This demo marries Corda with Hedera via the Hedera Consensus Service, providing double-spend checks by submitting transaction spends to HCS and ordering them with other spends on the same network.
You must have JDK 8 installed and set up (the JAVA_HOME environment variable must be set).
Open a terminal in the parent directory where you want to clone the repo. Unless otherwise specified, all following code blocks are entered in this terminal window with "Enter" being pressed after each line.
git clone git@github.com:hashgraph/hedera-hcs-corda
cd hedera-hcs-cordaThis will also remove node data from previous runs (for consistency)
./gradlew clean deployNodes./build/nodes/runnodes3 new terminal windows will open: "Notary", "PartyA" and "PartyB". They will go through
an initialization process that may take a minute or so. You will know when all the nodes are ready
when you see a >>> prompt in each terminal window.
The contract doesn't actually require the lending party to have sufficient balance for a loan but for the demo to make sense it's kind of important to show this step anyway.
In the "Party A" terminal window, type the following and press "Enter":
flow start CashIssueFlow amount: $100, issuerBankPartyRef: "some bank", notary: "Notary"amount may be any USD, GBP or Euro amount with their respective currency symbol prefixes;
this procedure assumes a US keyboard layout and so uses USD.
issuerBankPartyRef may be any text and exists purely for recording purposes; in the context of the
demo it would be the name of the bank that recorded the cash deposit.
notary must be "Notary", although notarisation is apparently not required for CashIssueFlow
as it never actually talks to the notary.
In the "Party B" terminal window, type the following and press "Enter":
flow start IssueObligation amount: $25, lender: "Party A", anonymous: falseamount has the same semantics as the previous step; for consistency purposes you should
use the same currency for all amounts.
lender must be a valid party name on the network, though the only other party who may
lend money in the current network configuration is "Party A".
anonymous may be set to true or false; true means that the obligation will not
record who is requesting the loan. For demonstration purposes we want the obligation to show
both parties so we specify false.
When you enter this command, when the transaction reaches the "Requesting signature from Notary service" step you will see activity in the "Notary" terminal window showing it submitting the HCS message to Hedera with a sequence number and then receiving back a message with that same sequence number.
In the "Party B" terminal window, enter:
run vaultQuery contractStateType: net.corda.examples.obligation.ObligationThis will print out a bunch of information about our IOU. The important keys to note are
the "Lender" and the "Borrower" parties, which should be "Party A" and "Party B", respectively,
and the amount: key showing the balance of our IOU.
Then you want to look for the linearId: key and the id: key underneath it. Copy that UUID
(that will look something like this: "2767ac1e-a8ec-4a1a-a0ab-1bafd4d98df2") as you will need
it in step 8.
This is the same as step 4, except this time we enter the command in the "Party B"
terminal window. Make sure the amount is greater than or equal to the balance of our IOU
(although you can actually make partial payments on IOUs, we won't be doing that for this demo
as those steps look identical to steps 6 - 8).
In the "Party B" terminal window, enter the following:
flow start SettleObligation linearId: <linear ID from vaultQuery>, amount: $25, anonymous: falseFor linearId, paste in the UUID that you got from step 6, including the double quotes "".
amount doesn't have to be the full balance of our IOU but would require repeating this step
(as well as the previous step if Party B's cash balance is insufficent).
anonymous has the same semantics as in step 5 but we're not going to bother with anonymity.
When you enter this command, you will see more activity in the "Notary" terminal window, again submitting the transaction to HCS for global ordering before checking for double-spends.
In the "Party B" terminal window, run the same command as step 6 again; this time you will see a much shorter response with no obligations listed. Our debt has been repaid.
If you wish to repeat the demo, return to step 4.
Otherwise, in each of "Notary", "Party A" and "Party B" terminal windows, type bye and press
"Enter" to shut down the nodes. Each terminal window should close a few moments after entering the
command.