Move parsing of file ident to udf.py.

It makes more sense there.

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

Author: clalancette

pycdlib/pycdlib.py

@@ -2124,15 +2124,12 @@ def _walk_udf_directories(self, extent_to_inode):
                 while offset < len(data):
                     current_extent = (abs_file_ident_extent * self.logical_block_size + offset) // self.logical_block_size
 
-                    desc_tag = udfmod.UDFTag()
-                    desc_tag.parse(data[offset:], current_extent - part_start)
-                    if desc_tag.tag_ident != 257:
-                        raise pycdlibexception.PyCdlibInvalidISO('UDF File Identifier Tag identifier not 257')
-                    file_ident = udfmod.UDFFileIdentifierDescriptor()
-                    offset += file_ident.parse(data[offset:],
-                                               current_extent,
-                                               desc_tag,
-                                               udf_file_entry)
+                    file_ident, bytes_forward = udfmod.parse_file_ident(data[offset:],
+                                                                        current_extent,
+                                                                        part_start,
+                                                                        udf_file_entry)
+                    offset += bytes_forward
+
                     if file_ident.is_parent():
                         # For a parent, no further work to do.
                         udf_file_entry.track_file_ident_desc(file_ident)

pycdlib/udf.py

@@ -5852,3 +5852,29 @@ def parse_file_entry(icbdata, abs_file_entry_extent, icb_log_block_num, parent):
     file_entry.parse(icbdata, abs_file_entry_extent, parent, desc_tag)
 
     return file_entry
+
+
+def parse_file_ident(data, current_extent, part_start, udf_file_entry):
+    # type: (bytes, int, int, UDFFileEntry) -> Tuple[UDFFileIdentifierDescriptor, int]
+    """
+    An internal method to parse a single UDF File Identifier and return the
+    corresponding object.
+
+    Parameters:
+     data - The data to parse.
+     current_extent - The extent number the data is located at.
+     part_start - The start of the logical partition.
+     udf_file_entry - The UDF File Entry that corresponds with this File
+                      Identifier.
+    Returns:
+     A tuple where the first item is a UDFFileIdentifierDescriptor, and the
+     second item is the number of bytes the descriptor consumed.
+    """
+    desc_tag = UDFTag()
+    desc_tag.parse(data, current_extent - part_start)
+    if desc_tag.tag_ident != 257:
+        raise pycdlibexception.PyCdlibInvalidISO('UDF File Identifier Tag identifier not 257')
+    file_ident = UDFFileIdentifierDescriptor()
+    bytes_forward = file_ident.parse(data, current_extent, desc_tag, udf_file_entry)
+
+    return file_ident, bytes_forward