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Chapter 7. Senders and receivers
The client uses sender and receiver links to represent channels for delivering messages. Senders and receivers are unidirectional, with a source end for the message origin, and a target end for the message destination.
Sources and targets often point to queues or topics on a message broker. Sources are also used to represent subscriptions.
7.1. Creating queues and topics on demand
Some message servers support on-demand creation of queues and topics. When a sender or receiver is attached, the server uses the sender target address or the receiver source address to create a queue or topic with a name matching the address.
The message server typically defaults to creating either a queue (for one-to-one message delivery) or a topic (for one-to-many message delivery). The client can indicate which it prefers by setting the queue or topic capability on the source or target.
To select queue or topic semantics, follow these steps:
- Configure your message server for automatic creation of queues and topics. This is often the default configuration.
-
Set either the
queueortopiccapability on your sender target or receiver source, as in the examples below.
Example: Sending to a queue created on demand
Target target = new Target() {
Address = "jobs",
Capabilities = new Symbol[] {"queue"},
};
SenderLink sender = new SenderLink(session, "s1", target, null);
Example: Receiving from a topic created on demand
Source source = new Source() {
Address = "notifications",
Capabilities = new Symbol[] {"topic"},
};
ReceiverLink receiver = new ReceiverLink(session, "r1", source, null);
For more information, see the following examples:
7.2. Creating durable subscriptions
A durable subscription is a piece of state on the remote server representing a message receiver. Ordinarily, message receivers are discarded when a client closes. However, because durable subscriptions are persistent, clients can detach from them and then re-attach later. Any messages received while detached are available when the client re-attaches.
Durable subscriptions are uniquely identified by combining the client container ID and receiver name to form a subscription ID. These must have stable values so that the subscription can be recovered.
To create a durable subscription, follow these steps:
Set the connection container ID to a stable value, such as
client-1:Connection conn = new Connection(new Address(connUrl), SaslProfile.Anonymous, new Open() { ContainerId = "client-1" }, null);Configure the receiver source for durability by setting the
DurableandExpiryPolicyproperties:Source source = new Source() { Address = "notifications", Durable = 2, ExpiryPolicy = new Symbol("never"), };Create a receiver with a stable name, such as
sub-1, and apply the source properties:ReceiverLink receiver = new ReceiverLink(session, "sub-1", source, null);
To detach from a subscription, close the connection without explicitly closing the receiver. To terminate the subscription, close the receiver directly.
For more information, see the DurableSubscribe.cs example.
