-error_code get_magic(const Twine &path, uint32_t len,
- SmallVectorImpl<char> &result) {
- SmallString<128> path_storage;
- SmallVector<wchar_t, 128> path_utf16;
- result.set_size(0);
-
- // Convert path to UTF-16.
- if (error_code ec = UTF8ToUTF16(path.toStringRef(path_storage),
- path_utf16))
- return ec;
-
- // Open file.
- HANDLE file = ::CreateFileW(c_str(path_utf16),
- GENERIC_READ,
- FILE_SHARE_READ,
- NULL,
- OPEN_EXISTING,
- FILE_ATTRIBUTE_READONLY,
- NULL);
- if (file == INVALID_HANDLE_VALUE)
- return windows_error(::GetLastError());
-
- // Allocate buffer.
- result.reserve(len);
-
- // Get magic!
- DWORD bytes_read = 0;
- BOOL read_success = ::ReadFile(file, result.data(), len, &bytes_read, NULL);
- error_code ec = windows_error(::GetLastError());
- ::CloseHandle(file);
- if (!read_success || (bytes_read != len)) {
- // Set result size to the number of bytes read if it's valid.
- if (bytes_read <= len)
- result.set_size(bytes_read);
- // ERROR_HANDLE_EOF is mapped to errc::value_too_large.
- return ec;
- }
-
- result.set_size(len);
- return error_code();
-}
-