diff --git a/core/call.ml b/core/call.ml
index c6ce74f..4b652e1 100644
--- a/core/call.ml
+++ b/core/call.ml
@@ -9,18 +9,54 @@ module Batch_stack = struct
   type t
 
   let t : t structure typ = Ctypes.structure "grpc_ocaml_run_batch_stack"
-  let recv_initial_metadata = Ctypes.field t "recv_initial_metadata" @@ ptr Metadata.raw
-  let recv_message = Ctypes.field t "recv_message" @@ ptr (ptr Byte_buffer.raw)
-  let status = Ctypes.field t "recv_status" @@ ptr Status.Code.t
-  let tr = Ctypes.field t "tr" @@ ptr Metadata.raw
-  let details = Ctypes.field t "details" @@ ptr Slice.t
-  let error_message = Ctypes.field t "error_message" @@ ptr Ctypes.string
-  let cancelled = Ctypes.field t "cancelled" @@ ptr int
+  let ops = Ctypes.field t "ops" @@ ptr Op.t
+  let ops_num = Ctypes.field t "ops_num" int
+  let send_metadata = Ctypes.field t "send_metadata" Metadata.t
+  let send_trailing_metadata = Ctypes.field t "send_trailing_metadata" Metadata.t
+  let send_status_details = Ctypes.field t "send_status_details" Slice.t
+  let recv_initial_metadata = Ctypes.field t "recv_initial_metadata" Metadata.t
+  let recv_message = Ctypes.field t "recv_message" @@ ptr Byte_buffer.raw
+  let status = Ctypes.field t "recv_status" @@ Status.Code.t
+  let recv_trailing_metadata = Ctypes.field t "recv_trailing_metadata" Metadata.t
+  let recv_status_details = Ctypes.field t "recv_status_details" Slice.t
+  let error_message = Ctypes.field t "error_message" string
+  let cancelled = Ctypes.field t "cancelled" int
   let () = seal t
-  let destroy = free
+
+  let destroy t =
+    (* let destroy_md_with_entries md = *)
+    (* Metadata.destroy_entries *)
+    (* (md |->* Metadata.metadata) *)
+    (* (md |->* Metadata.count |> Unsigned.Size_t.to_int); *)
+    (* Metadata.destroy md *)
+    (* in *)
+    (* destroy_md_with_entries (t |-> send_metadata); *)
+    (* destroy_md_with_entries (t |-> send_trailing_metadata); *)
+    Metadata.destroy (t |-> recv_initial_metadata);
+    Metadata.destroy (t |-> recv_trailing_metadata)
+  ;;
+
+  (* let recv_status_details = t |->* recv_status_details in *)
+  (* if Slice.start_ptr recv_status_details |> (not <@ is_null) *)
+  (* then Slice.unref recv_status_details *)
+
+  (* let recv_message = t |->* recv_message in *)
+  (* if not @@ is_null recv_message then Byte_buffer.destroy recv_message; *)
+  (* CArray.from_ptr (t |->* ops) (t |->* ops_num) *)
+  (* |> CArray.iter *)
+  (* @@ fun op' -> *)
+  (* match op' @.* Op.op with *)
+  (* | Op.Type.SEND_MESSAGE -> *)
+  (* Byte_buffer.destroy *)
+  (* (op' @. Op.data |-> Op.Data.send_message |->* Op.Data.Send_message.send_message) *)
+  (* | _ -> () *)
 
   let make_tag_pair () =
     let t = malloc t in
+    Metadata.init (t |-> send_metadata);
+    Metadata.init (t |-> send_trailing_metadata);
+    Metadata.init (t |-> recv_initial_metadata);
+    Metadata.init (t |-> recv_trailing_metadata);
     let tag = to_voidp t in
     t, tag
   ;;
@@ -107,17 +143,10 @@ let make
   wrap_raw ~cq ~call ~flags ()
 ;;
 
