s1monw1

class PrintingCustomizer { // PrintingCustomizer is a dispatch receiver
    private val separator = "________________"

    fun <K, V> Map<K, V>.customPrint() { // Map<T, V> is an extension receiver for customPrint
        forEach { (k, v) ->
            println("K: $k")
            println("V: $v")
            println(separator)
        }
    }

s1monw1

class PrintingCustomizer {
    private val separator = "________________"

    fun <T, V> Map<T, V>.customPrint() {
        forEach { (k, v) ->
            println("K: $k")
            println("V: $v")
            println(separator)
        }
    }

s1monw1

val request = Request(Method.GET, "https://kotlinexpertise.com/sitemap.xml")
val client: HttpHandler = JavaHttpClient()
val response = client(request)

s1monw1

val addExtraHeaderFilter = Filter { next ->
    {
        next(it).header("x-extra-header", "some value")
    }
}

@Test
fun adds_a_special_header() {
    val handler: HttpHandler = addExtraHeaderFilter.then { Response(OK) }
    val response: Response = handler(Request(GET, "/echo"))

s1monw1

import com.natpryce.hamkrest.assertion.assertThat
import org.http4k.core.Method
import org.http4k.core.Request
import org.http4k.core.Status
import org.http4k.hamkrest.hasStatus
import org.junit.jupiter.api.Test

class PersonHandlerProviderTest {

    val systemUnderTest = PersonHandlerProvider(PersonService())

s1monw1

[...]
import org.http4k.format.Jackson.auto
class PersonHandlerProvider(private val service: PersonService) {
    private val personLens: BiDiBodyLens<Person> = Body.auto<Person>().toLens()
    private val personListLens: BiDiBodyLens<List<Person>> = Body.auto<List<Person>>().toLens()

    fun getAllHandler(): HttpHandler = {
        Response(OK).with(
            personListLens of service.findAll()
        )

s1monw1

val req = Request(GET, "/greet/{name}")
val reqWithName = nameLens.inject("kotlin", req)
// alternatively, http4k offers a with function that can apply multiple lenses at once
val reqWithName = Request(GET, "/greet/{name}").with(
    nameLens of "simon" //, more lenses
)

s1monw1

// gzip omitted
val app: HttpHandler = ServerFilters.CatchLensFailure
 .then(requestTimeLogger)
 .then(routing)

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val nameLens: BiDiLens<Request, String> =
    Query.nonEmptyString().required("name")
val greetHandler: HttpHandler = { req: Request ->
     val name: String = nameLens.extract(req) //or nameLens(req)
     Response(OK).body("hello $name")
}

s1monw1

// lens focusing on the path variable name
val nameLens = Path.string().of("name")

// lens focusing on a required query parameter city
val requiredQuery = Query.required("city")

// lens focusing on a required and non-empty string city 
val nonEmptyQuery = Query.nonEmptyString().required("city")

// lens focusing on an optional header Content-Length with type int