Initial checkin of gRPC to third_party/

third_party/grpc/src/core/surface/call.c

+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+#include <assert.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <grpc/compression.h>
+#include <grpc/grpc.h>
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/string_util.h>
+#include <grpc/support/useful.h>
+
+#include "src/core/channel/channel_stack.h"
+#include "src/core/compression/algorithm_metadata.h"
+#include "src/core/iomgr/timer.h"
+#include "src/core/profiling/timers.h"
+#include "src/core/support/string.h"
+#include "src/core/surface/api_trace.h"
+#include "src/core/surface/call.h"
+#include "src/core/surface/channel.h"
+#include "src/core/surface/completion_queue.h"
+#include "src/core/transport/static_metadata.h"
+
+/** The maximum number of concurrent batches possible.
+    Based upon the maximum number of individually queueable ops in the batch
+   api:
+      - initial metadata send
+      - message send
+      - status/close send (depending on client/server)
+      - initial metadata recv
+      - message recv
+      - status/close recv (depending on client/server) */
+#define MAX_CONCURRENT_BATCHES 6
+
+typedef struct {
+  grpc_ioreq_completion_func on_complete;
+  void *user_data;
+  int success;
+} completed_request;
+
+#define MAX_SEND_EXTRA_METADATA_COUNT 3
+
+/* Status data for a request can come from several sources; this
+   enumerates them all, and acts as a priority sorting for which
+   status to return to the application - earlier entries override
+   later ones */
+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,
+  /* Status came from the server sending status */
+  STATUS_FROM_SERVER_STATUS,
+  STATUS_SOURCE_COUNT
+} status_source;
+
+typedef struct {
+  uint8_t is_set;
+  grpc_status_code code;
+  grpc_mdstr *details;
+} received_status;
+
+/* How far through the GRPC stream have we read? */
+typedef enum {
+  /* We are still waiting for initial metadata to complete */
+  READ_STATE_INITIAL = 0,
+  /* We have gotten initial metadata, and are reading either
+     messages or trailing metadata */
+  READ_STATE_GOT_INITIAL_METADATA,
+  /* The stream is closed for reading */
+  READ_STATE_READ_CLOSED,
+  /* The stream is closed for reading & writing */
+  READ_STATE_STREAM_CLOSED
+} read_state;
+
+typedef enum {
+  WRITE_STATE_INITIAL = 0,
+  WRITE_STATE_STARTED,
+  WRITE_STATE_WRITE_CLOSED
+} write_state;
+
+typedef struct batch_control {
+  grpc_call *call;
+  grpc_cq_completion cq_completion;
+  grpc_closure finish_batch;
+  void *notify_tag;
+  gpr_refcount steps_to_complete;
+
+  uint8_t send_initial_metadata;
+  uint8_t send_message;
+  uint8_t send_final_op;
+  uint8_t recv_initial_metadata;
+  uint8_t recv_message;
+  uint8_t recv_final_op;
+  uint8_t is_notify_tag_closure;
+  uint8_t success;
+} batch_control;
+
+struct grpc_call {
+  grpc_completion_queue *cq;
+  grpc_channel *channel;
+  grpc_call *parent;
+  grpc_call *first_child;
+  /* TODO(ctiller): share with cq if possible? */
+  gpr_mu mu;
+
+  /* client or server call */
+  uint8_t is_client;
+  /* is the alarm set */
+  uint8_t have_alarm;
+  /** has grpc_call_destroy been called */
+  uint8_t destroy_called;
+  /** flag indicating that cancellation is inherited */
+  uint8_t cancellation_is_inherited;
+  /** bitmask of live batches */
+  uint8_t used_batches;
+  /** which ops are in-flight */
+  uint8_t sent_initial_metadata;
+  uint8_t sending_message;
+  uint8_t sent_final_op;
+  uint8_t received_initial_metadata;
+  uint8_t receiving_message;
+  uint8_t received_final_op;
+
+  /* have we received initial metadata */
+  bool has_initial_md_been_received;
+
+  batch_control active_batches[MAX_CONCURRENT_BATCHES];
+
+  /* first idx: is_receiving, second idx: is_trailing */
+  grpc_metadata_batch metadata_batch[2][2];
+
+  /* Buffered read metadata waiting to be returned to the application.
+     Element 0 is initial metadata, element 1 is trailing metadata. */
+  grpc_metadata_array *buffered_metadata[2];
+
+  /* Received call statuses from various sources */
+  received_status status[STATUS_SOURCE_COUNT];
+
+  /* Compression algorithm for the call */
+  grpc_compression_algorithm compression_algorithm;
+  /* Supported encodings (compression algorithms), a bitset */
+  uint32_t encodings_accepted_by_peer;
+
+  /* Contexts for various subsystems (security, tracing, ...). */
+  grpc_call_context_element context[GRPC_CONTEXT_COUNT];
+
+  /* Deadline alarm - if have_alarm is non-zero */
+  grpc_timer alarm;
+
+  /* for the client, extra metadata is initial metadata; for the
+     server, it's trailing metadata */
+  grpc_linked_mdelem send_extra_metadata[MAX_SEND_EXTRA_METADATA_COUNT];
+  int send_extra_metadata_count;
+  gpr_timespec send_deadline;
+
+  /** siblings: children of the same parent form a list, and this list is
+     protected under
+      parent->mu */
+  grpc_call *sibling_next;
+  grpc_call *sibling_prev;
+
+  grpc_slice_buffer_stream sending_stream;
+  grpc_byte_stream *receiving_stream;
+  grpc_byte_buffer **receiving_buffer;
+  gpr_slice receiving_slice;
+  grpc_closure receiving_slice_ready;
+  grpc_closure receiving_stream_ready;
+  grpc_closure receiving_initial_metadata_ready;
+  uint32_t test_only_last_message_flags;
+
+  union {
+    struct {
+      grpc_status_code *status;
+      char **status_details;
+      size_t *status_details_capacity;
+    } client;
+    struct {
+      int *cancelled;
+    } server;
+  } final_op;
+
+  struct {
+    void *bctlp;
+    bool success;
+  } saved_receiving_stream_ready_ctx;
+};
+
+#define CALL_STACK_FROM_CALL(call) ((grpc_call_stack *)((call) + 1))
+#define CALL_FROM_CALL_STACK(call_stack) (((grpc_call *)(call_stack)) - 1)
+#define CALL_ELEM_FROM_CALL(call, idx) \
+  grpc_call_stack_element(CALL_STACK_FROM_CALL(call), idx)
+#define CALL_FROM_TOP_ELEM(top_elem) \
+  CALL_FROM_CALL_STACK(grpc_call_stack_from_top_element(top_elem))
+
+static void set_deadline_alarm(grpc_exec_ctx *exec_ctx, grpc_call *call,
+                               gpr_timespec deadline);
+static void execute_op(grpc_exec_ctx *exec_ctx, grpc_call *call,
+                       grpc_transport_stream_op *op);
+static grpc_call_error cancel_with_status(grpc_exec_ctx *exec_ctx, grpc_call *c,
+                                          grpc_status_code status,
+                                          const char *description);
+static void destroy_call(grpc_exec_ctx *exec_ctx, void *call_stack,
