h2. What are AMQP channels
To quote {files.travis-ci.org/docs/amqp/0.9.1/AMQP091Specification.pdf 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
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:
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 that extend Channel functionality. Learn more in {file:docs/VendorSpecificExtensions.textile}
@see files.travis-ci.org/docs/amqp/0.9.1/AMQP091Specification.pdf AMQP 0.9.1 specification (Section 2.2.5)
@return [Boolean] true if this channel is in automatic recovery mode @see auto_recovering?
AMQP connection this channel is part of @return [Connection]
AMQP connection this channel is part of @return [Connection]
Change publisher index. Publisher index is incremented by 1 after each Basic.Publish starting at 1. This is done on both client and server, hence this acknowledged messages can be matched via its delivery-tag.
@api private
Status of this channel (one of: :opening, :closing, :open, :closed) @return [Symbol]
Acknowledge one or all messages on the channel.
@api public @see reject @see recover @see files.travis-ci.org/docs/amqp/0.9.1/AMQP091Reference.pdf AMQP 0.9.1 protocol documentation (Section 1.8.3.13.)
# File lib/amqp/channel.rb, line 1020 def acknowledge(delivery_tag, multiple = false) @connection.send_frame(AMQ::Protocol::Basic::Ack.encode(self.id, delivery_tag, multiple)) self end
Called by associated connection object when AMQP connection has been re-established (for example, after a network failure).
@api plugin
# File lib/amqp/channel.rb, line 315 def auto_recover return unless auto_recovering? @channel_is_open_deferrable.fail @channel_is_open_deferrable = AMQP::Deferrable.new self.open do @channel_is_open_deferrable.succeed # re-establish prefetch self.prefetch(@options[:prefetch], false) if @options[:prefetch] # exchanges must be recovered first because queue recovery includes recovery of bindings. MK. @exchanges.each { |name, e| e.auto_recover } @queues.each { |name, q| q.auto_recover } end end
@return [Boolean] true if this channel uses automatic recovery mode
# File lib/amqp/channel.rb, line 307 def auto_recovering? @auto_recovery end
Defines a callback that will be executed after TCP connection has recovered after a network failure but before AMQP connection is re-opened. Only one callback can be defined (the one defined last replaces previously added ones).
@api public
# File lib/amqp/channel.rb, line 1242 def before_recovery(&block) self.redefine_callback(:before_recovery, &block) end
Closes AMQP channel.
@api public
# File lib/amqp/channel.rb, line 949 def close(reply_code = 200, reply_text = DEFAULT_REPLY_TEXT, class_id = 0, method_id = 0, &block) self.once_open do self.status = :closing @connection.send_frame(AMQ::Protocol::Channel::Close.encode(@id, reply_code, reply_text, class_id, method_id)) self.redefine_callback :close, &block end end
@return [Boolean] @api public
# File lib/amqp/channel.rb, line 942 def closing? self.status == :closing end
@group Publisher Confirms
# File lib/amqp/channel.rb, line 1118 def confirm_select(nowait = false, &block) self.once_open do if nowait && block raise ArgumentError, "confirm.select with nowait = true and a callback makes no sense" end @uses_publisher_confirmations = true reset_publisher_index! self.redefine_callback(:confirm_select, &block) unless nowait self.redefine_callback(:after_publish) do increment_publisher_index! end @connection.send_frame(AMQ::Protocol::Confirm::Select.encode(@id, nowait)) self end end
@return [Hash<String, Consumer>]
# File lib/amqp/channel.rb, line 1182 def consumers @consumers end
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 files.travis-ci.org/docs/amqp/0.9.1/AMQP091Specification.pdf AMQP 0.9.1 specification (Section 2.1.2.4)
@return [Exchange] @api public
# File lib/amqp/channel.rb, line 490 def default_exchange @default_exchange ||= Exchange.default(self) end
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.
@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 {#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 #default_exchange @see Exchange @see Exchange#initialize @see files.travis-ci.org/docs/amqp/0.9.1/AMQP091Specification.pdf AMQP 0.9.1 specification (Section 3.1.3.1)
@return [Exchange] @api public
# File lib/amqp/channel.rb, line 437 def direct(name = 'amq.direct', opts = {}, &block) if exchange = find_exchange(name) extended_opts = Exchange.add_default_options(:direct, name, opts, block) validate_parameters_match!(exchange, extended_opts, :exchange) block.call(exchange) if block exchange else register_exchange(Exchange.new(self, :direct, name, opts, &block)) end end
@return [Hash<Exchange>] Collection of exchanges that were declared on this channel.
