bpo-35018: Sax parser should provide user access to lexical handlers (GH-20958)

Co-Authored-By: Jonathan Gossage <jgossage@gmail.com>

Doc/library/xml.sax.handler.rst

@@ -11,12 +11,12 @@
 
 --------------
 
-The SAX API defines four kinds of handlers: content handlers, DTD handlers,
+The SAX API defines five kinds of handlers: content handlers, DTD handlers,
-error handlers, and entity resolvers. Applications normally only need to
+error handlers, entity resolvers and lexical handlers. Applications normally
-implement those interfaces whose events they are interested in; they can
+only need to implement those interfaces whose events they are interested in;
-implement the interfaces in a single object or in multiple objects. Handler
+they can implement the interfaces in a single object or in multiple objects.
-implementations should inherit from the base classes provided in the module
+Handler implementations should inherit from the base classes provided in the
-:mod:`xml.sax.handler`, so that all methods get default implementations.
+module :mod:`xml.sax.handler`, so that all methods get default implementations.
 
 
 .. class:: ContentHandler
@@ -47,6 +47,12 @@ implementations should inherit from the base classes provided in the module
    application.  The methods of this object control whether errors are immediately
    converted to exceptions or are handled in some other way.
 
+
+.. class:: LexicalHandler
+
+   Interface used by the parser to represent low freqency events which may not
+   be of interest to many applications.
+
 In addition to these classes, :mod:`xml.sax.handler` provides symbolic constants
 for the feature and property names.
 
@@ -114,7 +120,7 @@ for the feature and property names.
 .. data:: property_lexical_handler
 
    | value: ``"http://xml.org/sax/properties/lexical-handler"``
-   | data type: xml.sax.sax2lib.LexicalHandler (not supported in Python 2)
+   | data type: xml.sax.handler.LexicalHandler (not supported in Python 2)
    | description: An optional extension handler for lexical events like
      comments.
    | access: read/write
@@ -413,3 +419,45 @@ the passed-in exception object.
    information will continue to be passed to the application. Raising an exception
    in this method will cause parsing to end.
 
+
+.. _lexical-handler-objects:
+
+LexicalHandler Objects
+----------------------
+Optional SAX2 handler for lexical events.
+
+This handler is used to obtain lexical information about an XML
+document. Lexical information includes information describing the
+document encoding used and XML comments embedded in the document, as
+well as section boundaries for the DTD and for any CDATA sections.
+The lexical handlers are used in the same manner as content handlers.
+
+Set the LexicalHandler of an XMLReader by using the setProperty method
+with the property identifier
+``'http://xml.org/sax/properties/lexical-handler'``.
+
+
+.. method:: LexicalHandler.comment(content)
+
+   Reports a comment anywhere in the document (including the DTD and
+   outside the document element).
+
+.. method:: LexicalHandler.startDTD(name, public_id, system_id)
+
+   Reports the start of the DTD declarations if the document has an
+   associated DTD.
+
+.. method:: LexicalHandler.endDTD()
+
+   Reports the end of DTD declaration.
+
+.. method:: LexicalHandler.startCDATA()
+
+   Reports the start of a CDATA marked section.
+
+   The contents of the CDATA marked section will be reported through
+   the characters handler.
+
+.. method:: LexicalHandler.endCDATA()
+
+   Reports the end of a CDATA marked section.

Doc/whatsnew/3.10.rst

@@ -139,6 +139,13 @@ Add :data:`sys.orig_argv` attribute: the list of the original command line
 arguments passed to the Python executable.
 (Contributed by Victor Stinner in :issue:`23427`.)
 
+xml
+---
+
+Add a :class:`~xml.sax.handler.LexicalHandler` class to the
+:mod:`xml.sax.handler` module.
+(Contributed by Jonathan Gossage and Zackery Spytz in :issue:`35018`.)
+
 
 Optimizations
 =============

Lib/test/test_sax.py

@@ -13,7 +13,8 @@ except SAXReaderNotAvailable:
 from xml.sax.saxutils import XMLGenerator, escape, unescape, quoteattr, \
                              XMLFilterBase, prepare_input_source
 from xml.sax.expatreader import create_parser
-from xml.sax.handler import feature_namespaces, feature_external_ges
+from xml.sax.handler import (feature_namespaces, feature_external_ges,
+                             LexicalHandler)
 from xml.sax.xmlreader import InputSource, AttributesImpl, AttributesNSImpl
 from io import BytesIO, StringIO
 import codecs
@@ -1356,6 +1357,155 @@ class XmlReaderTest(XmlTestBase):
         self.assertEqual(attrs.getQNameByName((ns_uri, "attr")), "ns:attr")
 