+                         bool success);
+static void receiving_slice_ready(grpc_exec_ctx *exec_ctx, void *bctlp,
+                                  bool success);
+
+grpc_call *grpc_call_create(grpc_channel *channel, grpc_call *parent_call,
+                            uint32_t propagation_mask,
+                            grpc_completion_queue *cq,
+                            const void *server_transport_data,
+                            grpc_mdelem **add_initial_metadata,
+                            size_t add_initial_metadata_count,
+                            gpr_timespec send_deadline) {
+  size_t i, j;
+  grpc_channel_stack *channel_stack = grpc_channel_get_channel_stack(channel);
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  grpc_call *call;
+  GPR_TIMER_BEGIN("grpc_call_create", 0);
+  call = gpr_malloc(sizeof(grpc_call) + channel_stack->call_stack_size);
+  memset(call, 0, sizeof(grpc_call));
+  gpr_mu_init(&call->mu);
+  call->channel = channel;
+  call->cq = cq;
+  call->parent = parent_call;
+  call->is_client = server_transport_data == NULL;
+  if (call->is_client) {
+    GPR_ASSERT(add_initial_metadata_count < MAX_SEND_EXTRA_METADATA_COUNT);
+    for (i = 0; i < add_initial_metadata_count; i++) {
+      call->send_extra_metadata[i].md = add_initial_metadata[i];
+    }
+    call->send_extra_metadata_count = (int)add_initial_metadata_count;
+  } else {
+    GPR_ASSERT(add_initial_metadata_count == 0);
+    call->send_extra_metadata_count = 0;
+  }
+  for (i = 0; i < 2; i++) {
+    for (j = 0; j < 2; j++) {
+      call->metadata_batch[i][j].deadline = gpr_inf_future(GPR_CLOCK_MONOTONIC);
+    }
+  }
+  call->send_deadline = send_deadline;
+  GRPC_CHANNEL_INTERNAL_REF(channel, "call");
+  /* initial refcount dropped by grpc_call_destroy */
+  grpc_call_stack_init(&exec_ctx, channel_stack, 1, destroy_call, call,
+                       call->context, server_transport_data,
+                       CALL_STACK_FROM_CALL(call));
+  if (cq != NULL) {
+    GRPC_CQ_INTERNAL_REF(cq, "bind");
+    grpc_call_stack_set_pollset(&exec_ctx, CALL_STACK_FROM_CALL(call),
+                                grpc_cq_pollset(cq));
+  }
+  if (parent_call != NULL) {
+    GRPC_CALL_INTERNAL_REF(parent_call, "child");
+    GPR_ASSERT(call->is_client);
+    GPR_ASSERT(!parent_call->is_client);
+
+    gpr_mu_lock(&parent_call->mu);
+
+    if (propagation_mask & GRPC_PROPAGATE_DEADLINE) {
+      send_deadline = gpr_time_min(
+          gpr_convert_clock_type(send_deadline,
+                                 parent_call->send_deadline.clock_type),
+          parent_call->send_deadline);
+    }
+    /* for now GRPC_PROPAGATE_TRACING_CONTEXT *MUST* be passed with
+     * GRPC_PROPAGATE_STATS_CONTEXT */
+    /* TODO(ctiller): This should change to use the appropriate census start_op
+     * call. */
+    if (propagation_mask & GRPC_PROPAGATE_CENSUS_TRACING_CONTEXT) {
+      GPR_ASSERT(propagation_mask & GRPC_PROPAGATE_CENSUS_STATS_CONTEXT);
+      grpc_call_context_set(call, GRPC_CONTEXT_TRACING,
+                            parent_call->context[GRPC_CONTEXT_TRACING].value,
+                            NULL);
+    } else {
+      GPR_ASSERT(propagation_mask & GRPC_PROPAGATE_CENSUS_STATS_CONTEXT);
+    }
+    if (propagation_mask & GRPC_PROPAGATE_CANCELLATION) {
+      call->cancellation_is_inherited = 1;
+    }
+
+    if (parent_call->first_child == NULL) {
+      parent_call->first_child = call;
+      call->sibling_next = call->sibling_prev = call;
+    } else {
+      call->sibling_next = parent_call->first_child;
+      call->sibling_prev = parent_call->first_child->sibling_prev;
+      call->sibling_next->sibling_prev = call->sibling_prev->sibling_next =
+          call;
+    }
+
+    gpr_mu_unlock(&parent_call->mu);
+  }
+  if (gpr_time_cmp(send_deadline, gpr_inf_future(send_deadline.clock_type)) !=
+      0) {
+    set_deadline_alarm(&exec_ctx, call, send_deadline);
+  }
+  grpc_exec_ctx_finish(&exec_ctx);
+  GPR_TIMER_END("grpc_call_create", 0);
+  return call;
+}
+
+void grpc_call_set_completion_queue(grpc_exec_ctx *exec_ctx, grpc_call *call,
+                                    grpc_completion_queue *cq) {
+  GPR_ASSERT(cq);
+  call->cq = cq;
+  GRPC_CQ_INTERNAL_REF(cq, "bind");
+  grpc_call_stack_set_pollset(exec_ctx, CALL_STACK_FROM_CALL(call),
+                              grpc_cq_pollset(cq));
+}
+
+#ifdef GRPC_STREAM_REFCOUNT_DEBUG
+#define REF_REASON reason
+#define REF_ARG , const char *reason
+#else
+#define REF_REASON ""
+#define REF_ARG
+#endif
+void grpc_call_internal_ref(grpc_call *c REF_ARG) {
+  GRPC_CALL_STACK_REF(CALL_STACK_FROM_CALL(c), REF_REASON);
+}
+void grpc_call_internal_unref(grpc_exec_ctx *exec_ctx, grpc_call *c REF_ARG) {
+  GRPC_CALL_STACK_UNREF(exec_ctx, CALL_STACK_FROM_CALL(c), REF_REASON);
+}
+
+static void destroy_call(grpc_exec_ctx *exec_ctx, void *call, bool success) {
+  size_t i;
+  int ii;
+  grpc_call *c = call;
+  GPR_TIMER_BEGIN("destroy_call", 0);
+  for (i = 0; i < 2; i++) {
+    grpc_metadata_batch_destroy(
+        &c->metadata_batch[1 /* is_receiving */][i /* is_initial */]);
+  }
+  if (c->receiving_stream != NULL) {
+    grpc_byte_stream_destroy(exec_ctx, c->receiving_stream);
+  }
+  grpc_call_stack_destroy(exec_ctx, CALL_STACK_FROM_CALL(c));
+  GRPC_CHANNEL_INTERNAL_UNREF(exec_ctx, c->channel, "call");
+  gpr_mu_destroy(&c->mu);
+  for (i = 0; i < STATUS_SOURCE_COUNT; i++) {
+    if (c->status[i].details) {
+      GRPC_MDSTR_UNREF(c->status[i].details);
+    }
+  }
+  for (ii = 0; ii < c->send_extra_metadata_count; ii++) {
+    GRPC_MDELEM_UNREF(c->send_extra_metadata[ii].md);
+  }
+  for (i = 0; i < GRPC_CONTEXT_COUNT; i++) {
+    if (c->context[i].destroy) {
+      c->context[i].destroy(c->context[i].value);
+    }
+  }
+  if (c->cq) {
+    GRPC_CQ_INTERNAL_UNREF(c->cq, "bind");
+  }
+  gpr_free(c);
+  GPR_TIMER_END("destroy_call", 0);
+}
+
+static void set_status_code(grpc_call *call, status_source source,
+                            uint32_t status) {
+  if (call->status[source].is_set) return;
+
+  call->status[source].is_set = 1;
+  call->status[source].code = (grpc_status_code)status;
+
+  /* TODO(ctiller): what to do about the flush that was previously here */
+}
+
+static void set_compression_algorithm(grpc_call *call,
+                                      grpc_compression_algorithm algo) {
+  call->compression_algorithm = algo;
+}
+
+grpc_compression_algorithm grpc_call_test_only_get_compression_algorithm(
+    grpc_call *call) {
