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61 lines
3.3 KiB
ReStructuredText
61 lines
3.3 KiB
ReStructuredText
Flow library
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============
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There are a number of built-in flows supplied with Corda, which cover some core functionality.
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FinalityFlow
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------------
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The ``FinalityFlow`` verifies the given transactions, then sends them to the specified notary.
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If the notary agrees that the transactions are acceptable then they are from that point onwards committed to the ledger,
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and will be written through to the vault. Additionally they will be distributed to the parties reflected in the participants
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list of the states.
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The transactions will be topologically sorted before commitment to ensure that dependencies are committed before
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dependers, so you don't need to do this yourself.
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The transactions are expected to have already been resolved: if their dependencies are not available in local storage or
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within the given set, verification will fail. They must have signatures from all necessary parties other than the notary.
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If specified, the extra recipients are sent all the given transactions. The base set of parties to inform of each
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transaction are calculated on a per transaction basis from the contract-given set of participants.
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The flow returns the same transactions, in the same order, with the additional signatures.
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CollectSignaturesFlow
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---------------------
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The ``CollectSignaturesFlow`` is used to automate the collection of signatures from the counterparties to a transaction.
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You use the ``CollectSignaturesFlow`` by passing it a ``SignedTransaction`` which has at least been signed by yourself.
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The flow will handle the resolution of the counterparty identities and request a signature from each counterparty.
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Finally, the flow will verify all the signatures and return a ``SignedTransaction`` with all the collected signatures.
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When using this flow on the responding side you will have to subclass the ``AbstractCollectSignaturesFlowResponder`` and
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provide your own implementation of the ``checkTransaction`` method. This is to add additional verification logic on the
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responder side. Types of things you will need to check include:
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* Ensuring that the transaction you are receiving is the transaction you *EXPECT* to receive. I.e. is has the expected
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type of inputs and outputs
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* Checking that the properties of the outputs are as you would expect, this is in the absence of integrating reference
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data sources to facilitate this for us
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* Checking that the transaction is not incorrectly spending (perhaps maliciously) one of your asset states, as potentially
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the transaction creator has access to some of your state references
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Typically after calling the ``CollectSignaturesFlow`` you then called the ``FinalityFlow``.
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SendTransactionFlow/ReceiveTransactionFlow
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------------------------------------------
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The ``SendTransactionFlow`` and ``ReceiveTransactionFlow`` are used to automate the verification of the transaction by
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recursively checking the validity of all the dependencies. Once a transaction is received and checked it's inserted into
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local storage so it can be relayed and won't be checked again.
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The ``SendTransactionFlow`` sends the transaction to the counterparty and listen for data request as the counterparty
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validating the transaction, extra checks can be implemented to restrict data access by overriding the ``verifyDataRequest``
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method inside ``SendTransactionFlow``.
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The ``ReceiveTransactionFlow`` returns a verified ``SignedTransaction``. |