/*
 *
 * Copyright 2015 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_TRANSPORT_CHTTP2_TRANSPORT_INTERNAL_H
#define GRPC_CORE_EXT_TRANSPORT_CHTTP2_TRANSPORT_INTERNAL_H

#include <assert.h>
#include <stdbool.h>

#include "src/core/ext/transport/chttp2/transport/frame.h"
#include "src/core/ext/transport/chttp2/transport/frame_data.h"
#include "src/core/ext/transport/chttp2/transport/frame_goaway.h"
#include "src/core/ext/transport/chttp2/transport/frame_ping.h"
#include "src/core/ext/transport/chttp2/transport/frame_rst_stream.h"
#include "src/core/ext/transport/chttp2/transport/frame_settings.h"
#include "src/core/ext/transport/chttp2/transport/frame_window_update.h"
#include "src/core/ext/transport/chttp2/transport/hpack_encoder.h"
#include "src/core/ext/transport/chttp2/transport/hpack_parser.h"
#include "src/core/ext/transport/chttp2/transport/incoming_metadata.h"
#include "src/core/ext/transport/chttp2/transport/stream_map.h"
#include "src/core/lib/compression/stream_compression.h"
#include "src/core/lib/iomgr/combiner.h"
#include "src/core/lib/iomgr/endpoint.h"
#include "src/core/lib/iomgr/timer.h"
#include "src/core/lib/transport/bdp_estimator.h"
#include "src/core/lib/transport/connectivity_state.h"
#include "src/core/lib/transport/pid_controller.h"
#include "src/core/lib/transport/transport_impl.h"

/* streams are kept in various linked lists depending on what things need to
   happen to them... this enum labels each list */
typedef enum {
  GRPC_CHTTP2_LIST_WRITABLE,
  GRPC_CHTTP2_LIST_WRITING,
  GRPC_CHTTP2_LIST_STALLED_BY_TRANSPORT,
  GRPC_CHTTP2_LIST_STALLED_BY_STREAM,
  /** streams that are waiting to start because there are too many concurrent
      streams on the connection */
  GRPC_CHTTP2_LIST_WAITING_FOR_CONCURRENCY,
  STREAM_LIST_COUNT /* must be last */
} grpc_chttp2_stream_list_id;

typedef enum {
  GRPC_CHTTP2_WRITE_STATE_IDLE,
  GRPC_CHTTP2_WRITE_STATE_WRITING,
  GRPC_CHTTP2_WRITE_STATE_WRITING_WITH_MORE,
} grpc_chttp2_write_state;

typedef enum {
  GRPC_CHTTP2_PING_ON_NEXT_WRITE = 0,
  GRPC_CHTTP2_PING_BEFORE_TRANSPORT_WINDOW_UPDATE,
  GRPC_CHTTP2_PING_TYPE_COUNT /* must be last */
} grpc_chttp2_ping_type;

typedef enum {
  GRPC_CHTTP2_OPTIMIZE_FOR_LATENCY,
  GRPC_CHTTP2_OPTIMIZE_FOR_THROUGHPUT,
} grpc_chttp2_optimization_target;

typedef enum {
  GRPC_CHTTP2_PCL_INITIATE = 0,
  GRPC_CHTTP2_PCL_NEXT,
  GRPC_CHTTP2_PCL_INFLIGHT,
  GRPC_CHTTP2_PCL_COUNT /* must be last */
} grpc_chttp2_ping_closure_list;

typedef enum {
  GRPC_CHTTP2_INITIATE_WRITE_INITIAL_WRITE,
  GRPC_CHTTP2_INITIATE_WRITE_START_NEW_STREAM,
  GRPC_CHTTP2_INITIATE_WRITE_SEND_MESSAGE,
  GRPC_CHTTP2_INITIATE_WRITE_SEND_INITIAL_METADATA,
  GRPC_CHTTP2_INITIATE_WRITE_SEND_TRAILING_METADATA,
  GRPC_CHTTP2_INITIATE_WRITE_RETRY_SEND_PING,
  GRPC_CHTTP2_INITIATE_WRITE_CONTINUE_PINGS,
  GRPC_CHTTP2_INITIATE_WRITE_GOAWAY_SENT,
  GRPC_CHTTP2_INITIATE_WRITE_RST_STREAM,
  GRPC_CHTTP2_INITIATE_WRITE_CLOSE_FROM_API,
  GRPC_CHTTP2_INITIATE_WRITE_STREAM_FLOW_CONTROL,
  GRPC_CHTTP2_INITIATE_WRITE_TRANSPORT_FLOW_CONTROL,
  GRPC_CHTTP2_INITIATE_WRITE_SEND_SETTINGS,
  GRPC_CHTTP2_INITIATE_WRITE_BDP_ESTIMATOR_PING,
  GRPC_CHTTP2_INITIATE_WRITE_FLOW_CONTROL_UNSTALLED_BY_SETTING,
  GRPC_CHTTP2_INITIATE_WRITE_FLOW_CONTROL_UNSTALLED_BY_UPDATE,
  GRPC_CHTTP2_INITIATE_WRITE_APPLICATION_PING,
  GRPC_CHTTP2_INITIATE_WRITE_KEEPALIVE_PING,
  GRPC_CHTTP2_INITIATE_WRITE_TRANSPORT_FLOW_CONTROL_UNSTALLED,
  GRPC_CHTTP2_INITIATE_WRITE_PING_RESPONSE,
  GRPC_CHTTP2_INITIATE_WRITE_FORCE_RST_STREAM,
} grpc_chttp2_initiate_write_reason;