+  grpc_compression_algorithm algorithm;
+  gpr_mu_lock(&call->mu);
+  algorithm = call->compression_algorithm;
+  gpr_mu_unlock(&call->mu);
+  return algorithm;
+}
+
+uint32_t grpc_call_test_only_get_message_flags(grpc_call *call) {
+  uint32_t flags;
+  gpr_mu_lock(&call->mu);
+  flags = call->test_only_last_message_flags;
+  gpr_mu_unlock(&call->mu);
+  return flags;
+}
+
+static void destroy_encodings_accepted_by_peer(void *p) { return; }
+
+static void set_encodings_accepted_by_peer(grpc_call *call, grpc_mdelem *mdel) {
+  size_t i;
+  grpc_compression_algorithm algorithm;
+  gpr_slice_buffer accept_encoding_parts;
+  gpr_slice accept_encoding_slice;
+  void *accepted_user_data;
+
+  accepted_user_data =
+      grpc_mdelem_get_user_data(mdel, destroy_encodings_accepted_by_peer);
+  if (accepted_user_data != NULL) {
+    call->encodings_accepted_by_peer =
+        (uint32_t)(((uintptr_t)accepted_user_data) - 1);
+    return;
+  }
+
+  accept_encoding_slice = mdel->value->slice;
+  gpr_slice_buffer_init(&accept_encoding_parts);
+  gpr_slice_split(accept_encoding_slice, ",", &accept_encoding_parts);
+
+  /* No need to zero call->encodings_accepted_by_peer: grpc_call_create already
+   * zeroes the whole grpc_call */
+  /* Always support no compression */
+  GPR_BITSET(&call->encodings_accepted_by_peer, GRPC_COMPRESS_NONE);
+  for (i = 0; i < accept_encoding_parts.count; i++) {
+    const gpr_slice *accept_encoding_entry_slice =
+        &accept_encoding_parts.slices[i];
+    if (grpc_compression_algorithm_parse(
+            (const char *)GPR_SLICE_START_PTR(*accept_encoding_entry_slice),
+            GPR_SLICE_LENGTH(*accept_encoding_entry_slice), &algorithm)) {
+      GPR_BITSET(&call->encodings_accepted_by_peer, algorithm);
+    } else {
+      char *accept_encoding_entry_str =
+          gpr_dump_slice(*accept_encoding_entry_slice, GPR_DUMP_ASCII);
+      gpr_log(GPR_ERROR,
+              "Invalid entry in accept encoding metadata: '%s'. Ignoring.",
+              accept_encoding_entry_str);
+      gpr_free(accept_encoding_entry_str);
+    }
+  }
+
+  gpr_slice_buffer_destroy(&accept_encoding_parts);
+
+  grpc_mdelem_set_user_data(
+      mdel, destroy_encodings_accepted_by_peer,
+      (void *)(((uintptr_t)call->encodings_accepted_by_peer) + 1));
+}
+
+uint32_t grpc_call_test_only_get_encodings_accepted_by_peer(grpc_call *call) {
+  uint32_t encodings_accepted_by_peer;
+  gpr_mu_lock(&call->mu);
+  encodings_accepted_by_peer = call->encodings_accepted_by_peer;
+  gpr_mu_unlock(&call->mu);
+  return encodings_accepted_by_peer;
+}
+
+static void set_status_details(grpc_call *call, status_source source,
+                               grpc_mdstr *status) {
+  if (call->status[source].details != NULL) {
+    GRPC_MDSTR_UNREF(call->status[source].details);
+  }
+  call->status[source].details = status;
+}
+
+static void get_final_status(grpc_call *call,
+                             void (*set_value)(grpc_status_code code,
+                                               void *user_data),
+                             void *set_value_user_data) {
+  int i;
+  for (i = 0; i < STATUS_SOURCE_COUNT; i++) {
+    if (call->status[i].is_set) {
+      set_value(call->status[i].code, set_value_user_data);
+      return;
+    }
+  }
+  if (call->is_client) {
+    set_value(GRPC_STATUS_UNKNOWN, set_value_user_data);
+  } else {
+    set_value(GRPC_STATUS_OK, set_value_user_data);
+  }
+}
+
+static void get_final_details(grpc_call *call, char **out_details,
+                              size_t *out_details_capacity) {
+  int i;
+  for (i = 0; i < STATUS_SOURCE_COUNT; i++) {
+    if (call->status[i].is_set) {
+      if (call->status[i].details) {
+        gpr_slice details = call->status[i].details->slice;
+        size_t len = GPR_SLICE_LENGTH(details);
+        if (len + 1 > *out_details_capacity) {
+          *out_details_capacity =
+              GPR_MAX(len + 1, *out_details_capacity * 3 / 2);
+          *out_details = gpr_realloc(*out_details, *out_details_capacity);
+        }
+        memcpy(*out_details, GPR_SLICE_START_PTR(details), len);
+        (*out_details)[len] = 0;
+      } else {
+        goto no_details;
+      }
+      return;
+    }
+  }
+
+no_details:
+  if (0 == *out_details_capacity) {
+    *out_details_capacity = 8;
+    *out_details = gpr_malloc(*out_details_capacity);
+  }
+  **out_details = 0;
+}
+
+static grpc_linked_mdelem *linked_from_md(grpc_metadata *md) {
+  return (grpc_linked_mdelem *)&md->internal_data;
+}
+
+static int prepare_application_metadata(grpc_call *call, int count,
+                                        grpc_metadata *metadata,
+                                        int is_trailing,
+                                        int prepend_extra_metadata) {
+  int i;
+  grpc_metadata_batch *batch =
+      &call->metadata_batch[0 /* is_receiving */][is_trailing];
+  if (prepend_extra_metadata) {
+    if (call->send_extra_metadata_count == 0) {
+      prepend_extra_metadata = 0;
+    } else {
+      for (i = 0; i < call->send_extra_metadata_count; i++) {
+        GRPC_MDELEM_REF(call->send_extra_metadata[i].md);
+      }
+      for (i = 1; i < call->send_extra_metadata_count; i++) {
+        call->send_extra_metadata[i].prev = &call->send_extra_metadata[i - 1];
+      }
+      for (i = 0; i < call->send_extra_metadata_count - 1; i++) {
+        call->send_extra_metadata[i].next = &call->send_extra_metadata[i + 1];
+      }
+    }
+  }
+  for (i = 0; i < count; i++) {
+    grpc_metadata *md = &metadata[i];
+    grpc_linked_mdelem *l = (grpc_linked_mdelem *)&md->internal_data;
+    GPR_ASSERT(sizeof(grpc_linked_mdelem) == sizeof(md->internal_data));
+    l->md = grpc_mdelem_from_string_and_buffer(
+        md->key, (const uint8_t *)md->value, md->value_length);
+    if (!grpc_header_key_is_legal(grpc_mdstr_as_c_string(l->md->key),
+                                  GRPC_MDSTR_LENGTH(l->md->key))) {
+      gpr_log(GPR_ERROR, "attempt to send invalid metadata key: %s",
+              grpc_mdstr_as_c_string(l->md->key));
+      return 0;
+    } else if (!grpc_is_binary_header(grpc_mdstr_as_c_string(l->md->key),
+                                      GRPC_MDSTR_LENGTH(l->md->key)) &&
+               !grpc_header_nonbin_value_is_legal(
+                   grpc_mdstr_as_c_string(l->md->value),
+                   GRPC_MDSTR_LENGTH(l->md->value))) {
+      gpr_log(GPR_ERROR, "attempt to send invalid metadata value");
+      return 0;
+    }
+  }
+  for (i = 1; i < count; i++) {
