That bug is in HAProxy. The RFC clearly states that the presence of the Connection header makes the response malformed. "An endpoint MUST NOT generate an HTTP/

That bug is in HAProxy. The RFC clearly states that the presence of the Connection header makes the response malformed. "An endpoint MUST NOT generate an HTTP/2 message containing connection-specific header fields; any message containing connection-specific header fields MUST be treated as malformed (Section 8.1.2.6)." and "Clients MUST NOT accept a malformed response. Note that these requirements are intended to protect against several types of common attacks against HTTP [...]" (though Safari's response of repeatedly retrying as fast as possible is certainly problematic)