From d19eba1b845d1c73f9d5cb8a84d4a08902fc84b3 Mon Sep 17 00:00:00 2001
From: Niels Dossche <7771979+nielsdos@users.noreply.github.com>
Date: Tue, 22 Aug 2023 20:28:07 +0200
Subject: [PATCH] Improve warning when returning null from the resolver set by
 libxml_set_external_entity_loader

Fixes GH-11952.
---
 ext/libxml/libxml.c                           |  8 +++--
 .../tests/null_returned_by_resolver.phpt      | 32 +++++++++++++++++++
 2 files changed, 37 insertions(+), 3 deletions(-)
 create mode 100644 ext/libxml/tests/null_returned_by_resolver.phpt

diff --git a/ext/libxml/libxml.c b/ext/libxml/libxml.c
index 24ba80bd5de3..a6f28f0fbadb 100644
--- a/ext/libxml/libxml.c
+++ b/ext/libxml/libxml.c
@@ -784,10 +784,12 @@ static xmlParserInputPtr _php_libxml_external_entity_loader(const char *URL,
 	if (ret == NULL) {
 		if (resource == NULL) {
 			if (ID == NULL) {
-				ID = "NULL";
+				php_libxml_ctx_error(context,
+						"Failed to load external entity because the resolver function returned null\n");
+			} else {
+				php_libxml_ctx_error(context,
+						"Failed to load external entity \"%s\"\n", ID);
 			}
-			php_libxml_ctx_error(context,
-					"Failed to load external entity \"%s\"\n", ID);
 		} else {
 			/* we got the resource in the form of a string; open it */
 			ret = xmlNewInputFromFile(context, resource);
diff --git a/ext/libxml/tests/null_returned_by_resolver.phpt b/ext/libxml/tests/null_returned_by_resolver.phpt
new file mode 100644
index 000000000000..8fdfbc6dc8b4
--- /dev/null
+++ b/ext/libxml/tests/null_returned_by_resolver.phpt
@@ -0,0 +1,32 @@
+--TEST--
+null returned by resolver function
+--EXTENSIONS--
+libxml
+dom
+--FILE--
+<?php
+
+libxml_set_external_entity_loader(function ($public_id, $system_id, $context) {
+    var_dump($public_id, $system_id, $context);
+    return null;
+});
+
+$doc = new DOMDocument();
+$doc->loadHTMLFile("foobar");
+
+?>
+--EXPECTF--
+NULL
+string(6) "foobar"
+array(4) {
+  ["directory"]=>
+  NULL
+  ["intSubName"]=>
+  NULL
+  ["extSubURI"]=>
+  NULL
+  ["extSubSystem"]=>
+  NULL
+}
+
+Warning: DOMDocument::loadHTMLFile(): Failed to load external entity because the resolver function returned null in %s on line %d