+    linked_from_md(&metadata[i])->prev = linked_from_md(&metadata[i - 1]);
+  }
+  for (i = 0; i < count - 1; i++) {
+    linked_from_md(&metadata[i])->next = linked_from_md(&metadata[i + 1]);
+  }
+  switch (prepend_extra_metadata * 2 + (count != 0)) {
+    case 0:
+      /* no prepend, no metadata => nothing to do */
+      batch->list.head = batch->list.tail = NULL;
+      break;
+    case 1:
+      /* metadata, but no prepend */
+      batch->list.head = linked_from_md(&metadata[0]);
+      batch->list.tail = linked_from_md(&metadata[count - 1]);
+      batch->list.head->prev = NULL;
+      batch->list.tail->next = NULL;
+      break;
+    case 2:
+      /* prepend, but no md */
+      batch->list.head = &call->send_extra_metadata[0];
+      batch->list.tail =
+          &call->send_extra_metadata[call->send_extra_metadata_count - 1];
+      batch->list.head->prev = NULL;
+      batch->list.tail->next = NULL;
+      break;
+    case 3:
+      /* prepend AND md */
+      batch->list.head = &call->send_extra_metadata[0];
+      call->send_extra_metadata[call->send_extra_metadata_count - 1].next =
+          linked_from_md(&metadata[0]);
+      linked_from_md(&metadata[0])->prev =
+          &call->send_extra_metadata[call->send_extra_metadata_count - 1];
+      batch->list.tail = linked_from_md(&metadata[count - 1]);
+      batch->list.head->prev = NULL;
+      batch->list.tail->next = NULL;
+      break;
+    default:
+      GPR_UNREACHABLE_CODE(return 0);
+  }
+
+  return 1;
+}
+
+void grpc_call_destroy(grpc_call *c) {
+  int cancel;
+  grpc_call *parent = c->parent;
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+
+  GPR_TIMER_BEGIN("grpc_call_destroy", 0);
+  GRPC_API_TRACE("grpc_call_destroy(c=%p)", 1, (c));
+
+  if (parent) {
+    gpr_mu_lock(&parent->mu);
+    if (c == parent->first_child) {
+      parent->first_child = c->sibling_next;
+      if (c == parent->first_child) {
+        parent->first_child = NULL;
+      }
+      c->sibling_prev->sibling_next = c->sibling_next;
+      c->sibling_next->sibling_prev = c->sibling_prev;
+    }
+    gpr_mu_unlock(&parent->mu);
+    GRPC_CALL_INTERNAL_UNREF(&exec_ctx, parent, "child");
+  }
+
+  gpr_mu_lock(&c->mu);
+  GPR_ASSERT(!c->destroy_called);
+  c->destroy_called = 1;
+  if (c->have_alarm) {
+    grpc_timer_cancel(&exec_ctx, &c->alarm);
+  }
+  cancel = !c->received_final_op;
+  gpr_mu_unlock(&c->mu);
+  if (cancel) grpc_call_cancel(c, NULL);
+  GRPC_CALL_INTERNAL_UNREF(&exec_ctx, c, "destroy");
+  grpc_exec_ctx_finish(&exec_ctx);
+  GPR_TIMER_END("grpc_call_destroy", 0);
+}
+
+grpc_call_error grpc_call_cancel(grpc_call *call, void *reserved) {
+  GRPC_API_TRACE("grpc_call_cancel(call=%p, reserved=%p)", 2, (call, reserved));
+  GPR_ASSERT(!reserved);
+  return grpc_call_cancel_with_status(call, GRPC_STATUS_CANCELLED, "Cancelled",
+                                      NULL);
+}
+
+grpc_call_error grpc_call_cancel_with_status(grpc_call *c,
+                                             grpc_status_code status,
+                                             const char *description,
+                                             void *reserved) {
+  grpc_call_error r;
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  GRPC_API_TRACE(
+      "grpc_call_cancel_with_status("
+      "c=%p, status=%d, description=%s, reserved=%p)",
+      4, (c, (int)status, description, reserved));
+  GPR_ASSERT(reserved == NULL);
+  gpr_mu_lock(&c->mu);
+  r = cancel_with_status(&exec_ctx, c, status, description);
+  gpr_mu_unlock(&c->mu);
+  grpc_exec_ctx_finish(&exec_ctx);
+  return r;
+}
+
+typedef struct cancel_closure {
+  grpc_closure closure;
+  grpc_call *call;
+  grpc_status_code status;
+} cancel_closure;
+
+static void done_cancel(grpc_exec_ctx *exec_ctx, void *ccp, bool success) {
+  cancel_closure *cc = ccp;
+  GRPC_CALL_INTERNAL_UNREF(exec_ctx, cc->call, "cancel");
+  gpr_free(cc);
+}
+
+static void send_cancel(grpc_exec_ctx *exec_ctx, void *ccp, bool success) {
+  grpc_transport_stream_op op;
+  cancel_closure *cc = ccp;
+  memset(&op, 0, sizeof(op));
+  op.cancel_with_status = cc->status;
+  /* reuse closure to catch completion */
+  grpc_closure_init(&cc->closure, done_cancel, cc);
+  op.on_complete = &cc->closure;
+  execute_op(exec_ctx, cc->call, &op);
+}
+
+static grpc_call_error cancel_with_status(grpc_exec_ctx *exec_ctx, grpc_call *c,
+                                          grpc_status_code status,
+                                          const char *description) {
+  grpc_mdstr *details =
+      description ? grpc_mdstr_from_string(description) : NULL;
+  cancel_closure *cc = gpr_malloc(sizeof(*cc));
+
+  GPR_ASSERT(status != GRPC_STATUS_OK);
+
+  set_status_code(c, STATUS_FROM_API_OVERRIDE, (uint32_t)status);
+  set_status_details(c, STATUS_FROM_API_OVERRIDE, details);
+
+  grpc_closure_init(&cc->closure, send_cancel, cc);
+  cc->call = c;
+  cc->status = status;
+  GRPC_CALL_INTERNAL_REF(c, "cancel");
+  grpc_exec_ctx_enqueue(exec_ctx, &cc->closure, true, NULL);
+
+  return GRPC_CALL_OK;
+}
+
+static void execute_op(grpc_exec_ctx *exec_ctx, grpc_call *call,
+                       grpc_transport_stream_op *op) {
+  grpc_call_element *elem;
+
+  GPR_TIMER_BEGIN("execute_op", 0);
+  elem = CALL_ELEM_FROM_CALL(call, 0);
+  op->context = call->context;
+  elem->filter->start_transport_stream_op(exec_ctx, elem, op);
+  GPR_TIMER_END("execute_op", 0);
+}
+
+char *grpc_call_get_peer(grpc_call *call) {
+  grpc_call_element *elem = CALL_ELEM_FROM_CALL(call, 0);
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  char *result;
+  GRPC_API_TRACE("grpc_call_get_peer(%p)", 1, (call));
+  result = elem->filter->get_peer(&exec_ctx, elem);
+  if (result == NULL) {
+    result = grpc_channel_get_target(call->channel);
+  }
+  if (result == NULL) {
+    result = gpr_strdup("unknown");
+  }
+  grpc_exec_ctx_finish(&exec_ctx);
+  return result;
+}
+
+grpc_call *grpc_call_from_top_element(grpc_call_element *elem) {
+  return CALL_FROM_TOP_ELEM(elem);
+}
+
+static void call_alarm(grpc_exec_ctx *exec_ctx, void *arg, bool success) {
+  grpc_call *call = arg;
+  gpr_mu_lock(&call->mu);
+  call->have_alarm = 0;
+  if (success) {
+    cancel_with_status(exec_ctx, call, GRPC_STATUS_DEADLINE_EXCEEDED,
+                       "Deadline Exceeded");
+  }
+  gpr_mu_unlock(&call->mu);
+  GRPC_CALL_INTERNAL_UNREF(exec_ctx, call, "alarm");
+}
+
+static void set_deadline_alarm(grpc_exec_ctx *exec_ctx, grpc_call *call,
