ClickHouse/dbms/include/DB/IO/ConcatReadBuffer.h

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#pragma once
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#include <vector>
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#include <DB/IO/ReadBuffer.h>
namespace DB
{
/** Читает из конкатенации нескольких ReadBuffer-ов
*/
class ConcatReadBuffer : public ReadBuffer
{
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public:
using ReadBuffers = std::vector<ReadBuffer *>;
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protected:
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ReadBuffers buffers;
ReadBuffers::iterator current;
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bool nextImpl()
{
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if (buffers.end() == current)
return false;
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/// Первое чтение
if (working_buffer.size() == 0 && (*current)->hasPendingData())
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{
working_buffer = Buffer((*current)->position(), (*current)->buffer().end());
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return true;
}
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if (!(*current)->next())
{
++current;
if (buffers.end() == current)
return false;
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/// Пропускаем закончившиеся буферы; если буфер не закончился, но курсор на конце, то прочитаем следующую порцию данных.
while ((*current)->eof())
{
++current;
if (buffers.end() == current)
return false;
}
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}
working_buffer = Buffer((*current)->position(), (*current)->buffer().end());
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return true;
}
public:
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ConcatReadBuffer(const ReadBuffers & buffers_) : ReadBuffer(nullptr, 0), buffers(buffers_), current(buffers.begin()) {}
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ConcatReadBuffer(ReadBuffer & buf1, ReadBuffer & buf2) : ReadBuffer(nullptr, 0)
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{
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buffers.push_back(&buf1);
buffers.push_back(&buf2);
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current = buffers.begin();
}
};
}