%% This Source Code Form is subject to the terms of the Mozilla Public
%% License, v. 2.0. If a copy of the MPL was not distributed with this
%% file, You can obtain one at https://mozilla.org/MPL/2.0/.
%%
%% Copyright (c) 2007-2020 VMware, Inc. or its affiliates.  All rights reserved.
%%

%% @type close_reason(Type) = {shutdown, amqp_reason(Type)}.
%% @type amqp_reason(Type) = {Type, Code, Text}
%%      Code = non_neg_integer()
%%      Text = binary().
%% @doc This module encapsulates the client's view of an AMQP
%% channel. Each server side channel is represented by an amqp_channel
%% process on the client side. Channel processes are created using the
%% {@link amqp_connection} module. Channel processes are supervised
%% under amqp_client's supervision tree.<br/>
%% <br/>
%% In case of a failure or an AMQP error, the channel process exits with a
%% meaningful exit reason:<br/>
%% <br/>
%% <table>
%%   <tr>
%%     <td><strong>Cause</strong></td>
%%     <td><strong>Exit reason</strong></td>
%%   </tr>
%%   <tr>
%%     <td>Any reason, where Code would have been 200 otherwise</td>
%%     <td>```normal'''</td>
%%   </tr>
%%   <tr>
%%     <td>User application calls amqp_channel:close/3</td>
%%     <td>```close_reason(app_initiated_close)'''</td>
%%   </tr>
%%   <tr>
%%     <td>Server closes channel (soft error)</td>
%%     <td>```close_reason(server_initiated_close)'''</td>
%%   </tr>
%%   <tr>
%%     <td>Server misbehaved (did not follow protocol)</td>
%%     <td>```close_reason(server_misbehaved)'''</td>
%%   </tr>
%%   <tr>
%%     <td>Connection is closing (causing all channels to cleanup and
%%         close)</td>
%%     <td>```{shutdown, {connection_closing, amqp_reason(atom())}}'''</td>
%%   </tr>
%%   <tr>
%%     <td>Other error</td>
%%     <td>(various error reasons, causing more detailed logging)</td>
%%   </tr>
%% </table>
%% <br/>
%% See type definitions below.
-module(amqp_channel).

-include("amqp_client_internal.hrl").

-behaviour(gen_server).

-export([call/2, call/3, cast/2, cast/3, cast_flow/3]).
-export([close/1, close/3]).
-export([register_return_handler/2, unregister_return_handler/1,
         register_flow_handler/2, unregister_flow_handler/1,
         register_confirm_handler/2, unregister_confirm_handler/1]).
-export([call_consumer/2, subscribe/3]).
-export([next_publish_seqno/1, wait_for_confirms/1, wait_for_confirms/2,
         wait_for_confirms_or_die/1, wait_for_confirms_or_die/2]).
-export([start_link/5, set_writer/2, connection_closing/3, open/1,
         enable_delivery_flow_control/1, notify_received/1]).

-export([init/1, terminate/2, code_change/3, handle_call/3, handle_cast/2,
         handle_info/2]).

-define(TIMEOUT_FLUSH, 60000).

-record(state, {number,
                connection,
                consumer,
                driver,
                rpc_requests       = queue:new(),
                closing            = false, %% false |
                                            %%   {just_channel, Reason} |
                                            %%   {connection, Reason}
                writer,
                return_handler     = none,
                confirm_handler    = none,
                next_pub_seqno     = 0,
                flow_active        = true,
                flow_handler       = none,
                unconfirmed_set    = gb_sets:new(),
                waiting_set        = gb_trees:empty(),
                only_acks_received = true,

                %% true | false, only relevant in the direct
                %% client case.
                %% when true, consumers will manually notify
                %% queue pids using rabbit_amqqueue_common:notify_sent/2
                %% to prevent the queue from overwhelming slow
                %% consumers that use automatic acknowledgement
                %% mode.
                delivery_flow_control = false
               }).

%%---------------------------------------------------------------------------
%% Type Definitions
%%---------------------------------------------------------------------------

%% @type amqp_method().
%% This abstract datatype represents the set of methods that comprise
%% the AMQP execution model. As indicated in the overview, the
%% attributes of each method in the execution model are described in
%% the protocol documentation. The Erlang record definitions are
%% autogenerated from a parseable version of the specification. Most
%% fields in the generated records have sensible default values that
%% you need not worry in the case of a simple usage of the client
%% library.

%% @type amqp_msg() = #amqp_msg{}.
%% This is the content encapsulated in content-bearing AMQP methods. It
%% contains the following fields:
%% <ul>
%% <li>props :: class_property() - A class property record, defaults to
%%     #'P_basic'{}</li>
%% <li>payload :: binary() - The arbitrary data payload</li>
%% </ul>

%%---------------------------------------------------------------------------
%% AMQP Channel API methods
%%---------------------------------------------------------------------------

%% @spec (Channel, Method) -> Result
%% @doc This is equivalent to amqp_channel:call(Channel, Method, none).
call(Channel, Method) ->
    gen_server:call(Channel, {call, Method, none, self()}, amqp_util:call_timeout()).

