AMQP support

The gateway serves AMQP 1.0. Compatibility lists the clients and test suites that we test the gateway with.

Supported

Feature	Notes
TCP and TLS (amqps)	TLS comes from the tls settings
WebSocket	On a listener with ws-path, subprotocol amqp
SASL PLAIN and ANONYMOUS	The listener maps the credential to a NATS user
Sessions and links	Up to 256 sessions per connection and 256 links per session
Heartbeats and idle time-out	The gateway closes a client that is silent for 60s
Send to an address	The address is a NATS subject without wildcards
Anonymous relay	The to of each message names its subject
Presettled delivery	Core NATS
Unsettled delivery	Only to addresses that a binding stores
Receive from an address	The source can use the * and > wildcards
Queues (move mode)	The default on a stored address
Copy mode and the topic capability	Each link gets its own consumer
Queue browsing, such as a JMS QueueBrowser	The browser removes no messages
Operator queues	Use the source <address>::<queue>
JMS selectors	apache.org:selector-filter:string or amqp:sql-filter
Routes	amqp.routes puts application properties in the subject
Outcomes	accepted, rejected, released and modified. See Things to know
Delivery count	Counts only failed attempts, with amqp.delivery-counts
Credit, drain and echo
Request/reply and JMS temporary destinations	Dynamic sources and targets give reply addresses
ttl and absolute-expiry-time	The gateway does not deliver an expired message
Message fidelity	An AMQP receiver gets the sections that the sender sent
Message size	Up to the NATS server's max_payload

Not supported

• Transactions. The gateway refuses the coordinator with amqp:not-implemented.
• Shared subscriptions, and durable subscriptions other than the address's queue
• Link recovery and resumed deliveries
• rcv-settle-mode second. The gateway answers with first.
• Filters other than selectors, such as no-local
• Dead-letter addresses
• Priority, scheduled delivery and message groups. The gateway carries these fields but does not act on them.
• modified with message-annotations
• Management nodes ($management) and claims-based security ($cbs)
• SASL mechanisms other than PLAIN and ANONYMOUS
• Copy mode, and selectors that the gateway evaluates, on a work-queue stream

Things to know

• Settlement decides storage. An unsettled send to an address that no binding stores is rejected with amqp:not-allowed. The gateway does not change it to a presettled send. A JMS persistent send to a temporary queue is refused for the same reason.
• Receivers on an address share a queue. By default, every receiver on a stored address, on every gateway, reads one durable consumer, so each message goes to one receiver. A queue that no link uses for amqp.queue-inactive (1h) is removed. A new queue starts from the first message the stream holds on the address.
• Outcomes decide redelivery. accepted and rejected end the message, so the gateway never delivers it again. released returns it to the queue. modified also returns it, and with delivery-failed it counts as a failed attempt. With undeliverable-here, only other receivers get it again.
• A selector can have its own queue. A queue is named by the subjects it reads and by the part of its selector that the gateway evaluates. A message that one queue's receiver accepts is still delivered to the address's other queues. On a routed address, a selector that the subject alone answers, such as region = 'EU' on orders.{region}, shares the queue of a receiver on orders.EU.
• Duplicates after a failure. When a link or connection ends, its unsettled deliveries go back to the queue and are delivered again. A delivery left unsettled for amqp.ack-wait (30s) is also sent again. A client that must not process a message twice should discard duplicates.
• Send bodies as one data section. MQTT and NATS clients get any other body, such as the amqp-value that Qpid JMS uses for a TextMessage, in its AMQP encoding.
• Addresses are subjects. The address orders.eu is the NATS subject orders.eu, which the MQTT topic orders/eu also reaches. See Mapping to NATS.