diff --git a/src/core/channel/call_op_string.c b/src/core/channel/call_op_string.c
index 3e30d822f4a..12e9f03b41e 100644
--- a/src/core/channel/call_op_string.c
+++ b/src/core/channel/call_op_string.c
@@ -86,10 +86,6 @@ char *grpc_call_op_string(grpc_call_op *op) {
       gpr_strvec_add(&b, gpr_strdup("SEND_METADATA"));
       put_metadata_list(&b, op->data.metadata);
       break;
-    case GRPC_SEND_START:
-      gpr_asprintf(&tmp, "SEND_START pollset=%p", op->data.start.pollset);
-      gpr_strvec_add(&b, tmp);
-      break;
     case GRPC_SEND_MESSAGE:
       gpr_strvec_add(&b, gpr_strdup("SEND_MESSAGE"));
       break;
@@ -115,12 +111,19 @@ char *grpc_call_op_string(grpc_call_op *op) {
     case GRPC_RECV_FINISH:
       gpr_strvec_add(&b, gpr_strdup("RECV_FINISH"));
       break;
+    case GRPC_RECV_SYNTHETIC_STATUS:
+      gpr_asprintf(&tmp, "RECV_SYNTHETIC_STATUS status=%d message='%s'", op->data.synthetic_status.status, op->data.synthetic_status.message);
+      gpr_strvec_add(&b, tmp);
+      break;
     case GRPC_CANCEL_OP:
       gpr_strvec_add(&b, gpr_strdup("CANCEL_OP"));
       break;
   }
   gpr_asprintf(&tmp, " flags=0x%08x", op->flags);
   gpr_strvec_add(&b, tmp);
+  if (op->bind_pollset) {
+    gpr_strvec_add(&b, gpr_strdup("bind_pollset"));
+  }
 
   out = gpr_strvec_flatten(&b, NULL);
   gpr_strvec_destroy(&b);
diff --git a/src/core/channel/channel_stack.c b/src/core/channel/channel_stack.c
index cd3496b42bb..3a3a3a75b70 100644
--- a/src/core/channel/channel_stack.c
+++ b/src/core/channel/channel_stack.c
@@ -183,6 +183,9 @@ void grpc_call_stack_destroy(grpc_call_stack *stack) {
 
 void grpc_call_next_op(grpc_call_element *elem, grpc_call_op *op) {
   grpc_call_element *next_elem = elem + op->dir;
+  if (op->type == GRPC_SEND_METADATA || op->type == GRPC_RECV_METADATA) {
+    grpc_metadata_batch_assert_ok(&op->data.metadata);
+  }
   next_elem->filter->call_op(next_elem, elem, op);
 }
 
@@ -211,6 +214,7 @@ void grpc_call_element_send_cancel(grpc_call_element *cur_elem) {
   cancel_op.done_cb = do_nothing;
   cancel_op.user_data = NULL;
   cancel_op.flags = 0;
+  cancel_op.bind_pollset = NULL;
   grpc_call_next_op(cur_elem, &cancel_op);
 }
 
@@ -221,11 +225,19 @@ void grpc_call_element_send_finish(grpc_call_element *cur_elem) {
   finish_op.done_cb = do_nothing;
   finish_op.user_data = NULL;
   finish_op.flags = 0;
+  finish_op.bind_pollset = NULL;
   grpc_call_next_op(cur_elem, &finish_op);
 }
 
