# ESP32 Serial Swiss Army Knife

![ESP32 Serial Swiss Army Knife logo](/images/logo.png "ESP32 Serial Swiss Army Knife")

ESP32-S3 firmware for a secure, multi-transport RS-232 adapter. It operates one MAX3243-backed UART1 serial port and safely shares it between native USB CDC-ACM, an HTTPS/WebSocket browser terminal, and SSH: one connected client can write while others observe. The firmware also provides persistent serial and Wi-Fi configuration, a UART0 recovery console, and hardware diagnostics; it is not a general-purpose router, captive portal, or unauthenticated TCP serial server.

## Initial hardware target

- ESP32-S3-DevKitC-1-compatible development board
- ESP32-S3-WROOM-1-N16R8 module
- 16 MB flash
- 8 MB octal PSRAM
- Adafruit MAX3243 full-pinout RS-232 breakout; the male connector version is preferred (see [Hardware wiring](docs/wiring.md) for supported connector variants)

## Development status

Hardware characterization, the serial core, USB CDC-ACM, Wi-Fi, HTTPS/WebSocket, SSH serial transport, and the local display/control interface are implemented and Phase 7 target-hardware validated. Phase 8A's bounded role-based user database and UART0 administration, Phase 8B's role-aware HTTPS/SSH authentication and revocation, and Phase 8C's shared UART0/admin-SSH command shell are target-hardware validated. Phase 8D.3 browser login/logout is implemented, host-tested and build-verified; [M1 is validated by user sign-off](docs/phase8d3_implementation.md) after both-role login, mixed-client operation and post-soak evidence. Numeric memory reserve gates remain open. Browser admin-shell mode, typed settings, and contextual administration remain planned, including preserving serial writer ownership across future terminal-mode changes. Configurable STA-only mDNS naming as `sak-<suffix>.local` is implemented with independent NVS persistence; target-hardware validation is pending. See the [Roadmap](docs/roadmap.md) for phase status and validation details.

## Documentation

- [Hardware wiring](docs/wiring.md): hardware profile, GPIO assignments, connector guidance, and safety notes.
- [Electrical tests](docs/electrical_tests.md): OLED/buttons, MAX3243, UART loopback, and session-broker verification procedures.
- [Role-based user database and UART0 administration](docs/user_administration_tests.md): user migration and administration, HTTPS/SSH authentication, session revocation, and the planned integrated web-administration acceptance matrix.
- [Command reference](docs/command_reference.md): UART0/admin-SSH administration, serial, broker, USB, Wi-Fi, mDNS, web, SSH, and diagnostic commands.

## Flash partition layout

The N16R8 target has 16 MiB flash and 8 MiB octal PSRAM. PlatformIO uses the custom [`partitions.csv`](partitions.csv) layout:

| Partition | Offset | Size | Purpose |
|---|---:|---:|---|
| `nvs` | `0x009000` | 512 KiB | Serial, Wi-Fi, mDNS hostname, local-display, role-based user, legacy recovery credential, HTTPS identity, and SSH host-key data |
| `otadata` | `0x089000` | 8 KiB | Active OTA-slot selection metadata |
| `phy_init` | `0x08B000` | 4 KiB | Optional PHY initialization data |
| `nvs_key` | `0x08C000` | 4 KiB | Reserved for future encrypted-NVS keys |
| `coredump` | `0x08D000` | 128 KiB | Reserved for flash core dumps |
| `ota_0` | `0x0B0000` | 4 MiB | Primary application/OTA slot |
| `ota_1` | `0x4B0000` | 4 MiB | Alternate application/OTA slot |
| `storage` | `0x8B0000` | 7488 KiB | Reserved for future LittleFS web assets, logs, and files |

Application offsets are aligned to the ESP32-S3's required 64 KiB boundary. The final storage partition ends at `0x1000000`, exactly the end of the 16 MiB flash chip.

The table reserves OTA and storage space; it does not implement OTA downloads, rollback confirmation, core-dump handling, NVS encryption, or filesystem mounting.

### One-time migration from the default partition table

The previous 1 MiB factory application began at `0x10000`, which now lies inside the enlarged NVS range. A normal upload does not erase stale data in that range. When first switching to this layout, erase the flash completely:

```sh
pio run --target erase
pio run --target upload
pio device monitor -b 115200
```

This removes saved serial configuration and all other flash contents. The firmware recreates NVS with safe defaults. Subsequent ordinary uploads do not need a full erase.

## Build

```sh
pio run
```

## Upload and monitor

Connect the board's **USB-to-UART** port for firmware upload and the UART0 development console, then run:

```sh
pio run --target upload
pio device monitor -b 115200
```

The firmware provides an interactive UART0 console at `serial-tool>`. Run `help` for available commands. The USB-to-UART bridge normally appears as `/dev/ttyUSB*`; it is separate from the native USB CDC serial transport, which normally appears as `/dev/ttyACM*`.

The console supports session history, line editing, cursor movement, and hierarchical Tab completion. After an unattended boot, attach an ANSI-capable terminal and press Enter once to enable enhanced editing; this avoids blocking while no terminal is attached.

Serial, Wi-Fi, and mDNS hostname edits remain in RAM until explicitly saved with `serial save`, `wifi save`, or `mdns save`. Authenticated admin SSH sessions expose the shared operational administration registry, including interactive secrets, recovery-material management, network diagnostics, and deferred reboot/SSH lifecycle commands. Initial administrator bootstrap and explicit recovery of an unavailable user database remain UART0-only. An administrator also cannot generate a replacement password for its own account over SSH, preventing the one-time value from being lost when that mutation revokes the session. `web credentials show` exposes only the legacy migration/recovery credential, not an active Phase 8B network login.

## Security notes

The HTTPS interface uses a device-specific self-signed certificate and a same-origin login page with bounded server-side cookie sessions; HTTP Basic is no longer accepted. Open `/` or `/login`, sign in with a user-database password, and use **Sign out** before switching accounts. Four sessions have a one-hour absolute lifetime, including active serial connections; logout closes only that session's serial access. Login is globally limited to five credential verifications per 60 seconds, with explicit capacity/backoff errors. Direct-IP and mDNS access use separate host-only Secure/HttpOnly/SameSite=Strict cookies. Non-browser clients also require cookies, strict Origin and CSRF for mutations rather than Basic credentials. There is no plaintext HTTP or TCP serial listener. SSH accepts role-based passwords and authorized Ed25519/ECDSA P-256 public keys. User passwords are stored as salted PBKDF2-HMAC-SHA256 verifiers, but the legacy recovery password, HTTPS private key, SSH private key, and Wi-Fi credentials remain recoverable from unencrypted application-owned NVS blobs. Offline password guessing and stale append-oriented flash copies also remain possible. The reserved `nvs_key` partition does not enable encryption. Do not treat this firmware as resistant to physical flash or RAM extraction until the planned hardening work is complete.

## License

This project is licensed under the [GNU General Public License version 3 only](LICENSE) (`GPL-3.0-only`). Third-party components remain subject to their respective licenses. The integration baseline uses Espressif registry components `espressif/mdns` `1.12.0`, `wolfssl/wolfssl` `5.8.2~1`, and `wolfssl/wolfssh` `1.4.20`; review upstream security releases before production use.