const char *grpc_chttp2_initiate_write_reason_string(
    grpc_chttp2_initiate_write_reason reason);

typedef struct {
  grpc_closure_list lists[GRPC_CHTTP2_PCL_COUNT];
  uint64_t inflight_id;
} grpc_chttp2_ping_queue;

typedef struct {
  int max_pings_without_data;
  int max_ping_strikes;
  gpr_timespec min_sent_ping_interval_without_data;
  gpr_timespec min_recv_ping_interval_without_data;
} grpc_chttp2_repeated_ping_policy;

typedef struct {
  gpr_timespec last_ping_sent_time;
  int pings_before_data_required;
  grpc_timer delayed_ping_timer;
  bool is_delayed_ping_timer_set;
} grpc_chttp2_repeated_ping_state;

typedef struct {
  gpr_timespec last_ping_recv_time;
  int ping_strikes;
} grpc_chttp2_server_ping_recv_state;

/* deframer state for the overall http2 stream of bytes */
typedef enum {
  /* prefix: one entry per http2 connection prefix byte */
  GRPC_DTS_CLIENT_PREFIX_0 = 0,
  GRPC_DTS_CLIENT_PREFIX_1,
  GRPC_DTS_CLIENT_PREFIX_2,
  GRPC_DTS_CLIENT_PREFIX_3,
  GRPC_DTS_CLIENT_PREFIX_4,
  GRPC_DTS_CLIENT_PREFIX_5,
  GRPC_DTS_CLIENT_PREFIX_6,
  GRPC_DTS_CLIENT_PREFIX_7,
  GRPC_DTS_CLIENT_PREFIX_8,
  GRPC_DTS_CLIENT_PREFIX_9,
  GRPC_DTS_CLIENT_PREFIX_10,
  GRPC_DTS_CLIENT_PREFIX_11,
  GRPC_DTS_CLIENT_PREFIX_12,
  GRPC_DTS_CLIENT_PREFIX_13,
  GRPC_DTS_CLIENT_PREFIX_14,
  GRPC_DTS_CLIENT_PREFIX_15,
  GRPC_DTS_CLIENT_PREFIX_16,
  GRPC_DTS_CLIENT_PREFIX_17,
  GRPC_DTS_CLIENT_PREFIX_18,
  GRPC_DTS_CLIENT_PREFIX_19,
  GRPC_DTS_CLIENT_PREFIX_20,
  GRPC_DTS_CLIENT_PREFIX_21,
  GRPC_DTS_CLIENT_PREFIX_22,
  GRPC_DTS_CLIENT_PREFIX_23,
  /* frame header byte 0... */
  /* must follow from the prefix states */
  GRPC_DTS_FH_0,
  GRPC_DTS_FH_1,
  GRPC_DTS_FH_2,
  GRPC_DTS_FH_3,
  GRPC_DTS_FH_4,
  GRPC_DTS_FH_5,
  GRPC_DTS_FH_6,
  GRPC_DTS_FH_7,
  /* ... frame header byte 8 */
  GRPC_DTS_FH_8,
  /* inside a http2 frame */
  GRPC_DTS_FRAME
} grpc_chttp2_deframe_transport_state;

typedef struct {
  grpc_chttp2_stream *head;
  grpc_chttp2_stream *tail;
} grpc_chttp2_stream_list;

typedef struct {
  grpc_chttp2_stream *next;
  grpc_chttp2_stream *prev;
} grpc_chttp2_stream_link;

/* We keep several sets of connection wide parameters */
typedef enum {
  /* The settings our peer has asked for (and we have acked) */
  GRPC_PEER_SETTINGS = 0,
  /* The settings we'd like to have */
  GRPC_LOCAL_SETTINGS,
  /* The settings we've published to our peer */
  GRPC_SENT_SETTINGS,
  /* The settings the peer has acked */
  GRPC_ACKED_SETTINGS,
  GRPC_NUM_SETTING_SETS
} grpc_chttp2_setting_set;

typedef enum {
  GRPC_CHTTP2_NO_GOAWAY_SEND,
  GRPC_CHTTP2_GOAWAY_SEND_SCHEDULED,
  GRPC_CHTTP2_GOAWAY_SENT,
} grpc_chttp2_sent_goaway_state;

typedef struct grpc_chttp2_write_cb {
  int64_t call_at_byte;
  grpc_closure *closure;
  struct grpc_chttp2_write_cb *next;
} grpc_chttp2_write_cb;