+                               gpr_timespec deadline) {
+  if (call->have_alarm) {
+    gpr_log(GPR_ERROR, "Attempt to set deadline alarm twice");
+    assert(0);
+    return;
+  }
+  GRPC_CALL_INTERNAL_REF(call, "alarm");
+  call->have_alarm = 1;
+  call->send_deadline = gpr_convert_clock_type(deadline, GPR_CLOCK_MONOTONIC);
+  grpc_timer_init(exec_ctx, &call->alarm, call->send_deadline, call_alarm, call,
+                  gpr_now(GPR_CLOCK_MONOTONIC));
+}
+
+/* we offset status by a small amount when storing it into transport metadata
+   as metadata cannot store a 0 value (which is used as OK for grpc_status_codes
+   */
+#define STATUS_OFFSET 1
+static void destroy_status(void *ignored) {}
+
+static uint32_t decode_status(grpc_mdelem *md) {
+  uint32_t status;
+  void *user_data;
+  if (md == GRPC_MDELEM_GRPC_STATUS_0) return 0;
+  if (md == GRPC_MDELEM_GRPC_STATUS_1) return 1;
+  if (md == GRPC_MDELEM_GRPC_STATUS_2) return 2;
+  user_data = grpc_mdelem_get_user_data(md, destroy_status);
+  if (user_data != NULL) {
+    status = ((uint32_t)(intptr_t)user_data) - STATUS_OFFSET;
+  } else {
+    if (!gpr_parse_bytes_to_uint32(grpc_mdstr_as_c_string(md->value),
+                                   GPR_SLICE_LENGTH(md->value->slice),
+                                   &status)) {
+      status = GRPC_STATUS_UNKNOWN; /* could not parse status code */
+    }
+    grpc_mdelem_set_user_data(md, destroy_status,
+                              (void *)(intptr_t)(status + STATUS_OFFSET));
+  }
+  return status;
+}
+
+static uint32_t decode_compression(grpc_mdelem *md) {
+  grpc_compression_algorithm algorithm =
+      grpc_compression_algorithm_from_mdstr(md->value);
+  if (algorithm == GRPC_COMPRESS_ALGORITHMS_COUNT) {
+    const char *md_c_str = grpc_mdstr_as_c_string(md->value);
+    gpr_log(GPR_ERROR, "Invalid compression algorithm: '%s'", md_c_str);
+  }
+  return algorithm;
+}
+
+static grpc_mdelem *recv_common_filter(grpc_call *call, grpc_mdelem *elem) {
+  if (elem->key == GRPC_MDSTR_GRPC_STATUS) {
+    GPR_TIMER_BEGIN("status", 0);
+    set_status_code(call, STATUS_FROM_WIRE, decode_status(elem));
+    GPR_TIMER_END("status", 0);
+    return NULL;
+  } else if (elem->key == GRPC_MDSTR_GRPC_MESSAGE) {
+    GPR_TIMER_BEGIN("status-details", 0);
+    set_status_details(call, STATUS_FROM_WIRE, GRPC_MDSTR_REF(elem->value));
+    GPR_TIMER_END("status-details", 0);
+    return NULL;
+  }
+  return elem;
+}
+
+static grpc_mdelem *publish_app_metadata(grpc_call *call, grpc_mdelem *elem,
+                                         int is_trailing) {
+  grpc_metadata_array *dest;
+  grpc_metadata *mdusr;
+  GPR_TIMER_BEGIN("publish_app_metadata", 0);
+  dest = call->buffered_metadata[is_trailing];
+  if (dest->count == dest->capacity) {
+    dest->capacity = GPR_MAX(dest->capacity + 8, dest->capacity * 2);
+    dest->metadata =
+        gpr_realloc(dest->metadata, sizeof(grpc_metadata) * dest->capacity);
+  }
+  mdusr = &dest->metadata[dest->count++];
+  mdusr->key = grpc_mdstr_as_c_string(elem->key);
+  mdusr->value = grpc_mdstr_as_c_string(elem->value);
+  mdusr->value_length = GPR_SLICE_LENGTH(elem->value->slice);
+  GPR_TIMER_END("publish_app_metadata", 0);
+  return elem;
+}
+
+static grpc_mdelem *recv_initial_filter(void *callp, grpc_mdelem *elem) {
+  grpc_call *call = callp;
+  elem = recv_common_filter(call, elem);
+  if (elem == NULL) {
+    return NULL;
+  } else if (elem->key == GRPC_MDSTR_GRPC_ENCODING) {
+    GPR_TIMER_BEGIN("compression_algorithm", 0);
+    set_compression_algorithm(call, decode_compression(elem));
+    GPR_TIMER_END("compression_algorithm", 0);
+    return NULL;
+  } else if (elem->key == GRPC_MDSTR_GRPC_ACCEPT_ENCODING) {
+    GPR_TIMER_BEGIN("encodings_accepted_by_peer", 0);
+    set_encodings_accepted_by_peer(call, elem);
+    GPR_TIMER_END("encodings_accepted_by_peer", 0);
+    return NULL;
+  } else {
+    return publish_app_metadata(call, elem, 0);
+  }
+}
+
+static grpc_mdelem *recv_trailing_filter(void *callp, grpc_mdelem *elem) {
+  grpc_call *call = callp;
+  elem = recv_common_filter(call, elem);
+  if (elem == NULL) {
+    return NULL;
+  } else {
+    return publish_app_metadata(call, elem, 1);
+  }
+}
+
+grpc_call_stack *grpc_call_get_call_stack(grpc_call *call) {
+  return CALL_STACK_FROM_CALL(call);
+}
+
+/*
+ * BATCH API IMPLEMENTATION
+ */
+
+static void set_status_value_directly(grpc_status_code status, void *dest) {
+  *(grpc_status_code *)dest = status;
+}
+
+static void set_cancelled_value(grpc_status_code status, void *dest) {
+  *(int *)dest = (status != GRPC_STATUS_OK);
+}
+
+static int are_write_flags_valid(uint32_t flags) {
+  /* check that only bits in GRPC_WRITE_(INTERNAL?)_USED_MASK are set */
+  const uint32_t allowed_write_positions =
+      (GRPC_WRITE_USED_MASK | GRPC_WRITE_INTERNAL_USED_MASK);
+  const uint32_t invalid_positions = ~allowed_write_positions;
+  return !(flags & invalid_positions);
+}
+
+static batch_control *allocate_batch_control(grpc_call *call) {
+  size_t i;
+  for (i = 0; i < MAX_CONCURRENT_BATCHES; i++) {
+    if ((call->used_batches & (1 << i)) == 0) {
+      call->used_batches = (uint8_t)(call->used_batches | (uint8_t)(1 << i));
+      return &call->active_batches[i];
+    }
+  }
+  return NULL;
+}
+
+static void finish_batch_completion(grpc_exec_ctx *exec_ctx, void *user_data,
+                                    grpc_cq_completion *storage) {
+  batch_control *bctl = user_data;
+  grpc_call *call = bctl->call;
+  gpr_mu_lock(&call->mu);
+  call->used_batches = (uint8_t)(
+      call->used_batches & ~(uint8_t)(1 << (bctl - call->active_batches)));
+  gpr_mu_unlock(&call->mu);
+  GRPC_CALL_INTERNAL_UNREF(exec_ctx, call, "completion");
+}
+
+static void post_batch_completion(grpc_exec_ctx *exec_ctx,
+                                  batch_control *bctl) {
+  grpc_call *call = bctl->call;
+  if (bctl->is_notify_tag_closure) {
+    grpc_exec_ctx_enqueue(exec_ctx, bctl->notify_tag, bctl->success, NULL);
+    gpr_mu_lock(&call->mu);
+    bctl->call->used_batches =
+        (uint8_t)(bctl->call->used_batches &
+                  ~(uint8_t)(1 << (bctl - bctl->call->active_batches)));
+    gpr_mu_unlock(&call->mu);
+    GRPC_CALL_INTERNAL_UNREF(exec_ctx, call, "completion");
+  } else {
+    grpc_cq_end_op(exec_ctx, bctl->call->cq, bctl->notify_tag, bctl->success,
+                   finish_batch_completion, bctl, &bctl->cq_completion);
+  }
+}
+
+static void continue_receiving_slices(grpc_exec_ctx *exec_ctx,
