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Updates TwoPartyTradeFlow to use the CollectSignaturesFlow.

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Joel Dudley 2017-06-01 11:08:39 +01:00 committed by GitHub
parent f8e2766924
commit f646936ab8
4 changed files with 236 additions and 245 deletions
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1
core/src/main/kotlin/net/corda/flows/CollectSignaturesFlow.kt
View File

@ -61,7 +61,6 @@ import java.security.PublicKey
* @param partiallySignedTx Transaction to collect the remaining signatures for
*/
// TODO: AbstractStateReplacementFlow needs updating to use this flow.
// TODO: TwoPartyTradeFlow needs updating to use this flow.
// TODO: Update this flow to handle randomly generated keys when that works is complete.
class CollectSignaturesFlow(val partiallySignedTx: SignedTransaction,
override val progressTracker: ProgressTracker = tracker()): FlowLogic<SignedTransaction>() {

374
docs/source/flow-state-machines.rst
View File

@ -89,9 +89,10 @@ Our flow has two parties (B and S for buyer and seller) and will proceed as foll
2. B sends to S a ``SignedTransaction`` that includes the state as input, B's cash as input, the state with the new
owner key as output, and any change cash as output. It contains a single signature from B but isn't valid because
it lacks a signature from S authorising movement of the asset.
3. S signs it and *finalises* the transaction. This means sending it to the notary, which checks the transaction for
validity, recording the transaction in the local vault, and then sending it back to B who also checks it and commits
the transaction to their local vault.
3. S signs the transaction and sends it back to B.
4. B *finalises* the transaction by sending it to the notary who checks the transaction for validity,
recording the transaction in B's local vault, and then sending it on to S who also checks it and commits
the transaction to S's local vault.
You can find the implementation of this flow in the file ``finance/src/main/kotlin/net/corda/flows/TwoPartyTradeFlow.kt``.
@ -124,9 +125,6 @@ each side.
val sellerOwnerKey: PublicKey
)
data class SignaturesFromSeller(val sellerSig: DigitalSignature.WithKey,
val notarySig: DigitalSignature.LegallyIdentifiable)
open class Seller(val otherParty: Party,
val notaryNode: NodeInfo,
val assetToSell: StateAndRef<OwnableState>,
@ -156,8 +154,8 @@ simply flow messages or exceptions. The other two represent the buyer and seller
Going through the data needed to become a seller, we have:
- ``otherParty: Party`` - the party with which you are trading.
- ``notaryNode: NodeInfo`` - the entry in the network map for the chosen notary. See ":doc:`key-concepts-consensus-notaries`" for more
information on notaries.
- ``notaryNode: NodeInfo`` - the entry in the network map for the chosen notary. See
":doc:`key-concepts-consensus-notaries`" for more information on notaries.
- ``assetToSell: StateAndRef<OwnableState>`` - a pointer to the ledger entry that represents the thing being sold.
- ``price: Amount<Currency>`` - the agreed on price that the asset is being sold for (without an issuer constraint).
- ``myKey: PublicKey`` - the PublicKey part of the node's internal KeyPair that controls the asset being sold.
@ -243,87 +241,111 @@ Let's implement the ``Seller.call`` method. This will be run when the flow is in
:end-before: DOCEND 4
:dedent: 4
Here we see the outline of the procedure. We receive a proposed trade transaction from the buyer and check that it's
valid. The buyer has already attached their signature before sending it. Then we calculate and attach our own signature
so that the transaction is now signed by both the buyer and the seller. We then *finalise* this transaction by sending
it to a notary to assert (with another signature) that the timestamp in the transaction (if any) is valid and there are no
double spends. Finally, after the finalisation process is complete, we retrieve the now fully signed transaction from
local storage. It will have the same ID as the one we started with but more signatures.
We start by sending information about the asset we wish to sell to the buyer. We fill out the initial flow message with
the trade info, and then call ``send``. which takes two arguments:
Let's fill out the ``receiveAndCheckProposedTransaction()`` method.
- The party we wish to send the message to.
- The payload being sent.
``send`` will serialise the payload and send it to the other party automatically.
Next, we call a *subflow* called ``SignTransactionFlow`` (see :ref:`subflows`). ``SignTransactionFlow`` automates the
process of:
* Receiving a proposed trade transaction from the buyer, with the buyer's signature attached.
* Checking that the proposed transaction is valid.
* Calculating and attaching our own signature so that the transaction is now signed by both the buyer and the seller.
* Sending the transaction back to the buyer.
