corda/docs/source/tutorial-clientrpc-api.rst

.. highlight:: kotlin
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.. _graphstream: http://graphstream-project.org/

Using the client RPC API
========================

In this tutorial we will build a simple command line utility that connects to a node, creates some cash transactions
and dumps the transaction graph to the standard output. We will then put some simple visualisation on top. For an
explanation on how RPC works in Corda see :doc:`clientrpc`.

We start off by connecting to the node itself. For the purposes of the tutorial we will use the Driver to start up a notary
and a Alice node that can issue, move and exit cash.

Here's how we configure the node to create a user that has the permissions to start the ``CashIssueFlow``,
``CashPaymentFlow``, and ``CashExitFlow``:

.. literalinclude:: example-code/src/main/kotlin/net/corda/docs/ClientRpcTutorial.kt
    :language: kotlin
    :start-after: START 1
    :end-before: END 1

Now we can connect to the node itself using a valid RPC user login and start generating transactions in a different
thread using ``generateTransactions`` (to be defined later):

.. literalinclude:: example-code/src/main/kotlin/net/corda/docs/ClientRpcTutorial.kt
    :language: kotlin
    :start-after: START 2
    :end-before: END 2
    :dedent: 8

``proxy`` exposes the full RPC interface of the node:

.. literalinclude:: ../../core/src/main/kotlin/net/corda/core/messaging/CordaRPCOps.kt
    :language: kotlin
    :start-after: interface CordaRPCOps
    :end-before: }

The RPC operation we need in order to dump the transaction graph is ``internalVerifiedTransactionsFeed``. The type
signature tells us that the RPC operation will return a list of transactions and an ``Observable`` stream. This is a
general pattern, we query some data and the node will return the current snapshot and future updates done to it.
Observables are described in further detail in :doc:`clientrpc`

.. literalinclude:: example-code/src/main/kotlin/net/corda/docs/ClientRpcTutorial.kt
    :language: kotlin
    :start-after: START 3
    :end-before: END 3
    :dedent: 8

The graph will be defined as follows:

* Each transaction is a vertex, represented by printing ``NODE <txhash>``
* Each input-output relationship is an edge, represented by printing ``EDGE <txhash> <txhash>``

.. literalinclude:: example-code/src/main/kotlin/net/corda/docs/ClientRpcTutorial.kt
    :language: kotlin
    :start-after: START 4
    :end-before: END 4
    :dedent: 8

Now we just need to create the transactions themselves!

.. literalinclude:: example-code/src/main/kotlin/net/corda/docs/ClientRpcTutorial.kt
    :language: kotlin
    :start-after: START 6
    :end-before: END 6

We utilise several RPC functions here to query things like the notaries in the node cluster or our own vault. These RPC
functions also return ``Observable`` objects so that the node can send us updated values. However, we don't need updates
here and so we mark these observables as ``notUsed`` (as a rule, you should always either subscribe to an ``Observable``
or mark it as not used. Failing to do so will leak resources in the node).

Then in a loop we generate randomly either an Issue, a Pay or an Exit transaction.

The RPC we need to initiate a cash transaction is ``startFlow`` which starts an arbitrary flow given sufficient
permissions to do so.

Finally we have everything in place: we start a couple of nodes, connect to them, and start creating transactions while
listening on successfully created ones, which are dumped to the console. We just need to run it!

.. code-block:: text

    # Build the example
    ./gradlew docs/source/example-code:installDist
    # Start it
    ./docs/source/example-code/build/install/docs/source/example-code/bin/client-rpc-tutorial Print

Now let's try to visualise the transaction graph. We will use a graph drawing library called graphstream_.

.. literalinclude:: example-code/src/main/kotlin/net/corda/docs/ClientRpcTutorial.kt
    :language: kotlin
    :start-after: START 5
    :end-before: END 5
    :dedent: 8

If we run the client with ``Visualise`` we should see a simple random graph being drawn as new transactions are being created.

Whitelisting classes from your CorDapp with the Corda node
----------------------------------------------------------

As described in :doc:`clientrpc`, you have to whitelist any additional classes you add that are needed in RPC
requests or responses with the Corda node.  Here's an example of both ways you can do this for a couple of example classes.

.. literalinclude:: example-code/src/main/kotlin/net/corda/docs/ClientRpcTutorial.kt
    :language: kotlin
    :start-after: START 7
    :end-before: END 7

See more on plugins in :doc:`running-a-node`.

Security
--------
RPC credentials associated with a Client must match the permission set configured on the server node.
This refers to both authentication (username and password) and role-based authorisation (a permissioned set of RPC operations an
authenticated user is entitled to run).

.. note:: Permissions are represented as *String's* to allow RPC implementations to add their own permissioning. Currently
     the only permission type defined is *StartFlow*, which defines a list of whitelisted flows an authenticated use may
     execute. An administrator user (or a developer) may also be assigned the ``ALL`` permission, which grants access to
     any flow.

In the instructions above the server node permissions are configured programmatically in the driver code:

.. code-block:: text

        driver(driverDirectory = baseDirectory) {
            val user = User("user", "password", permissions = setOf(startFlow<CashFlow>()))
            val node = startNode("CN=Alice Corp,O=Alice Corp,L=London,C=GB", rpcUsers = listOf(user)).get()

When starting a standalone node using a configuration file we must supply the RPC credentials as follows:

.. code-block:: text

    rpcUsers : [
        { username=user, password=password, permissions=[ StartFlow.net.corda.finance.flows.CashFlow ] }
    ]

When using the gradle Cordformation plugin to configure and deploy a node you must supply the RPC credentials in a similar
manner:

.. code-block:: text

        rpcUsers = [
                ['username' : "user",
                 'password' : "password",
                 'permissions' : ["StartFlow.net.corda.finance.flows.CashFlow"]]
        ]

You can then deploy and launch the nodes (Notary and Alice) as follows:

.. code-block:: text

    # to create a set of configs and installs under ``docs/source/example-code/build/nodes`` run
    ./gradlew docs/source/example-code:deployNodes
    # to open up two new terminals with the two nodes run
    ./docs/source/example-code/build/nodes/runnodes
    # followed by the same commands as before:
    ./docs/source/example-code/build/install/docs/source/example-code/bin/client-rpc-tutorial Print
    ./docs/source/example-code/build/install/docs/source/example-code/bin/client-rpc-tutorial Visualise

With regards to the start flow RPCs, there is an extra layer of security whereby the flow to be executed has to be
annotated with ``@StartableByRPC``. Flows without this annotation cannot execute using RPC.

See more on security in :doc:`secure-coding-guidelines`, node configuration in :doc:`corda-configuration-file` and
Cordformation in :doc:`running-a-node`.