proto_frame.h

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#pragma once
 
/// @file proto_frame.h
/// @brief IO-Homecontrol 2W frame container: control bytes, IoFrame and (de)serialization.
/// @ingroup hioc_protocol
///
/// IO-Homecontrol is a proprietary wireless protocol used by Somfy, Velux, and other
/// manufacturers for controlling shutters, awnings, blinds, and similar devices.
/// "2W" means two-way: the controller sends commands and receives status feedback.
///
/// The protocol uses FSK modulation at 868 MHz with frequency hopping across 3 channels.
/// Communication is encrypted with AES-128 and authenticated with a 6-byte HMAC.
/// Each installation has a unique 16-byte "system key" shared between controller and devices.
///
/// This header owns only the frame container itself. The rest of the protocol model lives in
/// cohesive headers (proto_sizes/proto_timing/proto_constants/proto_device_model/proto_codecs).
/// New code should include the specific header it needs.
 
#include "proto_sizes.h"
 
#include <cstdint>
#include <cstring>
#include <string>
 
namespace esphome {
namespace home_io_control {
 
// ============================================================================
// Control Bytes
// ============================================================================
 
/// Control byte 0 (CTRL0) bit definitions.
/// CTRL0 encodes frame flags and the total frame length.
/// Bits [4:0] = frame_length - 1 (so 0x08 means 9 bytes total).
/// - START (bit 6): first frame in an exchange. Its TX preamble depends on CTRL1_LOW_POWER, not on
///   START alone: a low-power target gets the 1024-byte wake-up burst, others a normal preamble.
/// - END (bit 7): last frame in an exchange; set on responses and command completions.
/// - 1W (bit 5): 1=OneWay protocol (no response expected), 0=TwoWay (response expected).
/// For 2W operation, the controller sets START on initial command and device replies with END; subsequent frames in an
/// authenticated exchange also carry END.
static constexpr uint8_t CTRL0_END = 0x80;          ///< Bit 7: last frame in exchange
static constexpr uint8_t CTRL0_START = 0x40;        ///< Bit 6: first frame in exchange
static constexpr uint8_t CTRL0_PROTOCOL_1W = 0x20;  ///< Bit 5: 1=OneWay protocol, 0=TwoWay protocol
static constexpr uint8_t CTRL0_LENGTH_MASK = 0x1F;  ///< Bits [4:0]: frame length - 1
 
/// Ties `FRAME_MAX_DECLARED_SIZE` (proto_sizes.h) to the mask that actually defines it. The two
/// can't be expressed as one expression across the header boundary (proto_sizes.h can't include
/// this header back without a cycle), so this assert is the drift guard instead.
static_assert(FRAME_MAX_DECLARED_SIZE == CTRL0_LENGTH_MASK + 1,
              "FRAME_MAX_DECLARED_SIZE must track CTRL0_LENGTH_MASK's 5-bit field");
 
/// Control byte 1 (CTRL1) bit definitions.
/// CTRL1 carries protocol metadata flags that describe the frame's routing,
/// power mode, and priority characteristics.
/// - VERSION (bits [1:0]): protocol version number (usually 0 for current devices).
/// - PRIORITY (bit 2): marks a high-priority frame (e.g., discovery, security commands).
/// - ACK (bit 4): sender can handle 2W responses (set on all outbound 2W frames).
/// - LOW_POWER (bit 5): device is battery/solar powered; may sleep and requires long preamble to
///   wake. Set from the target's per-device YAML `low_power` class (default false); drives both
///   this bit and the start-frame preamble (see proto_commands.h, exchange_engine.cpp).
/// - ROUTED (bit 6): frame was relayed through a repeater node rather than direct.
/// - BEACON (bit 7): beacon announcement frame (device presence advertisement).
static constexpr uint8_t CTRL1_VERSION_MASK = 0x03;  ///< Bits [1:0]: protocol version (usually 0).
static constexpr uint8_t CTRL1_PRIORITY = 0x04;      ///< Bit 2: high-priority frame.
static constexpr uint8_t CTRL1_ACK = 0x10;           ///< Bit 4: sender can handle 2W responses (ACK-capable).
static constexpr uint8_t CTRL1_LOW_POWER = 0x20;     ///< Bit 5: low-power device (e.g., solar-powered).
static constexpr uint8_t CTRL1_ROUTED = 0x40;        ///< Bit 6: frame was relayed through a repeater.
static constexpr uint8_t CTRL1_BEACON = 0x80;        ///< Bit 7: beacon announcement frame.
 