+                                      batch_control *bctl) {
+  grpc_call *call = bctl->call;
+  for (;;) {
+    size_t remaining = call->receiving_stream->length -
+                       (*call->receiving_buffer)->data.raw.slice_buffer.length;
+    if (remaining == 0) {
+      call->receiving_message = 0;
+      grpc_byte_stream_destroy(exec_ctx, call->receiving_stream);
+      call->receiving_stream = NULL;
+      if (gpr_unref(&bctl->steps_to_complete)) {
+        post_batch_completion(exec_ctx, bctl);
+      }
+      return;
+    }
+    if (grpc_byte_stream_next(exec_ctx, call->receiving_stream,
+                              &call->receiving_slice, remaining,
+                              &call->receiving_slice_ready)) {
+      gpr_slice_buffer_add(&(*call->receiving_buffer)->data.raw.slice_buffer,
+                           call->receiving_slice);
+    } else {
+      return;
+    }
+  }
+}
+
+static void receiving_slice_ready(grpc_exec_ctx *exec_ctx, void *bctlp,
+                                  bool success) {
+  batch_control *bctl = bctlp;
+  grpc_call *call = bctl->call;
+
+  if (success) {
+    gpr_slice_buffer_add(&(*call->receiving_buffer)->data.raw.slice_buffer,
+                         call->receiving_slice);
+    continue_receiving_slices(exec_ctx, bctl);
+  } else {
+    grpc_byte_stream_destroy(exec_ctx, call->receiving_stream);
+    call->receiving_stream = NULL;
+    grpc_byte_buffer_destroy(*call->receiving_buffer);
+    *call->receiving_buffer = NULL;
+    if (gpr_unref(&bctl->steps_to_complete)) {
+      post_batch_completion(exec_ctx, bctl);
+    }
+  }
+}
+
+static void process_data_after_md(grpc_exec_ctx *exec_ctx, batch_control *bctl,
+                                  bool success) {
+  grpc_call *call = bctl->call;
+  if (call->receiving_stream == NULL) {
+    *call->receiving_buffer = NULL;
+    call->receiving_message = 0;
+    if (gpr_unref(&bctl->steps_to_complete)) {
+      post_batch_completion(exec_ctx, bctl);
+    }
+  } else if (call->receiving_stream->length >
+             grpc_channel_get_max_message_length(call->channel)) {
+    cancel_with_status(exec_ctx, call, GRPC_STATUS_INTERNAL,
+                       "Max message size exceeded");
+    grpc_byte_stream_destroy(exec_ctx, call->receiving_stream);
+    call->receiving_stream = NULL;
+    *call->receiving_buffer = NULL;
+    call->receiving_message = 0;
+    if (gpr_unref(&bctl->steps_to_complete)) {
+      post_batch_completion(exec_ctx, bctl);
+    }
+  } else {
+    call->test_only_last_message_flags = call->receiving_stream->flags;
+    if ((call->receiving_stream->flags & GRPC_WRITE_INTERNAL_COMPRESS) &&
+        (call->compression_algorithm > GRPC_COMPRESS_NONE)) {
+      *call->receiving_buffer = grpc_raw_compressed_byte_buffer_create(
+          NULL, 0, call->compression_algorithm);
+    } else {
+      *call->receiving_buffer = grpc_raw_byte_buffer_create(NULL, 0);
+    }
+    grpc_closure_init(&call->receiving_slice_ready, receiving_slice_ready,
+                      bctl);
+    continue_receiving_slices(exec_ctx, bctl);
+    /* early out */
+    return;
+  }
+}
+
+static void receiving_stream_ready(grpc_exec_ctx *exec_ctx, void *bctlp,
+                                   bool success) {
+  batch_control *bctl = bctlp;
+  grpc_call *call = bctl->call;
+
+  gpr_mu_lock(&bctl->call->mu);
+  if (bctl->call->has_initial_md_been_received) {
+    gpr_mu_unlock(&bctl->call->mu);
+    process_data_after_md(exec_ctx, bctlp, success);
+  } else {
+    call->saved_receiving_stream_ready_ctx.bctlp = bctlp;
+    call->saved_receiving_stream_ready_ctx.success = success;
+    gpr_mu_unlock(&bctl->call->mu);
+  }
+}
+
+static void receiving_initial_metadata_ready(grpc_exec_ctx *exec_ctx,
+                                             void *bctlp, bool success) {
+  batch_control *bctl = bctlp;
+  grpc_call *call = bctl->call;
+
+  gpr_mu_lock(&call->mu);
+
+  grpc_metadata_batch *md =
+      &call->metadata_batch[1 /* is_receiving */][0 /* is_trailing */];
+  grpc_metadata_batch_filter(md, recv_initial_filter, call);
+  call->has_initial_md_been_received = true;
+
+  if (gpr_time_cmp(md->deadline, gpr_inf_future(md->deadline.clock_type)) !=
+          0 &&
+      !call->is_client) {
+    GPR_TIMER_BEGIN("set_deadline_alarm", 0);
+    set_deadline_alarm(exec_ctx, call, md->deadline);
+    GPR_TIMER_END("set_deadline_alarm", 0);
+  }
+
+  if (call->saved_receiving_stream_ready_ctx.bctlp != NULL) {
+    grpc_closure *saved_rsr_closure = grpc_closure_create(
+        receiving_stream_ready, call->saved_receiving_stream_ready_ctx.bctlp);
+    grpc_exec_ctx_enqueue(exec_ctx, saved_rsr_closure,
+                          call->saved_receiving_stream_ready_ctx.success, NULL);
+    call->saved_receiving_stream_ready_ctx.bctlp = NULL;
+  }
+
+  gpr_mu_unlock(&call->mu);
+
+  if (gpr_unref(&bctl->steps_to_complete)) {
+    post_batch_completion(exec_ctx, bctl);
+  }
+}
+
+static void finish_batch(grpc_exec_ctx *exec_ctx, void *bctlp, bool success) {
+  batch_control *bctl = bctlp;
+  grpc_call *call = bctl->call;
+  grpc_call *child_call;
+  grpc_call *next_child_call;
+
+  gpr_mu_lock(&call->mu);
+  if (bctl->send_initial_metadata) {
+    grpc_metadata_batch_destroy(
+        &call->metadata_batch[0 /* is_receiving */][0 /* is_trailing */]);
+  }
+  if (bctl->send_message) {
+    call->sending_message = 0;
+  }
+  if (bctl->send_final_op) {
+    grpc_metadata_batch_destroy(
+        &call->metadata_batch[0 /* is_receiving */][1 /* is_trailing */]);
+  }
+  if (bctl->recv_final_op) {
+    grpc_metadata_batch *md =
+        &call->metadata_batch[1 /* is_receiving */][1 /* is_trailing */];
+    grpc_metadata_batch_filter(md, recv_trailing_filter, call);
+
+    if (call->have_alarm) {
+      grpc_timer_cancel(exec_ctx, &call->alarm);
+    }
+    /* propagate cancellation to any interested children */
+    child_call = call->first_child;
+    if (child_call != NULL) {
+      do {
+        next_child_call = child_call->sibling_next;
+        if (child_call->cancellation_is_inherited) {
+          GRPC_CALL_INTERNAL_REF(child_call, "propagate_cancel");
+          grpc_call_cancel(child_call, NULL);
+          GRPC_CALL_INTERNAL_UNREF(exec_ctx, child_call, "propagate_cancel");
+        }
+        child_call = next_child_call;
+      } while (child_call != call->first_child);
+    }
+
+    if (call->is_client) {
+      get_final_status(call, set_status_value_directly,
+                       call->final_op.client.status);
