JSON-RPC in Cougar

What is JSON-RPC?

It’s a JSON protocol for calling operations by name as defined by the following standard:

http://groups.google.com/group/json-rpc/web/json-rpc-2-0

The major new feature we realise is that you can make a batch of RPC calls in each Http request as a as follows:

[{ \"jsonrpc\": \"2.0\", \"method\": \"Baseline/v2/testSimpleGet\", \"params\": [\"Hello JSON-RPC\"], \"id\": 1},{ \"jsonrpc\": \"2.0\", \"method\": \"Baseline/v2/testSimpleGet\", \"params\": [\"Hello JSON-RPC\"], \"id\": 2}]

A couple of points to notice straight off:

• The data is sent JSON encoded as body data – so you’ll have to use Post to submit each JSON request.
• The above rpc request has 2 calls in the batch
• The id that you supply is free form, but whatever you supply, the server will return to you – so it’s a correlation id
• The Form of operation identifier is as follows:
• Service name / v major version . minor version / operation name
• Parameters are marshalled in order that corresponds to how they’re defined in the IDL – so they don’t need to be named
• Content type headers, Accept and Content-Type can be either application/json or text/json

The server replies with the following:

[{"jsonrpc":"2.0","result":{"message":"Hello JSON-RPC"},"id":1},{"jsonrpc":"2.0","result":{"message":"Hello JSON-RPC"},"id":2}]

Setting it up in your Cougar application

In order to enable JSON_RPC, you need to setup a endpoint binding for it (which should live along side the other endpoint bindings, likely defined in a spring document called http-transport-spring.xml):

<bean parent="cougar.transport.AbstractProtocolBinding">
        <property name="contextRoot" value="json-rpc"/>
        <property name="identityTokenResolver" ref="SimpleRescriptIdentityTokenResolver"/>
        <property name="protocol" value="JSON_RPC"/>
    </bean>

If your app is not providing security through tokens / chains, then you can omit the identityTokenResolver, but the context root (url) must be set, and the protocol must be “JSON_RPC”

You must also add your service’s JSON-RPC binding descriptor to the binding descriptor util:set in your service registration bean (in service-application.xml).

To test your JSON-RPC I suggest using curl or similar, and an example of that is as follows:

curl --header "Accept: application/json" --header "Content-Type: application/json" --data "[{ \"jsonrpc\": \"2.0\", \"method\": \"Baseline/v2/testSimpleGet\", \"params\": [\"Hello JSON-RPC\"], \"id\": 1},{ \"jsonrpc\": \"2.0\", \"method\": \"Baseline/v2/testSimpleGet\", \"params\": [\"Hello JSON-RPC\"], \"id\": 2}] " http://localhost:8080/json-rpc

Note that the url, unlike other protocols, needs nothing other than the JSON-RPC contextRoot (which you defined in your protocol binding).

So: • Jsonrpc:2.0 is always part of the result • The result contains the output from the operation. If it is a void method, then this will be null • The id supplied at invocation time is returned to you. The order the answers appear in the array should not be counted upon • If there is a failure for one of the calls – a situation you could arrange by omitting a mandatory parameter – then you would see something like the following:

[{"jsonrpc":"2.0","result":{"message":"Hello JSON-RPC"},"id":1},{"jsonrpc":"2.0","error":{"code":-32602,"message":"DSC-0018"},"id":2}]

• So it will successfully process requests as possible, but every request should have either a result or an error response

If you supply a request that cannot be parsed (I supplied alskdfjalksdjf as the json body), then you’ll get a total failure type response as follows:

{"jsonrpc":"2.0","error":{"code":-32700,"message":"DSC-0008"}}

Where possible, I’ve used the JSON error codes as they’ve supplied them. The spec documents them, with the exception of -32600 – invalid request

-32700 – Parse error – will be returned if there was some sort of complete fail parsing the RPC request -32601 – Method not found - if the command processor was unable to find the method you’ve asked for -32602 – if there was a problem parsing the parameters, or a mandatory parameter was not found -32603 – internal error – if there was an unexpected exception thrown processing the request -32099 – Server Error – if the invoked call threw a BSIDL defined exception

Quick tip: the JSON formatting for passing over list params would look like this:

\"params\": [[\"100590665\", \"100590666\"]]