// ============================================================================
// Frame Structure
// ============================================================================
 
/// @brief Parsed IO‑Homecontrol frame (CTRL0/1 + addresses + command + data).
/// @ingroup hioc_protocol
///
/// Over the air layout: [CTRL0][CTRL1][DST 3B][SRC 3B][CMD][DATA 0-23B][MAC 0/6B][CRC 2B].
/// The on-air CRC is the radio driver's responsibility (hardware or software,
/// depending on the chip); it is not included in this struct.
///
/// The MAC trailer exists because at least one frame shape's authenticator does not fit inside
/// CTRL0's 5-bit length field alongside its payload: a 1W CMD 0x30 "add controller" frame is 29
/// declared bytes plus a 6-byte MAC, and 35 has no 5-bit encoding. That MAC rides after the
/// declared length instead — still under the CRC, but outside what CTRL0's length bits describe
/// — so it is modeled as a distinct trailer rather than folded into `data[]`. `has_mac` is false
/// for every frame shape that predates this (i.e. everything except a MAC-bearing 1W frame), so
/// `data_len`/`frame_length()` keep meaning exactly what they meant before this field existed.
struct IoFrame {
  uint8_t ctrl0;                      ///< Control byte 0: flags + length.
  uint8_t ctrl1;                      ///< Control byte 1: low power, beacon, etc.
  uint8_t dst[NODE_ID_SIZE];          ///< Destination node ID (3 bytes).
  uint8_t src[NODE_ID_SIZE];          ///< Source node ID (3 bytes).
  uint8_t cmd;                        ///< Command ID.
  uint8_t data[FRAME_MAX_DATA_SIZE];  ///< Command parameters (0–23 bytes). Never includes `mac`.
  uint8_t data_len;                   ///< Actual length of data. `FRAME_MIN_SIZE + data_len == frame_length()`
                                      ///< always holds, trailer or not — see `mac`/`has_mac`.
  uint8_t mac[HMAC_SIZE];             ///< Out-of-length authenticator trailer; meaningful only when `has_mac`.
  bool has_mac = false;               ///< True if this frame carries the `mac` trailer (see struct doc).
};
 
