MTProto Proxy Architecture

MTProto Proxy Architecture (Current)

This project is a production MTProto proxy in Zig with FakeTLS fronting, active anti-replay protection, and Linux-first deployment.

Build Artifacts

The project produces two binaries via build.zig:

Cross-compile for production: make build (or zig build -Doptimize=ReleaseFast -Dtarget=x86_64-linux -Dcpu=x86_64_v3).

Runtime Model

• Single-threaded network core: one Linux epoll event loop handles socket I/O.
• No thread-per-connection: connection handling is state-machine driven.
• Connection slots are allocated lazily and reused.
• Per-connection heavy buffers are on-demand, not permanently embedded in idle slots.

Primary file: src/proxy/proxy.zig.

Core Flow

1. Accept client socket (non-blocking).
2. Parse TLS ClientHello record header/body incrementally.
3. Validate TLS-auth HMAC.
4. Validate SNI against configured tls_domain.
5. Build/send fake ServerHello (+ optional split/desync behavior).
6. Read 64-byte MTProto obfuscation handshake.
7. Resolve route: direct DC or MiddleProxy route.
8. Enter relay mode (C2S/S2C transform pipeline).

Relay Pipeline

C2S

• TLS unwrap
• client AES-CTR decrypt
• transport encapsulation:
  • direct DC: AES-CTR encrypt for DC
  • MiddleProxy: RPC_PROXY_REQ framing + CBC layer

S2C

• transport decapsulation/decrypt
• client-side AES-CTR encrypt (unless fast-mode path)
• TLS application record wrapping

MiddleProxy

• Runtime path is non-blocking and event-loop integrated.
• Legacy blocking handshake helpers were removed.
• Endpoint/secret metadata refresh is periodic.

Anti-Replay

• Handshake digest is validated with timestamp skew window.
• Replay cache key uses canonical HMAC value from validation path.

Message Queue Strategy

• Write path uses chained blocks + writev flush.
• Queue head uses index progression (not repeated orderedRemove(0) hot-path shifts).

mtbuddy (Installer & Control Panel)

Source tree: src/ctl/. Interactive TUI with raw terminal mode, arrow-key navigation, and Unicode box-drawing.

Key modules:

Deployment Layout (Server)

/opt/mtproto-proxy/
├── mtproto-proxy          # proxy binary
├── config.toml            # runtime configuration
├── env.sh                 # optional env vars (TAG, etc.)
└── monitor/               # dashboard assets (optional)

/usr/local/bin/mtbuddy     # installer/control binary
/etc/systemd/system/mtproto-proxy.service

Platform Scope

• Linux-only runtime target.
• macOS is supported for development/cross-compile, not for production runtime.

Design Principles

• Keep the hot path non-blocking.
• Favor explicit state transitions over hidden control flow.
• Keep security checks in the handshake path strict and cheap.
• Avoid stale parallel implementations of the same protocol path.