dbms: preparation [#METR-18603].

dbms/include/DB/DataStreams/BinaryRowOutputStream.h

@@ -22,6 +22,8 @@ public:
 
 	void flush() override { ostr.next(); }
 
+	String getContentType() const override { return "application/octet-stream"; }
+
 protected:
 	WriteBuffer & ostr;
 	const Block sample;

dbms/include/DB/DataStreams/BlockOutputStreamFromRowOutputStream.h

@@ -24,6 +24,8 @@ public:
 	void setTotals(const Block & totals) override;
 	void setExtremes(const Block & extremes) override;
 
+	String getContentType() const override { return row_output->getContentType(); }
+
 private:
 	RowOutputStreamPtr row_output;
 	bool first_row;

dbms/include/DB/DataStreams/IBlockOutputStream.h

@@ -42,6 +42,10 @@ public:
 	virtual void setTotals(const Block & totals) {}
 	virtual void setExtremes(const Block & extremes) {}
 
+	/** Выставлять такой Content-Type при отдаче по HTTP.
+	  */
+	virtual String getContentType() const { return "text/plain; charset=UTF-8"; }
+
 	virtual ~IBlockOutputStream() {}
 
 	/** Не давать изменить таблицу, пока жив поток блоков.

dbms/include/DB/DataStreams/IRowOutputStream.h

@@ -41,6 +41,9 @@ public:
 	virtual void setTotals(const Block & totals) {}
 	virtual void setExtremes(const Block & extremes) {}
 
+	/** Выставлять такой Content-Type при отдаче по HTTP. */
+	virtual String getContentType() const { return "text/plain; charset=UTF-8"; }
+
 	virtual ~IRowOutputStream() {}
 };
 

dbms/include/DB/DataStreams/JSONRowOutputStream.h

@@ -42,6 +42,8 @@ public:
 	void setTotals(const Block & totals_) override { totals = totals_; }
 	void setExtremes(const Block & extremes_) override { extremes = extremes_; }
 
+	String getContentType() const override { return "application/json; charset=UTF-8"; }
+
 protected:
 
 	void writeRowsBeforeLimitAtLeast();

dbms/include/DB/DataStreams/NativeBlockOutputStream.h

@@ -30,6 +30,8 @@ public:
 
 	static void writeData(const IDataType & type, const ColumnPtr & column, WriteBuffer & ostr, size_t offset, size_t limit);
 
+	String getContentType() const override { return "application/octet-stream"; }
+
 private:
 	WriteBuffer & ostr;
 	UInt64 client_revision;