-let run_batch ?(tag = Ctypes.null) t ops =
-  let ops_size = List.length ops in
-  let ops_size' = Unsigned.Size_t.of_int ops_size in
-  let ops =
-    (CArray.(start <@ of_list T.Op.t)
-    <@ List.map (fun op ->
-           op @. T.Op.flags <-@ t.flags;
-           op))
-      (Op.make_ops ops)
+let run_batch t ?(tag = null) ops ops_num =
+  let err =
+    F.Call.start_batch t.call ops (Unsigned.Size_t.of_int ops_num) tag __reserved__
   in
-  let err = F.Call.start_batch t.call ops ops_size' tag __reserved__ in
   let () =
     if err <> Error.OK
     then failwith @@ Printf.sprintf "prepare call error(%s)" @@ Error.show err
@@ -128,20 +157,17 @@ let run_batch ?(tag = Ctypes.null) t ops =
   then (
     let st = ev @.* T.Event.typ in
     failwith @@ Printf.sprintf "run_batch failed(%s)" @@ Completion_queue.Type.show st)
-  else ops, ops_size
 ;;
 
 let unary_request ?(metadata = []) ?message t =
-  let (`Recv_initial_metadata recv_initial_metadata' as rim) =
-    Op.make_ref_initial_metadata ()
-  in
-  let (`Recv_message recv_message' as rm) = Op.make_ref_recv_message () in
-  let (`Recv_status_on_client recv_status_on_client' as rsoc) =
-    Op.make_ref_recv_status_on_client ()
-  in
   let ops =
     let it =
-      [ `Send_initial_metadata metadata; `Send_close_from_client; rim; rm; rsoc ]
+      [ `Send_initial_metadata metadata
+      ; `Send_close_from_client
+      ; `Recv_initial_metadata
+      ; `Recv_message
+      ; `Recv_status_on_client
+      ]
     in
     let add_msg =
       match message with
@@ -150,62 +176,84 @@ let unary_request ?(metadata = []) ?message t =
     in
     add_msg it
   in
+  let ops' = Op.make_ops ops t.flags in
+  let ops_num = List.length ops in
+  let recv_message =
+    Op.(
+      get ops' ops_num `Recv_message @. Data.recv_message
+      |-> Data.Recv_message.recv_message)
+  in
+  let recv_initial_metadata =
+    Op.(get ops' ops_num `Recv_initial_metadata @. Data.recv_initial_metadata)
+  in
+  let recv_status_on_client =
+    Op.(get ops' ops_num `Recv_status_on_client @. Data.recv_status_on_client)
+  in
+  let md =
+    recv_initial_metadata |-> Op.Data.Recv_initial_metadata.recv_initial_metadata
+  in
+  let status = recv_status_on_client |-> Op.Data.Recv_status_on_client.status in
+  let status_details =
+    recv_status_on_client |-> Op.Data.Recv_status_on_client.status_details
+  in
+  let error_string =
+    recv_status_on_client |-> Op.Data.Recv_status_on_client.error_string
+  in
+  let tr = recv_status_on_client |-> Op.Data.Recv_status_on_client.trailing_metadata in
   let stack, tag = Batch_stack.make_tag_pair () in
-  Batch_stack.(
-    stack |-> recv_message <-@ recv_message'.message;
-    stack |-> recv_initial_metadata <-@ recv_initial_metadata'.metadata;
-    stack |-> status <-@ recv_status_on_client'.status;
-    stack |-> details <-@ recv_status_on_client'.details;
-    stack |-> error_message <-@ recv_status_on_client'.error_message;
-    stack |-> tr <-@ recv_status_on_client'.metadata);
-  let ops, len = run_batch ~tag t ops in
-  let status = !@(recv_status_on_client'.status) in
+  stack |-> Batch_stack.ops <-@ ops';
+  stack |-> Batch_stack.ops_num <-@ ops_num;
+  recv_message <-@ (stack |-> Batch_stack.recv_message);
+  md <-@ (stack |-> Batch_stack.recv_initial_metadata);
+  status <-@ (stack |-> Batch_stack.status);
+  status_details <-@ (stack |-> Batch_stack.recv_status_details);
+  error_string <-@ (stack |-> Batch_stack.error_message);
+  tr <-@ (stack |-> Batch_stack.recv_trailing_metadata);
+  let () = run_batch ~tag t ops' ops_num in
+  let status = !@status in
   let md =
-    let init_md = Metadata.to_bwd recv_initial_metadata'.metadata in
-    let md = Metadata.to_bwd recv_status_on_client'.metadata in
-    md @ init_md
+    let md = Metadata.to_bwd !@md in
+    let tr = Metadata.to_bwd !@tr in
+    tr @ md
   in
-  let status = Status.Code.to_bwd status in
+  let status = Status.Code.to_bwd !@status in
+  Fun.protect ~finally:(fun () -> Batch_stack.destroy stack)
+  @@ fun () ->
   match status with
   | `OK ->
-    let recv_message = Byte_buffer.to_string_opt !@(recv_message'.message) in
-    let () =
-      Batch_stack.destroy stack;
-      Op.destroy ops len
-    in
+    let recv_message = Byte_buffer.to_string_opt !@(!@recv_message) in
     Ok (recv_message, md)
   | #Status.Code.fail_bwd as status ->
     let details =
-      let slice = !@(recv_status_on_client'.details) in
-      if Slice.is_empty slice then None else Some (Slice.to_string slice)
-    in
-    let () =
-      Batch_stack.destroy stack;
-      Op.destroy ops len
+      let slice = !@status_details in
+      if is_null slice then None else Some (Slice.to_string !@slice)
     in
     Error (status, details, md)
 ;;
 