# File lib/amqp/channel.rb, line 1188 def exchanges @exchanges end
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.
@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 #default_exchange @see files.travis-ci.org/docs/amqp/0.9.1/AMQP091Specification.pdf AMQP 0.9.1 specification (Section 3.1.3.2)
@return [Exchange] @api public
# File lib/amqp/channel.rb, line 540 def fanout(name = 'amq.fanout', opts = {}, &block) if exchange = find_exchange(name) extended_opts = Exchange.add_default_options(:fanout, name, opts, block) validate_parameters_match!(exchange, extended_opts, :exchange) block.call(exchange) if block exchange else register_exchange(Exchange.new(self, :fanout, name, opts, &block)) end end
Finds exchange in the exchanges cache on this channel by name. Exchange only exists in the cache if it was previously instantiated on this channel.
@param [String] name Exchange name @return [AMQP::Exchange] Exchange (if found) @api plugin
# File lib/amqp/channel.rb, line 1393 def find_exchange(name) @exchanges[name] end
@api plugin @private
# File lib/amqp/channel.rb, line 1407 def find_queue(name) @queues[name] end
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 AMQP::Queue#get callers.
@param [Boolean] Desired flow state.
@see files.travis-ci.org/docs/amqp/0.9.1/AMQP091Reference.pdf AMQP 0.9.1 protocol documentation (Section 1.5.2.3.) @api public
# File lib/amqp/channel.rb, line 975 def flow(active = false, &block) @connection.send_frame(AMQ::Protocol::Channel::Flow.encode(@id, active)) self.redefine_callback :flow, &block self end
@return [Boolean] True if flow in this channel is active (messages will be delivered to consumers that use this channel).
@api public
# File lib/amqp/channel.rb, line 985 def flow_is_active? @flow_is_active end
Handler for Basic.Ack. By default, it just executes hook specified via the confirm method with a single argument, a protocol method class instance (an instance of AMQ::Protocol::Basic::Ack).
@api plugin
# File lib/amqp/channel.rb, line 1360 def handle_basic_ack(method) self.exec_callback(:ack, method) end
Handler for Basic.Nack. By default, it just executes hook specified via the confirm_failed method with a single argument, a protocol method class instance (an instance of AMQ::Protocol::Basic::Nack).
@api plugin
# File lib/amqp/channel.rb, line 1371 def handle_basic_nack(method) self.exec_callback(:nack, method) end
@api plugin @private
# File lib/amqp/channel.rb, line 1460 def handle_close(channel_close) self.status = :closed self.connection.clear_frames_on(self.id) self.exec_callback_yielding_self(:error, channel_close) end
@api plugin @private
# File lib/amqp/channel.rb, line 1450 def handle_close_ok(close_ok) self.status = :closed self.connection.clear_frames_on(self.id) self.exec_callback_once_yielding_self(:close, close_ok) @connection.release_channel_id(@id) end
Overrides superclass method to also re-create @channel_is_open_deferrable
@api plugin @private
# File lib/amqp/channel.rb, line 1170 def handle_connection_interruption(method = nil) @queues.each { |name, q| q.handle_connection_interruption(method) } @exchanges.each { |name, e| e.handle_connection_interruption(method) } self.exec_callback_yielding_self(:after_connection_interruption) self.reset_state! @connection.release_channel_id(@id) unless auto_recovering? @channel_is_open_deferrable = AMQP::Deferrable.new end
@api plugin @private
# File lib/amqp/channel.rb, line 1443 def handle_open_ok(open_ok) self.status = :opened self.exec_callback_once_yielding_self(:open, open_ok) end
Handler for Confirm.Select-Ok. By default, it just executes hook specified via the confirmations method with a single argument, a protocol method class instance (an instance of AMQ::Protocol::Confirm::SelectOk) and then it deletes the callback, since Confirm.Select is supposed to be sent just once.
@api plugin
# File lib/amqp/channel.rb, line 1350 def handle_select_ok(method) self.exec_callback_once(:confirm_select, method) end
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.
@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 #default_exchange @see files.travis-ci.org/docs/amqp/0.9.1/AMQP091Specification.pdf AMQP 0.9.1 specification (Section 3.1.3.3)
@return [Exchange] @api public
# File lib/amqp/channel.rb, line 753 def headers(name = 'amq.match', opts = {}, &block) if exchange = find_exchange(name) extended_opts = Exchange.add_default_options(:headers, name, opts, block) validate_parameters_match!(exchange, extended_opts, :exchange) block.call(exchange) if block exchange else register_exchange(Exchange.new(self, :headers, name, opts, &block)) end end
This method is executed after publishing of each message via {Exchage#publish}. Currently it just increments publisher index by 1, so messages can be actually matched.
