Class | AMQP::Channel
In: | lib/amqp/channel.rb
Parent: | AMQ::Client::Channel

h2. What are AMQP channels

To quote {bit.ly/hw2ELX AMQP 0.9.1 specification}:

AMQP is a multi-channelled protocol. Channels provide a way to multiplex a heavyweight TCP/IP connection into several light weight connections. This makes the protocol more “firewall friendly” since port usage is predictable. It also means that traffic shaping and other network QoS features can be easily employed. Channels are independent of each other and can perform different functions simultaneously with other channels, the available bandwidth being shared between the concurrent activities.

h2. Opening a channel

*Channels are opened asynchronously*. There are two ways to do it: using a callback or pseudo-synchronous mode.

@example Opening a channel with a callback

      # this assumes EventMachine reactor is running
      AMQP.connect("amqp://guest:guest@dev.rabbitmq.com:5672") do |client|
        AMQP::Channel.new(client) do |channel, open_ok|
          # when this block is executed, channel is open and ready for use
        end
      end

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Unless your application needs multiple channels, this approach is recommended. Alternatively, AMQP::Channel can be instantiated without a block. Then returned channel is not immediately open, however, it can be used as if it was a synchronous, blocking method:

@example Instantiating a channel that will be open eventually

      # this assumes EventMachine reactor is running
      AMQP.connect("amqp://guest:guest@dev.rabbitmq.com:5672") do |client|
        channel  = AMQP::Channel.new(client)
        exchange = channel.default_exchange

        # ...
      end

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Even though in the example above channel isn‘t immediately open, it is safe to declare exchanges using it. Exchange declaration will be delayed until after channel is open. Same applies to queue declaration and other operations on exchanges and queues. Library methods that rely on channel being open will be enqueued and executed in a FIFO manner when broker confirms channel opening. Note, however, that *this "pseudo-synchronous mode" is easy to abuse and introduce race conditions AMQP gem cannot resolve for you*. AMQP is an inherently asynchronous protocol and AMQP gem embraces this fact.

h2. Key methods

Key methods of Channel class are

- {Channel#queue}
- {Channel#default_exchange}
- {Channel#direct}
- {Channel#fanout}
- {Channel#topic}
- {Channel#close}

refer to documentation for those methods for usage examples.

Channel provides a number of convenience methods that instantiate queues and exchanges of various types associated with this channel:

- {Channel#queue}
- {Channel#default_exchange}
- {Channel#direct}
- {Channel#fanout}
- {Channel#topic}

h2. Error handling

It is possible (and, indeed, recommended) to handle channel-level exceptions by defining an errback using on_error:

@example Queue declaration with incompatible attributes results in a channel-level exception

      AMQP.start("amqp://guest:guest@dev.rabbitmq.com:5672") do |connection, open_ok|
        AMQP::Channel.new do |channel, open_ok|
          puts "Channel ##{channel.id} is now open!"

          channel.on_error do |ch, close|
            puts "Handling channel-level exception"

            connection.close {
              EM.stop { exit }
            }
          end

          EventMachine.add_timer(0.4) do
            # these two definitions result in a race condition. For sake of this example,
            # however, it does not matter. Whatever definition succeeds first, 2nd one will
            # cause a channel-level exception (because attributes are not identical)
            AMQP::Queue.new(channel, "amqpgem.examples.channel_exception", :auto_delete => true, :durable => false) do |queue|
              puts "#{queue.name} is ready to go"
            end

            AMQP::Queue.new(channel, "amqpgem.examples.channel_exception", :auto_delete => true, :durable => true) do |queue|
              puts "#{queue.name} is ready to go"
            end
          end
        end
      end

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When channel-level exception is indicated by the broker and errback defined using on_error is run, channel is already closed and all queue and exchange objects associated with this channel are reset. The recommended way to recover from channel-level exceptions is to open a new channel and re-instantiate queues, exchanges and bindings your application needs.

h2. Closing a channel

Channels are opened when objects is instantiated and closed using {close} method when application no longer needs it.

