usize, initial_port: u16) c_int {
-    SaprusClient.sendInitialConnection(payload[0..len], initial_port, allocator) catch return 1;
-    return 0;
-}
-
-export fn zaprus_connect(payload: [*]const u8, len: usize) ?*SaprusMessage {
-    return SaprusClient.connect(payload[0..len], allocator) catch null;
-}
-
-// message
-
-/// ptr should be freed by the caller.
-export fn zaprus_message_to_bytes(msg: SaprusMessage, ptr: *[*]u8, len: *usize) c_int {
-    const bytes = msg.toBytes(allocator) catch return 1;
-    ptr.* = bytes[0..].*;
-    len.* = bytes.len;
-    return 0;
-}
-
-/// Return value should be destroyed with zaprus_message_deinit.
-export fn zaprus_message_from_bytes(bytes: [*]const u8, len: usize) ?*SaprusMessage {
-    return SaprusMessage.fromBytes(bytes[0..len], allocator) catch null;
-}
-
-export fn zaprus_message_deinit(msg: *SaprusMessage) void {
-    msg.deinit(allocator);
-}
-
-const std = @import("std");
-
-const zaprus = @import("./root.zig");
-const SaprusClient = zaprus.Client;
-const SaprusMessage = zaprus.Message;
-
-const allocator = std.heap.c_allocator;
-
-test {
-    std.testing.refAllDeclsRecursively(@This());
-}

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,
@@ -59,23 +59,17 @@ 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, .{});
 }
 
-fn parseDest(in: ?[]const u8) ![4]u8 {
+fn parseDest(in: ?[]const u8) [4]u8 {
     if (in) |dest| {
         if (dest.len <= 4) {
             var res: [4]u8 = @splat(0);
@@ -83,10 +77,10 @@ fn parseDest(in: ?[]const u8) ![4]u8 {
             return res;
         }
 
-        const addr = try std.net.Ip4Address.parse(dest, 0);
+        const addr = std.net.Ip4Address.parse(dest, 0) catch return "FAIL".*;
         return @bitCast(addr.sa.addr);
     }
-    return .{ 70, 70, 70, 70 };
+    return "zap\x00".*;
 }
 
 const builtin = @import("builtin");

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) {
@@ -23,153 +20,195 @@ 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
 /// All Saprus messages
-pub const Message = union(PacketType) {
+pub const Message = packed struct {
-    pub const Relay = struct {
+    const Relay = packed struct {
-        pub const Header = packed struct {
+        dest: @Vector(4, u8),
-            dest: @Vector(4, u8),
+        payload: void,
-        };
-        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 getPayload(self: *align(1) Relay) []u8 {
-    pub fn deinit(self: Message, allocator: Allocator) void {
+            const len: *u16 = @ptrFromInt(@intFromPtr(self) - @sizeOf(u16));
-        switch (self) {
+            return @as([*]u8, @ptrCast(&self.payload))[0 .. len.* - @sizeOf(Relay)];
-            .relay => |r| allocator.free(r.payload),
+        }
-            .connection => |c| allocator.free(c.payload),
+    };
+    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) 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 {
+            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();
+    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));
+        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 {
+        return std.mem.bytesAsValue(Relay, &self.bytes);
+    }
+    fn getConnection(self: *Self) *align(1) Connection {
+        return std.mem.bytesAsValue(Connection, &self.bytes);
+    }
+
+    pub fn getSaprusTypePayload(self: *Self) MessageTypeError!(union(PacketType) {
+        relay: *align(1) Relay,
+        file_transfer: void,
+        connection: *align(1) Connection,
+    }) {
+        return switch (self.type) {
+            .relay => .{ .relay = self.getRelay() },
+            .connection => .{ .connection = self.getConnection() },
+            .file_transfer => MessageTypeError.NotImplementedSaprusType,
+            else => MessageTypeError.UnknownSaprusType,
+        };
+    }
+
+    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| con.*.nativeFromNetworkEndian(),
+            // We know other values are unreachable,
+            // because they would have returned an error from the switch condition.
             else => unreachable,
         }
     }
 
-    fn toBytesAux(
+    pub fn networkFromNativeEndian(self: *Self) MessageTypeError!void {
-        header: anytype,
+        try switch (try self.getSaprusTypePayload()) {
-        payload: []const u8,
+            .relay => {},
-        buf: *std.ArrayList(u8),
+            .connection => |*con| con.*.networkFromNativeEndian(),
-        allocator: Allocator,
+            .file_transfer => MessageTypeError.NotImplementedSaprusType,
-    ) !void {
+            else => MessageTypeError.UnknownSaprusType,
-        const Header = @TypeOf(header);
+        };
-        // Create a growable string to store the base64 bytes in.
+        self.type = @enumFromInt(nativeToBig(
-        // Doing this first so I can use the length of the encoded bytes for the length field.
+            @typeInfo(@TypeOf(self.type)).@"enum".tag_type,
-        var payload_list = std.ArrayList(u8).init(allocator);
+            @intFromEnum(self.type),
-        defer payload_list.deinit();
+        ));
-        const buf_w = payload_list.writer();
+        self.length = nativeToBig(@TypeOf(self.length), self.length);
-
-        // 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.
+    /// Deprecated.
-    pub fn toBytes(self: Message, allocator: Allocator) ![]u8 {
+    /// If I need the bytes, I should just pass around the slice that is backing this to begin with.
-        // Create a growable list of bytes to store the output in.
+    pub fn asBytes(self: *Self) SelfBytes {
-        var buf = std.ArrayList(u8).init(allocator);
+        const size = @sizeOf(Self) + self.length;
-        errdefer buf.deinit();
+        return @as([*]align(@alignOf(Self)) u8, @ptrCast(self))[0..size];
-
-        // 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,
-        }
     }
 };
 
+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);
+
+    {
+        // Set the message values
+        {
+            // These are both set by the init call.
+            // msg.type = .relay;
+            // msg.length = payload_len;
+        }
+        const relay = (try msg.getSaprusTypePayload()).relay;
+        relay.dest = .{ 1, 2, 3, 4 };
+        @memcpy(relay.getPayload(), payload);
+    }
+
+    {
+        const bytes = msg.asBytes();
+
+        // Print the message as hex using the network byte order
+        try msg.networkFromNativeEndian();
+        // We know the error from nativeFromNetworkEndian is unreachable because
+        // it would have returned an error from networkFromNativeEndian.
+        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 msg.getSaprusTypePayload()).connection});
+    }
+
+    try std.testing.expectEqualDeep(msg, try Message.bytesAsValue(msg.asBytes()));
+}
+
 const std = @import("std");
 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 +248,7 @@ test "Round trip Connection toBytes and fromBytes" {
 
     try std.testing.expectEqualDeep(msg, from_bytes);
 }
+
+test {
+    std.testing.refAllDeclsRecursive(@This());
+}

src/root.zig

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