The transaction then needs to be finalized. This is the the process of sending the transaction to a notary to assert
(with another signature) that the timestamp in the transaction (if any) is valid and there are no double spends.
In this flow, finalization is handled by the buyer, so we just wait for the signed transaction to appear in our
transaction storage. It will have the same ID as the one we started with but more signatures.
Implementing the buyer
----------------------
OK, let's do the same for the buyer side:
.. container:: codeset
.. literalinclude:: ../../finance/src/main/kotlin/net/corda/flows/TwoPartyTradeFlow.kt
:language: kotlin
:start-after: DOCSTART 5
:end-before: DOCEND 5
:start-after: DOCSTART 1
:end-before: DOCEND 1
:dedent: 4
Let's break this down. We fill out the initial flow message with the trade info, and then call ``sendAndReceive``.
This function takes a few arguments:
This code is longer but no more complicated. Here are some things to pay attention to:
- The party on the other side.
- The thing to send. It'll be serialised and sent automatically.
- Finally a type argument, which is the kind of object we're expecting to receive from the other side. If we get
back something else an exception is thrown.
1. We do some sanity checking on the proposed trade transaction received from the seller to ensure we're being offered
what we expected to be offered.
2. We create a cash spend using ``VaultService.generateSpend``. You can read the vault documentation to learn more about this.
3. We access the *service hub* as needed to access things that are transient and may change or be recreated
whilst a flow is suspended, such as the wallet or the network map.
4. We call ``CollectSignaturesFlow`` as a subflow to send the unfinished, still-invalid transaction to the seller so
they can sign it and send it back to us.
5. Last, we call ``FinalityFlow`` as a subflow to finalize the transaction.
Once ``sendAndReceive`` is called, the call method will be suspended into a continuation and saved to persistent
storage. If the node crashes or is restarted, the flow will effectively continue as if nothing had happened. Your
code may remain blocked inside such a call for seconds, minutes, hours or even days in the case of a flow that
needs human interaction!
As you can see, the flow logic is straightforward and does not contain any callbacks or network glue code, despite
the fact that it takes minimal resources and can survive node restarts.
.. note:: There are a couple of rules you need to bear in mind when writing a class that will be used as a continuation.
The first is that anything on the stack when the function is suspended will be stored into the heap and kept alive by
the garbage collector. So try to avoid keeping enormous data structures alive unless you really have to. You can
always use private methods to keep the stack uncluttered with temporary variables, or to avoid objects that
Kryo is not able to serialise correctly.
Flow sessions
-------------
The second is that as well as being kept on the heap, objects reachable from the stack will be serialised. The state
of the function call may be resurrected much later! Kryo doesn't require objects be marked as serialisable, but even so,
doing things like creating threads from inside these calls would be a bad idea. They should only contain business
logic and only do I/O via the methods exposed by the flow framework.
It will be useful to describe how flows communicate with each other. A node may have many flows running at the same
time, and perhaps communicating with the same counterparty node but for different purposes. Therefore flows need a
way to segregate communication channels so that concurrent conversations between flows on the same set of nodes do
not interfere with each other.
It's OK to keep references around to many large internal node services though: these will be serialised using a
special token that's recognised by the platform, and wired up to the right instance when the continuation is
loaded off disk again.
To achieve this the flow framework initiates a new flow session each time a flow starts communicating with a ``Party``
for the first time. A session is simply a pair of IDs, one for each side, to allow the node to route received messages to
the correct flow. If the other side accepts the session request then subsequent sends and receives to that same ``Party``
will use the same session. A session ends when either flow ends, whether as expected or pre-maturely. If a flow ends
pre-maturely then the other side will be notified of that and they will also end, as the whole point of flows is a known
sequence of message transfers. Flows end pre-maturely due to exceptions, and as described above, if that exception is
``FlowException`` or a sub-type then it will propagate to the other side. Any other exception will not propagate.
The buyer is supposed to send us a transaction with all the right inputs/outputs/commands in response to the opening
message, with their cash put into the transaction and their signature on it authorising the movement of the cash.
Taking a step back, we mentioned that the other side has to accept the session request for there to be a communication
channel. A node accepts a session request if it has registered the flow type (the fully-qualified class name) that is
making the request - each session initiation includes the initiating flow type. The registration is done by a CorDapp
which has made available the particular flow communication, using ``PluginServiceHub.registerServiceFlow``. This method
specifies a flow factory for generating the counter-flow to any given initiating flow. If this registration doesn't exist
then no further communication takes place and the initiating flow ends with an exception.
