RemJson

RemJson is a JSON-RPC 2.0 compliant server and client written in JavaScript for node.js that aims to be as simple as possible to use.

Table of contents

• Features
• Example
• Installation
• Changelog
• Requirements
• Class Documentation
• Running tests
• Usage
  • Client
    • Interface description
    • Notifications
    • Batches
    • Callback syntactic sugar
    • Events
  • Server
    • Interface description
    • Using many interfaces at the same time
    • Using the server as a relay
    • Method routing
    • Method definition
    • Events
    • Errors
• Revivers and replacers
• Named parameters
• Contributing

Features

• Servers that can listen to several interfaces at the same time
• Supports both HTTP and TCP client and server connections
• Server-side method - [Method routing]
• Relaying of requests to other servers
• JSON reviving and replacing for transparent serialization of complex objects
• CLI client
• Fully tested to comply with the official JSON-RPC 2.0 specification
• Also supports JSON-RPC 1.0

Example

A basic JSON-RPC 2.0 server via HTTP:

Server in examples/simple_example/server.js:

var remjson = require(__dirname + '/../..');

// create a server
var server = remjson.server({
  add: function(a, b, callback) {
    callback(null, a + b);
  }
});

// Bind a http interface to the server and let it listen to localhost:3000
server.http().listen(3000);

Client in examples/simple_example/client.js invoking add on the above server:

var remjson = require(__dirname + '/../..');

// create a client
var client = remjson.client.http({
  port: 3000,
  hostname: 'localhost'
});

// invoke "add"
client.request('add', [1, 1], function(err, error, response) {
  if(err) throw err;
  console.log(response); // 2!
});

Installation

Install the latest version of jayson from npm by executing npm install remjson in your shell. Do a global install with npm install --global remjson if you want the remjson client CLI in your PATH.

Changelog (notable milestones)

• 1.2
  • Greatly improved server method definition
• 1.1.1
  • More http server events
  • Remove fork server and client
  • Add server routing
• 1.0.11 Add support for a HTTPS client
• 1.0.10 Bugfixes
• 1.0.9 Add support for TCP servers and clients

CLI client

There is a CLI client in bin/remjson.js and it should be available as remjson in your shell if you installed the package with the --global switch. Run remjson --help to see how it works.

Requirements

RemJson does not have any special dependencies that cannot be resolved with a simple npm install. It is being continuously tested using travis-ci on the following versions:

• node.js v0.8.x
• node.js v0.10.x
• node.js v0.12.x
• iojs

Class documentation

In addition to this document, a comprehensive class documentation made with jsdoc is available at remjson.tedeh.net.

Running tests

• Change directory to the repository root
• Install the testing framework (mocha together with should) by executing npm install --dev
• Run the tests with make test or npm test

Usage

Client

The client is available as the Client or client property of require('remjson').

Client interface description

• Client Base class for interfacing with a server.
• Client.tcp TCP interface
• Client.tls TLS interface
• Client.http HTTP interface
• Client.https HTTPS interface

Every client supports these options:

• reviver -> Function to use as a JSON reviver
• replacer -> Function to use as a JSON replacer
• generator -> Function to generate request ids with. If omitted, RemJson will just generate a "random" number that is RFC4122 compliant and looks similar to this: 3d4be346-b5bb-4e28-bc4a-0b721d4f9ef9
• version -> Can be either 1 or 2 depending on which specification should be followed in communicating with the server. Defaults to 2 for JSON-RPC 2.0

Client.http

Uses the same options as http.request in addition to these options:

• encoding -> String that determines the encoding to use and defaults to utf8

Client.http Events

The HTTP server will emit the following events:

• http request Emitted when the client has just created a HTTP request. First argument is an instance of http.ClientRequest
• http response Emitted when the client has received an HTTP response. First argument is an instance of http.IncomingMessage and second argument an instance of http.ClientRequest.
• http error Emitted when the underlying stream emits error. First argument is the error.
• http timeout Emitter when the underlying stream emits timeout. When emitted, it will automatically cause the request to abort.

It is possible to pass a string URL as the first argument. The URL will be run through url.parse. Example:

var remjson = require(__dirname + '/../..');
var client = remjson.client.http('http://localhost:3000');
// client.options is now the result of url.parse

Client.https

Uses the same options as https.request in addition to the same options as Client.http. This means it is also possible to pass a string URL as the first argument and have it interpreted by url.parse.

