alternateExchange

[paxinos]

How does one specify an exchange has an alternateExchange? The methods exposed in this library do not seem to include any ability to specify an alternateExchange.

For some reason, the Java/Android jar does not cause this fault - even those the alternateExchange is not specified (?)

When attempting to connect to an exchange, rabbitmq's log shows:

2022-03-25 09:58:21.792136-04:00 [erro] <0.15216.8> operation exchange.declare caused a channel exception precondition_failed: inequivalent arg 'alternate-exchange' for exchange 'messages' in vhost 'ezlinq': received none but current is the value 'alternate-messages' of type 'longstr'

For reference, In node-red, the topology is described as below. WIthout the alternateExchnage the same error (above) is produced.

    {"name": "messages",   "type": "topic", "options": {"durable": true,  "alternateExchange": "alternate-messages"}}

[michaelklishin]

Apparently there is no RMQExchangeDeclareOptions (an exchange counterpart of RMQQueueDeclareOptions). I will file an issue.

[michaelklishin]

I'm wrong, the options class does exist but it's not exposed in the API.

[michaelklishin]

Just like with optional queue arguments, a much better idea would be to use a policy. See why policies exist and how to use them. Hardcoding such values in application code
is not recommended.

[michaelklishin]

Apparently it is possible to pass in both options and optional arguments, somehow GitHub search failed me :(

From ExchangeIntegrationTest.swift (modified a tiny bit):

let conn = RMQConnection()
conn.start()
let ch = conn.createChannel()
let x = ch.fanout("objc.tests.fanout", options: [], arguments: [])

From RMQMethods.h:

@interface RMQExchangeDeclare : RMQValue <RMQMethod>
@property (nonnull, copy, nonatomic, readonly) RMQShort *reserved1;
@property (nonnull, copy, nonatomic, readonly) RMQShortstr *exchange;
@property (nonnull, copy, nonatomic, readonly) RMQShortstr *type;
@property (nonatomic, readonly) RMQExchangeDeclareOptions options;
@property (nonnull, copy, nonatomic, readonly) RMQTable *arguments;
- (nonnull instancetype)initWithReserved1:(nonnull RMQShort *)reserved1
                                 exchange:(nonnull RMQShortstr *)exchange
                                     type:(nonnull RMQShortstr *)type
                                  options:(RMQExchangeDeclareOptions)options
                                arguments:(nonnull RMQTable *)arguments;
@end

[michaelklishin]

So you need to pass an RMQTable for arguments that matches the map you find in some other clients. Or, again, just use a policy. It's a better idea.