You get back a simple wrapper class, ``UntrustworthyData<SignedTransaction>``, which is just a marker class that reminds
us that the data came from a potentially malicious external source and may have been tampered with or be unexpected in
other ways. It doesn't add any functionality, but acts as a reminder to "scrub" the data before use.
Going back to our buyer and seller flows, we need a way to initiate communication between the two. This is typically done
with one side started manually using the ``startFlowDynamic`` RPC and this initiates the counter-flow on the other side.
In this case it doesn't matter which flow is the initiator and which is the initiated. If we choose the seller side as
the initiator then the buyer side would need to register their flow, perhaps with something like:
Our "scrubbing" has three parts:
.. container:: codeset
1. Check that the expected signatures are present and correct. At this point we expect our own signature to be missing,
because of course we didn't sign it yet, and also the signature of the notary because that must always come last.
2. We resolve the transaction, which we will cover below.
3. We verify that the transaction is paying us the demanded price.
.. sourcecode:: kotlin
Exception handling
------------------
class TwoPartyTradeFlowPlugin : CordaPluginRegistry() {
override val servicePlugins = listOf(Function(TwoPartyTradeFlowService::Service))
}
Flows can throw exceptions to prematurely terminate their execution. The flow framework gives special treatment to
``FlowException`` and its subtypes. These exceptions are treated as error responses of the flow and are propagated
to all counterparties it is communicating with. The receiving flows will throw the same exception the next time they do
a ``receive`` or ``sendAndReceive`` and thus end the flow session. If the receiver was invoked via ``subFlow`` (details below)
then the exception can be caught there enabling re-invocation of the sub-flow.
object TwoPartyTradeFlowService {
class Service(services: PluginServiceHub) {
init {
services.registerServiceFlow(TwoPartyTradeFlow.Seller::class.java) {
TwoPartyTradeFlow.Buyer(
it,
notary = services.networkMapCache.notaryNodes[0].notaryIdentity,
acceptablePrice = TODO(),
typeToBuy = TODO())
}
}
}
}
If the exception thrown by the erroring flow is not a ``FlowException`` it will still terminate but will not propagate to
the other counterparties. Instead they will be informed the flow has terminated and will themselves be terminated with a
generic exception.
This is telling the buyer node to fire up an instance of ``TwoPartyTradeFlow.Buyer`` (the code in the lambda) when
they receive a message from the initiating seller side of the flow (``TwoPartyTradeFlow.Seller::class.java``).
.. note:: A future version will extend this to give the node administrator more control on what to do with such erroring
flows.
.. _subflows:
Throwing a ``FlowException`` enables a flow to reject a piece of data it has received back to the sender. This is typically
done in the ``unwrap`` method of the received ``UntrustworthyData``. In the above example the seller checks the price
and throws ``FlowException`` if it's invalid. It's then up to the buyer to either try again with a better price or give up.
Sub-flows and finalisation
--------------------------
Sub-flows
---------
Flows can be composed via nesting. Invoking a sub-flow looks similar to an ordinary function call:
@ -345,130 +367,124 @@ Flows can be composed via nesting. Invoking a sub-flow looks similar to an ordin
subFlow(new FinalityFlow(unnotarisedTransaction))
}
In this code snippet we are using the ``FinalityFlow`` to finish off the transaction. It will:
Let's take a look at the three subflows we invoke in this flow.
FinalityFlow
^^^^^^^^^^^^
On the buyer side, we use ``FinalityFlow`` to finalise the transaction. It will:
* Send the transaction to the chosen notary and, if necessary, satisfy the notary that the transaction is valid.
* Record the transaction in the local vault, if it is relevant (i.e. involves the owner of the node).
* Send the fully signed transaction to the other participants for recording as well.
We simply create the flow object via its constructor, and then pass it to the ``subFlow`` method which
returns the result of the flow's execution directly. Behind the scenes all this is doing is wiring up progress
tracking (discussed more below) and then running the objects ``call`` method. Because the sub-flow might suspend,
we must mark the method that invokes it as suspendable.
Going back to the previous code snippet, we use a sub-flow called ``ResolveTransactionsFlow``. This is
responsible for downloading and checking all the dependencies of a transaction, which in Corda are always retrievable
from the party that sent you a transaction that uses them. This flow returns a list of ``LedgerTransaction``
objects, but we don't need them here so we just ignore the return value.