/* forward declared in frame_data.h */
struct grpc_chttp2_incoming_byte_stream {
  grpc_byte_stream base;
  gpr_refcount refs;

  grpc_chttp2_transport *transport; /* immutable */
  grpc_chttp2_stream *stream;       /* immutable */

  /* Accessed only by transport thread when stream->pending_byte_stream == false
   * Accessed only by application thread when stream->pending_byte_stream ==
   * true */
  uint32_t remaining_bytes;

  /* Accessed only by transport thread when stream->pending_byte_stream == false
   * Accessed only by application thread when stream->pending_byte_stream ==
   * true */
  struct {
    grpc_closure closure;
    size_t max_size_hint;
    grpc_closure *on_complete;
  } next_action;
  grpc_closure destroy_action;
  grpc_closure finished_action;
};

typedef enum {
  GRPC_CHTTP2_KEEPALIVE_STATE_WAITING,
  GRPC_CHTTP2_KEEPALIVE_STATE_PINGING,
  GRPC_CHTTP2_KEEPALIVE_STATE_DYING,
  GRPC_CHTTP2_KEEPALIVE_STATE_DISABLED,
} grpc_chttp2_keepalive_state;

typedef struct {
  /** initial window change. This is tracked as we parse settings frames from
   * the remote peer. If there is a positive delta, then we will make all
   * streams readable since they may have become unstalled */
  int64_t initial_window_update;

  /** Our bookkeeping for the remote peer's available window */
  int64_t remote_window;

  /** calculating what we should give for local window:
      we track the total amount of flow control over initial window size
      across all streams: this is data that we want to receive right now (it
      has an outstanding read)
      and the total amount of flow control under initial window size across all
      streams: this is data we've read early
      we want to adjust incoming_window such that:
      incoming_window = total_over - max(bdp - total_under, 0) */
  int64_t announced_stream_total_over_incoming_window;
  int64_t announced_stream_total_under_incoming_window;

  /** This is out window according to what we have sent to our remote peer. The
   * difference between this and target window is what we use to decide when
   * to send WINDOW_UPDATE frames. */
  int64_t announced_window;

  /** should we probe bdp? */
  bool enable_bdp_probe;

  /* bdp estimation */
  grpc_bdp_estimator bdp_estimator;

  /* pid controller */
  grpc_pid_controller pid_controller;
  gpr_timespec last_pid_update;

  // pointer back to transport for tracing
  const grpc_chttp2_transport *t;
} grpc_chttp2_transport_flowctl;

struct grpc_chttp2_transport {
  grpc_transport base; /* must be first */
  gpr_refcount refs;
  grpc_endpoint *ep;
  char *peer_string;

  grpc_combiner *combiner;

  grpc_closure *notify_on_receive_settings;

  /** write execution state of the transport */
  grpc_chttp2_write_state write_state;
  /** is this the first write in a series of writes?
      set when we initiate writing from idle, cleared when we
      initiate writing from writing+more */
  bool is_first_write_in_batch;

  /** is the transport destroying itself? */
  uint8_t destroying;
  /** has the upper layer closed the transport? */
  uint8_t closed;

  /** is there a read request to the endpoint outstanding? */
  uint8_t endpoint_reading;

  grpc_chttp2_optimization_target opt_target;

  /** various lists of streams */
  grpc_chttp2_stream_list lists[STREAM_LIST_COUNT];

  /** maps stream id to grpc_chttp2_stream objects */
  grpc_chttp2_stream_map stream_map;

  grpc_closure write_action_begin_locked;
  grpc_closure write_action;
  grpc_closure write_action_end_locked;

  grpc_closure read_action_locked;

  /** incoming read bytes */
  grpc_slice_buffer read_buffer;

  /** address to place a newly accepted stream - set and unset by
      grpc_chttp2_parsing_accept_stream; used by init_stream to
      publish the accepted server stream */
  grpc_chttp2_stream **accepting_stream;

  struct {
    /* accept stream callback */
    void (*accept_stream)(grpc_exec_ctx *exec_ctx, void *user_data,
                          grpc_transport *transport, const void *server_data);
    void *accept_stream_user_data;

    /** connectivity tracking */
    grpc_connectivity_state_tracker state_tracker;
  } channel_callback;

  /** data to write now */
  grpc_slice_buffer outbuf;
  /** hpack encoding */
  grpc_chttp2_hpack_compressor hpack_compressor;
  /** is this a client? */
  uint8_t is_client;

  /** data to write next write */
  grpc_slice_buffer qbuf;

  /** how much data are we willing to buffer when the WRITE_BUFFER_HINT is set?
   */
  uint32_t write_buffer_size;

  /** have we seen a goaway */
  uint8_t seen_goaway;
  /** have we sent a goaway */
  grpc_chttp2_sent_goaway_state sent_goaway_state;

