dash/src/fs.h

// Copyright (c) 2017-2019 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#ifndef BITCOIN_FS_H
#define BITCOIN_FS_H

#include <stdio.h>
#include <string>
#if defined WIN32 && defined __GLIBCXX__
#include <ext/stdio_filebuf.h>
#endif

#include <boost/filesystem.hpp>
#include <boost/filesystem/fstream.hpp>
#include <tinyformat.h>

/** Filesystem operations and types */
namespace fs {

using namespace boost::filesystem;

/**
 * Path class wrapper to prepare application code for transition from
 * boost::filesystem library to std::filesystem implementation. The main
 * purpose of the class is to define fs::path::u8string() and fs::u8path()
 * functions not present in boost. It also blocks calls to the
 * fs::path(std::string) implicit constructor and the fs::path::string()
 * method, which worked well in the boost::filesystem implementation, but have
 * unsafe and unpredictable behavior on Windows in the std::filesystem
 * implementation (see implementation note in \ref PathToString for details).
 */
class path : public boost::filesystem::path
{
public:
    using boost::filesystem::path::path;

    // Allow path objects arguments for compatibility.
    path(boost::filesystem::path path) : boost::filesystem::path::path(std::move(path)) {}
    path& operator=(boost::filesystem::path path) { boost::filesystem::path::operator=(std::move(path)); return *this; }
    path& operator/=(boost::filesystem::path path) { boost::filesystem::path::operator/=(std::move(path)); return *this; }

    // Allow literal string arguments, which are safe as long as the literals are ASCII.
    path(const char* c) : boost::filesystem::path(c) {}
    path& operator=(const char* c) { boost::filesystem::path::operator=(c); return *this; }
    path& operator/=(const char* c) { boost::filesystem::path::operator/=(c); return *this; }
    path& append(const char* c) { boost::filesystem::path::append(c); return *this; }

    // Disallow std::string arguments to avoid locale-dependent decoding on windows.
    path(std::string) = delete;
    path& operator=(std::string) = delete;
    path& operator/=(std::string) = delete;
    path& append(std::string) = delete;

    // Disallow std::string conversion method to avoid locale-dependent encoding on windows.
    std::string string() const = delete;

    // Define UTF-8 string conversion method not present in boost::filesystem but present in std::filesystem.
    std::string u8string() const { return boost::filesystem::path::string(); }
};

// Define UTF-8 string conversion function not present in boost::filesystem but present in std::filesystem.
static inline path u8path(const std::string& string)
{
    return boost::filesystem::path(string);
}

// Disallow implicit std::string conversion for system_complete to avoid
// locale-dependent encoding on windows.
static inline path system_complete(const path& p)
{
    return boost::filesystem::system_complete(p);
}

// Disallow implicit std::string conversion for exists to avoid
// locale-dependent encoding on windows.
static inline bool exists(const path& p)
{
    return boost::filesystem::exists(p);
}

// Allow explicit quoted stream I/O.
static inline auto quoted(const std::string& s)
{
    return boost::io::quoted(s, '&');
}

// Allow safe path append operations.
static inline path operator+(path p1, path p2)
{
    p1 += std::move(p2);
    return p1;
}

/**
 * Convert path object to byte string. On POSIX, paths natively are byte
 * strings, so this is trivial. On Windows, paths natively are Unicode, so an
 * encoding step is necessary. The inverse of \ref PathToString is \ref
 * PathFromString. The strings returned and parsed by these functions can be
 * used to call POSIX APIs, and for roundtrip conversion, logging, and
 * debugging.
 *
 * Because \ref PathToString and \ref PathFromString functions don't specify an
 * encoding, they are meant to be used internally, not externally. They are not
 * appropriate to use in applications requiring UTF-8, where
 * fs::path::u8string() and fs::u8path() methods should be used instead. Other
 * applications could require still different encodings. For example, JSON, XML,
 * or URI applications might prefer to use higher level escapes (\uXXXX or
 * &XXXX; or %XX) instead of multibyte encoding. Rust, Python, Java applications
 * may require encoding paths with their respective UTF-8 derivatives WTF-8,
 * PEP-383, and CESU-8 (see https://en.wikipedia.org/wiki/UTF-8#Derivatives).
 */
static inline std::string PathToString(const path& path)
{
    // Implementation note: On Windows, the std::filesystem::path(string)
    // constructor and std::filesystem::path::string() method are not safe to
    // use here, because these methods encode the path using C++'s narrow
    // multibyte encoding, which on Windows corresponds to the current "code
    // page", which is unpredictable and typically not able to represent all
    // valid paths. So std::filesystem::path::u8string() and
    // std::filesystem::u8path() functions are used instead on Windows. On
    // POSIX, u8string/u8path functions are not safe to use because paths are
    // not always valid UTF-8, so plain string methods which do not transform
    // the path there are used.
#ifdef WIN32
    return path.u8string();
#else
    static_assert(std::is_same<path::string_type, std::string>::value, "PathToString not implemented on this platform");
    return path.boost::filesystem::path::string();
#endif
}