.. note:: Transaction dependency resolution assumes that the peer you got the transaction from has all of the
dependencies itself. It must do, otherwise it could not have convinced itself that the dependencies were themselves
valid. It's important to realise that requesting only the transactions we require is a privacy leak, because if
we don't download a transaction from the peer, they know we must have already seen it before. Fixing this privacy
leak will come later.
After the dependencies, we check the proposed trading transaction for validity by running the contracts for that as
well (but having handled the fact that some signatures are missing ourselves).
.. warning:: If the seller stops before sending the finalised transaction to the buyer, the seller is left with a
valid transaction but the buyer isn't, so they can't spend the asset they just purchased! This sort of thing is not
always a risk (as the seller may not gain anything from that sort of behaviour except a lawsuit), but if it is, a future
version of the platform will allow you to ask the notary to send you the transaction as well, in case your counterparty
does not. This is not the default because it reveals more private info to the notary.
Implementing the buyer
----------------------
We simply create the flow object via its constructor, and then pass it to the ``subFlow`` method which
returns the result of the flow's execution directly. Behind the scenes all this is doing is wiring up progress
tracking (discussed more below) and then running the object's ``call`` method. Because the sub-flow might suspend,
we must mark the method that invokes it as suspendable.
OK, let's do the same for the buyer side:
Within FinalityFlow, we use a further sub-flow called ``ResolveTransactionsFlow``. This is responsible for downloading
and checking all the dependencies of a transaction, which in Corda are always retrievable from the party that sent you a
transaction that uses them. This flow returns a list of ``LedgerTransaction`` objects.
.. note:: Transaction dependency resolution assumes that the peer you got the transaction from has all of the
dependencies itself. It must do, otherwise it could not have convinced itself that the dependencies were themselves
valid. It's important to realise that requesting only the transactions we require is a privacy leak, because if
we don't download a transaction from the peer, they know we must have already seen it before. Fixing this privacy
leak will come later.
CollectSignaturesFlow/SignTransactionFlow
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
We also invoke two other subflows:
* ``CollectSignaturesFlow``, on the buyer side
* ``SignTransactionFlow``, on the seller side
These flows communicate to gather all the required signatures for the proposed transaction. ``CollectSignaturesFlow``
will:
* Verify any signatures collected on the transaction so far
* Verify the transaction itself
* Send the transaction to the remaining required signers and receive back their signatures
* Verify the collected signatures
``SignTransactionFlow`` responds by:
* Receiving the partially-signed transaction off the wire
* Verifying the existing signatures
* Resolving the transaction's dependencies
* Verifying the transaction itself
* Running any custom validation logic
* Sending their signature back to the buyer
* Waiting for the transaction to be recorded in their vault
We cannot instantiate ``SignTransactionFlow`` itself, as it's an abstract class. Instead, we need to subclass it and
override ``checkTransaction()`` to add our own custom validation logic:
.. container:: codeset
.. literalinclude:: ../../finance/src/main/kotlin/net/corda/flows/TwoPartyTradeFlow.kt
:language: kotlin
:start-after: DOCSTART 1
:end-before: DOCEND 1
:dedent: 4
:start-after: DOCSTART 5
:end-before: DOCEND 5
:dedent: 12
This code is longer but no more complicated. Here are some things to pay attention to:
In this case, our custom validation logic ensures that the amount of cash outputs in the transaction equals the
price of the asset.
1. We do some sanity checking on the received message to ensure we're being offered what we expected to be offered.
2. We create a cash spend using ``VaultService.generateSpend``. You can read the vault documentation to learn more about this.
3. We access the *service hub* when we need it to access things that are transient and may change or be recreated
whilst a flow is suspended, things like the wallet or the network map.
4. We send the unfinished, invalid transaction to the seller so they can sign it and finalise it.
5. Finally, we wait for the finished transaction to arrive in our local storage and vault.
Persisting flows
----------------
As you can see, the flow logic is straightforward and does not contain any callbacks or network glue code, despite
the fact that it takes minimal resources and can survive node restarts.
If you look at the code for ``FinalityFlow``, ``CollectSignaturesFlow`` and ``SignTransactionFlow``, you'll see calls
to both ``receive`` and ``sendAndReceive``. Once either of these methods is called, the ``call`` method will be
suspended into a continuation and saved to persistent storage. If the node crashes or is restarted, the flow will
effectively continue as if nothing had happened. Your code may remain blocked inside such a call for seconds,
minutes, hours or even days in the case of a flow that needs human interaction!
