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257 lines
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257 lines
12 KiB
ReStructuredText
Client RPC
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==========
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There are multiple ways to interact with a node from a *client program*, but if your client is written in a JVM
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compatible language the easiest way to do so is using the client library. The library connects to your running
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node using a message queue protocol and then provides a simple RPC interface to interact with it. You make calls
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on a Java object as normal, and the marshalling back and forth is handled for you.
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The starting point for the client library is the `CordaRPCClient`_ class. This provides a ``start`` method that
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returns a `CordaRPCConnection`_, holding an implementation of the `CordaRPCOps`_ that may be accessed with ``proxy``
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in Kotlin and ``getProxy()`` in Java. Observables that are returned by RPCs can be subscribed to in order to receive
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an ongoing stream of updates from the node. More detail on how to use this is provided in the docs for the proxy method.
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.. warning:: The returned `CordaRPCConnection`_ is somewhat expensive to create and consumes a small amount of
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server side resources. When you're done with it, call ``close`` on it. Alternatively you may use the ``use``
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method on `CordaRPCClient`_ which cleans up automatically after the passed in lambda finishes. Don't create
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a new proxy for every call you make - reuse an existing one.
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For a brief tutorial on how one can use the RPC API see :doc:`tutorial-clientrpc-api`.
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RPC permissions
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---------------
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If a node's owner needs to interact with their node via RPC (e.g. to read the contents of the node's storage), they
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must define one or more RPC users. Each user is authenticated with a username and password, and is assigned a set of
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permissions that RPC can use for fine-grain access control.
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These users are added to the node's ``node.conf`` file.
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The simplest way of adding an RPC user is to include it in the ``rpcUsers`` list:
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.. container:: codeset
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.. sourcecode:: groovy
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rpcUsers=[
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{
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username=exampleUser
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password=examplePass
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permissions=[]
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}
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...
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]
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Users need permissions to invoke any RPC call. By default, nothing is allowed. These permissions are specified as follows:
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.. container:: codeset
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.. sourcecode:: groovy
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rpcUsers=[
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{
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username=exampleUser
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password=examplePass
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permissions=[
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"StartFlow.net.corda.flows.ExampleFlow1",
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"StartFlow.net.corda.flows.ExampleFlow2"
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]
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}
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...
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]
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Permissions Syntax
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^^^^^^^^^^^^^^^^^^
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Fine grained permissions allow a user to invoke a specific RPC operation, or to start a specific flow. The syntax is:
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- to start a specific flow: ``StartFlow.<fully qualified flow name>`` e.g., ``StartFlow.net.corda.flows.ExampleFlow1``.
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- to invoke a RPC operation: ``InvokeRpc.<rpc method name>`` e.g., ``InvokeRpc.nodeInfo``.
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.. note:: Permission ``InvokeRpc.startFlow`` allows a user to initiate all flows.
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RPC security management
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-----------------------
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Setting ``rpcUsers`` provides a simple way of granting RPC permissions to a fixed set of users, but has some
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obvious shortcomings. To support use cases aiming for higher security and flexibility, Corda offers additional security
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features such as:
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* Fetching users credentials and permissions from an external data source (e.g.: a remote RDBMS), with optional in-memory
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caching. In particular, this allows credentials and permissions to be updated externally without requiring nodes to be
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restarted.
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* Password stored in hash-encrypted form. This is regarded as must-have when security is a concern. Corda currently supports
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a flexible password hash format conforming to the Modular Crypt Format provided by the `Apache Shiro framework <https://shiro.apache.org/static/1.2.5/apidocs/org/apache/shiro/crypto/hash/format/Shiro1CryptFormat.html>`_
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These features are controlled by a set of options nested in the ``security`` field of ``node.conf``.
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The following example shows how to configure retrieval of users credentials and permissions from a remote database with
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passwords in hash-encrypted format and enable in-memory caching of users data:
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.. container:: codeset
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.. sourcecode:: groovy
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security = {
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authService = {
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dataSource = {
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type = "DB",
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passwordEncryption = "SHIRO_1_CRYPT",
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connection = {
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jdbcUrl = "<jdbc connection string>"
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username = "<db username>"
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password = "<db user password>"
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driverClassName = "<JDBC driver>"
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}
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}
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options = {
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cache = {
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expireAfterSecs = 120
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maxEntries = 10000
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}
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}
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}
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}
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It is also possible to have a static list of users embedded in the ``security`` structure by specifying a ``dataSource``
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of ``INMEMORY`` type:
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.. container:: codeset
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.. sourcecode:: groovy
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security = {
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authService = {
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dataSource = {
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type = "INMEMORY",
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users = [
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{
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username = "<username>",
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password = "<password>",
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permissions = ["<permission 1>", "<permission 2>", ...]
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},
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...
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]
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}
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}
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}
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.. warning:: A valid configuration cannot specify both the ``rpcUsers`` and ``security`` fields. Doing so will trigger
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an exception at node startup.
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Authentication/authorisation data
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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The ``dataSource`` structure defines the data provider supplying credentials and permissions for users. There exist two
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supported types of such data source, identified by the ``dataSource.type`` field:
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:INMEMORY: A static list of user credentials and permissions specified by the ``users`` field.
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:DB: An external RDBMS accessed via the JDBC connection described by ``connection``. Note that, unlike the ``INMEMORY``
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case, in a user database permissions are assigned to *roles* rather than individual users. The current implementation
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expects the database to store data according to the following schema:
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- Table ``users`` containing columns ``username`` and ``password``. The ``username`` column *must have unique values*.