%% @spec (Channel, Method, Content) -> Result
%% where
%%      Channel = pid()
%%      Method = amqp_method()
%%      Content = amqp_msg() | none
%%      Result = amqp_method() | ok | blocked | closing
%% @doc This sends an AMQP method on the channel.
%% For content bearing methods, Content has to be an amqp_msg(), whereas
%% for non-content bearing methods, it needs to be the atom 'none'.<br/>
%% In the case of synchronous methods, this function blocks until the
%% corresponding reply comes back from the server and returns it.
%% In the case of asynchronous methods, the function blocks until the method
%% gets sent on the wire and returns the atom 'ok' on success.<br/>
%% This will return the atom 'blocked' if the server has
%% throttled the  client for flow control reasons. This will return the
%% atom 'closing' if the channel is in the process of shutting down.<br/>
%% Note that for asynchronous methods, the synchronicity implied by
%% 'call' only means that the client has transmitted the method to
%% the broker. It does not necessarily imply that the broker has
%% accepted responsibility for the message.
call(Channel, Method, Content) ->
    gen_server:call(Channel, {call, Method, Content, self()}, amqp_util:call_timeout()).

%% @spec (Channel, Method) -> ok
%% @doc This is equivalent to amqp_channel:cast(Channel, Method, none).
cast(Channel, Method) ->
    gen_server:cast(Channel, {cast, Method, none, self(), noflow}).

%% @spec (Channel, Method, Content) -> ok
%% where
%%      Channel = pid()
%%      Method = amqp_method()
%%      Content = amqp_msg() | none
%% @doc This function is the same as {@link call/3}, except that it returns
%% immediately with the atom 'ok', without blocking the caller process.
%% This function is not recommended with synchronous methods, since there is no
%% way to verify that the server has received the method.
cast(Channel, Method, Content) ->
    gen_server:cast(Channel, {cast, Method, Content, self(), noflow}).

%% @spec (Channel, Method, Content) -> ok
%% where
%%      Channel = pid()
%%      Method = amqp_method()
%%      Content = amqp_msg() | none
%% @doc Like cast/3, with flow control.
cast_flow(Channel, Method, Content) ->
    credit_flow:send(Channel),
    gen_server:cast(Channel, {cast, Method, Content, self(), flow}).

%% @spec (Channel) -> ok | closing
%% where
%%      Channel = pid()
%% @doc Closes the channel, invokes
%% close(Channel, 200, &lt;&lt;"Goodbye"&gt;&gt;).
close(Channel) ->
    close(Channel, 200, <<"Goodbye">>).

%% @spec (Channel, Code, Text) -> ok | closing
%% where
%%      Channel = pid()
%%      Code = integer()
%%      Text = binary()
%% @doc Closes the channel, allowing the caller to supply a reply code and
%% text. If the channel is already closing, the atom 'closing' is returned.
close(Channel, Code, Text) ->
    gen_server:call(Channel, {close, Code, Text}, amqp_util:call_timeout()).

%% @spec (Channel) -> integer()
%% where
%%      Channel = pid()
%% @doc When in confirm mode, returns the sequence number of the next
%% message to be published.
next_publish_seqno(Channel) ->
    gen_server:call(Channel, next_publish_seqno, amqp_util:call_timeout()).

%% @spec (Channel) -> boolean() | 'timeout'
%% where
%%      Channel = pid()
%% @doc Wait until all messages published since the last call have
%% been either ack'd or nack'd by the broker.  Note, when called on a
%% non-Confirm channel, waitForConfirms returns an error.
wait_for_confirms(Channel) ->
    wait_for_confirms(Channel, amqp_util:call_timeout()).

%% @spec (Channel, Timeout) -> boolean() | 'timeout'
%% where
%%      Channel = pid()
%%      Timeout = non_neg_integer() | 'infinity'
%% @doc Wait until all messages published since the last call have
%% been either ack'd or nack'd by the broker or the timeout expires.
%% Note, when called on a non-Confirm channel, waitForConfirms throws
%% an exception.
wait_for_confirms(Channel, Timeout) ->
    case gen_server:call(Channel, {wait_for_confirms, Timeout}, amqp_util:call_timeout()) of
        {error, Reason} -> throw(Reason);
        Other           -> Other
    end.

%% @spec (Channel) -> true
%% where
%%      Channel = pid()
%% @doc Behaves the same as wait_for_confirms/1, but if a nack is
%% received, the calling process is immediately sent an
%% exit(nack_received).
wait_for_confirms_or_die(Channel) ->
    wait_for_confirms_or_die(Channel, amqp_util:call_timeout()).

%% @spec (Channel, Timeout) -> true
%% where
%%      Channel = pid()
%%      Timeout = non_neg_integer() | 'infinity'
%% @doc Behaves the same as wait_for_confirms/1, but if a nack is
%% received, the calling process is immediately sent an
%% exit(nack_received). If the timeout expires, the calling process is
%% sent an exit(timeout).
wait_for_confirms_or_die(Channel, Timeout) ->
    case wait_for_confirms(Channel, Timeout) of
        timeout -> close(Channel, 200, <<"Confirm Timeout">>),
                   exit(timeout);
        false   -> close(Channel, 200, <<"Nacks Received">>),
                   exit(nacks_received);
        true    -> true
    end.

