Use Client as var type instead of singleton

Use this from the relay message

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
@@ -34,33 +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,
     });
-    static_lib.addIncludePath(.{ .cwd_relative = "include" });
-    static_lib.linkLibC();
 
-    b.installArtifact(static_lib);
+    b.installArtifact(lib);
-
-    const dynamic_lib = b.addLibrary(.{
-        .linkage = .dynamic,
-        .name = "zaprus",
-        .root_module = lib_mod,
-    });
-    dynamic_lib.addIncludePath(.{ .cwd_relative = "include" });
-    dynamic_lib.linkLibC();
-
-    b.installArtifact(dynamic_lib);
-
-    // C Headers
-    const c_header = b.addInstallHeaderFile(b.path("include/zaprus.h"), "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.git#0a97b666677501db4939e3e8245f88a19e015893",
+            .hash = "gatorcat-0.3.4-WcrpTcleBwCta_9TjomuIGb3bdg2Pke_FXI_WkMTEivH",
+        },
     },
     .paths = .{
         "build.zig",

include/zaprus.h

@@ -1,51 +0,0 @@
-// client
-
-#include<stdint.h>
-#include<stdlib.h>
-
-int zaprus_init(void);
-
-int zaprus_deinit(void);
-
-int zaprus_send_relay(const char* payload, size_t len, char dest[4]);
-
-int zaprus_send_initial_connection(const char* payload, size_t len, uint16_t initial_port);
-
-struct SaprusMessage* zaprus_connect(const char* payload, size_t len);
-
-// message
-#define SAPRUS_RELAY_MESSAGE_TYPE 0x003C
-#define SAPRUS_FILE_TRANSFER_MESSAGE_TYPE 0x8888
-#define SAPRUS_CONNECTION_MESSAGE_TYPE 0x00E9
-
-struct SaprusMessage {
-  uint16_t packet_type;
-  uint16_t payload_len;
-  union {
-    struct {
-      struct {
-	char dest[4];
-      };
-    } relay;
-    struct {
-      struct {
-	uint16_t src_port;
-	uint16_t dest_port;
-	uint32_t seq_num;
-	uint32_t msg_id;
-	char _reserved;
-	char options;
-      };
-      
-    } connection;
-  } headers;
-  char *payload;
-};
-
-// ptr should be freed by the caller.
-int zaprus_message_to_bytes(struct SaprusMessage msg, char** ptr, size_t* len);
-
-// Return value should be destroyed with zaprus_message_deinit.
-struct SaprusMessage* zaprus_message_from_bytes(const char* bytes, size_t len);
-
-void zaprus_message_deinit(struct SaprusMessage* msg);

src/Client.zig

@@ -1,22 +1,88 @@
-var rand: ?Random = null;
+const base64Enc = std.base64.Base64Encoder.init(std.base64.standard_alphabet_chars, '=');
+const base64Dec = std.base64.Base64Decoder.init(std.base64.standard_alphabet_chars, '=');
 
-pub fn init() !void {
+rand: Random,
+socket: gcat.nic.RawSocket,
+
+const Self = @This();
+
+const max_message_size = 2048;
+
+pub fn init(interface_name: [:0]const u8) !Self {
     var prng = Random.DefaultPrng.init(blk: {
         var seed: u64 = undefined;
         try posix.getrandom(mem.asBytes(&seed));
         break :blk seed;
     });
-    rand = prng.random();
+    const rand = prng.random();
-    try network.init();
+
+    const socket: gcat.nic.RawSocket = try .init(interface_name);
+
+    return .{
+        .rand = rand,
+        .socket = socket,
+    };
 }
 
-pub fn deinit() void {
+pub fn deinit(self: *Self) void {
-    network.deinit();
+    self.socket.deinit();
 }
 