  /** are the local settings dirty and need to be sent? */
  uint8_t dirtied_local_settings;
  /** have local settings been sent? */
  uint8_t sent_local_settings;
  /** bitmask of setting indexes to send out */
  uint32_t force_send_settings;
  /** settings values */
  uint32_t settings[GRPC_NUM_SETTING_SETS][GRPC_CHTTP2_NUM_SETTINGS];

  /** what is the next stream id to be allocated by this peer?
      copied to next_stream_id in parsing when parsing commences */
  uint32_t next_stream_id;

  /** last new stream id */
  uint32_t last_new_stream_id;

  /** ping queues for various ping insertion points */
  grpc_chttp2_ping_queue ping_queues[GRPC_CHTTP2_PING_TYPE_COUNT];
  grpc_chttp2_repeated_ping_policy ping_policy;
  grpc_chttp2_repeated_ping_state ping_state;
  uint64_t ping_ctr; /* unique id for pings */
  grpc_closure retry_initiate_ping_locked;

  /** ping acks */
  size_t ping_ack_count;
  size_t ping_ack_capacity;
  uint64_t *ping_acks;
  grpc_chttp2_server_ping_recv_state ping_recv_state;

  /** parser for headers */
  grpc_chttp2_hpack_parser hpack_parser;
  /** simple one shot parsers */
  union {
    grpc_chttp2_window_update_parser window_update;
    grpc_chttp2_settings_parser settings;
    grpc_chttp2_ping_parser ping;
    grpc_chttp2_rst_stream_parser rst_stream;
  } simple;
  /** parser for goaway frames */
  grpc_chttp2_goaway_parser goaway_parser;

  grpc_chttp2_transport_flowctl flow_control;

  /* deframing */
  grpc_chttp2_deframe_transport_state deframe_state;
  uint8_t incoming_frame_type;
  uint8_t incoming_frame_flags;
  uint8_t header_eof;
  bool is_first_frame;
  uint32_t expect_continuation_stream_id;
  uint32_t incoming_frame_size;
  uint32_t incoming_stream_id;

  /* active parser */
  void *parser_data;
  grpc_chttp2_stream *incoming_stream;
  grpc_error *(*parser)(grpc_exec_ctx *exec_ctx, void *parser_user_data,
                        grpc_chttp2_transport *t, grpc_chttp2_stream *s,
                        grpc_slice slice, int is_last);

  /* goaway data */
  grpc_status_code goaway_error;
  uint32_t goaway_last_stream_index;
  grpc_slice goaway_text;

  grpc_chttp2_write_cb *write_cb_pool;

  /* bdp estimator */
  grpc_closure start_bdp_ping_locked;
  grpc_closure finish_bdp_ping_locked;

  /* if non-NULL, close the transport with this error when writes are finished
   */
  grpc_error *close_transport_on_writes_finished;

  /* a list of closures to run after writes are finished */
  grpc_closure_list run_after_write;

  /* buffer pool state */
  /** have we scheduled a benign cleanup? */
  bool benign_reclaimer_registered;
  /** have we scheduled a destructive cleanup? */
  bool destructive_reclaimer_registered;
  /** benign cleanup closure */
  grpc_closure benign_reclaimer_locked;
  /** destructive cleanup closure */
  grpc_closure destructive_reclaimer_locked;

  /* keep-alive ping support */
  /** Closure to initialize a keepalive ping */
  grpc_closure init_keepalive_ping_locked;
  /** Closure to run when the keepalive ping is sent */
  grpc_closure start_keepalive_ping_locked;
  /** Cousure to run when the keepalive ping ack is received */
  grpc_closure finish_keepalive_ping_locked;
  /** Closrue to run when the keepalive ping timeouts */
  grpc_closure keepalive_watchdog_fired_locked;
  /** timer to initiate ping events */
  grpc_timer keepalive_ping_timer;
  /** watchdog to kill the transport when waiting for the keepalive ping */
  grpc_timer keepalive_watchdog_timer;
  /** time duration in between pings */
  gpr_timespec keepalive_time;
  /** grace period for a ping to complete before watchdog kicks in */
  gpr_timespec keepalive_timeout;
  /** if keepalive pings are allowed when there's no outstanding streams */
  bool keepalive_permit_without_calls;
  /** keep-alive state machine state */
  grpc_chttp2_keepalive_state keepalive_state;
};

typedef enum {
  GRPC_METADATA_NOT_PUBLISHED,
  GRPC_METADATA_SYNTHESIZED_FROM_FAKE,
  GRPC_METADATA_PUBLISHED_FROM_WIRE,
  GPRC_METADATA_PUBLISHED_AT_CLOSE
} grpc_published_metadata_method;

typedef struct {
  /** window available for us to send to peer, over or under the initial window
   * size of the transport... ie:
   * remote_window = remote_window_delta + transport.initial_window_size */
  int64_t remote_window_delta;

  /** window available for peer to send to us (as a delta on
   * transport.initial_window_size)
   * local_window = local_window_delta + transport.initial_window_size */
  int64_t local_window_delta;

  /** window available for peer to send to us over this stream that we have
   * announced to the peer */
  int64_t announced_window_delta;

