corda / net.corda.node.services.messaging / NodeMessagingClient

# NodeMessagingClient

`@ThreadSafe class NodeMessagingClient : ArtemisMessagingComponent, MessagingServiceInternal`

This class implements the MessagingService API using Apache Artemis, the successor to their ActiveMQ product. Artemis is a message queue broker and here we run a client connecting to the specified broker instance ArtemisMessagingServer. It's primarily concerned with peer-to-peer messaging.

Message handlers are run on the provided AffinityExecutor synchronously, that is, the Artemis callback threads are blocked until the handler is scheduled and completed. This allows backpressure to propagate from the given executor through into Artemis and from there, back through to senders.

An implementation of CordaRPCOps can be provided. If given, clients using the CordaMQClient RPC library can invoke methods on the provided implementation. There is more documentation on this in the docsite and the CordaRPCClient class.

### Parameters

`serverHostPort` - The address of the broker instance to connect to (might be running in the same process)

`myIdentity` - Either the public key to be used as the ArtemisMQ address and queue name for the node globally, or null to indicate that this is a NetworkMapService node which will be bound globally to the name "networkmap"

`nodeExecutor` - An executor to run received message tasks upon.

### Types

Handler | `data class Handler : MessageHandlerRegistration` A registration to handle messages of different types

### Constructors

<init> | `NodeMessagingClient(config: NodeConfiguration, serverHostPort: HostAndPort, myIdentity: CompositeKey?, nodeExecutor: AffinityExecutor, database: Database, networkMapRegistrationFuture: ListenableFuture<Unit>)` This class implements the MessagingService API using Apache Artemis, the successor to their ActiveMQ product. Artemis is a message queue broker and here we run a client connecting to the specified broker instance ArtemisMessagingServer. It's primarily concerned with peer-to-peer messaging.

### Properties

config | `val config: NodeConfiguration` The config object is used to pass in the passwords for the certificate KeyStore and TrustStore
database | `val database: Database`
myAddress | `val myAddress: SingleMessageRecipient` Apart from the NetworkMapService this is the only other address accessible to the node outside of lookups against the NetworkMapCache.
myIdentity | `val myIdentity: CompositeKey?`
networkMapRegistrationFuture | `val networkMapRegistrationFuture: ListenableFuture<Unit>`
nodeExecutor | `val nodeExecutor: AffinityExecutor`
serverHostPort | `val serverHostPort: HostAndPort`

### Functions

addMessageHandler | `fun addMessageHandler(topic: String, sessionID: Long, callback: (ReceivedMessage, MessageHandlerRegistration) -> Unit): MessageHandlerRegistration` The provided function will be invoked for each received message whose topic matches the given string. The callback will run on threads provided by the messaging service, and the callback is expected to be thread safe as a result. `fun addMessageHandler(topicSession: TopicSession, callback: (ReceivedMessage, MessageHandlerRegistration) -> Unit): MessageHandlerRegistration` The provided function will be invoked for each received message whose topic and session matches. The callback will run on the main server thread provided when the messaging service is constructed, and a database transaction is set up for you automatically.
createMessage | `fun createMessage(topicSession: TopicSession, data: ByteArray, uuid: UUID): Message` Returns an initialised Message with the current time, etc, already filled in.
getAddressOfParty | `fun getAddressOfParty(partyInfo: PartyInfo): MessageRecipients` Given information about either a specific node or a service returns its corresponding address
removeMessageHandler | `fun removeMessageHandler(registration: MessageHandlerRegistration): Unit` Removes a handler given the object returned from addMessageHandler. The callback will no longer be invoked once this method has returned, although executions that are currently in flight will not be interrupted.
run | `fun run(): Unit` Starts the p2p event loop: this method only returns once stop has been called.
send | `fun send(message: Message, target: MessageRecipients): Unit` Sends a message to the given receiver. The details of how receivers are identified is up to the messaging implementation: the type system provides an opaque high level view, with more fine grained control being available via type casting. Once this function returns the message is queued for delivery but not necessarily delivered: if the recipients are offline then the message could be queued hours or days later.
start | `fun start(rpcOps: RPCOps, userService: RPCUserService): Unit`
stop | `fun stop(): Unit` Initiates shutdown: if called from a thread that isn't controlled by the executor passed to the constructor then this will block until all in-flight messages have finished being handled and acknowledged. If called from a thread that's a part of the AffinityExecutor given to the constructor, it returns immediately and shutdown is asynchronous.

### Inherited Functions

checkStorePasswords | `fun checkStorePasswords(): Unit` Returns nothing if the keystore was opened OK or throws if not. Useful to check the password, as unfortunately Artemis tends to bury the exception when the password is wrong.
expectedOnDefaultFileSystem | `fun Path.expectedOnDefaultFileSystem(): Unit`
tcpTransport | `fun tcpTransport(direction: ConnectionDirection, host: String, port: Int, enableSSL: Boolean = true): TransportConfiguration`

### Companion Object Properties

SESSION_ID_PROPERTY | `const val SESSION_ID_PROPERTY: String`
TOPIC_PROPERTY | `const val TOPIC_PROPERTY: String`

### Extension Functions

createMessage | `fun MessagingService.createMessage(topic: String, sessionID: Long = DEFAULT_SESSION_ID, data: ByteArray): Message` Returns an initialised Message with the current time, etc, already filled in.
onNext | `fun <M : Any> MessagingService.onNext(topic: String, sessionId: Long): ListenableFuture<M>` Returns a ListenableFuture of the next message payload (Message.data) which is received on the given topic and sessionId. The payload is deserialized to an object of type M. Any exceptions thrown will be captured by the future.
runOnNextMessage | `fun MessagingService.runOnNextMessage(topic: String, sessionID: Long, callback: (ReceivedMessage) -> Unit): Unit` Registers a handler for the given topic and session ID that runs the given callback with the message and then removes itself. This is useful for one-shot handlers that aren't supposed to stick around permanently. Note that this callback doesn't take the registration object, unlike the callback to MessagingService.addMessageHandler, as the handler is automatically deregistered before the callback runs. `fun MessagingService.runOnNextMessage(topicSession: TopicSession, callback: (ReceivedMessage) -> Unit): Unit` Registers a handler for the given topic and session that runs the given callback with the message and then removes itself. This is useful for one-shot handlers that aren't supposed to stick around permanently. Note that this callback doesn't take the registration object, unlike the callback to MessagingService.addMessageHandler.
send | `fun MessagingService.send(topic: String, sessionID: Long, payload: Any, to: MessageRecipients, uuid: UUID = UUID.randomUUID()): Unit` `fun MessagingService.send(topicSession: TopicSession, payload: Any, to: MessageRecipients, uuid: UUID = UUID.randomUUID()): Unit`
sendRequest | `fun <R : Any> MessagingService.sendRequest(topic: String, request: ServiceRequestMessage, target: MessageRecipients): ListenableFuture<R>` Sends a ServiceRequestMessage to target and returns a ListenableFuture of the response.