fix(config): config classloader strategy for different attach scenarios

src/main/java/io/cryostat/agent/ConfigModule.java

@@ -27,7 +27,6 @@
 import java.security.AccessController;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
-import java.security.PrivilegedActionException;
 import java.security.PrivilegedExceptionAction;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -36,6 +35,8 @@
 import java.util.Map;
 import java.util.Optional;
 import java.util.UUID;
+import java.util.concurrent.Callable;
+import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.function.Supplier;
 import java.util.regex.Matcher;
@@ -46,10 +47,12 @@
 import javax.inject.Named;
 import javax.inject.Singleton;
 
+import io.cryostat.agent.util.ResourcesUtil;
 import io.cryostat.agent.util.StringUtils;
 
 import dagger.Module;
 import dagger.Provides;
+import org.apache.commons.lang3.tuple.Pair;
 import org.apache.http.client.utils.URIBuilder;
 import org.eclipse.microprofile.config.Config;
 import org.eclipse.microprofile.config.ConfigProvider;
@@ -177,6 +180,7 @@ public abstract class ConfigModule {
     public static final String CRYOSTAT_AGENT_WEBSERVER_CREDENTIALS_PASS_LENGTH =
             "cryostat.agent.webserver.credentials.pass.length";
 
+    public static final String CRYOSTAT_AGENT_CONFIG_LOADABLE = "cryostat.agent.config.loadable";
     public static final String CRYOSTAT_AGENT_APP_NAME = "cryostat.agent.app.name";
     public static final String CRYOSTAT_AGENT_HOSTNAME = "cryostat.agent.hostname";
     public static final String CRYOSTAT_AGENT_APP_JMX_PORT = "cryostat.agent.app.jmx.port";
@@ -231,24 +235,72 @@ public abstract class ConfigModule {
     @Provides
     @Singleton
     public static Config provideConfig() {
-        // if we don't do this then the SmallRye Config loader may end up with a null classloader in
-        // the case that the Agent starts separately and is dynamically attached to a running VM,
-        // which results in an NPE. Here we try to detect and preempt that case and ensure that
-        // there is a reasonable classloader for the SmallRye config loader to use.
-        PrivilegedExceptionAction<ClassLoader> pea =
-                () -> {
-                    ClassLoader cl = Thread.currentThread().getContextClassLoader();
-                    if (cl != null) {
-                        return cl;
-                    }
-                    return new URLClassLoader(new URL[] {Agent.selfJarLocation().toURL()});
-                };
-        try {
-            ClassLoader cl = AccessController.doPrivileged(pea);
-            return ConfigProvider.getConfig(cl);
-        } catch (PrivilegedActionException pae) {
-            throw new RuntimeException(pae);
+        List<Pair<String, Callable<Config>>> fns = new ArrayList<>();
+        fns.add(Pair.of("Simple", ConfigProvider::getConfig));
+        Function<Callable<ClassLoader>, Callable<Config>> clConfigLoader =
+                cl ->
+                        () -> {
+                            ClassLoader loader;
+                            try {
+                                loader =
+                                        AccessController.doPrivileged(
+                                                (PrivilegedExceptionAction<ClassLoader>)
+                                                        () -> cl.call());
+                            } catch (Exception e) {
+                                log.warn(
+                                        "ClassLoader AccessController failure - is this JVM too new"
+                                            + " to have the AccessController and SecurityManager?",
+                                        e);
+                                loader = cl.call();
+                            }
+                            return ConfigProvider.getConfig(loader);
+                        };
+        fns.add(
+                Pair.of(
+                        "ResourcesUtil ClassLoader",
+                        clConfigLoader.apply(ResourcesUtil::getClassLoader)));
+        fns.add(
+                Pair.of(
+                        "Config Class ClassLoader",
+                        clConfigLoader.apply(Config.class::getClassLoader)));
+        fns.add(
+                Pair.of(
+                        "Agent JAR URL ClassLoader",
+                        clConfigLoader.apply(
+                                () ->
+                                        new URLClassLoader(
+                                                new URL[] {Agent.selfJarLocation().toURL()}))));
+
+        Config config = null;
+        for (Pair<String, Callable<Config>> fn : fns) {
+            try {
+                log.trace(
+                        "Testing classloader \"{}\" for {} property",
+                        fn.getLeft(),
+                        CRYOSTAT_AGENT_CONFIG_LOADABLE);
+                Config candidate = fn.getRight().call();
+                if (!candidate.getValue(CRYOSTAT_AGENT_CONFIG_LOADABLE, boolean.class)) {
+                    log.warn(
+                            "{} was false. Assuming that this means the {} classloader"
+                                    + " cannot be used to load properties. Do not override this"
+                                    + " configuration property with a blank or false value!",
+                            CRYOSTAT_AGENT_CONFIG_LOADABLE,
+                            fn.getLeft());
+                    continue;
+                }
+                config = candidate;
+                break;
+            } catch (Exception e) {
+                config = null;
+                log.debug(
+                        String.format("Failed to load config from \"%s\" supplier", fn.getLeft()),
+                        e);
+            }
+        }
+        if (config == null || !config.getValue(CRYOSTAT_AGENT_CONFIG_LOADABLE, boolean.class)) {
+            log.error("Unable to load configuration from any classloader source!");
         }
+        return config;
     }
 