Flow sessions
-------------
.. note:: There are a couple of rules you need to bear in mind when writing a class that will be used as a continuation.
The first is that anything on the stack when the function is suspended will be stored into the heap and kept alive by
the garbage collector. So try to avoid keeping enormous data structures alive unless you really have to. You can
always use private methods to keep the stack uncluttered with temporary variables, or to avoid objects that
Kryo is not able to serialise correctly.
Before going any further it will be useful to describe how flows communicate with each other. A node may have many flows
running at the same time, and perhaps communicating with the same counterparty node but for different purposes. Therefore
flows need a way to segregate communication channels so that concurrent conversations between flows on the same set of nodes
do not interfere with each other.
The second is that as well as being kept on the heap, objects reachable from the stack will be serialised. The state
of the function call may be resurrected much later! Kryo doesn't require objects be marked as serialisable, but even so,
doing things like creating threads from inside these calls would be a bad idea. They should only contain business
logic and only do I/O via the methods exposed by the flow framework.
To achieve this the flow framework initiates a new flow session each time a flow starts communicating with a ``Party``
for the first time. A session is simply a pair of IDs, one for each side, to allow the node to route received messages to
the correct flow. If the other side accepts the session request then subsequent sends and receives to that same ``Party``
will use the same session. A session ends when either flow ends, whether as expected or pre-maturely. If a flow ends
pre-maturely then the other side will be notified of that and they will also end, as the whole point of flows is a known
sequence of message transfers. Flows end pre-maturely due to exceptions, and as described above, if that exception is
``FlowException`` or a sub-type then it will propagate to the other side. Any other exception will not propagate.
It's OK to keep references around to many large internal node services though: these will be serialised using a
special token that's recognised by the platform, and wired up to the right instance when the continuation is
loaded off disk again.
Taking a step back, we mentioned that the other side has to accept the session request for there to be a communication
channel. A node accepts a session request if it has registered the flow type (the fully-qualified class name) that is
making the request - each session initiation includes the initiating flow type. This registration is done automatically
by the node at startup by searching for flows which are annotated with ``@InitiatedBy``. This annotation points to the
flow that is doing the initiating, and this flow must be annotated with ``@InitiatingFlow``. The ``InitiatedBy`` flow
must have a constructor which takes in a single parameter of type ``Party`` - this is the initiating party.
``receive`` and ``sendAndReceive`` return a simple wrapper class, ``UntrustworthyData<T>``, which is
just a marker class that reminds us that the data came from a potentially malicious external source and may have been
tampered with or be unexpected in other ways. It doesn't add any functionality, but acts as a reminder to "scrub"
the data before use.
Going back to our buyer and seller flows, we need a way to initiate communication between the two. This is typically done
with one side started manually using the ``startFlowDynamic`` RPC and this initiates the flow on the other side. In our
case it doesn't matter which flow is the initiator and which is the initiated, which is why neither ``Buyer`` nor ``Seller``
are annotated with ``InitiatedBy`` or ``InitiatingFlow``. If we, for example, choose the seller side as the initiator then
we need to create a simple seller starter flow that has the annotation we need:
Exception handling
------------------
.. container:: codeset
Flows can throw exceptions to prematurely terminate their execution. The flow framework gives special treatment to
``FlowException`` and its subtypes. These exceptions are treated as error responses of the flow and are propagated
to all counterparties it is communicating with. The receiving flows will throw the same exception the next time they do
a ``receive`` or ``sendAndReceive`` and thus end the flow session. If the receiver was invoked via ``subFlow`` (details below)
then the exception can be caught there enabling re-invocation of the sub-flow.
.. sourcecode:: kotlin
If the exception thrown by the erroring flow is not a ``FlowException`` it will still terminate but will not propagate to
the other counterparties. Instead they will be informed the flow has terminated and will themselves be terminated with a
generic exception.
@InitiatingFlow
class SellerInitiator(val buyer: Party,
val notary: NodeInfo,
val assetToSell: StateAndRef<OwnableState>,
val price: Amount<Currency>) : FlowLogic<SignedTransaction>() {
@Suspendable
override fun call(): SignedTransaction {
send(buyer, Pair(notary.notaryIdentity, price))
return subFlow(Seller(
buyer,
notary,
assetToSell,
price,
serviceHub.legalIdentityKey))
}
}
.. note:: A future version will extend this to give the node administrator more control on what to do with such erroring
flows.
The buyer side would look something like this. Notice the constructor takes in a single ``Party`` object which represents
the seller.
