Move more of the UDF logical volume integrity parsing to udf.py

Signed-off-by: Chris Lalancette <clalancette@openrobotics.org>

Author: clalancette

pycdlib/pycdlib.py

@@ -2052,26 +2052,11 @@ def _parse_udf_descriptors(self):
             self._seek_to_extent(self.udf_main_descs.logical_volumes[0].integrity_sequence.extent_location)
             integrity_data = self._cdfp.read(self.udf_main_descs.logical_volumes[0].integrity_sequence.extent_length)
 
-            offset = 0
-            current_extent = self.udf_main_descs.logical_volumes[0].integrity_sequence.extent_location
-            desc_tag = udfmod.UDFTag()
-            desc_tag.parse(integrity_data[offset:], current_extent)
-            if desc_tag.tag_ident != 9:
-                raise pycdlibexception.PyCdlibInvalidISO('UDF Volume Integrity Tag identifier not 9')
-            self.udf_logical_volume_integrity = udfmod.UDFLogicalVolumeIntegrityDescriptor()
-            self.udf_logical_volume_integrity.parse(integrity_data[offset:offset + 512],
-                                                    current_extent, desc_tag)
-
-            offset += self.logical_block_size
-            if len(integrity_data) >= (offset + self.logical_block_size):
-                current_extent += 1
-                desc_tag = udfmod.UDFTag()
-                desc_tag.parse(integrity_data[offset:], current_extent)
-                if desc_tag.tag_ident != 8:
-                    raise pycdlibexception.PyCdlibInvalidISO('UDF Logical Volume Integrity Terminator Tag identifier not 8')
-                self.udf_logical_volume_integrity_terminator = udfmod.UDFTerminatingDescriptor()
-                self.udf_logical_volume_integrity_terminator.parse(current_extent,
-                                                                   desc_tag)
+        ulvi, ulvi_term = udfmod.parse_logical_volume_integrity(integrity_data,
+                                                                self.udf_main_descs.logical_volumes[0].integrity_sequence.extent_location,
+                                                                self.logical_block_size)
+        self.udf_logical_volume_integrity = ulvi
+        self.udf_logical_volume_integrity_terminator = ulvi_term
 
         # Now look for the File Set Descriptor.
         current_extent = self.udf_main_descs.partitions[0].part_start_location

pycdlib/udf.py

@@ -32,7 +32,7 @@
 
 # For mypy annotations
 if False:  # pylint: disable=using-constant-test
-    from typing import List, Optional, Type, Union  # NOQA pylint: disable=unused-import
+    from typing import List, Optional, Tuple, Type, Union  # NOQA pylint: disable=unused-import
     # NOTE: this import has to be here to avoid circular deps
     from pycdlib import inode  # NOQA pylint: disable=unused-import
 
@@ -5786,3 +5786,37 @@ def parse_anchor(anchor_data, anchor_location):
     anchor = UDFAnchorVolumeStructure()
     anchor.parse(anchor_data, anchor_location, anchor_tag)
     return anchor
+
+
+def parse_logical_volume_integrity(integrity_data, current_extent, logical_block_size):
+    # type: (bytes, int, int) -> Tuple[UDFLogicalVolumeIntegrityDescriptor, Optional[UDFTerminatingDescriptor]]
+    """
+    An internal method to parse Logical Volume Integrity data, and an optional
+    Logical Volume Integrity Terminator.
+
+    Parameters:
+     integrity_data - The data to parse.
+     current_extent - The extent location of the data.
+     logical_block_size - The logical block size of the ISO.
+    Returns:
+     A tuple where the first item is a UDFLogicalVolumeIntegrityDescriptor, and
+     the second item is a optional UDFTerminatorDescriptor.
+    """
+    desc_tag = UDFTag()
+    desc_tag.parse(integrity_data, current_extent)
+    if desc_tag.tag_ident != 9:
+        raise pycdlibexception.PyCdlibInvalidISO('UDF Volume Integrity Tag identifier not 9')
+    logical_volume_integrity = UDFLogicalVolumeIntegrityDescriptor()
+    logical_volume_integrity.parse(integrity_data[:512], current_extent, desc_tag)
+
+    logical_volume_integrity_terminator = None
+    offset = logical_block_size
+    if len(integrity_data) >= (offset + logical_block_size):
+        desc_tag = UDFTag()
+        desc_tag.parse(integrity_data[offset:], current_extent + 1)
+        if desc_tag.tag_ident != 8:
+            raise pycdlibexception.PyCdlibInvalidISO('UDF Logical Volume Integrity Terminator Tag identifier not 8')
+        logical_volume_integrity_terminator = UDFTerminatingDescriptor()
+        logical_volume_integrity_terminator.parse(current_extent + 1, desc_tag)
+
+    return logical_volume_integrity, logical_volume_integrity_terminator