 void grpc_call_element_recv_status(grpc_call_element *cur_elem,
                                    grpc_status_code status,
                                    const char *message) {
-  abort();
+  grpc_call_op op;
+  op.type = GRPC_RECV_SYNTHETIC_STATUS;
+  op.dir = GRPC_CALL_UP;
+  op.done_cb = do_nothing;
+  op.user_data = NULL;
+  op.data.synthetic_status.status = status;
+  op.data.synthetic_status.message = message;
+  grpc_call_next_op(cur_elem, &op);
 }
diff --git a/src/core/channel/channel_stack.h b/src/core/channel/channel_stack.h
index cc1eab7cf22..addc92b2727 100644
--- a/src/core/channel/channel_stack.h
+++ b/src/core/channel/channel_stack.h
@@ -62,8 +62,6 @@ typedef struct grpc_call_element grpc_call_element;
 typedef enum {
   /* send metadata to the channels peer */
   GRPC_SEND_METADATA,
-  /* start a connection (corresponds to start_invoke/accept) */
-  GRPC_SEND_START,
   /* send a message to the channels peer */
   GRPC_SEND_MESSAGE,
   /* send a pre-formatted message to the channels peer */
@@ -80,6 +78,8 @@ typedef enum {
   GRPC_RECV_HALF_CLOSE,
   /* full close was received from the channels peer */
   GRPC_RECV_FINISH,
+  /* a status has been sythesized locally */
+  GRPC_RECV_SYNTHETIC_STATUS,
   /* the call has been abnormally terminated */
   GRPC_CANCEL_OP
 } grpc_call_op_type;
@@ -103,13 +103,16 @@ typedef struct {
 
   /* Argument data, matching up with grpc_call_op_type names */
   union {
-    struct {
-      grpc_pollset *pollset;
-    } start;
     grpc_byte_buffer *message;
     grpc_metadata_batch metadata;
+    struct {
+      grpc_status_code status;
+      const char *message;
+    } synthetic_status;
   } data;
 
+  grpc_pollset *bind_pollset;
+
   /* Must be called when processing of this call-op is complete.
      Signature chosen to match transport flow control callbacks */
   void (*done_cb)(void *user_data, grpc_op_error error);
diff --git a/src/core/channel/client_channel.c b/src/core/channel/client_channel.c
index 018228b4e62..fb984f2878a 100644
--- a/src/core/channel/client_channel.c
+++ b/src/core/channel/client_channel.c
@@ -82,21 +82,16 @@ struct call_data {
   /* owning element */
   grpc_call_element *elem;
 
+  gpr_uint8 got_first_send;
+
   call_state state;
-  grpc_metadata_batch pending_metadata;
-  gpr_uint32 pending_metadata_flags;
   gpr_timespec deadline;
   union {
     struct {
       /* our child call stack */
       grpc_child_call *child_call;
     } active;
-    struct {
-      void (*on_complete)(void *user_data, grpc_op_error error);
-      void *on_complete_user_data;
-      gpr_uint32 start_flags;
-      grpc_pollset *pollset;
-    } waiting;
+    grpc_call_op waiting_op;
   } s;
 };
 
@@ -121,19 +116,9 @@ static void complete_activate(grpc_call_element *elem, grpc_call_op *op) {
   call_data *calld = elem->call_data;
   grpc_call_element *child_elem =
       grpc_child_call_get_top_element(calld->s.active.child_call);
-  grpc_call_op mop;
 
   GPR_ASSERT(calld->state == CALL_ACTIVE);
 
-  /* sending buffered metadata down the stack before the start call */
-  mop.type = GRPC_SEND_METADATA;
-  mop.dir = GRPC_CALL_DOWN;
-  mop.flags = calld->pending_metadata_flags;
-  mop.data.metadata = calld->pending_metadata;
-  mop.done_cb = do_nothing;
-  mop.user_data = NULL;
-  child_elem->filter->call_op(child_elem, elem, &mop);
-
   /* continue the start call down the stack, this nees to happen after metadata
      are flushed*/
   child_elem->filter->call_op(child_elem, elem, op);
@@ -177,10 +162,7 @@ static void start_rpc(grpc_call_element *elem, grpc_call_op *op) {
           gpr_realloc(chand->waiting_children,
                       chand->waiting_child_capacity * sizeof(call_data *));
     }
-    calld->s.waiting.on_complete = op->done_cb;
-    calld->s.waiting.on_complete_user_data = op->user_data;
-    calld->s.waiting.start_flags = op->flags;
-    calld->s.waiting.pollset = op->data.start.pollset;
+    calld->s.waiting_op = *op;
     chand->waiting_children[chand->waiting_child_count++] = calld;
     gpr_mu_unlock(&chand->mu);
 
