2017-10-25 11:32:31 +00:00
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.. highlight:: kotlin
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.. raw:: html
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<script type="text/javascript" src="_static/jquery.js"></script>
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<script type="text/javascript" src="_static/codesets.js"></script>
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Observer nodes
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==============
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Posting transactions to an observer node is a common requirement in finance, where regulators often want
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to receive comprehensive reporting on all actions taken. By running their own node, regulators can receive a stream
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of digitally signed, de-duplicated reports useful for later processing.
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Adding support for observer nodes to your application is easy. The IRS (interest rate swap) demo shows to do it.
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Just define a new flow that wraps the SendTransactionFlow/ReceiveTransactionFlow, as follows:
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.. container:: codeset
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.. literalinclude:: ../../samples/irs-demo/cordapp/src/main/kotlin/net/corda/irs/flows/AutoOfferFlow.kt
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:language: kotlin
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:start-after: DOCSTART 1
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:end-before: DOCEND 1
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In this example, the ``AutoOfferFlow`` is the business logic, and we define two very short and simple flows to send
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the transaction to the regulator. There are two important aspects to note here:
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1. The ``ReportToRegulatorFlow`` is marked as an ``@InitiatingFlow`` because it will start a new conversation, context
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free, with the regulator.
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2. The ``ReceiveRegulatoryReportFlow`` uses ``ReceiveTransactionFlow`` in a special way - it tells it to send the
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transaction to the vault for processing, including all states even if not involving our public keys. This is required
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because otherwise the vault will ignore states that don't list any of the node's public keys, but in this case,
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we do want to passively observe states we can't change. So overriding this behaviour is required.
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If the states define a relational mapping (see :doc:`api-persistence`) then the regulator will be able to query the
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2017-10-26 14:36:46 +00:00
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reports from their database and observe new transactions coming in via RPC.
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.. warning:: Nodes which act as both observers and which directly take part in the ledger are not supported at this
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time. In particular, coin selection may return states which you do not have the private keys to be able to sign
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for. Future versions of Corda may address this issue, but for now, if you wish to both participate in the ledger
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and also observe transactions that you can't sign for you will need to run two nodes and have two separate
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identities.
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