Restore missing file

src/DataStreams/NullAndDoCopyBlockInputStream.h

@@ -0,0 +1,56 @@
+#pragma once
+
+#include <DataStreams/IBlockInputStream.h>
+#include <DataStreams/copyData.h>
+
+
+namespace DB
+{
+
+class IBlockOutputStream;
+using BlockOutputStreamPtr = std::shared_ptr<IBlockOutputStream>;
+
+
+/** An empty stream of blocks.
+  * But at the first read attempt, copies the data from the passed `input` to the `output`.
+  * This is necessary to execute the query INSERT SELECT - the query copies data, but returns nothing.
+  * The query could be executed without wrapping it in an empty BlockInputStream,
+  *  but the progress of query execution and the ability to cancel the query would not work.
+  */
+class NullAndDoCopyBlockInputStream : public IBlockInputStream
+{
+public:
+    NullAndDoCopyBlockInputStream(const BlockInputStreamPtr & input_, BlockOutputStreamPtr output_)
+        : input(std::move(input_))
+        , output(std::move(output_))
+    {
+        children.push_back(input);
+    }
+
+    /// Suppress readPrefix and readSuffix, because they are called by copyData.
+    void readPrefix() override {}
+    void readSuffix() override {}
+
+    String getName() const override { return "NullAndDoCopy"; }
+
+    Block getHeader() const override { return {}; }
+    Block getTotals() override { return {}; }
+    Block getExtremes() override { return {}; }
+
+protected:
+    Block readImpl() override
+    {
+        /// We do not use cancel flag here.
+        /// If query was cancelled, it will be processed by child streams.
+        /// Part of the data will be processed.
+
+        copyData(*input, *output);
+        return Block();
+    }
+
+private:
+    BlockInputStreamPtr input;
+    BlockOutputStreamPtr output;
+};
+
+}