Presented By: Swantika Gupta
Dig Deeper With
http4s

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Our Agenda
Recap of http4s
Introducing Middleware in http4s
Demo with Basic http4s Routes
Demo with http4s Routes + middleware

Basics of http4s
type HttpRoutes = Kleisli [ OptionT [ F, * ], Request, Response ]
http4s - Recap
● Lightweight Library
● Typeful
● Purely Functional
● Based on Cats and fs2-streaming
● Streaming
● Performant
Heart of http4s

http4s DSL
object LocalDateVar {
def unapply(str: String): Option[LocalDate] = {
if (!str.isEmpty)
Try(LocalDate.parse(str)).toOption
else
None
}
}
case GET -> Root / "weather" / "temperature" / LocalDateVar(localDate) =>
Ok(getTemperatureForecast(localDate)
.map(s"The temperature on $localDate will be: " + _))
http4s - Recap
val route: HttpRoutes[IO] = HttpRoutes.of[IO] {
case GET -> Root / "length" / str => Ok(str.length.toString)
case GET -> Root / "hello" / name => Ok(s"""Hello, ${name}!""")
}
Handling Path Parameters

QueryParamDecoderMatcher
object OptionalYearQueryParamMatcher
extends OptionalQueryParamDecoderMatcher[Year]("year")
val routes = HttpRoutes.of[IO] {
case GET -> Root / "temperature" :?
OptionalYearQueryParamMatcher(maybeYear) =>
maybeYear match {
case None => Ok(getAverageTemperatureForCurrentYear)
case Some(year) => Ok(getAverageTemperatureForYear(year))
}
}
Ex: /temperature or /temperature?year=2005
http4s - Recap
implicit val yearQueryParamDecoder: QueryParamDecoder[Year] =
QueryParamDecoder[Int].map(Year.of)
object YearQueryParamMatcher
extends QueryParamDecoderMatcher[Year]("year")
case GET -> Root / "weather" / "temperature"
:? YearQueryParamMatcher(year) =>
Ok(getAverageTemperatureForYear(year)
.map(s"Average temperature for $country in $year was: " + _))
Ex: /weather/temperature?year=2005
OptionalQueryParamDecoderMatcher

ValidatingQueryParamDecoderMatcher
object LongParamMatcher
extends OptionalValidatingQueryParamDecoderMatcher[Long]("long")
case GET -> Root / "number" :? LongParamMatcher(maybeNumber) =>
maybeNumber match {
case Some(n) =>
n.fold(
parseFailures => BadRequest("unable to parse argument 'long'"),
year => Ok(n.toString)
)
case None => BadRequest("missing number")
}
Ex: /number?long=13
http4s - Recap
implicit val yearQueryParamDecoder = QueryParamDecoder[Int]
.emap(i => Try(Year.of(i))
.toEither
.leftMap(t => ParseFailure(t.getMessage, t.getMessage)))
object YearQueryParamMatcher
extends ValidatingQueryParamDecoderMatcher[Year]("year")
case GET -> Root / "temperature" :?
YearQueryParamMatcher(yearValidated) =>
yearValidated.fold(
parseFailures => BadRequest("unable to parse argument year"),
year => Ok(getAverageTemperatureForYear(year))
)
Ex: /temperature?year=2005
OptionalValidatingQueryParamDecoderMatcher

http4s Server
def healthCheck(client: Client[IO]): IO[String] =
client.expect[String](s"$baseUri/healthcheck")
EmberClientBuilder.default[IO].build
.use { client =>
healthCheck(client).unsafeRunSync()
}
http4s - Recap
EmberServerBuilder
.default[IO]
.withHost(Host.fromString(host).get)
.withPort(Port.fromInt(port).get)
.withHttpApp(new HttpService().combinedRoutes)
.build
.use(_ => IO.never)
.as(ExitCode.Success)
http4s Client

Demo
with
http4s Routes

● Abstraction around a service
● Manipulate the request sent to a service and/or response
returned by the service
● Function that takes one service and returns another service
● Ex: def addHeaders(
service: HttpRoutes[IO],
header: Header.ToRaw
): HttpRoutes[IO]
addHeaders(
userServiceAPI,
"extra-added-header" -> "extra-header-value"
)
http4s - Middleware
http4s includes some middleware OOB in the codebase:
● Authentication
● CORS
● Response Compression
● Metrics
● Loggers

Demo
with
http4s Routes
and
Middleware

Thank You !
Get in touch with us:
Scala Studio, Knoldus