JarCastingThis module interfaces with the TLS implementation of Oracle JDK8 to provide an implementation of ALPN. The module was written for use in Grizzly, but is intended as a general purpose solution to allow JDK8 based software to use ALPN.
How Grizzly Uses This Module
Grizzly has the concept of an AddOn. This facility allows Grizzly to be extended using an implementation of the Chain of Responsibility design pattern. In general, an AddOn implementation will insert one or more Filter implementations into the FilterChain which is used to process HTTP requests and cause HTTP responses to be sent.
Grizzly itself uses this AddOn concept to provide HTTP/2 support, in the form of Http2AddOn In addition to registering filters for HTTP/2 processing, this AddOn implementation registers a callback withthe ALPN extension to insert itself into the SSL Handshake process
Programmatic Configuration
AddOn has a setup method that is called to allow the implementation to do whatever one-time setup is required to make things work. The setup override in the Http2AddOn takes the following actions if the current connection is secure (that is, it is supposed to be using ALPN).
-
Use the
addHandshakeListenermethod of the existingSSLBaseFilterto cause an ALPN specific SSL handshake listener to be added to the existing list of listeners that are invoked when an ssl handshake happens.Grizzly's handshake listener has several methods, but the only one used is
onStart. This obtains the JDKSSLEngineand takes different action depending on the return from itsgetUseClientMode()method. Thegrizzly-npnmodule providesAlpnClientNegotiatorandAlpnServerNegotiatorinterfaces for these two cases. Please see the interfaces for the specification of the required actions.If
getUseClientModeis true,-
use the grizzly
addCloseListenerfacility to install a listener that callsNegotiationSupport.removeClientNegotiator(). This will ensure the client negotiator is removed when the connection closes. -
Call
NegotiationSupport.addNegotiatorpassing theSSLEngineand the client negotiator impl.
If
getUseClientmodeis false,- do the same as above, but use the server negotiator impl.
By the time
onStartis invoked, the handshake listener will have been initialized with implementations ofAlpnClientNegotiatorandAlpnServerNegotiatorby theHttp2AddOn. -
Deployment Configuration
The above programmatic configuration steps will make it so the simple act of including the module built from the bootstrap sub-module of this repository in the bootclasspath of the JVM will enable ALPN support in that JVM.
