Question about attachment upload and download - corda

Question

First I have read the doc from corda about using attachment. However I still have question about the process of uploading and downloading attachment.
My task was to write a simple cordapp for transferring file from NodeA to NodeB. After uploading a zip file from NodeA shell, I received a hash and then included this in the transaction. The flow was successful. However, in NodeB, I could not get the file back. Then I tried to get the file back from NodeA using that hash. However, the shell returned error message and said invalidInputSteam.
But then when I ran cordaftp (https://github.com/corda/cordaftp) and tried to upload a file and download this from the same shell, the shell correctly asked the path for storage. I had read various posts and knew that I need to include extra codes for successfully downloading. But I have no idea which file I should amend and what code I should write. Hope someone can help me solve my problem as I already spent days on reading previous posts and doc.
Here below is the flow part:
#InitiatingFlow
#StartableByRPC
class FileInitiateFlow(
val receiver: Party,
val comment: String,
val hash: SecureHash.SHA256) : FlowLogic<SignedTransaction>() {
companion object {
object GENERATING_TRANSACTION : Step("Generating transaction")
object VERIFYING_TRANSACTION : Step("Verifying contract constraints.")
object SIGNING_TRANSACTION : Step("Signing transaction with sender private key.")
object GATHERING_SIGS : Step("Gathering the receiver's signature."){
override fun childProgressTracker() = CollectSignaturesFlow.tracker()
}
object FINALISING_TRANSACTION : Step("Obtaining notary signature and recording transaction.") {
override fun childProgressTracker() = FinalityFlow.tracker()
}
fun tracker() = ProgressTracker(
GENERATING_TRANSACTION,
VERIFYING_TRANSACTION,
SIGNING_TRANSACTION,
GATHERING_SIGS,
FINALISING_TRANSACTION
)
}
override val progressTracker = tracker()
#Suspendable
override fun call(): SignedTransaction {
// Obtain a reference to the notary we want to use.
val notary = serviceHub.networkMapCache.notaryIdentities[0]
val sender = serviceHub.myInfo.legalIdentities.first()
// Stage 1.
progressTracker.currentStep = GENERATING_TRANSACTION
// Generate an unsigned transaction.
val fileState = FileState(sender, receiver,comment)
val txCommand = Command(RoamingContract.Commands.FileInitiate(), fileState.participants.map { it.owningKey })
val txBuilder = TransactionBuilder(notary)
.addOutputState(fileState, ID)
.addCommand(txCommand)
.addAttachment(hash)
// Stage 2.
progressTracker.currentStep = VERIFYING_TRANSACTION
// Verify that the transaction is valid.
txBuilder.verify(serviceHub)
// Stage 3.
progressTracker.currentStep = SIGNING_TRANSACTION
// Sign the transaction.
val partSignedTx = serviceHub.signInitialTransaction(txBuilder)
// Stage 4.
progressTracker.currentStep = GATHERING_SIGS
// Send the state to the counterparty, and receive it back with their signature.
val otherPartyFlow = initiateFlow(receiver)
val fullySignedTx = subFlow(CollectSignaturesFlow(partSignedTx, setOf(otherPartyFlow), GATHERING_SIGS.childProgressTracker()))
// Stage 5.
progressTracker.currentStep = FINALISING_TRANSACTION
// Notarise and record the transaction in both parties' vaults.
return subFlow(FinalityFlow(fullySignedTx, FINALISING_TRANSACTION.childProgressTracker()))
}
}
#InitiatedBy(FileInitiateFlow::class)
class FileInitiateRespond(val senderFlow: FlowSession) : FlowLogic<SignedTransaction>() {
#Suspendable
override fun call(): SignedTransaction{
val signedTransactionFlow = object : SignTransactionFlow(senderFlow) {
override fun checkTransaction(stx: SignedTransaction) = requireThat {
val output = stx.tx.outputs.single().data
"This must be an File State" using (output is FileState)
}
}
return subFlow(signedTransactionFlow)
}
}
So I first run uploadAttachment for uploading the zip file, I got the hash and then start the flow, with hash as input. The flow was succeeded, but in receiver's side, I could not get the hash key for the uploaded file from checking existing state.

Answer 1

Attachment hashes of instances of SecureHash. There is a bug in Corda 3.2/3.3 whereby the shell cannot convert strings into SecureHash objects.
The fix is here: https://github.com/corda/corda/pull/3248 and will be available in Corda 4.