@@ -233,7 +215,7 @@ static void cancel_rpc(grpc_call_element *elem, grpc_call_op *op) {
       calld->state = CALL_CANCELLED;
       gpr_mu_unlock(&chand->mu);
       send_up_cancelled_ops(elem);
-      calld->s.waiting.on_complete(calld->s.waiting.on_complete_user_data,
+      calld->s.waiting_op.done_cb(calld->s.waiting_op.user_data,
                                    GRPC_OP_ERROR);
       return; /* early out */
     case CALL_CREATED:
@@ -257,12 +239,13 @@ static void call_op(grpc_call_element *elem, grpc_call_element *from_elem,
 
   switch (op->type) {
     case GRPC_SEND_METADATA:
-      grpc_metadata_batch_merge(&calld->pending_metadata, &op->data.metadata);
-      op->done_cb(op->user_data, GRPC_OP_OK);
-      break;
-    case GRPC_SEND_START:
-      /* filter out the start event to find which child to send on */
-      start_rpc(elem, op);
+      if (!calld->got_first_send) {
+        /* filter out the start event to find which child to send on */
+        calld->got_first_send = 1;
+        start_rpc(elem, op);
+      } else {
+        grpc_call_next_op(elem, op);
+      }
       break;
     case GRPC_CANCEL_OP:
       cancel_rpc(elem, op);
@@ -365,12 +348,6 @@ static void channel_op(grpc_channel_element *elem,
   }
 }
 
-static void error_bad_on_complete(void *arg, grpc_op_error error) {
-  gpr_log(GPR_ERROR,
-          "Waiting finished but not started? Bad on_complete callback");
-  abort();
-}
-
 /* Constructor for call_data */
 static void init_call_elem(grpc_call_element *elem,
                            const void *server_transport_data) {
@@ -381,17 +358,13 @@ static void init_call_elem(grpc_call_element *elem,
   calld->elem = elem;
   calld->state = CALL_CREATED;
   calld->deadline = gpr_inf_future;
-  calld->s.waiting.on_complete = error_bad_on_complete;
-  calld->s.waiting.on_complete_user_data = NULL;
-  grpc_metadata_batch_init(&calld->pending_metadata);
+  calld->got_first_send = 0;
 }
 
 /* Destructor for call_data */
 static void destroy_call_elem(grpc_call_element *elem) {
   call_data *calld = elem->call_data;
 
-  /* if the metadata buffer is not flushed, destroy it here. */
-  grpc_metadata_batch_destroy(&calld->pending_metadata);
   /* if the call got activated, we need to destroy the child stack also, and
      remove it from the in-flight requests tracked by the child_entry we
      picked */
@@ -498,13 +471,7 @@ grpc_transport_setup_result grpc_client_channel_transport_setup_complete(
   call_ops = gpr_malloc(sizeof(grpc_call_op) * waiting_child_count);
 
   for (i = 0; i < waiting_child_count; i++) {
-    call_ops[i].type = GRPC_SEND_START;
-    call_ops[i].dir = GRPC_CALL_DOWN;
-    call_ops[i].flags = waiting_children[i]->s.waiting.start_flags;
-    call_ops[i].done_cb = waiting_children[i]->s.waiting.on_complete;
-    call_ops[i].user_data =
-        waiting_children[i]->s.waiting.on_complete_user_data;
-    call_ops[i].data.start.pollset = waiting_children[i]->s.waiting.pollset;
+    call_ops[i] = waiting_children[i]->s.waiting_op;
     if (!prepare_activate(waiting_children[i]->elem, chand->active_child)) {
       waiting_children[i] = NULL;
       call_ops[i].done_cb(call_ops[i].user_data, GRPC_OP_ERROR);
diff --git a/src/core/channel/connected_channel.c b/src/core/channel/connected_channel.c
index 17abba06be9..84d1f3569df 100644
--- a/src/core/channel/connected_channel.c
+++ b/src/core/channel/connected_channel.c
@@ -119,14 +119,13 @@ static void call_op(grpc_call_element *elem, grpc_call_element *from_elem,
   GPR_ASSERT(elem->filter == &grpc_connected_channel_filter);
   GRPC_CALL_LOG_OP(GPR_INFO, elem, op);
 
