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Angelo

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A Sinatra-like DSL for Reel.

tl;dr

What is Angelo?

Just like Sinatra, Angelo gives you an expressive DSL for creating web applications. There are some notable differences, but the basics remain the same: you can either create a "classic" application by requiring 'angelo/main' and using the DSL at the top level of your script, or a "modular" application by requiring 'angelo', subclassing Angelo::Base, and calling .run! on that class for the service to start. In addition, and perhaps more importantly, Angelo is built on Reel, which is built on Celluloid::IO and gives you a reactor with evented IO in Ruby!

Things will feel very familiar to anyone experienced with Sinatra. You can define route handlers denoted by HTTP verb and path with parameters set from path matching (using Mustermann), the query string, and post body. A route block may return:

Angelo also features before and after filter blocks, just like Sinatra. Filters are ordered as defined, and called in that order. When defined without a path, they run for all matched requests. With a path, the path is interpreted as a Mustermann pattern and params are merged. before filters can set instance variables which can be used in the route block and the after filter. For more info on the difference in how after blocks are handled, see the Errors section below for more info.

Websockets!

One of the main motivations for Angelo was the ability to define websocket handlers with ease. Through the addition of a websocket route builder and a websockets helper, Angelo attempts to make it easy for you to build real-time web applications.

Route Builder

The websocket route builder accepts a path and a block, and passes the actual websocket to the block as the only argument. This socket is an instance of Reel's WebSocket class, and, as such, responds to methods like on_message and on_close. A service-wide on_pong handler may be defined to customize the behavior when a pong frame comes back from a connected websocket client.

websockets helper

Angelo includes a "stash" helper for connected websockets. One can << a websocket into websockets from inside a websocket handler block. These can "later" be iterated over so one can do things like emit a message on every connected websocket when the service receives a POST request.

The websockets helper also includes a context ability, so you can stash connected websocket clients into different "sections". Also, by default, the helper will reject! any closed sockets before returning; you may optionally pass false to the helper to skip this step.

Example!

Here is an example of the websocket route builder, the websockets helper, and the context feature:

require 'angelo'

class Foo < Angelo::Base

  websocket '/' do |ws|
    websockets << ws
  end

  websocket '/bar' do |ws|
    websockets[:bar] << ws
  end

  post '/' do
    websockets.each {|ws| ws.write params[:foo]}
  end

  post '/bar' do
    websockets[:bar].each {|ws| ws.write params[:bar]}
  end

end

Foo.run!

In this case, any clients that connect to a websocket at the path '/' will be stashed in the default websockets array; clients that connect to '/bar' will be stashed in the :bar section.

Each "section" is accessed with a familiar, Hash-like syntax, and can be iterated over with a .each block.

When a POST / with a 'foo' param is received, any value is messaged out to all '/' connected websockets. When a POST /bar with a 'bar' param is received, any value is messaged out to all websockets connected to '/bar'.

SSE - Server-Sent Events

The eventsource route builder also accepts a path and a block, and passes the socket to the block, just like the websocket builder. This socket is actually the raw Celluloid::IO::TCPSocket and is "detached" from the regular handling. There are no "on-*" methods; the write method should suffice. To make it easier to deal with creation of the properly formatted Strings to send, Angelo provides a couple helpers.

sse_event helper

To create an "event" that a javascript EventListener on the client can respond to:

eventsource '/sse' do |s|
  event = sse_event :foo, some_key: 'blah', other_key: 'boo'
  s.write event
  s.close
end

In this case, the EventListener would have to be configured to listen for the foo event:

var sse = new EventSource('/sse');
sse.addEventListener('foo', function(e){ console.log("got foo event!\n" + JSON.parse(e.data)); });

The sse_event helper accepts a normal String for the data, but will automatically convert a Hash argument to a JSON object.