.. container:: codeset
.. sourcecode:: kotlin
@InitiatedBy(SellerInitiator::class)
class BuyerAcceptor(val seller: Party) : FlowLogic<Unit>() {
@Suspendable
override fun call() {
val (notary, price) = receive<Pair<Party, Amount<Currency>>>(seller).unwrap {
require(serviceHub.networkMapCache.isNotary(it.first)) { "${it.first} is not a notary" }
it
}
subFlow(Buyer(seller, notary, price, CommercialPaper.State::class.java))
}
}
Throwing a ``FlowException`` enables a flow to reject a piece of data it has received back to the sender. This is typically
done in the ``unwrap`` method of the received ``UntrustworthyData``. In the above example the seller checks the price
and throws ``FlowException`` if it's invalid. It's then up to the buyer to either try again with a better price or give up.
.. _progress-tracking:
@ -497,22 +513,28 @@ A flow might declare some steps with code inside the flow class like this:
.. sourcecode:: java
private final ProgressTracker progressTracker = new ProgressTracker(
CONSTRUCTING_OFFER,
SENDING_OFFER_AND_RECEIVING_PARTIAL_TRANSACTION,
VERIFYING
RECEIVING,
VERIFYING,
SIGNING,
COLLECTING_SIGNATURES,
RECORDING
);
private static final ProgressTracker.Step CONSTRUCTING_OFFER = new ProgressTracker.Step(
"Constructing proposed purchase order.");
private static final ProgressTracker.Step SENDING_OFFER_AND_RECEIVING_PARTIAL_TRANSACTION = new ProgressTracker.Step(
"Sending purchase order to seller for review, and receiving partially signed transaction from seller in return.");
private static final ProgressTracker.Step RECEIVING = new ProgressTracker.Step(
"Waiting for seller trading info");
private static final ProgressTracker.Step VERIFYING = new ProgressTracker.Step(
"Verifying signatures and contract constraints.");
"Verifying seller assets");
private static final ProgressTracker.Step SIGNING = new ProgressTracker.Step(
"Generating and signing transaction proposal");
private static final ProgressTracker.Step COLLECTING_SIGNATURES = new ProgressTracker.Step(
"Collecting signatures from other parties");
private static final ProgressTracker.Step RECORDING = new ProgressTracker.Step(
"Recording completed transaction");
Each step exposes a label. By default labels are fixed, but by subclassing ``RelabelableStep``
you can make a step that can update its label on the fly. That's useful for steps that want to expose non-structured
progress information like the current file being downloaded. By defining your own step types, you can export progress
in a way that's both human readable and machine readable.
Each step exposes a label. By default labels are fixed, but by subclassing ``RelabelableStep`` you can make a step
that can update its label on the fly. That's useful for steps that want to expose non-structured progress information
like the current file being downloaded. By defining your own step types, you can export progress in a way that's both
human readable and machine readable.
Progress trackers are hierarchical. Each step can be the parent for another tracker. By altering the
``ProgressTracker.childrenFor`` map, a tree of steps can be created. It's allowed to alter the hierarchy
@ -531,9 +553,9 @@ steps by overriding the ``Step`` class like this:
.. sourcecode:: java
private static final ProgressTracker.Step COMMITTING = new ProgressTracker.Step("Committing to the ledger.") {
private static final ProgressTracker.Step VERIFYING_AND_SIGNING = new ProgressTracker.Step("Verifying and signing transaction proposal") {
@Nullable @Override public ProgressTracker childProgressTracker() {
return FinalityFlow.Companion.tracker();
return SignTransactionFlow.Companion.tracker();
}
};

88
finance/src/main/kotlin/net/corda/flows/TwoPartyTradeFlow.kt
View File

@ -3,7 +3,6 @@ package net.corda.flows
import co.paralleluniverse.fibers.Suspendable
import net.corda.contracts.asset.sumCashBy
import net.corda.core.contracts.*
import net.corda.core.crypto.DigitalSignature
import net.corda.core.flows.FlowException
import net.corda.core.flows.FlowLogic
import net.corda.core.identity.AnonymousParty
@ -13,9 +12,7 @@ import net.corda.core.seconds
import net.corda.core.serialization.CordaSerializable
import net.corda.core.transactions.SignedTransaction
import net.corda.core.transactions.TransactionBuilder
import net.corda.core.transactions.WireTransaction
import net.corda.core.utilities.ProgressTracker
import net.corda.core.utilities.trace
import net.corda.core.utilities.unwrap
import java.security.PublicKey
import java.util.*
@ -36,8 +33,6 @@ import java.util.*
* that represents an atomic asset swap.