 let remote_read t =
-  let (`Recv_message recv_message as rm) = Op.make_ref_recv_message () in
-  let ops = [ rm ] in
-  let stack, tag = Batch_stack.make_tag_pair () in
-  stack |-> Batch_stack.recv_message <-@ recv_message.message;
-  let ops, len = run_batch ~tag t ops in
-  let message = Byte_buffer.to_string_opt !@(recv_message.message) in
-  let () =
-    Batch_stack.destroy stack;
-    Op.destroy ops len
+  let ops = [ `Recv_message ] in
+  let ops_num = 1 in
+  let ops' = Op.make_ops ops t.flags in
+  let recv_message =
+    Op.(
+      get ops' ops_num `Recv_message @. Data.recv_message
+      |-> Data.Recv_message.recv_message)
   in
+  let stack, tag = Batch_stack.make_tag_pair () in
+  stack |-> Batch_stack.ops <-@ ops';
+  stack |-> Batch_stack.ops_num <-@ ops_num;
+  recv_message <-@ (stack |-> Batch_stack.recv_message);
+  Fun.protect ~finally:(fun () -> Batch_stack.destroy stack)
+  @@ fun () ->
+  let () = run_batch ~tag t ops' ops_num in
+  let message = Byte_buffer.to_string_opt !@(!@recv_message) in
   message
 ;;
 