%% @spec (Channel, ReturnHandler) -> ok
%% where
%%      Channel = pid()
%%      ReturnHandler = pid()
%% @doc This registers a handler to deal with returned messages. The
%% registered process will receive #basic.return{} records.
register_return_handler(Channel, ReturnHandler) ->
    gen_server:cast(Channel, {register_return_handler, ReturnHandler} ).

%% @spec (Channel) -> ok
%% where
%%      Channel = pid()
%% @doc Removes the return handler, if it exists. Does nothing if there is no
%% such handler.
unregister_return_handler(Channel) ->
    gen_server:cast(Channel, unregister_return_handler).

%% @spec (Channel, ConfirmHandler) -> ok
%% where
%%      Channel = pid()
%%      ConfirmHandler = pid()

%% @doc This registers a handler to deal with confirm-related
%% messages. The registered process will receive #basic.ack{} and
%% #basic.nack{} commands.
register_confirm_handler(Channel, ConfirmHandler) ->
    gen_server:cast(Channel, {register_confirm_handler, ConfirmHandler} ).

%% @spec (Channel) -> ok
%% where
%%      Channel = pid()
%% @doc Removes the confirm handler, if it exists. Does nothing if there is no
%% such handler.
unregister_confirm_handler(Channel) ->
    gen_server:cast(Channel, unregister_confirm_handler).

%% @spec (Channel, FlowHandler) -> ok
%% where
%%      Channel = pid()
%%      FlowHandler = pid()
%% @doc This registers a handler to deal with channel flow notifications.
%% The registered process will receive #channel.flow{} records.
register_flow_handler(Channel, FlowHandler) ->
    gen_server:cast(Channel, {register_flow_handler, FlowHandler} ).

%% @spec (Channel) -> ok
%% where
%%      Channel = pid()
%% @doc Removes the flow handler, if it exists. Does nothing if there is no
%% such handler.
unregister_flow_handler(Channel) ->
    gen_server:cast(Channel, unregister_flow_handler).

%% @spec (Channel, Msg) -> ok
%% where
%%      Channel = pid()
%%      Msg    = any()
%% @doc This causes the channel to invoke Consumer:handle_call/2,
%% where Consumer is the amqp_gen_consumer implementation registered with
%% the channel.
call_consumer(Channel, Msg) ->
    gen_server:call(Channel, {call_consumer, Msg}, amqp_util:call_timeout()).

%% @spec (Channel, BasicConsume, Subscriber) -> ok
%% where
%%      Channel = pid()
%%      BasicConsume = amqp_method()
%%      Subscriber = pid()
%% @doc Subscribe the given pid to a queue using the specified
%% basic.consume method.
subscribe(Channel, BasicConsume = #'basic.consume'{}, Subscriber) ->
    gen_server:call(Channel, {subscribe, BasicConsume, Subscriber}, amqp_util:call_timeout()).

%%---------------------------------------------------------------------------
%% Internal interface
%%---------------------------------------------------------------------------

%% @private
start_link(Driver, Connection, ChannelNumber, Consumer, Identity) ->
    gen_server:start_link(
      ?MODULE, [Driver, Connection, ChannelNumber, Consumer, Identity], []).

set_writer(Pid, Writer) ->
    gen_server:cast(Pid, {set_writer, Writer}).

enable_delivery_flow_control(Pid) ->
    gen_server:cast(Pid, enable_delivery_flow_control).

notify_received({Pid, QPid, ServerChPid}) ->
    gen_server:cast(Pid, {send_notify, {QPid, ServerChPid}}).

%% @private
connection_closing(Pid, ChannelCloseType, Reason) ->
    gen_server:cast(Pid, {connection_closing, ChannelCloseType, Reason}).

%% @private
open(Pid) ->
    gen_server:call(Pid, open, amqp_util:call_timeout()).

%%---------------------------------------------------------------------------
%% gen_server callbacks
%%---------------------------------------------------------------------------

%% @private
init([Driver, Connection, ChannelNumber, Consumer, Identity]) ->
    ?store_proc_name(Identity),
    {ok, #state{connection = Connection,
                driver     = Driver,
                number     = ChannelNumber,
                consumer   = Consumer}}.

%% @private
handle_call(open, From, State) ->
    {noreply, rpc_top_half(#'channel.open'{}, none, From, none, noflow, State)};
%% @private
handle_call({close, Code, Text}, From, State) ->
    handle_close(Code, Text, From, State);
%% @private
handle_call({call, Method, AmqpMsg, Sender}, From, State) ->
    handle_method_to_server(Method, AmqpMsg, From, Sender, noflow, State);
%% Handles the delivery of messages from a direct channel
%% @private
handle_call({send_command_sync, Method, Content}, From, State) ->
    Ret = handle_method_from_server(Method, Content, State),
    gen_server:reply(From, ok),
    Ret;
%% Handles the delivery of messages from a direct channel
%% @private
handle_call({send_command_sync, Method}, From, State) ->
    Ret = handle_method_from_server(Method, none, State),
    gen_server:reply(From, ok),
    Ret;
%% @private
handle_call(next_publish_seqno, _From,
            State = #state{next_pub_seqno = SeqNo}) ->
    {reply, SeqNo, State};
handle_call({wait_for_confirms, Timeout}, From, State) ->
    handle_wait_for_confirms(From, Timeout, State);
%% @private
handle_call({call_consumer, Msg}, _From,
            State = #state{consumer = Consumer}) ->
    {reply, amqp_gen_consumer:call_consumer(Consumer, Msg), State};
%% @private
handle_call({subscribe, BasicConsume, Subscriber}, From, State) ->
    handle_method_to_server(BasicConsume, none, From, Subscriber, noflow,
                            State).

