Added TLV encoding example in Zig

3 files changed, 116 insertions, 16 deletions

diff --git a/README.md b/README.md
index be5ffcf..490931c 100644
--- a/README.md
+++ b/README.md
@@ -16,22 +16,23 @@ running it.
 > also written in the most explicit way and lacks massively when it
 > comes to checking of errors etc.
 
-| Example                          | Compiler   | What does it do?                                               |
-|----------------------------------|------------|----------------------------------------------------------------|
-| [c-asm](./c-asm)                 | clang-17   | Calls a function written in ASM from C code.                   |
-| [c-embed](./c-embed)             | clang-17   | Embedding external resources in compiled binary.               |
-| [c-signals](./c-signals)         | clang-17   | Uses SIGUSR1 and SIGUSR2 as IPC mechanism.                     |
-| [c-structs](./c-structs)         | clang-17   | Saves and reads structs in/from binary files.                  |
-| [zig-c-interop](./zig-c-interop) | zig-0.11.0 | Uses functions written in C from Zig code.                     |
-| [zig-ppm](./zig-ppm)             | zig-0.11.0 | Creates an image with random pixels in PPM image format.       |
-| [zig-structs](./zig-structs)     | zig-0.11.0 | Serialization of a struct into JSON and then reading it back.  |
-| [zig-telnet](./zig-telnet)       | zig-0.11.0 | Connects to Redis server like it is a basic telnet server.     |
-| [zig-x11](./zig-x11)             | zig-0.11.0 | Uses X11 to create a basic window without any bindings needed. |
-| [zig-http](./zig-http)           | zig-0.11.0 | Basic example of a HTTP 1.1 server without any routing etc.    |
-| [zig-x11-box](./zig-x11-box)     | zig-0.11.0 | Move a box around with arrow keys with Xlib and Zig.           |
-| [zig-kv-store](./zig-kv-store)   | zig-0.11.0 | Simple Key-value store that mimics memcached written in Zig.   |
-| [zig-wad](./zig-wad)             | zig-0.11.0 | Reads doom.wad and extracts the identification header.         |
-| [zig-os-props](./zig-os-props)   | zig-0.11.0 | Detects properties of the target operating system.             |
+| Example                                | Compiler   | What does it do?                                               |
+|----------------------------------------|------------|----------------------------------------------------------------|
+| [c-asm](./c-asm)                       | clang-17   | Calls a function written in ASM from C code.                   |
+| [c-embed](./c-embed)                   | clang-17   | Embedding external resources in compiled binary.               |
+| [c-signals](./c-signals)               | clang-17   | Uses SIGUSR1 and SIGUSR2 as IPC mechanism.                     |
+| [c-structs](./c-structs)               | clang-17   | Saves and reads structs in/from binary files.                  |
+| [zig-c-interop](./zig-c-interop)       | zig-0.11.0 | Uses functions written in C from Zig code.                     |
+| [zig-ppm](./zig-ppm)                   | zig-0.11.0 | Creates an image with random pixels in PPM image format.       |
+| [zig-structs](./zig-structs)           | zig-0.11.0 | Serialization of a struct into JSON and then reading it back.  |
+| [zig-telnet](./zig-telnet)             | zig-0.11.0 | Connects to Redis server like it is a basic telnet server.     |
+| [zig-x11](./zig-x11)                   | zig-0.11.0 | Uses X11 to create a basic window without any bindings needed. |
+| [zig-http](./zig-http)                 | zig-0.11.0 | Basic example of a HTTP 1.1 server without any routing etc.    |
+| [zig-x11-box](./zig-x11-box)           | zig-0.11.0 | Move a box around with arrow keys with Xlib and Zig.           |
+| [zig-kv-store](./zig-kv-store)         | zig-0.11.0 | Simple Key-value store that mimics memcached written in Zig.   |
+| [zig-wad](./zig-wad)                   | zig-0.11.0 | Reads doom.wad and extracts the identification header.         |
+| [zig-os-props](./zig-os-props)         | zig-0.11.0 | Detects properties of the target operating system.             |
+| [zig-tlv-encoding](./zig-tlv-encoding) | zig-0.13.0 | Naive implementation of TLV encoding in Zig.                   |
 