@example Closing a channel your application no longer needs

      # this assumes EventMachine reactor is running
      AMQP.connect("amqp://guest:guest@dev.rabbitmq.com:5672") do |client|
        AMQP::Channel.new(client) do |channel, open_ok|
          channel.close do |close_ok|
            # when this block is executed, channel is successfully closed
          end
        end
      end

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h2. RabbitMQ extensions.

AMQP gem supports several RabbitMQ extensions taht extend Channel functionality. Learn more in {file:docs/VendorSpecificExtensions.textile}

@see bit.ly/hw2ELX AMQP 0.9.1 specification (Section 2.2.5)

### Methods

acknowledge auto_recover auto_recovering? channel_id_mutex close default default_exchange direct error fanout find_rpc flow flow_is_active? handle_close handle_close_ok handle_connection_interruption headers id initialize_channel_id_allocator method_missing new next_channel_id on_error on_error once_open once_opened open open? prefetch queue queue! queues recover register_rpc reject release_channel_id reset reset_channel_id_allocator reset_state! reuse rpc rpcs topic tx_commit tx_rollback tx_select validate_parameters_match!

### External Aliases

connection | -> | conn

### Attributes

auto_recovery | [RW] | @return [Boolean] true if this channel is in automatic recovery mode @see auto_recovering?
connection | [R] | AMQP connection this channel is part of @return [Connection]
status | [R] | Status of this channel (one of: :opening, :closing, :open, :closed) @return [Symbol]

### Public Class methods

channel_id_mutex()

@private @api private

default()

@private @deprecated

error(msg = nil, &block)

Defines a global callback to be run on channel-level exception across all channels. Consider using Channel#on_error instead. This method is here for sake of backwards compatibility with 0.6.x and 0.7.x releases.

@param [String] msg Error message that passed to previously defined handler

@deprecated @api public @private

id()

unique identifier of the default thread-local channel @deprecated @private

initialize_channel_id_allocator()

@private

method_missing(meth, *args, &blk)

Allows for calls to all MQ instance methods. This implicitly calls AMQP::Channel.new so that a new channel is allocated for subsequent operations. @deprecated

new(connection = nil, id = self.class.next_channel_id, options = {}, &block)

@param [AMQP::Session] connection Connection to open this channel on. If not given, default AMQP

                                      connection (accessible via {AMQP.connection}) will be used.

@param [Integer] id Channel id. Must not be greater than max channel id client and broker

                                      negotiated on during connection setup. Almost always the right thing to do
                                      is to let AMQP gem pick channel identifier for you. If you want to get next
                                      channel id, use {AMQP::Channel.next_channel_id} (it is thread-safe).

@param [Hash] options A hash of options

@example Instantiating a channel for default connection (accessible as AMQP.connection)

      AMQP.connect do |connection|
        AMQP::Channel.new(connection) do |channel, open_ok|
          # channel is ready: set up your messaging flow by creating exchanges,
          # queues, binding them together and so on.
        end
      end

@example Instantiating a channel for explicitly given connection

      AMQP.connect do |connection|
        AMQP::Channel.new(connection) do |channel, open_ok|
          # ...
        end
      end

@example Instantiating a channel with a :prefetch option

      AMQP.connect do |connection|
        AMQP::Channel.new(connection, AMQP::Channel.next_channel_id, :prefetch => 5) do |channel, open_ok|
          # ...
        end
      end

@option options [Boolean] :prefetch (nil) Specifies number of messages to prefetch. Channel-specific. See {AMQP::Channel#prefetch}. @option options [Boolean] :auto_recovery (nil) Turns on automatic network failure recovery mode for this channel.

@yield [channel, open_ok] Yields open channel instance and AMQP method (channel.open-ok) instance. The latter is optional. @yieldparam [Channel] channel Channel that is successfully open @yieldparam [AMQP::Protocol::Channel::OpenOk] open_ok AMQP channel.open-ok) instance

@see AMQP::Channel#prefetch @api public

next_channel_id()

Returns next available channel id. This method is thread safe.