-fn broadcastSaprusMessage(msg: SaprusMessage, udp_port: u16, allocator: Allocator) !void {
+/// Used for relay messages and connection handshake.
-    const msg_bytes = try msg.toBytes(allocator);
+/// Assumes Client .init has been called.
-    defer allocator.free(msg_bytes);
+fn broadcastInitialInterestMessage(self: *Self, msg_bytes: []align(@alignOf(SaprusMessage)) u8) !void {
+    var packet_bytes: [max_message_size]u8 = comptime blk: {
+        var b: [max_message_size]u8 = @splat(0);
+
+        // Destination MAC addr to FF:FF:FF:FF:FF:FF
+        for (0..6) |i| {
+            b[i] = 0xff;
+        }
+
+        // Set Ethernet type to IPv4
+        b[0x0c] = 0x08;
+        b[0x0d] = 0x00;
+
+        // Set IPv4 version to 4
+        b[0x0e] = 0x45;
+
+        // Destination broadcast
+        for (0x1e..0x22) |i| {
+            b[i] = 0xff;
+        }
+
+        // Set TTL
+        b[0x16] = 0x40;
+
+        // Set IPv4 protocol to UDP
+        b[0x17] = 0x11;
+
+        // Set interest filter value to 8888.
+        b[0x24] = 0x22;
+        b[0x25] = 0xb8;
+        break :blk b;
+    };
+    var msg: *SaprusMessage = try .bytesAsValue(msg_bytes);
+    try msg.networkFromNativeEndian();
+    defer msg.nativeFromNetworkEndian() catch unreachable;
+
+    // The byte position within the packet that the saprus message starts at.
+    const saprus_start_byte = 42;
+    @memcpy(packet_bytes[saprus_start_byte .. saprus_start_byte + msg_bytes.len], msg_bytes);
+
+    try self.socket.linkLayer().send(packet_bytes[0 .. saprus_start_byte + msg_bytes.len]);
+}
+
+// fn broadcastSaprusMessage(msg_bytes: []align(@alignOf(SaprusMessage)) u8) !void {}
+
+fn broadcastSaprusMessage(msg_bytes: []align(@alignOf(SaprusMessage)) u8, udp_port: u16) !void {
+    if (false) {
+        var foo: gcat.nic.RawSocket = try .init("enp7s0"); // /proc/net/dev
+        defer foo.deinit();
+    }
+    const msg: *SaprusMessage = try .bytesAsValue(msg_bytes);
+    try msg.networkFromNativeEndian();
+    defer msg.nativeFromNetworkEndian() catch unreachable;
 
     var sock = try network.Socket.create(.ipv4, .udp);
     defer sock.close();
@@ -36,54 +102,57 @@ fn broadcastSaprusMessage(msg: SaprusMessage, udp_port: u16, allocator: Allocato
 
     try sock.bind(bind_addr);
 
+    std.debug.print("{x}\n", .{msg_bytes});
+
     _ = try sock.sendTo(dest_addr, msg_bytes);
 }
 
-pub fn sendRelay(payload: []const u8, dest: [4]u8, allocator: Allocator) !void {
+pub fn sendRelay(self: *Self, payload: []const u8, dest: [4]u8) !void {
-    const msg = SaprusMessage{
+    var buf: [max_message_size]u8 align(@alignOf(SaprusMessage)) = undefined;
-        .relay = .{
+    const msg_bytes = buf[0..try SaprusMessage.calcSize(
-            .header = .{ .dest = dest },
+        .relay,
-            .payload = payload,
+        base64Enc.calcSize(payload.len),
-        },
+    )];
-    };
+    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 self.broadcastInitialInterestMessage(msg_bytes);
 }
 
-fn randomPort() u16 {
+fn randomPort(self: Self) u16 {
-    var p: u16 = 0;
+    return self.rand.intRangeAtMost(u16, 1024, 65000);
-    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 {
+pub fn sendInitialConnection(
-    const dest_port = randomPort();
+    self: Self,
-    const msg = SaprusMessage{
+    payload: []const u8,
-        .connection = .{
+    output_bytes: []align(@alignOf(SaprusMessage)) u8,
-            .header = .{
+    initial_port: u16,
-                .src_port = initial_port,
+) !*SaprusMessage {
-                .dest_port = dest_port,
+    const dest_port = self.randomPort();
-            },
+    const msg_bytes = output_bytes[0..try SaprusMessage.calcSize(
-            .payload = payload,
+        .connection,
-        },
+        base64Enc.calcSize(payload.len),
-    };
+    )];
+    const msg: *SaprusMessage = .init(.connection, msg_bytes);
 
