# ZMQ JSON-RPC Client

JSON-RPC 2.0 client implementation using a ZeroMQ socket as transport mechanism. 
More precisely a `dealer` socket is used for the client, in line with the [asynchronous clients / servers pattern](http://zguide.zeromq.org/page:all#The-Asynchronous-Client-Server-Pattern)
of ZeroMQ.

For corresponding server implementation, see [zmq-json-rpc-server](https://github.com/claudijo/zmq-json-rpc-server).

## Installation

```
npm install zmq-json-rpc-client
```

## Usage

Create a JSON RPC client with a ZeroMQ endpoint and emit requests or 
notifications.

### client = zmqJsonRpcClient(endpoint, options)

This module exports a factory faction that accepts a ZeroMQ endpoint, eg. 
`'tcp:127.0.0.1:3030'` and options. 

#### Options

Options can be passed to the factory function as an object, specified by the 
following keys and values.


##### nextId

Value: Function that is called each time a new request is created. Defaults to a 
built-in incrementer starting at `1`.

##### timeout

Value: The number of milliseconds the client will wait for a reply when sending 
a request, until returning a timeout error. Defaults to `30000` (30 seconds).

##### socketId

Value: Identity that will be used for the underlaying ZeroMQ socket. Defaults to 
five random bytes.

### client.emit(method, params, callback)

Sends a JSON-RPC request or notification. Params and callback are optional. A 
notification is sent if callback is omitted. A request that expetct a reply
will be sent if passing a callback. The callback will receive `error` and  
`result` as arguments.

### client.socket

Exposes the underlying ZeroMQ socket object.

## Example

```js

var zmqJsonRpcClient = require('zmq-json-rpc-client');
var client = zmqJsonRpcClient('tcp:127.0.0.1', { socketId: 'client' });

// Send a notification
client.emit('update', [1, 2, 3, 4, 5]);  

// Send a request
client.emit('subtract', {"subtrahend": 23, "minuend": 42}, function(err, result) {
  // ...
});

```

## Test

Run unit tests:

`$ npm test`

## License

MIT