 (** send unary response: run RECV_CLOSE_ON_SERVER, SEND_INITIAL_METADATA and SEND_STATUS_FROM_SERVER ops *)
 let unary_response ?(code = `OK) ?details ?(md = []) ?(tr = []) t res =
   let code = Status.Code.of_bwd code in
-  let (`Recv_close_on_server recv_close_on_server as rcos) =
-    Op.make_ref_recv_close_on_server ()
-  in
   let ops =
     let add_msg =
       match res with
@@ -215,17 +263,44 @@ let unary_response ?(code = `OK) ?details ?(md = []) ?(tr = []) t res =
     add_msg
       [ `Send_initial_metadata md
       ; `Send_status_from_server Status.{ code; details; metadata = tr }
-      ; rcos
+      ; `Recv_close_on_server
       ]
   in
+  let ops_num = List.length ops in
+  let ops' = Op.make_ops ops t.flags in
   let stack, tag = Batch_stack.make_tag_pair () in
-  stack |-> Batch_stack.cancelled <-@ recv_close_on_server.cancelled;
-  let ops, len = run_batch ~tag t ops in
-  let closed_on_server = deref @@ recv_close_on_server.cancelled in
-  let () =
-    Batch_stack.destroy stack;
-    Op.destroy ops len
+  let send_initial_metadata =
+    Op.(get ops' ops_num `Send_initial_metadata @. Data.send_initial_metadata)
+  in
+  let send_status_from_server =
+    Op.(get ops' ops_num `Send_status_from_server @. Data.send_status_from_server)
+  in
+  let send_md = send_initial_metadata |-> Op.Data.Send_initial_metadata.metadata in
+  let send_md_count = send_initial_metadata |-> Op.Data.Send_initial_metadata.count in
+  let send_metadata = stack |-> Batch_stack.send_metadata in
+  send_metadata |-> Metadata.metadata <-@ !@send_md;
+  send_metadata |-> Metadata.count <-@ !@send_md_count;
+  (* let tr'' = Metadata.make tr in *)
+  let send_tr =
+    send_status_from_server |->* Op.Data.Send_status_from_server.trailing_metadata
+  in
+  let send_tr_count =
+    send_status_from_server |->* Op.Data.Send_status_from_server.trailing_metadata_count
+  in
+  let send_trailing_metadata = stack |-> Batch_stack.send_trailing_metadata in
+  send_trailing_metadata |-> Metadata.metadata <-@ send_tr;
+  send_trailing_metadata |-> Metadata.count <-@ send_tr_count;
+  let recv_close_on_server =
+    Op.(get ops' ops_num `Recv_close_on_server @. Data.recv_close_on_server)
   in
+  let cancelled = recv_close_on_server |-> Op.Data.Recv_close_on_server.cancelled in
+  stack |-> Batch_stack.ops <-@ ops';
+  stack |-> Batch_stack.ops_num <-@ ops_num;
+  cancelled <-@ (stack |-> Batch_stack.cancelled);
+  Fun.protect ~finally:(fun () -> Batch_stack.destroy stack)
+  @@ fun () ->
+  let () = run_batch ~tag t ops' ops_num in
+  let closed_on_server = !@(!@cancelled) in
   if closed_on_server <= 0
   then Log.message __FILE__ __LINE__ `Info "not (properly) closed request by server"
 ;;
diff --git a/core/import.ml b/core/import.ml
index 5d6bd5c..af470c7 100644
--- a/core/import.ml
+++ b/core/import.ml
@@ -17,7 +17,8 @@ let[@inline] malloc ?finalise t =
   ptr
 ;;
 
-let[@inline] free t = F.Alloc.free @@ Ctypes.to_voidp t
+let[@inline] free v = F.Alloc.free @@ Ctypes.to_voidp v
+let[@inline] nullof t = Ctypes.from_voidp t Ctypes.null
 
 (** [NULL] *)
 let __reserved__ = Ctypes.null
diff --git a/core/metadata.ml b/core/metadata.ml
index 1062ca9..fbeb6ca 100644
--- a/core/metadata.ml
+++ b/core/metadata.ml
@@ -31,14 +31,16 @@ let destroy_entries md len =
 let allocate ?(size = 0) ?(count = 0) () =
   let t = malloc Array.t in
   let () = init t in
+  let msize = Unsigned.Size_t.of_int (size * sizeof elem) in
   let size = Unsigned.Size_t.of_int size in
+  t |-> Array.metadata <-@ from_voidp elem @@ F.Alloc.zalloc msize;
   t |-> Array.capacity <-@ size;
   t |-> Array.count <-@ Unsigned.Size_t.of_int count;
   t
 ;;
 
 open struct
-  let fwd1 (k, v) =
+  let fwd1 (k, v) elem =
     let k' = Slice.from_string ~copy:true k in
     let key_is_valid = F.Header.key_is_legal k' > 0 in
     let () =
@@ -55,12 +57,8 @@ open struct
         Slice.unref v';
         failwith @@ Printf.sprintf "invalid value: %s" v)
     in
-    let vl = Ctypes.make elem in
-    let () =
-      vl @. key <-@ k';
-      vl @. value <-@ v'
-    in
-    vl
+    elem @. key <-@ k';
+    elem @. value <-@ v'
   ;;
 