@api plugin
# File lib/amqp/channel.rb, line 1301 def increment_publisher_index! @publisher_index += 1 end
Turn on confirmations for this channel and, if given, register callback for basic.ack from the broker.
@raise [RuntimeError] Occurs when confirmations are already activated. @raise [RuntimeError] Occurs when nowait is true and block is given. @param [Boolean] nowait Whether we expect Confirm.Select-Ok to be returned by the broker or not.
@yield [basick_ack] Callback which will be executed every time we receive Basic.Ack from the broker. @yieldparam [AMQ::Protocol::Basic::Ack] basick_ack Protocol method class instance.
@return [self] self.
# File lib/amqp/channel.rb, line 1322 def on_ack(nowait = false, &block) self.define_callback(:ack, &block) if block self end
Defines a callback that will be executed after TCP connection is interrupted (typically because of a network failure). Only one callback can be defined (the one defined last replaces previously added ones).
@api public
# File lib/amqp/channel.rb, line 1231 def on_connection_interruption(&block) self.redefine_callback(:after_connection_interruption, &block) end
Defines a callback that will be executed when channel is closed after channel-level exception.
@api public
# File lib/amqp/channel.rb, line 1109 def on_error(&block) self.define_callback(:error, &block) end
Register error callback for Basic.Nack. It’s called when message(s) is rejected.
@return [self] self
# File lib/amqp/channel.rb, line 1333 def on_nack(&block) self.define_callback(:nack, &block) if block self end
Defines a callback that will be executed after AMQP connection has recovered after a network failure. Only one callback can be defined (the one defined last replaces previously added ones).
@api public
# File lib/amqp/channel.rb, line 1260 def on_recovery(&block) self.redefine_callback(:after_recovery, &block) end
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
# File lib/amqp/channel.rb, line 931 def once_open(&block) @channel_is_open_deferrable.callback do # guards against cases when deferred operations # don't complete before the channel is closed block.call if open? end end
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
# File lib/amqp/channel.rb, line 907 def open(&block) @connection.send_frame(AMQ::Protocol::Channel::Open.encode(@id, AMQ::Protocol::EMPTY_STRING)) @connection.channels[@id] = self self.status = :opening self.redefine_callback :open, &block end
@return [Boolean] true if channel is not closed. @api public
# File lib/amqp/channel.rb, line 919 def open? self.status == :opened || self.status == :opening end
@param [Fixnum] Message count @param [Boolean] global (false)
@return [Channel] self
@api public
# File lib/amqp/channel.rb, line 997 def prefetch(count, global = false, &block) self.once_open do # RabbitMQ does not support prefetch_size. self.qos(0, count, global, &block) @options[:prefetch] = count end self end
Publisher index is an index of the last message since the confirmations were activated, started with 0. It’s incremented by 1 every time a message is published. This is done on both client and server, hence this acknowledged messages can be matched via its delivery-tag.
@return [Integer] Current publisher index. @api public
# File lib/amqp/channel.rb, line 1284 def publisher_index @publisher_index ||= 0 end
Requests a specific quality of service. The QoS can be specified for the current channel or for all channels on the connection.
@note RabbitMQ as of 2.3.1 does not support prefetch_size. @api public
# File lib/amqp/channel.rb, line 1213 def qos(prefetch_size = 0, prefetch_count = 32, global = false, &block) @connection.send_frame(AMQ::Protocol::Basic::Qos.encode(@id, prefetch_size, prefetch_count, global)) self.redefine_callback :qos, &block self end
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 #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.
@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 files.travis-ci.org/docs/amqp/0.9.1/AMQP091Specification.pdf AMQP 0.9.1 specification (Section 2.1.4)
@return [Queue] @api public
# File lib/amqp/channel.rb, line 848 def queue(name = AMQ::Protocol::EMPTY_STRING, opts = {}, &block) raise ArgumentError.new("queue name must not be nil; if you want broker to generate queue name for you, pass an empty string") if name.nil? if name && !name.empty? && (queue = find_queue(name)) extended_opts = Queue.add_default_options(name, opts, block) validate_parameters_match!(queue, extended_opts, :queue) block.call(queue) if block queue else self.queue!(name, opts, &block) end end
Same as {#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 {#queue} instead.