%% @private
handle_cast({set_writer, Writer}, State = #state{driver = direct}) ->
    link(Writer),
    {noreply, State#state{writer = Writer}};
handle_cast({set_writer, Writer}, State) ->
    {noreply, State#state{writer = Writer}};
%% @private
handle_cast(enable_delivery_flow_control, State) ->
    {noreply, State#state{delivery_flow_control = true}};
%% @private
handle_cast({send_notify, {QPid, ChPid}}, State) ->
    rabbit_amqqueue_common:notify_sent(QPid, ChPid),
    {noreply, State};
%% @private
handle_cast({cast, Method, AmqpMsg, Sender, noflow}, State) ->
    handle_method_to_server(Method, AmqpMsg, none, Sender, noflow, State);
handle_cast({cast, Method, AmqpMsg, Sender, flow}, State) ->
    credit_flow:ack(Sender),
    handle_method_to_server(Method, AmqpMsg, none, Sender, flow, State);
%% @private
handle_cast({register_return_handler, ReturnHandler}, State) ->
    Ref = erlang:monitor(process, ReturnHandler),
    {noreply, State#state{return_handler = {ReturnHandler, Ref}}};
%% @private
handle_cast(unregister_return_handler,
            State = #state{return_handler = {_ReturnHandler, Ref}}) ->
    erlang:demonitor(Ref),
    {noreply, State#state{return_handler = none}};
%% @private
handle_cast({register_confirm_handler, ConfirmHandler}, State) ->
    Ref = erlang:monitor(process, ConfirmHandler),
    {noreply, State#state{confirm_handler = {ConfirmHandler, Ref}}};
%% @private
handle_cast(unregister_confirm_handler,
            State = #state{confirm_handler = {_ConfirmHandler, Ref}}) ->
    erlang:demonitor(Ref),
    {noreply, State#state{confirm_handler = none}};
%% @private
handle_cast({register_flow_handler, FlowHandler}, State) ->
    Ref = erlang:monitor(process, FlowHandler),
    {noreply, State#state{flow_handler = {FlowHandler, Ref}}};
%% @private
handle_cast(unregister_flow_handler,
            State = #state{flow_handler = {_FlowHandler, Ref}}) ->
    erlang:demonitor(Ref),
    {noreply, State#state{flow_handler = none}};
%% Received from channels manager
%% @private
handle_cast({method, Method, Content, noflow}, State) ->
    handle_method_from_server(Method, Content, State);
%% Handles the situation when the connection closes without closing the channel
%% beforehand. The channel must block all further RPCs,
%% flush the RPC queue (optional), and terminate
%% @private
handle_cast({connection_closing, CloseType, Reason}, State) ->
    handle_connection_closing(CloseType, Reason, State);
%% @private
handle_cast({shutdown, Shutdown}, State) ->
    handle_shutdown(Shutdown, State).

%% Received from rabbit_channel in the direct case
%% @private
handle_info({send_command, Method}, State) ->
    handle_method_from_server(Method, none, State);
%% Received from rabbit_channel in the direct case
%% @private
handle_info({send_command, Method, Content}, State) ->
    handle_method_from_server(Method, Content, State);
%% Received from rabbit_channel in the direct case
%% @private
handle_info({send_command_and_notify, QPid, ChPid,
             Method = #'basic.deliver'{}, Content},
            State = #state{delivery_flow_control = MFC}) ->
    case MFC of
        false -> handle_method_from_server(Method, Content, State),
                 rabbit_amqqueue_common:notify_sent(QPid, ChPid);
        true  -> handle_method_from_server(Method, Content,
                                           {self(), QPid, ChPid}, State)
    end,
    {noreply, State};
%% This comes from the writer or rabbit_channel
%% @private
handle_info({channel_exit, _ChNumber, Reason}, State) ->
    handle_channel_exit(Reason, State);
%% This comes from rabbit_channel in the direct case
handle_info({channel_closing, ChPid}, State) ->
    ok = rabbit_channel_common:ready_for_close(ChPid),
    {noreply, State};
%% @private
handle_info({bump_credit, Msg}, State) ->
    credit_flow:handle_bump_msg(Msg),
    {noreply, State};
%% @private
handle_info(timed_out_flushing_channel, State) ->
    ?LOG_WARN("Channel (~p) closing: timed out flushing while "
              "connection closing~n", [self()]),
    {stop, timed_out_flushing_channel, State};
%% @private
handle_info({'DOWN', _, process, ReturnHandler, shutdown},
            State = #state{return_handler = {ReturnHandler, _Ref}}) ->
    {noreply, State#state{return_handler = none}};
handle_info({'DOWN', _, process, ReturnHandler, Reason},
            State = #state{return_handler = {ReturnHandler, _Ref}}) ->
    ?LOG_WARN("Channel (~p): Unregistering return handler ~p because it died. "
              "Reason: ~p~n", [self(), ReturnHandler, Reason]),
    {noreply, State#state{return_handler = none}};
%% @private
handle_info({'DOWN', _, process, ConfirmHandler, shutdown},
            State = #state{confirm_handler = {ConfirmHandler, _Ref}}) ->
    {noreply, State#state{confirm_handler = none}};
handle_info({'DOWN', _, process, ConfirmHandler, Reason},
            State = #state{confirm_handler = {ConfirmHandler, _Ref}}) ->
    ?LOG_WARN("Channel (~p): Unregistering confirm handler ~p because it died. "
              "Reason: ~p~n", [self(), ConfirmHandler, Reason]),
    {noreply, State#state{confirm_handler = none}};
%% @private
handle_info({'DOWN', _, process, FlowHandler, shutdown},
            State = #state{flow_handler = {FlowHandler, _Ref}}) ->
    {noreply, State#state{flow_handler = none}};
handle_info({'DOWN', _, process, FlowHandler, Reason},
            State = #state{flow_handler = {FlowHandler, _Ref}}) ->
    ?LOG_WARN("Channel (~p): Unregistering flow handler ~p because it died. "
              "Reason: ~p~n", [self(), FlowHandler, Reason]),
    {noreply, State#state{flow_handler = none}};
handle_info({'DOWN', _, process, QPid, _Reason}, State) ->
    rabbit_amqqueue_common:notify_sent_queue_down(QPid),
    {noreply, State};
handle_info({confirm_timeout, From}, State = #state{waiting_set = WSet}) ->
    case gb_trees:lookup(From, WSet) of
        none ->
            {noreply, State};
        {value, _} ->
            gen_server:reply(From, timeout),
            {noreply, State#state{waiting_set = gb_trees:delete(From, WSet)}}
    end.

