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Refactor ESPNowBridge packet handling to use 2-byte magic header and improve packet size validation

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This commit is contained in:
João Brázio
2025-09-07 22:00:06 +01:00
parent 04e70829a4
commit 537449e6af
3 changed files with 89 additions and 38 deletions
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33
src/helpers/bridges/ESPNowBridge.h
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@@ -25,9 +25,9 @@
* - Maximum packet size of 250 bytes (ESP-NOW limitation)
*
* Packet Structure:
* [1 byte] Magic Header (0xAB) - Used to identify ESPNowBridge packets
* [2 bytes] Magic Header - Used to identify ESPNowBridge packets
* [2 bytes] Fletcher-16 checksum of encrypted payload (calculated over payload only)
* [n bytes] Encrypted payload containing the mesh packet
* [246 bytes max] Encrypted payload containing the mesh packet
*
* The Fletcher-16 checksum is used to validate packet integrity and detect
* corrupted or tampered packets. It's calculated over the encrypted payload
@@ -47,7 +47,7 @@
class ESPNowBridge : public AbstractBridge {
private:
static ESPNowBridge *_instance;
static void recv_cb(const uint8_t *mac, const uint8_t *data, int len);
static void recv_cb(const uint8_t *mac, const uint8_t *data, int32_t len);
static void send_cb(const uint8_t *mac, esp_now_send_status_t status);
/** Packet manager for allocating and queuing mesh packets */
@@ -60,18 +60,29 @@ private:
SimpleMeshTables _seen_packets;
/**
* Maximum ESP-NOW packet size (250 bytes)
* This is a hardware limitation of ESP-NOW protocol:
* - ESP-NOW header: 20 bytes
* - Max payload: 250 bytes
* Source: ESP-NOW API documentation
* ESP-NOW Protocol Structure:
* - ESP-NOW header: 20 bytes (handled by ESP-NOW protocol)
* - ESP-NOW payload: 250 bytes maximum
* Total ESP-NOW packet: 270 bytes
*
* Our Bridge Packet Structure (must fit in ESP-NOW payload):
* - Magic header: 2 bytes
* - Checksum: 2 bytes
* - Available payload: 246 bytes
*/
static const size_t MAX_ESPNOW_PACKET_SIZE = 250;
/**
* Magic byte to identify ESPNowBridge packets (0xAB)
* Size constants for packet parsing
*/
static const uint8_t ESPNOW_HEADER_MAGIC = 0xAB;
static const size_t MAGIC_HEADER_SIZE = 2;
static const size_t CHECKSUM_SIZE = 2;
static const size_t MAX_PAYLOAD_SIZE = MAX_ESPNOW_PACKET_SIZE - (MAGIC_HEADER_SIZE + CHECKSUM_SIZE);
/**
* Magic bytes to identify ESPNowBridge packets
*/
static const uint16_t ESPNOW_HEADER_MAGIC = 0xC03E;
/** Buffer for receiving ESP-NOW packets */
uint8_t _rx_buffer[MAX_ESPNOW_PACKET_SIZE];
@@ -106,7 +117,7 @@ private:
* @param data Received data
* @param len Length of received data
*/
void onDataRecv(const uint8_t *mac, const uint8_t *data, int len);
void onDataRecv(const uint8_t *mac, const uint8_t *data, int32_t len);
/**
* ESP-NOW send callback