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diff --git a/src/core/ext/filters/client_channel/health/health_check_client.h b/src/core/ext/filters/client_channel/health/health_check_client.h
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+++ b/src/core/ext/filters/client_channel/health/health_check_client.h
@@ -0,0 +1,173 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_HEALTH_HEALTH_CHECK_CLIENT_H
+#define GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_HEALTH_HEALTH_CHECK_CLIENT_H
+
+#include <grpc/support/port_platform.h>
+
+#include <grpc/grpc.h>
+#include <grpc/support/atm.h>
+#include <grpc/support/sync.h>
+
+#include "src/core/ext/filters/client_channel/client_channel_channelz.h"
+#include "src/core/ext/filters/client_channel/subchannel.h"
+#include "src/core/lib/backoff/backoff.h"
+#include "src/core/lib/gpr/arena.h"
+#include "src/core/lib/gprpp/orphanable.h"
+#include "src/core/lib/gprpp/ref_counted_ptr.h"
+#include "src/core/lib/iomgr/call_combiner.h"
+#include "src/core/lib/iomgr/closure.h"
+#include "src/core/lib/iomgr/polling_entity.h"
+#include "src/core/lib/iomgr/timer.h"
+#include "src/core/lib/transport/byte_stream.h"
+#include "src/core/lib/transport/metadata_batch.h"
+#include "src/core/lib/transport/transport.h"
+
+namespace grpc_core {
+
+class HealthCheckClient
+    : public InternallyRefCountedWithTracing<HealthCheckClient> {
+ public:
+  HealthCheckClient(const char* service_name,
+                    RefCountedPtr<ConnectedSubchannel> connected_subchannel,
+                    grpc_pollset_set* interested_parties,
+                    RefCountedPtr<channelz::SubchannelNode> channelz_node);
+
+  ~HealthCheckClient();
+
+  // When the health state changes from *state, sets *state to the new
+  // value and schedules closure.
+  // Only one closure can be outstanding at a time.
+  void NotifyOnHealthChange(grpc_connectivity_state* state,
+                            grpc_closure* closure);
+
+  void Orphan() override;
+
+ private:
+  // Contains a call to the backend and all the data related to the call.
+  class CallState : public InternallyRefCountedWithTracing<CallState> {
+   public:
+    CallState(RefCountedPtr<HealthCheckClient> health_check_client,
+              grpc_pollset_set* interested_parties_);
+    ~CallState();
+
+    void Orphan() override;
+
+    void StartCall();
+
+   private:
+    void Cancel();
+
+    void StartBatch(grpc_transport_stream_op_batch* batch);
+    static void StartBatchInCallCombiner(void* arg, grpc_error* error);
+
+    static void CallEndedRetry(void* arg, grpc_error* error);
+    void CallEnded(bool retry);
+
+    static void OnComplete(void* arg, grpc_error* error);
+    static void RecvInitialMetadataReady(void* arg, grpc_error* error);
+    static void RecvMessageReady(void* arg, grpc_error* error);
+    static void RecvTrailingMetadataReady(void* arg, grpc_error* error);
+    static void StartCancel(void* arg, grpc_error* error);
+    static void OnCancelComplete(void* arg, grpc_error* error);
+
+    static void OnByteStreamNext(void* arg, grpc_error* error);
+    void ContinueReadingRecvMessage();
+    grpc_error* PullSliceFromRecvMessage();
+    void DoneReadingRecvMessage(grpc_error* error);
+
+    RefCountedPtr<HealthCheckClient> health_check_client_;
+    grpc_polling_entity pollent_;
+
+    gpr_arena* arena_;
+    grpc_call_combiner call_combiner_;
+    grpc_call_context_element context_[GRPC_CONTEXT_COUNT] = {};
+
+    // The streaming call to the backend. Always non-NULL.
+    grpc_subchannel_call* call_;
+
+    grpc_transport_stream_op_batch_payload payload_;
+    grpc_transport_stream_op_batch batch_;
+    grpc_transport_stream_op_batch recv_message_batch_;
+    grpc_transport_stream_op_batch recv_trailing_metadata_batch_;
+
+    grpc_closure on_complete_;
+
+    // send_initial_metadata
+    grpc_metadata_batch send_initial_metadata_;
+    grpc_linked_mdelem path_metadata_storage_;
+
+    // send_message
+    ManualConstructor<SliceBufferByteStream> send_message_;
+
+    // send_trailing_metadata
+    grpc_metadata_batch send_trailing_metadata_;
+
+    // recv_initial_metadata
+    grpc_metadata_batch recv_initial_metadata_;
+    grpc_closure recv_initial_metadata_ready_;
+
+    // recv_message
+    OrphanablePtr<ByteStream> recv_message_;
+    grpc_closure recv_message_ready_;
+    grpc_slice_buffer recv_message_buffer_;
+    gpr_atm seen_response_;
+
+    // recv_trailing_metadata
+    grpc_metadata_batch recv_trailing_metadata_;
+    grpc_transport_stream_stats collect_stats_;
+    grpc_closure recv_trailing_metadata_ready_;
+  };
+
+  void StartCall();
+  void StartCallLocked();  // Requires holding mu_.
+
+  void StartRetryTimer();
+  static void OnRetryTimer(void* arg, grpc_error* error);
+
+  void SetHealthStatus(grpc_connectivity_state state, grpc_error* error);
+  void SetHealthStatusLocked(grpc_connectivity_state state,
+                             grpc_error* error);  // Requires holding mu_.
+
+  const char* service_name_;  // Do not own.
+  RefCountedPtr<ConnectedSubchannel> connected_subchannel_;
+  grpc_pollset_set* interested_parties_;  // Do not own.
+  RefCountedPtr<channelz::SubchannelNode> channelz_node_;
+
+  gpr_mu mu_;
+  grpc_connectivity_state state_ = GRPC_CHANNEL_CONNECTING;
+  grpc_error* error_ = GRPC_ERROR_NONE;
+  grpc_connectivity_state* notify_state_ = nullptr;
+  grpc_closure* on_health_changed_ = nullptr;
+  bool shutting_down_ = false;
+
+  // The data associated with the current health check call.  It holds a ref
+  // to this HealthCheckClient object.
+  OrphanablePtr<CallState> call_state_;
+
+  // Call retry state.
+  BackOff retry_backoff_;
+  grpc_timer retry_timer_;
+  grpc_closure retry_timer_callback_;
+  bool retry_timer_callback_pending_ = false;
+};
+
+}  // namespace grpc_core
+
+#endif /* GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_HEALTH_HEALTH_CHECK_CLIENT_H */