 
+class LexicalHandlerTest(unittest.TestCase):
+    def setUp(self):
+        self.parser = None
+
+        self.specified_version = '1.0'
+        self.specified_encoding = 'UTF-8'
+        self.specified_doctype = 'wish'
+        self.specified_entity_names = ('nbsp', 'source', 'target')
+        self.specified_comment = ('Comment in a DTD',
+                                  'Really! You think so?')
+        self.test_data = StringIO()
+        self.test_data.write('<?xml version="{}" encoding="{}"?>\n'.
+                             format(self.specified_version,
+                                    self.specified_encoding))
+        self.test_data.write('<!DOCTYPE {} [\n'.
+                             format(self.specified_doctype))
+        self.test_data.write('<!-- {} -->\n'.
+                             format(self.specified_comment[0]))
+        self.test_data.write('<!ELEMENT {} (to,from,heading,body,footer)>\n'.
+                             format(self.specified_doctype))
+        self.test_data.write('<!ELEMENT to (#PCDATA)>\n')
+        self.test_data.write('<!ELEMENT from (#PCDATA)>\n')
+        self.test_data.write('<!ELEMENT heading (#PCDATA)>\n')
+        self.test_data.write('<!ELEMENT body (#PCDATA)>\n')
+        self.test_data.write('<!ELEMENT footer (#PCDATA)>\n')
+        self.test_data.write('<!ENTITY {} "&#xA0;">\n'.
+                             format(self.specified_entity_names[0]))
+        self.test_data.write('<!ENTITY {} "Written by: Alexander.">\n'.
+                             format(self.specified_entity_names[1]))
+        self.test_data.write('<!ENTITY {} "Hope it gets to: Aristotle.">\n'.
+                             format(self.specified_entity_names[2]))
+        self.test_data.write(']>\n')
+        self.test_data.write('<{}>'.format(self.specified_doctype))
+        self.test_data.write('<to>Aristotle</to>\n')
+        self.test_data.write('<from>Alexander</from>\n')
+        self.test_data.write('<heading>Supplication</heading>\n')
+        self.test_data.write('<body>Teach me patience!</body>\n')
+        self.test_data.write('<footer>&{};&{};&{};</footer>\n'.
+                             format(self.specified_entity_names[1],
+                                    self.specified_entity_names[0],
+                                    self.specified_entity_names[2]))
+        self.test_data.write('<!-- {} -->\n'.format(self.specified_comment[1]))
+        self.test_data.write('</{}>\n'.format(self.specified_doctype))
+        self.test_data.seek(0)
+
+        # Data received from handlers - to be validated
+        self.version = None
+        self.encoding = None
+        self.standalone = None
+        self.doctype = None
+        self.publicID = None
+        self.systemID = None
+        self.end_of_dtd = False
+        self.comments = []
+
+    def test_handlers(self):
+        class TestLexicalHandler(LexicalHandler):
+            def __init__(self, test_harness, *args, **kwargs):
+                super().__init__(*args, **kwargs)
+                self.test_harness = test_harness
+
+            def startDTD(self, doctype, publicID, systemID):
+                self.test_harness.doctype = doctype
+                self.test_harness.publicID = publicID
+                self.test_harness.systemID = systemID
+
+            def endDTD(self):
+                self.test_harness.end_of_dtd = True
+
+            def comment(self, text):
+                self.test_harness.comments.append(text)
+
+        self.parser = create_parser()
+        self.parser.setContentHandler(ContentHandler())
+        self.parser.setProperty(
+            'http://xml.org/sax/properties/lexical-handler',
+            TestLexicalHandler(self))
+        source = InputSource()
+        source.setCharacterStream(self.test_data)
+        self.parser.parse(source)
+        self.assertEqual(self.doctype, self.specified_doctype)
+        self.assertIsNone(self.publicID)
+        self.assertIsNone(self.systemID)
+        self.assertTrue(self.end_of_dtd)
+        self.assertEqual(len(self.comments),
+                         len(self.specified_comment))
+        self.assertEqual(f' {self.specified_comment[0]} ', self.comments[0])
+
+
+class CDATAHandlerTest(unittest.TestCase):
+    def setUp(self):
+        self.parser = None
+        self.specified_chars = []
+        self.specified_chars.append(('Parseable character data', False))
+        self.specified_chars.append(('<> &% - assorted other XML junk.', True))
+        self.char_index = 0  # Used to index specified results within handlers
+        self.test_data = StringIO()
+        self.test_data.write('<root_doc>\n')
+        self.test_data.write('<some_pcdata>\n')
+        self.test_data.write(f'{self.specified_chars[0][0]}\n')
+        self.test_data.write('</some_pcdata>\n')
+        self.test_data.write('<some_cdata>\n')
+        self.test_data.write(f'<![CDATA[{self.specified_chars[1][0]}]]>\n')
+        self.test_data.write('</some_cdata>\n')
+        self.test_data.write('</root_doc>\n')
+        self.test_data.seek(0)
+
+        # Data received from handlers - to be validated
+        self.chardata = []
+        self.in_cdata = False
+
+    def test_handlers(self):
+        class TestLexicalHandler(LexicalHandler):
+            def __init__(self, test_harness, *args, **kwargs):
+                super().__init__(*args, **kwargs)
+                self.test_harness = test_harness
+
+            def startCDATA(self):
+                self.test_harness.in_cdata = True
+
+            def endCDATA(self):
+                self.test_harness.in_cdata = False
+
+        class TestCharHandler(ContentHandler):
+            def __init__(self, test_harness, *args, **kwargs):
+                super().__init__(*args, **kwargs)
+                self.test_harness = test_harness
+
+            def characters(self, content):
+                if content != '\n':
+                    h = self.test_harness
+                    t = h.specified_chars[h.char_index]
+                    h.assertEqual(t[0], content)
+                    h.assertEqual(t[1], h.in_cdata)
+                    h.char_index += 1
+
+        self.parser = create_parser()
+        self.parser.setContentHandler(TestCharHandler(self))
+        self.parser.setProperty(
+            'http://xml.org/sax/properties/lexical-handler',
+            TestLexicalHandler(self))
+        source = InputSource()
+        source.setCharacterStream(self.test_data)
+        self.parser.parse(source)
+
+        self.assertFalse(self.in_cdata)
+        self.assertEqual(self.char_index, 2)
+
+
 def test_main():
     run_unittest(MakeParserTest,
                  ParseTest,
@@ -1368,7 +1518,10 @@ def test_main():
                  StreamReaderWriterXmlgenTest,
                  ExpatReaderTest,
                  ErrorReportingTest,
-                 XmlReaderTest)
+                 XmlReaderTest,
+                 LexicalHandlerTest,
+                 CDATAHandlerTest)
+
 