   let bwd1 md =
@@ -73,11 +71,12 @@ end
 let make bwd =
   let len = List.length bwd in
   let arr = allocate ~size:len ~count:len () in
-  bwd
-  |> List.map fwd1
-  |> fun l ->
-  let md = CArray.(of_list elem l |> start) in
-  arr |-> metadata <-@ md;
+  let count = ref 0 in
+  CArray.from_ptr (arr |->* metadata) len
+  |> CArray.iter (fun elem ->
+         let kv = List.nth bwd !count in
+         fwd1 kv elem;
+         incr count);
   arr
 ;;
 
diff --git a/core/op.ml b/core/op.ml
index c011716..e078366 100644
--- a/core/op.ml
+++ b/core/op.ml
@@ -5,61 +5,26 @@ type raw = t
 
 let raw = t
 
-type ref_recv_initial_metadata = { metadata : Metadata.raw structure ptr }
-type ref_recv_message = { message : Byte_buffer.raw structure ptr ptr }
-
-type ref_recv_status_on_client =
-  { status : Status.Code.t ptr
-  ; metadata : Metadata.raw structure ptr
-  ; details : Slice.raw structure ptr
-  ; error_message : string ptr
-  }
-
-type ref_recv_close_on_server = { cancelled : int ptr }
-
 type bwd =
   [ `Send_initial_metadata of Metadata.bwd
   | `Send_message of string
   | `Send_status_from_server of Status.t
   | `Send_close_from_client
-  | `Recv_initial_metadata of ref_recv_initial_metadata
-  | `Recv_message of ref_recv_message
-  | `Recv_status_on_client of ref_recv_status_on_client
-  | `Recv_close_on_server of ref_recv_close_on_server
+  | `Recv_initial_metadata
+  | `Recv_message
+  | `Recv_status_on_client
+  | `Recv_close_on_server
   ]
 
-let make_ref_initial_metadata () =
-  let metadata = Metadata.allocate () in
-  `Recv_initial_metadata { metadata }
-;;
-
-let make_ref_recv_message () =
-  let message = malloc (ptr Byte_buffer.t) in
-  `Recv_message { message }
-;;
-
-let make_ref_recv_status_on_client () =
-  let status = Status.allocate () in
-  let metadata = Metadata.allocate () in
-  let details = malloc Slice.t in
-  let error_message = malloc string in
-  `Recv_status_on_client { status; metadata; details; error_message }
-;;
-
-let make_ref_recv_close_on_server () =
-  let cancelled = malloc int in
-  `Recv_close_on_server { cancelled }
-;;
-
 let to_op_type = function
   | `Send_initial_metadata _ -> Type.SEND_INITIAL_METADATA
   | `Send_message _ -> Type.SEND_MESSAGE
   | `Send_status_from_server _ -> Type.SEND_STATUS_FROM_SERVER
   | `Send_close_from_client -> Type.SEND_CLOSE_FROM_CLIENT
-  | `Recv_initial_metadata _ -> Type.RECV_INITIAL_METADATA
-  | `Recv_message _ -> Type.RECV_MESSAGE
-  | `Recv_status_on_client _ -> Type.RECV_STATUS_ON_CLIENT
-  | `Recv_close_on_server _ -> Type.RECV_CLOSE_ON_SERVER
+  | `Recv_initial_metadata -> Type.RECV_INITIAL_METADATA
+  | `Recv_message -> Type.RECV_MESSAGE
+  | `Recv_status_on_client -> Type.RECV_STATUS_ON_CLIENT
+  | `Recv_close_on_server -> Type.RECV_CLOSE_ON_SERVER
 ;;
 