-    try broadcastSaprusMessage(msg, 8888, allocator);
+    const connection = (try msg.getSaprusTypePayload()).connection;
+    connection.src_port = initial_port;
+    connection.dest_port = dest_port;
+    _ = base64Enc.encode(connection.getPayload(), payload);
+
+    try broadcastSaprusMessage(msg_bytes, 8888);
 
     return msg;
 }
 
-pub fn connect(payload: []const u8, allocator: Allocator) !?SaprusMessage {
+pub fn connect(self: Self, payload: []const u8) !?SaprusConnection {
-    var initial_port: u16 = 0;
+    const initial_port = self.randomPort();
-    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();
@@ -98,21 +167,26 @@ pub fn connect(payload: []const u8, allocator: Allocator) !?SaprusMessage {
     try sock.setReadTimeout(1 * std.time.us_per_s);
     try sock.bind(bind_addr);
 
-    const msg = try sendInitialConnection(payload, initial_port, allocator);
+    var sent_msg_bytes: [max_message_size]u8 align(@alignOf(SaprusMessage)) = undefined;
+    const msg = try self.sendInitialConnection(payload, &sent_msg_bytes, initial_port);
 
-    var response_buf: [4096]u8 = undefined;
+    var response_buf: [max_message_size]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);
+    initial_conn_res = try .networkBytesAsValue(response_buf[0..len]);
 
     // Complete handshake after awaiting response
-    try broadcastSaprusMessage(msg, randomPort(), allocator);
+    try broadcastSaprusMessage(msg.asBytes(), self.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 +194,4 @@ const posix = std.posix;
 const mem = std.mem;
 
 const network = @import("network");
-
+const gcat = @import("gatorcat");
-const Allocator = mem.Allocator;

src/c_api.zig

@@ -1,115 +0,0 @@
-const c = @cImport({
-    @cInclude("zaprus.h");
-});
-
-fn zigToCMessage(msg: ?*zaprus.Message) !?*c.SaprusMessage {
-    if (msg) |m| {
-        var res = c.SaprusMessage{
-            .packet_type = @intFromEnum(m.*),
-        };
-        switch (m.*) {
-            .relay => |r| {
-                res.headers.relay = .{
-                    .unnamed_0 = .{
-                        .dest = r.header.dest,
-                    },
-                };
-                res.payload_len = @intCast(r.payload.len);
-                res.payload = (try allocator.alloc(u8, r.payload.len)).ptr;
-            },
-            .connection => |con| {
-                res.headers.connection = .{
-                    .unnamed_0 = .{
-                        .src_port = con.header.src_port,
-                        .dest_port = con.header.dest_port,
-                        .seq_num = con.header.seq_num,
-                        .msg_id = con.header.msg_id,
-                        ._reserved = con.header.reserved,
-                        .options = @bitCast(con.header.options),
-                    },
-                };
-
-                res.payload_len = @intCast(con.payload.len);
-                res.payload = (try allocator.alloc(u8, con.payload.len)).ptr;
-            },
-            .file_transfer => return zaprus.Error.NotImplementedSaprusType,
-            else => return zaprus.Error.UnknownSaprusType,
-        }
-        return &res;
-    } else return null;
-}
-
-fn cToZigMessage(msg: ?*c.SaprusMessage) ?*zaprus.Message {
-    _ = msg;
-    return @constCast(&zaprus.Message{
-        .relay = .{
-            .header = .{ .dest = @splat(0) },
-            .payload = &.{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: [*]u8) c_int {
-    SaprusClient.sendRelay(payload[0..len], dest[0..4].*, 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) ?*c.SaprusMessage {
-    if (SaprusClient.connect(payload[0..len], allocator)) |msg| {
-        return zigToCMessage(@constCast(&(msg.?))) catch null;
-    } else |_| {
-        return null;
-    }
-}
-
-// message
-
-/// ptr should be freed by the caller.
-export fn zaprus_message_to_bytes(msg: c.SaprusMessage, ptr: *[*]u8, len: *usize) c_int {
-    if (cToZigMessage(@constCast(&msg))) |m| {
-        const bytes = m.toBytes(allocator) catch return 1;
-        ptr.* = bytes.ptr;
-        len.* = bytes.len;
-        return 0;
-    } else return 1;
-}
-
-/// Return value should be destroyed with zaprus_message_deinit.
-export fn zaprus_message_from_bytes(bytes: [*]const u8, len: usize) ?*c.SaprusMessage {
-    if (zaprus.Message.fromBytes(bytes[0..len], allocator)) |msg| {
-        return zigToCMessage(@constCast(&msg)) catch null;
-    } else |_| return null;
-}
-
-export fn zaprus_message_deinit(msg: *c.SaprusMessage) void {
-    // noop
-    _ = msg;
-    // msg.*.deinit(allocator);
-}
-
-const std = @import("std");
-
-const zaprus = @import("./root.zig");
-const SaprusClient = zaprus.Client;
-
-const allocator = std.heap.c_allocator;
-
-test {
-    std.testing.refAllDeclsRecursively(@This());
-}

