com.r3corda.protocols / NotaryProtocol / Service

# Service

`class Service : ProtocolLogic<Unit>`

Checks that the timestamp command is valid (if present) and commits the input state, or returns a conflict if any of the input states have been previously committed.

Extend this class, overriding beforeCommit to add custom transaction processing/validation logic.

TODO: the notary service should only be able to see timestamp commands and inputs

### Constructors

<init> | `Service(otherSide: Party, sendSessionID: Long, receiveSessionID: Long, timestampChecker: TimestampChecker, uniquenessProvider: UniquenessProvider)` Checks that the timestamp command is valid (if present) and commits the input state, or returns a conflict if any of the input states have been previously committed.

### Properties

otherSide | `val otherSide: Party`
receiveSessionID | `val receiveSessionID: Long`
sendSessionID | `val sendSessionID: Long`
timestampChecker | `val timestampChecker: TimestampChecker`
topic | `open val topic: String` The topic to use when communicating with other parties. If more than one topic is required then use sub-protocols. Note that this is temporary until protocol sessions are properly implemented.
uniquenessProvider | `val uniquenessProvider: UniquenessProvider`

### Inherited Properties

logger | `val logger: <ERROR CLASS>` This is where you should log things to.
progressTracker | `open val progressTracker: ProgressTracker?` Override this to provide a ProgressTracker. If one is provided and stepped, the framework will do something helpful with the progress reports. If this protocol is invoked as a sub-protocol of another, then the tracker will be made a child of the current step in the parent. If its null, this protocol doesnt track progress.
psm | `lateinit var psm: ProtocolStateMachine<*>` Reference to the Fiber instance that is the top level controller for the entire flow.
serviceHub | `val serviceHub: ServiceHub` Provides access to big, heavy classes that may be reconstructed from time to time, e.g. across restarts. It is only available once the protocol has started, which means it cannnot be accessed in the constructor. Either access this lazily or from inside call.

### Functions

beforeCommit | `open fun beforeCommit(stx: SignedTransaction, reqIdentity: Party): Unit` No pre-commit processing is done. Transaction is not checked for contract-validity, as that would require fully resolving it into a TransactionForVerification, for which the caller would have to reveal the whole transaction history chain. As a result, the Notary will commit invalid transactions as well, but as it also records the identity of the caller, it is possible to raise a dispute and verify the validity of the transaction and subsequently undo the commit of the input states (the exact mechanism still needs to be worked out).
call | `open fun call(): Unit` This is where you fill out your business logic.

### Inherited Functions

receive | `fun <T : Any> receive(sessionIDForReceive: Long): UntrustworthyData<T>` `fun <T : Any> receive(sessionIDForReceive: Long, receiveType: Class<T>): UntrustworthyData<T>`
send | `fun send(destination: Party, sessionID: Long, payload: Any): Unit`
sendAndReceive | `fun <T : Any> sendAndReceive(destination: Party, sessionIDForSend: Long, sessionIDForReceive: Long, payload: Any): UntrustworthyData<T>`
subProtocol | `fun <R> subProtocol(subLogic: ProtocolLogic<R>): R` Invokes the given subprotocol by simply passing through this ProtocolLogics reference to the ProtocolStateMachine and then calling the call method.

### Inheritors

ValidatingNotaryProtocol | `class ValidatingNotaryProtocol : Service` A notary commit protocol that makes sure a given transaction is valid before committing it. This does mean that the calling party has to reveal the whole transaction history; however, we avoid complex conflict resolution logic where a party has its input states "blocked" by a transaction from another party, and needs to establish whether that transaction was indeed valid.