Client.tcp

Uses the same options as the base class.

Client.tls

Uses the same options as tls.connect.

Notifications

Notification requests are for cases where the reply from the server is not important and should be ignored. This is accomplished by setting the id property of a request object to null.

Client in examples/notifications/client.js doing a notification request:

var remjson = require(__dirname + '/../..');

var client = remjson.client.http({
  host: 'localhost',
  port: 3000
});

// the third parameter is set to "null" to indicate a notification
client.request('ping', [], null, function(err) {
  if(err) throw err;
  // request was received successfully
});

A server in examples/notifications/server.js:

var remjson = require(__dirname + '/../..');

var server = remjson.server({
  ping: function(callback) {
    // do something
    callback();
  }
});

server.http().listen(3000);

Notes

• Any value that the server returns will be discarded when doing a notification request.
• Omitting the third argument null to Client.prototype.request does not generate a notification request. This argument has to be set explicitly to null for this to happen.
• Network errors and the like will still reach the callback. When the callback is invoked (with or without error) one can be certain that the server has received the request.
• See the Official JSON-RPC 2.0 Specification for additional information on how RemJson handles notifications that are erroneous.

Batches

A batch request is an array of individual requests that are sent to the server as one. Doing a batch request is very simple in RemJson and consists of constructing an Array of individual requests (created by not passing a callback to Client.prototype.request) that is then itself passed to Client.prototype.request.

Client example in examples/batch_request/client.js:

var remjson = require(__dirname + '/../..');
var client = remjson.client.http({
  host: 'localhost',
  port: 3000
});

var batch = [
  client.request('does_not_exist', [10, 5]),
  client.request('add', [1, 1]),
  client.request('add', [0, 0], null) // a notification
];

// callback takes two arguments (first type of callback)
client.request(batch, function(err, responses) {
  if(err) throw err;
  // responses is an array of errors and successes together
  console.log('responses', responses);
});

// callback takes three arguments (second type of callback)
client.request(batch, function(err, errors, successes) {
  if(err) throw err;
  // errors is an array of the requests that errored
  console.log('errors', errors);
  // successes is an array of requests that succeded
  console.log('successes', successes);
});

Server example in examples/batch_request/server.js:

var remjson = require(__dirname + '/../..');

var server = remjson.server({
  add: function(a, b, callback) {
    callback(null, a + b);
  }
});

server.http().listen(3000);

Notes

• See the Official JSON-RPC 2.0 Specification for additional information on how RemJson handles different types of batches, mainly with regards to notifications, request errors and so forth.
• There is no guarantee that the results will be in the same order as request Array request. To find the right result, compare the ID from the request with the ID in the result yourself.

Client callback syntactic sugar

When the length (number of arguments) of a client callback function is either 2 or 3 it receives slightly different values when invoked.

• 2 arguments: first argument is an error or null, second argument is the response object as returned (containing either a result or a error property) or null for notifications.
• 3 arguments: first argument is an error or null, second argument is a JSON-RPC error property or null (if success), third argument is a JSON-RPC result property or null (if error).

When doing a batch request with a 3-length callback, the second argument will be an array of requests with a error property and the third argument will be an array of requests with a result property.

Client events

A client will emit the following events (in addition to any special ones emitted by a specific interface):

• request Emitted when a client is just about to dispatch a request. First argument is the request object.
• response Emitted when a client has just received a reponse. First argument is the request object, second argument is the response as received.

Server

The server classes are available as the Server or server property of require('remjson').

The server also sports several interfaces that can be accessed as properties of an instance of Server.

Server interface description

• Server - Base interface for a server that supports receiving JSON-RPC 2.0 requests.
• Server.tcp - TCP server that inherits from net.Server.
• Server.tls - TLS server that inherits from tls.Server.
• Server.http - HTTP server that inherits from http.Server.
• Server.https - HTTPS server that inherits from https.Server.
• Server.middleware - Method that returns a Connect/Express compatible middleware function.

