How do HTTP verbs, URI path variables, and parameter qualifiers work in EK9 services?

defines module qa.services.uripath.params

  defines constant

    JSON_TYPE <- "application/json"

  defines class

    <?-
      Models a user lookup response.
      Demonstrates how path variables bind to parameters in services.
    -?>
    UserResponse
      userId as Integer: 0
      contentKind as String: JSON_TYPE

      UserResponse()
        -> givenUserId as Integer
        this.userId :=: givenUserId

      userId()
        <- rtn as Integer: Integer(userId)

      contentKind()
        <- rtn as String: String(contentKind)

      toJson()
        <- rtn as String: `{"userId": ${userId}}`

      operator $ as pure
        <- rtn as String: `UserResponse[${userId}]`
      operator #^ as pure
        <- rtn as String: $this
      default operator ?

    <?-
      Models a user list response.
    -?>
    UserListResponse
      userCount as Integer: 0

      UserListResponse()
        -> givenCount as Integer
        this.userCount :=: givenCount

      toJson()
        <- rtn as String: `{"users": [], "count": ${userCount}}`

      operator $ as pure
        <- rtn as String: `UserListResponse[${userCount}]`
      operator #^ as pure
        <- rtn as String: $this
      default operator ?

    <?-
      Simulates a user service with path parameter binding.
      In real services, GET /users/{userId} binds userId from the URI.
    -?>
    UserEndpoint

      findUser()
        -> userId as Integer
        <- rtn as UserResponse: UserResponse(userId)

      listUsers()
        <- rtn as UserListResponse: UserListResponse(0)

      operator $ as pure
        <- rtn as String: "UserEndpoint"
      operator #^ as pure
        <- rtn as String: $this
      default operator ?

  defines program

    ServiceUriParamsDemo()
      stdout <- Stdout()
      endpoint <- UserEndpoint()
      userResult <- endpoint.findUser(42)
      listResult <- endpoint.listUsers()

      stdout.println("Service URI parameters:")
      stdout.println("  GET /users/{userId} -> path variable binding")
      stdout.println("  GET /users/list -> no parameters")
      stdout.println(userResult.toJson())
      stdout.println(listResult.toJson())