Improved handling of XML parser errors

src/s3fs.cpp

@@ -3597,9 +3597,16 @@ static int list_bucket(const char* path, S3ObjList& head, const char* delimiter,
         }
 
         // xmlDocPtr
+        s3fsXmlBufferParserError parserError;
+        parserError.SetXmlParseError();
+
         std::unique_ptr<xmlDoc, decltype(&xmlFreeDoc)> doc(xmlReadMemory(encbody.c_str(), static_cast<int>(encbody.size()), "", nullptr, 0), xmlFreeDoc);
         if(nullptr == doc){
-            S3FS_PRN_ERR("xmlReadMemory returns with error.");
+            if(parserError.IsXmlParseError()){
+                S3FS_PRN_ERR("xmlReadMemory returns with error: %s", parserError.GetXmlParseError().c_str());
+            }else{
+                S3FS_PRN_ERR("xmlReadMemory returns with error.");
+            }
             return -EIO;
         }
         if(0 != append_objects_from_xml(path, doc.get(), head)){

src/s3fs_xml.cpp

@@ -461,8 +461,16 @@ bool simple_parse_xml(const char* data, size_t len, const char* key, std::string
     // ":1: parser error : Document is empty" to stderr.
     // Make sure len is not 0 beforehand.
     //
+    s3fsXmlBufferParserError parserError;
+    parserError.SetXmlParseError();
+
     std::unique_ptr<xmlDoc, decltype(&xmlFreeDoc)> doc(xmlReadMemory(data, static_cast<int>(len), "", nullptr, 0), xmlFreeDoc);
     if(nullptr == doc){
+        if(parserError.IsXmlParseError()){
+            S3FS_PRN_ERR("xmlReadMemory returns with error: %s", parserError.GetXmlParseError().c_str());
+        }else{
+            S3FS_PRN_ERR("xmlReadMemory returns with error.");
+        }
         return false;
     }
 

src/s3fs_xml.h

@@ -25,6 +25,8 @@
 #include <libxml/parser.h>  // [NOTE] nessetially include this header in some environments
 #include <memory>
 #include <string>
+#include <array>
+#include <cstring>
 
 #include "mpu_util.h"
 
@@ -35,6 +37,44 @@ typedef std::unique_ptr<xmlXPathObject, decltype(&xmlXPathFreeObject)> unique_pt
 typedef std::unique_ptr<xmlXPathContext, decltype(&xmlXPathFreeContext)> unique_ptr_xmlXPathContext;
 typedef std::unique_ptr<xmlDoc, decltype(&xmlFreeDoc)> unique_ptr_xmlDoc;
 
+//-------------------------------------------------------------------
+// Utility Class
+//-------------------------------------------------------------------
+class s3fsXmlBufferParserError
+{
+    private:
+        static constexpr int  ERROR_BUFFER_SIZE = 1024;
+        std::array<char, ERROR_BUFFER_SIZE> error_buffer{};
+
+        static void ParserErrorHandler(void* ctx, const char *msg, ...)
+        {
+            auto* errbuf = static_cast<char*>(ctx);
+            if(errbuf){
+                va_list args;
+                va_start(args, msg);
+                vsnprintf(errbuf + strlen(errbuf), ERROR_BUFFER_SIZE - strlen(errbuf) - 1, msg, args);
+                va_end(args);
+            }
+        }
+
+    public:
+        void SetXmlParseError()
+        {
+            error_buffer.fill(0);
+            xmlSetGenericErrorFunc(error_buffer.data(), s3fsXmlBufferParserError::ParserErrorHandler);
+        }
+
+        std::string GetXmlParseError() const
+        {
+            return strlen(error_buffer.data()) ? error_buffer.data() : "";
+        }
+
+        bool IsXmlParseError() const
+        {
+            return (0 < strlen(error_buffer.data()));
+        }
+};
+
 //-------------------------------------------------------------------
 // Functions
 //-------------------------------------------------------------------