%% @private
terminate(_Reason, State) ->
    flush_writer(State),
    State.

%% @private
code_change(_OldVsn, State, _Extra) ->
    {ok, State}.

%%---------------------------------------------------------------------------
%% RPC mechanism
%%---------------------------------------------------------------------------

handle_method_to_server(Method, AmqpMsg, From, Sender, Flow,
                        State = #state{unconfirmed_set = USet}) ->
    case {check_invalid_method(Method), From,
          check_block(Method, AmqpMsg, State)} of
        {ok, _, ok} ->
            State1 = case {Method, State#state.next_pub_seqno} of
                         {#'confirm.select'{}, 0} ->
                             %% The confirm seqno is set to 1 on the
                             %% first confirm.select only.
                             State#state{next_pub_seqno = 1};
                         {#'basic.publish'{}, 0} ->
                             State;
                         {#'basic.publish'{}, SeqNo} ->
                             State#state{unconfirmed_set =
                                             gb_sets:add(SeqNo, USet),
                                         next_pub_seqno = SeqNo + 1};
                         _ ->
                             State
                     end,
            {noreply, rpc_top_half(Method, build_content(AmqpMsg),
                                   From, Sender, Flow, State1)};
        {ok, none, BlockReply} ->
            ?LOG_WARN("Channel (~p): discarding method ~p in cast.~n"
                      "Reason: ~p~n", [self(), Method, BlockReply]),
            {noreply, State};
        {ok, _, BlockReply} ->
            {reply, BlockReply, State};
        {{_, InvalidMethodMessage}, none, _} ->
            ?LOG_WARN("Channel (~p): ignoring cast of ~p method. " ++
                      InvalidMethodMessage ++ "~n", [self(), Method]),
            {noreply, State};
        {{InvalidMethodReply, _}, _, _} ->
            {reply, {error, InvalidMethodReply}, State}
    end.

handle_close(Code, Text, From, State) ->
    Close = #'channel.close'{reply_code = Code,
                             reply_text = Text,
                             class_id   = 0,
                             method_id  = 0},
    case check_block(Close, none, State) of
        ok         -> {noreply, rpc_top_half(Close, none, From, none, noflow,
                                             State)};
        BlockReply -> {reply, BlockReply, State}
    end.

rpc_top_half(Method, Content, From, Sender, Flow,
             State0 = #state{rpc_requests = RequestQueue}) ->
    State1 = State0#state{
        rpc_requests = queue:in({From, Sender, Method, Content, Flow},
                                RequestQueue)},
    IsFirstElement = queue:is_empty(RequestQueue),
    if IsFirstElement -> do_rpc(State1);
       true           -> State1
    end.

rpc_bottom_half(Reply, State = #state{rpc_requests = RequestQueue}) ->
    {{value, {From, _Sender, _Method, _Content, _Flow}}, RequestQueue1} =
        queue:out(RequestQueue),
    case From of
        none -> ok;
        _    -> gen_server:reply(From, Reply)
    end,
    do_rpc(State#state{rpc_requests = RequestQueue1}).

