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

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#pragma once
#include <unistd.h>
#include <errno.h>
#include <Poco/NumberFormatter.h>
#include <DB/Core/Exception.h>
#include <DB/Core/ErrorCodes.h>
#include <DB/IO/ReadBuffer.h>
#include <DB/IO/BufferWithOwnMemory.h>
namespace DB
{
/** Работает с готовым файловым дескриптором. Не открывает и не закрывает файл.
*/
class ReadBufferFromFileDescriptor : public BufferWithOwnMemory<ReadBuffer>
{
protected:
int fd;
bool nextImpl()
{
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size_t bytes_read = 0;
while (!bytes_read)
{
ssize_t res = ::read(fd, internal_buffer.begin(), internal_buffer.size());
if (!res)
break;
if (-1 == res && errno != EINTR)
throwFromErrno("Cannot read from file " + getFileName(), ErrorCodes::CANNOT_READ_FROM_FILE_DESCRIPTOR);
if (res > 0)
bytes_read += res;
}
if (bytes_read)
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working_buffer.resize(bytes_read);
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else
return false;
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return true;
}
/// Имя или описание файла
virtual std::string getFileName()
{
return "(fd = " + Poco::NumberFormatter::format(fd) + ")";
}
public:
ReadBufferFromFileDescriptor(int fd_, size_t buf_size = DBMS_DEFAULT_BUFFER_SIZE, char * existing_memory = NULL)
: BufferWithOwnMemory<ReadBuffer>(buf_size, existing_memory), fd(fd_) {}
int getFD()
{
return fd;
}
off_t seek(off_t offset, int whence = SEEK_SET)
{
off_t res = lseek(fd, offset, whence);
if (-1 == res)
throwFromErrno("Cannot seek through file " + getFileName(), ErrorCodes::CANNOT_SEEK_THROUGH_FILE);
return res;
}
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};
}