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- Table ``user_roles`` containing columns ``username`` and ``role_name`` associating a user to a set of *roles*.
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- Table ``roles_permissions`` containing columns ``role_name`` and ``permission`` associating a role to a set of
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permission strings.
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.. note:: There is no prescription on the SQL type of each column (although our tests were conducted on ``username`` and
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``role_name`` declared of SQL type ``VARCHAR`` and ``password`` of ``TEXT`` type). It is also possible to have extra columns
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in each table alongside the expected ones.
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Password encryption
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^^^^^^^^^^^^^^^^^^^
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Storing passwords in plain text is discouraged in applications where security is critical. Passwords are assumed
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to be in plain format by default, unless a different format is specified by the ``passwordEncryption`` field, like:
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.. container:: codeset
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.. sourcecode:: groovy
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passwordEncryption = SHIRO_1_CRYPT
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``SHIRO_1_CRYPT`` identifies the `Apache Shiro fully reversible
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Modular Crypt Format <https://shiro.apache.org/static/1.2.5/apidocs/org/apache/shiro/crypto/hash/format/Shiro1CryptFormat.html>`_,
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it is currently the only non-plain password hash-encryption format supported. Hash-encrypted passwords in this
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format can be produced by using the `Apache Shiro Hasher command line tool <https://shiro.apache.org/command-line-hasher.html>`_.
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Caching user accounts data
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^^^^^^^^^^^^^^^^^^^^^^^^^^
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A cache layer on top of the external data source of users credentials and permissions can significantly improve
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performances in some cases, with the disadvantage of causing a (controllable) delay in picking up updates to the underlying data.
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Caching is disabled by default, it can be enabled by defining the ``options.cache`` field in ``security.authService``,
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for example:
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.. container:: codeset
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.. sourcecode:: groovy
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options = {
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cache = {
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expireAfterSecs = 120
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maxEntries = 10000
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}
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}
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This will enable a non-persistent cache contained in the node's memory with maximum number of entries set to ``maxEntries``
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where entries are expired and refreshed after ``expireAfterSecs`` seconds.
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Observables
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-----------
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The RPC system handles observables in a special way. When a method returns an observable, whether directly or
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as a sub-object of the response object graph, an observable is created on the client to match the one on the
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server. Objects emitted by the server-side observable are pushed onto a queue which is then drained by the client.
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The returned observable may even emit object graphs with even more observables in them, and it all works as you
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would expect.
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This feature comes with a cost: the server must queue up objects emitted by the server-side observable until you
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download them. Note that the server side observation buffer is bounded, once it fills up the client is considered
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slow and kicked. You are expected to subscribe to all the observables returned, otherwise client-side memory starts
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filling up as observations come in. If you don't want an observable then subscribe then unsubscribe immediately to
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clear the client-side buffers and to stop the server from streaming. If your app quits then server side resources
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will be freed automatically.
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.. warning:: If you leak an observable on the client side and it gets garbage collected, you will get a warning
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printed to the logs and the observable will be unsubscribed for you. But don't rely on this, as garbage collection
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is non-deterministic.
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Futures
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-------
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A method can also return a ``ListenableFuture`` in its object graph and it will be treated in a similar manner to
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observables. Calling the ``cancel`` method on the future will unsubscribe it from any future value and release any resources.
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Versioning
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----------
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The client RPC protocol is versioned using the node's Platform Version (see :doc:`versioning`). When a proxy is created
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the server is queried for its version, and you can specify your minimum requirement. Methods added in later versions
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are tagged with the ``@RPCSinceVersion`` annotation. If you try to use a method that the server isn't advertising support
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of, an ``UnsupportedOperationException`` is thrown. If you want to know the version of the server, just use the
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``protocolVersion`` property (i.e. ``getProtocolVersion`` in Java).
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Thread safety
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-------------
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A proxy is thread safe, blocking, and allows multiple RPCs to be in flight at once. Any observables that are returned and
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you subscribe to will have objects emitted in order on a background thread pool. Each Observable stream is tied to a single
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thread, however note that two separate Observables may invoke their respective callbacks on different threads.
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Error handling
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--------------
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If something goes wrong with the RPC infrastructure itself, an ``RPCException`` is thrown. If you call a method that
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requires a higher version of the protocol than the server supports, ``UnsupportedOperationException`` is thrown.
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Otherwise, if the server implementation throws an exception, that exception is serialised and rethrown on the client
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side as if it was thrown from inside the called RPC method. These exceptions can be caught as normal.
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Wire protocol
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-------------
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The client RPC wire protocol is defined and documented in ``net/corda/client/rpc/RPCApi.kt``.
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Whitelisting classes with the Corda node
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----------------------------------------
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CorDapps must whitelist any classes used over RPC with Corda's serialization framework, unless they are whitelisted by
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default in ``DefaultWhitelist``. The whitelisting is done either via the plugin architecture or by using the
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``@CordaSerializable`` annotation. See :doc:`serialization`. An example is shown in :doc:`tutorial-clientrpc-api`.
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.. _CordaRPCClient: api/javadoc/net/corda/client/rpc/CordaRPCClient.html
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.. _CordaRPCOps: api/javadoc/net/corda/core/messaging/CordaRPCOps.html
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.. _CordaRPCConnection: api/javadoc/net/corda/client/rpc/CordaRPCConnection.html
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