Fixed ETag parsing at completing the Multipart upload part

src/string_util.cpp

@@ -125,6 +125,14 @@ std::string trim(std::string s, const char *t /* = SPACES */)
     return trim_left(trim_right(std::move(s), t), t);
 }
 
+std::string peeloff(std::string s)
+{
+    if(s.size() < 2 || *s.begin() != '"' || *s.rbegin() != '"'){
+        return s;
+    }
+    return s.substr(1, s.size() - 2);
+}
+
 //
 // Three url encode functions
 //