bpo-13611: C14N 2.0 implementation for ElementTree (GH-12966)
* Implement C14N 2.0 as a new canonicalize() function in ElementTree.
Missing features:
- prefix renaming in XPath expressions (tag and attribute text is supported)
- preservation of original prefixes given redundant namespace declarations
diff --git a/Lib/xml/etree/ElementTree.py b/Lib/xml/etree/ElementTree.py
index 5b26ac7..645e999 100644
--- a/Lib/xml/etree/ElementTree.py
+++ b/Lib/xml/etree/ElementTree.py
@@ -87,6 +87,7 @@
"XML", "XMLID",
"XMLParser", "XMLPullParser",
"register_namespace",
+ "canonicalize", "C14NWriterTarget",
]
VERSION = "1.3.0"
@@ -1711,6 +1712,336 @@
del self.target, self._target
+# --------------------------------------------------------------------
+# C14N 2.0
+
+def canonicalize(xml_data=None, *, out=None, from_file=None, **options):
+ """Convert XML to its C14N 2.0 serialised form.
+
+ If *out* is provided, it must be a file or file-like object that receives
+ the serialised canonical XML output (text, not bytes) through its ``.write()``
+ method. To write to a file, open it in text mode with encoding "utf-8".
+ If *out* is not provided, this function returns the output as text string.
+
+ Either *xml_data* (an XML string) or *from_file* (a file path or
+ file-like object) must be provided as input.
+
+ The configuration options are the same as for the ``C14NWriterTarget``.
+ """
+ if xml_data is None and from_file is None:
+ raise ValueError("Either 'xml_data' or 'from_file' must be provided as input")
+ sio = None
+ if out is None:
+ sio = out = io.StringIO()
+
+ parser = XMLParser(target=C14NWriterTarget(out.write, **options))
+
+ if xml_data is not None:
+ parser.feed(xml_data)
+ parser.close()
+ elif from_file is not None:
+ parse(from_file, parser=parser)
+
+ return sio.getvalue() if sio is not None else None
+
+
+_looks_like_prefix_name = re.compile(r'^\w+:\w+$', re.UNICODE).match
+
+
+class C14NWriterTarget:
+ """
+ Canonicalization writer target for the XMLParser.
+
+ Serialises parse events to XML C14N 2.0.
+
+ The *write* function is used for writing out the resulting data stream
+ as text (not bytes). To write to a file, open it in text mode with encoding
+ "utf-8" and pass its ``.write`` method.
+
+ Configuration options:
+
+ - *with_comments*: set to true to include comments
+ - *strip_text*: set to true to strip whitespace before and after text content
+ - *rewrite_prefixes*: set to true to replace namespace prefixes by "n{number}"
+ - *qname_aware_tags*: a set of qname aware tag names in which prefixes
+ should be replaced in text content
+ - *qname_aware_attrs*: a set of qname aware attribute names in which prefixes
+ should be replaced in text content
+ - *exclude_attrs*: a set of attribute names that should not be serialised
+ - *exclude_tags*: a set of tag names that should not be serialised
+ """
+ def __init__(self, write, *,
+ with_comments=False, strip_text=False, rewrite_prefixes=False,
+ qname_aware_tags=None, qname_aware_attrs=None,
+ exclude_attrs=None, exclude_tags=None):
+ self._write = write
+ self._data = []
+ self._with_comments = with_comments
+ self._strip_text = strip_text
+ self._exclude_attrs = set(exclude_attrs) if exclude_attrs else None
+ self._exclude_tags = set(exclude_tags) if exclude_tags else None
+
+ self._rewrite_prefixes = rewrite_prefixes
+ if qname_aware_tags:
+ self._qname_aware_tags = set(qname_aware_tags)
+ else:
+ self._qname_aware_tags = None
+ if qname_aware_attrs:
+ self._find_qname_aware_attrs = set(qname_aware_attrs).intersection
+ else:
+ self._find_qname_aware_attrs = None
+
+ # Stack with globally and newly declared namespaces as (uri, prefix) pairs.
+ self._declared_ns_stack = [[
+ ("http://www.w3.org/XML/1998/namespace", "xml"),
+ ]]
+ # Stack with user declared namespace prefixes as (uri, prefix) pairs.