 ## License
 
diff --git a/zig-tlv-encoding/Makefile b/zig-tlv-encoding/Makefile
new file mode 100644
index 0000000..98beea6
--- /dev/null
+++ b/zig-tlv-encoding/Makefile
@@ -0,0 +1,2 @@
+default:
+	zig test main.zig
diff --git a/zig-tlv-encoding/main.zig b/zig-tlv-encoding/main.zig
new file mode 100644
index 0000000..d7e2809
--- /dev/null
+++ b/zig-tlv-encoding/main.zig
@@ -0,0 +1,97 @@
+// TLV format: https://devopedia.org/tlv-format
+// Real world example: https://www.rfc-editor.org/rfc/rfc8609
+// Cool article: https://www.huy.rocks/everyday/12-11-2022-zig-using-zig-for-advent-of-code
+
+// Dummy TLV spec for encoding Linux devicei information
+//
+// Packet specification
+//   1byte    ... Tag
+//   2bytes   ... Length
+//   unknown  ... Value
+//
+// Available tags: { 0x00 = vendor_name, 0x01 = model_name }
+// Packet presented as a struct: Packet{ .vendor_name, .model_name }
+// This assumes that the max value length can be 255.
+//
+// Test data from `lsusb` (`lscpu`):
+// Bus 002 Device 003: ID 046d:086b Logitech, Inc. BRIO 4K Stream Edition
+// Bus 001 Device 009: ID 3434:0350 Keychron Keychron V5
+// Bus 001 Device 006: ID 2433:b200 ASETEK [NZXT Kraken X60]
+// Bus 001 Device 005: ID 046d:c548 Logitech, Inc. Logi Bolt Receiver
+
+const std = @import("std");
+
+const TLVTag = enum(u8) {
+    VENDOR_NAME = 0x00,
+    MODEL_NAME = 0x01,
+};
+
+const TLVPacket = struct {
+    tag: TLVTag,
+    length: u8,
+    value: std.ArrayList(u8),
+
+    pub fn printEncoded(self: *TLVPacket) void {
+        std.debug.print("\t", .{});
+        std.debug.print("{X:0>2}-", .{@intFromEnum(self.tag)});
+        std.debug.print("{X:0>2}-", .{self.length});
+
+        for (self.value.items) |val| {
+            std.debug.print("{X:0>2}", .{val});
+        }
+
+        std.debug.print("\n", .{});
+    }
+};
+
+const TLVPayload = struct {
+    packets: std.ArrayList(TLVPacket),
+    allocator: std.mem.Allocator,
+
+    pub fn init(allocator: std.mem.Allocator) TLVPayload {
+        return TLVPayload{
+            .packets = std.ArrayList(TLVPacket).init(allocator),
+            .allocator = allocator,
+        };
+    }
+
+    pub fn deinit(self: *TLVPayload) void {
+        for (self.packets.items) |*packet| {
+            packet.value.deinit();
+        }
+        self.packets.deinit();
+    }
+
+    pub fn append(self: *TLVPayload, tag: TLVTag, message: []const u8) !void {
+        var value = try std.ArrayList(u8).initCapacity(self.allocator, message.len);
+        try value.appendSlice(message);
+
+        try self.packets.append(.{
+            .tag = tag,
+            .length = @intCast(message.len),
+            .value = value,
+        });
+    }
+};
+
+test "Create TLV payload manually" {
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    defer _ = gpa.deinit();
+
+    var payload = TLVPayload.init(gpa.allocator());
+    defer payload.deinit();
+
+    try payload.append(.VENDOR_NAME, "Logitech, Inc.");
+    try payload.append(.MODEL_NAME, "BRIO 4K Stream Edition");
+
+    std.debug.print("Capacity: {d}\n", .{payload.packets.capacity});
+
+    for (payload.packets.items) |*packet| {
+        std.debug.print("Tag: {}, Length: {d}\n", .{ packet.tag, packet.length });
+        packet.printEncoded();
+    }
+}
+
+pub fn main() void {
+    std.debug.print("Use `make test` or `zig test main.zig` instead.\n", .{});
+}