do_rpc(State = #state{rpc_requests = Q,
                      closing      = Closing}) ->
    case queue:out(Q) of
        {{value, {From, Sender, Method, Content, Flow}}, NewQ} ->
            State1 = pre_do(Method, Content, Sender, State),
            DoRet = do(Method, Content, Flow, State1),
            case ?PROTOCOL:is_method_synchronous(Method) of
                true  -> State1;
                false -> case {From, DoRet} of
                             {none, _} -> ok;
                             {_, ok}   -> gen_server:reply(From, ok);
                             _         -> ok
                             %% Do not reply if error in do. Expecting
                             %% {channel_exit, _, _}
                         end,
                         do_rpc(State1#state{rpc_requests = NewQ})
            end;
        {empty, NewQ} ->
            case Closing of
                {connection, Reason} ->
                    gen_server:cast(self(),
                                    {shutdown, {connection_closing, Reason}});
                _ ->
                    ok
            end,
            State#state{rpc_requests = NewQ}
    end.

pending_rpc_method(#state{rpc_requests = Q}) ->
    {value, {_From, _Sender, Method, _Content, _Flow}} = queue:peek(Q),
    Method.

pre_do(#'channel.close'{reply_code = Code, reply_text = Text}, none,
       _Sender, State) ->
    State#state{closing = {just_channel, {app_initiated_close, Code, Text}}};
pre_do(#'basic.consume'{} = Method, none, Sender, State) ->
    ok = call_to_consumer(Method, Sender, State),
    State;
pre_do(#'basic.cancel'{} = Method, none, Sender, State) ->
    ok = call_to_consumer(Method, Sender, State),
    State;
pre_do(_, _, _, State) ->
    State.

%%---------------------------------------------------------------------------
%% Handling of methods from the server
%%---------------------------------------------------------------------------

safely_handle_method_from_server(Method, Content,
                                 Continuation,
                                 State = #state{closing = Closing}) ->
    case is_connection_method(Method) of
        true -> server_misbehaved(
                    #amqp_error{name        = command_invalid,
                                explanation = "connection method on "
                                              "non-zero channel",
                                method      = element(1, Method)},
                    State);
        false -> Drop = case {Closing, Method} of
                            {{just_channel, _}, #'channel.close'{}}    -> false;
                            {{just_channel, _}, #'channel.close_ok'{}} -> false;
                            {{just_channel, _}, _}                     -> true;
                            _                                          -> false
                        end,
                 if Drop -> ?LOG_INFO("Channel (~p): dropping method ~p from "
                                      "server because channel is closing~n",
                                      [self(), {Method, Content}]),
                            {noreply, State};
                    true ->
                         Continuation()
                 end
    end.

handle_method_from_server(Method, Content, State) ->
    Fun = fun () ->
                  handle_method_from_server1(Method,
                                             amqp_msg(Content), State)
          end,
    safely_handle_method_from_server(Method, Content, Fun, State).

handle_method_from_server(Method = #'basic.deliver'{},
                          Content, DeliveryCtx, State) ->
    Fun = fun () ->
                  handle_method_from_server1(Method,
                                             amqp_msg(Content),
                                             DeliveryCtx,
                                             State)
          end,
    safely_handle_method_from_server(Method, Content, Fun, State).

handle_method_from_server1(#'channel.open_ok'{}, none, State) ->
    {noreply, rpc_bottom_half(ok, State)};
handle_method_from_server1(#'channel.close'{reply_code = Code,
                                            reply_text = Text},
                           none,
                           State = #state{closing = {just_channel, _}}) ->
    %% Both client and server sent close at the same time. Don't shutdown yet,
    %% wait for close_ok.
    do(#'channel.close_ok'{}, none, noflow, State),
    {noreply,
     State#state{
         closing = {just_channel, {server_initiated_close, Code, Text}}}};
handle_method_from_server1(#'channel.close'{reply_code = Code,
                                            reply_text = Text}, none, State) ->
    do(#'channel.close_ok'{}, none, noflow, State),
    handle_shutdown({server_initiated_close, Code, Text}, State);
handle_method_from_server1(#'channel.close_ok'{}, none,
                           State = #state{closing = Closing}) ->
    case Closing of
        {just_channel, {app_initiated_close, _, _} = Reason} ->
            handle_shutdown(Reason, rpc_bottom_half(ok, State));
        {just_channel, {server_initiated_close, _, _} = Reason} ->
            handle_shutdown(Reason,
                            rpc_bottom_half(closing, State));
        {connection, Reason} ->
            handle_shutdown({connection_closing, Reason}, State)
    end;
handle_method_from_server1(#'basic.consume_ok'{} = ConsumeOk, none, State) ->
    Consume = #'basic.consume'{} = pending_rpc_method(State),
    ok = call_to_consumer(ConsumeOk, Consume, State),
    {noreply, rpc_bottom_half(ConsumeOk, State)};
handle_method_from_server1(#'basic.cancel_ok'{} = CancelOk, none, State) ->
    Cancel = #'basic.cancel'{} = pending_rpc_method(State),
    ok = call_to_consumer(CancelOk, Cancel, State),
    {noreply, rpc_bottom_half(CancelOk, State)};
handle_method_from_server1(#'basic.cancel'{} = Cancel, none, State) ->
    ok = call_to_consumer(Cancel, none, State),
    {noreply, State};
handle_method_from_server1(#'basic.deliver'{} = Deliver, AmqpMsg, State) ->
    ok = call_to_consumer(Deliver, AmqpMsg, State),
    {noreply, State};
handle_method_from_server1(#'channel.flow'{active = Active} = Flow, none,
                           State = #state{flow_handler = FlowHandler}) ->
    case FlowHandler of none        -> ok;
                        {Pid, _Ref} -> Pid ! Flow
    end,
    %% Putting the flow_ok in the queue so that the RPC queue can be
    %% flushed beforehand. Methods that made it to the queue are not
    %% blocked in any circumstance.
    {noreply, rpc_top_half(#'channel.flow_ok'{active = Active}, none, none,
                           none, noflow, State#state{flow_active = Active})};
handle_method_from_server1(
        #'basic.return'{} = BasicReturn, AmqpMsg,
        State = #state{return_handler = ReturnHandler}) ->
    case ReturnHandler of
        none        -> ?LOG_WARN("Channel (~p): received {~p, ~p} but there is "
                                 "no return handler registered~n",
                                 [self(), BasicReturn, AmqpMsg]);
        {Pid, _Ref} -> Pid ! {BasicReturn, AmqpMsg}
    end,
    {noreply, State};
handle_method_from_server1(#'basic.ack'{} = BasicAck, none,
                           #state{confirm_handler = none} = State) ->
    {noreply, update_confirm_set(BasicAck, State)};
handle_method_from_server1(#'basic.ack'{} = BasicAck, none,
                           #state{confirm_handler = {CH, _Ref}} = State) ->
    CH ! BasicAck,
    {noreply, update_confirm_set(BasicAck, State)};
handle_method_from_server1(#'basic.nack'{} = BasicNack, none,
                           #state{confirm_handler = none} = State) ->
    ?LOG_WARN("Channel (~p): received ~p but there is no "
              "confirm handler registered~n", [self(), BasicNack]),
    {noreply, update_confirm_set(BasicNack, State)};
handle_method_from_server1(#'basic.nack'{} = BasicNack, none,
                           #state{confirm_handler = {CH, _Ref}} = State) ->
    CH ! BasicNack,
    {noreply, update_confirm_set(BasicNack, State)};

