scala - Issue serving static files in spray -

i'm having problems serving static files route @ core using spray 1.3.2:

ctx.withhttpresponseheadersmapped(hm => hm ++ list(`content-disposition`("attachment",    map(("filename", attachment.name),    `content-length`(attachment.bytes.length)))    .withhttpresponseentitymapped { e =>      httpentity(new contenttype(        mediatypes.forextension(attachment.name.split('.').last.tolowercase).getorelse(mediatypes.`application/octet-stream`), none), e.data)  //also tried mediatypes.`application/octet-stream` default    }    .complete(attachment.bytes) 

where attachment.name string , attachment.bytes array[byte].

in way i'm able download file represented array[byte] browser interface, problem when file in excel formats (xls, xlsx) downloaded file seem corrupted during process , wont open.
strange thing corrupted files dimension of downloaded copy bigger original , in browser console possible notice transfer-encoding set chunked content-length header removed.
removing specific media type has no effect.

i can't find solution make excel files working smooth piece of code.

i don't understand transfer-encoding set chunked , file size seems not cause because it's possible serve big file without issue other formats (pdf, txt, jpeg, ...)

if can give hint on happening appreciate it, thanks.