new configuation key for setting debug log level

dd-java-agent/src/main/java/datadog/trace/agent/TracingAgent.java

@@ -145,6 +145,11 @@ private static void configureLogger() {
     setSystemPropertyDefault(SIMPLE_LOGGER_SHOW_DATE_TIME_PROPERTY, "true");
     setSystemPropertyDefault(
         SIMPLE_LOGGER_DATE_TIME_FORMAT_PROPERTY, SIMPLE_LOGGER_DATE_TIME_FORMAT_DEFAULT);
+
+    final boolean debugEnabled = isDebugMode();
+    if (debugEnabled) {
+      setSystemPropertyDefault(SIMPLE_LOGGER_DEFAULT_LOG_LEVEL_PROPERTY, "DEBUG");
+    }
   }
 
   private static void setSystemPropertyDefault(final String property, final String value) {
@@ -285,15 +290,42 @@ private static ClassLoader getPlatformClassLoader()
     return (ClassLoader) method.invoke(null);
   }
 
+  /**
+   * Determine if we should log in debug level according to dd.trace.debug
+   *
+   * @return true if we should
+   */
+  private static boolean isDebugMode() {
+    final String tracerDebugLevelSysprop = "dd.trace.debug";
+    final String tracerDebugLevelProp = System.getProperty(tracerDebugLevelSysprop);
+
+    if (tracerDebugLevelProp != null) {
+      return Boolean.parseBoolean(tracerDebugLevelProp);
+    }
+
+    final String tracerDebugLevelEnv =
+        System.getenv(tracerDebugLevelSysprop.replace('.', '_').toUpperCase());
+
+    if (tracerDebugLevelEnv != null) {
+      return Boolean.parseBoolean(tracerDebugLevelEnv);
+    }
+    return false;
+  }
+
   /**
    * Search for java or datadog-tracer sysprops which indicate that a custom log manager will be
    * used. Also search for any app classes known to set a custom log manager.
    *
    * @return true if we detect a custom log manager being used.
    */
   private static boolean isAppUsingCustomLogManager() {
-    final boolean debugEnabled =
-        "debug".equalsIgnoreCase(System.getProperty(SIMPLE_LOGGER_DEFAULT_LOG_LEVEL_PROPERTY));
+    boolean debugEnabled = false;
+    if (System.getProperty(SIMPLE_LOGGER_DEFAULT_LOG_LEVEL_PROPERTY) != null) {
+      debugEnabled =
+          "debug".equalsIgnoreCase(System.getProperty(SIMPLE_LOGGER_DEFAULT_LOG_LEVEL_PROPERTY));
+    } else {
+      debugEnabled = isDebugMode();
+    }
 
     final String tracerCustomLogManSysprop = "dd.app.customlogmanager";
     final String customLogManagerProp = System.getProperty(tracerCustomLogManSysprop);

dd-java-agent/src/test/groovy/datadog/trace/agent/LogLevelTest.groovy

@@ -0,0 +1,90 @@
+package datadog.trace.agent
+
+import datadog.trace.agent.test.IntegrationTestUtils
+
+import jvmbootstraptest.LogLevelChecker
+import spock.lang.Specification
+
+
+class LogLevelTest extends Specification {
+
+
+  /* Priority: datadog.slf4j.simpleLogger.defaultLogLevel > dd.trace.debug > DD_TRACE_DEBUG
+  1: INFO LOGS
+  0: DEBUG Logs
+   */
+
+  def "dd.trace.debug false"() {
+    expect:
+    IntegrationTestUtils.runOnSeparateJvm(LogLevelChecker.getName()
+      , ["-Ddd.trace.debug=false","-Ddd.jmxfetch.enabled=false","-Ddd.trace.enabled=false"] as String[]
+      , "" as String[]
+      , [:]
+      , true) == 1
+  }
+  def "SLF4J DEBUG &&  dd.trace.debug is false"() {
+    expect:
+    IntegrationTestUtils.runOnSeparateJvm(LogLevelChecker.getName()
+      , ["-Ddd.trace.debug=false","-Ddatadog.slf4j.simpleLogger.defaultLogLevel=debug","-Ddd.jmxfetch.enabled=false","-Ddd.trace.enabled=false"] as String[]
+      , "" as String[]
+      , [:]
+      , true) == 0
+  }
+  def "dd.trace.debug is false && DD_TRACE_DEBUG is true"() {
+    expect:
+    IntegrationTestUtils.runOnSeparateJvm(LogLevelChecker.getName()
+      , ["-Ddd.trace.debug=false","-Ddd.jmxfetch.enabled=false","-Ddd.trace.enabled=false"] as String[]
+      , "" as String[]
+      , ["DD_TRACE_DEBUG": "true"]
+      , true) == 1
+  }
+
+  def "dd.trace.debug is true"() {
+    expect:
+    IntegrationTestUtils.runOnSeparateJvm(LogLevelChecker.getName()
+      , ["-Ddd.trace.debug=true","-Ddd.jmxfetch.enabled=false","-Ddd.trace.enabled=false"] as String[]
+      , "" as String[]
+      , [:]
+      , true) == 0
+  }
+
+
+  def "DD_TRACE_DEBUG is true"() {
+    expect:
+    IntegrationTestUtils.runOnSeparateJvm(LogLevelChecker.getName()
+      , ["-Ddd.jmxfetch.enabled=false","-Ddd.trace.enabled=false"] as String[]
+      , "" as String[]
+      , ["DD_TRACE_DEBUG": "true"]
+      , true) == 0
+  }
+
+  def "dd.trace.debug is true && DD_TRACE_DEBUG is false"() {
+    expect:
+    IntegrationTestUtils.runOnSeparateJvm(LogLevelChecker.getName()
+      , ["-Ddd.trace.debug=true","-Ddd.jmxfetch.enabled=false","-Ddd.trace.enabled=false"] as String[]
+      , "" as String[]
+      , ["DD_TRACE_DEBUG": "false"]
+      , true) == 0
+  }
+
+
+
+  def "SLF4J DEBUG && DD_TRACE_DEBUG is false"() {
+    expect:
+    IntegrationTestUtils.runOnSeparateJvm(LogLevelChecker.getName()
+      , ["-Ddatadog.slf4j.simpleLogger.defaultLogLevel=debug","-Ddd.jmxfetch.enabled=false","-Ddd.trace.enabled=false"] as String[]
+      , "" as String[]
+      , ["DD_TRACE_DEBUG": "false"]
+      , true) == 0
+  }
+
+  def "SLF4J INFO && DD_TRACE_DEBUG is true"() {
+    expect:
+    IntegrationTestUtils.runOnSeparateJvm(LogLevelChecker.getName()
+      , ["-Ddatadog.slf4j.simpleLogger.defaultLogLevel=info","-Ddd.jmxfetch.enabled=false","-Ddd.trace.enabled=false"] as String[]
+      , "" as String[]
+      , ["DD_TRACE_DEBUG": "true"]
+      , true) == 1
+  }
+
+}

dd-java-agent/src/test/java/jvmbootstraptest/LogLevelChecker.java

@@ -0,0 +1,13 @@
+package jvmbootstraptest;
+
+public class LogLevelChecker {
+  // returns an exception if logs are not in DEBUG
+  public static void main(final String[] args) throws ClassNotFoundException {
+
+    String str = System.getProperty("datadog.slf4j.simpleLogger.defaultLogLevel");
+
+    if ((str == null) || (str != null && !str.equalsIgnoreCase("debug"))) {
+      throw new RuntimeException("debug mode not set");
+    }
+  }
+}