ClickHouse/dbms/src/Processors/Formats/IOutputFormat.h

#pragma once

#include <string>
#include <Processors/IProcessor.h>
#include <IO/Progress.h>


namespace DB
{

class WriteBuffer;

/** Output format have three inputs and no outputs. It writes data from WriteBuffer.
  *
  * First input is for main resultset, second is for "totals" and third is for "extremes".
  * It's not necessarily to connect "totals" or "extremes" ports (they may remain dangling).
  *
  * Data from input ports are pulled in order: first, from main input, then totals, then extremes.
  *
  * By default, data for "totals" and "extremes" is ignored.
  */
class IOutputFormat : public IProcessor
{
public:
    enum PortKind { Main = 0, Totals = 1, Extremes = 2 };

protected:
    WriteBuffer & out;

    Chunk current_chunk;
    PortKind current_block_kind = PortKind::Main;
    bool has_input = false;
    bool finished = false;
    bool finalized = false;

    virtual void consume(Chunk) = 0;
    virtual void consumeTotals(Chunk) {}
    virtual void consumeExtremes(Chunk) {}
    virtual void finalize() {}

public:
    IOutputFormat(const Block & header, WriteBuffer & out);

    Status prepare() override;
    void work() override;

    /// Flush output buffers if any.
    virtual void flush();

    /// Value for rows_before_limit_at_least field.
    virtual void setRowsBeforeLimit(size_t /*rows_before_limit*/) {}

    /// Notify about progress. Method could be called from different threads.
    /// Passed value are delta, that must be summarized.
    virtual void onProgress(const Progress & /*progress*/) {}

    /// Content-Type to set when sending HTTP response.
    virtual std::string getContentType() const { return "text/plain; charset=UTF-8"; }

    InputPort & getPort(PortKind kind) { return *std::next(inputs.begin(), kind); }

public:
    /// Compatible to IBlockOutputStream interface

    void write(const Block & block) { consume(Chunk(block.getColumns(), block.rows())); }

    void doWritePrefix() {}
    void doWriteSuffix() { finalize(); }

    void setTotals(const Block & totals) { consumeTotals(Chunk(totals.getColumns(), totals.rows())); }
    void setExtremes(const Block & extremes) { consumeExtremes(Chunk(extremes.getColumns(), extremes.rows())); }
};
}