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package sttp.client

import sttp.capabilities._
import sttp.monad.MonadError

/**
  * A backend is used to send HTTP requests described by [[RequestT]]. Backends might wrap Java or Scala HTTP
  * clients, or other backends.
  *
  * @note Backends should try to classify exceptions into one of the categories specified by [[SttpClientException]].
  *       Other exceptions should be thrown unchanged.
  * @tparam F The effect type used when returning responses. E.g. [[Identity]] for synchronous backends,
  *           [[scala.concurrent.Future]] for asynchronous backends.
  * @tparam P Capabilities supported by this backend, in addition to [[Effect]]. This might be `Any` (no special
  *           capabilities), [[Streams]] (the ability to send and receive streaming bodies) or
  *           [[WebSockets]] (the ability to handle websocket requests).
  */
trait SttpBackend[F[_], +P] {

  /**
    * @tparam R The capabilities required by the request. This must be a subset of the the capabilities supported
    *           by the backend (which always includes `Effect[F]`).
    */
  def send[T, R >: P with Effect[F]](request: Request[T, R]): F[Response[T]]

  def close(): F[Unit]

  /**
    * A monad instance for the effect type used when returning responses. Allows writing wrapper backends, which
    * map/flatMap over the return value of [[send]].
    */
  def responseMonad: MonadError[F]
}