编解码器组合器:Header 包含用于区分类型的幻数
Scodec combinators: Header contains magic number that is used to discriminate types
我正在寻找一种方法来处理如下示例中的协议:
case class Request(bodyType: Int, foo: Int, bar: Int, body: RequestBody)
sealed trait RequestBody
case class Read(key: String) extends RequestBody
case class Write(key: String, value: Array[Byte]) extends RequestBody
这里,bodyType == 0
代表Read
,bodyType != 0
代表Write
。
请注意,有几个字段将鉴别器与鉴别值分开。
我看过an example with byte-ordering。
但据我所知,这个 "squid" 编码的鉴别器不会往返。
解决此类问题的正确方法是什么?
有几种方法可以做到这一点,但这是我用过的一种:
import scodec._
import scodec.codecs._
import scodec.bits._
case class Request(bodyType: Int, foo: Int, bar: Int, body: RequestBody)
sealed trait RequestBody
case class Read(key: String) extends RequestBody
object Read {
implicit val codec: Codec[Read] = ("key" | utf8).as[Read]
implicit val discriminator: Discriminator[RequestBody, Read, Int] = Discriminator(0)
}
case class Write(key: String, value: ByteVector) extends RequestBody
object Write {
implicit val codec: Codec[Write] = {
("key" | utf8 ) ::
("value" | bytes )
}.as[Write]
implicit val discriminator: Discriminator[RequestBody, Write, Int] = Discriminator(1)
}
object Request {
implicit val codec: Codec[Request] = {
("bodyType" | uint16 ).flatPrepend { bodyType =>
("foo" | uint16 ) ::
("bar" | uint16 ) ::
("body" | Codec.coproduct[RequestBody].discriminatedBy(provide(bodyType)).auto)
}}.as[Request]
}
我正在寻找一种方法来处理如下示例中的协议:
case class Request(bodyType: Int, foo: Int, bar: Int, body: RequestBody)
sealed trait RequestBody
case class Read(key: String) extends RequestBody
case class Write(key: String, value: Array[Byte]) extends RequestBody
这里,bodyType == 0
代表Read
,bodyType != 0
代表Write
。
请注意,有几个字段将鉴别器与鉴别值分开。
我看过an example with byte-ordering。 但据我所知,这个 "squid" 编码的鉴别器不会往返。 解决此类问题的正确方法是什么?
有几种方法可以做到这一点,但这是我用过的一种:
import scodec._
import scodec.codecs._
import scodec.bits._
case class Request(bodyType: Int, foo: Int, bar: Int, body: RequestBody)
sealed trait RequestBody
case class Read(key: String) extends RequestBody
object Read {
implicit val codec: Codec[Read] = ("key" | utf8).as[Read]
implicit val discriminator: Discriminator[RequestBody, Read, Int] = Discriminator(0)
}
case class Write(key: String, value: ByteVector) extends RequestBody
object Write {
implicit val codec: Codec[Write] = {
("key" | utf8 ) ::
("value" | bytes )
}.as[Write]
implicit val discriminator: Discriminator[RequestBody, Write, Int] = Discriminator(1)
}
object Request {
implicit val codec: Codec[Request] = {
("bodyType" | uint16 ).flatPrepend { bodyType =>
("foo" | uint16 ) ::
("bar" | uint16 ) ::
("body" | Codec.coproduct[RequestBody].discriminatedBy(provide(bodyType)).auto)
}}.as[Request]
}