mirror of
https://github.com/corda/corda.git
synced 2024-12-28 08:48:57 +00:00
81 lines
3.3 KiB
ReStructuredText
81 lines
3.3 KiB
ReStructuredText
|
Transaction tear-offs
|
|||
|
|
=====================
|
|||
|
|
|
|||
|
|
Example of usage
|
|||
|
|
----------------
|
|||
|
|
Let’s focus on a code example. We want to construct a transaction with commands containing interest rate fix data as in:
|
|||
|
|
:doc:`oracles`. After construction of a partial transaction, with included ``Fix`` commands in it, we want to send it
|
|||
|
|
to the Oracle for checking and signing. To do so we need to specify which parts of the transaction are going to be
|
|||
|
|
revealed. That can be done by constructing filtering function over fields of ``WireTransaction`` of type ``(Any) ->
|
|||
|
|
Boolean``.
|
|||
|
|
|
|||
|
|
.. container:: codeset
|
|||
|
|
|
|||
|
|
.. sourcecode:: kotlin
|
|||
|
|
|
|||
|
|
val partialTx = ...
|
|||
|
|
val oracle: Party = ...
|
|||
|
|
fun filtering(elem: Any): Boolean {
|
|||
|
|
return when (elem) {
|
|||
|
|
is Command -> oracleParty.owningKey in elem.signers && elem.value is Fix
|
|||
|
|
else -> false
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
Assuming that we already assembled partialTx with some commands and know the identity of Oracle service, we construct
|
|||
|
|
filtering function over commands - ``filtering``. It performs type checking and filters only ``Fix`` commands as in
|
|||
|
|
IRSDemo example. Then we can construct ``FilteredTransaction``:
|
|||
|
|
|
|||
|
|
.. container:: codeset
|
|||
|
|
|
|||
|
|
.. sourcecode:: kotlin
|
|||
|
|
|
|||
|
|
val wtx: WireTransaction = partialTx.toWireTransaction()
|
|||
|
|
val ftx: FilteredTransaction = wtx.buildFilteredTransaction(filtering)
|
|||
|
|
|
|||
|
|
In the Oracle example this step takes place in ``RatesFixFlow`` by overriding ``filtering`` function, see:
|
|||
|
|
:ref:`filtering_ref`.
|
|||
|
|
|
|||
|
|
``FilteredTransaction`` holds ``filteredLeaves`` (data that we wanted to reveal) and Merkle branch for them.
|
|||
|
|
|
|||
|
|
.. container:: codeset
|
|||
|
|
|
|||
|
|
.. sourcecode:: kotlin
|
|||
|
|
|
|||
|
|
// Direct accsess to included commands, inputs, outputs, attachments etc.
|
|||
|
|
val cmds: List<Command> = ftx.filteredLeaves.commands
|
|||
|
|
val ins: List<StateRef> = ftx.filteredLeaves.inputs
|
|||
|
|
val timestamp: Timestamp? = ftx.filteredLeaves.timestamp
|
|||
|
|
...
|
|||
|
|
|
|||
|
|
.. literalinclude:: ../../samples/irs-demo/src/main/kotlin/net/corda/irs/api/NodeInterestRates.kt
|
|||
|
|
:language: kotlin
|
|||
|
|
:start-after: DOCSTART 1
|
|||
|
|
:end-before: DOCEND 1
|
|||
|
|
|
|||
|
|
Above code snippet is taken from ``NodeInterestRates.kt`` file and implements a signing part of an Oracle. You can
|
|||
|
|
check only leaves using ``leaves.checkWithFun { check(it) }`` and then verify obtained ``FilteredTransaction`` to see
|
|||
|
|
if data from ``PartialMerkleTree`` belongs to ``WireTransaction`` with provided ``id``. All you need is the root hash
|
|||
|
|
of the full transaction:
|
|||
|
|
|
|||
|
|
.. container:: codeset
|
|||
|
|
|
|||
|
|
.. sourcecode:: kotlin
|
|||
|
|
|
|||
|
|
if (!ftx.verify(merkleRoot)){
|
|||
|
|
throw MerkleTreeException("Rate Fix Oracle: Couldn't verify partial Merkle tree.")
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
Or combine the two steps together:
|
|||
|
|
|
|||
|
|
.. container:: codeset
|
|||
|
|
|
|||
|
|
.. sourcecode:: kotlin
|
|||
|
|
|
|||
|
|
ftx.verifyWithFunction(merkleRoot, ::check)
|
|||
|
|
|
|||
|
|
.. note:: The way the ``FilteredTransaction`` is constructed ensures that after signing of the root hash it's impossible to add or remove
|
|||
|
|
leaves. However, it can happen that having transaction with multiple commands one party reveals only subset of them to the Oracle.
|
|||
|
|
As signing is done now over the Merkle root hash, the service signs all commands of given type, even though it didn't see
|
|||
|
|
all of them. This issue will be handled after implementing partial signatures.
|