A simple interface to find temporary files by their logical names when building pipeline from query plan

src/Processors/QueryPlan/BuildQueryPipelineSettings.h

@@ -12,12 +12,15 @@ namespace DB
 struct Settings;
 class QueryStatus;
 using QueryStatusPtr = std::shared_ptr<QueryStatus>;
+struct ITemporaryFileLookup;
+using TemporaryFileLookupPtr = std::shared_ptr<ITemporaryFileLookup>;
 
 struct BuildQueryPipelineSettings
 {
     ExpressionActionsSettings actions_settings;
     QueryStatusPtr process_list_element;
     ProgressCallback progress_callback = nullptr;
+    TemporaryFileLookupPtr temporary_file_lookup;
 
     const ExpressionActionsSettings & getActionsSettings() const { return actions_settings; }
     static BuildQueryPipelineSettings fromContext(ContextPtr from);

src/Processors/QueryPlan/TemporaryFiles.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <base/types.h>
+#include <boost/noncopyable.hpp>
+#include <vector>
+#include <memory>
+
+namespace DB
+{
+
+class WriteBuffer;
+class ReadBuffer;
+
+/// Interface for accessing temporary files by some logical name (or id).
+/// While building query pipeline processors can lookup temporary files by some id and use them for writing and/or reading temporary data
+/// without knowing what exactly is behind the name: local file, memory buffer, object in cloud storage, etc.
+struct ITemporaryFileLookup : boost::noncopyable
+{
+    virtual ~ITemporaryFileLookup() = default;
+
+    /// Give the caller a temporary write buffer, but don't give away the ownership.
+    virtual WriteBuffer & getTemporaryFileForWriting(const String & file_id) = 0;
+
+    /// Give the caller a temporary read buffer, it exclusively belongs to the caller.
+    /// Other callers can get their own read buffer for the same temporary file.
+    virtual std::unique_ptr<ReadBuffer> getTemporaryFileForReading(const String & file_id) = 0;
+};
+
+using TemporaryFileLookupPtr = std::shared_ptr<ITemporaryFileLookup>;
+
+}