Content-Length header missing after proxying

[James Fidell]

I have nginx configured to proxy to an upstream using the following
in nginx.conf:

http {
     upstream app {
         server localhost:8080;
     }

     server {
         listen       80;

         location / {
		proxy_pass http://app;
		# proxy_pass_header Content-Length;
	}
     }
}

The upstream returns some data with the HTTP Content-Length header
set.  Using wget to connect directly I see:

Connecting to localhost|127.0.0.1|:8080... connected.
HTTP request sent, awaiting response...
   HTTP/1.0 200 OK
   Content-Type: application/x-javascript
   Connection: keep-alive
   Content-Length: 44552
Length: 44552 (44K) [application/x-javascript]


When I make a request via nginx however, the Content-Length header is
no longer present (again using wget):

Connecting to localhost|127.0.0.1|:80... connected.
HTTP request sent, awaiting response...
   HTTP/1.1 200 OK
   Server: nginx/1.0.5
   Date: Tue, 23 Aug 2011 18:40:30 GMT
   Content-Type: application/x-javascript
   Connection: close
Length: unspecified [application/x-javascript]


Is there any obvious reason this should be happening, or something I'm
doing wrong?  The proxy_pass_header directive in the configuration file
seems to make no difference to the outcome when I uncomment it.

Thanks,
James