Switching to batch oriented metadata passing
diff --git a/include/grpc/grpc.h b/include/grpc/grpc.h
index ffab65f..5180424 100644
--- a/include/grpc/grpc.h
+++ b/include/grpc/grpc.h
@@ -186,6 +186,13 @@
   const char *key;
   const char *value;
   size_t value_length;
+
+  /* The following fields are reserved for grpc internal use.
+     There is no need to initialize them, and they will be set to garbage during
+     calls to grpc. */
+  struct {
+    void *some_random_pointers[3];
+  } internal_data;
 } grpc_metadata;
 
 typedef enum grpc_completion_type {
@@ -295,7 +302,7 @@
   union {
     struct {
       size_t count;
-      const grpc_metadata *metadata;
+      grpc_metadata *metadata;
     } send_initial_metadata;
     grpc_byte_buffer *send_message;
     struct {