arm: async echo app

arm/buffer.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include <span>
+#include <utility>
+ 
+struct buffer {
+  std::span<std::byte> data;
+ 
+  buffer() = default;
+  buffer(std::span<std::byte> d) : data(d) {}
+ 
+  static buffer make(size_t size) {
+    return buffer({new std::byte[size], size});
+  }
+ 
+  buffer(buffer& other) = delete;
+  buffer& operator=(buffer& other) = delete;
+ 
+  buffer(buffer&& other) : data(std::exchange(other.data, {})) {}
+  buffer& operator=(buffer&& other) { data = std::exchange(other.data, {}); return *this; }
+ 
+  ~buffer() { if (data.data()) { delete[] data.data(); }; }
+};