move pointer tag common utility functions to xml_utils and add pointer tag support in HTML XBlock

xblocks_contrib/common/xml_utils.py

@@ -0,0 +1,187 @@
+"""Shared utilities for pointer tag handling across XBlocks.
+
+This module centralizes detection, path computation, and attribute application
+for OLX "pointer" tags used by XBlocks during import/export.
+Also provides helpers to load definition XML files referenced by pointer tags.
+
+Note: The functionality has been taken from the edx-platform's XmlMixin class.
+https://github.com/openedx/edx-platform/blob/18d5abb2f641db7f364f7566187e57bebdae9fe9/xmodule/xml_block.py
+"""
+
+import datetime
+import json
+
+from django.core.serializers.json import DjangoJSONEncoder
+from lxml import etree
+from opaque_keys.edx.keys import CourseKey, UsageKey
+from xblock.fields import Scope
+
+# Assume all XML files are persisted as utf-8.
+EDX_XML_PARSER = etree.XMLParser(dtd_validation=False, load_dtd=False, remove_blank_text=True, encoding="utf-8")
+
+filename_extension = "xml"
+
+
+class EdxJSONEncoder(DjangoJSONEncoder):
+    """
+    Custom JSONEncoder that handles ``Location`` and ``datetime.datetime`` objects.
+    Encodes ``Location`` as its URL string form, and ``datetime.datetime`` as an ISO 8601 string.
+    """
+
+    def default(self, o):
+        if isinstance(o, (CourseKey, UsageKey)):
+            return str(o)
+        elif isinstance(o, datetime.datetime):
+            if o.tzinfo is not None:
+                if o.utcoffset() is None:
+                    return o.isoformat() + "Z"
+                else:
+                    return o.isoformat()
+            else:
+                return o.isoformat()
+        else:
+            return super().default(o)
+
+
+def name_to_pathname(name):
+    """
+    Convert a location name for use in a path: replace ':' with '/'.
+    This allows users of the xml format to organize content into directories
+    """
+    return name.replace(":", "/")
+
+
+def is_pointer_tag(xml_obj):
+    """
+    Check if xml_obj is a pointer tag: <blah url_name="something" />.
+    No children, one attribute named url_name, no text.
+
+    Special case for course roots: the pointer is
+      <course url_name="something" org="myorg" course="course">
+
+    xml_obj: an etree Element
+
+    Returns a bool.
+    """
+    if xml_obj.tag != "course":
+        expected_attr = {"url_name"}
+    else:
+        expected_attr = {"url_name", "course", "org"}
+
+    actual_attr = set(xml_obj.attrib.keys())
+
+    has_text = xml_obj.text is not None and len(xml_obj.text.strip()) > 0
+
+    return len(xml_obj) == 0 and actual_attr == expected_attr and not has_text
+
+
+def serialize_field(value):
+    """
+    Return a string version of the value (where value is the JSON-formatted, internally stored value).
+
+    If the value is a string, then we simply return what was passed in.
+    Otherwise, we return json.dumps on the input value.
+    """
+    if isinstance(value, str):
+        return value
+    elif isinstance(value, datetime.datetime):
+        if value.tzinfo is not None and value.utcoffset() is None:
+            return value.isoformat() + "Z"
+        return value.isoformat()
+
+    return json.dumps(value, cls=EdxJSONEncoder)
+
+
+def deserialize_field(field, value):
+    """
+    Deserialize the string version to the value stored internally.
+
+    Note that this is not the same as the value returned by from_json, as model types typically store
+    their value internally as JSON. By default, this method will return the result of calling json.loads
+    on the supplied value, unless json.loads throws a TypeError, or the type of the value returned by json.loads
+    is not supported for this class (from_json throws an Error). In either of those cases, this method returns
+    the input value.
+    """
+    try:
+        deserialized = json.loads(value)
+        if deserialized is None:
+            return deserialized
+        try:
+            field.from_json(deserialized)
+            return deserialized
+        except (ValueError, TypeError):
+            # Support older serialized version, which was just a string, not result of json.dumps.
+            # If the deserialized version cannot be converted to the type (via from_json),
+            # just return the original value. For example, if a string value of '3.4' was
+            # stored for a String field (before we started storing the result of json.dumps),
+            # then it would be deserialized as 3.4, but 3.4 is not supported for a String
+            # field. Therefore field.from_json(3.4) will throw an Error, and we should
+            # actually return the original value of '3.4'.
+            return value
+
+    except (ValueError, TypeError):
+        # Support older serialized version.
+        return value
+
+
+def own_metadata(block):
+    """
+    Return a JSON-friendly dictionary that contains only non-inherited field
+    keys, mapped to their serialized values
+    """
+    return block.get_explicitly_set_fields_by_scope(Scope.settings)
+
+
+def apply_pointer_attributes(node, block) -> None:
+    """Apply required pointer attributes to the export node for a block.
+
+    Sets "url_name" for all blocks. For course blocks, also sets "org" and
+    "course" attributes.
+    """
+    if not node.get("url_name"):
+        node.set("url_name", block.url_name)
+
+    if getattr(block, "category", None) == "course":
+        # These attributes are required on course pointers
+        node.set("org", block.location.org)
+        node.set("course", block.location.course)
+
+
+def format_filepath(category, name):
+    """Formats a path to an XML definition file."""
+    return f"{category}/{name}.{filename_extension}"
+
+
+def file_to_xml(file_object):
+    """
+    Used when this module wants to parse a file object to xml
+    that will be converted to the definition.
+
+    Returns an lxml Element
+    """
+    return etree.parse(file_object, parser=EDX_XML_PARSER).getroot()
+
+
+def load_file(filepath, fs, def_id):
+    """
+    Open the specified file in fs, and call `file_to_xml` on it,
+    returning the lxml object.
+
+    Add details and reraise on error.
+    """
+    try:
+        with fs.open(filepath) as xml_file:
+            return file_to_xml(xml_file)
+    except Exception as err:
+        # Add info about where we are, but keep the traceback
+        raise Exception(f"Unable to load file contents at path {filepath} for item {def_id}: {err}") from err
+
+
+def load_definition_xml(node, runtime, def_id):
+    """
+    Loads definition_xml stored in a dedicated file
+    """
+    url_name = node.get("url_name")
+    filepath = format_filepath(node.tag, name_to_pathname(url_name))
+    definition_xml = load_file(filepath, runtime.resources_fs, def_id)
+    return definition_xml, filepath