Gave talk at 第4回Reactive System Meetup in 西新宿.

1. sbt,
history of JSON libraries,
microservices, and
schema evolution
Eugene Yokota (@eed3si9n)
February, 2017

2. • Scala hobbyist since 2010
• scalaxb (XML data binding)
• treehugger.scala
• sbt-assembly, sbt-buildinfo, etc
• “learning Scalaz” / “herding Cats”
• ScalaMatsuri
• Lightbend/Typesafe since 2014
• tech lead of Reactive Platform team
• current maintainer / tech lead of sbt
who is this guy (@eed3si9n)?

3. Lightbend Production Suite

5. big picture: development at scale

6. • How do you scale a technological organization?
• Goal: Sustainable development
development at scale

7. • Bezos mandate (written circa 2002 before AWS) https://plus.google.com/
+RipRowan/posts/eVeouesvaVX
microservice is a social stack
1. All teams will henceforth expose their data and functionality through service interfaces.
2. Teams must communicate with each other through these interfaces.
3. There will be no other form of inter-process communication allowed: no direct linking, no direct
reads of another team’s data store, no shared-memory model, no back-doors whatsoever. The only
communication allowed is via service interface calls over the network.
4. It doesn’t matter what technology they use. HTTP, Corba, Pubsub, custom protocols -- doesn't
matter. Bezos doesn't care.
5. All service interfaces, without exception, must be designed from the ground up to be externalizable.
That is to say, the team must plan and design to be able to expose the interface to developers in the
outside world. No exceptions.
6. Anyone who doesn't do this will be fired.

8. Brief history of
JSON libraries
Eugene Yokota (@eed3si9n)
2016

9. Brief history of JSON libraries
Dispatch JSON
literaljson
Lift JSON
sjson
Spray JSON
Play JSON
Argonaut
json4s
Circe
Jawn
SLIP-28 JSON
Rapture JSON
sjson-new
2009 2010 2014

10. 2008

11. Two books

12. Programming in Scala
import scala.util.parsing.combinator._
class JSON extends JavaTokenParsers {
def value : Parser[Any] = obj | arr |
stringLiteral |
floatingPointNumber |
"null" | "true" | "false"
def obj : Parser[Any] = "{"~repsep(member, ",")~"}"
def arr : Parser[Any] = "["~repsep(value, ",")~"]"
def member: Parser[Any] = stringLiteral~":"~value
}
https://www.artima.com/pins1ed/combinator-parsing.html#31.4

13. • Chapter 5. Writing a library: working with JSON data
Real World Haskell
data JValue = JString String
| JNumber Double
| JBool Bool
| JNull
| JObject [(String, JValue)]
| JArray [JValue]
deriving (Eq, Ord, Show)

14. 2009

15. • https://github.com/dispatch/dispatch/commit/
41edb939baa5c6edb4378c1bd8e1d2f10f3350f2
• Contributed by Jorge Ortiz
• Parsing using parser combinator
• Values stored in AST, JsValue
Dispatch JSON

16. • https://github.com/jonifreeman/literaljson
• Authored by Joni Freeman
• Custom parser
• Values stored in AST, JValue
• On August 11, 2009, Joni contributed literaljson to
Lift, and became Lift-JSON
jonifreeman/literaljson

17. 2010

18. • https://github.com/debasishg/sjson
• Authored by Debasish Ghosh
• sjson: Now offers Type Class based JSON
Serialization in Scala
• Uses Dispatch JSON for AST
sjson

19. Typeclass

20. • Allows adding capability to a class after the fact in a
typesafe manner.
Typeclass
trait Eq[A] {
def equals(x: A, y: A): Boolean
}
• Eq typeclass can enable === operator to compare
only the supported types, and prevent compilation
of "1" === 1
• Scala Implicits : Type Classes Here I Come

21. JsonFormat
trait CanRead[A] {
def reads(json: JsValue): A
}
trait CanWrite[A] {
def writes(a: A): JsValue
}
trait JsonFormat[A] extends CanRead[A]
with CanWrite[A]
implicit val intFormat: JsonFormat[Int] = ...

22. JsonFormat
• JsonFormat typeclass allows conversion to and
from an arbitrary type to a JSON AST.

23. 2011

24. • https://github.com/spray/spray-json
• Authored by Mathias Dönitz
• Original parser
• Ported AST from Dispatch JSON and type classes
from sjson
spray-json

25. • https://github.com/playframework/playframework/commit/
63448578b15dcc7bf4806878c7b3aa4c74193af6
• Started out as port of Dispatch JSON and sjson typeclasses, but quickly
added its own implementations.
Play JSON

26. 2012

27. • http://argonaut.io/
• Purely functional JSON library
• Authored by Mark Hibberd, Tony Morris, Sean Parsons
• Uses Scalaz or Cats
• Very feature rich (Lenses, Cursor, History Cursor)
Argonaut

28. 2013

29. • https://github.com/json4s/json4s
• Fork of Lift-json. JSON library that is not strongly tied to a web
framework.
json4s

30. 2014

31. • https://github.com/non/jawn
• Authored by Erik Osheim (@d6)
• Backend-independent JSON parser
Jawn

32. • http://rapture.io/mod/json
• Authored by Jon Pretty
• Backend-independent JSON library
Rapture JSON

33. 2015

34. • https://github.com/travisbrown/circe
• Authored by Travis Brown
• Port of Argonaut
Circe

35. 2016

36. • https://github.com/mdedetrich/scala-json-ast
• Authored by Matthew de Detrich
• Aiming to be the common JSON AST
Scala JSON AST (SLIP-28)

37. • https://github.com/eed3si9n/sjson-new
• Backend-independent typeclass based JSON codec
• No macros
sjson-new

38. Brief history of JSON libraries
Dispatch JSON
literaljson
Lift JSON
sjson
Spray JSON
Play JSON
Argonaut
json4s
Circe
Jawn
SLIP-28 JSON
Rapture JSON
sjson-new
2009 2010 2014

39. Contract-first approach
Eugene Yokota (@eed3si9n)
2016

40. • “Serialization” tends to start from a programming language construct, and it
generates String or byte array.
• Data binding starts with a contract or a schema of the wire format, and generates
the binding in a programming language.
• XML Schema / WSDL
• Google Protocol Buffer
• Apache Thrift
• Apache Avro
• Facebook GraphQL
Serialization vs Data binding

41. • sealed traits
• case classes
Representing data in Scala

42. • sealed traits
• case classes
Representing data in Scala
Cannot evolve in a binary compatible way.

