We had put a test for libxml2's xmlStructuredErrorContext variable in
configure, but of course that doesn't work on Windows builds.  The next
best alternative seems to be to test the LIBXML_VERSION symbol provided
by xmlversion.h.

Per report from Talha Bin Rizwan, though this fixes it in a different way
than his proposed patch.

xml_parse() would attempt to fetch external files or URLs as needed to
resolve DTD and entity references in an XML value, thus allowing
unprivileged database users to attempt to fetch data with the privileges
of the database server.  While the external data wouldn't get returned
directly to the user, portions of it could be exposed in error messages
if the data didn't parse as valid XML; and in any case the mere ability
to check existence of a file might be useful to an attacker.

The ideal solution to this would still allow fetching of references that
are listed in the host system's XML catalogs, so that documents can be
validated according to installed DTDs.  However, doing that with the
available libxml2 APIs appears complex and error-prone, so we're not going
to risk it in a security patch that necessarily hasn't gotten wide review.
So this patch merely shuts off all access, causing any external fetch to
silently expand to an empty string.  A future patch may improve this.

In HEAD and 9.2, also suppress warnings about undefined entities, which
would otherwise occur as a result of not loading referenced DTDs.  Previous
branches don't show such warnings anyway, due to different error handling
arrangements.

Credit to Noah Misch for first reporting the problem, and for much work
towards a solution, though this simplistic approach was not his preference.
Also thanks to Daniel Veillard for consultation.

Security: CVE-2012-3489

commit-fest.

The tzn value might come from tm->tm_zone, which libc declares as
const, so it's prudent that the upper layers know about this as well.

Use an explicit argument to tell whether to include the time zone in
the output, rather than using some undocumented pointer magic.

This only produces warnings under -Wcast-qual, but it's more correct
and consistent in any case.

This addresses only those cases that are easy to fix by adding or
moving a const qualifier or removing an unnecessary cast.  There are
many more complicated cases remaining.

It turns out to be possible to link against a libxml2.so that does this
differently than the version we configured and built against, so we need
a runtime check to avoid bizarre behavior.  Per report from Bernd Helmle.
Patch by Florian Pflug.

Previously, xpath() simply returned an empty array if the expression did
not yield a node set.  This is useless for expressions that return scalars,
such as one with name() at the top level.  Arrange to return the scalar
value as a single-element xml array, instead.  (String values will be
suitably escaped.)

This change will also cause xpath_exists() to return true, not false,
for such expressions.

Florian Pflug, reviewed by Radoslaw Smogura

Without this it's possible for the output to not be legal XML, as
illustrated by the added regression test cases.

NB: this change will need to be called out as an incompatibility in the
9.2 release notes, since it's possible somebody was relying on the old
behavior, even though it's clearly wrong.

Florian Pflug, reviewed by Radoslaw Smogura

libxml reports some errors (like invalid xmlns attributes) via the error
handler hook, but still returns a success indicator to the library caller.
This causes us to miss some errors that are important to report.  Since the
"generic" error handler hook doesn't know whether the message it's getting
is for an error, warning, or notice, stop using that and instead start
using the "structured" error handler hook, which gets enough information
to be useful.

While at it, arrange to save and restore the error handler hook setting in
each libxml-using function, rather than assuming we can set and forget the
hook.  This should improve the odds of working nicely with third-party
libraries that also use libxml.

In passing, volatile-ize some local variables that get modified within
PG_TRY blocks.  I noticed this while testing with an older gcc version
than I'd previously tried to compile xml.c with.

Florian Pflug and Tom Lane, with extensive review/testing by Noah Misch

There may be some other places where we should use errdetail_internal,
but they'll have to be evaluated case-by-case.  This commit just hits
a bunch of places where invoking gettext is obviously a waste of cycles.

This lets us stop including rel.h into execnodes.h, which is a widely
used header.

parse_xml_decl's header comment says you can pass NULL for any unwanted
output parameter, but it failed to honor this contract for the "standalone"
flag.  The only currently-affected caller is xml_recv, so the net effect is
that sending a binary XML value containing a standalone parameter in its
xml declaration would crash the backend.  Per bug #6044 from Christopher
Dillard.

In passing, remove useless initializations of parse_xml_decl's output
parameters in xml_parse.

Back-patch to 8.3, where this code was introduced.

This patch eliminates various bizarre behaviors caused by sloppy thinking
about the difference between a domain type and its underlying array type.
In particular, the operation of updating one element of such an array
has to be considered as yielding a value of the underlying array type,
*not* a value of the domain, because there's no assurance that the
domain's CHECK constraints are still satisfied.  If we're intending to
store the result back into a domain column, we have to re-cast to the
domain type so that constraints are re-checked.

