Map headers for all responses using Spray - scala

Question

I am using spray to serve an api. I am trying to create a directive to add a list of headers to all responses, including rejections and failures. I have tried the following but both only work for successful responses:
val impl1: Directive0 = respondWithSingletonHeaders(myHeaderList)
val impl2: Directive0 = mapRequestContext { ctx =>
ctx.withHttpResponseHeadersMapped { headers =>
myHeaderList ::: headers
}
}
Is there an equivalent construct that could work for ALL responses? I suppose I can define custom error handlers, but, correct me if I am wrong, they are expected to work by calling ctx.complete(...), since it a side effect, I think I will have to override every failure case. I haven't found a place where I can simply map HttpResponses to add the headers.

Answer 1

An exception will bubble up the route as an exception, until it reaches an exception handler. And you can't add headers to an exception. But you can re-use your directives in your exception handlers. You can avoid repetition by making an implicit ExceptionHandler at the runRoute level, use your directive to add headers for the general case (all exceptions) and delegate the actual exception-to-response mapping to an inner pattern match:
implicit def exceptionHandler: ExceptionHandler = ExceptionHandler {
case exception => impl1 {
exception match {
case e: IllegalArgumentException => ctx =>
ctx.complete(BadRequest)
...
case e: Exception => ctx =>
ctx.complete(InternalServerError)
}
}
}