@return [Fixnum] @api public @see Channel.release_channel_id @see Channel.reset_channel_id_allocator

on_error(&block)

Defines a global callback to be run on channel-level exception across all channels. Consider using Channel#on_error instead. This method is here for sake of backwards compatibility with 0.6.x and 0.7.x releases. @see AMQP::Channel#on_error @deprecated @api public

release_channel_id(i)

Releases previously allocated channel id. This method is thread safe.

@param [Fixnum] Channel id to release @api public @see Channel.next_channel_id @see Channel.reset_channel_id_allocator

reset_channel_id_allocator()

Resets channel allocator. This method is thread safe. @api public @see Channel.next_channel_id @see Channel.release_channel_id

### Public Instance methods

acknowledge(delivery_tag, multiple = false)

Acknowledge one or all messages on the channel.

@api public @see reject @see recover @see bit.ly/htCzCX AMQP 0.9.1 protocol documentation (Section 1.8.3.13.)

auto_recover()

Called by associated connection object when AMQP connection has been re-established (for example, after a network failure).

@api plugin

auto_recovering?()

@return [Boolean] true if this channel uses automatic recovery mode

close(reply_code = 200, reply_text = DEFAULT_REPLY_TEXT, class_id = 0, method_id = 0, &block)

Closes AMQP channel.

@api public

default_exchange()

Returns exchange object with the same name as default (aka unnamed) exchange. Default exchange is a direct exchange and automatically routes messages to queues when routing key matches queue name exactly. This feature is known as "automatic binding" (of queues to default exchange).

*Use default exchange when you want to route messages directly to specific queues* (queue names are known, you don‘t mind this kind of coupling between applications).

@example Using default exchange to publish messages to queues with known names

      AMQP.start(:host => 'localhost') do |connection|
        ch        = AMQP::Channel.new(connection)

        queue1    = ch.queue("queue1").subscribe do |payload|
          puts "[#{queue1.name}] => #{payload}"
        end
        queue2    = ch.queue("queue2").subscribe do |payload|
          puts "[#{queue2.name}] => #{payload}"
        end
        queue3    = ch.queue("queue3").subscribe do |payload|
          puts "[#{queue3.name}] => #{payload}"
        end
        queues    = [queue1, queue2, queue3]

        # Rely on default direct exchange binding, see section 2.1.2.4 Automatic Mode in AMQP 0.9.1 spec.
        exchange = AMQP::Exchange.default
        EM.add_periodic_timer(1) do
          q = queues.sample

          exchange.publish "Some payload from #{Time.now.to_i}", :routing_key => q.name
        end
      end

@see Exchange @see bit.ly/hw2ELX AMQP 0.9.1 specification (Section 2.1.2.4)

@return [Exchange] @api public

direct(name = 'amq.direct', opts = {}, &block)

Defines, intializes and returns a direct Exchange instance.

Learn more about direct exchanges in {Exchange Exchange class documentation}.

@param [String] name (amq.direct) Exchange name.

@option opts [Boolean] :passive (false) If set, the server will not create the exchange if it does not

                                             already exist. The client can use this to check whether an exchange
                                             exists without modifying the server state.

@option opts [Boolean] :durable (false) If set when creating a new exchange, the exchange will be marked as

                                             durable. Durable exchanges and their bindings are recreated upon a server
                                             restart (information about them is persisted). Non-durable (transient) exchanges
                                             do not survive if/when a server restarts (information about them is stored exclusively
                                             in RAM).

@option opts [Boolean] :auto_delete (false) If set, the exchange is deleted when all queues have finished

                                                  using it. The server waits for a short period of time before
                                                  determining the exchange is unused to give time to the client code
                                                  to bind a queue to it.

@option opts [Boolean] :internal (default false) If set, the exchange may not be used directly by publishers, but

                                                       only when bound to other exchanges. Internal exchanges are used to
                                                       construct wiring that is not visible to applications. This is a RabbitMQ-specific
                                                       extension.

@option opts [Boolean] :nowait (true) If set, the server will not respond to the method. The client should

                                                       not wait for a reply method.  If the server could not complete the
                                                       method it will raise a channel or connection exception.

@raise [AMQP::Error] Raised when exchange is redeclared with parameters different from original declaration. @raise [AMQP::Error] Raised when exchange is declared with :passive => true and the exchange does not exist.

