WLED/wled00/wled_metadata.cpp

#include "ota_update.h"
#include "wled.h"

#define WLED_CUSTOM_DESC_MAGIC 0x57535453  // "WSTS" (WLED System Tag Structure)
#define WLED_CUSTOM_DESC_VERSION 1
#define WLED_RELEASE_NAME_MAX_LEN 48

// Compile-time validation that release name doesn't exceed maximum length
static_assert(sizeof(WLED_RELEASE_NAME) <= WLED_RELEASE_NAME_MAX_LEN, 
              "WLED_RELEASE_NAME exceeds maximum length of WLED_RELEASE_NAME_MAX_LEN characters");


/**
 * DJB2 hash function (C++11 compatible constexpr)
 * Used for compile-time hash computation to validate structure contents
 * Recursive for compile time: not usable at runtime due to stack depth
 * 
 * Note that this only works on strings; there is no way to produce a compile-time
 * hash of a struct in C++11 without explicitly listing all the struct members.
 * So for now, we hash only the release name.  This suffices for a "did you find 
 * valid structure" check.
 * 
 */
constexpr uint32_t djb2_hash_constexpr(const char* str, uint32_t hash = 5381) {
    return (*str == '\0') ? hash : djb2_hash_constexpr(str + 1, ((hash << 5) + hash) + *str);
}

/**
 * Runtime DJB2 hash function for validation
 */
inline uint32_t djb2_hash_runtime(const char* str) {
    uint32_t hash = 5381;
    while (*str) {
        hash = ((hash << 5) + hash) + *str++;
    }
    return hash;
}

// ------------------------------------
// GLOBAL VARIABLES
// ------------------------------------
// Structure instantiation for this build 
const wled_custom_desc_t __attribute__((section(BUILD_METADATA_SECTION))) WLED_BUILD_DESCRIPTION = {
    WLED_CUSTOM_DESC_MAGIC,                   // magic
    WLED_CUSTOM_DESC_VERSION,                 // version 
    TOSTRING(WLED_VERSION),
    WLED_RELEASE_NAME,                        // release_name
    std::integral_constant<uint32_t, djb2_hash_constexpr(WLED_RELEASE_NAME)>::value, // hash - computed at compile time; integral_constant enforces this
};

static const char repoString_s[] PROGMEM = WLED_REPO;
const __FlashStringHelper* repoString = FPSTR(repoString_s);

static const char productString_s[] PROGMEM = WLED_PRODUCT_NAME;
const __FlashStringHelper* productString = FPSTR(productString_s);

static const char brandString_s [] PROGMEM = WLED_BRAND;
const __FlashStringHelper* brandString = FPSTR(brandString_s);



/**
 * Extract WLED custom description structure from binary
 * @param binaryData Pointer to binary file data
 * @param dataSize Size of binary data in bytes
 * @param extractedDesc Buffer to store extracted custom description structure
 * @return true if structure was found and extracted, false otherwise
 */
bool findWledMetadata(const uint8_t* binaryData, size_t dataSize, wled_custom_desc_t* extractedDesc) {
    if (!binaryData || !extractedDesc || dataSize < sizeof(wled_custom_desc_t)) {
        return false;
    }

    for (size_t offset = 0; offset <= dataSize - sizeof(wled_custom_desc_t); offset++) {
        const wled_custom_desc_t* custom_desc = (const wled_custom_desc_t*)(binaryData + offset);
        
        // Check for magic number
        if (custom_desc->magic == WLED_CUSTOM_DESC_MAGIC) {
            // Found potential match, validate version
            if (custom_desc->desc_version != WLED_CUSTOM_DESC_VERSION) {
                DEBUG_PRINTF_P(PSTR("Found WLED structure at offset %u but version mismatch: %u\n"), 
                              offset, custom_desc->version);
                continue;
            }
            
            // Validate hash using runtime function
            uint32_t expected_hash = djb2_hash_runtime(custom_desc->release_name);
            if (custom_desc->hash != expected_hash) {
                DEBUG_PRINTF_P(PSTR("Found WLED structure at offset %u but hash mismatch\n"), offset);
                continue;
            }
            
            // Valid structure found - copy entire structure
            memcpy(extractedDesc, custom_desc, sizeof(wled_custom_desc_t));
            
            DEBUG_PRINTF_P(PSTR("Extracted WLED structure at offset %u: '%s'\n"), 
                          offset, extractedDesc->release_name);
            return true;
        }
    }
    
    DEBUG_PRINTLN(F("No WLED custom description found in binary"));
    return false;
}


/**
 * Check if OTA should be allowed based on release compatibility using custom description
 * @param binaryData Pointer to binary file data (not modified)
 * @param dataSize Size of binary data in bytes
 * @param errorMessage Buffer to store error message if validation fails 
 * @param errorMessageLen Maximum length of error message buffer
 * @return true if OTA should proceed, false if it should be blocked
 */

bool shouldAllowOTA(const wled_custom_desc_t& firmwareDescription, char* errorMessage, size_t errorMessageLen) {
  // Clear error message
  if (errorMessage && errorMessageLen > 0) {
    errorMessage[0] = '\0';
  }

  // Validate compatibility using extracted release name
  // We make a stack copy so we can print it safely
  char safeFirmwareRelease[WLED_RELEASE_NAME_MAX_LEN];
  strncpy(safeFirmwareRelease, firmwareDescription.release_name, WLED_RELEASE_NAME_MAX_LEN - 1);
  safeFirmwareRelease[WLED_RELEASE_NAME_MAX_LEN - 1] = '\0';
  
  if (strlen(safeFirmwareRelease) == 0) {
    return false;
  }  

  if (strncmp_P(safeFirmwareRelease, releaseString, WLED_RELEASE_NAME_MAX_LEN) != 0) {
    if (errorMessage && errorMessageLen > 0) {
      snprintf_P(errorMessage, errorMessageLen, PSTR("Firmware compatibility mismatch: current='%s', uploaded='%s'."), 
               releaseString, safeFirmwareRelease);
      errorMessage[errorMessageLen - 1] = '\0'; // Ensure null termination
    }
    return false;
  }

  // TODO: additional checks go here

  return true;
}