@see #queue
@return [Queue] @api public
# File lib/amqp/channel.rb, line 871 def queue!(name, opts = {}, &block) queue = if block.nil? Queue.new(self, name, opts) else shim = Proc.new { |q, method| if block.arity == 1 block.call(q) else queue = find_queue(method.queue) block.call(queue, method.consumer_count, method.message_count) end } Queue.new(self, name, opts, &shim) end register_queue(queue) end
@return [Array<AMQP::Queue>] Queues cache for this channel @api plugin @private
# File lib/amqp/channel.rb, line 892 def queues @queues end
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 files.travis-ci.org/docs/amqp/0.9.1/AMQP091Reference.pdf AMQP 0.9.1 protocol documentation (Section 1.8.3.16.) @see acknowledge @api public
# File lib/amqp/channel.rb, line 1051 def recover(requeue = true, &block) @connection.send_frame(AMQ::Protocol::Basic::Recover.encode(@id, requeue)) self.redefine_callback :recover, &block self end
Implementation
# File lib/amqp/channel.rb, line 1381 def register_exchange(exchange) raise ArgumentError, "argument is nil!" if exchange.nil? @exchanges[exchange.name] = exchange end
@api plugin @private
# File lib/amqp/channel.rb, line 1399 def register_queue(queue) raise ArgumentError, "argument is nil!" if queue.nil? @queues[queue.name] = queue end
Reject a message with given delivery tag.
@api public @see acknowledge @see recover @see files.travis-ci.org/docs/amqp/0.9.1/AMQP091Reference.pdf AMQP 0.9.1 protocol documentation (Section 1.8.3.14.)
# File lib/amqp/channel.rb, line 1032 def reject(delivery_tag, requeue = true, multi = false) if multi @connection.send_frame(AMQ::Protocol::Basic::Nack.encode(self.id, delivery_tag, multi, requeue)) else @connection.send_frame(AMQ::Protocol::Basic::Reject.encode(self.id, delivery_tag, requeue)) end self end
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
# File lib/amqp/channel.rb, line 1151 def reset(&block) # See AMQP::Channel self.reset_state! # there is no way to reset a deferrable; we have to use a new instance. MK. @channel_is_open_deferrable = AMQP::Deferrable.new @channel_is_open_deferrable.callback(&block) @connection.on_connection do @channel_is_open_deferrable.succeed self.prefetch(@options[:prefetch], false) if @options[:prefetch] end end
Resets publisher index to 0
@api plugin
# File lib/amqp/channel.rb, line 1291 def reset_publisher_index! @publisher_index = 0 end
@api plugin @private
# File lib/amqp/channel.rb, line 1417 def reset_state! @flow_is_active = true @queues_awaiting_declare_ok = Array.new @exchanges_awaiting_declare_ok = Array.new @exchanges_awaiting_bind_ok = Array.new @exchanges_awaiting_unbind_ok = Array.new @queues_awaiting_delete_ok = Array.new @exchanges_awaiting_delete_ok = Array.new @queues_awaiting_purge_ok = Array.new @queues_awaiting_bind_ok = Array.new @queues_awaiting_unbind_ok = Array.new @consumers_awaiting_consume_ok = Array.new @consumers_awaiting_cancel_ok = Array.new @queues_awaiting_get_response = Array.new @callbacks = @callbacks.delete_if { |k, v| !RECOVERY_EVENTS.include?(k) } @uses_publisher_confirmations = false end
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.
This includes recovery of known exchanges, queues and bindings, exactly the same way as when the client recovers from a network failure.
@api public
# File lib/amqp/channel.rb, line 340 def reuse old_id = @id # must release after we allocate a new id, otherwise we will end up # with the same value. MK. @id = @connection.next_channel_id @connection.release_channel_id(old_id) @channel_is_open_deferrable.fail @channel_is_open_deferrable = AMQP::Deferrable.new self.open do @channel_is_open_deferrable.succeed # re-establish prefetch self.prefetch(@options[:prefetch], false) if @options[:prefetch] # exchanges must be recovered first because queue recovery includes recovery of bindings. MK. @exchanges.each { |name, e| e.auto_recover } @queues.each { |name, q| q.auto_recover } end end
@private
# File lib/amqp/channel.rb, line 1266 def run_after_recovery_callbacks self.exec_callback_yielding_self(:after_recovery) @queues.each { |name, q| q.run_after_recovery_callbacks } @exchanges.each { |name, e| e.run_after_recovery_callbacks } end
@private
# File lib/amqp/channel.rb, line 1247 def run_before_recovery_callbacks self.exec_callback_yielding_self(:before_recovery) @queues.each { |name, q| q.run_before_recovery_callbacks } @exchanges.each { |name, e| e.run_before_recovery_callbacks } end
Synchronizes given block using this channel’s mutex. @api public
# File lib/amqp/channel.rb, line 1202 def synchronize(&block) @mutex.synchronize(&block) end
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.