+      get_final_details(call, call->final_op.client.status_details,
+                        call->final_op.client.status_details_capacity);
+    } else {
+      get_final_status(call, set_cancelled_value,
+                       call->final_op.server.cancelled);
+    }
+
+    success = 1;
+  }
+  bctl->success = success != 0;
+  gpr_mu_unlock(&call->mu);
+  if (gpr_unref(&bctl->steps_to_complete)) {
+    post_batch_completion(exec_ctx, bctl);
+  }
+}
+
+static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
+                                        grpc_call *call, const grpc_op *ops,
+                                        size_t nops, void *notify_tag,
+                                        int is_notify_tag_closure) {
+  grpc_transport_stream_op stream_op;
+  size_t i;
+  const grpc_op *op;
+  batch_control *bctl;
+  int num_completion_callbacks_needed = 1;
+  grpc_call_error error = GRPC_CALL_OK;
+
+  GPR_TIMER_BEGIN("grpc_call_start_batch", 0);
+
+  GRPC_CALL_LOG_BATCH(GPR_INFO, call, ops, nops, notify_tag);
+
+  memset(&stream_op, 0, sizeof(stream_op));
+
+  /* TODO(ctiller): this feels like it could be made lock-free */
+  gpr_mu_lock(&call->mu);
+  bctl = allocate_batch_control(call);
+  memset(bctl, 0, sizeof(*bctl));
+  bctl->call = call;
+  bctl->notify_tag = notify_tag;
+  bctl->is_notify_tag_closure = (uint8_t)(is_notify_tag_closure != 0);
+
+  if (nops == 0) {
+    GRPC_CALL_INTERNAL_REF(call, "completion");
+    bctl->success = 1;
+    if (!is_notify_tag_closure) {
+      grpc_cq_begin_op(call->cq, notify_tag);
+    }
+    gpr_mu_unlock(&call->mu);
+    post_batch_completion(exec_ctx, bctl);
+    error = GRPC_CALL_OK;
+    goto done;
+  }
+
+  /* rewrite batch ops into a transport op */
+  for (i = 0; i < nops; i++) {
+    op = &ops[i];
+    if (op->reserved != NULL) {
+      error = GRPC_CALL_ERROR;
+      goto done_with_error;
+    }
+    switch (op->op) {
+      case GRPC_OP_SEND_INITIAL_METADATA:
+        /* Flag validation: currently allow no flags */
+        if (op->flags != 0) {
+          error = GRPC_CALL_ERROR_INVALID_FLAGS;
+          goto done_with_error;
+        }
+        if (call->sent_initial_metadata) {
+          error = GRPC_CALL_ERROR_TOO_MANY_OPERATIONS;
+          goto done_with_error;
+        }
+        if (op->data.send_initial_metadata.count > INT_MAX) {
+          error = GRPC_CALL_ERROR_INVALID_METADATA;
+          goto done_with_error;
+        }
+        bctl->send_initial_metadata = 1;
+        call->sent_initial_metadata = 1;
+        if (!prepare_application_metadata(
+                call, (int)op->data.send_initial_metadata.count,
+                op->data.send_initial_metadata.metadata, 0, call->is_client)) {
+          error = GRPC_CALL_ERROR_INVALID_METADATA;
+          goto done_with_error;
+        }
+        /* TODO(ctiller): just make these the same variable? */
+        call->metadata_batch[0][0].deadline = call->send_deadline;
+        stream_op.send_initial_metadata =
+            &call->metadata_batch[0 /* is_receiving */][0 /* is_trailing */];
+        break;
+      case GRPC_OP_SEND_MESSAGE:
+        if (!are_write_flags_valid(op->flags)) {
+          error = GRPC_CALL_ERROR_INVALID_FLAGS;
+          goto done_with_error;
+        }
+        if (op->data.send_message == NULL) {
+          error = GRPC_CALL_ERROR_INVALID_MESSAGE;
+          goto done_with_error;
+        }
+        if (call->sending_message) {
+          error = GRPC_CALL_ERROR_TOO_MANY_OPERATIONS;
+          goto done_with_error;
+        }
+        bctl->send_message = 1;
+        call->sending_message = 1;
+        grpc_slice_buffer_stream_init(
+            &call->sending_stream,
+            &op->data.send_message->data.raw.slice_buffer, op->flags);
+        stream_op.send_message = &call->sending_stream.base;
+        break;
+      case GRPC_OP_SEND_CLOSE_FROM_CLIENT:
+        /* Flag validation: currently allow no flags */
+        if (op->flags != 0) {
+          error = GRPC_CALL_ERROR_INVALID_FLAGS;
+          goto done_with_error;
+        }
+        if (!call->is_client) {
+          error = GRPC_CALL_ERROR_NOT_ON_SERVER;
+          goto done_with_error;
+        }
+        if (call->sent_final_op) {
+          error = GRPC_CALL_ERROR_TOO_MANY_OPERATIONS;
+          goto done_with_error;
+        }
+        bctl->send_final_op = 1;
+        call->sent_final_op = 1;
+        stream_op.send_trailing_metadata =
+            &call->metadata_batch[0 /* is_receiving */][1 /* is_trailing */];
+        break;
+      case GRPC_OP_SEND_STATUS_FROM_SERVER:
+        /* Flag validation: currently allow no flags */
+        if (op->flags != 0) {
+          error = GRPC_CALL_ERROR_INVALID_FLAGS;
+          goto done_with_error;
+        }
+        if (call->is_client) {
+          error = GRPC_CALL_ERROR_NOT_ON_CLIENT;
+          goto done_with_error;
+        }
+        if (call->sent_final_op) {
+          error = GRPC_CALL_ERROR_TOO_MANY_OPERATIONS;
+          goto done_with_error;
+        }
+        if (op->data.send_status_from_server.trailing_metadata_count >
+            INT_MAX) {
+          error = GRPC_CALL_ERROR_INVALID_METADATA;
+          goto done_with_error;
+        }
+        bctl->send_final_op = 1;
+        call->sent_final_op = 1;
+        call->send_extra_metadata_count = 1;
+        call->send_extra_metadata[0].md = grpc_channel_get_reffed_status_elem(
+            call->channel, op->data.send_status_from_server.status);
+        if (op->data.send_status_from_server.status_details != NULL) {
+          call->send_extra_metadata[1].md = grpc_mdelem_from_metadata_strings(
+              GRPC_MDSTR_GRPC_MESSAGE,
+              grpc_mdstr_from_string(
+                  op->data.send_status_from_server.status_details));
+          call->send_extra_metadata_count++;
+          set_status_details(
+              call, STATUS_FROM_API_OVERRIDE,
+              GRPC_MDSTR_REF(call->send_extra_metadata[1].md->value));
+        }
+        set_status_code(call, STATUS_FROM_API_OVERRIDE,
+                        (uint32_t)op->data.send_status_from_server.status);
+        if (!prepare_application_metadata(
+                call,
+                (int)op->data.send_status_from_server.trailing_metadata_count,
+                op->data.send_status_from_server.trailing_metadata, 1, 1)) {
+          error = GRPC_CALL_ERROR_INVALID_METADATA;
+          goto done_with_error;
+        }
+        stream_op.send_trailing_metadata =
