[英]How to write idiomatic scala code for http4s
我正在为如何将命令式风格转换为功能风格而苦苦挣扎。
在命令式 web 请求中,我习惯于说以下伪代码:
public Response controllerAction(Request request) {
val (req, parserErrors) = parser.parseRequest(request);
if (parserErrors.any()) {
return FourHundredError(parserErrors);
}
val businessErrors = model.validate(req);
if (businessErrors.any()){
return FourOhFour(businessErrors);
}
val (response, errorsWithOurStuff) = model.doBusinessLogicStuff(req);
if (errorsWithOurStuff.any()) {
return FiveHundredError(errorsWithOurStuff);
}
return OK(response)
}
我正在尝试使用 http4s 将其转换为功能样式。
def businessRoutes[F[_]: Sync](BL: BusinessLogic[F]): HttpRoutes[F] = {
val dsl = new Http4sDsl[F]{}
import dsl._
HttpRoutes.of[F] {
case req @ POST -> Root / "sms" =>
for {
request <- req.as[BL.BuisnessRequest]
requestErrors <- BL.validateRequest(request)
response <- if (requestErrors.isEmpty) {
BL.processRequest(request) match {
case Failure(e) => InternalServerError(e)
case Success(response) => Ok(response)
}
} else {
BadRequest(requestErrors)
}
} yield response
}
}
上面的代码看起来......对我来说很糟糕,我不知道如何让它变得更好。 我的目标是保留此处包含的所有 http 样式抽象,因为我不想泄漏 http4s 或绕过业务层。 我觉得我有一个for
then 一个if
,然后是一个match
并且响应都乱七八糟地混在一起。 我在这里编写难以理解的代码,我希望一些 scala 大师可以告诉我如何清理它并使其可读。
恕我直言,问题根源在于您对数据进行建模的方式; 主要用validateRequest
永远记住, 解析,不要验证。
此外,我会 go 使用这样的主处理程序将无类型错误路由:
import cats.syntax.all._
import io.circe.{Error => CirceError}
object model {
final case class RawRequest(...)
final case class BuisnessRequest(...)
final case class BuisnessResponse(...)
}
object errors {
// Depending on how you end up using those,
// it may be good to use scala.util.control.NoStackTrace with these.
// They may also be case classes to hold some context.
final case object ValidationError extends Throwable
final case object BusinessError extends Throwable
}
trait BusinessLogic {
def validateRequest(rawRequest: RawRequest): IO[BusinessRequets]
def processRequest(request: BusinessRequets): IO[BuisnessResponse]
}
final class HttpLayer(bl: BusinessLogic) extends Http4sDsl[IO] {
private final val errorHanlder: PartialFunction[Throwable, IO[Response[IO]] = {
case circeError: CirceError =>
BadRequest(...)
case ValidationError =>
NotFound(...)
case BusinessError =>
InternalServerError(...)
}
val routes: HttpRoutes[IO] = HttpRoutes[F] {
case req @ POST -> Root / "sms" =>
req
.as[RawRequest] // This may fail with CirceError.
.flatMap(bl.validateRequest) // This may fail with ValidationError.
.flatMap(bl.processRequest) // This may fail with BusinessError.
.redeemWith(recover = errorHandler, response => Ok(response))
}
}
为了简单起见,我在这里使用了具体的
IO
,如果您愿意,可以使用F[_]
。
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