Responses with known Content-Length should take "Range" request headers into account.
This problem appeared when trying to serve an mp4 Video from a Resteasy-Service. It will only be served in one piece. The iOS-Safari for example tries to request the first two bytes only to detect byte range capability. (Range: bytes=0-1) Resteasy 2.6.4 ignores that, sends the whole file, Safari disconnects and will not show any video that would otherwise be loaded within an html5 video tag.
=> Resteasy should interpret Range headers and respond accordingly with status 206 and the appropriate slices of data.