Zig for network daemons: MTProto and AI experience

Zig in High-Load Network Services: Real-World Project Insights

In high-performance network services and edge applications, Zig shines with its explicit memory control and minimalist architecture. Two projects—a MTProto proxy and an AI agent infrastructure—demonstrate how the language handles zero-allocation parsing, bit manipulation, and strict RAM limits without C's security pitfalls or Rust's rigidity.

MTProto.zig disguises traffic as HTTPS to bypass deep packet inspection (DPI). Nullclaw packs an entire AI stack into a binary for 32 MB RAM devices, supporting hot-swappable providers.

Language Comparison on Key Aspects

| Criterion | C | Rust | Zig |

|-------------------|----------------------------|-----------------------------------|----------------------------------|

| Memory | Implicit, malloc in libs | Implicit, global allocator | Explicit, allocator as argument |

| Multithreading | Pthreads, manual sync | Send/Sync, Borrow Checker | Atomics, devolved to code |

| Errors | Return codes, errno | Result<T, E>, ? | !T, catch, errdefer |

| Metaprogramming | Preprocessor macros | Procedural macros | comptime |

| Build | CMake, Makefiles | Cargo | build.zig, LLVM out of the box |

Zig's explicit memory management eliminates hidden allocations, crucial for event loops on epoll.

MTProto.zig Architecture: Zero-Allocation and Slots

The server runs a single-threaded event loop with no per-connection threads. Instead of allocating for each client, it uses a pre-allocated pool of slots:

• Startup: Allocate an array of slots in static memory.
• New client: Grab a free slot in O(1).
• Reading: Async via epoll.
• Disconnect: Reset slot state.

This avoids heap fragmentation and OOM errors from long-lived idle sockets. In Rust, threads with 256 KB stacks would quickly exhaust RAM.

The classic threads + malloc approach leads to allocations in hot paths. Zig state machines deliver predictability.

Logging and Optimization Challenges

Zig's default logger blocks the event loop with blocking write() calls under load. Hundreds of log.debug calls from connections triggered cascading failures.

Solution: ReleaseFast build profile strips debug logs at compile time. Logging is moved out of hot paths.

Dynamic Dispatch in Nullclaw

For hot-swapping AI providers, it uses a vtable similar to the Linux kernel:

const AiProvider = struct {
    ptr: *anyopaque, // Raw pointer to state
    vtable: const VTable,

    pub const VTable = struct {
        generate_response: *const fn(ptr: *anyopaque, prompt: []const u8) anyerror![]const u8,
        deinit: *const fn(ptr: *anyopaque) void,
    };

    pub fn ask(self: AiProvider, prompt: []const u8) ![]const u8 {
        return self.vtable.generate_response(self.ptr, prompt);
    }
};

This enables fat-pointer-free calls with 2 ms cold starts. Rust's dyn Trait + Arc<Mutex<Box<dyn Provider>>> + Tokio bloats the binary.

Comptime for Fake TLS

Fake TLS 1.3 ServerHello generation happens at compile time:

const NGINX_HELLO_BYTES = comptime blk: {
    var template: [128]u8 = undefined;
    fillFakeTlsExtensions(&template);
    std.debug.assert(template.len == EXPECTED_TLS_SIZE);
    break :blk template;
};

The byte array is baked into .rodata. Runtime only patches session data—no allocations. Rust would need procedural macros.

Key Takeaways

• Explicit Memory: No hidden allocations, perfect for zero-copy parsing and edge devices.
• Comptime: Metaprogramming as regular code, generating valid packet structures at build time.
• Minimalism: Runtime-free binaries, cold starts <3 ms, strict RAM compliance.
• Vtable Dispatch: Plugin architecture without Rust trait overhead.
• Epoll + Slots: Scalability without threads, O(1) per connection.

Final Recommendations

Zig replaces C in low-level daemons with tight memory and performance demands. For complex team backends, Rust wins with compile-time checks. Zig's ecosystem is growing but requires caution with dependencies.

— Editorial Team