@example Using default pre-declared direct exchange and no callbacks (pseudo-synchronous style)

       # an exchange application A will be using to publish updates
       # to some search index
       exchange = channel.direct("index.updates")

       # In the same (or different) process declare a queue that broker will
       # generate name for, bind it to aforementioned exchange using method chaining
       queue    = channel.queue("").
                          # queue will be receiving messages that were published with
                          # :routing_key attribute value of "search.index.updates"
                          bind(exchange, :routing_key => "search.index.updates").
                          # register a callback that will be run when messages arrive
                          subscribe { |header, message| puts("Received #{message}") }

       # now publish a new document contents for indexing,
       # message will be delivered to the queue we declared and bound on the line above
       exchange.publish(document.content, :routing_key => "search.index.updates")

@example Instantiating a direct exchange using {Channel#direct} with a callback

      AMQP.connect do |connection|
        AMQP::Channel.new(connection) do |channel|
          channel.direct("email.replies_listener") do |exchange, declare_ok|
            # by now exchange is ready and waiting
          end
        end
      end

@see Channel#default_exchange @see Exchange @see Exchange#initialize @see bit.ly/hw2ELX AMQP 0.9.1 specification (Section 3.1.3.1)

@return [Exchange] @api public

fanout(name = 'amq.fanout', opts = {}, &block)

Defines, intializes and returns a fanout Exchange instance.

Learn more about fanout exchanges in {Exchange Exchange class documentation}.

@param [String] name (amq.fanout) Exchange name.

@option opts [Boolean] :passive (false) If set, the server will not create the exchange if it does not

                                             already exist. The client can use this to check whether an exchange
                                             exists without modifying the server state.

@option opts [Boolean] :durable (false) If set when creating a new exchange, the exchange will be marked as

                                             durable. Durable exchanges and their bindings are recreated upon a server
                                             restart (information about them is persisted). Non-durable (transient) exchanges
                                             do not survive if/when a server restarts (information about them is stored exclusively
                                             in RAM).

@option opts [Boolean] :auto_delete (false) If set, the exchange is deleted when all queues have finished

                                                  using it. The server waits for a short period of time before
                                                  determining the exchange is unused to give time to the client code
                                                  to bind a queue to it.

@option opts [Boolean] :internal (default false) If set, the exchange may not be used directly by publishers, but

                                                       only when bound to other exchanges. Internal exchanges are used to
                                                       construct wiring that is not visible to applications. This is a RabbitMQ-specific
                                                       extension.

@option opts [Boolean] :nowait (true) If set, the server will not respond to the method. The client should

                                                       not wait for a reply method.  If the server could not complete the
                                                       method it will raise a channel or connection exception.

@raise [AMQP::Error] Raised when exchange is redeclared with parameters different from original declaration. @raise [AMQP::Error] Raised when exchange is declared with :passive => true and the exchange does not exist.

@example Using fanout exchange to deliver messages to multiple consumers

      # open up a channel
      # declare a fanout exchange
      # declare 3 queues, binds them
      # publish a message

@see Exchange @see Exchange#initialize @see Channel#default_exchange @see bit.ly/hw2ELX AMQP 0.9.1 specification (Section 3.1.3.2)

@return [Exchange] @api public

find_rpc(name)

@private @api plugin

flow(active = false, &block)

Asks the peer to pause or restart the flow of content data sent to a consumer. This is a simple flowcontrol mechanism that a peer can use to avoid overflowing its queues or otherwise finding itself receiving more messages than it can process. Note that this method is not intended for window control. It does not affect contents returned to Queue#get callers.

@param [Boolean] Desired flow state.

@see bit.ly/htCzCX AMQP 0.9.1 protocol documentation (Section 1.5.2.3.) @api public

flow_is_active?()

@return [Boolean] True if flow in this channel is active (messages will be delivered to consumers that use this channel).

@api public

handle_close(method)

Overrides AMQ::Client::Channel version to also call global callback (if defined) for backwards compatibility.

