going off the deep end with with generic message type

Callers can instead use std.mem.bytesAsValue directly.

build.zig

@@ -15,6 +15,12 @@ pub fn build(b: *std.Build) void {
     // set a preferred release mode, allowing the user to decide how to optimize.
     const optimize = b.standardOptimizeOption(.{});
 
+    const lib_mod = b.createModule(.{
+        .root_source_file = b.path("src/root.zig"),
+        .target = target,
+        .optimize = optimize,
+    });
+
     // We will also create a module for our other entry point, 'main.zig'.
     const exe_mod = b.createModule(.{
         // `root_source_file` is the Zig "entry point" of the module. If a module
@@ -26,7 +32,19 @@ pub fn build(b: *std.Build) void {
         .optimize = optimize,
     });
 
-    exe_mod.addImport("network", b.dependency("network", .{}).module("network"));
+    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 lib = b.addLibrary(.{
+        .linkage = .static,
+        .name = "zaprus",
+        .root_module = lib_mod,
+    });
+
+    b.installArtifact(lib);
 
     // This creates another `std.Build.Step.Compile`, but this one builds an executable
     // rather than a static library.

build.zig.zon

@@ -40,6 +40,14 @@
             .url = "https://github.com/ikskuh/zig-network/archive/c76240d2240711a3dcbf1c0fb461d5d1f18be79a.zip",
             .hash = "network-0.1.0-AAAAAOwlAQAQ6zKPUrsibdpGisxld9ftUKGdMvcCSpaj",
         },
+        .clap = .{
+            .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

@@ -0,0 +1,137 @@
+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 {
+    var prng = Random.DefaultPrng.init(blk: {
+        var seed: u64 = undefined;
+        try posix.getrandom(mem.asBytes(&seed));
+        break :blk seed;
+    });
+    rand = prng.random();
+    try network.init();
+}
+
+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;
+
+    var sock = try network.Socket.create(.ipv4, .udp);
+    defer sock.close();
+
+    try sock.setBroadcast(true);
+
+    // Bind to 0.0.0.0:0
+    const bind_addr = network.EndPoint{
+        .address = network.Address{ .ipv4 = network.Address.IPv4.any },
+        .port = 0,
+    };
+
+    const dest_addr = network.EndPoint{
+        .address = network.Address{ .ipv4 = network.Address.IPv4.broadcast },
+        .port = udp_port,
+    };
+
+    try sock.bind(bind_addr);
+
+    _ = try sock.sendTo(dest_addr, msg_bytes);
+}
+
+pub fn sendRelay(payload: []const u8, dest: [4]u8, allocator: Allocator) !void {
+    const msg: *SaprusMessageNew(.relay) = try .init(
+        allocator,
+        @intCast(base64Enc.calcSize(payload.len)),
+    );
+    defer msg.deinit(allocator);
+    msg.dest = dest;
+    _ = base64Enc.encode(msg.getPayload(), payload);
+
+    try broadcastSaprusMessage(try SaprusMessage.bytesAsValue(msg.asBytes()), 8888);
+}
+
+fn randomPort() u16 {
+    var p: u16 = 0;
+    if (rand) |r| {
+        p = r.intRangeAtMost(u16, 1024, 65000);
+    } else unreachable;
+
+    return p;
+}
+
+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 connection = (try msg.getSaprusTypePayload()).connection;
+    connection.src_port = initial_port;
+    connection.dest_port = dest_port;
+    @memcpy(connection.getPayload(), payload);
+
+    try broadcastSaprusMessage(msg, 8888);
+
+    return msg;
+}
+
+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;
+    errdefer if (initial_conn_res) |*c| c.deinit(allocator);
+
+    var sock = try network.Socket.create(.ipv4, .udp);
+    defer sock.close();
+
+    // Bind to 255.255.255.255:8888
+    const bind_addr = network.EndPoint{
+        .address = network.Address{ .ipv4 = network.Address.IPv4.broadcast },
+        .port = 8888,
+    };
+
+    // timeout 1s
+    try sock.setReadTimeout(1 * std.time.us_per_s);
+    try sock.bind(bind_addr);
+
+    const msg = try sendInitialConnection(payload, initial_port, allocator);
+
+    var response_buf: [4096]u8 align(4) = @splat(0);
+    _ = 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])).*;
+
+    // Complete handshake after awaiting response
+    try broadcastSaprusMessage(msg, randomPort());
+
+    if (false) {
+        return initial_conn_res.?;
+    }
+    return null;
+}
+
+const SaprusMessage = @import("message.zig").Message;
+const SaprusMessageNew = @import("message.zig").MessageNew;
+const SaprusConnection = @import("Connection.zig");
+
+const std = @import("std");
+const Random = std.Random;
+const posix = std.posix;
+const mem = std.mem;
+
+const network = @import("network");
+const gcat = @import("gatorcat");
+
+const Allocator = mem.Allocator;

