json_util.h

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#pragma once
 
#include <cstring>
#include <string>
#include <vector>
 
#include "esphome/core/defines.h"
#include "esphome/core/helpers.h"
 
#define ARDUINOJSON_ENABLE_STD_STRING 1  // NOLINT
 
#define ARDUINOJSON_USE_LONG_LONG 1  // NOLINT
 
#include <ArduinoJson.h>
 
namespace esphome::json {
 
template<size_t STACK_SIZE = 640> class SerializationBuffer {
 public:
  static constexpr size_t BUFFER_SIZE = STACK_SIZE;  
 
  explicit SerializationBuffer(size_t size) : size_(size) {
    if (size + 1 <= STACK_SIZE) {
      buffer_ = stack_buffer_;
    } else {
      heap_buffer_ = new char[size + 1];
      buffer_ = heap_buffer_;
    }
    buffer_[0] = '\0';
  }
 
  ~SerializationBuffer() { delete[] heap_buffer_; }
 
  // Move constructor - works with same template instantiation
  SerializationBuffer(SerializationBuffer &&other) noexcept : heap_buffer_(other.heap_buffer_), size_(other.size_) {
    if (other.buffer_ == other.stack_buffer_) {
      // Stack buffer - must copy content
      std::memcpy(stack_buffer_, other.stack_buffer_, size_ + 1);
      buffer_ = stack_buffer_;
    } else {
      // Heap buffer - steal ownership
      buffer_ = heap_buffer_;
      other.heap_buffer_ = nullptr;
    }
    // Leave moved-from object in valid empty state
    other.stack_buffer_[0] = '\0';
    other.buffer_ = other.stack_buffer_;
    other.size_ = 0;
  }
 
  // Move assignment
  SerializationBuffer &operator=(SerializationBuffer &&other) noexcept {
    if (this != &other) {
      delete[] heap_buffer_;
      heap_buffer_ = other.heap_buffer_;
      size_ = other.size_;
      if (other.buffer_ == other.stack_buffer_) {
        std::memcpy(stack_buffer_, other.stack_buffer_, size_ + 1);
        buffer_ = stack_buffer_;
      } else {
        buffer_ = heap_buffer_;
        other.heap_buffer_ = nullptr;
      }
      // Leave moved-from object in valid empty state
      other.stack_buffer_[0] = '\0';
      other.buffer_ = other.stack_buffer_;
      other.size_ = 0;
    }
    return *this;
  }
 
  // Delete copy operations
  SerializationBuffer(const SerializationBuffer &) = delete;
  SerializationBuffer &operator=(const SerializationBuffer &) = delete;
 
  const char *c_str() const { return buffer_; }
  const char *data() const { return buffer_; }
  size_t size() const { return size_; }
 
  operator std::string() const { return std::string(buffer_, size_); }  // NOLINT(google-explicit-constructor)
 
 private:
  friend class JsonBuilder;  
 
  char *data_writable_() { return buffer_; }
  void set_size_(size_t size) {
    size_ = size;
    buffer_[size] = '\0';
  }
 
  void reallocate_heap_(size_t size) {
    delete[] heap_buffer_;
    heap_buffer_ = new char[size + 1];
    buffer_ = heap_buffer_;
    size_ = size;
    buffer_[0] = '\0';
  }
 
  char stack_buffer_[STACK_SIZE];
  char *heap_buffer_{nullptr};
  char *buffer_;
  size_t size_;
};
 
#ifdef USE_PSRAM
// Build an allocator for the JSON Library using the RAMAllocator class
// This is only compiled when PSRAM is enabled
struct SpiRamAllocator : ArduinoJson::Allocator {
  void *allocate(size_t size) override {
    RAMAllocator<uint8_t> allocator;
    return allocator.allocate(size);
  }
 
  void deallocate(void *ptr) override {
    // ArduinoJson's Allocator interface doesn't provide the size parameter in deallocate.
    // RAMAllocator::deallocate() requires the size, which we don't have access to here.
    // RAMAllocator::deallocate implementation just calls free() regardless of whether
    // the memory was allocated with heap_caps_malloc or malloc.
    // This is safe because ESP-IDF's heap implementation internally tracks the memory region
    // and routes free() to the appropriate heap.
    free(ptr);  // NOLINT(cppcoreguidelines-owning-memory,cppcoreguidelines-no-malloc)
  }
 
  void *reallocate(void *ptr, size_t new_size) override {
    RAMAllocator<uint8_t> allocator;
    return allocator.reallocate(static_cast<uint8_t *>(ptr), new_size);
  }
};
#endif
 
using json_parse_t = std::function<bool(JsonObject)>;
 
using json_build_t = std::function<void(JsonObject)>;
 
SerializationBuffer<> build_json(const json_build_t &f);
 
bool parse_json(const std::string &data, const json_parse_t &f);
bool parse_json(const uint8_t *data, size_t len, const json_parse_t &f);
 
JsonDocument parse_json(const uint8_t *data, size_t len);
inline JsonDocument parse_json(const std::string &data) {
  return parse_json(reinterpret_cast<const uint8_t *>(data.c_str()), data.size());
}
 
class JsonBuilder {
 public:
  JsonObject root() {
    if (!root_created_) {
      root_ = doc_.to<JsonObject>();
      root_created_ = true;
    }
    return root_;
  }
 
  SerializationBuffer<> serialize();
 
 private:
#ifdef USE_PSRAM
  SpiRamAllocator allocator_;
  JsonDocument doc_{&allocator_};
#else
  JsonDocument doc_;
#endif
  JsonObject root_;
  bool root_created_{false};
};
 
}  // namespace esphome::json