Repo created

libs/coding/buffer_reader.hpp

@@ -0,0 +1,70 @@
+#pragma once
+
+#include "coding/reader.hpp"
+
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+#include <memory>
+
+/// Reader from buffer with ownership on it, but cheap copy constructor.
+class BufferReader : public Reader
+{
+public:
+  template <class ReaderT>
+  explicit BufferReader(ReaderT const & reader, uint64_t offset = 0)
+  {
+    uint64_t const rSize = reader.Size();
+    ASSERT_LESS_OR_EQUAL(offset, rSize, (offset, rSize));
+
+    InitBuffer(static_cast<size_t>(rSize - offset));
+    reader.Read(offset, m_data.get(), m_size);
+  }
+
+  explicit BufferReader(char const * p, size_t count)
+  {
+    InitBuffer(count);
+    memcpy(m_data.get(), p, count);
+  }
+
+  uint64_t Size() const { return m_size; }
+
+  void Read(uint64_t pos, void * p, size_t size) const
+  {
+    ASSERT_LESS_OR_EQUAL(pos + size, Size(), (pos, size));
+    memcpy(p, m_data.get() + static_cast<size_t>(pos) + m_offset, size);
+  }
+
+  BufferReader SubReader(uint64_t pos, uint64_t size) const { return BufferReader(*this, pos, size); }
+
+  std::unique_ptr<Reader> CreateSubReader(uint64_t pos, uint64_t size) const
+  {
+    // Can't use make_unique with private constructor.
+    return std::unique_ptr<Reader>(new BufferReader(*this, pos, size));
+  }
+
+private:
+  BufferReader(BufferReader const & src, uint64_t pos, uint64_t size) : m_data(src.m_data)
+  {
+    ASSERT_LESS_OR_EQUAL(pos + size, src.Size(), (pos, size));
+
+    m_offset = static_cast<size_t>(src.m_offset + pos);
+    m_size = static_cast<size_t>(size);
+  }
+
+  void InitBuffer(size_t count)
+  {
+    m_offset = 0;
+    m_size = count;
+    m_data.reset(new char[m_size], Deleter());
+  }
+
+  size_t m_offset, m_size;
+
+  struct Deleter
+  {
+    void operator()(char * p) { delete[] p; }
+  };
+
+  std::shared_ptr<char> m_data;
+};