NOTE: there is a shortcut helper on the actual SSE object itself:

eventsource '/sse' do |sse|
  sse.event :foo, some_key: 'blah', other_key: 'boo'
  sse.event :close
end
sse_message helper

The sse_message helper behaves exactly the same as sse_event, but does not take an event name:

eventsource '/sse' do |s|
  msg = sse_message some_key: 'blah', other_key: 'boo'
  s.write msg
  s.close
end

The client javascript would need to be altered to use the EventSource.onmessage property as well:

var sse = new EventSource('/sse');
sse.onmessage = function(e){ console.log("got message!\n" + JSON.parse(e.data)); };

NOTE: there is a shortcut helper on the actual SSE object itself:

eventsource '/sse' do |sse|
  sse.message some_key: 'blah', other_key: 'boo'
  sse.event :close
end
sses helper

Angelo also includes a "stash" helper for SSE connections. One can << a socket into sses from inside an eventsource handler block. These can "later" be iterated over so one can do things like emit a message on every SSE connection when the service receives a POST request.

The sses helper includes the same context ability as the websockets helper. Also, by default, the helper will reject! any closed sockets before returning, just like websockets. You may optionally pass false to the helper to skip this step. In addition, the sses stash includes methods for easily sending events or messages to all stashed connections. Note that the Stash::SSE#event method only works on non-default contexts and uses the context name as the event name.

eventsource '/sse' do |s|
  sses[:foo] << s
end

post '/sse_message' do
  sses[:foo].message params[:data]
end

post '/sse_event' do
  sses[:foo].event params[:data]
end
eventsource instance helper

Additionally, you can also start SSE handling conditionally from inside a GET block:

get '/sse_maybe' do
  if params[:sse]
    eventsource do |c|
      sses << c
      c.write sse_message 'wooo fancy SSE for you!'
    end
  else
    'boring regular old get response'
  end
end

post '/sse_event' do
  sses.each {|sse| sse.write sse_event(:foo, 'fancy sse event!')}
end

Handling this on the client may require conditionals for browsers that do not support EventSource yet, since this will respond with a non-"text/event-stream" Content-Type if 'sse' is not present in the params.

EventSource#on_close helper

When inside an eventsource block, you may want to do something specific when a client closes the connection. For this case, there are on_close and on_close= methods on the object passed to the block that will get called if the client closes the socket. The assignment method takes a proc object and the other one takes a block:

get '/' do
  eventsource do |es|

    # assignment!
    es.on_close = ->{sses(false).remove_socket es}

    sses << es
  end
end

eventsource '/sse' do |es|

  # just passing a block here
  es.on_close {sses(false).remove_socket es}

  sses << es
end

Note the use of the optional parameter of the stashes here; by default, stash accessors (websockets and sses) will reject! any closed sockets before letting you in. If you pass false to the stash accessors, they will skip the reject! step.

Tasks + Async / Future

Angelo is built on Reel and Celluloid::IO, giving your web application the ability to define "tasks" and call them from route handler blocks in an async or future style.

task builder

You can define a task on the reactor using the task class method and giving it a symbol and a block. The block can take arguments that you can pass later, with async or future.

# defining a task on the reactor called `:in_sec` which will sleep for
# the given number of seconds, then return the given message.
#
task :in_sec do |sec, msg|
  sleep sec.to_i
  msg
end
async helper

This helper is directly analogous to the Celluoid method of the same name. Once tasks are defined, you can call them with this helper method, passing the symbol of the task name and any arguments. The task will run on the reactor, asynchronously, and return immediately.

get '/' do
  # run the task defined above asynchronously, return immediately
  #
  async :in_sec, params[:sec], params[:msg]

  # NOTE: params[:msg] is discarded, the return value of tasks called with `async` is nil.

  # return this response body while the task is still running
  # assuming params[:sec] is > 0
  #
  'hi'
end
future helper

Just like async, this comes from Celluloid as well. It behaves exactly like async, with the notable exception of returning a "future" object that you can call #value on later to retrieve the return value of the task. Calling #value will "block" until the task is finished, while the reactor continues to process requests.

get '/' do
  # run the task defined above asynchronously, return immediately
  #
  f = future :in_sec, params[:sec], params[:msg]

  # now, block until the task is finished and return the task's value
  # as a response body
  #
  f.value
end

Errors and Halting

Angelo gives you two ordained methods of stopping route processing:

The main difference is that halt will still run after blocks, and raising RequestError will bypass after blocks.