43. Representing data in Scala
class Greeting(name: String) {
def copy(name: String = name): Greeting = ???
def unapply(v: Greeting): Option[String] = ???
}
class Greeting(name: String, x: Int) {
def copy(name: String = name,
x: Int = x): Greeting = ???
def unapply(v: Greeting): Option[(String, Int)] =
???
}

44. • sealed traits
• case classes
• Cannot evolve in a binary compatible way.
• But generating equals, hash, and toString is generally useful.
Representing data in Scala

45. Contraband

46. • http://www.scala-sbt.org/contraband/
• Contraband is a description language for your datatypes and APIs, currently
targeting Java and Scala.
• Based on GraphQL schema.
Contraband

47. Record types
package com.example
@target(Scala)
## Character represents the characters in Star Wars.
type Character {
name: String!
appearsIn: [com.example.Episode]!
}

48. @since annotation
package com.example
@target(Scala)
type Greeting {
value: String!
x: Int @since("0.2.0")
}

49. Enumeration types
package com.example
@target(Scala)
## Star Wars trilogy.
enum Episode {
NewHope
Empire
Jedi
}

50. Interfaces
package com.example
@target(Scala)
## Character represents the characters in Star Wars.
interface Character {
name: String!
appearsIn: [com.example.Episode]!
friends: lazy [com.example.Character]
}

51. Record type example
package com.example
@target(Scala)
type Person {
name: String!
age: Int
}

52. Record type example
// DO NOT EDIT MANUALLY
package com.example
final class Person private (
val name: String,
val age: Option[Int]) extends Serializable {
override def equals(o: Any): Boolean = o match {
case x: Person => (this.name == x.name) && (this.age ==
x.age)
case _ => false
}
override def hashCode: Int = {
37 * (37 * (17 + name.##) + age.##)
}
override def toString: String = {

53. Record type example
override def toString: String = {
"Person(" + name + ", " + age + ")"
}
protected[this] def copy(name: String = name,
age: Option[Int] = age): Person = {
new Person(name, age)
}
def withName(name: String): Person = {
copy(name = name)
}
def withAge(age: Option[Int]): Person = {
copy(age = age)
}
def withAge(age: Int): Person = {

54. Record type example
object Person {
def apply(name: String, age: Option[Int]): Person =
new Person(name, age)
def apply(name: String, age: Int): Person =
new Person(name, Option(age))
}

55. Record type example
> val x = Person("Alice", 20)
> x.withAge(21)

56. Contraband can derive sjson-new codecs

57. JSON codec generation
package com.example
@target(Scala)
type Person {
name: String!
age: Int
}

58. JSON codec generation
package generated
import _root_.sjsonnew.{ deserializationError,
serializationError, Builder, JsonFormat, Unbuilder }
trait PersonFormats { self: sjsonnew.BasicJsonProtocol =>
implicit lazy val personFormat: JsonFormat[_root_.Person] =
JsonFormat[_root_.Person] {
override def read[J](jsOpt: Option[J], unbuilder:
Unbuilder[J]): _root_.Person = {
jsOpt match {
case Some(js) =>
unbuilder.beginObject(js)
val name = unbuilder.readField[String]("name")
val age = unbuilder.readField[Option[Int]]("age")
unbuilder.endObject()
_root_.Person(name)

59. JSON codec generation
scala> import sjsonnew.support.scalajson.unsafe.{ Converter,
CompactPrinter, Parser }
scala> import com.example.codec.CustomJsonProtocol._
scala> import com.example.Person
scala> val p = Person("Bob", 20)
p: com.example.Person = Person(Bob, 20)
scala> val j = Converter.toJsonUnsafe(p)
j: scala.json.ast.unsafe.JValue =
JObject([Lscala.json.ast.unsafe.JField;@6731ad72)
scala> val s = CompactPrinter(j)
s: String = {"name":"Bob","age":20}
scala> val x = Parser.parseUnsafe(s)

60. JSON codec generation
scala> val s = CompactPrinter(j)
s: String = {"name":"Bob","age":20}
scala> val x = Parser.parseUnsafe(s)
x: scala.json.ast.unsafe.JValue =
JObject([Lscala.json.ast.unsafe.JField;@7331f7f8)
scala> val q = Converter.fromJsonUnsafe[Person](x)
q: com.example.Person = Person(Bob, 20)
scala> assert(p == q)

61. • http://www.scala-sbt.org/contraband/
• Contraband is a description language for your datatypes and APIs, currently
targeting Java and Scala.
• Low-tech metaprogramming (code generation)
• Binary compatible evolution of pseudo case class.
• Auto derivation of backend-independent JSON codec.
Contraband

62. • An opportunity for datatype-generic programming.
• For example, one backend is Int
Contraband

63. • An opportunity for datatype-generic programming.
• For example, one backend is Int (Murmurhash support)
• Builder API is used to build one-way hash.
Contraband