fix(cruby): patch libxml2 to address GNOME/libxml2#200

This patch shrinks the libxml2 input buffer in a few parser functions.

Fixes #2132

CHANGELOG.md

@@ -9,6 +9,7 @@ Nokogiri follows [Semantic Versioning](https://semver.org/), please see the [REA
 ### Fixed
 
 * [CRuby] `NodeSet` may now safely contain `Node` objects from multiple documents. Previously the GC lifecycle of the parent `Document` objects could lead to contained nodes being GCed while still in scope. [[#1952](https://github.com/sparklemotion/nokogiri/issues/1952)]
+* [CRuby] Patch libxml2 to avoid "huge input lookup" errors on large CDATA elements. (See upstream [GNOME/libxml2#200](https://gitlab.gnome.org/GNOME/libxml2/-/issues/200) and [GNOME/libxml2!100](https://gitlab.gnome.org/GNOME/libxml2/-/merge_requests/100).) [[#2132](https://github.com/sparklemotion/nokogiri/issues/2132)].
 * [CRuby] `{XML,HTML}::Document.parse` now invokes `#initialize` exactly once. Previously `#initialize` was invoked twice on each object.
 * [JRuby] `{XML,HTML}::Document.parse` now invokes `#initialize` exactly once. Previously `#initialize` was not called, which was a problem for subclassing such as done by `Loofah`.
 

patches/libxml2/0010-parser.c-shrink-the-input-buffer-when-appropriate.patch

@@ -0,0 +1,70 @@
+From ca565c1edef9a455453fa8564270cc9c5813e1b9 Mon Sep 17 00:00:00 2001
+From: Mike Dalessio <mike.dalessio@gmail.com>
+Date: Sun, 31 Jan 2021 09:53:56 -0500
+Subject: [PATCH] parser.c: shrink the input buffer when appropriate
+
+Fixes GNOME/libxml2#200
+
+Also see discussions at:
+- GNOME/libxml2#192
+- https://gitlab.gnome.org/nwellnhof/libxml2/-/commit/99bda1e
+- https://github.com/sparklemotion/nokogiri/issues/2132
+---
+ parser.c | 6 ++++++
+ 1 file changed, 6 insertions(+)
+
+diff --git a/parser.c b/parser.c
+index a7bdc7f..efde672 100644
+--- a/parser.c
++++ b/parser.c
+@@ -4204,6 +4204,7 @@ xmlParseSystemLiteral(xmlParserCtxtPtr ctxt) {
+ 	}
+ 	count++;
+ 	if (count > 50) {
++	    SHRINK;
+ 	    GROW;
+ 	    count = 0;
+             if (ctxt->instate == XML_PARSER_EOF) {
+@@ -4291,6 +4292,7 @@ xmlParsePubidLiteral(xmlParserCtxtPtr ctxt) {
+ 	buf[len++] = cur;
+ 	count++;
+ 	if (count > 50) {
++	    SHRINK;
+ 	    GROW;
+ 	    count = 0;
+             if (ctxt->instate == XML_PARSER_EOF) {
+@@ -4571,6 +4573,7 @@ xmlParseCharDataComplex(xmlParserCtxtPtr ctxt, int cdata) {
+ 	}
+ 	count++;
+ 	if (count > 50) {
++	    SHRINK;
+ 	    GROW;
+ 	    count = 0;
+             if (ctxt->instate == XML_PARSER_EOF)
+@@ -4776,6 +4779,7 @@ xmlParseCommentComplex(xmlParserCtxtPtr ctxt, xmlChar *buf,
+
+ 	count++;
+ 	if (count > 50) {
++	    SHRINK;
+ 	    GROW;
+ 	    count = 0;
+             if (ctxt->instate == XML_PARSER_EOF) {
+@@ -5186,6 +5190,7 @@ xmlParsePI(xmlParserCtxtPtr ctxt) {
+ 		}
+ 		count++;
+ 		if (count > 50) {
++		    SHRINK;
+ 		    GROW;
+                     if (ctxt->instate == XML_PARSER_EOF) {
+                         xmlFree(buf);
+@@ -9783,6 +9788,7 @@ xmlParseCDSect(xmlParserCtxtPtr ctxt) {
+ 	sl = l;
+ 	count++;
+ 	if (count > 50) {
++	    SHRINK;
+ 	    GROW;
+             if (ctxt->instate == XML_PARSER_EOF) {
+ 		xmlFree(buf);
+-- 
+2.25.1
+