[xml/sgml-pkgs] Bug#845552: libxml2: Error when resolving relative URLs in XML catalogs, resulting in "file:/..." URLs

[Matthias Pigulla]

Package: libxml2
Version: 2.9.1+dfsg1-5+deb8u3
Severity: important

The 0034-xmlSaveUri-incorrectly-recomposes-URIs-with-rootless.patch patch
was added back in 2.9.1+dfsg1-4, probably following the bug report at
https://bugzilla.gnome.org/show_bug.cgi?id=731063.

This patch, however, caused additional issues:

The first one was addressed in
https://git.gnome.org/browse/libxml2/commit/?id=beb7281055dbf0ed4d041022a67
c6c5cfd126f25. As far as I can tell, this change has not yet been
cherry-picked.

Second, the change caused a break with resolution of relative URLs, see
https://mail.gnome.org/archives/xml/2016-November/msg00012.html. The
result is that when using the default DTDs as provided by, for example,
the w3c-dtd-xhtml package, libxml will construct invalid URLs like
"file:/usr/share/xml/xhtml/schema/dtd/1.0/xhtml1-strict.dtd". This is
missing two "//" slashes in the beginning. libxml will wrongly interpret
this URL (including the file: prefix!) as a local file path and fail
during catalog resolution.

The error message typically would be something like

failed to load external entity
"file:/usr/share/xml/xhtml/schema/dtd/1.0/xhtml1-strict.dtd" in Entity,
line ...

A simple check is to run the testURI command which is contained in/build
by libxml:

./testURI --base file:///some/where file


Result without patch: file:/some/file
Result with patch: file:///some/file

Suggestion:

- Cherry pick 
https://git.gnome.org/browse/libxml2/commit/?id=beb7281055dbf0ed4d041022a67
c6c5cfd126f25
- Additionally, apply the attached patch

Thanks!
-mp.

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