@private @api private

handle_close_ok(method)

Overrides AMQ::Client::Channel version to also release the channel id

@private @api private

handle_connection_interruption(reason = nil)

Overrides superclass method to also re-create @channel_is_open_deferrable

@api plugin @private

headers(name = 'amq.match', opts = {}, &block)

Defines, intializes and returns a headers Exchange instance.

Learn more about headers exchanges in {Exchange Exchange class documentation}.

@param [String] name (amq.match) Exchange name.

@option opts [Boolean] :passive (false) If set, the server will not create the exchange if it does not

                                             already exist. The client can use this to check whether an exchange
                                             exists without modifying the server state.

@option opts [Boolean] :durable (false) If set when creating a new exchange, the exchange will be marked as

                                             durable. Durable exchanges and their bindings are recreated upon a server
                                             restart (information about them is persisted). Non-durable (transient) exchanges
                                             do not survive if/when a server restarts (information about them is stored exclusively
                                             in RAM).

@option opts [Boolean] :auto_delete (false) If set, the exchange is deleted when all queues have finished

                                                  using it. The server waits for a short period of time before
                                                  determining the exchange is unused to give time to the client code
                                                  to bind a queue to it.

@option opts [Boolean] :internal (default false) If set, the exchange may not be used directly by publishers, but

                                                       only when bound to other exchanges. Internal exchanges are used to
                                                       construct wiring that is not visible to applications. This is a RabbitMQ-specific
                                                       extension.

@option opts [Boolean] :nowait (true) If set, the server will not respond to the method. The client should

                                                       not wait for a reply method.  If the server could not complete the
                                                       method it will raise a channel or connection exception.

@raise [AMQP::Error] Raised when exchange is redeclared with parameters different from original declaration. @raise [AMQP::Error] Raised when exchange is declared with :passive => true and the exchange does not exist.

@example Using headers exchange to route messages based on multiple attributes (OS, architecture, # of cores)

      puts "=> Headers routing example"
      puts
      AMQP.start do |connection|
        channel   = AMQP::Channel.new(connection)
        channel.on_error do |ch, channel_close|
          puts "A channel-level exception: #{channel_close.inspect}"
        end

        exchange = channel.headers("amq.match", :durable => true)

        channel.queue("", :auto_delete => true).bind(exchange, :arguments => { 'x-match' => 'all', :arch => "x64", :os => 'linux' }).subscribe do |metadata, payload|
          puts "[linux/x64] Got a message: #{payload}"
        end
        channel.queue("", :auto_delete => true).bind(exchange, :arguments => { 'x-match' => 'all', :arch => "x32", :os => 'linux' }).subscribe do |metadata, payload|
          puts "[linux/x32] Got a message: #{payload}"
        end
        channel.queue("", :auto_delete => true).bind(exchange, :arguments => { 'x-match' => 'any', :os => 'linux', :arch => "__any__" }).subscribe do |metadata, payload|
          puts "[linux] Got a message: #{payload}"
        end
        channel.queue("", :auto_delete => true).bind(exchange, :arguments => { 'x-match' => 'any', :os => 'macosx', :cores => 8 }).subscribe do |metadata, payload|
          puts "[macosx|octocore] Got a message: #{payload}"
        end

        EventMachine.add_timer(0.5) do
          exchange.publish "For linux/x64",   :headers => { :arch => "x64", :os => 'linux' }
          exchange.publish "For linux/x32",   :headers => { :arch => "x32", :os => 'linux' }
          exchange.publish "For linux",       :headers => { :os => 'linux'  }
          exchange.publish "For OS X",        :headers => { :os => 'macosx' }
          exchange.publish "For solaris/x64", :headers => { :os => 'solaris', :arch => 'x64' }
          exchange.publish "For ocotocore",   :headers => { :cores => 8  }
        end

        show_stopper = Proc.new do
          $stdout.puts "Stopping..."
          connection.close {
            EventMachine.stop { exit }
          }
        end

        Signal.trap "INT", show_stopper
        EventMachine.add_timer(2, show_stopper)
      end

@see Exchange @see Exchange#initialize @see Channel#default_exchange @see bit.ly/hw2ELX AMQP 0.9.1 specification (Section 3.1.3.3)

@return [Exchange] @api public

on_error(&block)

Defines a callback that will be executed when channel is closed after channel-level exception.