src/main.zig

@@ -42,40 +42,33 @@ pub fn main() !void {
     };
     defer res.deinit();
 
-    try SaprusClient.init();
-    defer SaprusClient.deinit();
-
     if (res.args.help != 0) {
         return clap.help(std.io.getStdErr().writer(), clap.Help, &params, .{});
     }
 
+    var client = try SaprusClient.init("enp7s0");
+    defer client.deinit();
+
     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(
+        try client.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| {
-        const conn_res: ?SaprusMessage = SaprusClient.connect(if (c.len > 0) c else "Hello darkness my old friend", gpa) catch |err| switch (err) {
+        _ = client.connect(if (c.len > 0) c else "Hello darkness my old friend") 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 +76,10 @@ 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) {
@@ -23,155 +20,255 @@ 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),
+        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.* - @bitSizeOf(Relay) / 8];
+        }
     };
-        header: Header,
+    const Connection = packed struct {
-        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 = .{},
-        };
+        payload: void,
-        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) Connection) []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.* - @bitSizeOf(Connection) / 8];
-            .relay => |r| allocator.free(r.payload),
+        }
-            .connection => |c| allocator.free(c.payload),
+
+        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.
+    /// This is used for creating new messages. For reading messages from the network,
+    /// see: networkBytesAsValue.
+    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;
+    }
+
+    /// Compute the number of bytes required to store a given payload size for a given message type.
+    pub fn calcSize(comptime @"type": PacketType, payload_len: usize) MessageTypeError!u16 {
+        const header_size = @bitSizeOf(switch (@"type") {
+            .relay => Relay,
+            .connection => Connection,
+            .file_transfer => return MessageTypeError.NotImplementedSaprusType,
+            else => return MessageTypeError.UnknownSaprusType,
+        }) / 8;
+        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);
+    }
+
+    /// Access the message Saprus payload.
+    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,
+        };
+    }
+
+    /// Convert the message to native endianness from network endianness in-place.
+    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(
+    /// Convert the message to network endianness from native endianness in-place.
-        header: anytype,
+    pub fn networkFromNativeEndian(self: *Self) MessageTypeError!void {
-        payload: []const u8,
+        try switch (try self.getSaprusTypePayload()) {
-        buf: *std.ArrayList(u8),
+            .relay => {},
-        allocator: Allocator,
+            .connection => |*con| con.*.networkFromNativeEndian(),
-    ) !void {
+            .file_transfer => MessageTypeError.NotImplementedSaprusType,
-        const Header = @TypeOf(header);
+            else => MessageTypeError.UnknownSaprusType,
-        // 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.
+        self.type = @enumFromInt(nativeToBig(
-        var payload_list = std.ArrayList(u8).init(allocator);
+            @typeInfo(@TypeOf(self.type)).@"enum".tag_type,
-        defer payload_list.deinit();
+            @intFromEnum(self.type),
-        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.
+    /// Convert network endian bytes to a native endian value in-place.
-    pub fn toBytes(self: Message, allocator: Allocator) ![]u8 {
+    pub fn networkBytesAsValue(bytes: SelfBytes) MessageParseError!*Self {
-        // Create a growable list of bytes to store the output in.
+        const res = std.mem.bytesAsValue(Self, bytes);
-        var buf = std.ArrayList(u8).init(allocator);
+        try res.nativeFromNetworkEndian();
-        errdefer buf.deinit();
+        return .bytesAsValue(bytes);
-
-        // 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.
+    /// Create a structured view of the bytes without initializing the length or type,
-        return buf.toOwnedSlice();
+    /// and without converting the endianness.
+    pub fn bytesAsValue(bytes: SelfBytes) MessageParseError!*Self {
+        const res = std.mem.bytesAsValue(Self, bytes);
+        return switch (res.type) {
+            .relay, .connection => if (bytes.len == res.length + @sizeOf(Self))
+                res
+            else
+                MessageParseError.InvalidMessage,
+            .file_transfer => MessageParseError.NotImplementedSaprusType,
+            else => MessageParseError.UnknownSaprusType,
+        };
     }
 
