def conditional(eTag: EntityTag): Directive0
def conditional(lastModified: DateTime): Directive0
def conditional(eTag: EntityTag, lastModified: DateTime): Directive0
def conditional(eTag: Option[EntityTag], lastModified: Option[DateTime]): Directive0


Wraps its inner route with support for Conditional Requests as defined by

Depending on the given eTag and lastModified values this directive immediately responds with 304 Not Modified or 412 Precondition Failed (without calling its inner route) if the request comes with the respective conditional headers. Otherwise the request is simply passed on to its inner route.

The algorithm implemented by this directive closely follows what is defined in this section of the HTTPbis spec.

All responses (the ones produces by this directive itself as well as the ones coming back from the inner route) are augmented with respective ETagETag and Last-Modified response headers.

Since this directive requires the EntityTagEntityTag and lastModified time stamp for the resource as concrete arguments it is usually used quite deep down in the route structure (i.e. close to the leaf-level), where the exact resource targeted by the request has already been established and the respective ETag/Last-Modified values can be determined.

The FileAndResourceDirectives internally use the conditional directive for ETag and Last-Modified support (if the akka.http.routing.file-get-conditional setting is enabled).

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