     @Provides

src/main/java/io/cryostat/agent/VersionInfo.java

@@ -26,6 +26,7 @@
 
 import io.cryostat.agent.util.ResourcesUtil;
 
+import org.apache.commons.lang3.StringUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -36,6 +37,8 @@ public class VersionInfo {
     static final String MIN_VERSION_KEY = "cryostat.server.version.min";
     static final String MAX_VERSION_KEY = "cryostat.server.version.max";
 
+    private static Logger log = LoggerFactory.getLogger(VersionInfo.class);
+
     private final Semver agentVersion;
     private final Semver serverMin;
     private final Semver serverMax;
@@ -50,7 +53,15 @@ public class VersionInfo {
     public static VersionInfo load() throws IOException {
         Properties prop = new Properties();
         try (InputStream is = ResourcesUtil.getResourceAsStream(RESOURCE_LOCATION)) {
-            prop.load(is);
+            if (is == null) {
+                log.warn("Could not locate resource {}", RESOURCE_LOCATION);
+            } else {
+                try {
+                    prop.load(is);
+                } catch (Exception e) {
+                    log.warn(String.format("Failed to load resource %s", RESOURCE_LOCATION), e);
+                }
+            }
         }
         Semver agentVersion = Semver.fromString(prop.getProperty(AGENT_VERSION_KEY));
         Semver serverMin = Semver.fromString(prop.getProperty(MIN_VERSION_KEY));
@@ -111,6 +122,9 @@ public Semver(int major, int minor, int patch) {
         }
 
         public static Semver fromString(String in) {
+            if (StringUtils.isBlank(in)) {
+                return UNKNOWN;
+            }
             try {
                 Matcher m = VERSION_PATTERN.matcher(in);
                 if (!m.matches()) {

src/main/java/io/cryostat/agent/util/ResourcesUtil.java

@@ -17,12 +17,21 @@
 
 import java.io.InputStream;
 
+import io.cryostat.agent.Agent;
+
 public class ResourcesUtil {
 
     private ResourcesUtil() {}
 
     public static ClassLoader getClassLoader() {
-        ClassLoader cl = Thread.currentThread().getContextClassLoader();
+        return getClassLoader(Agent.class);
+    }
+
+    public static ClassLoader getClassLoader(Class<?> klazz) {
+        ClassLoader cl = klazz.getClassLoader();
+        if (cl == null) {
+            cl = Thread.currentThread().getContextClassLoader();
+        }
         if (cl == null) {
             cl = ClassLoader.getSystemClassLoader();
         }

src/main/resources/META-INF/microprofile-config.properties

@@ -2,6 +2,8 @@ cryostat.agent.app.name=cryostat-agent
 cryostat.agent.baseuri-range=dns_local
 cryostat.agent.baseuri=
 
+cryostat.agent.config.loadable=true
+
 cryostat.agent.api.writes-enabled=false
 
 cryostat.agent.webserver.host=0.0.0.0