*
* Note that it's the *seller* who initiates contact with the buyer, not vice-versa as you might imagine.
*
* TODO: Refactor this using the [CollectSignaturesFlow]. Note. It requires a large docsite update!
*/
object TwoPartyTradeFlow {
// TODO: Common elements in multi-party transaction consensus and signing should be refactored into a superclass of this
@ -57,10 +52,6 @@ object TwoPartyTradeFlow {
val sellerOwnerKey: PublicKey
)
@CordaSerializable
data class SignaturesFromSeller(val sellerSig: DigitalSignature.WithKey,
val notarySig: DigitalSignature.WithKey)
open class Seller(val otherParty: PartyAndCertificate,
val notaryNode: NodeInfo,
val assetToSell: StateAndRef<OwnableState>,
@ -70,62 +61,42 @@ object TwoPartyTradeFlow {
companion object {
object AWAITING_PROPOSAL : ProgressTracker.Step("Awaiting transaction proposal")
object VERIFYING : ProgressTracker.Step("Verifying transaction proposal")
object SIGNING : ProgressTracker.Step("Signing transaction")
// DOCSTART 3
object COMMITTING : ProgressTracker.Step("Committing transaction to the ledger") {
override fun childProgressTracker() = FinalityFlow.tracker()
object VERIFYING_AND_SIGNING : ProgressTracker.Step("Verifying and signing transaction proposal") {
override fun childProgressTracker() = SignTransactionFlow.tracker()
}
// DOCEND 3
object SENDING_FINAL_TX : ProgressTracker.Step("Sending final transaction to buyer")
fun tracker() = ProgressTracker(AWAITING_PROPOSAL, VERIFYING, SIGNING, COMMITTING, SENDING_FINAL_TX)
fun tracker() = ProgressTracker(AWAITING_PROPOSAL, VERIFYING_AND_SIGNING)
}
// DOCSTART 4
@Suspendable
override fun call(): SignedTransaction {
val partialSTX: SignedTransaction = receiveAndCheckProposedTransaction()
val ourSignature = calculateOurSignature(partialSTX)
val unnotarisedSTX: SignedTransaction = partialSTX + ourSignature
val finishedSTX = subFlow(FinalityFlow(unnotarisedSTX)).single()
return finishedSTX
}
// DOCEND 4
// DOCSTART 5
@Suspendable
private fun receiveAndCheckProposedTransaction(): SignedTransaction {
progressTracker.currentStep = AWAITING_PROPOSAL
// Make the first message we'll send to kick off the flow.
val hello = SellerTradeInfo(assetToSell, price, myKey)
// What we get back from the other side is a transaction that *might* be valid and acceptable to us,
// but we must check it out thoroughly before we sign!
val untrustedSTX = sendAndReceive<SignedTransaction>(otherParty, hello)
send(otherParty, hello)
progressTracker.currentStep = VERIFYING
return untrustedSTX.unwrap {
// Check that the tx proposed by the buyer is valid.
val wtx: WireTransaction = it.verifySignatures(myKey, notaryNode.notaryIdentity.owningKey)
logger.trace { "Received partially signed transaction: ${it.id}" }
// Download and check all the things that this transaction depends on and verify it is contract-valid,
// even though it is missing signatures.
subFlow(ResolveTransactionsFlow(wtx, otherParty))
if (wtx.outputs.map { it.data }.sumCashBy(AnonymousParty(myKey)).withoutIssuer() != price)
// Verify and sign the transaction.
progressTracker.currentStep = VERIFYING_AND_SIGNING
// DOCSTART 5
val signTransactionFlow = object : SignTransactionFlow(otherParty, VERIFYING_AND_SIGNING.childProgressTracker()) {
override fun checkTransaction(stx: SignedTransaction) {
if (stx.tx.outputs.map { it.data }.sumCashBy(AnonymousParty(myKey)).withoutIssuer() != price)
throw FlowException("Transaction is not sending us the right amount of cash")
it
}
}
return subFlow(signTransactionFlow)
// DOCEND 5
}
// DOCEND 4
// Following comment moved here so that it doesn't appear in the docsite:
// There are all sorts of funny games a malicious secondary might play with it sends maybeSTX (in
// receiveAndCheckProposedTransaction), we should fix them:
// There are all sorts of funny games a malicious secondary might play with it sends maybeSTX,
// we should fix them:
//
// - This tx may attempt to send some assets we aren't intending to sell to the secondary, if
// we're reusing keys! So don't reuse keys!
