Use custom isc_mem based allocator for libxml2

The libxml2 library provides a way to replace the default allocator with
user supplied allocator (malloc, realloc, strdup and free).

Create a memory context specifically for libxml2 to allow tracking the
memory usage that has originated from within libxml2.  This will provide
a separate memory context for libxml2 to track the allocations and when
shutting down the application it will check that all libxml2 allocations
were returned to the allocator.

Additionally, move the xmlInitParser() and xmlCleanupParser() calls from
bin/named/main.c to library constructor/destructor in libisc library.

lib/isc/Makefile.am

@@ -105,6 +105,7 @@ libisc_la_HEADERS =			\
 	include/isc/utf8.h		\
 	include/isc/util.h		\
 	include/isc/uv.h		\
+	include/isc/xml.h		\
 	include/isc/work.h
 
 libisc_la_SOURCES =		\
@@ -210,6 +211,7 @@ libisc_la_SOURCES =		\
 	url.c			\
 	utf8.c			\
 	uv.c			\
+	xml.c			\
 	work.c
 
 libisc_la_CPPFLAGS =		\

lib/isc/include/isc/xml.h

@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ *
+ * SPDX-License-Identifier: MPL-2.0
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, you can obtain one at https://mozilla.org/MPL/2.0/.
+ *
+ * See the COPYRIGHT file distributed with this work for additional
+ * information regarding copyright ownership.
+ */
+
+#pragma once
+
+#include <stdbool.h>
+
+void
+isc__xml_initialize(void);
+
+void
+isc__xml_shutdown(void);
+
+void
+isc__xml_setdestroycheck(bool check);

lib/isc/lib.c

@@ -19,6 +19,7 @@
 #include <isc/tls.h>
 #include <isc/util.h>
 #include <isc/uv.h>
+#include <isc/xml.h>
 
 #include "config.h"
 #include "mem_p.h"
@@ -47,11 +48,13 @@ isc__initialize(void) {
 	isc__tls_initialize();
 	isc__trampoline_initialize();
 	isc__uv_initialize();
+	isc__xml_initialize();
 	(void)isc_os_ncpus();
 }
 
 void
 isc__shutdown(void) {
+	isc__xml_shutdown();
 	isc__uv_shutdown();
 	isc__trampoline_shutdown();
 	isc__tls_shutdown();

lib/isc/xml.c

@@ -0,0 +1,79 @@
+/*
+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ *
+ * SPDX-License-Identifier: MPL-2.0
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, you can obtain one at https://mozilla.org/MPL/2.0/.
+ *
+ * See the COPYRIGHT file distributed with this work for additional
+ * information regarding copyright ownership.
+ */
+
+#include <isc/mem.h>
+#include <isc/util.h>
+#include <isc/xml.h>
+
+#ifdef HAVE_LIBXML2
+#include <libxml/parser.h>
+#include <libxml/xmlversion.h>
+
+static isc_mem_t *isc__xml_mctx = NULL;
+
+static void *
+isc__xml_malloc(size_t size) {
+	return (isc_mem_allocate(isc__xml_mctx, size));
+}
+
+static void *
+isc__xml_realloc(void *ptr, size_t size) {
+	return (isc_mem_reallocate(isc__xml_mctx, ptr, size));
+}
+
+static char *
+isc__xml_strdup(const char *str) {
+	return (isc_mem_strdup(isc__xml_mctx, str));
+}
+
+static void
+isc__xml_free(void *ptr) {
+	if (ptr == NULL) {
+		return;
+	}
+	isc_mem_free(isc__xml_mctx, ptr);
+}
+
+#endif /* HAVE_LIBXML2 */
+
+void
+isc__xml_initialize(void) {
+#ifdef HAVE_LIBXML2
+	isc_mem_create(&isc__xml_mctx);
+	isc_mem_setname(isc__xml_mctx, "libxml2");
+	isc_mem_setdestroycheck(isc__xml_mctx, false);
+
+	RUNTIME_CHECK(xmlGcMemSetup(isc__xml_free, isc__xml_malloc,
+				    isc__xml_malloc, isc__xml_realloc,
+				    isc__xml_strdup) == 0);
+
+	xmlInitParser();
+#endif /* HAVE_LIBXML2 */
+}
+
+void
+isc__xml_shutdown(void) {
+#ifdef HAVE_LIBXML2
+	xmlCleanupParser();
+	isc_mem_destroy(&isc__xml_mctx);
+#endif /* HAVE_LIBXML2 */
+}
+
+void
+isc__xml_setdestroycheck(bool check) {
+#ifdef HAVE_LIBXML2
+	isc_mem_setdestroycheck(isc__xml_mctx, check);
+#else
+	UNUSED(check);
+#endif
+}