Functions like xmlStrdup are called in the error handling code
(__xmlRaiseError) which can cause problems like use-after-free or
infinite loops when invoked recursively.

Calling xmlErrMemory without a context argument isn't helpful anyway.

Found with libFuzzer, see #344.

Store xmlRealloc result in temporary variable to avoid null deref in
error handler.

Found with libFuzzer, see #344.

Fix error handling in xmlCtxtGrowAttrs.

Found with libFuzzer, see #344.

Unfortunately, there's no way to properly report memory errors.

Found with libFuzzer, see #344.

Memory errors can set `instate` to `XML_PARSER_EOF` which results in
`NEXT` making no progress.

Found with libFuzzer, see #344.

Found with libFuzzer, see #344.

Also add some error checks.

Found with libFuzzer, see #344.

Found with libFuzzer, see #344.

Found with libFuzzer, see #344.

Found with libFuzzer, see #344.

Avoid infinite loop. Short-lived regression from f61b8a62.

Found with libFuzzer.

Fix -fsanitize=implicit-conversion error. We should probably
percent-escape the host name here.

Don't return (size_t) -1 in error case.

Found with libFuzzer and -fsanitize=implicit-conversion.

If we try to continue parsing after an error in the internal or external
subset, entity expansion accounting gets more complicated. Simply halt
the parser.

Found with libFuzzer.

Make sure that we never move past the current position in
xmlParserPrintFileContextInternal.

Found with libFuzzer and -fsanitize=implicit-conversion.

Fixes libxslt#81

The version script didn't account for symbols disabled by configuration
options. This has caused problems on some OSs in the past and breaks
lld 16 which enables --no-undefined-version by default.

A proper fix would be rather involved, so we simply remove all symbols
from the version script. This is an ELF-only feature and libxml2 never
made use of symbol versioning anyway. Ultimately, this removes the need
for a lot of bookkeeping without tangible benefits.

We have to keep the version nodes to avoid errors when running binaries
linked against older versions of libxml2.

Fixes #473.

Use the new entity flag to check for recursion.

Don't set the "checked" flag when checking entities in default attribute
values. These entities could reference other entities which weren't
defined yet, so the check isn't reliable.

This fixes a short-lived regression which could lead to a call stack
overflow later in xmlStringGetNodeList.

Reporting errors is expensive and some abusive test cases can generate
an error for each invalid input byte. This causes the parser to spend
most of the time with error handling. Limit the number of errors and
warnings to 100.

XIncludes involve XPath processing which can still lead to timeouts when
fuzzing. This will probably take a while to fix. The rest of the XML
parsing code should hopefully run without timeouts now. OSS-Fuzz only
shows a single timeout test case, so separate the XInclude from the core
XML fuzzer.

Short-lived regression from commit b1f9c193. Found by OSS-Fuzz.

Short-lived regression.

Now that entity expansion issues should be fixed, we should get more
interesting timeout errors from OSS-Fuzz. Disable XInclude for now,
since it often timeouts in XPath computations. The XInclude tests should
be moved to a separate fuzz target.

Only add consumed bytes if

- we're not parsing an entity
- we're parsing external parameter entities for the first time.

Always ignore internal parameter entities.

The old limit of 1024 could lead to excessively deep call stacks. This
could probably be set much lower without causing issues.

Fix xmlParseBalancedChunkMemoryInternal.

Set a flag to detect entity loops at once instead of processing until
the depth limit is exceeded.

Don't report errors multiple times for nested entity references.

Applies a patch from Chromium. Also stop incrementing input ID of
subcontexts. This isn't necessary.

Fixes #465.

xmlParseStartTag2() contains typo when checking for default definitions for an attribute in a namespace

* parser.c:
(xmlParseStartTag2):
- Fix index into defaults->values.  It is only correct the first
  time through the loop when i == 0.

Fixes #467.

Commit 3aaaf5ca shouldn't have changed this line. We need these
libraries for a full libxml2 build.

These are internal functions.

If ent->etype is invalid, ret can't equal XML_ERR_OK.

The if-block before always returns if ent->children == NULL.