Any other exceptions or errors raised by your route handler will be handled with a 500 status code and the message will be the body of the response.

RequestError

Raising an instance of Angelo::RequestError causes a 400 status code response, and the message in the instance is the body of the the response. If the route or class was set to respond with JSON, the body is converted to a JSON object with one key, error, that has the value of the message. If the message is a Hash, the hash is converted to a JSON object, or to a string for other content types.

If you want to return a different status code, you can pass it as a second argument to RequestError.new. See example below.

Halting

You can halt from within any route handler, optionally passing status code and a body. The body is handled the same way as raising RequestError.

Example
get '/' do
  raise RequestError.new '"foo" is a required parameter' unless params[:foo]
  params[:foo]
end

get '/json' do
  content_type :json
  raise RequestError.new foo: "required!"
  {foo: params[:foo]}
end

get '/not_found' do
  raise RequestError.new 'not found', 404
end

get '/halt' do
  halt 200, "everything's fine"
  raise RequestError.new "won't get here"
end

$ curl -i http://127.0.0.1:4567/
HTTP/1.1 400 Bad Request
Content-Type: text/html
Connection: Keep-Alive
Content-Length: 29

"foo" is a required parameter

$ curl -i http://127.0.0.1:4567/?foo=bar
HTTP/1.1 200 OK
Content-Type: text/html
Connection: Keep-Alive
Content-Length: 3

bar

$ curl -i http://127.0.0.1:4567/json
HTTP/1.1 400 Bad Request
Content-Type: application/json
Connection: Keep-Alive
Content-Length: 29

{"error":{"foo":"required!"}}

$ curl -i http://127.0.0.1:4567/not_found
HTTP/1.1 404 Not Found
Content-Type: text/html
Connection: Keep-Alive
Content-Length: 9

not found

$ curl -i http://127.0.0.1:4567/halt
HTTP/1.1 200 OK
Content-Type: text/html
Connection: Keep-Alive
Content-Length: 18

everything's fine

Tilt / ERB

class Foo < Angelo::Base

  views_dir 'some/other/path' # defaults to './views'

  get '/' do
    erb :index
  end

end

The Angleo::Tilt::ERB module and the erb method do some extra work for you:

See views for examples.

Mustermann

class Foo < Angelo::Base

  get '/:foo/things/:bar' do

    # `params` is merged with the Mustermann object#params hash, so
    # a "GET /some/things/are_good?foo=other&bar=are_bad" would have:
    #   params: {
    #     'foo' => 'some',
    #     'bar' => 'are_good'
    #   }

    @foo = params[:foo]
    @bar = params[:bar]
    erb :index
  end

  before '/:fu/things/*' do

    # `params` is merged with the Mustermann object#params hash, as
    # parsed with the current request path against this before block's
    # pattern. in the route handler, `params[:fu]` is no longer available.

    @fu = params[:fu]
  end

end

Classic vs. modular apps

Like Sinatra, Angelo apps can be written in either "classic" style or so-called "modular" style. Which style you use is more of a personal preference than anything else.

A classic-style app requires "angelo/main" and defines the app directly at the top level using the DSL. In addition, classic apps:

Note: unlike Sinatra, define a classic app by requiring "angelo/main" and a modular app by requiring "angelo". Sinatra uses "sinatra" and "sinatra/base" to do the same things.

Here's a classic app:

require 'angelo/main'

helpers do
  def say_hello
    "Hello"
  end
end

get "/hello" do
  "#{say_hello} to you, too."
end

And the same app in modular style:

require 'angelo'

class HelloApp < Angelo::Base
  def say_hello
    "Hello"
  end

  get "/hello" do
    "#{say_hello} to you, too."
  end
end

HelloApp.run!