@api public

once_open(&block)

Takes a block that will be deferred till the moment when channel is considered open (channel.open-ok is received from the broker). If you need to delay an operation till the moment channel is open, this method is what you are looking for.

Multiple callbacks are supported. If when this moment is called, channel is already open, block is executed immediately.

@api public

once_opened(&block)

Alias for once_open

open(&block)

Opens AMQP channel.

@note Instantiated channels are opened by default. This method should only be used for error recovery after network connection loss. @api public

open?()

@return [Boolean] true if channel is not closed. @api public

prefetch(count, global = false, &block)

@param [Fixnum] Message count @param [Boolean] global (false)

@return [Channel] self

@api public

queue(name = AMQ::Protocol::EMPTY_STRING, opts = {}, &block)

Declares and returns a Queue instance associated with this channel. See {Queue Queue class documentation} for more information about queues.

To make broker generate queue name for you (a classic example is exclusive queues that are only used for a short period of time), pass empty string as name value. Then queue will get it‘s name as soon as broker‘s response (queue.declare-ok) arrives. Note that in this case, block is required.

Like for exchanges, queue names starting with ‘amq.’ cannot be modified and should not be used by applications.

@example Declaring a queue in a mail delivery app using Channel#queue without a block

      AMQP.connect do |connection|
        AMQP::Channel.new(connection) do |ch|
          # message producers will be able to send messages to this queue
          # using direct exchange and routing key = "mail.delivery"
          queue = ch.queue("mail.delivery", :durable => true)
          queue.subscribe do |headers, payload|
            # ...
          end
        end
      end

@example Declaring a server-named exclusive queue that receives all messages related to events, using a block.

      AMQP.connect do |connection|
        AMQP::Channel.new(connection) do |ch|
          # message producers will be able to send messages to this queue
          # using amq.topic exchange with routing keys that begin with "events"
          ch.queue("", :exclusive => true) do |queue|
            queue.bind(ch.exchange("amq.topic"), :routing_key => "events.#").subscribe do |headers, payload|
              # ...
            end
          end
        end
      end

@param [String] name Queue name. If you want a server-named queue, you can omit the name (note that in this case, using block is mandatory).

                                     See {Queue Queue class documentation} for discussion of queue lifecycles and when use of server-named queues
                                     is optimal.

@option opts [Boolean] :passive (false) If set, the server will not create the exchange if it does not

                                             already exist. The client can use this to check whether an exchange
                                             exists without modifying the server state.

@option opts [Boolean] :durable (false) If set when creating a new exchange, the exchange will be marked as

                                             durable. Durable exchanges and their bindings are recreated upon a server
                                             restart (information about them is persisted). Non-durable (transient) exchanges
                                             do not survive if/when a server restarts (information about them is stored exclusively
                                             in RAM). Any remaining messages in the queue will be purged when the queue
                                             is deleted regardless of the message's persistence setting.

@option opts [Boolean] :auto_delete (false) If set, the exchange is deleted when all queues have finished

                                                  using it. The server waits for a short period of time before
                                                  determining the exchange is unused to give time to the client code
                                                  to bind a queue to it.

@option opts [Boolean] :exclusive (false) Exclusive queues may only be used by a single connection.

                                                       Exclusivity also implies that queue is automatically deleted when connection
                                                       is closed. Only one consumer is allowed to remove messages from exclusive queue.

@option opts [Boolean] :nowait (true) If set, the server will not respond to the method. The client should

                                                       not wait for a reply method.  If the server could not complete the
                                                       method it will raise a channel or connection exception.

@raise [AMQP::Error] Raised when queue is redeclared with parameters different from original declaration. @raise [AMQP::Error] Raised when queue is declared with :passive => true and the queue does not exist. @raise [AMQP::Error] Raised when queue is declared with :exclusive => true and queue with that name already exist.