+  if (op->bind_pollset) {
+    grpc_transport_add_to_pollset(chand->transport, op->bind_pollset);
+  }
+
   switch (op->type) {
     case GRPC_SEND_METADATA:
       grpc_sopb_add_metadata(&calld->outgoing_sopb, op->data.metadata);
-      grpc_sopb_add_flow_ctl_cb(&calld->outgoing_sopb, op->done_cb,
-                                op->user_data);
-      break;
-    case GRPC_SEND_START:
-      grpc_transport_add_to_pollset(chand->transport, op->data.start.pollset);
       end_bufferable_op(op, chand, calld, 0);
       break;
     case GRPC_SEND_MESSAGE:
diff --git a/src/core/channel/http_server_filter.c b/src/core/channel/http_server_filter.c
index 0e50f408b5f..77f204c7a71 100644
--- a/src/core/channel/http_server_filter.c
+++ b/src/core/channel/http_server_filter.c
@@ -188,8 +188,11 @@ static void call_op(grpc_call_element *elem, grpc_call_element *from_elem,
     case GRPC_SEND_METADATA:
       /* If we haven't sent status 200 yet, we need to so so because it needs to
          come before any non : prefixed metadata. */
-      grpc_metadata_batch_add_head(&op->data.metadata, &calld->status,
-                                     grpc_mdelem_ref(channeld->status_ok));
+      if (!calld->sent_status) {
+        calld->sent_status = 1;
+        grpc_metadata_batch_add_head(&op->data.metadata, &calld->status,
+                                       grpc_mdelem_ref(channeld->status_ok));
+      }
       grpc_call_next_op(elem, op);
       break;
     default:
diff --git a/src/core/security/auth.c b/src/core/security/auth.c
index f61287ad3fa..0b9d566c90d 100644
--- a/src/core/security/auth.c
+++ b/src/core/security/auth.c
@@ -175,10 +175,6 @@ static void call_op(grpc_call_element *elem, grpc_call_element *from_elem,
           calld->method = grpc_mdstr_ref(md->value);
         }
       }
-      grpc_call_next_op(elem, op);
-      break;
-
-    case GRPC_SEND_START:
       if (calld->host != NULL) {
         grpc_security_status status;
         const char *call_host = grpc_mdstr_as_c_string(calld->host);
@@ -200,7 +196,6 @@ static void call_op(grpc_call_element *elem, grpc_call_element *from_elem,
       }
       send_security_metadata(elem, op);
       break;
-
     default:
       /* pass control up or down the stack depending on op->dir */
       grpc_call_next_op(elem, op);
diff --git a/src/core/surface/call.c b/src/core/surface/call.c
index 5facaa503d2..0d5fe225d9a 100644
--- a/src/core/surface/call.c
+++ b/src/core/surface/call.c
@@ -94,6 +94,8 @@ typedef enum {
   /* Status came from the application layer overriding whatever
      the wire says */
   STATUS_FROM_API_OVERRIDE = 0,
+  /* Status was created by some internal channel stack operation */
+  STATUS_FROM_CORE,
   /* Status came from 'the wire' - or somewhere below the surface
      layer */
   STATUS_FROM_WIRE,
@@ -363,6 +365,7 @@ static void request_more_data(grpc_call *call) {
   op.flags = 0;
   op.done_cb = do_nothing;
   op.user_data = NULL;
+  op.bind_pollset = NULL;
 
