HTTP/2 with HttpServletRequest.getHeader("Host") returns null on Jetty 10, but a valid value on Jetty 9

[joakime]

Jetty version
10.0.x

Description
If you make an HTTP/2 request, and then in your servlet you use HttpServletRequest.getHeader("Host") the value is null on Jetty 10.
But it returns a value on Jetty 9.

Screenshot of Jetty 9 (notice the "Host" header in the enumerated headers)

Screenshot of Jetty 10 (no "Host" header in the enumerated headers)

[gregw]

I don't think we should always add a Host header for HTTP/2, as that is a lot of wasted work for apps that don't use the Host header. Instead we could either write an optional customizer and/or rewrite rule that will add a Host header from the authority of a HTTP/2 request

[joakime]

Note (to others that read this) that to get the authority from the HttpServletRequest, you can use the existing methods ...

• HttpServletRequest.getServerName()
• HttpServletRequest.getServerPort()

See: https://github.com/eclipse-ee4j/servlet-api/blob/4.0.4-RELEASE/api/src/main/java/javax/servlet/ServletRequest.java#L214-L228

[joakime]

We could probably improve the HostHeaderCustomizer to set the Host header too.

https://github.com/eclipse/jetty.project/blob/jetty-10.0.x/jetty-server/src/main/java/org/eclipse/jetty/server/HostHeaderCustomizer.java

[joakime]

@gregw I think we should have a module to enable the HostHeaderCustomizer for http2 on jetty-home.