AMQPClassic Component

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An easy-to-use AMQP 0.9.1 client implementation, with support for RabbitMQ extensions.

Syntax

TiotAMQPClassic

Remarks

The AMQPClassic component provides an easy-to-use AMQP 0.9.1 client implementation, and it also supports certain RabbitMQ extensions to the AMQP 0.9.1 specification. The component supports both plaintext and TLS-enabled connections over TCP.

Connecting

The AMQP 0.9.1 transport protocol has two layers: an overall connection between the client and server, and one or more channels running over that connection.

The component implements both layers, so the first step is to initiate the overall connection. Set the AuthScheme, User, Password, SSLEnabled, and VirtualHost properties if necessary, then call the Connect method, passing it the server's hostname and port number. (If the server in question is not running RabbitMQ, disabling the RabbitMQCompatible configuration setting before connecting is also recommended.)

The next step is to create at least one channel, which can be accomplished by using the CreateChannel method. The component allows creating any number of channels, up to the limit specified by the MaxChannelCount configuration setting.

Connecting and Creating a Channel

Once the component has connected to the server, and one or more channels have been opened, the component can begin manipulating exchanges and queues, publishing messages, and creating consumers.

Note that most AMQP 0.9.1 operations can themselves vary in their complexity. The examples below are intentionally simple for the sake of clarity and brevity, but links are provided for many other parts of the component's API where more detail can be found.

Declaring Exchanges

The DeclareExchange method is used to declare (i.e., create, or verify the existence of) exchanges on the server. While all AMQP servers provide a default, direct-type exchange that all queues are bound to automatically (using their name as the routing key), more complex use-cases will often require creating additional exchanges of varying types.

Declaring an Exchange

Exchanges can also be deleted using the DeleteExchange method.

Declaring Queues

The DeclareQueue method is used to declare (i.e., create, or verify the existence of) queues on the server. Unlike with exchanges, the server does not provide any queues by default, so declaring a queue is always necessary (unless one has already been created by another client, or configured ahead-of-time on the server itself).

Declaring a Queue

Queues may also be deleted or purged using the DeleteQueue and PurgeQueue methods.

Binding Queues to Exchanges

The BindQueue method is used to bind a queue to an exchange. Exchanges use the information held by their queue bindings to determine which messages to forward to which queues.

Note that all AMQP 0.9.1 servers automatically bind all queues to their default exchange (which is always a direct exchange with no name) using each queue's name as the binding's routing key. This makes it easy to send a message to a specific queue without having to declare bindings; just call PublishMessage, pass empty string for ExchangeName, and the name of the desired queue for RoutingKey.

Binding a Queue to an Exchange

Queues can also be unbound from exchanges using the UnbindQueue method.

Publishing Messages

To publish a message, populate the Message* properties, and then call the PublishMessage method.

Publishing a Message

Note that outgoing messages may be handled differently by the server if the channel they are sent over is in transaction or (for RabbitMQ only) "publish confirmations" mode. Refer to the EnableTransactionMode and EnablePublishConfirms methods for more information.

Receiving Messages

There are two possible ways for the component to receive a message:

• Messages can be asynchronously pushed to the component from the server. At any point in time, the server may push a message to the component from a queue that the Consume method has been used to attach a consumer to.
• Messages can be synchronously pulled from the server by the component. The FetchMessage method is used to attempt to pull (or "fetch") messages from a specific queue.

Regardless of how they are received, all incoming messages cause the ReceivedMessage* properties to be populated and the MessageIn event to fire.

Receiving a Message

Note that the MessageIn event always fires if FetchMessage is called successfully, even if there were no messages available to fetch; refer to MessageIn for more information.