WebSockets + Akka, on Scalatra

Yuvi Masory - @ymasory

Bay Area Scalatra Hackers (BASH)

January 30, 2013

Slides live at http://yuvimasory.com/talks.

What is this group about?

Scalatra!
Scalatra + Spray?
Scala Web Development?
What do you think?

Is this the last BASH meetup?

I'm delighted to do the organizing.
But I'm not giving every talk!
Giving talks isn't all that hard.
- Step 1: Pick a topic you'd like to learn about.
- Step 2: Sign up for a talk one month out.
- Step 3: Learn about the topic when you have time.
- Step 4: Share your findings!

Where are we going?

I. Intro to Scalatra
II. Intro to WebSockets
III. Intro to Akka
IV. Mashup!

Some banter

ScalaTypes podcast - http://scalatypes.com

Episode 22: Derek Wyatt on Akka Concurrency
Episode 24: Ivan Porto Carrero on Scalatra
Episodes 27-28: Mathias Doenitz on Spray
Episode 29: James Roper on Play!

/Advertisement

Warning

This is mostly a "concepts" talk. Very little code will be shown.
If you want particulars, ask!

Section I
Intro to Scalatra

Hello Scalatra

    import org.scalatra._

    class HelloScalatra extends ScalatraServlet {

      get("/") {
        "Hello, world!"
      }
    }

BEFORE I FORGET!

Use Scalatra version 2.2, currently in RC3.
http://scalatra.org/2.2
Scalatra in Action is in pre-release from Manning.

Scalatra's philosophy: transparency

No magic!
It's elephants all the way down.
More a set of libraries than a "framework".
Source code is extremely readable.

Scalatra's philosophy: unobtrusiveness

Absolute minimum of configuration. Did you see hello world?
Not "opinionated".
No fancy build system.
Everything is modifiable via idiomatic Scala.
Integrations are all optional, and often independent.

Scalatra's philosophy: scalability

High performance out of the box.
Stateless by default. Sessions if you want them.
Async via Akka.

Scalatra's philosophy:
don't reinvent the wheel!

Servlet-based
Use the best of the ecosystem.

Implementation side: Atmosphere, Json4s, Akka, etc.
Application side: love thy InputStream

NIH isn't in the vocabulary.

The dark side of Scalatra ...

Routes parameters are not typed.
Core DSL is mutable. (The DSL is a Sinatra port, so go figure.)
Servlets
- Not as asynchronous as Netty until Servlet 3.5
- Some people really hate servlet containers. Why?!
- Generally can't penetrate the Servlet API without bring in classes specific to your container.
- Not Scala elephants all the way down. (See spray-io.)

Section II
Intro to WebSockets

HTTP history

HTTP/1 only has simple request-response.
HTTP/1.1
- Persistent connections
- HTTP pipelining
- Comet
SPDY (working draft of HTTP/2.0)
- Multiplexing
- Prioritization
- Full compression

What are WebSockets?

WebSocket is a web technology providing full-duplex communications channels over a single TCP connection.
WebSockets is an independent TCP/IP protocol not based on HTTP.
Clients can be web browsers or servers.

Browser support

Firefox >= v6
Chrome >= v14
Internet Explorer >= v10
Opera >= v12.10
Yes, web browsers briefly disabled WebSockets last year, but that's over now.
Safari not re-enabled yet
Not much mobile support yet

HTTP handshake

    GET /mychat HTTP/1.1
    Host: server.example.com
    Upgrade: websocket
    Connection: Upgrade
    Sec-WebSocket-Key: x3JJHMbDL1EzLkh9GBhXDw==
    Sec-WebSocket-Protocol: chat
    Sec-WebSocket-Version: 13
    Origin: http://example.com
    Server response:
    HTTP/1.1 101 Switching Protocols
    Upgrade: websocket
    Connection: Upgrade
    Sec-WebSocket-Accept: HSmrc0sMlYUkAGmm5OPpG2HaGWk=
    Sec-WebSocket-Protocol: chat

Advantages of WebSockets

Communication is over port 80
Proxy traversal
Full-duplex communication
- That includes "browser push" and many other models.
- Between connection & disconnection the parties send arbitrary messages at arbitrary times.
Reduced latency & overhead, improved scalability, compared to Comet (reverse AJAX).
Simpler implementation than Comet.

Disadvantages of WebSockets

Client support isn't all there.
May encourage stateful design.
Lower level
Unfamiliar

Section III
Intro to Akka

What is Akka?

Concurrency framework
Increasingly integrated with Scala standard library
Supports many styles of concurrency
- Actors
- Futures
- Agents
- Dataflow
- STM from Scala

Actors in one slide

Actors are objects that ...

define a method for handling messages of any type.
have a first-in-first-out mailbox of messages.
send messages to other actors asynchronously.
can safely maintain mutable state.
don't need to worry about thread scheduling, message routing, or locking.

Sound familiar?

