minidom Level 1 DOM compliance

[jorend]

BPO	1704134
Nosy	@loewis, @devdanzin
Files	minidom-level-1-compliance.patch: patch against trunk rev 54884 minidom-level-1-compliance.3.patch: updated patch against trunk rev 54954 minidom-level-1-compliance.4.patch: updated patch against trunk rev 55014

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2007-04-20.07:39:47.000>
labels = ['expert-XML', 'type-bug']
title = 'minidom Level 1 DOM compliance'
updated_at = <Date 2014-02-03.19:20:23.877>
user = 'https://bugs.python.org/jorend'

bugs.python.org fields:

activity = <Date 2014-02-03.19:20:23.877>
actor = 'BreamoreBoy'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['XML']
creation = <Date 2007-04-20.07:39:47.000>
creator = 'jorend'
dependencies = []
files = ['7952', '7953', '7954']
hgrepos = []
issue_num = 1704134
keywords = ['patch']
message_count = 12.0
messages = ['52470', '52471', '52472', '52473', '52474', '52475', '52476', '52477', '52478', '52479', '52480', '110582']
nosy_count = 4.0
nosy_names = ['loewis', 'nnorwitz', 'jorend', 'ajaksu2']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue1704134'
versions = ['Python 3.1', 'Python 2.7', 'Python 3.2']

Linked PRs

• gh-44871: Improve DOM Level 1 conformance of xml.dom.minidom #155641

[jorend]

Tested on: Mac OS X 10.4.9

This patch fixes numerous bugs in xml.dom.minidom and expatbuilder.
It fixes all the small-to-middling bugs in minidom's DOM Level 1
compliance that I'm aware of; only large bugs remain (see below).

Changes: These are mainly fixes for bugs found by the W3C DOM Test
Suite for DOM Level 1. Python 2.5 fails over 120 of these tests; I
got the number down to 48.

• Exposed expat's XML_GetSpecifiedAttributeCount() as a method of
  pyexpat parser objects. (This is needed to set Attr.specified
  correctly.) Documented the new method in Doc/lib/libpyexpat.tex.

• Attributes that got default values from the DTD didn't show up in
  the DOM. (This was a violation of the XML 1.0 spec! See
  http://www.w3.org/TR/REC-xml/#proc-types section 5.1, "Validating
  and Non-Validating Processors". Even non-validating processors
  must "supply default attribute values" based on a certain subset
  of the DTD!)

• Attr.specified is now set correctly. Before, it was always False
  (should have been True).

• Inserting a node into one of its descendants caused an infinite
  loop! :-) Now it throws HierarchyMalarkey, per the spec.

• Many error conditions specified in the DOM were not detected. In
  particular, InvalidCharacterErr was never raised. The new version
  does a lot more checking.

• Assigning to nodeValue is now a no-op for node types where it's
  defined to be null.

• Document.createEntityReference() is implemented. It returns an
  EntityReference node, but the node is not populated from the DTD.
  (That is, the new EntityReference implementation is compliant as
  far as it goes, but incomplete.)

• Element.removeAttributeNode(attr) now raises NotFoundErr if
  attr belongs to some other Element and merely has the same name as
  an attribute of this Element.

• Element.setAttributeNode() would sometimes return None erroneously.

• Element.removeAttributeNode() now returns the removed node.

• Several CharacterData methods would incorrectly throw if you
  passed node.length as the index.

• Added Document.xmlVersion (from DOM Level 3). This affects
  INVALID_CHARACTER_ERR checking as specified.

• Added tests for all of the above.

• Removed trailing whitespace from lines in Lib/test/test_minidom.py.

• Deleted obsolete gc testing from test_minidom.

• In one or two places, broke very large asserts into many small
  asserts. (I was debugging something. This change is inessential,
  but it's a good change, so I kept it.)

DOM Level 1 bugs remaining:

• A lot of the readonly properties are not implemented as readonly.
  This would be easy to fix with new-style classes, but these are
  old-style classes that are using property() for a few things--I
  haven't tried to understand it yet. I'm putting this off until
  the present patch lands.

• All NodeLists should be live views, even the one returned by
  getElementsByName(). It will be hard to fix this while retaining
  pickle backward compatibility, and still harder to do it without
  hurting performance.

• Attribute nodes' nodeValue and childNodes are supposed to stay in
  sync. This has all the same problems.

• EntityReference nodes should be populated with child nodes. The
  descendants of EntityReference nodes should be readonly. This is
  slightly less of a headache.

I haven't even tried to run DOMTS level2 tests yet. I'm sure it'll be
pretty gruesome.

[jorend]

Justification for the most significant changes:

1. I added a __setattr__() method to class xml.dom.minidom.Node. This means existing code that subclasses any of the Node classes *and* overrides __setattr__() *and* isn't calling the base class __setattr__... will not get the new __setattr__ functionality, which basically implements a DOM-compatibility quirk. I think it's OK. :)

2. There's a flag in pyexpat that lets you turn off default attribute values. The flag is marked "use with caution", because turning this off is not XML-compliant. expatbuilder was using the flag. I can't tell why. There was no comment in the code. I think it was just a mistake; I changed it, and minidom passes more DOMTS tests as a result.

3. To implement Attr.specified, I had to expose another Expat API via pyexpat. This was actually a pretty minor change, but I mention it because I'm sure anyone opening this patch will be shocked that it touches any C code. :)

4. Added some big regexes to check for non-XML-compliant names and raise InvalidCharacterErr. I didn't see a better way to do this. If anyone is worried about the performance hit from doing these checks, I'll look at it.