  // read only pointer back to stream for data
  const grpc_chttp2_stream *s;
} grpc_chttp2_stream_flowctl;

struct grpc_chttp2_stream {
  grpc_chttp2_transport *t;
  grpc_stream_refcount *refcount;

  grpc_closure destroy_stream;
  grpc_closure *destroy_stream_arg;

  grpc_chttp2_stream_link links[STREAM_LIST_COUNT];
  uint8_t included[STREAM_LIST_COUNT];

  /** HTTP2 stream id for this stream, or zero if one has not been assigned */
  uint32_t id;

  /** things the upper layers would like to send */
  grpc_metadata_batch *send_initial_metadata;
  grpc_closure *send_initial_metadata_finished;
  grpc_metadata_batch *send_trailing_metadata;
  grpc_closure *send_trailing_metadata_finished;

  grpc_byte_stream *fetching_send_message;
  uint32_t fetched_send_message_length;
  grpc_slice fetching_slice;
  int64_t next_message_end_offset;
  int64_t flow_controlled_bytes_written;
  int64_t flow_controlled_bytes_flowed;
  grpc_closure complete_fetch_locked;
  grpc_closure *fetching_send_message_finished;

  grpc_metadata_batch *recv_initial_metadata;
  grpc_closure *recv_initial_metadata_ready;
  bool *trailing_metadata_available;
  grpc_byte_stream **recv_message;
  grpc_closure *recv_message_ready;
  grpc_metadata_batch *recv_trailing_metadata;
  grpc_closure *recv_trailing_metadata_finished;

  grpc_transport_stream_stats *collecting_stats;
  grpc_transport_stream_stats stats;

  /** Is this stream closed for writing. */
  bool write_closed;
  /** Is this stream reading half-closed. */
  bool read_closed;
  /** Are all published incoming byte streams closed. */
  bool all_incoming_byte_streams_finished;
  /** Has this stream seen an error.
      If true, then pending incoming frames can be thrown away. */
  bool seen_error;
  /** Are we buffering writes on this stream? If yes, we won't become writable
      until there's enough queued up in the flow_controlled_buffer */
  bool write_buffering;
  /** Has trailing metadata been received. */
  bool received_trailing_metadata;

  /** the error that resulted in this stream being read-closed */
  grpc_error *read_closed_error;
  /** the error that resulted in this stream being write-closed */
  grpc_error *write_closed_error;

  grpc_published_metadata_method published_metadata[2];
  bool final_metadata_requested;

  grpc_chttp2_incoming_metadata_buffer metadata_buffer[2];

  grpc_slice_buffer frame_storage; /* protected by t combiner */

  /* Accessed only by transport thread when stream->pending_byte_stream == false
   * Accessed only by application thread when stream->pending_byte_stream ==
   * true */
  grpc_slice_buffer unprocessed_incoming_frames_buffer;
  grpc_closure *on_next;    /* protected by t combiner */
  bool pending_byte_stream; /* protected by t combiner */
  grpc_closure reset_byte_stream;
  grpc_error *byte_stream_error; /* protected by t combiner */
  bool received_last_frame;      /* protected by t combiner */

  gpr_timespec deadline;

  /** saw some stream level error */
  grpc_error *forced_close_error;
  /** how many header frames have we received? */
  uint8_t header_frames_received;
  /** parsing state for data frames */
  /* Accessed only by transport thread when stream->pending_byte_stream == false
   * Accessed only by application thread when stream->pending_byte_stream ==
   * true */
  grpc_chttp2_data_parser data_parser;
  /** number of bytes received - reset at end of parse thread execution */
  int64_t received_bytes;

  bool sent_initial_metadata;
  bool sent_trailing_metadata;

  grpc_chttp2_stream_flowctl flow_control;

  grpc_slice_buffer flow_controlled_buffer;

  grpc_chttp2_write_cb *on_flow_controlled_cbs;
  grpc_chttp2_write_cb *on_write_finished_cbs;
  grpc_chttp2_write_cb *finish_after_write;
  size_t sending_bytes;

  /* Stream compression method to be used. */
  grpc_stream_compression_method stream_compression_method;
  /* Stream decompression method to be used. */
  grpc_stream_compression_method stream_decompression_method;
  /** Stream compression decompress context */
  grpc_stream_compression_context *stream_decompression_ctx;
  /** Stream compression compress context */
  grpc_stream_compression_context *stream_compression_ctx;

  /** Buffer storing data that is compressed but not sent */
  grpc_slice_buffer compressed_data_buffer;
  /** Amount of uncompressed bytes sent out when compressed_data_buffer is
   * emptied */
  size_t uncompressed_data_size;
  /** Temporary buffer storing decompressed data */
  grpc_slice_buffer decompressed_data_buffer;
  /** Whether bytes stored in unprocessed_incoming_byte_stream is decompressed
   */
  bool unprocessed_incoming_frames_decompressed;
  /** gRPC header bytes that are already decompressed */
  size_t decompressed_header_bytes;
};

/** Transport writing call flow:
    grpc_chttp2_initiate_write() is called anywhere that we know bytes need to
    go out on the wire.
    If no other write has been started, a task is enqueued onto our workqueue.
    When that task executes, it obtains the global lock, and gathers the data
    to write.
    The global lock is dropped and we do the syscall to write.
    After writing, a follow-up check is made to see if another round of writing
    should be performed.

