David

David is a CoAP server with Rack interface to bring the illustrious family of
Rack compatible web frameworks into the Internet of Things. It is tested with
MRI >= 2.3, and JRuby >= 9.1. David version ~> 0.5.0 aims for Rack 2 (and Rails
5). Compatibility to Rails 4 is available in version ~> 0.4.5.

Quick Start

Just include David in your Gemfile!

gem 'david'

It will hook into Rack and make itself the default handler, so running rails s starts David. If you want to start WEBrick for example, you can do so by
executing rails s webrick.

For now, you have to remove the web-console gem from the Gemfile (which is
HTTP specific anyway) if you use Rails/David in CoAP only mode. You probably
also want to disable CSRF
protection
by removing the protect_from_forgery line from
app/controllers/application_controller.rb (or use :null_session if you know
what you are doing).

The coap-rails-dummy repository
documents changes to a newly generated Ruby on Rails application for a quick
start.

After the server is started, the Rails application is available at
coap://[::1]:3000/ by default. (Although you have to set a route for / in
config/routes.rb, of course.)

Copper is a CoAP
client for Firefox and can be used for development. The Ruby coap
gem is used by David for example for message
parsing and also includes a command line utility (named coap) that can also
be used for development.

As CoAP is a protocol for constrained
environments and machine to machine communications, returning HTML from your
controllers will not be of much use. JSON for example is more suitable in that
context. The Accept header is set to “application/json” by default, so that
Rails responds with the JSON resource representation. David works well with the
default ways to handle JSON responses from controllers such as render json:.
You can also utilize Jbuilder templates
for easy generation of more complex JSON structures.

CBOR can be used to compress your JSON.
Automatic transcoding between JSON and CBOR is activated by setting the Rack
environment option CBOR or config.coap.cbor in your Rails application
config to true.

Tested Rack Frameworks

By providing a Rack interface, David does not only work with Rails but also
with the following Rack compatible web frameworks.

• Grape
• Hobbit
• NYNY
• Plain Rack
• Sinatra
• Rails
• Roda

Configuration

The following table lists available configuration options for the CoAP server.
Rack keys can be specified with the -O option of rackup. The listed Rails
keys can be accessed for example from the config/application.rb file of your
Rails application.

The server can be started with debug log level for example with the following
command provided that a rackup config file (config.ru) exists like in a Rails
application.

rackup -O Log=debug

In a Rails application, CBOR transcoding is activated for any controller and
action by inserting the third line of the following code into
config/application.rb.

module Example
  class Application < Rails::Application
    config.coap.cbor = true
  end
end

In Copper for example the default block size for Blockwise Transfers is set to
64 bytes. That’s even small for most exception messages. It is recommended to
set the block size to the maximum (1024B) during development.

Discovery

The CoAP Discovery will be
activated by default. A .well-known/core resource automatically returns the
resources you defined in Rails. You can annotate this resources with attributes
like an interface description (if) or the content type (ct). (See
RFC6690 or the
code for
further documentation.)

class ThingsController < ApplicationController
  discoverable \
    default: { if: 'urn:things', ct: 'application/cbor' },
    index:   { if: 'urn:index' }
  def show
    render json: Thing.find(params[:id])
  end
  def index
    render json: Thing.all
  end
end

Rack environment

David sets the following server (and protocol) specific Rack environment
entries that can be read from your Rack application if necessary.

Benchmarks

David handles about 12,500 requests per second in MRI and 14,000 in JRuby
(tested in MRI 2.3.0 and JRuby 1.7.19 with up to 10,000 concurrent clients on a
single core of a Core i7-3520M CPU running Linux 3.18.6).

Caveats

• Incoming block-wise transfer is not supported.
• Automatically generating .well-known/core is only supported in Rails.

Copyright

The code is published under the MIT license (see the LICENSE file).

Authors

• henning mueller