[nnorwitz]

Wow this patch is big!

I notice a lot of whitespace changes, can you drop those from the patch, it will make it easier to review. I don't see any extra whitespace in the original, so maybe if you ran Tools/scripts/reindent.py over the code that would clean it up. I think that's what Tim uses to normalize whitespace.

The new tests are good to see. I see you added doc for a new method in xmlparser, but the new class EntityReference from minidom.py is not documented.

In xml/dom/minidom.py, it seems odd to see if cond: pass else: # do something. What about inverting the condition so pass/else is not necessary. The comment could be improved here as to why this is a no-op.

The patch itself looked fine to me. I didn't review in complete context (ie, I didn't apply it and review all the code), just the patch itself. I don't know enough about minidom to know if this change it good or not. Other than what I noted above, the patch looks decent on the surface.

[jorend]

Neal, thanks for looking at this.

Size: Yeah. :-\ I don't know what to do about this. There were a lot of bugs, so there are a lot of diffs. :(

Whitespace: I checked, and the extra whitespace is definitely in trunk's Lib/test/test_minidom.py; a recent change added it. This patch removes it. (I could revert the whitespace anyway, just to reduce the size of the patch. Let me know if I should do this.)

Doc: Oops! I will fix this today and upload a new patch.

pass: Thanks, I'll change as suggested. (Just to explain myself-- I used "if name == 'nodeValue': pass; else: ..." because 'nodeValue' is the special case, and the special behavior is "do nothing". But I'm not attached to that wording. I'll change it.)

[jorend]

OK, the updated patch has the suggested changes (Doc for EntityReference; eliminated "pass" and added comment in Node.__setattr__).

File Added: minidom-level-1-compliance.2.patch

[nnorwitz]

Jason, don't worry about the size, I was mostly complaining about the whitespace diffs. I know Tim hadn't done a normalization step for a while. I just did it and am running the tests now. Damn there are a lot! :-(

The good news is that your patch will go down. The bad news for you is that you are going to have to regenerate it and there will probably be conflicts. I'm hoping Martin will review it as he's quite knowledgeable about XML. I doubt there is any more that I can contribute to this patch other than to say it needs some expert eyes on it, but generally looks good.

The tests should be done within 15 minutes or so. Then I'll check in whitespace normalization.

[jorend]

File Added: minidom-level-1-compliance.3.patch

[loewis]

I guess we'll need a number of iterations. Some observations:

• I read the nodeValue specification so that it raises DOMException if you try to set it, and it is "readonly", where I interpret "readonly" as "always null" (because it appears to be the only case where the value is never changing). So __setattr__ should raise that exception, IMO.
• I think that the checks for correct names should be moved out of the minidom module, into a more global place (because it might be useful independent of minidom), e.g. xml.names. See also xml.utils.characters in PyXML.
• Setting the xmlVersion to 1.1 should raise NOT_SUPPORTED_ERR IMO: we cannot guarantee that we will write out correct XML 1.1 (i.e. a document that is in Unicode normal form NFC).

More later.

[jorend]

Martin, thank you very, very much for looking at this. Happy to
iterate. I'll turn it around as fast as I can, probably tomorrow.

• Node.nodeValue isn't readonly; setting it raises an exception only
  if the *node* is readonly. DOM Level 2 clarifies: "When it is defined
  to be null, setting it has no effect."

http://www.w3.org/TR/REC-DOM-Level-1/level-one-core.html#ID-1950641247
http://www.w3.org/TR/DOM-Level-2-Core/core.html#ID-F68D080

• I agree about moving the name-checking code out of minidom.
  "xml.names" sounds fine. Should it be official and documented?

  xml.names.is_name(name, [xmlVersion="1.0"]) -> bool
  Returns True if name matches the Name construction in the
  specified version of XML. Raises ValueError if xmlVersion is not
  a known version of XML (currently either "1.0" or "1.1").

• Regarding xmlVersion = "1.1": I don't think writing "fully
  normalized" XML is required. It's only a "SHOULD" in XML 1.1:

"All XML parsed entities (including document entities) SHOULD be fully
normalized [...] However, a document is still well-formed even if it
is not fully normalized. XML processors SHOULD provide a user option
to verify that the document being processed is in fully normalized
form, and report to the application whether it is or not."

http://www.w3.org/TR/xml11/#sec-normalization-checking

DOM Level 3 provides a "normalize-characters" option. Implementations
are not required to support it:

http://www.w3.org/TR/2004/REC-DOM-Level-3-LS-20040407/load-save.html#parameter-normalize-characters

I want to add normalization to writexml() and toxml(), but I hope it
can wait until after this patch lands.

[jorend]

Martin,

This version of the patch moves name-checking into a separate module, "xml.names". But for now it is undocumented (intentionally).

Also, DOMImplementation.hasFeature("XMLVersion", v) now returns True for v in ("1.0", "1.1"), and setting doc.xmlVersion to any other value raises NotSupportedErr. (Both these things are specified in DOM Level 3 Core under the Document.xmlVersion attribute.) Added a test for this, too.

I didn't make any other changes. Let me know if I'm wrong about those other two things.

File Added: minidom-level-1-compliance.4.patch

[jorend]

Martin, do I need to change anything else?