 let destroy ops len =
@@ -69,10 +34,7 @@ let destroy ops len =
   let data = op' @. data in
   let typ = op' @.* op in
   match typ with
-  | Type.SEND_CLOSE_FROM_CLIENT | Type.RECV_CLOSE_ON_SERVER -> ()
-  | Type.SEND_MESSAGE ->
-    let it = data |-> Data.send_message in
-    Byte_buffer.destroy (it |->* Data.Send_message.send_message)
+  | Type.SEND_CLOSE_FROM_CLIENT | Type.RECV_CLOSE_ON_SERVER | Type.SEND_MESSAGE -> ()
   | Type.SEND_INITIAL_METADATA ->
     let it = data |-> Data.send_initial_metadata in
     Data.Send_initial_metadata.(
@@ -87,7 +49,8 @@ let destroy ops len =
         let len = it |->* trailing_metadata_count |> Unsigned.Size_t.to_int in
         Metadata.destroy_entries md len
       in
-      ignore @@ Option.map (Slice.unref <@ deref) (it |->* status_details))
+      let status_details = it |->* status_details in
+      if not @@ is_null status_details then Slice.unref !@status_details)
   | Type.RECV_INITIAL_METADATA ->
     let it = data |-> Data.recv_initial_metadata in
     let md' = it |->* Data.Recv_initial_metadata.recv_initial_metadata in
@@ -97,7 +60,8 @@ let destroy ops len =
     Metadata.destroy md'
   | Type.RECV_MESSAGE ->
     let it = data |-> Data.recv_message in
-    Byte_buffer.destroy !@(it |->* Data.Recv_message.recv_message)
+    let recv_message = !@(it |->* Data.Recv_message.recv_message) in
+    if not @@ is_null recv_message then Byte_buffer.destroy recv_message
   | Type.RECV_STATUS_ON_CLIENT ->
     let it = data |-> Data.recv_status_on_client in
     Data.Recv_status_on_client.(
@@ -107,8 +71,10 @@ let destroy ops len =
         let len = md |->* count |> Unsigned.Size_t.to_int in
         destroy_entries md' len;
         destroy md);
-      ignore @@ Option.map free (it |->* error_string);
-      ignore @@ Option.map (Slice.unref <@ deref) (it |->* status_details))
+      let error_string = it |-> error_string in
+      F.Alloc.free (to_voidp error_string);
+      let status_details = it |->* status_details in
+      if not @@ is_null status_details then Slice.unref !@status_details)
 ;;
 
 let make (bwd : bwd) =
@@ -133,7 +99,9 @@ let make (bwd : bwd) =
       it |-> Data.Send_message.send_message <-@ msg'
     | `Send_status_from_server st ->
       let status_details' =
-        Option.map (Ctypes.addr <@ Slice.from_string ~copy:true) st.Status.details
+        match st.Status.details with
+        | Some details -> (Ctypes.addr <@ Slice.from_string ~copy:true) details
+        | None -> from_voidp T.Slice.t null
       in
       let metadata = Metadata.(make st.metadata |->* metadata) in
       let it = data |-> Data.send_status_from_server in
@@ -144,24 +112,55 @@ let make (bwd : bwd) =
         it
         |-> trailing_metadata_count
         <-@ Unsigned.Size_t.of_int @@ List.length st.metadata)
-    | `Recv_initial_metadata ref ->
+    | `Recv_initial_metadata ->
       let it = data |-> Data.recv_initial_metadata in
-      it |-> Data.Recv_initial_metadata.recv_initial_metadata <-@ ref.metadata
-    | `Recv_message ref ->
-      let it = data |-> Data.recv_message in
-      it |-> Data.Recv_message.recv_message <-@ ref.message
-    | `Recv_status_on_client ref ->
+      let metadata = Metadata.allocate () in
+      it |-> Data.Recv_initial_metadata.recv_initial_metadata <-@ metadata
+    | `Recv_status_on_client ->
       let it = data |-> Data.recv_status_on_client in
-      Data.Recv_status_on_client.(
-        it |-> trailing_metadata <-@ ref.metadata;
-        it |-> status <-@ ref.status;
-        it |-> status_details <-@ Some ref.details;
-        it |-> error_string <-@ Some ref.error_message)
-    | `Recv_close_on_server ref ->
-      let it = data |-> Data.recv_close_on_server in
-      it |-> Data.Recv_close_on_server.cancelled <-@ ref.cancelled
+      let tr = Metadata.allocate () in
+      Data.Recv_status_on_client.(it |-> trailing_metadata <-@ tr)
+    | _ -> ()
   in
   t
 ;;
 
