intermediate changes

ref:cde9a383711a11544ce7e107a78147fb96cc4029

1 files changed, 57 insertions, 0 deletions

diff --git a/util/stream/zerocopy_output.h b/util/stream/zerocopy_output.h
new file mode 100644
index 00000000000..a388be04b04
--- /dev/null
+++ b/util/stream/zerocopy_output.h
@@ -0,0 +1,57 @@
+#pragma once
+
+#include <util/system/yassert.h>
+
+#include "output.h"
+
+/**
+ * @addtogroup Streams
+ * @{
+ */
+
+/**
+ * Output stream with direct access to the output buffer.
+ *
+ * Derived classes must implement `DoNext` and `DoUndo` methods.
+ */
+class IZeroCopyOutput: public IOutputStream {
+public:
+    IZeroCopyOutput() noexcept = default;
+    ~IZeroCopyOutput() override = default;
+
+    IZeroCopyOutput(IZeroCopyOutput&&) noexcept = default;
+    IZeroCopyOutput& operator=(IZeroCopyOutput&&) noexcept = default;
+
+    /**
+     * Returns the next buffer to write to from this output stream.
+     *
+     * @param ptr[out]                  Pointer to the start of the buffer.
+     * @returns                         Size of the returned buffer, in bytes.
+     *                                  Return value is always nonzero.
+     */
+    template <class T>
+    inline size_t Next(T** ptr) {
+        Y_ASSERT(ptr);
+
+        return DoNext((void**)ptr);
+    }
+
+    /**
+     * Tells the stream that `len` bytes at the end of the buffer returned previously
+     * by Next were actually not written so the current position in stream must be moved backwards.
+     * `len` must not be greater than the size of the buffer previously returned by `Next`.
+     *
+     * @param len[in]                  Number of bytes at the end to move the position by.
+     *
+     */
+    inline void Undo(size_t len) {
+        return DoUndo(len);
+    }
+
+protected:
+    void DoWrite(const void* buf, size_t len) override;
+    virtual size_t DoNext(void** ptr) = 0;
+    virtual void DoUndo(size_t len) = 0;
+};
+
+/** @} */