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