Corda customising transaction validation - Base responder

SendMessageResponder.kt

@InitiatedBy(SendMessageFlow::class)
open class SendMessageResponder(private val session: FlowSession) : FlowLogic<SignedTransaction>() {

  open fun extraTransactionValidation(stx: SignedTransaction) {
    // to be implemented by subtype flows - otherwise do nothing
  }

  @Suspendable
  final override fun call(): SignedTransaction {
    val stx = subFlow(object : SignTransactionFlow(session) {
      override fun checkTransaction(stx: SignedTransaction) {
        extraTransactionValidation(stx)
      }
    })
    // save transaction
  }
}