- Как пришли к использованию и разработки своих DSL - Посмотрим примеры используемых в экосистеме DSL - gradle, spek, spring - Рассмотрим базис для конструирования DSL на примере kohttp

1. Production Koltin DSL
Сергей Рыбалкин
@lightdelay@rybalkinsd

2. Speaker
Principal Engineer @ Alibaba Group
Kotlin & Java Lecturer in MSU
9 years of experience
3 years with Kotlin
2

3. Agenda
1.[Путь к DSL]
2.DSL в экосистеме Kotlin
3.Строим свой DSL
4.Проблемки и решения
3

4. Serverless. FaaS
4
Gateways
MQRPCHTTP
Security
Routing

5. Serverless. FaaS
5
val result = httpPost {
host = "s.alibab-inc.com"
path = "/order"
header {
"version" to 1688
cookie {
"sender" to "alibaba"
}
}
body {
json { ... }
}
}
val result = rpcCall {
group = "alibaba"
method = "OrderService.orders"
args {
"id" to productId
"referrer" to json { ... }
}
}

6. Agenda
1.Путь к DSL
2.[DSL в экосистеме Kotlin]
3.Строим свой DSL
4.Проблемки и решения
6

7. Domain Specific Language
7
SQL
HTML
CSS Markdown
Regex

8. Domain Specific Language
8
DSL =
Problem Context + Syntax =
F(Productivity, Concision, Safety)

9. Successful DSL
∥FDSL∥ > ∥FGeneral Purpose Language∥
9

10. Embedded DSL. Kotlin
• Null-safety
• Статическая типизация
• Средства построения DSL
• IDE
10

11. Embedded DSL. Kotlin
• Gradle
• Bean definition DSL (Spring)
• WebFlux Functional DSL (Spring)
• Spek
• kotlinx.html
• kohttp
11

12. Gradle DSL
12
plugins {
kotlin("jvm") version "1.3.40"
`maven-publish`
}
repositories {
mavenCentral()
}
dependencies {
implementation(kotlin("stdlib-jdk8"))
implementation(kotlin("reflect"))
implementation(kotlinx("coroutines-core")
}
publishing {
publications {
create<MavenPublication>("artifact") {
...

13. Spek
13
object SetFeature: Spek({
Feature("Set addition") {
val set by memoized { mutableSetOf<String>() }
Scenario("getting the first item") {
val item = "foo"
Given("a non-empty set") {
set.add(item)
}
lateinit var result: String
When("getting the first item") {
result = set.first()
}
Then("it should return the first item") {
assertEquals(item, result)
}
}
}

14. WebFlux router
14
router {
accept(TEXT_HTML).nest {
GET("/") { ok().render("index") }
GET("/users", userHandler::findAllView)
}
"/api".nest {
accept(APPLICATION_JSON).nest {
GET("/users", userHandler::findAll)
}
}
resources("/**", ClassPathResource("static/"))
}

15. HTTP. BC
15
OkHttpClient client = new OkHttpClient();
MediaType mediaType = MediaType.parse("multipart/form-data; boundary=----
WebKitFormBoundary7MA4YWxkTrZu0gW");
RequestBody body = RequestBody.create(mediaType, "------
WebKitFormBoundary7MA4YWxkTrZu0gWrnContent-Disposition: form-data;
name="key"rnrnxxxxxrn------WebKitFormBoundary7MA4YWxkTrZu0gWrnContent-Disposition: form-
data; name="b"; filename="Screen Shot 2019-06-07 at 10.22.21.png"rnContent-Type: image/
pngrnrnrn------WebKitFormBoundary7MA4YWxkTrZu0gW--");
Request request = new Request.Builder()
.url("https://github.com/search")
.get()
.addHeader("content-type", "multipart/form-data; boundary=----
WebKitFormBoundary7MA4YWxkTrZu0gW")
.addHeader("username", "rybalkinsd")
.addHeader("security-policy", "{ "max-age": 2592000 }")
.addHeader("script-src", ""github.com", "github.io"")
.addHeader("cookie", "{ "user_session" : "toFycNV", "expires" : "Fri, 31 Jul 2019
20:30:00 -0000" }")
.build();
Response response = client.newCall(request).execute();

16. HTTP. AD
16
httpGet {
url("https://github.com/search")
header {
"username" to "rybalkinsd"
"security-policy" to json {
"max-age" to 2592000
}
"script-src" to listOf("github.com", "github.io")
cookie {
"user_session" to "toFycNV"
"expires" to "Fri, 31 Jul 2019 20:30:00 -0000"
}
}
param { ... }
}

17. kohttp. Kotlin DSL http client
17
https://github.com/rybalkinsd/kohttp
‣ Asnyc/sync DSL for http methods
‣ Coroutines support
‣ Built-in Interceptors

18. Agenda
1.Путь к DSL
2.DSL в экосистеме Koltin
3.[Строим свой DSL]
4.Platform
18

19. Building Kotlin DSL. Tools
19

20. Tools. Lambda as last argument
20
fun measureTimeMillis(block: () -> Unit): Long {
val start = System.currentTimeMillis()
block()
return System.currentTimeMillis() - start
}
val time = measureTimeMillis {
task()
}