Every server supports these options:

• reviver -> Function to use as a JSON reviver
• replacer -> Function to use as a JSON replacer
• router -> Function to find which method to use for a request. See the chapter on method routing.
• collect -> Collect JSON-RPC parameters inside a single function argument. Default false. See method definition
• params -> Force collected JSON-RPC parameters to be Object or Array. Default false. See method definition
• version -> Can be either 1 or 2 depending on which specification clients are expected to follow. Defaults to 2 for JSON-RPC 2.0

Server.tcp

Uses the same options as the base class. Inherits from net.Server.

Server.tls

Uses the same options as the base class. Inherits from tls.Server.

Server.http

Uses the same options as the base class. Inherits from http.Server.

Server.https

Uses the same options as the base class. Inherits from https.Server and remjson.Server.http. For information on how to configure certificates, see the documentation on https.Server.

Server.middleware

Uses the same options as the base class. Returns a function that is compatible with Connect or Express. Will expect the request to be req.body, meaning that the request body must be parsed (typically using connect.bodyParser) before the middleware is invoked.

The middleware supports the following options:

• end Defaults to true. If set to false will cause the middleware to next() instead of res.end() at the end of a request. res.body and the response header may or may not be set when the next middleware is called.

Middleware example in examples/middleware/server.js:

var remjson = require(__dirname + '/../..');
var connect = require('connect');
var app = connect();

var server = remjson.server({
  add: function(a, b, callback) {
    callback(null, a + b);
  }
});

// parse request body before the remjson middleware
app.use(connect.bodyParser());
app.use(server.middleware());

app.listen(3000);

Using many server interfaces at the same time

A RemJson server can use many interfaces at the same time.

Server in examples/many_interfaces/server.js that listens to both http and a https requests:

var remjson = require(__dirname + '/../..');

var server = remjson.server({
  add: function(a, b, callback) {
    return callback(null, a + b);
  }
});

// "http" will be an instance of require('http').Server
var http = server.http();

// "https" will be an instance of require('https').Server
var https = server.https({
  //cert: require('fs').readFileSync('cert.pem'),
  //key require('fs').readFileSync('key.pem')
});

http.listen(80, function() {
  console.log('Listening on *:80')
});

https.listen(443, function() {
  console.log('Listening on *:443')
});

Using the server as a relay

Passing an instance of a client as a method to the server makes the server relay incoming requests to wherever the client is pointing to. This might be used to delegate computationally expensive functions into a separate server or to abstract a cluster of servers behind a common interface.

Public server in examples/relay/server_public.js listening on *:3000:

var remjson = require(__dirname + '/../..');

// create a server where "add" will relay a localhost-only server
var server = remjson.server({
  add: remjson.client.http({
    hostname: 'localhost',
    port: 3001
  })
});

// let the server listen to *:3000
server.http().listen(3000, function() {
  console.log('Listening on *:3000');
});

Private server in examples/relay/server_private.js listening on localhost:3001:

var remjson = require(__dirname + '/../..');

var server = remjson.server({
  add: function(a, b, callback) {
    callback(null, a + b);
  }
});

// let the private server listen to localhost:3001
server.http().listen(3001, '127.0.0.1', function() {
  console.log('Listening on 127.0.0.1:3001');
});

Every request to add on the public server will now relay the request to the private server. See the client example in examples/relay/client.js.

Method routing

Passing a property named router in the server options will enable you to write your own logic for routing requests to specific functions.

Server with custom routing logic in examples/method_routing/server.js:

var remjson = require(__dirname + '/../..');
var format = require('util').format;

var methods = {
  add: function(a, b, callback) {
    callback(null, a + b);
  }
};

var server = remjson.server(methods, {
  router: function(method) {
    // regular by-name routing first
    if(typeof(this._methods[method]) === 'function') return this._methods[method];
    if(method === 'add_2') return this._methods.add.bind(this, 2);
  }
});

server.http().listen(3000);

Client in examples/method_routing/client.js invoking add_2 on the above server:

var remjson = require(__dirname + '/../..');

// create a client
var client = remjson.client.http({
  port: 3000,
  hostname: 'localhost'
});

// invoke "add_2"
client.request('add_2', [3], function(err, error, response) {
  if(err) throw err;
  console.log(response); // 5!
});