+            &call->metadata_batch[0 /* is_receiving */][1 /* is_trailing */];
+        break;
+      case GRPC_OP_RECV_INITIAL_METADATA:
+        /* Flag validation: currently allow no flags */
+        if (op->flags != 0) {
+          error = GRPC_CALL_ERROR_INVALID_FLAGS;
+          goto done_with_error;
+        }
+        if (call->received_initial_metadata) {
+          error = GRPC_CALL_ERROR_TOO_MANY_OPERATIONS;
+          goto done_with_error;
+        }
+        call->received_initial_metadata = 1;
+        call->buffered_metadata[0] = op->data.recv_initial_metadata;
+        grpc_closure_init(&call->receiving_initial_metadata_ready,
+                          receiving_initial_metadata_ready, bctl);
+        bctl->recv_initial_metadata = 1;
+        stream_op.recv_initial_metadata =
+            &call->metadata_batch[1 /* is_receiving */][0 /* is_trailing */];
+        stream_op.recv_initial_metadata_ready =
+            &call->receiving_initial_metadata_ready;
+        num_completion_callbacks_needed++;
+        break;
+      case GRPC_OP_RECV_MESSAGE:
+        /* Flag validation: currently allow no flags */
+        if (op->flags != 0) {
+          error = GRPC_CALL_ERROR_INVALID_FLAGS;
+          goto done_with_error;
+        }
+        if (call->receiving_message) {
+          error = GRPC_CALL_ERROR_TOO_MANY_OPERATIONS;
+          goto done_with_error;
+        }
+        call->receiving_message = 1;
+        bctl->recv_message = 1;
+        call->receiving_buffer = op->data.recv_message;
+        stream_op.recv_message = &call->receiving_stream;
+        grpc_closure_init(&call->receiving_stream_ready, receiving_stream_ready,
+                          bctl);
+        stream_op.recv_message_ready = &call->receiving_stream_ready;
+        num_completion_callbacks_needed++;
+        break;
+      case GRPC_OP_RECV_STATUS_ON_CLIENT:
+        /* Flag validation: currently allow no flags */
+        if (op->flags != 0) {
+          error = GRPC_CALL_ERROR_INVALID_FLAGS;
+          goto done_with_error;
+        }
+        if (!call->is_client) {
+          error = GRPC_CALL_ERROR_NOT_ON_SERVER;
+          goto done_with_error;
+        }
+        if (call->received_final_op) {
+          error = GRPC_CALL_ERROR_TOO_MANY_OPERATIONS;
+          goto done_with_error;
+        }
+        call->received_final_op = 1;
+        call->buffered_metadata[1] =
+            op->data.recv_status_on_client.trailing_metadata;
+        call->final_op.client.status = op->data.recv_status_on_client.status;
+        call->final_op.client.status_details =
+            op->data.recv_status_on_client.status_details;
+        call->final_op.client.status_details_capacity =
+            op->data.recv_status_on_client.status_details_capacity;
+        bctl->recv_final_op = 1;
+        stream_op.recv_trailing_metadata =
+            &call->metadata_batch[1 /* is_receiving */][1 /* is_trailing */];
+        break;
+      case GRPC_OP_RECV_CLOSE_ON_SERVER:
+        /* Flag validation: currently allow no flags */
+        if (op->flags != 0) {
+          error = GRPC_CALL_ERROR_INVALID_FLAGS;
+          goto done_with_error;
+        }
+        if (call->is_client) {
+          error = GRPC_CALL_ERROR_NOT_ON_CLIENT;
+          goto done_with_error;
+        }
+        if (call->received_final_op) {
+          error = GRPC_CALL_ERROR_TOO_MANY_OPERATIONS;
+          goto done_with_error;
+        }
+        call->received_final_op = 1;
+        call->final_op.server.cancelled =
+            op->data.recv_close_on_server.cancelled;
+        bctl->recv_final_op = 1;
+        stream_op.recv_trailing_metadata =
+            &call->metadata_batch[1 /* is_receiving */][1 /* is_trailing */];
+        break;
+    }
+  }
+
+  GRPC_CALL_INTERNAL_REF(call, "completion");
+  if (!is_notify_tag_closure) {
+    grpc_cq_begin_op(call->cq, notify_tag);
+  }
+  gpr_ref_init(&bctl->steps_to_complete, num_completion_callbacks_needed);
+
+  stream_op.context = call->context;
+  grpc_closure_init(&bctl->finish_batch, finish_batch, bctl);
+  stream_op.on_complete = &bctl->finish_batch;
+  gpr_mu_unlock(&call->mu);
+
+  execute_op(exec_ctx, call, &stream_op);
+
+done:
+  GPR_TIMER_END("grpc_call_start_batch", 0);
+  return error;
+
+done_with_error:
+  /* reverse any mutations that occured */
+  if (bctl->send_initial_metadata) {
+    call->sent_initial_metadata = 0;
+    grpc_metadata_batch_clear(&call->metadata_batch[0][0]);
+  }
+  if (bctl->send_message) {
+    call->sending_message = 0;
+    grpc_byte_stream_destroy(exec_ctx, &call->sending_stream.base);
+  }
+  if (bctl->send_final_op) {
+    call->sent_final_op = 0;
+    grpc_metadata_batch_clear(&call->metadata_batch[0][1]);
+  }
+  if (bctl->recv_initial_metadata) {
+    call->received_initial_metadata = 0;
+  }
+  if (bctl->recv_message) {
+    call->receiving_message = 0;
+  }
+  if (bctl->recv_final_op) {
+    call->received_final_op = 0;
+  }
+  gpr_mu_unlock(&call->mu);
+  goto done;
+}
+
+grpc_call_error grpc_call_start_batch(grpc_call *call, const grpc_op *ops,
+                                      size_t nops, void *tag, void *reserved) {
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  grpc_call_error err;
+
+  GRPC_API_TRACE(
+      "grpc_call_start_batch(call=%p, ops=%p, nops=%lu, tag=%p, reserved=%p)",
+      5, (call, ops, (unsigned long)nops, tag, reserved));
+
+  if (reserved != NULL) {
+    err = GRPC_CALL_ERROR;
+  } else {
+    err = call_start_batch(&exec_ctx, call, ops, nops, tag, 0);
+  }
+
+  grpc_exec_ctx_finish(&exec_ctx);
+  return err;
+}
+
+grpc_call_error grpc_call_start_batch_and_execute(grpc_exec_ctx *exec_ctx,
+                                                  grpc_call *call,
+                                                  const grpc_op *ops,
+                                                  size_t nops,
+                                                  grpc_closure *closure) {
+  return call_start_batch(exec_ctx, call, ops, nops, closure, 1);
+}
+
+void grpc_call_context_set(grpc_call *call, grpc_context_index elem,
+                           void *value, void (*destroy)(void *value)) {
+  if (call->context[elem].destroy) {
+    call->context[elem].destroy(call->context[elem].value);
+  }
+  call->context[elem].value = value;
+  call->context[elem].destroy = destroy;
+}
+
+void *grpc_call_context_get(grpc_call *call, grpc_context_index elem) {
+  return call->context[elem].value;
+}
+
+uint8_t grpc_call_is_client(grpc_call *call) { return call->is_client; }