    The actual call chain is documented in the implementation of this function.
    */
void grpc_chttp2_initiate_write(grpc_exec_ctx *exec_ctx,
                                grpc_chttp2_transport *t,
                                grpc_chttp2_initiate_write_reason reason);

typedef struct {
  /** are we writing? */
  bool writing;
  /** if writing: was it a complete flush (false) or a partial flush (true) */
  bool partial;
  /** did we queue any completions as part of beginning the write */
  bool early_results_scheduled;
} grpc_chttp2_begin_write_result;

grpc_chttp2_begin_write_result grpc_chttp2_begin_write(
    grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t);
void grpc_chttp2_end_write(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
                           grpc_error *error);

/** Process one slice of incoming data; return 1 if the connection is still
    viable after reading, or 0 if the connection should be torn down */
grpc_error *grpc_chttp2_perform_read(grpc_exec_ctx *exec_ctx,
                                     grpc_chttp2_transport *t,
                                     grpc_slice slice);

bool grpc_chttp2_list_add_writable_stream(grpc_chttp2_transport *t,
                                          grpc_chttp2_stream *s);
/** Get a writable stream
    returns non-zero if there was a stream available */
bool grpc_chttp2_list_pop_writable_stream(grpc_chttp2_transport *t,
                                          grpc_chttp2_stream **s);
bool grpc_chttp2_list_remove_writable_stream(
    grpc_chttp2_transport *t, grpc_chttp2_stream *s) GRPC_MUST_USE_RESULT;

bool grpc_chttp2_list_add_writing_stream(grpc_chttp2_transport *t,
                                         grpc_chttp2_stream *s);
bool grpc_chttp2_list_have_writing_streams(grpc_chttp2_transport *t);
bool grpc_chttp2_list_pop_writing_stream(grpc_chttp2_transport *t,
                                         grpc_chttp2_stream **s);

void grpc_chttp2_list_add_written_stream(grpc_chttp2_transport *t,
                                         grpc_chttp2_stream *s);
bool grpc_chttp2_list_pop_written_stream(grpc_chttp2_transport *t,
                                         grpc_chttp2_stream **s);

void grpc_chttp2_list_add_waiting_for_concurrency(grpc_chttp2_transport *t,
                                                  grpc_chttp2_stream *s);
bool grpc_chttp2_list_pop_waiting_for_concurrency(grpc_chttp2_transport *t,
                                                  grpc_chttp2_stream **s);
void grpc_chttp2_list_remove_waiting_for_concurrency(grpc_chttp2_transport *t,
                                                     grpc_chttp2_stream *s);

void grpc_chttp2_list_add_stalled_by_transport(grpc_chttp2_transport *t,
                                               grpc_chttp2_stream *s);
bool grpc_chttp2_list_pop_stalled_by_transport(grpc_chttp2_transport *t,
                                               grpc_chttp2_stream **s);
void grpc_chttp2_list_remove_stalled_by_transport(grpc_chttp2_transport *t,
                                                  grpc_chttp2_stream *s);

void grpc_chttp2_list_add_stalled_by_stream(grpc_chttp2_transport *t,
                                            grpc_chttp2_stream *s);
bool grpc_chttp2_list_pop_stalled_by_stream(grpc_chttp2_transport *t,
                                            grpc_chttp2_stream **s);
bool grpc_chttp2_list_remove_stalled_by_stream(grpc_chttp2_transport *t,
                                               grpc_chttp2_stream *s);

/********* Flow Control ***************/

// we have sent data on the wire
void grpc_chttp2_flowctl_sent_data(grpc_chttp2_transport_flowctl *tfc,
                                   grpc_chttp2_stream_flowctl *sfc,
                                   int64_t size);

// we have received data from the wire
grpc_error *grpc_chttp2_flowctl_recv_data(grpc_chttp2_transport_flowctl *tfc,
                                          grpc_chttp2_stream_flowctl *sfc,
                                          int64_t incoming_frame_size);

// returns an announce if we should send a transport update to our peer,
// else returns zero
uint32_t grpc_chttp2_flowctl_maybe_send_transport_update(
    grpc_chttp2_transport_flowctl *tfc);

// returns an announce if we should send a stream update to our peer, else
// returns zero
uint32_t grpc_chttp2_flowctl_maybe_send_stream_update(
    grpc_chttp2_transport_flowctl *tfc, grpc_chttp2_stream_flowctl *sfc);

// we have received a WINDOW_UPDATE frame for a transport
void grpc_chttp2_flowctl_recv_transport_update(
    grpc_chttp2_transport_flowctl *tfc, uint32_t size);