Like the client & host on a socket connection, actors send messages whenever they wish.
Scalatra uses Akka to make sure socket messages are processed asynchronously.
Biggest difference: actors must handle messages in order.

That does not mean that the "reply" comes in the same order, like pipelining.

What Akka looks like

    class MyActor extends Actor {

      var count = 0

      def receive = {
        case "hi" => sender ! "and hello to you"

        case Inc =>
          count += 1
          sender ! count

        case quotesRequest: GetStockQuotes =>
          actorOf[StockChecker] ! (quotesRequest, sender)
      }
    }

    val ref: ActorRef = actorOf[MyActor]
    val res: Future[Any] = ref ? Inc
    res foreach println

Section IV
Mashup!

Atmosphere

Written by Jeanfrancois Arcand of GlassFish & async-http-client fame.
Provides automatic fallback from WebSockets to other transports.

OMFG!
Java server implementation, Javascript client implementation.
async-http-client provides a Java client.
Comes with implementations of high-level patterns.
Integration with Swagger.

Scalatra's Atmosphere integration

class ChatController extends ScalatraServlet 
  with JValueResult with JacksonJsonSupport    //let's use json!
  with SessionSupport with AtmosphereSupport { //let's use atmosphere!

  atmosphere("/the-chat") {
    new AtmosphereClient {
      def receive = { //this is a *partial* function, just like Akka
        case Connected =>
          broadcast(
            ("author" -> "Someone") ~
            ("message" -> "joined the room"))
          send("welcome!")
        case Disconnected(ClientDisconnected, cause) =>
        case Disconnected(ServerDisconnected, cause) =>
        case TextMessage(str) =>
        case JsonMessage(json) =>
        case BinaryMessage(array) =>
      }
    }
  }

Conclusion

My opinion

Scalatra is a full-featured web framework that is easy for beginners, but lets power users be power users.
Atmosphere is its killer app.
If you don't need "full-featured" then Spray is seriously hot.

WebSockets + Akka, on Scalatra

Yuvi Masory - @ymasory

Bay Area Scalatra Hackers (BASH)

January 30, 2013

Slides live at http://yuvimasory.com/talks.

What is this group about?

Scalatra!

Scalatra + Spray?

Scala Web Development?

What do you think?

Is this the last BASH meetup?

I'm delighted to do the organizing.

But I'm not giving every talk!

Giving talks isn't all that hard.

Where are we going?

I. Intro to Scalatra

II. Intro to WebSockets

III. Intro to Akka

IV. Mashup!

Some banter

ScalaTypes podcast - http://scalatypes.com

Episode 22: Derek Wyatt on Akka Concurrency

Episode 24: Ivan Porto Carrero on Scalatra

Episodes 27-28: Mathias Doenitz on Spray

Episode 29: James Roper on Play!

/Advertisement

Warning

This is mostly a "concepts" talk. Very little code will be shown.

If you want particulars, ask!

Section IIntro to Scalatra

Hello Scalatra

BEFORE I FORGET!

Use Scalatra version 2.2, currently in RC3.

http://scalatra.org/2.2

Scalatra in Action is in pre-release from Manning.

Scalatra's philosophy: transparency

No magic!

It's elephants all the way down.

More a set of libraries than a "framework".

Source code is extremely readable.

Scalatra's philosophy: unobtrusiveness

Absolute minimum of configuration. Did you see hello world?

Not "opinionated".

No fancy build system.

Everything is modifiable via idiomatic Scala.

Integrations are all optional, and often independent.

Scalatra's philosophy: scalability

High performance out of the box.

Stateless by default. Sessions if you want them.

Async via Akka.

Scalatra's philosophy: don't reinvent the wheel!

Servlet-based

Use the best of the ecosystem.

NIH isn't in the vocabulary.

The dark side of Scalatra ...

Routes parameters are not typed.

Core DSL is mutable. (The DSL is a Sinatra port, so go figure.)

Servlets

Section IIIntro to WebSockets

HTTP history

HTTP/1 only has simple request-response.

HTTP/1.1

Persistent connections

HTTP pipelining

Comet

SPDY (working draft of HTTP/2.0)

Multiplexing

Prioritization

Full compression

What are WebSockets?

WebSocket is a web technology providing full-duplex communications channels over a single TCP connection.

WebSockets is an independent TCP/IP protocol not based on HTTP.

Clients can be web browsers or servers.

Browser support

Firefox >= v6

Chrome >= v14

Internet Explorer >= v10

Opera >= v12.10

Yes, web browsers briefly disabled WebSockets last year, but that's over now.

Safari not re-enabled yet

Section I
Intro to Scalatra

Scalatra's philosophy:
don't reinvent the wheel!

Section II
Intro to WebSockets

Section III
Intro to Akka

Biggest difference: actors must handle messages in order.

That does not mean that the "reply" comes in the same order, like pipelining.

Section IV
Mashup!