From df87b19645650293f5c78a0d20bac2c88d259041 Mon Sep 17 00:00:00 2001
From: Jeroen Ooms <jeroenooms@gmail.com>
Date: Sun, 16 Nov 2025 20:03:46 +0100
Subject: [PATCH 1/2] Implement ExternalEntityLoader for http downloads

---
 R/init.R        |  7 +++++++
 src/xml2_init.c | 35 ++++++++++++++++++++++++++++++++++-
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/R/init.R b/R/init.R
index ae0f6e6..1ecc7c5 100644
--- a/R/init.R
+++ b/R/init.R
@@ -9,3 +9,10 @@ xml_parse_options <- function() {
 xml_save_options <- function() {
   .Call(xml_save_options_)
 }
+
+download_file_callback <- function(url){
+  tmp <- tempfile()
+  on.exit(unlink(tmp))
+  download.file(url, tmp, quiet = TRUE)
+  readBin(tmp, raw(), file.info(tmp)$size)
+}
diff --git a/src/xml2_init.c b/src/xml2_init.c
index 6451a83..34a1010 100644
--- a/src/xml2_init.c
+++ b/src/xml2_init.c
@@ -4,6 +4,8 @@
 #include <libxml/parser.h>
 #include <string.h>
 
+static xmlExternalEntityLoader defaultLoader = NULL;
+
 /* * *
  * Author: Nick Wellnhofer <wellnhofer@aevum.de>
  * Date:   Tue, 24 Oct 2023 15:02:36 +0200
@@ -49,6 +51,34 @@ void handleGenericError(void *ctx, const char *fmt, ...){
   Rf_error("%s", buffer);
 }
 
+xmlParserInput *download_file_callback(const char *url){
+  SEXP arg = PROTECT(Rf_mkString(url));
+  SEXP expr = PROTECT(Rf_install("download_file_callback"));
+  SEXP call = PROTECT(Rf_lang2(expr, arg));
+  SEXP env = R_FindNamespace(Rf_mkString("xml2"));
+  int err = 1;
+  SEXP out = PROTECT(R_tryEvalSilent(call, env, &err));
+  if(err) return NULL;
+  xmlParserInputFlags flags = XML_INPUT_BUF_STATIC | XML_INPUT_USE_SYS_CATALOG;
+  xmlParserInput *buf = xmlNewInputFromMemory(url, RAW(out), Rf_length(out), flags);
+  //xmlParserInputBuffer *buf = xmlParserInputBufferCreateMem((char*) RAW(out), Rf_length(out), XML_CHAR_ENCODING_UTF8);
+  UNPROTECT(4);
+  return buf;
+}
+
+static xmlParserInputPtr myExternalEntityLoader(const char *URL, const char *ID, xmlParserCtxtPtr ctxt){
+  if (URL && (strncmp(URL, "http://", 7) == 0 || strncmp(URL, "https://", 8) == 0)) {
+    //REprintf("Fetching external resource %s\n", URL);
+    xmlParserInput *buf = download_file_callback(URL);
+    if(buf) return buf;
+  }
+  // Fallback to default behavior
+  if (defaultLoader)
+    return defaultLoader(URL, ID, ctxt);
+  return NULL;
+}
+
+
 void init_libxml2_library(void) {
   // Check that header and libs are compatible
   LIBXML_TEST_VERSION
@@ -56,5 +86,8 @@ void init_libxml2_library(void) {
   xmlInitParser();
   xmlSetStructuredErrorFunc(NULL, handleStructuredError);
   xmlSetGenericErrorFunc(NULL, handleGenericError);
-}
 
+  // Set custom download callback
+  defaultLoader = xmlGetExternalEntityLoader();
+  xmlSetExternalEntityLoader(myExternalEntityLoader);
+}

From dd3b54f58b89e7a753ddaa5a5ec57cdcb7a812de Mon Sep 17 00:00:00 2001
From: Jeroen Ooms <jeroenooms@gmail.com>
Date: Sun, 16 Nov 2025 21:37:57 +0100
Subject: [PATCH 2/2] Experimental custom myExternalEntityLoader on libxml2
 2.15 and up

---
 DESCRIPTION     | 2 +-
 NEWS.md         | 4 ++++
 src/xml2_init.c | 6 ++++++
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/DESCRIPTION b/DESCRIPTION
index 9f5a64d..9f7d53c 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,6 +1,6 @@
 Package: xml2
 Title: Parse XML
-Version: 1.4.1
+Version: 1.5.0
 Authors@R: c(
     person("Hadley", "Wickham", role = "aut"),
     person("Jim", "Hester", role = "aut"),
diff --git a/NEWS.md b/NEWS.md
index 32864d4..01947a3 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,3 +1,7 @@
+# xml2 1.5.0
+
+* Experimental custom myExternalEntityLoader on libxml2 2.15 and up.
+
 # xml2 1.4.1
 
 * Remove a test that broke with libxml2 2.15
diff --git a/src/xml2_init.c b/src/xml2_init.c
index 34a1010..1484c9a 100644
--- a/src/xml2_init.c
+++ b/src/xml2_init.c
@@ -51,6 +51,8 @@ void handleGenericError(void *ctx, const char *fmt, ...){
   Rf_error("%s", buffer);
 }
 
+#if LIBXML_VERSION >= 21500
+
 xmlParserInput *download_file_callback(const char *url){
   SEXP arg = PROTECT(Rf_mkString(url));
   SEXP expr = PROTECT(Rf_install("download_file_callback"));
@@ -78,6 +80,8 @@ static xmlParserInputPtr myExternalEntityLoader(const char *URL, const char *ID,
   return NULL;
 }
 
+#endif
+
 
 void init_libxml2_library(void) {
   // Check that header and libs are compatible
@@ -88,6 +92,8 @@ void init_libxml2_library(void) {
   xmlSetGenericErrorFunc(NULL, handleGenericError);
 
   // Set custom download callback
+#if LIBXML_VERSION >= 21500
   defaultLoader = xmlGetExternalEntityLoader();
   xmlSetExternalEntityLoader(myExternalEntityLoader);
+#endif
 }