+ self._ns_stack = []
+ if not rewrite_prefixes:
+ self._ns_stack.append(list(_namespace_map.items()))
+ self._ns_stack.append([])
+ self._prefix_map = {}
+ self._preserve_space = [False]
+ self._pending_start = None
+ self._root_seen = False
+ self._root_done = False
+ self._ignored_depth = 0
+
+ def _iter_namespaces(self, ns_stack, _reversed=reversed):
+ for namespaces in _reversed(ns_stack):
+ if namespaces: # almost no element declares new namespaces
+ yield from namespaces
+
+ def _resolve_prefix_name(self, prefixed_name):
+ prefix, name = prefixed_name.split(':', 1)
+ for uri, p in self._iter_namespaces(self._ns_stack):
+ if p == prefix:
+ return f'{{{uri}}}{name}'
+ raise ValueError(f'Prefix {prefix} of QName "{prefixed_name}" is not declared in scope')
+
+ def _qname(self, qname, uri=None):
+ if uri is None:
+ uri, tag = qname[1:].rsplit('}', 1) if qname[:1] == '{' else ('', qname)
+ else:
+ tag = qname
+
+ prefixes_seen = set()
+ for u, prefix in self._iter_namespaces(self._declared_ns_stack):
+ if u == uri and prefix not in prefixes_seen:
+ return f'{prefix}:{tag}' if prefix else tag, tag, uri
+ prefixes_seen.add(prefix)
+
+ # Not declared yet => add new declaration.
+ if self._rewrite_prefixes:
+ if uri in self._prefix_map:
+ prefix = self._prefix_map[uri]
+ else:
+ prefix = self._prefix_map[uri] = f'n{len(self._prefix_map)}'
+ self._declared_ns_stack[-1].append((uri, prefix))
+ return f'{prefix}:{tag}', tag, uri
+
+ if not uri and '' not in prefixes_seen:
+ # No default namespace declared => no prefix needed.
+ return tag, tag, uri
+
+ for u, prefix in self._iter_namespaces(self._ns_stack):
+ if u == uri:
+ self._declared_ns_stack[-1].append((uri, prefix))
+ return f'{prefix}:{tag}' if prefix else tag, tag, uri
+
+ raise ValueError(f'Namespace "{uri}" is not declared in scope')
+
+ def data(self, data):
+ if not self._ignored_depth:
+ self._data.append(data)
+
+ def _flush(self, _join_text=''.join):
+ data = _join_text(self._data)
+ del self._data[:]
+ if self._strip_text and not self._preserve_space[-1]:
+ data = data.strip()
+ if self._pending_start is not None:
+ args, self._pending_start = self._pending_start, None
+ qname_text = data if data and _looks_like_prefix_name(data) else None
+ self._start(*args, qname_text)
+ if qname_text is not None:
+ return
+ if data and self._root_seen:
+ self._write(_escape_cdata_c14n(data))
+
+ def start_ns(self, prefix, uri):
+ if self._ignored_depth:
+ return
+ # we may have to resolve qnames in text content
+ if self._data:
+ self._flush()
+ self._ns_stack[-1].append((uri, prefix))
+
+ def start(self, tag, attrs):
+ if self._exclude_tags is not None and (
+ self._ignored_depth or tag in self._exclude_tags):
+ self._ignored_depth += 1
+ return
+ if self._data:
+ self._flush()
+
+ new_namespaces = []
+ self._declared_ns_stack.append(new_namespaces)
+
+ if self._qname_aware_tags is not None and tag in self._qname_aware_tags:
+ # Need to parse text first to see if it requires a prefix declaration.
+ self._pending_start = (tag, attrs, new_namespaces)
+ return
+ self._start(tag, attrs, new_namespaces)
+
+ def _start(self, tag, attrs, new_namespaces, qname_text=None):
+ if self._exclude_attrs is not None and attrs:
+ attrs = {k: v for k, v in attrs.items() if k not in self._exclude_attrs}
+
+ qnames = {tag, *attrs}
+ resolved_names = {}
+
+ # Resolve prefixes in attribute and tag text.
+ if qname_text is not None:
+ qname = resolved_names[qname_text] = self._resolve_prefix_name(qname_text)
+ qnames.add(qname)
+ if self._find_qname_aware_attrs is not None and attrs:
+ qattrs = self._find_qname_aware_attrs(attrs)
+ if qattrs:
+ for attr_name in qattrs:
+ value = attrs[attr_name]
+ if _looks_like_prefix_name(value):
+ qname = resolved_names[value] = self._resolve_prefix_name(value)
+ qnames.add(qname)
+ else:
+ qattrs = None
+ else:
+ qattrs = None
+
+ # Assign prefixes in lexicographical order of used URIs.
