jetty-maven-plugin does not correctly pass JVM arguments for external deployMode

[kazkansouh]

Jetty version

jetty-maven-plugin: 10.0.2

Java version

$ java -version
openjdk version "11.0.11-ea" 2021-04-20
OpenJDK Runtime Environment (build 11.0.11-ea+4-post-Debian-1)
OpenJDK 64-Bit Server VM (build 11.0.11-ea+4-post-Debian-1, mixed mode, sharing)

OS type/version

debian/rolling

Description

I have been attempting use jetty-maven-plugin during development phase of a webapp but have come across an issue with the jvmArgs configuration parameter when running with deployMode=EXTERNAL.

From inspecting the code that generates the command which launches the java it treats the jvmArgs as arguments to the jetty jar, which means its not possible to enable the java debug server. That is, I want to set jvmArgs to -agentlib:jdwp=transport=dt_socket,address=8000,server=y so I can actually debug the code but this is instead passed to jetty and not jvm and then ignored. See excerpt of the code used to build the command line below:

https://github.com/eclipse/jetty.project/blob/e163b001c34704154edb45c7aa37908e0d9aafd7/jetty-maven-plugin/src/main/java/org/eclipse/jetty/maven/plugin/JettyHomeForker.java#L168-L187

I think it would be useful to have both a jettyArgs and jvmArgs configuration parameter as there are cases where it is useful to pass options directly to jetty as well.

In case its of use, here is the plugin configuration (it tries to make use of both jetty and jvm arguments and fails):

          <configuration>
            <webApp>
              <contextPath>/${project.build.finalName}</contextPath>
            </webApp>
            <contextXml>${project.basedir}/jetty-context.xml</contextXml>
            <scanIntervalSeconds>10</scanIntervalSeconds>
            <scanTargets>
              <scanTarget>src/main/webapp/WEB-INF/web.xml</scanTarget>
            </scanTargets>
            <deployMode>EXTERNAL</deployMode>
            <jvmArgs>--lib=${project.basedir}/../jetty-auth/target/jetty-auth-1.0-SNAPSHOT.jar -agentlib:jdwp=transport=dt_socket,address=8000,server=y,suspend=n</jvmArgs>
            <modules>jaas,jsp</modules>
            <jettyProperties>
              <jetty.jaas.login.conf>${project.basedir}/jaas.conf</jetty.jaas.login.conf>
            </jettyProperties>
          </configuration>

[janbartel]

@kazkansouh using the EXTERNAL mode of running jetty will fork a new process and execute the equivalent of java -jar $jetty.home/start.jar. When using the jetty start.jar mechanism with a remote debugger (and many other types of jvm args), you need to use the --exec parameter in order to fork yet another process to which the jvm args are applied. So, put this line into your pom.xml:

<jvmArgs>--lib=${project.basedir}/../jetty-auth/target/jetty-auth-1.0-SNAPSHOT.jar --exec -agentlib:jdwp=transport=dt_socket,address=8000,server=y,suspend=n</jvmArgs>

[janbartel]

@kazkansouh it appears that if I swap the ordering of the jvmArgs passed into the forked process they are correctly interpreted by the jvm. I've opened a PR for that here: #6155. If you want to build the branch https://github.com/eclipse/jetty.project/tree/jetty-10.0.x-6153-swap-jvmArgs-order and give it a try, that would be helpful.