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The Kamon Instrumentation Agent

There is a newer version: 1.0.18

package kanela.agent.util.classloader;

import lombok.val;
import net.bytebuddy.matcher.ElementMatcher;

import java.net.URL;
import java.net.URLClassLoader;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

public class ScalaCompilerClassLoaderMatcher extends ElementMatcher.Junction.AbstractBase {

  @Override
  public boolean matches(ClassLoader classLoader) {
    return isScalaCompilerClassLoader(classLoader);
  }

  private static Map knownClassLoaders = new ConcurrentHashMap<>();

  /**
   * Tries to determine whether a ClassLoader is the Scala Compiler ClassLoader on SBT. Since there is no special naming
   * or treatment of this particular ClassLoader it is impossible to have a 100% reliable way to filter it out from the
   * instrumentation process, but given that the jars found on it are quite particular (the compiler and jline) and
   * there are usually just a handful of jars in that ClassLoader, we can have a level of certainty that if a
   * ClassLoader has less than 6 jars and some of those are the compiler-related libraries then it must be the compiler
   * ClassLoader.
   *
   * We are doing this check here instead of using a ClassLoaderNameMatcher because this is a relatively expensive
   * check which might only be necessary in a few cases, so we rather filter the error than putting the burden of this
   * check on every single class load.
   */
  public static boolean isScalaCompilerClassLoader(ClassLoader classLoader) {
    if(classLoader instanceof URLClassLoader) {
      Boolean isScalaCompilerLoader = knownClassLoaders.get(classLoader);

      if(isScalaCompilerLoader != null)
        return isScalaCompilerLoader;
      else {
        val urlClassLoader = (URLClassLoader) classLoader;
        boolean foundScalaCompiler = false;
        boolean foundJLine = false;
        boolean hasLessThanSixJars = urlClassLoader.getURLs().length < 6;

        if(hasLessThanSixJars) {
          for (URL url : urlClassLoader.getURLs()) {
            if (url.getFile().contains("scala-compiler"))
              foundScalaCompiler = true;

            if (url.getFile().contains("jline"))
              foundJLine = true;
          }
        }

        val isScalaCompiler = hasLessThanSixJars && foundScalaCompiler && foundJLine;
        knownClassLoaders.put(classLoader, isScalaCompiler);
        return isScalaCompiler;
      }
    } else return false;
  }

}