   grpc_call_execute_op(call, &op);
 }
@@ -660,15 +663,9 @@ static void enact_send_action(grpc_call *call, send_action sa) {
         grpc_metadata_batch_link_head(&op.data.metadata,
                                         &call->send_initial_metadata[i]);
       }
-      op.done_cb = do_nothing;
-      op.user_data = NULL;
-      grpc_call_execute_op(call, &op);
-      op.type = GRPC_SEND_START;
-      op.dir = GRPC_CALL_DOWN;
-      op.flags = flags;
-      op.data.start.pollset = grpc_cq_pollset(call->cq);
       op.done_cb = finish_start_step;
       op.user_data = call;
+      op.bind_pollset = grpc_cq_pollset(call->cq);
       grpc_call_execute_op(call, &op);
       break;
     case SEND_BUFFERED_MESSAGE:
@@ -682,6 +679,7 @@ static void enact_send_action(grpc_call *call, send_action sa) {
       op.data.message = data.send_message;
       op.done_cb = finish_write_step;
       op.user_data = call;
+      op.bind_pollset = NULL;
       grpc_call_execute_op(call, &op);
       break;
     case SEND_TRAILING_METADATA_AND_FINISH:
@@ -694,6 +692,7 @@ static void enact_send_action(grpc_call *call, send_action sa) {
           call, data.send_metadata.count, data.send_metadata.metadata);
       op.data.metadata.garbage.head = op.data.metadata.garbage.tail = NULL;
       op.data.metadata.deadline = call->send_deadline;
+      op.bind_pollset = NULL;
       /* send status */
       /* TODO(ctiller): cache common status values */
       data = call->request_data[GRPC_IOREQ_SEND_STATUS];
@@ -723,6 +722,7 @@ static void enact_send_action(grpc_call *call, send_action sa) {
       op.flags = 0;
       op.done_cb = finish_finish_step;
       op.user_data = call;
+      op.bind_pollset = NULL;
       grpc_call_execute_op(call, &op);
       break;
   }
@@ -876,6 +876,7 @@ grpc_call_error grpc_call_cancel(grpc_call *c) {
   op.flags = 0;
   op.done_cb = do_nothing;
   op.user_data = NULL;
+  op.bind_pollset = NULL;
 
   elem = CALL_ELEM_FROM_CALL(c, 0);
   elem->filter->call_op(elem, NULL, &op);
@@ -983,6 +984,14 @@ void grpc_call_recv_message(grpc_call_element *elem,
   unlock(call);
 }
 
+void grpc_call_recv_synthetic_status(grpc_call_element *elem, grpc_status_code status, const char *message) {
+  grpc_call *call = CALL_FROM_TOP_ELEM(elem);
+  lock(call);
+  set_status_code(call, STATUS_FROM_CORE, status);
+  set_status_details(call, STATUS_FROM_CORE, grpc_mdstr_from_string(call->metadata_context, message));
+  unlock(call);
+}
+
 int grpc_call_recv_metadata(grpc_call_element *elem,
                             grpc_metadata_batch *md) {
   grpc_call *call = CALL_FROM_TOP_ELEM(elem);
@@ -990,6 +999,7 @@ int grpc_call_recv_metadata(grpc_call_element *elem,
   grpc_metadata_array *dest;
   grpc_metadata *mdusr;
   int is_trailing;
+  grpc_mdctx *mdctx = call->metadata_context;
 
   lock(call);
   is_trailing = call->read_state >= READ_STATE_GOT_INITIAL_METADATA;
@@ -998,10 +1008,8 @@ int grpc_call_recv_metadata(grpc_call_element *elem,
     grpc_mdstr *key = md->key;
     if (key == grpc_channel_get_status_string(call->channel)) {
       set_status_code(call, STATUS_FROM_WIRE, decode_status(md));
-      grpc_mdelem_unref(md);
     } else if (key == grpc_channel_get_message_string(call->channel)) {
       set_status_details(call, STATUS_FROM_WIRE, grpc_mdstr_ref(md->value));
-      grpc_mdelem_unref(md);
     } else {
       dest = &call->buffered_metadata[is_trailing];
       if (dest->count == dest->capacity) {
@@ -1022,6 +1030,7 @@ int grpc_call_recv_metadata(grpc_call_element *elem,
                         sizeof(grpc_mdelem *) * call->owned_metadata_capacity);
       }
       call->owned_metadata[call->owned_metadata_count++] = md;
+      l->md = 0;
     }
   }
   if (gpr_time_cmp(md->deadline, gpr_inf_future) != 0) {
@@ -1032,6 +1041,15 @@ int grpc_call_recv_metadata(grpc_call_element *elem,
   }
   unlock(call);
 
