Add ArenaStlAllocator, and use arena throughout CommitRequest

src/arena_allocator.hpp

@@ -423,3 +423,55 @@ private:
   /// Current offset within the current block's data area
   size_t current_offset_;
 };
+
+/**
+ * @brief STL-compatible allocator that uses ArenaAllocator for memory
+ * management.
+ * @tparam T The type of objects to allocate
+ */
+template <typename T> class ArenaStlAllocator {
+public:
+  using value_type = T;
+  using pointer = T *;
+  using const_pointer = const T *;
+  using reference = T &;
+  using const_reference = const T &;
+  using size_type = std::size_t;
+  using difference_type = std::ptrdiff_t;
+
+  template <typename U> struct rebind {
+    using other = ArenaStlAllocator<U>;
+  };
+
+  explicit ArenaStlAllocator(ArenaAllocator *arena) noexcept : arena_(arena) {}
+
+  template <typename U>
+  ArenaStlAllocator(const ArenaStlAllocator<U> &other) noexcept
+      : arena_(other.arena_) {}
+
+  T *allocate(size_type n) {
+    if (n == 0)
+      return nullptr;
+    return static_cast<T *>(arena_->allocate(n * sizeof(T), alignof(T)));
+  }
+
+  void deallocate(T *ptr, size_type n) noexcept {
+    // Arena allocator doesn't support individual deallocation
+    (void)ptr;
+    (void)n;
+  }
+
+  template <typename U>
+  bool operator==(const ArenaStlAllocator<U> &other) const noexcept {
+    return arena_ == other.arena_;
+  }
+
+  template <typename U>
+  bool operator!=(const ArenaStlAllocator<U> &other) const noexcept {
+    return arena_ != other.arena_;
+  }
+
+  ArenaAllocator *arena_;
+
+  template <typename U> friend class ArenaStlAllocator;
+};