Request connection on startup

[genuss]

Solves #376

Looks like I was a bit too optimistic about this task. It's not that easy to check that connection was established in GRPC. It doesn't even have such thing as "connection timeout" becase GRPC internally handles connections and retries on failures.

I came out with this solution:

1. Use separate method to check connection on startup if grpc-spring-boot-starter was configured to do so.
2. As far as I understand ConnectivityState state-machine it should work like this:

IDLE -> CONNECTING -> READY                 for happy path
IDLE -> CONNECTING -> TRANSIENT_FAILURE     for connection failure

3. So my method initiates connection via channel.getState(true), registers two callbacks and awaits on CountDownLatch for some period of time.
4. If ConnectivityState is in wrong status or timeout has passed then we throw exception which stops context from starting.

Well any feedback will be highly appreciated. If you suppose design is OK, I'll make connection timeout configurable too.

[ST-DDT]

If you suppose design is OK, I'll make connection timeout configurable too.

Maybe we could change the immediateConnect to a immediateConnectTimeout duration and define it as "do it if > 0"?

[genuss]

Maybe we could change the immediateConnect to a immediateConnectTimeout duration and define it as "do it if > 0"?

That's a great idea. Applied it.

[ST-DDT]

Could you please add a test for this feature?
If possible for both code paths:

• Connect success -> app starts
• Connect fails -> app fails to start

I can help you with that, if necessary.

[genuss]

I created three tests and arranged them in one file. I think it’s ok to group them so.

• When connection is not requested, channel must be in IDLE state
• When connection is requested and successful channel must be in READY state when user-code interacts with a channel
• When connection is requested but was unsuccessful, context fails to start. That is the tricky one.

[genuss]

Do you have some ideas why build fails? I can't see issues.

[ST-DDT]

ImmediateConnectTest$ImmediateConnectEnabledAndSuccessfulTest > testFailingCall() FAILED
    java.lang.IllegalStateException: Failed to create channel: test
        at net.devh.boot.grpc.client.inject.GrpcClientBeanPostProcessor.processInjectionPoint(GrpcClientBeanPostProcessor.java:126)
		[...]
	Caused by:
        java.lang.IllegalStateException: Can't connect to channel test
            at net.devh.boot.grpc.client.channelfactory.AbstractChannelFactory.connectOnStartup(AbstractChannelFactory.java:172)
            at net.devh.boot.grpc.client.channelfactory.AbstractChannelFactory.newManagedChannel(AbstractChannelFactory.java:140)

[ST-DDT]

I cannot reproduce the error at my place either. But I assume, that the server might be a bit slow starting up.
Could you do me a favor and change the check to wait for ready? If that does work, we at least know, that it is related to the startup speed.

As an alternative you can also try to uncomment:

// failFast = true
// showStandardStreams = true

in the main build.gradle.

[genuss]

This issue with tests was the following. A channel can move to READY state too fast (looks like CI on github is), however in my assumption was wrong in the first place. So state diagram can be:

IDLE -> CONNECTING -> READY                 for happy path
READY                                       for super-happy path
IDLE -> CONNECTING -> TRANSIENT_FAILURE     for connection failure

And I applied your suggestion to wait for ready state. When I actually made it, I understood you're right. The code looks much better now 👍 .

[ST-DDT]

No star imports please.

[genuss]

Fixed.

[ST-DDT]

Functionality wise this is already good to go 👍 . Just some minor changes left.

[ST-DDT]

Looks good to me. Thanks for addressing all the small issues this fast.

[genuss]

Thanks guys! Looking forward to release 🚀

[ST-DDT]

FYI: I try to finish the remaining issues within the next two weeks and do a release afterwards.