Implement Consumers Pause

[MauriceVanVeen]

Resolves #1084

Adds support for pausing and resuming consumers.

• The JetStreamManagement now has methods to jsm.pauseConsumer(stream, consumer, pauseUntil), as well as jsm.resumeConsumer(stream, consumer).
• An example for the above is also added to src/examples.
• ConsumerConfiguration/builder now has support for setting pauseUntil as well. Allowing to set it during consumer creation.

An optional addition (not implemented now) could be:

• Not allowing pause/resume when not running the appropriate server version. Throwing a custom exception, instead of a timeout (since the server is not listening to the subjects). What do you think?

[MauriceVanVeen]

Waiting for a fix to nats-io/nats-server#5163. Currently fails the consumer info check that's been added in the last commit.

EDIT: Fix has been merged, the tests now pass 🎉

[scottf]

Looks great, just some minor changes. Also can you add this to the example:

// 8. Try to pause a consumer that does not exist and you will get an exception
System.out.println("\n----------\n8. Pause non-existent consumer .");
try
{
    jsm.pauseConsumer(exArgs.stream, durable1, ZonedDateTime.now());
}
catch (JetStreamApiException e)
{
    System.out.println("Exception was: '" + e.getMessage() + "'");
}

[scottf]

I think there should be two api here, one that does not take pauseUntil, since it is not required.

[MauriceVanVeen]

Do you mean having three methods in the end:

• pauseConsumer(streamName, consumerName, pauseUntil)
• pauseConsumer(streamName, consumerName)
• resumeConsumer(streamName, consumerName)

When not sending a pauseUntil, the consumer does not get paused and should be equivalent to calling resumeConsumer instead. So pauseConsumer is used to pause a consumer until the set date, and resumeConsumer resumes it. Could you explain why you'd expect two api here?

[scottf]

Sorry, I thought no pauseUntil meant pause until resume. So just ignore this comment.

[scottf]

Please add a test for this, otherwise coverage goes down. Usually I just assign it and do something like contains("true"). Or just remove it since someone could call toJson

[MauriceVanVeen]

Have removed it

[scottf]

LGTM