Shell

The Corda shell is an embedded command line that allows an administrator to control and monitor the node. Some of its features include:

  • Invoking any of the RPCs the node exposes to applications.
  • Starting flows.
  • View a dashboard of threads, heap usage, VM properties.
  • Uploading and downloading zips from the attachment store.
  • Issue SQL queries to the underlying database.
  • View JMX metrics and monitoring exports.
  • UNIX style pipes for both text and objects, an egrep command and a command for working with columnular data.

Note

A future version of Corda will add SSH access to the node.

It is based on the popular CRaSH shell used in various other projects and supports many of the same features.

The shell may be disabled by passing the --no-local-shell flag to the node.

Getting help

You can run help to list the available commands.

The shell has a man command that can be used to get interactive help on many commands. You can also use the --help or -h flags to a command to get info about what switches it supports.

Commands may have subcommands, in the same style as git. In that case running the command by itself will list the supported subcommands.

Starting flows and performing remote method calls

Flows are the way the ledger is changed. If you aren’t familiar with them, please review “Writing flows” first. The flow list command can be used to list the flows understood by the node and flow start can be used to start them. The flow start command takes the class name of a flow, or any unambiguous substring and then the data to be passed to the flow constructor. The unambiguous substring feature is helpful for reducing the needed typing. If the match is ambiguous the possible matches will be printed out. If a flow has multiple constructors then the names and types of the arguments will be used to try and determine which to use automatically. If the match against available constructors is unclear, the reasons each available constructor failed to match will be printed out. In the case of an ambiguous match, the first applicable will be used.

RPCs (remote procedure calls) are commands that can be sent to the node to query it, control it and manage it. RPCs don’t typically do anything that changes the global ledger, but they may change node-specific data in the database. Each RPC is one method on the CordaRPCOps interface, and may return a stream of events that will be shown on screen until you press Ctrl-C. You perform an RPC by using run followed by the name.

Documentation of available RPCs

Whichever form of change is used, there is a need to provide parameters to either the RPC or the flow constructor. Because parameters can be any arbitrary Java object graph, we need a convenient syntax to express this sort of data. The shell uses a syntax called Yaml to do this.

Data syntax

Yaml (yet another markup language) is a simple JSON-like way to describe object graphs. It has several features that make it helpful for our use case, like a lightweight syntax and support for “bare words” which mean you can often skip the quotes around strings. Here is an example of how this syntax is used:

flow start CashIssue amount: $1000, issueRef: 1234, recipient: "CN=Bank A,O=Bank A,L=London,C=UK", notary: "CN=Notary Service,O=R3,OU=corda,L=London,C=UK"

This invokes a constructor of a flow with the following prototype in the code:

class CashIssueFlow(val amount: Amount<Currency>,
                    val issueRef: OpaqueBytes,
                    val recipient: Party,
                    val notary: Party) : AbstractCashFlow(progressTracker)

Here, everything after CashIssue is specifying the arguments to the constructor of a flow. In Yaml, an object is specified as a set of key: value pairs and in our form, we separate them by commas. There are a few things to note about this syntax:

  • When a parameter is of type Amount<Currency> you can write it as either one of the dollar symbol ($), pound (£), euro (€) followed by the amount as a decimal, or as the value followed by the ISO currency code e.g. “100.12 CHF”
  • OpaqueBytes is filled with the contents of whatever is provided as a string.
  • Party objects are looked up by name.
  • Strings do not need to be surrounded by quotes unless they contain a comma or embedded quotes. This makes it a lot more convenient to type such strings.

Other types also have sensible mappings from strings. See the defined parsers for more information.

Nested objects can be created using curly braces, as in { a: 1, b: 2}. This is helpful when no particular parser is defined for the type you need, for instance, if an API requires a Pair<String, Int> which could be represented as { first: foo, second: 123 }.

The same syntax is also used to specify the parameters for RPCs, accessed via the run command, like this:

run getCashBalances

Attachments

The shell can be used to upload and download attachments from the node interactively. To learn more, see the tutorial “Using attachments”.

Extending the shell

The shell can be extended using commands written in either Java or Groovy (Groovy is a scripting language that is Java compatible). Such commands have full access to the node internal APIs and thus can be used to achieve almost anything.

A full tutorial on how to write such commands is out of scope for this documentation, to learn more please refer to the CRaSH documentation. New commands can be placed in the shell-commands subdirectory in the node directory. Edits to existing commands will be used automatically, but at this time commands added after the node has started won’t be automatically detected. Commands should be named in all lower case with either a .java or .groovy extension.

Warning

Commands written in Groovy ignore Java security checks, so have unrestricted access to node and JVM internals regardless of any sandboxing that may be in place. Don’t allow untrusted users to edit files in the shell-commands directory!

Limitations

The shell will be enhanced over time. The currently known limitations include:

  • SSH access is currently not available.
  • There is no command completion for flows or RPCs.
  • Command history is not preserved across restarts.
  • The jdbc command requires you to explicitly log into the database first.
  • Commands placed in the shell-commands directory are only noticed after the node is restarted.
  • The jul command advertises access to logs, but it doesn’t work with the logging framework we’re using.