Use of RequestHeader "Proxy-Connection": "keep-alive" vs. "Connection": "keep-alive"

[Martin Schmiedel]

In our project we had some issues with the browser not keeping alive connections because of a "strange / legacy?" behaviour of the Chromium engine.

We use a inhouse Proxy-Server which follows RFC-2616 (https://tools.ietf.org/html/rfc2616). This means, it just ignores Proxy-Connection Header (it does not formally exist), but works fine with Connection (as described in the RFC). However Chromium sends the "Proxy-Connection" Header when behind of a Proxy, and NOT the "Connection" header. Other Browsers (at least Firefox) have changed this behaviour a "long time ago". 

We are using Chromium embedded in JXBrowser, the concrete Chromium Version we have at the moment is 55. 

In some Tests we made directly with Chrome, we noticed that Chrome 57 still sends the Proxy-Connection Header, but Chrome 58 seems to be behaving as expected according to the RFC sending the Connection Header even behind a Proxy. 

However, we could not find any evidence in the releasenotes or source code (https://cs.chromium.org/chromium/src/net/http/proxy_client_socket.cc?q=kProxyConnection&sq=package:chromium&type=cs&l=37) of such a change from Version 57 to 58.

Can someone confirm if this change was really introduced since Chromium 58 as we are suspecting, and if we can rely on Chromium to behave as described in RFC-2616 from now on?

Thank you very much and kind regards...