@ -134,11 +105,6 @@ object TwoPartyTradeFlow {
//
// but the goal of this code is not to be fully secure (yet), but rather, just to find good ways to
// express flow state machines on top of the messaging layer.
open fun calculateOurSignature(partialTX: SignedTransaction): DigitalSignature.WithKey {
progressTracker.currentStep = SIGNING
return serviceHub.createSignature(partialTX, myKey)
}
}
open class Buyer(val otherParty: PartyAndCertificate,
@ -149,10 +115,15 @@ object TwoPartyTradeFlow {
object RECEIVING : ProgressTracker.Step("Waiting for seller trading info")
object VERIFYING : ProgressTracker.Step("Verifying seller assets")
object SIGNING : ProgressTracker.Step("Generating and signing transaction proposal")
object SENDING_SIGNATURES : ProgressTracker.Step("Sending signatures to the seller")
object WAITING_FOR_TX : ProgressTracker.Step("Waiting for the transaction to finalise.")
object COLLECTING_SIGNATURES : ProgressTracker.Step("Collecting signatures from other parties") {
override fun childProgressTracker() = CollectSignaturesFlow.tracker()
}
object RECORDING : ProgressTracker.Step("Recording completed transaction") {
// TODO: Currently triggers a race condition on Team City. See https://github.com/corda/corda/issues/733.
// override fun childProgressTracker() = FinalityFlow.tracker()
}
override val progressTracker = ProgressTracker(RECEIVING, VERIFYING, SIGNING, SENDING_SIGNATURES, WAITING_FOR_TX)
override val progressTracker = ProgressTracker(RECEIVING, VERIFYING, SIGNING, COLLECTING_SIGNATURES, RECORDING)
// DOCEND 2
// DOCSTART 1
@ -165,16 +136,16 @@ object TwoPartyTradeFlow {
// Put together a proposed transaction that performs the trade, and sign it.
progressTracker.currentStep = SIGNING
val (ptx, cashSigningPubKeys) = assembleSharedTX(tradeRequest)
val stx = signWithOurKeys(cashSigningPubKeys, ptx)
val partSignedTx = signWithOurKeys(cashSigningPubKeys, ptx)
// Send the signed transaction to the seller, who must then sign it themselves and commit
// it to the ledger by sending it to the notary.
progressTracker.currentStep = SENDING_SIGNATURES
send(otherParty, stx)
progressTracker.currentStep = COLLECTING_SIGNATURES
val twiceSignedTx = subFlow(CollectSignaturesFlow(partSignedTx, COLLECTING_SIGNATURES.childProgressTracker()))
// Wait for the finished, notarised transaction to arrive in our transaction store.
progressTracker.currentStep = WAITING_FOR_TX
return waitForLedgerCommit(stx.id)
// Notarise and record the transaction.
progressTracker.currentStep = RECORDING
return subFlow(FinalityFlow(twiceSignedTx, setOf(otherParty, serviceHub.myInfo.legalIdentity))).single()
}
@Suspendable
@ -186,7 +157,6 @@ object TwoPartyTradeFlow {
// What is the seller trying to sell us?
val asset = it.assetForSale.state.data
val assetTypeName = asset.javaClass.name
logger.trace { "Got trade request for a $assetTypeName: ${it.assetForSale}" }
if (it.price > acceptablePrice)
throw UnacceptablePriceException(it.price)

4
node/src/test/kotlin/net/corda/node/messaging/TwoPartyTradeFlowTests.kt
View File

@ -308,7 +308,7 @@ class TwoPartyTradeFlowTests {
attachment(ByteArrayInputStream(stream.toByteArray()))
}
val extraKey = bobNode.keyManagement.freshKey()
val extraKey = bobNode.keyManagement.keys.single()
val bobsFakeCash = fillUpForBuyer(false, AnonymousParty(extraKey),
DUMMY_CASH_ISSUER.party,
notaryNode.info.notaryIdentity).second
@ -407,7 +407,7 @@ class TwoPartyTradeFlowTests {
attachment(ByteArrayInputStream(stream.toByteArray()))
}
val bobsKey = bobNode.keyManagement.freshKey()
val bobsKey = bobNode.keyManagement.keys.single()
val bobsFakeCash = fillUpForBuyer(false, AnonymousParty(bobsKey),
DUMMY_CASH_ISSUER.party,
notaryNode.info.notaryIdentity).second