Add StringWiden function

StringWiden converts a narrow C-style string to a wide string. It serves the opposite role of StringNarrow function. The function is useful on Windows platforms where the OS favors wide functions with the UTF-16 character set. For example, the Data Proction API (DPAPI) allows a description, but its a wide character C-string. There is no narrwo version of the API.

misc.cpp

@@ -197,6 +197,70 @@ std::string StringNarrow(const wchar_t *str, bool throwOnError)
 	return result;
 }
 
+std::wstring StringWiden(const char *str, bool throwOnError)
+{
+	CRYPTOPP_ASSERT(str);
+	std::wstring result;
+
+	// Safer functions on Windows for C&A, https://github.com/weidai11/cryptopp/issues/55
+#if (CRYPTOPP_MSC_VERSION >= 1400)
+	size_t len=0, size=0;
+	errno_t err = 0;
+
+	//const char* ptr = str;
+	//while (*ptr++) len++;
+	len = std::strlen(str)+1;
+
+	err = mbstowcs_s(&size, NULLPTR, 0, str, len);
+	CRYPTOPP_ASSERT(err == 0);
+	if (err != 0)
+	{
+		if (throwOnError)
+			throw InvalidArgument("StringWiden: wcstombs_s() call failed with error " + IntToString(err));
+		else
+			return std::wstring();
+	}
+
+	result.resize(size);
+	err = mbstowcs_s(&size, &result[0], size, str, len);
+	CRYPTOPP_ASSERT(err == 0);
+	if (err != 0)
+	{
+		if (throwOnError)
+			throw InvalidArgument("StringWiden: wcstombs_s() call failed with error " + IntToString(err));
+		else
+			return std::wstring();
+	}
+
+	// The safe routine's size includes the NULL.
+	if (!result.empty() && result[size - 1] == '\0')
+		result.erase(size - 1);
+#else
+	size_t size = mbstowcs(NULLPTR, str, 0);
+	CRYPTOPP_ASSERT(size != (size_t)-1);
+	if (size == (size_t)-1)
+	{
+		if (throwOnError)
+			throw InvalidArgument("StringWiden: mbstowcs() call failed");
+		else
+			return std::wstring();
+	}
+
+	result.resize(size);
+	size = mbstowcs(&result[0], str, size);
+	CRYPTOPP_ASSERT(size != (size_t)-1);
+	if (size == (size_t)-1)
+	{
+		if (throwOnError)
+			throw InvalidArgument("StringWiden: mbstowcs() call failed");
+		else
+			return std::wstring();
+	}
+#endif
+
+	return result;
+}
+
 void CallNewHandler()
 {
 	using std::new_handler;

misc.h

@@ -163,7 +163,6 @@ struct CompileAssert
 {
 	static char dummy[2*b-1];
 };
-//! \endif
 
 #define CRYPTOPP_COMPILE_ASSERT(assertion) CRYPTOPP_COMPILE_ASSERT_INSTANCE(assertion, __LINE__)
 #if defined(CRYPTOPP_EXPORTS) || defined(CRYPTOPP_IMPORTS)
@@ -1293,9 +1292,9 @@ inline void SecureWipeArray(T *buf, size_t n)
 
 //! \brief Converts a wide character C-string to a multibyte string
 //! \param str C-string consisting of wide characters
-//! \param throwOnError flag indication the function should throw on error
+//! \param throwOnError flag indicating the function should throw on error
 //! \returns str converted to a multibyte string or an empty string.
-//! \details StringNarrow converts a wide string to a narrow string using C++ std::wcstombs() under
+//! \details StringNarrow() converts a wide string to a narrow string using C++ std::wcstombs() under
 //!   the executing thread's locale. A locale must be set before using this function, and it can be
 //!   set with std::setlocale() if needed. Upon success, the converted string is returned.
 //! \details Upon failure with throwOnError as false, the function returns an empty string. If
@@ -1305,6 +1304,20 @@ inline void SecureWipeArray(T *buf, size_t n)
 //!   then a 0x21 error is returned on Windows which eventually results in an InvalidArgument() exception.
 std::string StringNarrow(const wchar_t *str, bool throwOnError = true);
 
+//! \brief Converts a multibyte C-string to a wide character string
+//! \param str C-string consisting of wide characters
+//! \param throwOnError flag indicating the function should throw on error
+//! \returns str converted to a multibyte string or an empty string.
+//! \details StringWiden() converts a narrow string to a wide string using C++ std::mbstowcs() under
+//!   the executing thread's locale. A locale must be set before using this function, and it can be
+//!   set with std::setlocale() if needed. Upon success, the converted string is returned.
+//! \details Upon failure with throwOnError as false, the function returns an empty string. If
+//!   throwOnError as true, the function throws an InvalidArgument() exception.
+//! \note If you try to convert, say, the Chinese character for "bone" from UTF-8 (0xE9 0xAA 0xA8)
+//!   to UTF-16 (0x9AA8), then you must ensure the locale is available. If the locale is not available,
+//!   then a 0x21 error is returned on Windows which eventually results in an InvalidArgument() exception.
+std::wstring StringWiden(const char *str, bool throwOnError = true);
+
 #ifdef CRYPTOPP_DOXYGEN_PROCESSING
 
 //! \brief Allocates a buffer on 16-byte boundary