// --- Frame construction and parsing ---
/// Initialize an IoFrame header (ctrl0/ctrl1) with flags.
///
/// Note: CTRL1_ACK is NOT automatically set on outbound frames. Some real-world
/// devices reject frames with unexpected CTRL1 bits, causing total communication
/// failure. The ACK constant is retained for inbound frame parsing and logging only.
/// @param f Frame to initialize.
/// @param is_2w True for 2‑way (default), false for 1‑way.
/// @param start Set START flag (first frame in exchange).
/// @param end Set END flag (final frame in exchange).
/// @param low_power Set LOW_POWER flag.
void init_frame(IoFrame &f, bool is_2w = true, bool start = false, bool end = false, bool low_power = false);
/// Set destination node ID.
/// @param f Frame to modify.
/// @param id 3‑byte destination address.
void set_dst(IoFrame &f, const uint8_t id[NODE_ID_SIZE]);
/// Set source node ID.
/// @param f Frame to modify.
/// @param id 3‑byte source address.
void set_src(IoFrame &f, const uint8_t id[NODE_ID_SIZE]);
/// Set command and payload.
/// @param f Frame to modify.
/// @param cmd Command ID.
/// @param params Pointer to payload bytes (may be nullptr for zero‑length).
/// @param params_len Payload length (0–23).
/// @return true if frame fits within size limits; false otherwise.
bool set_cmd(IoFrame &f, uint8_t cmd, const uint8_t *params = nullptr, uint8_t params_len = 0);
/// Get total frame length from ctrl0.
/// @param f Parsed frame.
/// @return Length in bytes.
uint8_t frame_length(const IoFrame &f);
/// Check START flag.
/// @param f Parsed frame.
/// @return true if START flag is set.
bool is_start(const IoFrame &f);
/// Check END flag.
/// @param f Parsed frame.
/// @return true if END flag is set.
bool is_end(const IoFrame &f);
/// Whether wire frames for a command carry the out-of-length MAC trailer described on
/// `IoFrame::has_mac`/`IoFrame::mac`. This exists because CTRL0's 5-bit length field cannot
/// describe every command's declared payload plus a 6-byte authenticator in one span — one
/// command's authenticator is carried outside the declared length instead (see the command's own
/// Doxygen in proto_constants.h for why). `parse()` consults this before it will accept the
/// wider `declared_len + HMAC_SIZE` buffer shape for a given command, so an unrelated frame that
/// merely happens to arrive with 6 extra trailing bytes is never mistaken for a trailer-bearing
/// one — only a command that genuinely carries a trailer gets the wider shape considered at all.
/// @param cmd Command byte (`IoFrame::cmd`, or the raw byte at `FRAME_CMD_OFFSET` in a wire buffer).
/// @return true if `cmd`'s wire frames carry the `mac` trailer after the declared length.
bool frame_carries_mac_trailer(uint8_t cmd);
/// Serialize a parsed frame into a wire buffer (without CRC).
/// @param f Parsed frame. When `f.has_mac`, the 6-byte `mac` trailer is appended after the
///   declared payload and counted in the returned length, so a caller's CRC (computed over the
///   returned length) covers it.
/// @param buf Output buffer (must be at least frame_length(f) bytes, or +HMAC_SIZE when `f.has_mac`).
/// @param buf_size Size of buf.
/// @return Number of bytes written (declared length, plus HMAC_SIZE when `f.has_mac`), or 0 on failure.
uint8_t serialize(const IoFrame &f, uint8_t *buf, uint8_t buf_size);
/// Parse a wire buffer into a parsed IoFrame (validates length and CTRL0).
/// @param buf Raw byte buffer.
/// @param buf_len Number of bytes in buf. Accepted shapes: exactly the CTRL0-declared length
///   (`has_mac` comes out false), or — only for a command where `frame_carries_mac_trailer()` is
///   true — that length plus HMAC_SIZE (the trailing bytes are copied into `f.mac` and `has_mac`
///   comes out true). Any other length, or that same wider length for a command that doesn't
///   carry a trailer, is rejected. `data_len` is always `buf_len`'s declared portion minus
///   FRAME_MIN_SIZE — the trailer is never data.
/// @param f Output parsed frame.
/// @return true if parse succeeded; false otherwise.
bool parse(const uint8_t *buf, uint8_t buf_len, IoFrame &f);
 
// ============================================================================
// Node ID Helpers
// ============================================================================
 
/// @brief Convert a hex string (e.g., "123ABC") to a byte array.
/// @param hex Hex string (must be exactly len*2 characters).
/// @param out Output buffer (at least len bytes).
/// @param len Number of bytes to produce.
/// @return true on success; false if hex length mismatch or non‑hex characters.
bool hex_to_bytes(const std::string &hex, uint8_t *out, uint8_t len);
/// @brief Format a 3‑byte node ID as a 6‑character uppercase hex string.
/// @param id 3‑byte node ID.
/// @return Hex string (e.g., "123ABC").
std::string node_id_to_string(const uint8_t id[NODE_ID_SIZE]);
 
// ============================================================================
// CRC
// ============================================================================
 
/// @brief Compute CRC‑CCITT (poly 0x1021, init 0x0000) over a buffer.
/// Used by radio drivers without hardware IO-Homecontrol CRC support and by
/// frame validation in tests.
/// @param data Pointer to data bytes.
/// @param len Number of bytes.
/// @return 16‑bit CRC value.
uint16_t crc_ccitt(const uint8_t *data, uint8_t len);
 
}  // namespace home_io_control
}  // namespace esphome