With the following query, the webserver abruptly closes the connection:

(cat ; sleep 2) <<EOF | openssl s_client -connect download.samba.org:443
GET /pub/samba/ HTTP/1.1
TE: deflate, gzip;q=0.3
Connection: TE, close
Host: download.samba.org
User-Agent: Debian uscan

EOF

This one works:

(cat ; sleep 2) <<EOF | openssl s_client -connect download.samba.org:443
GET /pub/samba/ HTTP/1.1
Host: download.samba.org
User-Agent: Debian uscan

EOF

The reason is probably related to HTTP/2 were the "TE" header is forbidden unless set to "traillers".

Refs:
- https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/TE
- https://tools.ietf.org/html/rfc7540#section-8.1.2.2


What is the webserver used?

If there is a reverse-proxy, it should probably drop TE headers unconditionally.

On Apache:

RequestHeader unset TE

On nginx:

proxy_set_header TE "";

Refs:
- http://httpd.apache.org/docs/2.4/mod/mod_headers.html#requestheader
- https://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_set_header