feat(util): add restore_read function in rpc_message

include/dsn/tool-api/rpc_message.h

@@ -209,6 +209,12 @@ class message_ex : public ref_counter,
     size_t body_size() { return (size_t)header->body_length; }
     DSN_API void *rw_ptr(size_t offset_begin);
 
+    // rpc_read_stream can read a msg many times by restore()
+    // rpc_read_stream stream1(msg)
+    // msg->restore()
+    // rpc_read_stream stream2(msg)
+    DSN_API void restore();
+
     bool is_backup_request() const { return header->context.u.is_backup_request; }
 
 private:

src/core/core/rpc_message.cpp

@@ -520,6 +520,13 @@ void message_ex::read_commit(size_t size)
     this->_rw_committed = true;
 }
 
+void message_ex::restore()
+{
+    this->_rw_index = -1;
+    this->_rw_committed = true;
+    this->_rw_offset = 0;
+}
+
 void *message_ex::rw_ptr(size_t offset_begin)
 {
     // printf("%p %s\n", this, __FUNCTION__);