BUG: Fix locale-dependent parsing in NRRD reader causing metadata corruption

Modules/Core/Common/include/itkNumericLocale.h

@@ -0,0 +1,111 @@
+/*=========================================================================
+ *
+ *  Copyright NumFOCUS
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *         https://www.apache.org/licenses/LICENSE-2.0.txt
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *=========================================================================*/
+#ifndef itkNumericLocale_h
+#define itkNumericLocale_h
+
+#include "itkMacro.h"
+#include "ITKCommonExport.h"
+
+#include <locale.h>
+#include <cstring>
+#include <cstdlib>
+
+// Platform-specific includes for thread-safe locale handling
+#if defined(_WIN32)
+#  include <windows.h>
+#elif defined(__APPLE__) || defined(__linux__) || defined(__unix__)
+// POSIX systems provide newlocale/uselocale in locale.h (C11) or xlocale.h (older)
+#  if defined(__APPLE__)
+#    include <xlocale.h>
+#  elif defined(__GLIBC__)
+// glibc provides locale_t in locale.h
+#  else
+// Try xlocale.h for other systems, fall back to locale.h
+#    if __has_include(<xlocale.h>)
+#      include <xlocale.h>
+#    endif
+#  endif
+#endif
+
+namespace itk
+{
+
+/** \class NumericLocale
+ * \brief RAII class for thread-safe temporary setting of LC_NUMERIC locale to "C".
+ *
+ * This class provides a thread-safe mechanism to temporarily set the LC_NUMERIC
+ * locale to "C" for locale-independent parsing and formatting of floating-point
+ * numbers. The original locale is automatically restored when the object goes
+ * out of scope.
+ *
+ * This is particularly useful when parsing file formats that use dot as decimal
+ * separator (like NRRD, VTK, etc.) regardless of the system locale setting.
+ *
+ * Thread safety:
+ * - On POSIX systems (Linux, macOS, BSD): Uses thread-local locale via uselocale()
+ * - On Windows: Uses thread-local locale via _configthreadlocale()
+ * - Fallback: Uses global setlocale() with mutex protection (not fully thread-safe
+ *   for concurrent I/O operations, but prevents corruption of locale state)
+ *
+ * Example usage:
+ * \code
+ * {
+ *   NumericLocale cLocale;
+ *   // Parse file with dot decimal separator
+ *   double value = std::strtod("3.14159", nullptr);
+ *   // Locale automatically restored here
+ * }
+ * \endcode
+ *
+ * \ingroup ITKCommon
+ */
+class ITKCommon_EXPORT NumericLocale
+{
+public:
+  /** Constructor: Saves current LC_NUMERIC locale and sets it to "C" */
+  NumericLocale();
+
+  /** Destructor: Restores the original LC_NUMERIC locale */
+  ~NumericLocale();
+
+  // Delete copy and move operations
+  NumericLocale(const NumericLocale &) = delete;
+  NumericLocale &
+  operator=(const NumericLocale &) = delete;
+  NumericLocale(NumericLocale &&) = delete;
+  NumericLocale &
+  operator=(NumericLocale &&) = delete;
+
+private:
+#if defined(_WIN32)
+  // Windows: store previous thread-specific locale setting
+  int m_PreviousThreadLocaleSetting{ -1 };
+  char * m_SavedLocale{ nullptr };
+#elif defined(__APPLE__) || defined(__linux__) || defined(__unix__)
+  // POSIX: store previous thread-local locale
+  locale_t m_PreviousLocale{ nullptr };
+  locale_t m_CLocale{ nullptr };
+#else
+  // Fallback: global locale (protected by mutex in implementation)
+  char * m_SavedLocale{ nullptr };
+#endif
+};
+
+} // end namespace itk
+
+#endif // itkNumericLocale_h

Modules/Core/Common/src/CMakeLists.txt

@@ -66,6 +66,7 @@ set(
   itkLogger.cxx
   itkLogOutput.cxx
   itkLoggerOutput.cxx
+  itkNumericLocale.cxx
   itkProgressAccumulator.cxx
   itkTotalProgressReporter.cxx
   itkNumericTraits.cxx