@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 files.travis-ci.org/docs/amqp/0.9.1/AMQP091Specification.pdf AMQP 0.9.1 specification (Section 3.1.3.3)
@return [Exchange] @api public
# File lib/amqp/channel.rb, line 651 def topic(name = 'amq.topic', opts = {}, &block) if exchange = find_exchange(name) extended_opts = Exchange.add_default_options(:topic, name, opts, block) validate_parameters_match!(exchange, extended_opts, :exchange) block.call(exchange) if block exchange else register_exchange(Exchange.new(self, :topic, name, opts, &block)) end end
Commits AMQP transaction.
@api public
# File lib/amqp/channel.rb, line 1079 def tx_commit(&block) @connection.send_frame(AMQ::Protocol::Tx::Commit.encode(@id)) self.redefine_callback :tx_commit, &block self end
Rolls AMQP transaction back.
@api public
# File lib/amqp/channel.rb, line 1089 def tx_rollback(&block) @connection.send_frame(AMQ::Protocol::Tx::Rollback.encode(@id)) self.redefine_callback :tx_rollback, &block self end
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
# File lib/amqp/channel.rb, line 1069 def tx_select(&block) @connection.send_frame(AMQ::Protocol::Tx::Select.encode(@id)) self.redefine_callback :tx_select, &block self end
@return [Boolean]
# File lib/amqp/channel.rb, line 1306 def uses_publisher_confirmations? @uses_publisher_confirmations end
# File lib/amqp/channel.rb, line 1545 def validate_parameters_match!(entity, parameters, type) unless entity.opts.values_at(*@parameter_checks[type]) == parameters.values_at(*@parameter_checks[type]) || parameters[:passive] raise AMQP::IncompatibleOptionsError.new(entity.name, entity.opts, parameters) end end
@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.
@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, :prefetch => 5) do |channel, open_ok| # ... end end
@option options [Boolean] :prefetch (nil) Specifies number of messages to prefetch. Channel-specific. See {#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 #prefetch @api public
# File lib/amqp/channel.rb, line 232 def initialize(connection = nil, id = nil, options = {}, &block) raise 'AMQP can only be used from within EM.run {}' unless EM.reactor_running? @connection = connection || AMQP.connection || AMQP.start # this means 2nd argument is options if id.kind_of?(Hash) options = options.merge(id) id = @connection.next_channel_id end super(@connection) @id = id || @connection.next_channel_id @exchanges = Hash.new @queues = Hash.new @consumers = Hash.new @options = { :auto_recovery => @connection.auto_recovering? }.merge(options) @auto_recovery = (!!@options[:auto_recovery]) # we must synchronize frameset delivery. MK. @mutex = Mutex.new reset_state! # 65536 is here for cases when channel is opened without passing a callback in, # otherwise channel_mix would be nil and it causes a lot of needless headaches. # lets just have this default. MK. channel_max = if @connection.open? @connection.channel_max || 65536 else 65536 end if channel_max != 0 && !(0..channel_max).include?(@id) raise ArgumentError.new("Max channel for the connection is #{channel_max}, given: #{@id}") end # we need this deferrable to mimic what AMQP gem 0.7 does to enable # the following (pseudo-synchronous) style of programming some people use in their # existing codebases: # # connection = AMQP.connect # channel = AMQP::Channel.new(connection) # queue = AMQP::Queue.new(channel) # # ... # # Read more about EM::Deferrable#callback behavior in EventMachine documentation. MK. @channel_is_open_deferrable = AMQP::Deferrable.new @parameter_checks = {:queue => [:durable, :exclusive, :auto_delete, :arguments], :exchange => [:type, :durable, :arguments]} # only send channel.open when connection is actually open. Makes it possible to # do c = AMQP.connect; AMQP::Channel.new(c) that is what some people do. MK. @connection.on_connection do self.open do |ch, open_ok| @channel_is_open_deferrable.succeed if block case block.arity when 1 then block.call(ch) else block.call(ch, open_ok) end # case end # if self.prefetch(@options[:prefetch], false) if @options[:prefetch] end # self.open end # @connection.on_open end