// we have received a WINDOW_UPDATE frame for a stream
void grpc_chttp2_flowctl_recv_stream_update(grpc_chttp2_transport_flowctl *tfc,
                                            grpc_chttp2_stream_flowctl *sfc,
                                            uint32_t size);

// the application is asking for a certain amount of bytes
void grpc_chttp2_flowctl_incoming_bs_update(grpc_chttp2_transport_flowctl *tfc,
                                            grpc_chttp2_stream_flowctl *sfc,
                                            size_t max_size_hint,
                                            size_t have_already);

void grpc_chttp2_flowctl_destroy_stream(grpc_chttp2_transport_flowctl *tfc,
                                        grpc_chttp2_stream_flowctl *sfc);

typedef enum {
  // Nothing to be done.
  GRPC_CHTTP2_FLOWCTL_NO_ACTION_NEEDED = 0,
  // Initiate a write to update the initial window immediately.
  GRPC_CHTTP2_FLOWCTL_UPDATE_IMMEDIATELY,
  // Push the flow control update into a send buffer, to be sent
  // out the next time a write is initiated.
  GRPC_CHTTP2_FLOWCTL_QUEUE_UPDATE,
} grpc_chttp2_flowctl_urgency;

typedef struct {
  grpc_chttp2_flowctl_urgency send_stream_update;
  grpc_chttp2_flowctl_urgency send_transport_update;
  grpc_chttp2_flowctl_urgency send_setting_update;
  uint32_t initial_window_size;
  uint32_t max_frame_size;
  bool need_ping;
} grpc_chttp2_flowctl_action;

// Reads the flow control data and returns and actionable struct that will tell
// chttp2 exactly what it needs to do
grpc_chttp2_flowctl_action grpc_chttp2_flowctl_get_action(
    grpc_chttp2_transport_flowctl *tfc, grpc_chttp2_stream_flowctl *sfc);

grpc_chttp2_flowctl_action grpc_chttp2_flowctl_get_bdp_action(
    grpc_chttp2_transport_flowctl *tfc);

// Takes in a flow control action and performs all the needed operations.
void grpc_chttp2_act_on_flowctl_action(grpc_exec_ctx *exec_ctx,
                                       grpc_chttp2_flowctl_action action,
                                       grpc_chttp2_transport *t,
                                       grpc_chttp2_stream *s);

/********* End of Flow Control ***************/

grpc_chttp2_stream *grpc_chttp2_parsing_lookup_stream(grpc_chttp2_transport *t,
                                                      uint32_t id);
grpc_chttp2_stream *grpc_chttp2_parsing_accept_stream(grpc_exec_ctx *exec_ctx,
                                                      grpc_chttp2_transport *t,
                                                      uint32_t id);

void grpc_chttp2_add_incoming_goaway(grpc_exec_ctx *exec_ctx,
                                     grpc_chttp2_transport *t,
                                     uint32_t goaway_error,
                                     grpc_slice goaway_text);

void grpc_chttp2_parsing_become_skip_parser(grpc_exec_ctx *exec_ctx,
                                            grpc_chttp2_transport *t);

void grpc_chttp2_complete_closure_step(grpc_exec_ctx *exec_ctx,
                                       grpc_chttp2_transport *t,
                                       grpc_chttp2_stream *s,
                                       grpc_closure **pclosure,
                                       grpc_error *error, const char *desc);

#define GRPC_HEADER_SIZE_IN_BYTES 5
#define MAX_SIZE_T (~(size_t)0)

#define GRPC_CHTTP2_CLIENT_CONNECT_STRING "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n"
#define GRPC_CHTTP2_CLIENT_CONNECT_STRLEN \
  (sizeof(GRPC_CHTTP2_CLIENT_CONNECT_STRING) - 1)

extern grpc_tracer_flag grpc_http_trace;
extern grpc_tracer_flag grpc_flowctl_trace;

#ifndef NDEBUG
#define GRPC_FLOW_CONTROL_IF_TRACING(stmt)   \
  if (!(GRPC_TRACER_ON(grpc_flowctl_trace))) \
    ;                                        \
  else                                       \
  stmt
#else
#define GRPC_FLOW_CONTROL_IF_TRACING(stmt)
#endif

#define GRPC_CHTTP2_IF_TRACING(stmt)      \
  if (!(GRPC_TRACER_ON(grpc_http_trace))) \
    ;                                     \
  else                                    \
  stmt

void grpc_chttp2_fake_status(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
                             grpc_chttp2_stream *stream, grpc_error *error);
void grpc_chttp2_mark_stream_closed(grpc_exec_ctx *exec_ctx,
                                    grpc_chttp2_transport *t,
                                    grpc_chttp2_stream *s, int close_reads,
                                    int close_writes, grpc_error *error);
void grpc_chttp2_start_writing(grpc_exec_ctx *exec_ctx,
                               grpc_chttp2_transport *t);