21. Tools. Extension functions
21
val response: Deferred<Response> =
“https://google.com/search/?q=iphone”.httpGetAsync()
fun String.httpGetAsync(
client: Call.Factory = defaultHttpClient
): Deferred<Response> =
GlobalScope.async(context = Dispatchers.Unconfined) {
...
}

22. Tools. Lambda with receiver
22
httpGet {
url("https://github.com/search")
header {
"username" to "rybalkinsd"
"security-policy" to json {
"max-age" to 2592000
}
cookie {
"user_session" to "toFycNV"
"expires" to "Fri, 31 Jul 2019 20:30:00 -0000"
}
}
}

23. Tools. Lambda with receiver
23
fun httpGet(
client: Call.Factory = defaultHttpClient,
init: HttpGetContext.() -> Unit): Response {
val context = HttpGetContext().apply(init)
return client.newCall(
context.makeRequest()
).execute()
}

24. Lambda with receiver. HttpContext
24
class HttpContext(private val method: Method = GET) {
private val paramContext = ParamContext()
private val headerContext = HeaderContext()
var scheme: String = "http"
var host: String = ""
var port: Int? = null
var path: String? = null
...
}

25. Tools. Infix function
25
httpGet {
param {
"id" to Id("42")
"sender" to "localhost"
}
}
class ParamContext {
private val params = mutableMapOf<>()
infix fun String.to(v: Any?) { params[this] = v }
}

26. Tools. Type alias
26
typealias Header = Pair<String, String>
fun Request.headers(): Sequence<Header> = Sequence { ... }
httpRequest.headers().forEach {
(name, value) -> log("$name: $value")
}

27. Tools. Inline classes
27
inline class Token(val v: String)
infix fun String.to(token: Token) {
specific action
}
val response = httpPost {
url("https://googleapis.com/upload/drive/v3/files")
header {
"Authorization" to Token(“secret-token”)
}
https://kotlinlang.org/docs/reference/inline-classes.html
Inline classes are available only since Kotlin 1.3 and currently are experimental

28. Tools. Operator overloading
28
+item
-item
++item
--item
!importantAction
jsonArray[1, 2, 3, null]

29. Tools. Operator overloading
29
+item .unaryPlus()
-item .unaryMinus()
++item .inc()
--item .dec()
!importantAction .not()
jsonArray[1, 2, 3, null] .get(vararg content: Any?)

30. Tools. Operator overloading
30
val client = client {
interceptors {
+RetryInterceptor(failureThreshold = 5)
+LoggingInterceptor()
}
}
class Interceptors(val interceptors = Storage()) {
operator fun Interceptor.unaryPlus() {
interceptors += this
}
}

31. Agenda
1.Путь к DSL
2.DSL в экосистеме Koltin
3.Строим свой DSL
4.[Проблемки и решения]
31

32. Problem 1. Public setter, private getter
32
val client = client {
interceptors = listOf(
RetryInterceptor(failureThreshold = 5),
LoggingInterceptor()
)
interceptors.forEach { ... }
}
https://youtrack.jetbrains.com/issue/KT-3110

33. 33

34. Problem 1. Public setter, private getter
34
interface ClientBuilder {
@get:Deprecated(
level = DeprecationLevel.ERROR,
message = "Write only field")
var interceptors: List<Interceptor>
}
override var interceptors: List<Interceptor>
set(value) { ... }
get() = throw UnsupportedOperationException()

35. Problem 1. Public setter, private getter
35
val client = client {
interceptors = listOf(
RetryInterceptor(failureThreshold = 5),
LoggingInterceptor()
)
interceptors.forEach { ... } <— COMPILATION ERROR
}
https://youtrack.jetbrains.com/issue/KT-3110

36. Problem 2. Java 11 & dokka
36
val dokkaJar = task<Jar>("dokkaJar") {
group = JavaBasePlugin.DOCUMENTATION_GROUP
classifier = "javadoc"
}
publishing {
publications {
create<MavenPublication>("kohttp") {
from(components["java"])
artifacts {
artifact(sourcesJar)
artifact(dokkaJar)
}
}
}
}
https://youtrack.jetbrains.com/issue/KT-31710

37. 37

38. Problem 3. Context control
38
httpGet {
param {
"text" to "iphone"
param {
"lr" to 213
}
}
}

39. Problem 3. Context control
39
@DslMarker
annotation class HttpDslMarker
@HttpDslMarker
class ParamContext
httpGet {
param {
param { } <— COMPILATION ERROR
}
}

40. Outline
‣ DSL это круто, если и только если
помогает вашим пользователям
‣ Работайте над DevX. Пользовательский
фидбек - это единственное что важно при
построении DSL
‣ Уже наступило время делать async-first DSL
40

41. THANK YOU!
Q/A
@lightdelay@rybalkinsd