extracta parse_buffer for config

@@ -1161,7 +1161,14 @@ int SrsConfig::parse_file(const char* filename)
         return ret;
     }
     
-    if ((ret = root->parse(&buffer)) != ERROR_SUCCESS) {
+    return parse_buffer(&buffer);
+}
+
+int SrsConfig::parse_buffer(_srs_internal::SrsConfigBuffer* buffer)
+{
+    int ret = ERROR_SUCCESS;
+    
+    if ((ret = root->parse(buffer)) != ERROR_SUCCESS) {
         return ret;
     }
     

@@ -210,7 +210,7 @@ private:
 };
 
 /**
-* the config parser.
+* the config service provider.
 * for the config supports reload, so never keep the reference cross st-thread,
 * that is, never save the SrsConfDirective* get by any api of config,
 * for it maybe free in the reload st-thread cycle.
@@ -248,6 +248,13 @@ private:
     virtual int parse_argv(int& i, char** argv);
     virtual void print_help(char** argv);
     virtual int parse_file(const char* filename);
+protected:
+    /**
+    * parse config from the buffer.
+    * @param buffer, the config buffer, user must delete it.
+    * @remark, protected for the utest to override with mock.
+    */
+    virtual int parse_buffer(_srs_internal::SrsConfigBuffer* buffer);
 public:
     virtual std::string         cwd();
     virtual std::string         argv();