#ifndef NDEBUG
#define GRPC_CHTTP2_STREAM_REF(stream, reason) \
  grpc_chttp2_stream_ref(stream, reason)
#define GRPC_CHTTP2_STREAM_UNREF(exec_ctx, stream, reason) \
  grpc_chttp2_stream_unref(exec_ctx, stream, reason)
void grpc_chttp2_stream_ref(grpc_chttp2_stream *s, const char *reason);
void grpc_chttp2_stream_unref(grpc_exec_ctx *exec_ctx, grpc_chttp2_stream *s,
                              const char *reason);
#else
#define GRPC_CHTTP2_STREAM_REF(stream, reason) grpc_chttp2_stream_ref(stream)
#define GRPC_CHTTP2_STREAM_UNREF(exec_ctx, stream, reason) \
  grpc_chttp2_stream_unref(exec_ctx, stream)
void grpc_chttp2_stream_ref(grpc_chttp2_stream *s);
void grpc_chttp2_stream_unref(grpc_exec_ctx *exec_ctx, grpc_chttp2_stream *s);
#endif

#ifndef NDEBUG
#define GRPC_CHTTP2_REF_TRANSPORT(t, r) \
  grpc_chttp2_ref_transport(t, r, __FILE__, __LINE__)
#define GRPC_CHTTP2_UNREF_TRANSPORT(cl, t, r) \
  grpc_chttp2_unref_transport(cl, t, r, __FILE__, __LINE__)
void grpc_chttp2_unref_transport(grpc_exec_ctx *exec_ctx,
                                 grpc_chttp2_transport *t, const char *reason,
                                 const char *file, int line);
void grpc_chttp2_ref_transport(grpc_chttp2_transport *t, const char *reason,
                               const char *file, int line);
#else
#define GRPC_CHTTP2_REF_TRANSPORT(t, r) grpc_chttp2_ref_transport(t)
#define GRPC_CHTTP2_UNREF_TRANSPORT(cl, t, r) grpc_chttp2_unref_transport(cl, t)
void grpc_chttp2_unref_transport(grpc_exec_ctx *exec_ctx,
                                 grpc_chttp2_transport *t);
void grpc_chttp2_ref_transport(grpc_chttp2_transport *t);
#endif

grpc_chttp2_incoming_byte_stream *grpc_chttp2_incoming_byte_stream_create(
    grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t, grpc_chttp2_stream *s,
    uint32_t frame_size, uint32_t flags);
grpc_error *grpc_chttp2_incoming_byte_stream_push(
    grpc_exec_ctx *exec_ctx, grpc_chttp2_incoming_byte_stream *bs,
    grpc_slice slice, grpc_slice *slice_out);
grpc_error *grpc_chttp2_incoming_byte_stream_finished(
    grpc_exec_ctx *exec_ctx, grpc_chttp2_incoming_byte_stream *bs,
    grpc_error *error, bool reset_on_error);
void grpc_chttp2_incoming_byte_stream_notify(
    grpc_exec_ctx *exec_ctx, grpc_chttp2_incoming_byte_stream *bs,
    grpc_error *error);

void grpc_chttp2_ack_ping(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
                          uint64_t id);

/** Add a new ping strike to ping_recv_state.ping_strikes. If
    ping_recv_state.ping_strikes > ping_policy.max_ping_strikes, it sends GOAWAY
    with error code ENHANCE_YOUR_CALM and additional debug data resembling
    "too_many_pings" followed by immediately closing the connection. */
void grpc_chttp2_add_ping_strike(grpc_exec_ctx *exec_ctx,
                                 grpc_chttp2_transport *t);

/** add a ref to the stream and add it to the writable list;
    ref will be dropped in writing.c */
void grpc_chttp2_mark_stream_writable(grpc_exec_ctx *exec_ctx,
                                      grpc_chttp2_transport *t,
                                      grpc_chttp2_stream *s);

void grpc_chttp2_cancel_stream(grpc_exec_ctx *exec_ctx,
                               grpc_chttp2_transport *t, grpc_chttp2_stream *s,
                               grpc_error *due_to_error);

void grpc_chttp2_maybe_complete_recv_initial_metadata(grpc_exec_ctx *exec_ctx,
                                                      grpc_chttp2_transport *t,
                                                      grpc_chttp2_stream *s);
void grpc_chttp2_maybe_complete_recv_message(grpc_exec_ctx *exec_ctx,
                                             grpc_chttp2_transport *t,
                                             grpc_chttp2_stream *s);
void grpc_chttp2_maybe_complete_recv_trailing_metadata(grpc_exec_ctx *exec_ctx,
                                                       grpc_chttp2_transport *t,
                                                       grpc_chttp2_stream *s);

void grpc_chttp2_fail_pending_writes(grpc_exec_ctx *exec_ctx,
                                     grpc_chttp2_transport *t,
                                     grpc_chttp2_stream *s, grpc_error *error);

/** Set the default keepalive configurations, must only be called at
    initialization */
void grpc_chttp2_config_default_keepalive_args(grpc_channel_args *args,
                                               bool is_client);

#endif /* GRPC_CORE_EXT_TRANSPORT_CHTTP2_TRANSPORT_INTERNAL_H */