@yield [queue, declare_ok] Yields successfully declared queue instance and AMQP method (queue.declare-ok) instance. The latter is optional. @yieldparam [Queue] queue Queue that is successfully declared and is ready to be used. @yieldparam [AMQP::Protocol::Queue::DeclareOk] declare_ok AMQP queue.declare-ok) instance.

@see Queue @see Queue#initialize @see bit.ly/hw2ELX AMQP 0.9.1 specification (Section 2.1.4)

@return [Queue] @api public

queue!(name, opts = {}, &block)

Same as {Channel#queue} but when queue with the same name already exists in this channel object‘s cache, this method will replace existing queue with a newly defined one. Consider using {Channel#queue} instead.

@see Channel#queue

@return [Queue] @api public

queues()

@return [Array<AMQP::Queue>] Queues cache for this channel @api plugin @private

recover(requeue = true, &block)

Notifies AMQ broker that consumer has recovered and unacknowledged messages need to be redelivered.

@return [Channel] self

@note RabbitMQ as of 2.3.1 does not support basic.recover with requeue = false. @see bit.ly/htCzCX AMQP 0.9.1 protocol documentation (Section 1.8.3.16.) @see acknowledge @api public

register_rpc(rpc)

@private @api plugin

reject(delivery_tag, requeue = true)

Reject a message with given delivery tag.

@api public @see acknowledge @see recover @see bit.ly/htCzCX AMQP 0.9.1 protocol documentation (Section 1.8.3.14.)

reset(&block)

Resets channel state (for example, list of registered queue objects and so on).

Most of the time, this method is not called by application code.

@private @api plugin

reset_state!()

@private @api plugin

reuse()

Can be used to recover channels from channel-level exceptions. Allocates a new channel id and reopens itself with this new id, releasing the old id after the new one is allocated.

@api public

rpc(name, obj = nil)

Instantiates and returns an RPC instance associated with this channel.

The optional object may be a class name, module name or object instance. When given a class or module name, the object is instantiated during this setup. The passed queue is automatically subscribed to so it passes all messages (and their arguments) to the object.

Marshalling and unmarshalling the objects is handled internally. This marshalling is subject to the same restrictions as defined in the [ruby-doc.org/core/classes/Marshal.html Marshal module} in the Ruby standard library.

When the optional object is not passed, the returned rpc reference is used to send messages and arguments to the queue. See {AMQP::RPC#method_missing} which does all of the heavy lifting with the proxy. Some client elsewhere must call this method with the optional block so that there is a valid destination. Failure to do so will just enqueue marshalled messages that are never consumed.

@example Use of RPC

      # TODO

@param [String, Queue] Queue to be used by RPC server. @return [RPC] @api public

rpcs()

Returns a hash of all rpc proxy objects.

Most of the time, this method is not called by application code. @api plugin

topic(name = 'amq.topic', opts = {}, &block)

Defines, intializes and returns a topic Exchange instance.

Learn more about topic exchanges in {Exchange Exchange class documentation}.

@param [String] name (amq.topic) Exchange name.

@option opts [Boolean] :passive (false) If set, the server will not create the exchange if it does not

                                             already exist. The client can use this to check whether an exchange
                                             exists without modifying the server state.

@option opts [Boolean] :durable (false) If set when creating a new exchange, the exchange will be marked as

                                             durable. Durable exchanges and their bindings are recreated upon a server
                                             restart (information about them is persisted). Non-durable (transient) exchanges
                                             do not survive if/when a server restarts (information about them is stored exclusively
                                             in RAM).

@option opts [Boolean] :auto_delete (false) If set, the exchange is deleted when all queues have finished

                                                  using it. The server waits for a short period of time before
                                                  determining the exchange is unused to give time to the client code
                                                  to bind a queue to it.

@option opts [Boolean] :internal (default false) If set, the exchange may not be used directly by publishers, but

                                                       only when bound to other exchanges. Internal exchanges are used to
                                                       construct wiring that is not visible to applications. This is a RabbitMQ-specific
                                                       extension.

@option opts [Boolean] :nowait (true) If set, the server will not respond to the method. The client should

                                                       not wait for a reply method.  If the server could not complete the
                                                       method it will raise a channel or connection exception.