+ parse_qname = self._qname
+ parsed_qnames = {n: parse_qname(n) for n in sorted(
+ qnames, key=lambda n: n.split('}', 1))}
+
+ # Write namespace declarations in prefix order ...
+ if new_namespaces:
+ attr_list = [
+ ('xmlns:' + prefix if prefix else 'xmlns', uri)
+ for uri, prefix in new_namespaces
+ ]
+ attr_list.sort()
+ else:
+ # almost always empty
+ attr_list = []
+
+ # ... followed by attributes in URI+name order
+ if attrs:
+ for k, v in sorted(attrs.items()):
+ if qattrs is not None and k in qattrs and v in resolved_names:
+ v = parsed_qnames[resolved_names[v]][0]
+ attr_qname, attr_name, uri = parsed_qnames[k]
+ # No prefix for attributes in default ('') namespace.
+ attr_list.append((attr_qname if uri else attr_name, v))
+
+ # Honour xml:space attributes.
+ space_behaviour = attrs.get('{http://www.w3.org/XML/1998/namespace}space')
+ self._preserve_space.append(
+ space_behaviour == 'preserve' if space_behaviour
+ else self._preserve_space[-1])
+
+ # Write the tag.
+ write = self._write
+ write('<' + parsed_qnames[tag][0])
+ if attr_list:
+ write(''.join([f' {k}="{_escape_attrib_c14n(v)}"' for k, v in attr_list]))
+ write('>')
+
+ # Write the resolved qname text content.
+ if qname_text is not None:
+ write(_escape_cdata_c14n(parsed_qnames[resolved_names[qname_text]][0]))
+
+ self._root_seen = True
+ self._ns_stack.append([])
+
+ def end(self, tag):
+ if self._ignored_depth:
+ self._ignored_depth -= 1
+ return
+ if self._data:
+ self._flush()
+ self._write(f'</{self._qname(tag)[0]}>')
+ self._preserve_space.pop()
+ self._root_done = len(self._preserve_space) == 1
+ self._declared_ns_stack.pop()
+ self._ns_stack.pop()
+
+ def comment(self, text):
+ if not self._with_comments:
+ return
+ if self._ignored_depth:
+ return
+ if self._root_done:
+ self._write('\n')
+ elif self._root_seen and self._data:
+ self._flush()
+ self._write(f'<!--{_escape_cdata_c14n(text)}-->')
+ if not self._root_seen:
+ self._write('\n')
+
+ def pi(self, target, data):
+ if self._ignored_depth:
+ return
+ if self._root_done:
+ self._write('\n')
+ elif self._root_seen and self._data:
+ self._flush()
+ self._write(
+ f'<?{target} {_escape_cdata_c14n(data)}?>' if data else f'<?{target}?>')
+ if not self._root_seen:
+ self._write('\n')
+
+
+def _escape_cdata_c14n(text):
+ # escape character data
+ try:
+ # it's worth avoiding do-nothing calls for strings that are
+ # shorter than 500 character, or so. assume that's, by far,
+ # the most common case in most applications.
+ if '&' in text:
+ text = text.replace('&', '&')
+ if '<' in text:
+ text = text.replace('<', '<')
+ if '>' in text:
+ text = text.replace('>', '>')
+ if '\r' in text:
+ text = text.replace('\r', '
')
+ return text
+ except (TypeError, AttributeError):
+ _raise_serialization_error(text)
+
+
+def _escape_attrib_c14n(text):
+ # escape attribute value
+ try:
+ if '&' in text:
+ text = text.replace('&', '&')
+ if '<' in text:
+ text = text.replace('<', '<')
+ if '"' in text:
+ text = text.replace('"', '"')
+ if '\t' in text:
+ text = text.replace('\t', '	')
+ if '\n' in text:
+ text = text.replace('\n', '
')
+ if '\r' in text:
+ text = text.replace('\r', '
')
+ return text
+ except (TypeError, AttributeError):
+ _raise_serialization_error(text)
+
+
+# --------------------------------------------------------------------
+
# Import the C accelerators
try:
# Element is going to be shadowed by the C implementation. We need to keep