Extract Json from Spray POST as string, not by marshaling to entity - apache-kafka

Question

There is an existing question that has much of what I'm after:
Extracting Raw JSON as String inside a Spray POST route
But it stops short without explaining how to get the actual Json string representation out of the Directive[String]. I'm trying to send Json data to Kafka as a string (which the Kafka Producer serializes), so I'm trying to extract the Json in string form. I will do the marshalling to an entity at the other end in the Kafka consumer. The answer link above gets me close:
def rawJson = extract { _.request.entity.asString}
case "value2" => rawJson{ json =>// use the json }
But I end up with Directive[String]. How do I get the String out?

Answer 1

The example you referenced should work. You would use the rawJson directive they defined to wrap your inner route, and the json string would be made available within that inner route.
In the example below, personJson is a String, extracted by the body of the request via the rawJson directive, and made available to the inner route where the rest of the work is done.
def rawJson = extract { _.request.entity.asString}
val personRoute = {
(post & path("persons")){
rawJson{ personJson =>
onSuccess(personService.addPerson(person)){ personWithId =>
complete(StatusCodes.Created, personWithId)
}
}
}

Answer 2

I came up with the following syntax which accomplishes my need to extract the Json in String form. At first I thought it inefficient that I was unmarshaling and then remarshaling again, but then I realized that this provides a form of immediate Json validation. But there may be more efficient ways to do that.
The API is all Spray. handleWith uses an implicit conversion to the RawWeatherData case class.
path("weather"/"data"/"json") {
handleWith { rawRecord: RawWeatherData =>
val rawJsonStr = rawRecord.toJson.toString
kafkaJsonRecordIngest(rawJsonStr)
rawRecord
}
}