src/main.zig

@@ -1,119 +1,95 @@
 const is_debug = builtin.mode == .Debug;
-const base64 = std.base64.Base64Encoder.init(std.base64.standard_alphabet_chars, '=');
 
-const SaprusPacketType = enum(u16) {
+/// This creates a debug allocator that can only be referenced in debug mode.
-    relay = 0x003C,
+/// You should check for is_debug around every reference to dba.
-    file_transfer = 0x8888,
+var dba: DebugAllocator =
-    connection = 0x00E9,
+    if (is_debug)
-};
+        DebugAllocator.init
-
+    else
-const SaprusConnectionOptions = packed struct(u8) {
+        @compileError("Should not use debug allocator in release mode");
-    opt1: bool = false,
-    opt2: bool = false,
-    opt3: bool = false,
-    opt4: bool = false,
-    opt5: bool = false,
-    opt6: bool = false,
-    opt7: bool = false,
-    opt8: bool = false,
-};
-
-const SaprusMessage = union(SaprusPacketType) {
-    const Relay = struct {
-        header: packed struct {
-            dest: @Vector(4, u8),
-        },
-        payload: []const u8,
-    };
-    const Connection = struct {
-        header: packed struct {
-            src_port: u16,
-            dest_port: u16,
-            seq_num: u32 = 0,
-            msg_id: u32 = 0,
-            reserved: u8 = 0,
-            options: SaprusConnectionOptions = .{},
-        },
-        payload: []const u8,
-    };
-    relay: Relay,
-    file_transfer: void, // unimplemented
-    connection: Connection,
-
-    fn toBytes(self: SaprusMessage, allocator: Allocator) ![]u8 {
-        var buf = std.ArrayList(u8).init(allocator);
-        const w = buf.writer();
-        try w.writeInt(u16, @intFromEnum(self), .big);
-
-        switch (self) {
-            .relay => |r| {
-                try w.writeStructEndian(r.header, .big);
-                try w.writeInt(u16, @intCast(r.payload.len), .big);
-                try base64.encodeWriter(w, r.payload);
-            },
-            .file_transfer => unreachable,
-            .connection => |c| {
-                try w.writeStructEndian(c.header, .big);
-                try w.writeInt(u16, @intCast(c.payload.len), .big);
-                try base64.encodeWriter(w, c.payload);
-            },
-        }
-
-        return buf.toOwnedSlice();
-    }
-};
 
 pub fn main() !void {
-    const DBA = std.heap.DebugAllocator(.{});
+    defer if (is_debug) {
-    var dba: ?DBA = if (comptime is_debug) DBA.init else null;
+        _ = dba.deinit();
-    defer if (dba) |*d| {
-        _ = d.deinit();
     };
 
-    var allocator = if (dba) |*d|
+    const gpa = if (is_debug) dba.allocator() else std.heap.smp_allocator;
-        d.allocator()
+
-    else blk: {
+    // CLI parsing adapted from the example here
-        var buf: [128]u8 = undefined;
+    // https://github.com/Hejsil/zig-clap/blob/e47028deaefc2fb396d3d9e9f7bd776ae0b2a43a/README.md#examples
-        var fba = std.heap.FixedBufferAllocator.init(&buf);
+
-        break :blk fba.allocator();
+    // First we specify what parameters our program can take.
+    // We can use `parseParamsComptime` to parse a string into an array of `Param(Help)`.
+    const params = comptime clap.parseParamsComptime(
+        \\-h, --help           Display this help and exit.
+        \\-r, --relay <str>    A relay message to send.
+        \\-d, --dest <str>     An IPv4 or <= 4 ASCII byte string.
+        \\-c, --connect <str>  A connection message to send.
+        \\
+    );
+
+    // Initialize our diagnostics, which can be used for reporting useful errors.
+    // This is optional. You can also pass `.{}` to `clap.parse` if you don't
+    // care about the extra information `Diagnostics` provides.
+    var diag = clap.Diagnostic{};
+    var res = clap.parse(clap.Help, &params, clap.parsers.default, .{
+        .diagnostic = &diag,
+        .allocator = gpa,
+    }) catch |err| {
+        // Report useful error and exit.
+        diag.report(std.io.getStdErr().writer(), err) catch {};
+        return err;
     };
+    defer res.deinit();
 
