From 5b893fa9994295c6e2ced909d84c7f562f861c0e Mon Sep 17 00:00:00 2001
From: Nick Wellnhofer <wellnhofer@aevum.de>
Date: Sat, 22 Jun 2024 19:15:17 +0200
Subject: [PATCH] encoding: Fix encoding lookup with xmlOpenCharEncodingHandler

Make xmlOpenCharEncodingHandler call xmlParseCharEncoding first so we
prefer our own handlers for names like "UTF8". Only UTF-16 needs an
exception.

Make callers check the return value. For UTF-8, a NULL encoding doesn't
mean an error.

Remove unnecessary UTF-8 check from htmlFindOutputEncoder. Don't try to
look up ASCII handler since the HTML handler is always available.

Fix return code of xmlParseCharEncoding.

Should fix #744.
---
 HTMLtree.c | 19 +++++++------------
 encoding.c | 29 ++++++++++++++++-------------
 xmlsave.c  | 18 +++++++++++-------
 3 files changed, 34 insertions(+), 32 deletions(-)

diff --git a/HTMLtree.c b/HTMLtree.c
index 6e8baf488..8fa022c11 100644
--- a/HTMLtree.c
+++ b/HTMLtree.c
@@ -385,22 +385,17 @@ htmlFindOutputEncoder(const char *encoding) {
     xmlCharEncodingHandler *handler = NULL;
 
     if (encoding != NULL) {
-	xmlCharEncoding enc;
+        int res;
 
-	enc = xmlParseCharEncoding(encoding);
-	if (enc != XML_CHAR_ENCODING_UTF8) {
-	    xmlOpenCharEncodingHandler(encoding, /* output */ 1, &handler);
-	    if (handler == NULL)
-		htmlSaveErr(XML_SAVE_UNKNOWN_ENCODING, NULL, encoding);
-	}
+        res = xmlOpenCharEncodingHandler(encoding, /* output */ 1,
+                                         &handler);
+        if (res != XML_ERR_OK)
+            htmlSaveErr(XML_SAVE_UNKNOWN_ENCODING, NULL, encoding);
     } else {
         /*
-         * Fallback to HTML or ASCII when the encoding is unspecified
+         * Fallback to HTML when the encoding is unspecified
          */
-        if (handler == NULL)
-            xmlOpenCharEncodingHandler("HTML", /* output */ 1, &handler);
-        if (handler == NULL)
-            xmlOpenCharEncodingHandler("ascii", /* output */ 1, &handler);
+        xmlOpenCharEncodingHandler("HTML", /* output */ 1, &handler);
     }
 
     return(handler);
diff --git a/encoding.c b/encoding.c
index edfa1c457..de14c596a 100644
--- a/encoding.c
+++ b/encoding.c
@@ -1161,7 +1161,7 @@ xmlParseCharEncoding(const char* name)
     if (!strcmp(upper, "SHIFT_JIS")) return(XML_CHAR_ENCODING_SHIFT_JIS);
     if (!strcmp(upper, "EUC-JP")) return(XML_CHAR_ENCODING_EUC_JP);
 
-    return(XML_CHAR_ENCODING_ERROR);
+    return(XML_CHAR_ENCODING_NONE);
 }
 
 /**
@@ -1931,9 +1931,7 @@ int
 xmlOpenCharEncodingHandler(const char *name, int output,
                            xmlCharEncodingHandler **out) {
     const char *nalias;
-    const char *norig;
     xmlCharEncoding enc;
-    int ret;
 
     if (out == NULL)
         return(XML_ERR_ARGUMENT);
@@ -1945,22 +1943,27 @@ xmlOpenCharEncodingHandler(const char *name, int output,
     /*
      * Do the alias resolution
      */
-    norig = name;
     nalias = xmlGetEncodingAlias(name);
     if (nalias != NULL)
 	name = nalias;
 
-    ret = xmlFindHandler(name, output, out);
-    if (*out != NULL)
-        return(0);
-    if (ret != XML_ERR_UNSUPPORTED_ENCODING)
-        return(ret);
-
     /*
-     * Fallback using the canonical names
+     * UTF-16 needs the built-in handler which is only available via
+     * xmlFindHandler.
      */
-    enc = xmlParseCharEncoding(norig);
-    return(xmlLookupCharEncodingHandler(enc, out));
+    if (xmlStrcasecmp(BAD_CAST name, BAD_CAST "UTF16") == 0) {
+        name = "UTF-16";
+    } else if (xmlStrcasecmp(BAD_CAST name, BAD_CAST "UTF-16") != 0) {
+        enc = xmlParseCharEncoding(name);
+        if (enc != XML_CHAR_ENCODING_NONE) {
+            int res = xmlLookupCharEncodingHandler(enc, out);
+
+            if (res != XML_ERR_UNSUPPORTED_ENCODING)
+                return(res);
+        }
+    }
+
+    return(xmlFindHandler(name, output, out));
 }
 
 /**
diff --git a/xmlsave.c b/xmlsave.c
index 5bd3445e6..8e30229d9 100644
--- a/xmlsave.c
+++ b/xmlsave.c
@@ -343,7 +343,7 @@ xmlNewSaveCtxt(const char *encoding, int options)
 
         res = xmlOpenCharEncodingHandler(encoding, /* output */ 1,
                                          &ret->handler);
-	if (ret->handler == NULL) {
+	if (res != XML_ERR_OK) {
 	    xmlSaveErr(NULL, res, NULL, encoding);
             xmlFreeSaveCtxt(ret);
 	    return(NULL);
@@ -801,7 +801,7 @@ static int xmlSaveSwitchEncoding(xmlSaveCtxtPtr ctxt, const char *encoding) {
         int res;
 
 	res = xmlOpenCharEncodingHandler(encoding, /* output */ 1, &handler);
-        if (handler == NULL) {
+        if (res != XML_ERR_OK) {
             xmlSaveErr(buf, res, NULL, encoding);
             return(-1);
         }
@@ -2669,7 +2669,7 @@ xmlDocDumpFormatMemoryEnc(xmlDocPtr out_doc, xmlChar **doc_txt_ptr,
 
 	res = xmlOpenCharEncodingHandler(txt_encoding, /* output */ 1,
                                          &conv_hdlr);
-	if (conv_hdlr == NULL) {
+	if (res != XML_ERR_OK) {
             xmlSaveErr(NULL, res, NULL, txt_encoding);
 	    return;
 	}
@@ -2784,8 +2784,10 @@ xmlDocFormatDump(FILE *f, xmlDocPtr cur, int format) {
     encoding = (const char *) cur->encoding;
 
     if (encoding != NULL) {
-	xmlOpenCharEncodingHandler(encoding, /* output */ 1, &handler);
-	if (handler == NULL) {
+        int res;
+
+	res = xmlOpenCharEncodingHandler(encoding, /* output */ 1, &handler);
+	if (res != XML_ERR_OK) {
 	    xmlFree((char *) cur->encoding);
 	    cur->encoding = NULL;
 	    encoding = NULL;
@@ -2921,8 +2923,10 @@ xmlSaveFormatFileEnc( const char * filename, xmlDocPtr cur,
 	encoding = (const char *) cur->encoding;
 
     if (encoding != NULL) {
-        xmlOpenCharEncodingHandler(encoding, /* output */ 1, &handler);
-        if (handler == NULL)
+        int res;
+
+        res = xmlOpenCharEncodingHandler(encoding, /* output */ 1, &handler);
+        if (res != XML_ERR_OK)
             return(-1);
     }