+  grpc_mdctx_lock(mdctx);
+  for (l = md->list.head; l; l = l->next) {
+    if (l->md) grpc_mdctx_locked_mdelem_unref(mdctx, l->md);
+  }
+  for (l = md->garbage.head; l; l = l->next) {
+    grpc_mdctx_locked_mdelem_unref(mdctx, l->md);
+  }
+  grpc_mdctx_unlock(mdctx);
+
   return !is_trailing;
 }
 
diff --git a/src/core/surface/call.h b/src/core/surface/call.h
index 2848ccc5a13..16de197af11 100644
--- a/src/core/surface/call.h
+++ b/src/core/surface/call.h
@@ -113,6 +113,8 @@ grpc_call_error grpc_call_start_ioreq_and_call_back(
 
 grpc_call_stack *grpc_call_get_call_stack(grpc_call *call);
 
+void grpc_call_recv_synthetic_status(grpc_call_element *elem, grpc_status_code status, const char *message);
+
 /* Given the top call_element, get the call object. */
 grpc_call *grpc_call_from_top_element(grpc_call_element *surface_element);
 
diff --git a/src/core/surface/client.c b/src/core/surface/client.c
index b987c2de5f6..719346689a8 100644
--- a/src/core/surface/client.c
+++ b/src/core/surface/client.c
@@ -61,6 +61,9 @@ static void call_op(grpc_call_element *elem, grpc_call_element *from_elem,
     case GRPC_RECV_FINISH:
       grpc_call_stream_closed(elem);
       break;
+    case GRPC_RECV_SYNTHETIC_STATUS:
+      grpc_call_recv_synthetic_status(elem, op->data.synthetic_status.status, op->data.synthetic_status.message);
+      break;
     default:
       GPR_ASSERT(op->dir == GRPC_CALL_DOWN);
       grpc_call_next_op(elem, op);
diff --git a/src/core/surface/lame_client.c b/src/core/surface/lame_client.c
index 74e9628385c..b7b3d929589 100644
--- a/src/core/surface/lame_client.c
+++ b/src/core/surface/lame_client.c
@@ -51,14 +51,11 @@ static void call_op(grpc_call_element *elem, grpc_call_element *from_elem,
   GRPC_CALL_LOG_OP(GPR_INFO, elem, op);
 
   switch (op->type) {
-    case GRPC_SEND_START:
+    case GRPC_SEND_METADATA:
       grpc_call_element_recv_status(elem, GRPC_STATUS_UNKNOWN,
                                     "Rpc sent on a lame channel.");
       grpc_call_stream_closed(elem);
       break;
-    case GRPC_SEND_METADATA:
-      abort();
-      break;
     default:
       break;
   }
diff --git a/src/core/transport/chttp2/stream_encoder.c b/src/core/transport/chttp2/stream_encoder.c
index 8c66171b078..f50d1428abb 100644
--- a/src/core/transport/chttp2/stream_encoder.c
+++ b/src/core/transport/chttp2/stream_encoder.c
@@ -479,8 +479,9 @@ gpr_uint32 grpc_chttp2_preencode(grpc_stream_op *inops, size_t *inops_count,
         /* skip */
         curop++;
         break;
-      case GRPC_OP_FLOW_CTL_CB:
       case GRPC_OP_METADATA:
+        grpc_metadata_batch_assert_ok(&op->data.metadata);
+      case GRPC_OP_FLOW_CTL_CB:
         /* these just get copied as they don't impact the number of flow
            controlled bytes */
         grpc_sopb_append(outops, op, 1);
@@ -527,6 +528,12 @@ exit_loop:
   *inops_count -= curop;
   memmove(inops, inops + curop, *inops_count * sizeof(grpc_stream_op));
 