JSON HTTP API

If you post JSON data with a JSON Content-Type, angelo will:

N.B. request_body is functionally equivalent to request.body.to_s otherwise.

If your content_type is set to :json, angelo will convert:

Documentation

I'm bad at documentation and I feel bad.

Others have helped, and there is a YaRD plugin for Angelo here if you would like to document your apps built with Angelo. (thanks: @katjaeinsfeld, @artcom)

WORK LEFT TO DO

Lots of work left to do!

Full-ish example

require 'angelo'

class Foo < Angelo::Base

  # just some constants to use in routes later...
  #
  TEST = {foo: "bar", baz: 123, bat: false}.to_json
  HEART = '<3'

  # a flag to know if the :heart task is running
  #
  @@hearting = false

  # you can define instance methods, just like Sinatra!
  #
  def pong; 'pong'; end
  def foo; params[:foo]; end

  # standard HTTP GET handler
  #
  get '/ping' do
    pong
  end

  # standard HTTP POST handler
  #
  post '/foo' do
    foo
  end

  post '/bar' do
    params.to_json
  end

  # emit the TEST JSON value on all :emit_test websockets
  # return the params posted as JSON
  #
  post '/emit' do
    websockets[:emit_test].each {|ws| ws.write TEST}
    params.to_json
  end

  # handle websocket requests at '/ws'
  # stash them in the :emit_test context
  # write 6 messages to the websocket whenever a message is received
  #
  websocket '/ws' do |ws|
    websockets[:emit_test] << ws
    ws.on_message do |msg|
      5.times { ws.write TEST }
      ws.write foo.to_json
    end
  end

  # emit the TEST JSON value on all :other websockets
  #
  post '/other' do
    websockets[:other].each {|ws| ws.write TEST}
    ''
  end

  # stash '/other/ws' connected websockets in the :other context
  #
  websocket '/other/ws' do |ws|
    websockets[:other] << ws
  end

  websocket '/hearts' do |ws|

    # this is a call to Base#async, actually calling
    # the reactor to start the task
    #
    async :hearts unless @@hearting

    websockets[:hearts] << ws
  end

  # this is a call to Base.task, defining the task
  # to perform on the reactor
  #
  task :hearts do
    @@hearting = true
    every(10){ websockets[:hearts].each {|ws| ws.write HEART } }
  end

  post '/in/:sec/sec/:msg' do

    # this is a call to Base#future, telling the reactor
    # do this thing and we'll want the value eventually
    #
    f = future :in_sec, params[:sec], params[:msg]
    f.value
  end

  # define a task on the reactor that sleeps for the given number of
  # seconds and returns the given message
  #
  task :in_sec do |sec, msg|
    sleep sec.to_i
    msg
  end

  # return a chunked response of JSON for 5 seconds
  #
  get '/chunky_json' do
    content_type :json

    # this helper requires a block that takes one arg, the response
    # proc to call with each chunk (i.e. the block that is passed to
    # `#each`)
    #
    chunked_response do |response|
      5.times do
        response.call time: Time.now.to_i
        sleep 1
      end
    end
  end

end

Foo.run!

Contributing

Anyone is welcome to contribute. Conduct is guided by the Contributor Covenant. See code_of_conduct.md.

To contribute to Angelo, please:

After review and acceptance, your changes will be merged and noted in CHANGLOG.md.

Testing

Unit tests are done with Minitest. Run them with :

bundle install
rake test

License

Apache 2.0

Name

Why the name "Angelo"? Since the project mimics Sinatra's DSL, I thought it best to keep a reference to The Chairman in the name. It turns out that Frank Sinatra won an Academy Award for his role 'Angelo Maggio' in 'From Here to Eternity'. I appropriated the name since this is like Sinatra on Reel (film).