CORDA-296: added rpc that returns an observable for node state (#2004)

* CORDA-296: added rpc that returns an observable for node state; used to let rpc clients know that the know is about to shut down

* replaced node shut down observation String with enum

node/src/main/kotlin/net/corda/node/internal/AbstractNode.kt

@@ -62,6 +62,7 @@ import net.corda.node.utilities.*
 import org.apache.activemq.artemis.utils.ReusableLatch
 import org.slf4j.Logger
 import rx.Observable
+import rx.subjects.PublishSubject
 import java.io.IOException
 import java.lang.reflect.InvocationTargetException
 import java.security.KeyPair
@@ -124,6 +125,7 @@ abstract class AbstractNode(val configuration: NodeConfiguration,
     protected val services: ServiceHubInternal get() = _services
     private lateinit var _services: ServiceHubInternalImpl
     protected lateinit var info: NodeInfo
+    protected val nodeStateObservable: PublishSubject<NodeState> = PublishSubject.create<NodeState>()
     protected var myNotaryIdentity: PartyAndCertificate? = null
     protected lateinit var checkpointStorage: CheckpointStorage
     protected lateinit var smm: StateMachineManager
@@ -636,6 +638,9 @@ abstract class AbstractNode(val configuration: NodeConfiguration,
         // Meanwhile, we let the remote service send us updates until the acknowledgment buffer overflows and it
         // unsubscribes us forcibly, rather than blocking the shutdown process.
 
+        // Notify observers that the node is shutting down
+        nodeStateObservable.onNext(NodeState.SHUTTING_DOWN)
+
         // Run shutdown hooks in opposite order to starting
         for (toRun in runOnStop.reversed()) {
             toRun()
@@ -737,6 +742,7 @@ abstract class AbstractNode(val configuration: NodeConfiguration,
         override val networkService: MessagingService get() = network
         override val clock: Clock get() = platformClock
         override val myInfo: NodeInfo get() = info
+        override val myNodeStateObservable: Observable<NodeState> get() = nodeStateObservable
         override val database: CordaPersistence get() = this@AbstractNode.database
         override val configuration: NodeConfiguration get() = this@AbstractNode.configuration
         override fun <T : SerializeAsToken> cordaService(type: Class<T>): T {

node/src/main/kotlin/net/corda/node/internal/CordaRPCOpsImpl.kt

@@ -115,6 +115,10 @@ internal class CordaRPCOpsImpl(
         return services.myInfo
     }
 
+    override fun nodeStateObservable(): Observable<NodeState> {
+        return services.myNodeStateObservable
+    }
+
     override fun notaryIdentities(): List<Party> {
         return services.networkMapCache.notaryIdentities
     }

node/src/main/kotlin/net/corda/node/internal/RpcAuthorisationProxy.kt

@@ -8,6 +8,7 @@ import net.corda.core.identity.CordaX500Name
 import net.corda.core.identity.Party
 import net.corda.core.messaging.CordaRPCOps
 import net.corda.core.messaging.DataFeed
+import net.corda.core.messaging.NodeState
 import net.corda.core.node.NodeInfo
 import net.corda.core.node.services.NetworkMapCache
 import net.corda.core.node.services.Vault
@@ -16,6 +17,7 @@ import net.corda.core.node.services.vault.QueryCriteria
 import net.corda.core.node.services.vault.Sort
 import net.corda.node.services.messaging.RpcContext
 import net.corda.node.services.messaging.requireEitherPermission
+import rx.Observable
 import java.io.InputStream
 import java.security.PublicKey
 
@@ -60,6 +62,8 @@ class RpcAuthorisationProxy(private val implementation: CordaRPCOps, private val
 
     override fun nodeInfo(): NodeInfo = guard("nodeInfo", implementation::nodeInfo)
 
+    override fun nodeStateObservable(): Observable<NodeState> = guard("nodeStateObservable", implementation::nodeStateObservable)
+
     override fun notaryIdentities(): List<Party> = guard("notaryIdentities", implementation::notaryIdentities)
 
     override fun addVaultTransactionNote(txnId: SecureHash, txnNote: String) = guard("addVaultTransactionNote") {