libcruft-util/io_posix.cpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2010-2014 Danny Robson <danny@nerdcruft.net>
 */

#include "io.hpp"

#include "cast.hpp"
#include "except.hpp"
#include "posix/fd.hpp"
#include "posix/except.hpp"

#include <sys/stat.h>

using cruft::detail::posix::mapped_file;


///////////////////////////////////////////////////////////////////////////////
namespace {
    struct overflow_error : public cruft::error {
        std::ostream& describe (std::ostream &os) const override
        {
            return os << "mapping is too large for the system";
        }
    };
}

//////////////////////////////////////////////////////////////////////////////
mapped_file::mapped_file (const std::filesystem::path &path,
                          int fflags,
                          int mflags):
    mapped_file (cruft::posix::fd (path, fflags), mflags)
{ ; }


//-----------------------------------------------------------------------------
mapped_file::mapped_file (::cruft::posix::fd const &src, int const mflags)
{
    struct stat meta;
    ::cruft::posix::error::try_value (fstat (src, &meta));

    // Zero length mappings aren't allowed by POSIX (even though they're
    // accepted by some systems; like Linux)
    if (meta.st_size == 0) {
        m_data = nullptr;
        m_size = 0;
        return;
    }

    // Ensure we're not trying to map more than our address space allows.
    //
    // It's a little nasty, but we protect a
    if constexpr (sizeof (meta.st_size) > sizeof (size_t)) {
        auto const hi = cruft::cast::lossless<off_t> (std::numeric_limits<size_t>::max ());
        if (meta.st_size > hi)
            throw overflow_error ();
    }

    m_size = cruft::cast::lossless<size_t> (meta.st_size);
    m_data = static_cast<u08*> (mmap (nullptr, m_size, mflags, MAP_SHARED, src, 0));
    if (m_data == MAP_FAILED)
        ::cruft::posix::error::throw_code ();
}


//-----------------------------------------------------------------------------
mapped_file::mapped_file (cruft::mapped_file &&rhs) noexcept
  : m_data (std::exchange (rhs.m_data, nullptr))
  , m_size (std::exchange (rhs.m_size, 0))
{ ; }


//----------------------------------------------------------------------------
mapped_file::~mapped_file ()
{
    if (!m_data)
        return;

    munmap (m_data, m_size);
}


//////////////////////////////////////////////////////////////////////////////
size_t
mapped_file::size (void) const
{
    return m_size;
}


//-----------------------------------------------------------------------------
bool
mapped_file::empty (void) const
{
    return size () == 0;
}


//////////////////////////////////////////////////////////////////////////////
uint8_t*
mapped_file::data (void) &
{
    return m_data;
}


//----------------------------------------------------------------------------
const uint8_t*
mapped_file::data (void) const &
{
    return m_data;
}


//----------------------------------------------------------------------------
uint8_t*
mapped_file::begin (void) &
{
    return data ();
}


//----------------------------------------------------------------------------
uint8_t*
mapped_file::end (void) &
{
    return data () + size ();
}


//-----------------------------------------------------------------------------
const uint8_t*
mapped_file::begin (void) const &
{
    return data ();
}


//-----------------------------------------------------------------------------
const uint8_t*
mapped_file::end (void) const &
{
    return data () + size ();
}


//----------------------------------------------------------------------------
const uint8_t*
mapped_file::cbegin (void) const &
{
    return data ();
}


//----------------------------------------------------------------------------
const uint8_t*
mapped_file::cend (void) const &
{
    return data () + size ();
}