Modules/Core/Common/src/itkNumericLocale.cxx

@@ -0,0 +1,139 @@
+/*=========================================================================
+ *
+ *  Copyright NumFOCUS
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *         https://www.apache.org/licenses/LICENSE-2.0.txt
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *=========================================================================*/
+
+#include "itkNumericLocale.h"
+
+#include <mutex>
+
+namespace itk
+{
+
+#if defined(_WIN32)
+
+// Windows implementation using thread-specific locale
+NumericLocale::NumericLocale()
+{
+  // Enable thread-specific locale for this thread
+  m_PreviousThreadLocaleSetting = _configthreadlocale(_ENABLE_PER_THREAD_LOCALE);
+
+  // Save current LC_NUMERIC locale
+  const char * currentLocale = setlocale(LC_NUMERIC, nullptr);
+  if (currentLocale)
+  {
+    m_SavedLocale = _strdup(currentLocale);
+    // If _strdup fails (returns nullptr), m_SavedLocale remains nullptr
+    // and the locale will not be restored in the destructor
+  }
+
+  // Set to C locale for parsing
+  setlocale(LC_NUMERIC, "C");
+}
+
+NumericLocale::~NumericLocale()
+{
+  // Restore original locale
+  if (m_SavedLocale)
+  {
+    setlocale(LC_NUMERIC, m_SavedLocale);
+    free(m_SavedLocale);
+  }
+
+  // Restore previous thread-specific locale setting
+  if (m_PreviousThreadLocaleSetting != -1)
+  {
+    _configthreadlocale(m_PreviousThreadLocaleSetting);
+  }
+}
+
+#elif defined(__APPLE__) || defined(__linux__) || defined(__unix__)
+
+// POSIX implementation using thread-local locale (uselocale/newlocale)
+NumericLocale::NumericLocale()
+{
+  // Create a new C locale
+  // If newlocale fails (returns nullptr), m_CLocale remains nullptr
+  // and the locale will not be changed - this is a safe fallback
+  m_CLocale = newlocale(LC_NUMERIC_MASK, "C", nullptr);
+
+  if (m_CLocale)
+  {
+    // Set the C locale for this thread and save the previous locale
+    // uselocale returns the previous locale, which may be LC_GLOBAL_LOCALE
+    m_PreviousLocale = uselocale(m_CLocale);
+  }
+}
+
+NumericLocale::~NumericLocale()
+{
+  // If we created and installed a C locale for this thread,
+  // restore the previous locale and free the C locale.
+  // Always restore if m_CLocale is set, as m_PreviousLocale may be
+  // LC_GLOBAL_LOCALE which is a valid non-null value.
+  if (m_CLocale)
+  {
+    uselocale(m_PreviousLocale);
+    freelocale(m_CLocale);
+  }
+}
+
+#else
+
+// Fallback implementation using global locale with mutex protection
+// This is not ideal but provides some protection against concurrent access
+namespace
+{
+std::mutex localeMutex;
+}
+
+NumericLocale::NumericLocale()
+{
+  // Lock mutex to protect global locale state
+  // Using direct lock/unlock instead of lock_guard to maintain compatibility
+  // with the RAII pattern where unlock happens in destructor
+  localeMutex.lock();
+
+  // Save current LC_NUMERIC locale
+  const char * currentLocale = setlocale(LC_NUMERIC, nullptr);
+  if (currentLocale)
+  {
+    m_SavedLocale = strdup(currentLocale);
+    // If strdup fails (returns nullptr), m_SavedLocale remains nullptr
+    // and the locale will not be restored in the destructor
+  }
+
+  // Set to C locale for parsing
+  // Note: setlocale is a C function and does not throw exceptions
+  setlocale(LC_NUMERIC, "C");
+}
+
+NumericLocale::~NumericLocale() noexcept
+{
+  // Restore original locale
+  if (m_SavedLocale)
+  {
+    setlocale(LC_NUMERIC, m_SavedLocale);
+    free(m_SavedLocale);
+  }
+
+  // Unlock mutex - must always happen to avoid deadlock
+  localeMutex.unlock();
+}
+
+#endif
+
+} // end namespace itk

Modules/IO/NRRD/src/itkNrrdImageIO.cxx

@@ -22,6 +22,7 @@
 #include "itkMetaDataObject.h"
 #include "itkIOCommon.h"
 #include "itkFloatingPointExceptions.h"
+#include "itkNumericLocale.h"
 
 #include <sstream>
 
@@ -395,6 +396,12 @@ NrrdImageIO::ReadImageInformation()
       FloatingPointExceptions::Disable();
     }
 
+    // Set LC_NUMERIC to "C" locale to ensure locale-independent parsing
+    // of floating-point values in NRRD headers (spacing, origin, direction, etc.).
+    // This prevents issues in locales that use comma as decimal separator.
+    // Using thread-safe NumericLocale from ITKCommon.
+    NumericLocale cLocale;
+
     // this is the mechanism by which we tell nrrdLoad to read
     // just the header, and none of the data
     nrrdIoStateSet(nio, nrrdIoStateSkipData, 1);
@@ -923,6 +930,11 @@ NrrdImageIO::Read(void * buffer)
   FloatingPointExceptions::Disable();
 #endif
 
+  // Set LC_NUMERIC to "C" locale to ensure locale-independent parsing
+  // of floating-point values in NRRD headers.
+  // Using thread-safe NumericLocale from ITKCommon.
+  NumericLocale cLocale;
+
   // Read in the nrrd.  Yes, this means that the header is being read
   // twice: once by NrrdImageIO::ReadImageInformation, and once here
   if (nrrdLoad(nrrd, this->GetFileName(), nullptr) != 0)
@@ -1338,6 +1350,11 @@ NrrdImageIO::Write(const void * buffer)
       break;
   }
 
+  // Set LC_NUMERIC to "C" locale to ensure locale-independent formatting
+  // of floating-point values when writing NRRD headers.
+  // Using thread-safe NumericLocale from ITKCommon.
+  NumericLocale cLocale;
+
   // Write the nrrd to file.
   if (nrrdSave(this->GetFileName(), nrrd, nio))
   {

Modules/IO/NRRD/test/CMakeLists.txt

@@ -17,6 +17,7 @@ set(
   itkNrrdVectorImageUnitLabelReadTest.cxx
   itkNrrd5dVectorImageReadWriteTest.cxx
   itkNrrdMetaDataTest.cxx
+  itkNrrdLocaleTest.cxx
 )
 
 # For itkNrrdImageIOTest.h.
@@ -356,3 +357,11 @@ itk_add_test(
     itkNrrdMetaDataTest
     ${ITK_TEST_OUTPUT_DIR}
 )
+
+itk_add_test(
+  NAME itkNrrdLocaleTest
+  COMMAND
+    ITKIONRRDTestDriver
+    itkNrrdLocaleTest
+    ${ITK_TEST_OUTPUT_DIR}
+)