DynamicAgent for attaching the dynamically to JVM without javaagent option

[gmokki]

Usage

• add the jetty-alpn-agent as normal dependency into classpath
• invoke DynamicAgent before starting the listening socket

The DynamicAgent works by

• dynamically creating a dymmy agent jar that only contains Agent-Class parameter
• searching for tools.jar under the java home
• attaching the agent at on-the-fly by using VirtualMachine.attach

[sbordet]

Is this complete ? I don't see class DynamicAgent.

Also, I need a better description of what the problem is, and how the solution addresses the problem.

[gmokki]

Sorry about the missing files, I forgot them when I redid the PR with signoff. The missing files are now back.

The goal is to get alpn working without any need to add anything to JVM options. My goals it to make an jar that can be run with java -jar application.jar

[gmokki]

Actually even jetty itself could just depend on this agent and install it dynamically in its main method. Instead of needing to provide documentation to the users on where to download and how to enable the agent manually.

[markelliot]

This is a cool approach, but for those that want a workaround while this hasn't merged:

• use https://github.com/electronicarts/ea-agent-loader

• then create a class like:

  public final class Http2Agent {
      private Http2Agent() {}
  
      public static void install() {
          AgentLoader.loadAgentClass(Http2Agent.class.getName(), "");
      }
  
      public static void agentmain(String args, Instrumentation inst) throws Exception {
          Premain.premain(args, inst);
      }
  }

• then invoke Http2Agent.install() somewhere useful

[xkr47]

Is this ok for merge?