An example of nested routes where each property is separated by a dot (you do not need to use the router option for this):

var _ = require('lodash');
var remjson = require(__dirname + '/../..');

var methods = {
  foo: {
    bar: function(callback) {
      callback(null, 'ping pong');
    }
  },
  math: {
    add: function(a, b, callback) {
      callback(null, a + b);
    }
  }
};

// this reduction produces an object like this: {'foo.bar': [Function], 'math.add': [Function]}
var map = _.reduce(methods, collapse('', '.'), {});
var server = remjson.server(map);

function collapse(stem, sep) {
  return function(map, value, key) {
    var prop = stem ? stem + sep + key : key;
    if(_.isFunction(value)) map[prop] = value;
    else if(_.isObject(value)) map = _.reduce(value, collapse(prop, sep), map);
    return map;
  }
}

Notes

• If router does not return anything, the reserver will respond with a Method Not Found error.
• The Server.prototype methods method, methods, removeMethod and hasMethod will not use the router method, but will operate on the internal Server.prototype._methods map.
• The router method is expected to return instances of remjson.Method (new in 1.2)

Method definition

You can also define server methods inside a wrapping object named remjson.Method. This allows additional options about the method to be specified. It is possible to define what kind of params it expects, default values for these params, and wheter or not all JSON-RPC params should be collected in a single argument to the function. Using this wrapper, it is for instance trivial to have your method accept a variable amount of arguments.

Server example showcasing most features in examples/method_definitions/server.js:

var remjson = require(__dirname + '/../..');
var _ = require('lodash');

var methods = {

  // this method gets the raw params as first arg to handler
  addCollect: new remjson.Method({
    handler: function(args, done) {
      var total = sum(args);
      done(null, total);
    },
    collect: true // means "collect all JSON-RPC parameters in one arg"
  }),

  // specifies some default values (alternate definition too)
  addDefault: remjson.Method(function(args, done) {
    var total = sum(args);
    done(null, total);
  }, {
    collect: true,
    params: {a: 2, b: 5} // map of defaults
  }),

  // this method returns true when it gets an array (which it always does)
  acceptArray: new remjson.Method({
    handler: function(args, done) {
      var result = _.isArray(args);
      done(null, result);
    },
    collect: true,
    params: Array // could also be "Object"
  })

};

var server = remjson.server(methods);

server.http().listen(3000);

// sums all enumerable properties in a list
function sum(list) {
  return _.reduce(list, function(sum, val) {
    return sum + val;
  }, 0);
}

Client example in examples/method_definitions/client.js:

var remjson = require(__dirname + '/../..');

// create a client
var client = remjson.client.http({
  port: 3000,
  hostname: 'localhost'
});

// invoke "addCollect" with array
client.request('addCollect', [3, 5, 9, 11], function(err, response) {
  if(err) throw err;
  console.log(response.result); // 28
});

// invoke "addCollect" with object
client.request('addCollect', {a: 2, b: 3, c: 4}, function(err, response) {
  if(err) throw err;
  console.log(response.result); // 9
});

// invoke "addDefault" with object missing some defined members
client.request('addDefault', {b: 10}, function(err, response) {
  if(err) throw err;
  console.log(response.result); // 12
});

// invoke "acceptArray" with an Object
client.request('acceptArray', {a: 5, b: 2, c: 9}, function(err, response) {
  if(err) throw err;
  console.log(response.result); // true
});

Notes

• Adding methods as a plain JavaScript function creates an instance of remjson.Method internally. For backwards compatibility it will be created with the option "collect" set to false. It is possible to affect this by passing the collect option to the server. This works similarly for the params option.

Server events

In addition to events that are specific to certain interfaces, all servers will emit the following events:

• request Emitted when the server receives an interpretable (non-batch) request. First argument is the request object.
• response Emitted when the server is returning a response. First argument is the request object, the second is the response object.
• batch Emitted when the server receives a batch request. First argument is an array of requests. Will emit request for each interpretable request in the batch.

