feat: generate OLX with single-quoted attributes (WIP)

mypy.ini

@@ -12,7 +12,8 @@ files =
     openedx/core/djangoapps/xblock,
     openedx/core/types,
     openedx/core/djangoapps/content_tagging,
-    xmodule/util/keys.py
+    xmodule/util/keys.py,
+    xmodule/util/olx.py
 
 [mypy.plugins.django-stubs]
 # content_staging only works with CMS; others work with either, so we run mypy with CMS settings.

xmodule/modulestore/xml_exporter.py

@@ -1,10 +1,11 @@
 """
 Methods for exporting course data to XML
 """
-
+from __future__ import annotations
 
 import logging
 import os
+import typing as t
 from abc import abstractmethod
 from json import dumps
 
@@ -24,6 +25,7 @@
 from xmodule.modulestore.draft_and_published import DIRECT_ONLY_CATEGORIES
 from xmodule.modulestore.inheritance import own_metadata
 from xmodule.modulestore.store_utilities import draft_node_constructor, get_draft_subtree_roots
+from xmodule.util.olx import write_xml_to_file
 
 DRAFT_DIR = "drafts"
 PUBLISHED_DIR = "published"
@@ -202,8 +204,8 @@ def get_courselike(self):
         return self.modulestore.get_course(self.courselike_key, depth=None, lazy=False)
 
     def process_root(self, root, export_fs):
-        with export_fs.open('course.xml', 'wb') as course_xml:
-            lxml.etree.ElementTree(root).write(course_xml, encoding='utf-8')
+        with export_fs.open('course.xml', 'w') as course_xml:
+            write_xml_to_file(root, course_xml)
 
     def process_extra(self, root, courselike, root_courselike_dir, xml_centric_courselike_key, export_fs):
         # Export the modulestore's asset metadata.
@@ -216,8 +218,8 @@ def process_extra(self, root, courselike, root_courselike_dir, xml_centric_cours
             # All asset types are exported using the "asset" tag - but their asset type is specified in each asset key.
             asset = lxml.etree.SubElement(asset_root, AssetMetadata.ASSET_XML_TAG)
             asset_md.to_xml(asset)
-        with OSFS(asset_dir).open(AssetMetadata.EXPORTED_ASSET_FILENAME, 'wb') as asset_xml_file:
-            lxml.etree.ElementTree(asset_root).write(asset_xml_file, encoding='utf-8')
+        with OSFS(asset_dir).open(AssetMetadata.EXPORTED_ASSET_FILENAME, 'w') as asset_xml_file:
+            write_xml_to_file(asset_root, asset_xml_file)
 
         # export the static assets
         policies_dir = export_fs.makedir('policies', recreate=True)
@@ -344,9 +346,8 @@ def post_process(self, root, export_fs):
         called library.xml.
         """
         # Create the Library.xml file, which acts as the index of all library contents.
-        xml_file = export_fs.open(LIBRARY_ROOT, 'wb')
-        xml_file.write(lxml.etree.tostring(root, pretty_print=True, encoding='utf-8'))
-        xml_file.close()
+        with export_fs.open(LIBRARY_ROOT, 'w') as xml_file:
+            write_xml_to_file(root, xml_file)
 
 
 def export_course_to_xml(modulestore, contentstore, course_key, root_dir, course_dir):

xmodule/util/olx.py

@@ -0,0 +1,98 @@
+"""
+Utility methods for parsing/generating OLX.
+"""
+from __future__ import annotations
+
+import typing as t
+from abc import abstractmethod
+
+from lxml import etree
+
+
+def write_xml_to_file(root_node: etree._Element, target_file: t.IO[str]) -> None:
+    """
+    @@TODO docstring
+    @@TODO unit tests
+    """
+    xml_str = etree.tostring(root_node, pretty_print=True, encoding='utf-8').decode('utf-8')
+    convert_quotes = lambda: True  # @@TODO: Make this a waffle flag?
+    if convert_quotes():
+        xml_chars = iter(xml_str)  # @@TODO: try to optimize this by streaming xml rather than rendering xml_str?
+        target_file.write("".join(_convert_attrs_to_single_quotes(xml_str)))
+    else:
+        target_file.write(xml_str)
+
+
+def _convert_attrs_to_single_quotes(xml_chars: t.Iterator[str]) -> t.Iterable[str]:
+    """
+    Given a stream of chars in an XML string, convert the quoutes around attrs from double to single.
+
+    This means exchanging double-quote escape sequences in attributes values (") for literal double quotes (").
+    It also means exchanging literal single quotes (') for single-quote escape sequences (').
+    Since OLX heavily uses JSON it our XML attribute values, this conversion generally nets clearner XML.
+
+    Example:
+        Before:
+            <problem data="{&quot;xyz&quot;: &quot;xyz's value&quot;}">...</problem>
+        After:
+            <problem data='{"xyz": "xyz&apos;s value"}'>...</problem>
+
+    ASSUMPTIONS:
+    * String is valid XML based on: <@@TODO link to spec>
+    * String is rendered by Python's LXML library.
+    * @@TODO state other syntax assumptions
+    """
+    try:
+        while c := next(xml_chars):
+
+            # We're outside of any tag until we see <
+
+            if c == "<":
+                yield "<"
+
+                # We're inside a tag: < ... >
+
+                while c := next(xml_chars):
+                    if c == ">":
+                        yield ">"
+
+                        break  # Done with the tag, back to the outside
+
+                    elif c == "\"":
+
+                        yield "'"  # Convert double-quote close to single-quote close
+
+                        # We're inside an attribute value: <tagname yada=" ... ">
+
+                        while c := next(xml_chars):
+                            if c == "\"":
+                                yield "'"  # Convert double-quote close to single-quote close
+
+                                break  # Done with the attribute value, back to the tag
+
+                            elif c == "'":
+
+                                yield "&apos;"  # Single quote in attr --> convert to escape sequence
+
+                            elif c == "&":
+
+                                # We're inside an escape sequence: <tagname yada="blah &...; blah">
+                                escape_code = ""
+                                while c := next(xml_chars):
+                                    if c == ";":
+                                        break  # Done with escape sequence
+                                    else:
+                                        escape_code += c
+                                if escape_code == "quot":
+                                    yield "\""  # Escape sequence is &quot; --> convert to literal double-qoute
+                                else:
+                                    yield "&{escape_code};"  # Any other escape sequence --> leave it as-is
+
+                            else:
+                                yield c  # yield char from attribute value
+                    else:
+                        yield c  # yield char from inside a tag
+            else:
+                yield c  # yield char from outside tags
+    except StopIteration:
+        pass

xmodule/xml_block.py

@@ -12,6 +12,7 @@
 from xblock.runtime import KvsFieldData
 from xmodule.modulestore import EdxJSONEncoder
 from xmodule.modulestore.inheritance import InheritanceKeyValueStore, own_metadata
+from xmodule.util.olx import write_xml_to_file
 
 log = logging.getLogger(__name__)
 
@@ -472,8 +473,8 @@ def add_xml_to_node(self, node):
                 self.location.run if self.category == 'course' else url_path,
             )
             self.runtime.export_fs.makedirs(os.path.dirname(filepath), recreate=True)
-            with self.runtime.export_fs.open(filepath, 'wb') as fileobj:
-                ElementTree(xml_object).write(fileobj, pretty_print=True, encoding='utf-8')
+            with self.runtime.export_fs.open(filepath, 'w') as fileobj:
+                write_xml_to_file(xml_object, fileobj)
         else:
             # Write all attributes from xml_object onto node
             node.clear()