@raise [AMQP::Error] Raised when exchange is redeclared with parameters different from original declaration. @raise [AMQP::Error] Raised when exchange is declared with :passive => true and the exchange does not exist.

@example Using topic exchange to deliver relevant news updates

      AMQP.connect do |connection|
        channel  = AMQP::Channel.new(connection)
        exchange = channel.topic("pub/sub")

        # Subscribers.
        channel.queue("development").bind(exchange, :key => "technology.dev.#").subscribe do |payload|
          puts "A new dev post: '#{payload}'"
        end
        channel.queue("ruby").bind(exchange, :key => "technology.#.ruby").subscribe do |payload|
          puts "A new post about Ruby: '#{payload}'"
        end

        # Let's publish some data.
        exchange.publish "Ruby post",     :routing_key => "technology.dev.ruby"
        exchange.publish "Erlang post",   :routing_key => "technology.dev.erlang"
        exchange.publish "Sinatra post",  :routing_key => "technology.web.ruby"
        exchange.publish "Jewelery post", :routing_key => "jewelery.ruby"
      end

@example Using topic exchange to deliver geographically-relevant data

      AMQP.connect do |connection|
        channel  = AMQP::Channel.new(connection)
        exchange = channel.topic("pub/sub")

        # Subscribers.
        channel.queue("americas.north").bind(exchange, :routing_key => "americas.north.#").subscribe do |headers, payload|
          puts "An update for North America: #{payload}, routing key is #{headers.routing_key}"
        end
        channel.queue("americas.south").bind(exchange, :routing_key => "americas.south.#").subscribe do |headers, payload|
          puts "An update for South America: #{payload}, routing key is #{headers.routing_key}"
        end
        channel.queue("us.california").bind(exchange, :routing_key => "americas.north.us.ca.*").subscribe do |headers, payload|
          puts "An update for US/California: #{payload}, routing key is #{headers.routing_key}"
        end
        channel.queue("us.tx.austin").bind(exchange, :routing_key => "#.tx.austin").subscribe do |headers, payload|
          puts "An update for Austin, TX: #{payload}, routing key is #{headers.routing_key}"
        end
        channel.queue("it.rome").bind(exchange, :routing_key => "europe.italy.rome").subscribe do |headers, payload|
          puts "An update for Rome, Italy: #{payload}, routing key is #{headers.routing_key}"
        end
        channel.queue("asia.hk").bind(exchange, :routing_key => "asia.southeast.hk.#").subscribe do |headers, payload|
          puts "An update for Hong Kong: #{payload}, routing key is #{headers.routing_key}"
        end

        exchange.publish("San Diego update", :routing_key => "americas.north.us.ca.sandiego").
          publish("Berkeley update",         :routing_key => "americas.north.us.ca.berkeley").
          publish("San Francisco update",    :routing_key => "americas.north.us.ca.sanfrancisco").
          publish("New York update",         :routing_key => "americas.north.us.ny.newyork").
          publish("São Paolo update",        :routing_key => "americas.south.brazil.saopaolo").
          publish("Hong Kong update",        :routing_key => "asia.southeast.hk.hongkong").
          publish("Kyoto update",            :routing_key => "asia.southeast.japan.kyoto").
          publish("Shanghai update",         :routing_key => "asia.southeast.prc.shanghai").
          publish("Rome update",             :routing_key => "europe.italy.roma").
          publish("Paris update",            :routing_key => "europe.france.paris")
      end

@see Exchange @see Exchange#initialize @see www.rabbitmq.com/faq.html#Binding-and-Routing RabbitMQ FAQ on routing & wildcards @see bit.ly/hw2ELX AMQP 0.9.1 specification (Section 3.1.3.3)

@return [Exchange] @api public

tx_commit(&block)

Commits AMQP transaction.

@api public

tx_rollback(&block)

Rolls AMQP transaction back.

@api public

tx_select(&block)

Sets the channel to use standard transactions. One must use this method at least once on a channel before using tx_tommit or tx_rollback methods.

@api public

### Protected Instance methods

validate_parameters_match!(entity, parameters, type)

[Validate]