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#include "constrainedfilestreambuf.hpp"
#include <algorithm>
#include <filesystem>
#include <limits>
namespace Files
{
namespace File = Platform::File;
ConstrainedFileStreamBuf::ConstrainedFileStreamBuf(
const std::filesystem::path& fname, std::size_t start, std::size_t length)
: mOrigin(start)
{
mFile = File::open(fname);
mSize = length != std::numeric_limits<std::size_t>::max() ? length : File::size(mFile) - start;
if (start != 0)
File::seek(mFile, start);
setg(nullptr, nullptr, nullptr);
}
std::streambuf::int_type ConstrainedFileStreamBuf::underflow()
{
if (gptr() == egptr())
{
const std::size_t toRead = std::min((mOrigin + mSize) - (File::tell(mFile)), sizeof(mBuffer));
// Read in the next chunk of data, and set the read pointers on success
// Failure will throw exception.
const std::size_t got = File::read(mFile, mBuffer, toRead);
setg(mBuffer, mBuffer, mBuffer + got);
}
if (gptr() == egptr())
return traits_type::eof();
return traits_type::to_int_type(*gptr());
}
std::streambuf::pos_type ConstrainedFileStreamBuf::seekoff(
off_type offset, std::ios_base::seekdir whence, std::ios_base::openmode mode)
{
if ((mode & std::ios_base::out) || !(mode & std::ios_base::in))
return traits_type::eof();
// new file position, relative to mOrigin
size_t newPos;
switch (whence)
{
case std::ios_base::beg:
newPos = offset;
break;
case std::ios_base::cur:
newPos = (File::tell(mFile) - mOrigin - (egptr() - gptr())) + offset;
break;
case std::ios_base::end:
newPos = mSize + offset;
break;
default:
return traits_type::eof();
}
if (newPos > mSize)
return traits_type::eof();
File::seek(mFile, mOrigin + newPos);
// Clear read pointers so underflow() gets called on the next read attempt.
setg(nullptr, nullptr, nullptr);
return newPos;
}
std::streambuf::pos_type ConstrainedFileStreamBuf::seekpos(pos_type pos, std::ios_base::openmode mode)
{
if ((mode & std::ios_base::out) || !(mode & std::ios_base::in))
return traits_type::eof();
if (static_cast<std::size_t>(pos) > mSize)
return traits_type::eof();
File::seek(mFile, mOrigin + pos);
// Clear read pointers so underflow() gets called on the next read attempt.
setg(nullptr, nullptr, nullptr);
return pos;
}
}
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