Add macros for access to the underlying buffer and offset.

Useful for using passing the buffer through to another writer
such as LogFileCtx.

src/util-buffer.h

@@ -43,6 +43,16 @@ void MemBufferFree(MemBuffer *buffer);
         (mem_buffer)->offset = 0;                           \
     } while (0)
 
+/**
+ * \brief Get the MemBuffers underlying buffer.
+ */
+#define MEMBUFFER_BUFFER(mem_buffer) (mem_buffer)->buffer
+
+/**
+ * \brief Get the MemBuffers current offset.
+ */
+#define MEMBUFFER_OFFSET(mem_buffer) (mem_buffer)->offset
+
 /**
  * \brief Write a buffer to the file pointer.
  *