handle_method_from_server1(#'basic.credit_drained'{} = CreditDrained, none,
                           #state{consumer = Consumer} = State) ->
    Consumer ! CreditDrained,
    {noreply, State};
handle_method_from_server1(Method, none, State) ->
    {noreply, rpc_bottom_half(Method, State)};
handle_method_from_server1(Method, Content, State) ->
    {noreply, rpc_bottom_half({Method, Content}, State)}.

%% only used with manual consumer-to-queue flow control
handle_method_from_server1(#'basic.deliver'{} = Deliver, AmqpMsg,
                           DeliveryCtx, State) ->
    ok = call_to_consumer(Deliver, AmqpMsg, DeliveryCtx, State),
    {noreply, State}.

%%---------------------------------------------------------------------------
%% Other handle_* functions
%%---------------------------------------------------------------------------

handle_connection_closing(CloseType, Reason,
                          State = #state{rpc_requests = RpcQueue,
                                         closing      = Closing}) ->
    NewState = State#state{closing = {connection, Reason}},
    case {CloseType, Closing, queue:is_empty(RpcQueue)} of
        {flush, false, false} ->
            erlang:send_after(?TIMEOUT_FLUSH, self(),
                              timed_out_flushing_channel),
            {noreply, NewState};
        {flush, {just_channel, _}, false} ->
            {noreply, NewState};
        _ ->
            handle_shutdown({connection_closing, Reason}, NewState)
    end.

handle_channel_exit(Reason = #amqp_error{name = ErrorName, explanation = Expl},
                    State = #state{connection = Connection, number = Number}) ->
    %% Sent by rabbit_channel for hard errors in the direct case
    ?LOG_ERR("connection ~p, channel ~p - error:~n~p~n",
             [Connection, Number, Reason]),
    {true, Code, _} = ?PROTOCOL:lookup_amqp_exception(ErrorName),
    ReportedReason = {server_initiated_close, Code, Expl},
    amqp_gen_connection:hard_error_in_channel(
      Connection, self(), ReportedReason),
    handle_shutdown({connection_closing, ReportedReason}, State);
handle_channel_exit(Reason, State) ->
    %% Unexpected death of a channel infrastructure process
    {stop, {infrastructure_died, Reason}, State}.

handle_shutdown({_, 200, _}, State) ->
    {stop, normal, State};
handle_shutdown({connection_closing, {_, 200, _}}, State) ->
    {stop, normal, State};
handle_shutdown({connection_closing, normal}, State) ->
    {stop, normal, State};
handle_shutdown(Reason, State) ->
    {stop, {shutdown, Reason}, State}.