-    fn fromBytesAux(
+    /// Deprecated.
-        comptime packet: PacketType,
+    /// If I need the bytes, I should just pass around the slice that is backing this to begin with.
-        len: u16,
+    pub fn asBytes(self: *Self) SelfBytes {
-        r: std.io.FixedBufferStream([]const u8).Reader,
+        const size = @sizeOf(Self) + self.length;
-        allocator: Allocator,
+        return @as([*]align(@alignOf(Self)) u8, @ptrCast(self))[0..size];
-    ) !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" {
+    {
+        // Relay test
+        const payload = "Hello darkness my old friend";
+        var msg_bytes: [try Message.calcSize(.relay, payload.len)]u8 align(@alignOf(Message)) = undefined;
+
+        // Create a view of the byte slice as a Message
+        const msg: *Message = .init(.relay, &msg_bytes);
+
+        {
+            // 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);
+        }
+
+        {
+            // 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("relay network bytes: {x}\n", .{msg_bytes});
+            std.debug.print("bytes len: {d}\n", .{msg_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()));
+    }
+
+    {
+        // Connection test
+        const payload = "Hello darkness my old friend";
+        var msg_bytes: [try Message.calcSize(.connection, payload.len)]u8 align(@alignOf(Message)) = undefined;
+
+        // Create a view of the byte slice as a Message
+        const msg: *Message = .init(.connection, &msg_bytes);
+
+        {
+            // Initializing connection header values
+            const connection = (try msg.getSaprusTypePayload()).connection;
+            connection.src_port = 1;
+            connection.dest_port = 2;
+            connection.seq_num = 3;
+            connection.msg_id = 4;
+            connection.reserved = 5;
+            connection.options = @bitCast(@as(u8, 6));
+            @memcpy(connection.getPayload(), payload);
+        }
+
+        {
+            // 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("connection network bytes: {x}\n", .{msg_bytes});
+            std.debug.print("bytes len: {d}\n", .{msg_bytes.len});
+        }
+    }
+}
+
 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" {
+    if (false) {
         const gpa = std.testing.allocator;
         const msg = Message{
             .relay = .{
@@ -187,9 +284,12 @@ test "Round trip Relay toBytes and fromBytes" {
         defer from_bytes.deinit(gpa);
 
         try std.testing.expectEqualDeep(msg, from_bytes);
+    }
+    return error.SkipZigTest;
 }
 
 test "Round trip Connection toBytes and fromBytes" {
+    if (false) {
         const gpa = std.testing.allocator;
         const msg = Message{
             .connection = .{
@@ -208,4 +308,10 @@ test "Round trip Connection toBytes and fromBytes" {
         defer from_bytes.deinit(gpa);
 
         try std.testing.expectEqualDeep(msg, from_bytes);
+    }
+    return error.SkipZigTest;
+}
+
+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");