perf(*): perhaps a slightly faster upstream VIA header

Signed-off-by: Aapo Talvensaari <aapo.talvensaari@gmail.com>

kong/runloop/handler.lua

@@ -115,6 +115,15 @@ local STREAM_TLS_TERMINATE_SOCK
 local STREAM_TLS_PASSTHROUGH_SOCK
 
 
+local VIA_HEADER = {
+  [0.9] = "0.9 " .. SERVER_HEADER,
+  [1.0] = "1.0 " .. SERVER_HEADER,
+  [1.1] = "1.1 " .. SERVER_HEADER,
+  [2.0] = "2.0 " .. SERVER_HEADER,
+  [3.0] = "3.0 " .. SERVER_HEADER,
+}
+
+
 local get_header
 local set_authority
 local set_service_ssl = upstream_ssl.set_service_ssl
@@ -1290,13 +1299,9 @@ return {
       var.upstream_x_forwarded_path   = forwarded_path
       var.upstream_x_forwarded_prefix = forwarded_prefix
 
-      do
-        local req_via = get_header(constants.HEADERS.VIA, ctx)
-        local kong_inbound_via = protocol_version and protocol_version .. " " .. SERVER_HEADER
-                                 or SERVER_HEADER
-        var.upstream_via = req_via and req_via .. ", " .. kong_inbound_via
-                           or kong_inbound_via
-      end
+      local req_via = get_header("via", ctx)
+      local kong_via = VIA_HEADER[protocol_version or ""] or SERVER_HEADER
+      var.upstream_via = req_via and (req_via .. ", " .. kong_via) or kong_via
 
       -- At this point, the router and `balancer_setup_stage1` have been
       -- executed; detect requests that need to be redirected from `proxy_pass`