+  for (curop = 0; curop < *inops_count; curop++) {
+    if (inops[curop].type == GRPC_OP_METADATA) {
+      grpc_metadata_batch_assert_ok(&inops[curop].data.metadata);
+    }
+  }
+
   return flow_controlled_bytes_taken;
 }
 
diff --git a/src/core/transport/stream_op.c b/src/core/transport/stream_op.c
index 1a8b4174ff1..9589599257f 100644
--- a/src/core/transport/stream_op.c
+++ b/src/core/transport/stream_op.c
@@ -33,11 +33,11 @@
 
 #include "src/core/transport/stream_op.h"
 
+#include <string.h>
+
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 
-#include <string.h>
-
 /* Exponential growth function: Given x, return a larger x.
    Currently we grow by 1.5 times upon reallocation. */
 #define GROW(x) (3 * (x) / 2)
@@ -91,19 +91,32 @@ void grpc_stream_ops_unref_owned_objects(grpc_stream_op *ops, size_t nops) {
   }
 }
 
+static void assert_contained_metadata_ok(grpc_stream_op *ops, size_t nops) {
+  size_t i;
+  for (i = 0; i < nops; i++) {
+    if (ops[i].type == GRPC_OP_METADATA) {
+      grpc_metadata_batch_assert_ok(&ops[i].data.metadata);
+    }
+  }
+}
+
 static void expandto(grpc_stream_op_buffer *sopb, size_t new_capacity) {
   sopb->capacity = new_capacity;
+  assert_contained_metadata_ok(sopb->ops, sopb->nops);
   if (sopb->ops == sopb->inlined_ops) {
     sopb->ops = gpr_malloc(sizeof(grpc_stream_op) * new_capacity);
     memcpy(sopb->ops, sopb->inlined_ops, sopb->nops * sizeof(grpc_stream_op));
   } else {
     sopb->ops = gpr_realloc(sopb->ops, sizeof(grpc_stream_op) * new_capacity);
   }
+  assert_contained_metadata_ok(sopb->ops, sopb->nops);
 }
 
 static grpc_stream_op *add(grpc_stream_op_buffer *sopb) {
   grpc_stream_op *out;
 
+  assert_contained_metadata_ok(sopb->ops, sopb->nops);
+
   if (sopb->nops == sopb->capacity) {
     expandto(sopb, GROW(sopb->capacity));
   }
@@ -114,6 +127,7 @@ static grpc_stream_op *add(grpc_stream_op_buffer *sopb) {
 
 void grpc_sopb_add_no_op(grpc_stream_op_buffer *sopb) {
   add(sopb)->type = GRPC_NO_OP;
+  assert_contained_metadata_ok(sopb->ops, sopb->nops);
 }
 
 void grpc_sopb_add_begin_message(grpc_stream_op_buffer *sopb, gpr_uint32 length,
@@ -122,6 +136,7 @@ void grpc_sopb_add_begin_message(grpc_stream_op_buffer *sopb, gpr_uint32 length,
   op->type = GRPC_OP_BEGIN_MESSAGE;
   op->data.begin_message.length = length;
   op->data.begin_message.flags = flags;
+  assert_contained_metadata_ok(sopb->ops, sopb->nops);
 }
 
 void grpc_sopb_add_metadata(grpc_stream_op_buffer *sopb, grpc_metadata_batch b) {
@@ -129,12 +144,15 @@ void grpc_sopb_add_metadata(grpc_stream_op_buffer *sopb, grpc_metadata_batch b)
   grpc_metadata_batch_assert_ok(&b);
   op->type = GRPC_OP_METADATA;
   op->data.metadata = b;
+  grpc_metadata_batch_assert_ok(&op->data.metadata);
+  assert_contained_metadata_ok(sopb->ops, sopb->nops);
 }
 