%%---------------------------------------------------------------------------
%% Internal plumbing
%%---------------------------------------------------------------------------

do(Method, Content, Flow, #state{driver = network, writer = W}) ->
    %% Catching because it expects the {channel_exit, _, _} message on error
    catch case {Content, Flow} of
              {none, _}      -> rabbit_writer:send_command(W, Method);
              {_,    flow}   -> rabbit_writer:send_command_flow(W, Method,
                                                                Content);
              {_,    noflow} -> rabbit_writer:send_command(W, Method, Content)
          end;
do(Method, Content, Flow, #state{driver = direct, writer = W}) ->
    %% ditto catching because...
    catch case {Content, Flow} of
              {none, _}      -> rabbit_channel_common:do(W, Method);
              {_,    flow}   -> rabbit_channel_common:do_flow(W, Method, Content);
              {_,    noflow} -> rabbit_channel_common:do(W, Method, Content)
          end.


flush_writer(#state{driver = network, writer = Writer}) ->
    try
        rabbit_writer:flush(Writer)
    catch
        exit:noproc -> ok
    end;
flush_writer(#state{driver = direct}) ->
    ok.
amqp_msg(none) ->
    none;
amqp_msg(Content) ->
    {Props, Payload} = rabbit_basic_common:from_content(Content),
    #amqp_msg{props = Props, payload = Payload}.

build_content(none) ->
    none;
build_content(#amqp_msg{props = Props, payload = Payload}) ->
    rabbit_basic_common:build_content(Props, Payload).

check_block(_Method, _AmqpMsg, #state{closing = {just_channel, _}}) ->
    closing;
check_block(_Method, _AmqpMsg, #state{closing = {connection, _}}) ->
    closing;
check_block(_Method, none, #state{}) ->
    ok;
check_block(_Method, #amqp_msg{}, #state{flow_active = false}) ->
    blocked;
check_block(_Method, _AmqpMsg, #state{}) ->
    ok.

check_invalid_method(#'channel.open'{}) ->
    {use_amqp_connection_module,
     "Use amqp_connection:open_channel/{1,2} instead"};
check_invalid_method(#'channel.close'{}) ->
    {use_close_function, "Use close/{1,3} instead"};
check_invalid_method(Method) ->
    case is_connection_method(Method) of
        true  -> {connection_methods_not_allowed,
                  "Sending connection methods is not allowed"};
        false -> ok
    end.

is_connection_method(Method) ->
    {ClassId, _} = ?PROTOCOL:method_id(element(1, Method)),
    ?PROTOCOL:lookup_class_name(ClassId) == connection.

server_misbehaved(#amqp_error{} = AmqpError, State = #state{number = Number}) ->
    case rabbit_binary_generator:map_exception(Number, AmqpError, ?PROTOCOL) of
        {0, _} ->
            handle_shutdown({server_misbehaved, AmqpError}, State);
        {_, Close} ->
            ?LOG_WARN("Channel (~p) flushing and closing due to soft "
                      "error caused by the server ~p~n", [self(), AmqpError]),
            Self = self(),
            spawn(fun () -> call(Self, Close) end),
            {noreply, State}
    end.

update_confirm_set(#'basic.ack'{delivery_tag = SeqNo,
                                multiple     = Multiple},
                   State = #state{unconfirmed_set = USet}) ->
    maybe_notify_waiters(
      State#state{unconfirmed_set =
                      update_unconfirmed(SeqNo, Multiple, USet)});
update_confirm_set(#'basic.nack'{delivery_tag = SeqNo,
                                 multiple     = Multiple},
                   State = #state{unconfirmed_set = USet}) ->
    maybe_notify_waiters(
      State#state{unconfirmed_set = update_unconfirmed(SeqNo, Multiple, USet),
                  only_acks_received = false}).

update_unconfirmed(SeqNo, false, USet) ->
    gb_sets:del_element(SeqNo, USet);
update_unconfirmed(SeqNo, true, USet) ->
    case gb_sets:is_empty(USet) of
        true  -> USet;
        false -> {S, USet1} = gb_sets:take_smallest(USet),
                 case S > SeqNo of
                     true  -> USet;
                     false -> update_unconfirmed(SeqNo, true, USet1)
                 end
    end.

maybe_notify_waiters(State = #state{unconfirmed_set = USet}) ->
    case gb_sets:is_empty(USet) of
        false -> State;
        true  -> notify_confirm_waiters(State)
    end.

notify_confirm_waiters(State = #state{waiting_set        = WSet,
                                      only_acks_received = OAR}) ->
    [begin
         safe_cancel_timer(TRef),
         gen_server:reply(From, OAR)
     end || {From, TRef} <- gb_trees:to_list(WSet)],
    State#state{waiting_set        = gb_trees:empty(),
                only_acks_received = true}.

handle_wait_for_confirms(_From, _Timeout, State = #state{next_pub_seqno = 0}) ->
    {reply, {error, not_in_confirm_mode}, State};
handle_wait_for_confirms(From, Timeout,
                         State = #state{unconfirmed_set = USet,
                                        waiting_set     = WSet}) ->
    case gb_sets:is_empty(USet) of
        true  -> {reply, true, State};
        false -> TRef = case Timeout of
                            infinity -> undefined;
                            _        -> erlang:send_after(
                                          Timeout * 1000, self(),
                                          {confirm_timeout, From})
                        end,
                 {noreply,
                  State#state{waiting_set = gb_trees:insert(From, TRef, WSet)}}
    end.

call_to_consumer(Method, Args, #state{consumer = Consumer}) ->
    amqp_gen_consumer:call_consumer(Consumer, Method, Args).

call_to_consumer(Method, Args, DeliveryCtx, #state{consumer = Consumer}) ->
    amqp_gen_consumer:call_consumer(Consumer, Method, Args, DeliveryCtx).

safe_cancel_timer(undefined) -> ok;
safe_cancel_timer(TRef)      -> erlang:cancel_timer(TRef).