-    const msg = SaprusMessage{
+    try SaprusClient.init();
-        .relay = .{
+    defer SaprusClient.deinit();
-            .header = .{ .dest = .{ 255, 255, 255, 255 } },
+
-            .payload = "Hello darkness my old friend",
+    if (res.args.help != 0) {
-        },
+        return clap.help(std.io.getStdErr().writer(), clap.Help, &params, .{});
+    }
+
+    if (res.args.relay) |r| {
+        const dest = parseDest(res.args.dest);
+        try SaprusClient.sendRelay(
+            if (r.len > 0) r else "Hello darkness my old friend",
+            dest,
+            gpa,
+        );
+        // std.debug.print("Sent: {s}\n", .{r});
+        return;
+    } else if (res.args.connect) |c| {
+        _ = SaprusClient.connect(if (c.len > 0) c else "Hello darkness my old friend", gpa) catch |err| switch (err) {
+            error.WouldBlock => null,
+            else => return err,
         };
+        return;
+    }
 
-    const msg_bytes = try msg.toBytes(allocator);
+    return clap.help(std.io.getStdErr().writer(), clap.Help, &params, .{});
-    defer allocator.free(msg_bytes);
+}
 
-    try network.init();
+fn parseDest(in: ?[]const u8) [4]u8 {
-    defer network.deinit();
+    if (in) |dest| {
+        if (dest.len <= 4) {
+            var res: [4]u8 = @splat(0);
+            @memcpy(res[0..dest.len], dest);
+            return res;
+        }
 
-    var sock = try network.Socket.create(.ipv4, .udp);
+        const addr = std.net.Ip4Address.parse(dest, 0) catch return "FAIL".*;
-    defer sock.close();
+        return @bitCast(addr.sa.addr);
-
+    }
-    try sock.setBroadcast(true);
+    return "zap\x00".*;
-
-    // Bind to 0.0.0.0:0
-    const bind_addr = network.EndPoint{
-        .address = network.Address{ .ipv4 = network.Address.IPv4.any },
-        .port = 0,
-    };
-
-    const dest_addr = network.EndPoint{
-        .address = network.Address{ .ipv4 = network.Address.IPv4.broadcast },
-        .port = 8888,
-    };
-
-    try sock.bind(bind_addr);
-
-    _ = try sock.sendTo(dest_addr, msg_bytes);
 }
 
 const builtin = @import("builtin");
 const std = @import("std");
-const Allocator = std.mem.Allocator;
+const DebugAllocator = std.heap.DebugAllocator(.{});
+const ArrayList = std.ArrayList;
 
-const network = @import("network");
+const zaprus = @import("zaprus");
+const SaprusClient = zaprus.Client;
+const SaprusMessage = zaprus.Message;
+
+const clap = @import("clap");

src/message.zig

@@ -0,0 +1,339 @@
+/// Type tag for Message union.
+/// This is the first value in the actual packet sent over the network.
+pub const PacketType = enum(u16) {
+    relay = 0x003C,
+    file_transfer = 0x8888,
+    connection = 0x00E9,
+    _,
+};
+
+/// Reserved option values.
+/// Currently unused.
+pub const ConnectionOptions = packed struct(u8) {
+    opt1: bool = false,
+    opt2: bool = false,
+    opt3: bool = false,
+    opt4: bool = false,
+    opt5: bool = false,
+    opt6: bool = false,
+    opt7: bool = false,
+    opt8: bool = false,
+};
+
+pub const Error = error{
+    NotImplementedSaprusType,
+    UnknownSaprusType,
+    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
+pub const Message = 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)];
+        }
+    };
+    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 = {},
+
+    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);
+        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(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) Error!(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 => 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);
+        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,
+        }
+    }
+
+    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 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,
+        };
+    }
+
+    pub fn asBytes(self: *Self) SelfBytes {
+        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 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 {
+    std.testing.refAllDeclsRecursive(@This());
+}

src/root.zig

@@ -0,0 +1,4 @@
+pub const Client = @import("Client.zig");
+pub const Connection = @import("Connection.zig");
+
+pub usingnamespace @import("message.zig");