-let make_ops = List.map make
+let make_ops ops write_flag =
+  let ops' = List.map make ops in
+  List.iter
+    (fun op' ->
+      match op' @.* op with
+      | Type.SEND_MESSAGE -> op' @. flags <-@ write_flag
+      | _ -> ())
+    ops';
+  CArray.(start <@ of_list T.Op.t) ops'
+;;
+
+let get ops len typ =
+  let r = ref None in
+  let open CArray in
+  (let exception Break in
+  try
+    from_ptr ops len
+    |> iter
+       @@ fun op' ->
+       let data = op' @.* data in
+       r := Some data;
+       match op' @.* op with
+       | Type.SEND_INITIAL_METADATA when typ = `Send_initial_metadata -> raise Break
+       | Type.SEND_MESSAGE when typ = `Send_message ->
+         r := Some data;
+         raise Break
+       | Type.SEND_STATUS_FROM_SERVER when typ = `Send_status_from_server -> raise Break
+       | Type.SEND_CLOSE_FROM_CLIENT when typ = `Send_close_from_client -> raise Break
+       | Type.RECV_INITIAL_METADATA when typ = `Recv_initial_metadata -> raise Break
+       | Type.RECV_MESSAGE when typ = `Recv_message -> raise Break
+       | Type.RECV_STATUS_ON_CLIENT when typ = `Recv_status_on_client -> raise Break
+       | Type.RECV_CLOSE_ON_SERVER when typ = `Recv_close_on_server -> raise Break
+       | _ -> ()
+  with
+  | Break -> ());
+  match !r with
+  | Some v -> v
+  | None -> failwith "failed to get metadata"
+;;
diff --git a/core/server.ml b/core/server.ml
index f414a61..2165f64 100644
--- a/core/server.ml
+++ b/core/server.ml
@@ -264,10 +264,10 @@ let dispatch t (Rpc.{ methd; host; metadata; call; deadline } as rpc) =
           (fun () ->
             try
               match res with
-              | Some (Ok (res, md)) -> Call.unary_response call ~md (Some res)
-              | Some (Error (code, details, md)) ->
+              | Some (Ok (res, tr)) -> Call.unary_response call ~tr (Some res)
+              | Some (Error (code, details, tr)) ->
                 let code = (code :> Status.Code.bwd) in
-                Call.unary_response call ~code ~md ?details None
+                Call.unary_response call ~code ~tr ?details None
               (* deadline exceeded *)
               | None -> ()
             with
diff --git a/stub/type_description.ml b/stub/type_description.ml
index 7ca5ca9..a1a117f 100644
--- a/stub/type_description.ml
+++ b/stub/type_description.ml
@@ -839,7 +839,7 @@ module Types (F : Ctypes.TYPE) = struct
         let trailing_metadata_count = "trailing_metadata_count" <-. size_t
         let trailing_metadata = "trailing_metadata" <-. ptr Metadata.t
         let status = "status" <-. Status_code.t
-        let status_details = "status_details" <-. ptr_opt Slice.t
+        let status_details = "status_details" <-. ptr Slice.t
         let () = seal t
       end
 
@@ -868,8 +868,8 @@ module Types (F : Ctypes.TYPE) = struct
 
         let trailing_metadata = "trailing_metadata" <-. ptr Metadata.Array.t
         let status = "status" <-. ptr Status_code.t
-        let status_details = "status_details" <-. ptr_opt Slice.t
-        let error_string = "error_string" <-. ptr_opt string
+        let status_details = "status_details" <-. ptr Slice.t
+        let error_string = "error_string" <-. ptr string
         let () = seal t
       end