 void grpc_sopb_add_slice(grpc_stream_op_buffer *sopb, gpr_slice slice) {
   grpc_stream_op *op = add(sopb);
   op->type = GRPC_OP_SLICE;
   op->data.slice = slice;
+  assert_contained_metadata_ok(sopb->ops, sopb->nops);
 }
 
 void grpc_sopb_add_flow_ctl_cb(grpc_stream_op_buffer *sopb,
@@ -144,6 +162,7 @@ void grpc_sopb_add_flow_ctl_cb(grpc_stream_op_buffer *sopb,
   op->type = GRPC_OP_FLOW_CTL_CB;
   op->data.flow_ctl_cb.cb = cb;
   op->data.flow_ctl_cb.arg = arg;
+  assert_contained_metadata_ok(sopb->ops, sopb->nops);
 }
 
 void grpc_sopb_append(grpc_stream_op_buffer *sopb, grpc_stream_op *ops,
@@ -151,12 +170,15 @@ void grpc_sopb_append(grpc_stream_op_buffer *sopb, grpc_stream_op *ops,
   size_t orig_nops = sopb->nops;
   size_t new_nops = orig_nops + nops;
 
+  assert_contained_metadata_ok(ops, nops);
+  assert_contained_metadata_ok(sopb->ops, sopb->nops);
   if (new_nops > sopb->capacity) {
     expandto(sopb, GPR_MAX(GROW(sopb->capacity), new_nops));
   }
 
   memcpy(sopb->ops + orig_nops, ops, sizeof(grpc_stream_op) * nops);
   sopb->nops = new_nops;
+  assert_contained_metadata_ok(sopb->ops, sopb->nops);
 }
 
 
@@ -183,13 +205,19 @@ void grpc_metadata_batch_assert_ok(grpc_metadata_batch *comd) {
   assert_valid_list(&comd->garbage);
 }
 
-void grpc_metadata_batch_init(grpc_metadata_batch *comd) { abort(); }
-
-void grpc_metadata_batch_destroy(grpc_metadata_batch *comd) { abort(); }
+void grpc_metadata_batch_init(grpc_metadata_batch *comd) { 
+  comd->list.head = comd->list.tail = comd->garbage.head = comd->garbage.tail = NULL;
+  comd->deadline = gpr_inf_future;
+}
 
-void grpc_metadata_batch_merge(grpc_metadata_batch *target,
-                                 grpc_metadata_batch *add) {
-  abort();
+void grpc_metadata_batch_destroy(grpc_metadata_batch *comd) { 
+  grpc_linked_mdelem *l;
+  for (l = comd->list.head; l; l = l->next) {
+    grpc_mdelem_unref(l->md);
+  }
+  for (l = comd->garbage.head; l; l = l->next) {
+    grpc_mdelem_unref(l->md);
+  }
 }
 
 void grpc_metadata_batch_add_head(grpc_metadata_batch *comd,
@@ -246,6 +274,20 @@ void grpc_metadata_batch_link_tail(grpc_metadata_batch *comd,
   link_tail(&comd->list, storage);
 }
 
+void grpc_metadata_batch_merge(grpc_metadata_batch *target,
+                                 grpc_metadata_batch *add) {
+  grpc_linked_mdelem *l;
+  grpc_linked_mdelem *next;
+  for (l = add->list.head; l; l = next) {
+    next = l->next;
+    link_tail(&target->list, l);
+  }  
+  for (l = add->garbage.head; l; l = next) {
+    next = l->next;
+    link_tail(&target->garbage, l);
+  }  
+}
+
 void grpc_metadata_batch_filter(grpc_metadata_batch *comd,
                                   grpc_mdelem *(*filter)(void *user_data,
                                                          grpc_mdelem *elem),