Strange. I am using Dancer 1.3202, the same as the version of the source you linked to, but wget doesn't show a Content-Length header as being present: 
$ wget -S http://foo/bar.pdf
--2017-01-12 15:43:26--  http://foo/bar.pdf
Resolving foo
Connecting to foo:80... connected.
HTTP request sent, awaiting response... 
  HTTP/1.1 200 OK
  Date: Thu, 12 Jan 2017 14:43:26 GMT
  Server: Apache/2.4.10 (Debian)
  Content-Type: application/pdf
  Content-Disposition: inline; filename="bar.pdf"
  Keep-Alive: timeout=15, max=100
  Connection: Keep-Alive
  Transfer-Encoding: chunked
Length: unspecified [application/pdf]

[download]

In reply to Re^2: EOF problem with Dancer streaming proxy by dsheroh
in thread EOF problem with Dancer streaming proxy by dsheroh

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