HTTP/1.0 Connection: keep-alive header should not be removed from response

[jusmaki]

Title: HTTP/1.0 Connection: keep-alive requests are not processed correctly

Description:
The envoy-proxy removes the connection-header for HTTP/1.0 clients causing some HTTP/1.0 clients like apache-bench to stuck when keep-alives are enabled because the envoy-proxy does not copy the connection -header value from the client request to the response.

If envoy is configured to support HTTP/1.0 it should copy and respect the Connection-header value from the client request to the response.
So the rules for HTTP/1.0 client connections should be:

• If a client like Apache Bench that is HTTP 1.0 doesn't provide the connection: keep-alive header the socket connection should be closed after replying with Connection: close header.
• If the client provides the connection: keep-alive header the socket should remain open and Connection: keep-alive header should be returned.

Repro steps:
Install apache-bench (for example in ubuntu "sudo apt get apache2-utils", setup envoy to proxy requests to some upstream server and enable support for HTTP/1.0 with accept_http_10: true,
send requests with apache-bench e.g. "ab -v 9 -n 2 -k http://localhost:10000" and see that the connection is stuck because the envoy does not return connection header.

Relevant Links:
See: https://tools.ietf.org/html/rfc2068#section-19.7.1

[mattklein123]

cc @alyssawilk @PiotrSikora

[alyssawilk]

Yeah, looks like a bug to me. We correctly perform connection close or not based on request headers, but don't do the inverted "send keep alive if there's no explicit close" we ought to.