From 936e3d529a6fc17d552f4b6544ba8e51646069df Mon Sep 17 00:00:00 2001
From: Nick Wellnhofer <wellnhofer@aevum.de>
Date: Sun, 20 Apr 2025 19:25:04 +0200
Subject: [PATCH] save: Fix xmlSave with NULL encoding

Regressed with cc45f618.
---
 testparser.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 xmlsave.c    | 48 ++++++++++++++++++++++++++----------------------
 2 files changed, 71 insertions(+), 22 deletions(-)

diff --git a/testparser.c b/testparser.c
index 85fee9b4..a9a85a60 100644
--- a/testparser.c
+++ b/testparser.c
@@ -288,6 +288,50 @@ testNoBlanks(void) {
 
     return err;
 }
+
+static int
+testSaveNullEncDoc(const char *xml, const char *expect) {
+    xmlDocPtr doc;
+    xmlBufferPtr buffer;
+    xmlSaveCtxtPtr save;
+    const xmlChar *result;
+    int err = 0;
+
+    doc = xmlReadDoc(BAD_CAST xml, NULL, NULL, 0);
+
+    buffer = xmlBufferCreate();
+    save = xmlSaveToBuffer(buffer, NULL, 0);
+    xmlSaveDoc(save, doc);
+    xmlSaveClose(save);
+
+    result = xmlBufferContent(buffer);
+    if (strcmp((char *) result, expect) != 0) {
+        fprintf(stderr, "xmlSave with NULL encodíng failed\n");
+        err = 1;
+    }
+
+    xmlBufferFree(buffer);
+    xmlFreeDoc(doc);
+
+    return err;
+}
+
+static int
+testSaveNullEnc(void) {
+    int err = 0;
+
+    err |= testSaveNullEncDoc(
+        "<?xml version=\"1.0\"?><doc>\xC3\x98</doc>",
+        "<?xml version=\"1.0\"?>\n<doc>&#xD8;</doc>\n");
+    err |= testSaveNullEncDoc(
+        "<?xml version=\"1.0\" encoding=\"utf-8\"?><doc>\xC3\x98</doc>",
+        "<?xml version=\"1.0\" encoding=\"utf-8\"?>\n<doc>\xC3\x98</doc>\n");
+    err |= testSaveNullEncDoc(
+        "<?xml version=\"1.0\" encoding=\"iso-8859-1\"?><doc>\xD8</doc>",
+        "<?xml version=\"1.0\" encoding=\"iso-8859-1\"?>\n<doc>\xD8</doc>\n");
+
+    return err;
+}
 #endif /* LIBXML_OUTPUT_ENABLED */
 
 #ifdef LIBXML_SAX1_ENABLED
@@ -1157,6 +1201,7 @@ main(void) {
 #ifdef LIBXML_OUTPUT_ENABLED
     err |= testCtxtParseContent();
     err |= testNoBlanks();
+    err |= testSaveNullEnc();
 #endif
 #ifdef LIBXML_SAX1_ENABLED
     err |= testBalancedChunk();
diff --git a/xmlsave.c b/xmlsave.c
index 38ccdbfd..6d3e6cac 100644
--- a/xmlsave.c
+++ b/xmlsave.c
@@ -778,13 +778,19 @@ static int xmlSaveSwitchEncoding(xmlSaveCtxtPtr ctxt, const char *encoding) {
             xmlSaveErr(buf, res, NULL, encoding);
             return(-1);
         }
-	buf->conv = xmlBufCreate(4000 /* MINLEN */);
-	if (buf->conv == NULL) {
-	    xmlCharEncCloseFunc(handler);
-            xmlSaveErrMemory(buf);
-	    return(-1);
-	}
-        buf->encoder = handler;
+
+        if (handler != NULL) {
+            buf->conv = xmlBufCreate(4000 /* MINLEN */);
+            if (buf->conv == NULL) {
+                xmlCharEncCloseFunc(handler);
+                xmlSaveErrMemory(buf);
+                return(-1);
+            }
+            buf->encoder = handler;
+        }
+
+        ctxt->encoding = (const xmlChar *) encoding;
+
 	/*
 	 * initialize the state, e.g. if outputting a BOM
 	 */
@@ -795,11 +801,15 @@ static int xmlSaveSwitchEncoding(xmlSaveCtxtPtr ctxt, const char *encoding) {
 
 static int xmlSaveClearEncoding(xmlSaveCtxtPtr ctxt) {
     xmlOutputBufferPtr buf = ctxt->buf;
+
     xmlOutputBufferFlush(buf);
     xmlCharEncCloseFunc(buf->encoder);
     xmlBufFree(buf->conv);
     buf->encoder = NULL;
     buf->conv = NULL;
+
+    ctxt->encoding = NULL;
+
     return(0);
 }
 
@@ -1342,7 +1352,6 @@ xmlDocContentDumpOutput(xmlSaveCtxtPtr ctxt, xmlDocPtr cur) {
     const xmlChar *oldctxtenc = ctxt->encoding;
     const xmlChar *encoding = ctxt->encoding;
     xmlOutputBufferPtr buf = ctxt->buf;
-    xmlCharEncoding enc;
     int switched_encoding = 0;
 
     xmlInitParser();
@@ -1370,6 +1379,7 @@ xmlDocContentDumpOutput(xmlSaveCtxtPtr ctxt, xmlDocPtr cur) {
 	    if (xmlSaveSwitchEncoding(ctxt, (const char*) encoding) < 0) {
 		return(-1);
 	    }
+            switched_encoding = 1;
 	}
         if (ctxt->options & XML_SAVE_FORMAT)
 	    htmlDocContentDumpFormatOutput(buf, cur,
@@ -1377,29 +1387,23 @@ xmlDocContentDumpOutput(xmlSaveCtxtPtr ctxt, xmlDocPtr cur) {
 	else
 	    htmlDocContentDumpFormatOutput(buf, cur,
 	                                   (const char *)encoding, 0);
-	return(0);
 #else
         return(-1);
 #endif
     } else if ((cur->type == XML_DOCUMENT_NODE) ||
                (ctxt->options & XML_SAVE_AS_XML) ||
                (ctxt->options & XML_SAVE_XHTML)) {
-	enc = xmlParseCharEncoding((const char*) encoding);
 	if ((encoding != NULL) && (oldctxtenc == NULL) &&
 	    (buf->encoder == NULL) && (buf->conv == NULL) &&
 	    ((ctxt->options & XML_SAVE_NO_DECL) == 0)) {
-	    if ((enc != XML_CHAR_ENCODING_UTF8) &&
-		(enc != XML_CHAR_ENCODING_NONE) &&
-		(enc != XML_CHAR_ENCODING_ASCII)) {
-		/*
-		 * we need to switch to this encoding but just for this
-		 * document since we output the XMLDecl the conversion
-		 * must be done to not generate not well formed documents.
-		 */
-		if (xmlSaveSwitchEncoding(ctxt, (const char*) encoding) < 0)
-		    return(-1);
-		switched_encoding = 1;
-	    }
+            /*
+             * we need to switch to this encoding but just for this
+             * document since we output the XMLDecl the conversion
+             * must be done to not generate not well formed documents.
+             */
+            if (xmlSaveSwitchEncoding(ctxt, (const char *) encoding) < 0)
+                return(-1);
+            switched_encoding = 1;
 	}