A data service library for node.
- An API for creating services that support asynchronous communication
- Socket.IO integration
- [TODO] Express integration
- Hooks so you can validate, authorize or do whatever
- Frequent, wistful imaginings involving crow's nests and shouting
npm install --save landho// Create a landho instance
var landho = require('landho'),
api = landho()
api
// Setup the landho instance to use the web socket server
.configure(landho.socket(wss))
// Create a new service with a couple of methods
.service('calc',
{
add: function (params, done)
{
// Use the regular node callback style
done(null, params.a + params.b)
},
counter: function (params, done)
{
var channel = new landho.Channel(),
interval = null,
counter = 0
channel.on('close', function ()
{
clearInterval(interval)
})
interval = setInterval(function ()
{
channel.emit('update', counter++)
}, 500)
done(null, channel)
}
})
// add a hook before the add method that messes with the parameters
.before(
{
add: function (params, next)
{
params.a = params.a * params.a
// Don't foregt to call next(). You can pass it an error
// if something bad happens.
next()
}
})
// Lookup the service and call the counter() method
api.service('foo').counter({}, function (err, channel)
{
channel.on('update', function (x)
{
if (x == 10)
{
channel.close()
}
})
})To start, you create an API object and add services to it.
// Create a landho instance.
var api = require('landho')()
// Define a service
api.service('calculator',
{
add: function (params, done)
{
done(null, params.a + params.b)
},
subtract: function (params, done)
{
done(null, params.a - params.b)
}
})
// Fetch the service and call one of its methods
api.service('calculator').add(
{ a: 5, b: 72 },
function (err, result)
{
console.log(result) // 77
}
)As you can see, services are basically collections of methods written in standard node continuation style. There is more you can do, though.
To create a service that provides asynchronous communication, return a channel object from a service method. Channels are bi-directional communication streams with the same interface as EventEmitter.
// Fetch the service and extend
// it with a new method.
api.service('counter',
{
create: function (params, done)
{
var channel = new landho.Channel(),
interval = null,
counter = 0
// This event will be emitted when the caller
// calls channel.close()
channel.on('close', function ()
{
clearInterval(interval)
})
// You can also subscribe to arbitrary events
channel.on('foo', function (data)
{
console.log(data)
})
interval = setInterval(function ()
{
// Emit arbitrary events
channel.emit('update', counter++)
}, 500)
// Send the channel to the caller
done(null, channel)
}
})
// The caller gets the other end of the channel.
api.service('counter').create(
{},
function (err, channel)
{
// Listen for events
channel.on('update', function (counter)
{
console.log(counter) // 0...1...2..3...
})
// Send arbitrary events
channel.emit('foo', 123)
// And when we are done, close the channel
setTimeout(function ()
{
channel.close()
}, 1000)
}
)Hooks can be registered on a service method either before or after the method is called. Here is an example of using a before hook for validation.
api.service('list').before(
{
push: function (params, next)
{
if (params.value == undefined)
{
next(new Error('A value parameter must be provided'))
}
else
{
next()
}
}
})
// Now we have to provide a value when calling `list.push()` or it won't be run
api.service('list').push({}, function (err, result)
{
console.log(err) // 'A value parameter must be provided'
})Hooks are run in the order they are registered. If any hook fails by calling next with an error, processing stops and the method callback is called with the error object. If the caller provided a subscriber object, it has its error() method called.
after hooks are like before hooks but they run after the method successfully returns a result. They have access to the result of the method call in params.result and can transform it like so:
api.service('list').after(
{
get: function (params, next)
{
params.result = { list: params.result, other_thing: 123 }
next()
}
})
// Now when we call get(), we will get the transformed result
api.service('list').get({}, function (err, result)
{
console.log(result) // { list: ['foo', 'bar', 'baz'], other_thing: 123 }
})It's important to note that after hooks are never called for feed events.
Landho can expose services over web sockets. You can write your own clients but there is also a landho-client that uses native web sockets.