Server Errors

If you should like to return an error from an method request to indicate a failure, remember that the JSON-RPC 2.0 specification requires the error to be an Object with a code (Integer/Number) to be regarded as valid. You can also provide a message (String) and a data (Object) with additional information. Example:

var remjson = require(__dirname + '/../..');

var server = remjson.server({
  i_cant_find_anything: function(id, callback) {
    var error = {code: 404, message: 'Cannot find ' + id};
    callback(error); // will return the error object as given
  },
  i_cant_return_a_valid_error: function(callback) {
    callback({message: 'I forgot to enter a code'}); // will return a pre-defined "Internal Error"
  }
});

Predefined Errors

It is also possible to cause a method to return one of the predefined JSON-RPC 2.0 error codes using the server helper function Server.prototype.error inside of a server method. Example:

var remjson = require(__dirname + '/../..');

var server = remjson.server({
  invalid_params: function(id, callback) {
    var error = this.error(-32602); // returns an error with the default properties set
    callback(error);
  }
});

You can even override the default messages:

var remjson = require(__dirname + '/../..');

var server = remjson.server({
  error_giver_of_doom: function(callback) {
    callback(true) // invalid error format, which causes an Internal Error to be returned instead
  }
});

// Override the default message
server.errorMessages[Server.errors.INTERNAL_ERROR] = 'I has a sad. I cant do anything right';

Revivers and Replacers

JSON lacks support for representing types other than the simple ones defined in the JSON specification. Fortunately the JSON methods in JavaScript (JSON.parse and JSON.stringify) provide options for custom serialization/deserialization routines. RemJson allows you to pass your own routines as options to both clients and servers.

Simple example transferring the state of an object between a client and a server:

Shared code between the server and the client in examples/reviving_and_replacing/shared.js:

var Counter = exports.Counter = function(value) {
  this.count = value || 0;
};

Counter.prototype.increment = function() {
  this.count += 1;
};

exports.replacer = function(key, value) {
  if(value instanceof Counter) {
    return {$class: 'counter', $props: {count: value.count}};
  }
  return value;
};

exports.reviver = function(key, value) {
  if(value && value.$class === 'counter') {
    var obj = new Counter;
    for(var prop in value.$props) obj[prop] = value.$props[prop];
    return obj;
  }
  return value;
};

Server in examples/reviving_and_replacing/server.js:

var remjson = require(__dirname + '/../..');
var shared = require('./shared');

// Set the reviver/replacer options
var options = {
  reviver: shared.reviver,
  replacer: shared.replacer
};

// create a server
var server = remjson.server({
  increment: function(counter, callback) {
    counter.increment();
    callback(null, counter);
  }
}, options);

// let the server listen to for http connections on localhost:3000
server.http().listen(3000);

A client in examples/reviving_and_replacing/client.js invoking "increment" on the server:

var remjson = require(__dirname + '/../..');
var shared = require('./shared');

// create a client with the shared reviver and replacer
var client = remjson.client.http({
  port: 3000,
  hostname: 'localhost',
  reviver: shared.reviver,
  replacer: shared.replacer
});

// create the object
var instance = new shared.Counter(2);

// invoke "increment"
client.request('increment', [instance], function(err, error, result) {
  if(err) throw err;
  console.log(result instanceof shared.Counter); // true
  console.log(result.count); // 3!
  console.log(instance === result); // false - it won't be the same object, naturally
});

Notes

• Instead of using a replacer, it is possible to define a toJSON method for any JavaScript object. Unfortunately there is no corresponding method for reviving objects (that would not work, obviously), so the reviver always has to be set up manually.

Named parameters

It is possible to specify named parameters when doing a client request by passing an Object instead of an Array.

Client example in examples/named_parameters/client.js:

var remjson = require(__dirname + '/../../');

var client = remjson.client.http({
  host: 'localhost',
  port: 3000
});

client.request('add', {b: 1, a: 2}, function(err, error, response) {
  if(err) throw err;
  console.log(response); // 3!
});

Server example in examples/named_parameters/server.js:

var remjson = require(__dirname + '/../..');

var server = remjson.server({
  add: function(a, b, callback) {
    callback(null, a + b);
  }
});

server.http().listen(3000);

Notes

• If requesting methods on a RemJson server, arguments left out will be undefined
• Too many arguments or arguments with invalid names will be ignored
• It is assumed that the last argument to a server method is the callback and it will not be filled with something else

Contributing

Highlighting issues or submitting pull requests on Github is most welcome.