opentelemetry-java-instrumentation/CONTRIBUTING.md

Contributing

Pull requests for bug fixes are welcome, but before submitting new features or changes to current functionality open an issue and discuss your ideas or propose the changes you wish to make. After a resolution is reached a PR can be submitted for review.

In order to fully build and test this whole repository you need the following:

• Installed both JDK 8 and 9.
• Java 8 should be set as default: java -version should give you version 8.
• Defined environment variables JAVA_8_HOME and JAVA_9_HOME which point to the corresponding java homes.

Plugin structure

OpenTelemetry Auto Instrumentation java agent's jar can logically be divided into 3 parts.

java-agent module

This module consists of single class io.opentelemetry.auto.bootstrap.AgentBootstrap which implements Java instrumentation agent. This class is loaded during application startup by application classloader. Its sole responsibility is to push agent's classes into JVM's bootstrap classloader and immediately delegate to io.opentelemetry.auto.bootstrap.Agent (now in the bootstrap class loader) class from there.

agent-bootstrap module

This module contains support classes for actual instrumentations to be loaded later and separately. These classes should be available from all possible classloaders in the running application. For this reason java-agent puts all these classes into JVM's bootstrap classloader. For the same reason this module should be as small as possible and have as few dependencies as possible. Otherwise, there is a risk of accidentally exposing this classes to the actual application.

agent-tooling module and instrumentation submodules

Contains everything necessary to make instrumentation machinery work, including integration with ByteBuddy and actual library-specific instrumentations. As these classes depend on many classes from different libraries, it is paramount to hide all these classes from the host application. This is achieved in the following way:

• When java-agent module builds the final agent, it moves all classes from instrumentation submodules and agent-tooling module into a separate folder inside final jar file, called auto-tooling-and-instrumentation.isolated. In addition, the extension of all class files is changed from class to classdata. This ensures that general classloaders cannot find nor load these classes.
• When io.opentelemetry.auto.bootstrap.Agent starts up, it creates an instance of io.opentelemetry.auto.bootstrap.AgentClassLoader, loads an io.opentelemetry.auto.tooling.AgentInstaller from that AgentClassLoader and then passes control on to the AgentInstaller (now in the AgentClassLoader). The AgentInstaller then installs all of the instrumentations with the help of ByteBuddy.

The complicated process above ensures that the majority of auto-instrumentation agent's classes are totally isolated from application classes, and an instrumented class from arbitrary classloader in JVM can still access helper classes from bootstrap classloader.

Agent jar structure

If you now look inside java-agent/build/libs/opentelemetry-auto-<version>.jar, you will see the following "clusters" of classes:

• auto-tooling-and-instrumentation.isolated/ - contains agent-tooling module and instrumentation submodules, loaded and isolated inside AgentClassLoader. Including OpenTelemetry SDK.
• io/opentelemetry/auto/bootstrap/ - contains agent-bootstrap module and available in bootstrap classloader.
• io/opentelemetry/auto/shaded/ - contains OpenTelemetry API and its dependencies. Shaded during creation of java-agent jar file by Shadow Gradle plugin.

Testing

Java versions

Open Telemetry Auto Instrumentation's minimal supported version is java 7. All jar files that we produce, unless noted otherwise, have bytecode compatible with java 7 runtime. In addition to that we test our code with all later java versions as well: from 8 to 14.

Some libraries that we auto-instrument may have higher minimal requirements. In this case we compile and test corresponding auto-instrumentation with higher java version as required by library. The resulting classes will have higher bytecode level, but as it matches library's java version, no runtime problem arise.

Instrumentation tests

Executing ./gradlew instrumentation:test will run tests for all supported auto-instrumentations using that java version which runs the Gradle build itself. These tests usually use the minimal supported version of the instrumented library.

In addition to that each instrumentation has a separate test set called latestDepTest. It was created by Gradle test sets plugin. It uses the very same tests as before, but declares a dynamic dependency on the latest available version of this library. You can run them all by executing ./gradlew latestDepTest.

Executing tests with specific java version

In order to run tests on a specific java version, just execute ./gradlew testJava7 (or testJava11 or latestDepTestJava14 etc). Then Gradle task rule will kick in and do the following:

• check, if Gradle already runs on a java with required version
• if not, look for an environment variable named JAVA_N_HOME, where N is the requested java version
• if Gradle could not found requested java version, then build will fail
• Gradle will now find all corresponding test tasks and configure them to use java executable of the requested version.

This works both for tasks named test and latestDepTest. But currently does not work for other custom test tasks, such as those created by test sets plugin.

Style guideline

We follow the Google Java Style Guide. Our build will fail if source code is not formatted according to that style.

To verify code style manually run the following command, which uses google-java-format library:

./gradlew verifyGoogleJavaFormat

or on Windows

gradlew.bat verifyGoogleJavaFormat

Instead of fixing style inconsistencies by hand, you can run gradle task googleJavaFormat to automatically fix all found issues:

./gradlew googleJavaFormat

or on Windows

gradlew.bat googleJavaFormat

Pre-commit hook

To completely delegate code style formatting to the machine, you can add git pre-commit hook. We provide an example script in buildscripts/pre-commit file. Just copy or symlink it into .git/hooks folder.

Editorconfig

As additional convenience for IntelliJ Idea users, we provide .editorconfig file. Idea will automatically use it to adjust its code formatting settings. It does not support all required rules, so you still have to run googleJavaFormat from time to time.

Intellij IDEA

Required plugins:

• Lombok

Suggested plugins and settings:

• Editor > Code Style > Java/Groovy > Imports
  • Class count to use import with '*': 9999 (some number sufficiently large that is unlikely to matter)
  • Names count to use static import with '*': 9999
  • With java use the following import layout (groovy should still use the default) to ensure consistency with google-java-format:
• Google Java Format
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