/**
 * Convert byte string to path object. Inverse of \ref PathToString.
 */
static inline path PathFromString(const std::string& string)
{
#ifdef WIN32
    return u8path(string);
#else
    return boost::filesystem::path(string);
#endif
}
} // namespace fs

/** Bridge operations to C stdio */
namespace fsbridge {
    FILE *fopen(const fs::path& p, const char *mode);

    /**
     * Helper function for joining two paths
     *
     * @param[in] base  Base path
     * @param[in] path  Path to combine with base
     * @returns path unchanged if it is an absolute path, otherwise returns base joined with path. Returns base unchanged if path is empty.
     * @pre  Base path must be absolute
     * @post Returned path will always be absolute
     */
    fs::path AbsPathJoin(const fs::path& base, const fs::path& path);

    class FileLock
    {
    public:
        FileLock() = delete;
        FileLock(const FileLock&) = delete;
        FileLock(FileLock&&) = delete;
        explicit FileLock(const fs::path& file);
        ~FileLock();
        bool TryLock();
        std::string GetReason() { return reason; }

    private:
        std::string reason;
#ifndef WIN32
        int fd = -1;
#else
        void* hFile = (void*)-1; // INVALID_HANDLE_VALUE
#endif
    };

    std::string get_filesystem_error_message(const fs::filesystem_error& e);

    // GNU libstdc++ specific workaround for opening UTF-8 paths on Windows.
    //
    // On Windows, it is only possible to reliably access multibyte file paths through
    // `wchar_t` APIs, not `char` APIs. But because the C++ standard doesn't
    // require ifstream/ofstream `wchar_t` constructors, and the GNU library doesn't
    // provide them (in contrast to the Microsoft C++ library, see
    // https://stackoverflow.com/questions/821873/how-to-open-an-stdfstream-ofstream-or-ifstream-with-a-unicode-filename/822032#822032),
    // Boost is forced to fall back to `char` constructors which may not work properly.
    //
    // Work around this issue by creating stream objects with `_wfopen` in
    // combination with `__gnu_cxx::stdio_filebuf`. This workaround can be removed
    // with an upgrade to C++17, where streams can be constructed directly from
    // `std::filesystem::path` objects.

#if defined WIN32 && defined __GLIBCXX__
    class ifstream : public std::istream
    {
    public:
        ifstream() = default;
        explicit ifstream(const fs::path& p, std::ios_base::openmode mode = std::ios_base::in) { open(p, mode); }
        ~ifstream() { close(); }
        void open(const fs::path& p, std::ios_base::openmode mode = std::ios_base::in);
        bool is_open() { return m_filebuf.is_open(); }
        void close();

    private:
        __gnu_cxx::stdio_filebuf<char> m_filebuf;
        FILE* m_file = nullptr;
    };
    class ofstream : public std::ostream
    {
    public:
        ofstream() = default;
        explicit ofstream(const fs::path& p, std::ios_base::openmode mode = std::ios_base::out) { open(p, mode); }
        ~ofstream() { close(); }
        void open(const fs::path& p, std::ios_base::openmode mode = std::ios_base::out);
        bool is_open() { return m_filebuf.is_open(); }
        void close();

    private:
        __gnu_cxx::stdio_filebuf<char> m_filebuf;
        FILE* m_file = nullptr;
    };
#else  // !(WIN32 && __GLIBCXX__)
    typedef fs::ifstream ifstream;
    typedef fs::ofstream ofstream;
#endif // WIN32 && __GLIBCXX__
};

// Disallow path operator<< formatting in tinyformat to avoid locale-dependent
// encoding on windows.
namespace tinyformat {
template<> inline void formatValue(std::ostream&, const char*, const char*, int, const boost::filesystem::path&) = delete;
template<> inline void formatValue(std::ostream&, const char*, const char*, int, const fs::path&) = delete;
} // namespace tinyformat

#endif // BITCOIN_FS_H