[英]Scodec combinators: Header contains magic number that is used to discriminate types
我正在尋找一種方法來處理類似以下示例的協議:
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
這里, bodyType == 0
代表Read
,而bodyType != 0
Write
。 注意,有一些字段將區分符和區分值分開。
我看過一個字節排序的例子 。 但是據我了解,這種“烏賊”編碼的鑒別器不會往返。 解決此類問題的正確方法是什么?
有幾種方法可以做到這一點,但這是我使用的一種方法:
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]
}
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