 if __name__ == "__main__":
     test_main()

Lib/xml/sax/handler.py

@@ -340,3 +340,48 @@ all_properties = [property_lexical_handler,
                   property_xml_string,
                   property_encoding,
                   property_interning_dict]
+
+
+class LexicalHandler:
+    """Optional SAX2 handler for lexical events.
+
+    This handler is used to obtain lexical information about an XML
+    document, that is, information about how the document was encoded
+    (as opposed to what it contains, which is reported to the
+    ContentHandler), such as comments and CDATA marked section
+    boundaries.
+
+    To set the LexicalHandler of an XMLReader, use the setProperty
+    method with the property identifier
+    'http://xml.org/sax/properties/lexical-handler'."""
+
+    def comment(self, content):
+        """Reports a comment anywhere in the document (including the
+        DTD and outside the document element).
+
+        content is a string that holds the contents of the comment."""
+
+    def startDTD(self, name, public_id, system_id):
+        """Report the start of the DTD declarations, if the document
+        has an associated DTD.
+
+        A startEntity event will be reported before declaration events
+        from the external DTD subset are reported, and this can be
+        used to infer from which subset DTD declarations derive.
+
+        name is the name of the document element type, public_id the
+        public identifier of the DTD (or None if none were supplied)
+        and system_id the system identfier of the external subset (or
+        None if none were supplied)."""
+
+    def endDTD(self):
+        """Signals the end of DTD declarations."""
+
+    def startCDATA(self):
+        """Reports the beginning of a CDATA marked section.
+
+        The contents of the CDATA marked section will be reported
+        through the characters event."""
+
+    def endCDATA(self):
+        """Reports the end of a CDATA marked section."""

Misc/NEWS.d/next/Library/2020-06-17-23-49-45.bpo-35018.NP5_Qk.rst

@@ -0,0 +1,2 @@
+Add the :class:`xml.sax.handler.LexicalHandler` class that is present in
+other SAX XML implementations.