corda / net.corda.flows / FetchDataFlow

FetchDataFlow

abstract class FetchDataFlow<T : NamedByHash, in W : Any> : FlowLogic<Result<T>>

An abstract flow for fetching typed data from a remote peer.

Given a set of hashes (IDs), either loads them from local disk or asks the remote peer to provide them.

A malicious response in which the data provided by the remote peer does not hash to the requested hash results in DownloadedVsRequestedDataMismatch being thrown. If the remote peer doesn't have an entry, it results in a HashNotFound exception being thrown.

By default this class does not insert data into any local database, if you want to do that after missing items were fetched then override maybeWriteToDisk. You must override load. If the wire type is not the same as the ultimate type, you must also override convert.

Parameters

T - The ultimate type of the data being fetched.

W - The wire type of the data being fetched, for when it isn't the same as the ultimate type.

Types

Request data class Request
Result data class Result<out T : NamedByHash>

Exceptions

DownloadedVsRequestedDataMismatch class DownloadedVsRequestedDataMismatch : IllegalArgumentException
DownloadedVsRequestedSizeMismatch class DownloadedVsRequestedSizeMismatch : IllegalArgumentException
HashNotFound class HashNotFound : FlowException

Constructors

<init> FetchDataFlow(requests: Set<SecureHash>, otherSide: Party)

An abstract flow for fetching typed data from a remote peer.

Properties

otherSide val otherSide: Party
requests val requests: Set<SecureHash>

Inherited Properties

logger val logger: Logger

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 flow is invoked as a subflow of another, then the tracker will be made a child of the current step in the parent. If it's null, this flow doesn't track progress.

runId val runId: StateMachineRunId

Returns a wrapped UUID object that identifies this state machine run (i.e. subflows have the same identifier as their parents).

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 flow has started, which means it cannnot be accessed in the constructor. Either access this lazily or from inside call.

stateMachine var stateMachine: FlowStateMachine<*>

Internal only. Reference to the Fiber instance that is the top level controller for the entire flow. When inside a flow this is equivalent to Strand.currentStrand. This is public only because it must be accessed across module boundaries.

Functions

call open fun call(): Result<T>

This is where you fill out your business logic. The returned object will usually be ignored, but can be helpful if this flow is meant to be used as a subflow.

convert open fun convert(wire: W): T
load abstract fun load(txid: SecureHash): T?
maybeWriteToDisk open fun maybeWriteToDisk(downloaded: List<T>): Unit

Inherited Functions

getCounterpartyMarker open fun getCounterpartyMarker(party: Party): Class<*>

Return the marker Class which party has used to register the counterparty flow that is to execute on the other side. The default implementation returns the class object of this FlowLogic, but any Class instance will do as long as the other side registers with it.

receive open fun <R : Any> receive(receiveType: Class<R>, otherParty: Party): UntrustworthyData<R>

Suspends until the specified otherParty sends us a message of type receiveType.

fun <R : Any> receive(otherParty: Party): UntrustworthyData<R>

Suspends until the specified otherParty sends us a message of type R.

send open fun send(otherParty: Party, payload: Any): Unit

Queues the given payload for sending to the otherParty and continues without suspending.

sendAndReceive fun <R : Any> sendAndReceive(otherParty: Party, payload: Any): UntrustworthyData<R>

Serializes and queues the given payload object for sending to the otherParty. Suspends until a response is received, which must be of the given R type.

open fun <R : Any> sendAndReceive(receiveType: Class<R>, otherParty: Party, payload: Any): UntrustworthyData<R>

Serializes and queues the given payload object for sending to the otherParty. Suspends until a response is received, which must be of the given receiveType. Remember that when receiving data from other parties the data should not be trusted until it's been thoroughly verified for consistency and that all expectations are satisfied, as a malicious peer may send you subtly corrupted data in order to exploit your code.

subFlow open fun <R> subFlow(subLogic: FlowLogic<R>, shareParentSessions: Boolean = false): R

Invokes the given subflow. This function returns once the subflow completes successfully with the result returned by that subflows call method. If the subflow has a progress tracker, it is attached to the current step in this flow's progress tracker.

track fun track(): Pair<String, Observable<String>>?

Returns a pair of the current progress step, as a string, and an observable of stringified changes to the progressTracker.

Inheritors

FetchAttachmentsFlow class FetchAttachmentsFlow : FetchDataFlow<Attachment, ByteArray>

Given a set of hashes either loads from from local storage or requests them from the other peer. Downloaded attachments are saved to local storage automatically.

FetchTransactionsFlow class FetchTransactionsFlow : FetchDataFlow<SignedTransaction, SignedTransaction>

Given a set of tx hashes (IDs), either loads them from local disk or asks the remote peer to provide them.