keep-alive

# allows the sender to hint about how the connection may be used to set
# a timeout and a maximum amount of requests.

 * Connection and Keep-Alive are prohibited in HTTP/2 and HTTP/3
 * Connection and Keep-Alive are hop-by-hop headers (not forward them by proxy)

HTTP Header

Client -> Server

curl -I -H"Connection: keep-alive" http://server

Server -> Client # Response header

當支援時

Connection: keep-alive / close

HTTP/1.1 200 OK
Connection: Keep-Alive
Content-Encoding: gzip
Content-Type: text/html; charset=utf-8
Date: Thu, 11 Aug 2016 15:23:13 GMT
Keep-Alive: timeout=5, max=1000
Last-Modified: Mon, 25 Jul 2016 04:32:39 GMT
Server: Apache