Here is an example using ws.
var landho = require('landho'),
api = landho(),
WebSocket = require('ws'),
wss = new WebSocket.Server({ port:5000 })
api.configure(landho.socket(wss))That's all that's needed. To call methods over a websocket, send a message including a service method name, data and a unique id. Below we show a raw WebSocket client.
api.service('calc',
{
add: function (params, done)
{
done(null, params.a + params.b)
}
})
var client = new WebSocket('http://0.0.0.0:5000')
client.on('open', function ()
{
client.on('message', function (raw)
{
var message = JSON.parse(raw)
console.log(message)
// {
// id: 'some-id',
// name: 'initial',
// data: 5
// }
})
client.send(JSON.stringify(
{
id: 'some-id',
name: 'calc add',
data: { a: 2, b: 3 }
}))
})Channels are also supported. Here is what a client for the counter service from the channels section section looks like.
api.service('counter', ...
var client = ...
client.on('open', function ()
{
var channel_id = null
client.on('message', function (raw)
{
var message = JSON.parse(raw)
if (message.id == 'some-id')
{
assert(message.name == 'result')
channel_id = message.data.channel
}
else if (message.id == channel_id)
{
assert(message.name == 'channel')
assert(message.data.name == 'update')
console.log(message.data.data) // 0...1...2...3...
if (message.data.data == 10)
{
client.send(JSON.stringify(
{
id: channel_id,
name: 'channel',
data:
{
name: 'close'
}
}))
}
}
})
client.send(JSON.stringify(
{
id: 'some-id',
name: 'calc add',
data: { a: 2, b: 3 }
}))
})The landho package.
var landho = require('landho')Create a new landho application instance.
var api = landho()A landho application instance. Use it to create and fetch services and configure app-wide plugins. Create one using landho()
Create a new service.
var foo = api.service(
'foo',
{
add: function (params, done)
{
done(null, params.a + params.b)
}
}
)This method will throw an error if you try to register a service name that has already been registered.
var foo = api.service('foo', {}),
foo2 = api.service('foo', {}) -> Error('There is already a service registered with the name "foo"')Fetch a service, if it exists.
api.service(
'foo',
{
add: function (params, done)
{
done(null, params.a + params.b)
}
}
)
var foo = api.service('foo')
foo.add({a:1, b:2})It will return null if the service does not exist.
var bar = api.service('bar')
console.log(bar) // -> nullA service is a named collection of methods and hooks.
Create a new service.
You should not use this method to create services. To create a service use Application.service(). That method takes the same arguments as this one but it will register the service on the application. This documentation is here mostly to explain the service configuration parameter.
Creating a service works like this:
var api = landho()
api.service('foo', {
add: function (params, done)
{
done(null, params.a + params.b)
},
multiply: function (params, done)
{
done(null, params.a * params.b)
}
})The keys of the configuration object are the names of the service methods and the values are their implementations. Service methods all have the same signature method_name(<params>, <callback>) and the callback uses the standard node form callback(error, result).
Add methods to an existing service. The configuration object is exactly like the one used when creating a service. Attempting to use a method name that has already been registered either during creation or a previous call to extend() will throw an error.
Add one or more hooks that will run before service methods. The hooks argument is an object where the keys are the names of service methods and the values are before hook implementations. A before hook has this signature:
Hooks may modify the params object. When a hook is complete, it should call the next() function that was passed as the second argument. next() should be called with an error argument if the hook wants to stop execution of the service method, otherwise it should be called with no arguments. If next() is not called, execution will silently stop.
Add one or more hooks that will run after a service method completes successfully but before the caller receives the response. After hooks are run for request/response calls and before the callback of the initial method of a feed but not for the messages emitted to a subscriber of a feed.
After hooks are almost the same as before hooks. The main difference is when they run and the fact that the params object will have a result property. This is the result of the service method call and it can be manipulated by the after hook.
See the hooks section of the guide for examples of before and after hooks.