HttpServer performance issue / improvement

[Robert Engels]

 When doing some testing on github.com/robaho/httpserver - which is a fork of the jdk http server, I discovered a significant performance issue. When an http connection is in ‘keep-alive’ - the default for http 1.1 - the headers are “flushed” here https://github.com/openjdk/jdk21/blob/890adb6410dab4606a4f26a942aed02fb2f55387/src/jdk.httpserver/share/classes/sun/net/httpserver/ExchangeImpl.java#L281 This means that after the handler runs and it sends data - e.g. /hello sends “hello” on the connection, the connection will stall due to the Nagel algorithm - usually incurring a 50 ms delay. The stall occurs since the client will not see the expected data until after the delay, so it is unable to send the next (when reusing the same connection/HttpClient). You can set the TCP_NODELAY on the server to work-around this, but a better solution would be to override the flush() on the BufferedOutputStream to not flush() the underlying connection - i.e. only write the buffered bytes, or rework it a bit to only flush when there is no content to send.