utils: Add fsbridge fstream function wrapper

src/fs.cpp

@@ -113,4 +113,106 @@ std::string get_filesystem_error_message(const fs::filesystem_error& e)
 #endif
 }
 
+#ifdef WIN32
+#ifdef __GLIBCXX__
+
+// reference: https://github.com/gcc-mirror/gcc/blob/gcc-7_3_0-release/libstdc%2B%2B-v3/include/std/fstream#L270
+
+static std::string openmodeToStr(std::ios_base::openmode mode)
+{
+    switch (mode & ~std::ios_base::ate) {
+    case std::ios_base::out:
+    case std::ios_base::out | std::ios_base::trunc:
+        return "w";
+    case std::ios_base::out | std::ios_base::app:
+    case std::ios_base::app:
+        return "a";
+    case std::ios_base::in:
+        return "r";
+    case std::ios_base::in | std::ios_base::out:
+        return "r+";
+    case std::ios_base::in | std::ios_base::out | std::ios_base::trunc:
+        return "w+";
+    case std::ios_base::in | std::ios_base::out | std::ios_base::app:
+    case std::ios_base::in | std::ios_base::app:
+        return "a+";
+    case std::ios_base::out | std::ios_base::binary:
+    case std::ios_base::out | std::ios_base::trunc | std::ios_base::binary:
+        return "wb";
+    case std::ios_base::out | std::ios_base::app | std::ios_base::binary:
+    case std::ios_base::app | std::ios_base::binary:
+        return "ab";
+    case std::ios_base::in | std::ios_base::binary:
+        return "rb";
+    case std::ios_base::in | std::ios_base::out | std::ios_base::binary:
+        return "r+b";
+    case std::ios_base::in | std::ios_base::out | std::ios_base::trunc | std::ios_base::binary:
+        return "w+b";
+    case std::ios_base::in | std::ios_base::out | std::ios_base::app | std::ios_base::binary:
+    case std::ios_base::in | std::ios_base::app | std::ios_base::binary:
+        return "a+b";
+    default:
+        return std::string();
+    }
+}
+
+void ifstream::open(const fs::path& p, std::ios_base::openmode mode)
+{
+    close();
+    m_file = fsbridge::fopen(p, openmodeToStr(mode).c_str());
+    if (m_file == nullptr) {
+        return;
+    }
+    m_filebuf = __gnu_cxx::stdio_filebuf<char>(m_file, mode);
+    rdbuf(&m_filebuf);
+    if (mode & std::ios_base::ate) {
+        seekg(0, std::ios_base::end);
+    }
+}
+
+void ifstream::close()
+{
+    if (m_file != nullptr) {
+        m_filebuf.close();
+        fclose(m_file);
+    }
+    m_file = nullptr;
+}
+
+void ofstream::open(const fs::path& p, std::ios_base::openmode mode)
+{
+    close();
+    m_file = fsbridge::fopen(p, openmodeToStr(mode).c_str());
+    if (m_file == nullptr) {
+        return;
+    }
+    m_filebuf = __gnu_cxx::stdio_filebuf<char>(m_file, mode);
+    rdbuf(&m_filebuf);
+    if (mode & std::ios_base::ate) {
+        seekp(0, std::ios_base::end);
+    }
+}
+
+void ofstream::close()
+{
+    if (m_file != nullptr) {
+        m_filebuf.close();
+        fclose(m_file);
+    }
+    m_file = nullptr;
+}
+#else // __GLIBCXX__
+
+static_assert(sizeof(*fs::path().BOOST_FILESYSTEM_C_STR) == sizeof(wchar_t),
+    "Warning: This build is using boost::filesystem ofstream and ifstream "
+    "implementations which will fail to open paths containing multibyte "
+    "characters. You should delete this static_assert to ignore this warning, "
+    "or switch to a different C++ standard library like the Microsoft C++ "
+    "Standard Library (where boost uses non-standard extensions to construct "
+    "stream objects with wide filenames), or the GNU libstdc++ library (where "
+    "a more complicated workaround has been implemented above).");
+
+#endif // __GLIBCXX__
+#endif // WIN32
+
 } // fsbridge

src/fs.h

@@ -7,6 +7,9 @@
 
 #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>
@@ -39,6 +42,54 @@ namespace fsbridge {
     };
 
     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__
 };
 
 #endif // BITCOIN_FS_H