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

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#pragma once
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#include <DB/IO/CompressedReadBufferBase.h>
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namespace DB
{
class CompressedReadBuffer : public CompressedReadBufferBase, public BufferWithOwnMemory<ReadBuffer>
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{
private:
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size_t size_compressed = 0;
bool nextImpl() override
{
size_t size_decompressed;
size_t size_compressed_without_checksum;
size_compressed = readCompressedData(size_decompressed, size_compressed_without_checksum);
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if (!size_compressed)
return false;
memory.resize(size_decompressed);
working_buffer = Buffer(&memory[0], &memory[size_decompressed]);
decompress(working_buffer.begin(), size_decompressed, size_compressed_without_checksum);
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return true;
}
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public:
CompressedReadBuffer(ReadBuffer & in_)
: CompressedReadBufferBase(&in_), BufferWithOwnMemory<ReadBuffer>(0)
{
}
size_t readBig(char * to, size_t n)
{
size_t bytes_read = 0;
/// Если в буфере есть непрочитанные байты, то скопируем сколько надо в to.
if (pos < working_buffer.end())
bytes_read += read(to, std::min(static_cast<size_t>(working_buffer.end() - pos), n));
/// Если надо ещё прочитать - будем, по возможности, разжимать сразу в to.
while (bytes_read < n)
{
size_t size_decompressed;
size_t size_compressed_without_checksum;
if (!readCompressedData(size_decompressed, size_compressed_without_checksum))
return bytes_read;
/// Если разжатый блок помещается целиком туда, куда его надо скопировать.
if (size_decompressed <= n - bytes_read)
{
decompress(to + bytes_read, size_decompressed, size_compressed_without_checksum);
bytes_read += size_decompressed;
bytes += size_decompressed;
}
else
{
bytes += offset();
memory.resize(size_decompressed);
working_buffer = Buffer(&memory[0], &memory[size_decompressed]);
pos = working_buffer.begin();
decompress(working_buffer.begin(), size_decompressed, size_compressed_without_checksum);
bytes_read += read(to + bytes_read, n - bytes_read);
break;
}
}
return bytes_read;
}
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/// Сжатый размер текущего блока.
size_t getSizeCompressed() const
{
return size_compressed;
}
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};
}