For similar reasons, such a domain can't be blindly matched to an ANYARRAY
polymorphic parameter, because the polymorphic function is likely to apply
array-ish operations that could invalidate the domain constraints.  For the
moment, we just forbid such matching.  We might later wish to insert an
automatic downcast to the underlying array type, but such a change should
also change matching of domains to ANYELEMENT for consistency.

To ensure that all such logic is rechecked, this patch removes the original
hack of setting a domain's pg_type.typelem field to match its base type;
the typelem will always be zero instead.  In those places where it's really
okay to look through the domain type with no other logic changes, use the
newly added get_base_element_type function in place of get_element_type.
catversion bumped due to change in pg_type contents.

Per bug #5717 from Richard Huxton and subsequent discussion.

functions to the core XML code.  Per discussion, the former depends on
XMLOPTION while the others do not.  These supersede a version previously
offered by contrib/xml2.

Mike Fowler, reviewed by Pavel Stehule

it offers support for namespace mapping.

Mike Fowler, reviewed by David Fetter

by Mike Fowler, reviewed by Peter Eisentraut

too, instead of duplicating the functionality (badly).

I renamed xml_init to pg_xml_init, because the former seemed just a bit too
generic to be safe as a global symbol.  I considered likewise renaming
xml_ereport to pg_xml_ereport, but felt that the reference to ereport probably
made it sufficiently PG-centric already.

The purpose of this change is to eliminate the need for every caller
of SearchSysCache, SearchSysCacheCopy, SearchSysCacheExists,
GetSysCacheOid, and SearchSysCacheList to know the maximum number
of allowable keys for a syscache entry (currently 4).  This will
make it far easier to increase the maximum number of keys in a
future release should we choose to do so, and it makes the code
shorter, too.

Design and review by Tom Lane.

specify an encoding explicitly, we used to treat it as being in database
encoding when we parsed it, but then perform a UTF-8 -> database encoding
conversion on it, which was completely bogus. It's now consistently treated as
UTF-8.

There are probably still some adjustments to be made in the details
of the output, but this gets the basic structure in place.

Robert Haas

provided by Andrew.

Sergey Burladyan, there are at least some dank corners of libxml2 that
assume this behavior, even though their published documentation suggests
they shouldn't.

This is only really a live problem in 8.3, but the code is still there
for possible debugging use in HEAD, so patch both branches.

Author: Itagaki Takahiro <itagaki.takahiro@oss.ntt.co.jp>

also backpatched to 8.3

redirecting libxml's allocations into a Postgres context.  Instead, just let
it use malloc directly, and add PG_TRY blocks as needed to be sure we release
libxml data structures in error recovery code paths.  This is ugly but seems
much more likely to play nicely with third-party uses of libxml, as seen in
recent trouble reports about using Perl XML facilities in pl/perl and bug
#4774 about contrib/xml2.

I left the code for allocation redirection in place, but it's only
built/used if you #define USE_LIBXMLCONTEXT.  This is because I found it
useful to corral libxml's allocations in a palloc context when hunting
for libxml memory leaks, and we're surely going to have more of those
in the future with this type of approach.  But we don't want it turned on
in a normal build because it breaks exactly what we need to fix.

I have not re-indented most of the code sections that are now wrapped
by PG_TRY(); that's for ease of review.  pg_indent will fix it.

This is a pre-existing bug in 8.3, but I don't dare back-patch this change
until it's gotten a reasonable amount of field testing.

xml_parse, all arising from the same sloppy usage of parse_xml_decl.
The original coding had that function returning its output string
parameters in the libxml context, which is long-lived, and all but one
of its callers neglected to free the strings afterwards.  The easiest
and most bulletproof fix is to return the strings in the local palloc
context instead, since that's short-lived.  This was only costing a
dozen or two bytes per function call, but that adds up fast if the
function is called repeatedly ...

Noted while poking at the more general problem of what to do with our
libxml memory allocation hooks.  Back-patch to 8.3, which has the
identical coding.

map_sql_value_to_xml_value() instead of directly through the data type output
function.  This is per SQL standard, and consistent with XMLELEMENT().

while converting to XML.  Bernd Helmle

not include postgres.h nor anything else it doesn't directly need.  Add
#includes to calling files as needed to compensate.  Per my proposal of
yesterday.

This should be noted as a source code change in the 8.4 release notes,
since it's likely to require changes in add-on modules.