DataDog · labbati · Jun 17, 2019 · Jun 3, 2019 · Jun 3, 2019 · Jun 3, 2019
@@ -1,5 +1,9 @@
 package datadog.trace.api;
 
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.FileReader;
+import java.io.IOException;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
 import java.util.Arrays;
@@ -19,8 +23,8 @@
 import lombok.extern.slf4j.Slf4j;
 
 /**
- * Config gives priority to system properties and falls back to environment variables. It also
- * includes default values to ensure a valid config.
+ * Config reads values with the following priority: 1) system properties, 2) environment variables,
+ * 3) optional configuration file. It also includes default values to ensure a valid config.
  *
  * <p>
  *
@@ -35,6 +39,7 @@ public class Config {
 
   private static final Pattern ENV_REPLACEMENT = Pattern.compile("[^a-zA-Z0-9_]");
 
+  public static final String CONFIGURATION_FILE = "trace.config";
   public static final String SERVICE_NAME = "service.name";
   public static final String SERVICE = "service";
   public static final String TRACE_ENABLED = "trace.enabled";
@@ -190,9 +195,14 @@ public enum PropagationStyle {
 
   @Getter private final boolean traceAnalyticsEnabled;
 
-  // Read order: System Properties -> Env Variables, [-> default value]
+  // Values from an optionally provided properties file
+  private static Properties propertiesFromConfigFile;
+
+  // Read order: System Properties -> Env Variables, [-> properties file], [-> default value]
   // Visible for testing
   Config() {
+    propertiesFromConfigFile = loadConfigurationFile();
+
     runtimeId = UUID.randomUUID().toString();
 
     serviceName = getSettingFromEnvironment(SERVICE_NAME, DEFAULT_SERVICE_NAME);
@@ -566,25 +576,43 @@ public static boolean traceAnalyticsIntegrationEnabled(
   /**
    * Helper method that takes the name, adds a "dd." prefix then checks for System Properties of
    * that name. If none found, the name is converted to an Environment Variable and used to check
-   * the env. If setting not configured in either location, defaultValue is returned.
+   * the env. If none of the above returns a value, then an optional properties file if checked. If
+   * setting is not configured in either location, <code>defaultValue</code> is returned.
    *
    * @param name
    * @param defaultValue
    * @return
    * @deprecated This method should only be used internally. Use the explicit getter instead.
    */
   public static String getSettingFromEnvironment(final String name, final String defaultValue) {
-    final String completeName = PREFIX + name;
-    final String value =
-        System.getProperties()
-            .getProperty(completeName, System.getenv(propertyToEnvironmentName(completeName)));
-    return value == null ? defaultValue : value;
+    String value;
+
+    // System properties and properties provided from command line have the highest precedence
+    value = System.getProperties().getProperty(propertyNameToSystemPropertyName(name));
+    if (null != value) {
+      return value;
+    }
+
+    // If value not provided from system properties, looking at env variables
+    value = System.getenv(propertyNameToEnvironmentVariableName(name));
+    if (null != value) {
+      return value;
+    }
+
+    // If value is not defined yet, we look at properties optionally defined in a properties file
+    value = propertiesFromConfigFile.getProperty(propertyNameToSystemPropertyName(name));
+    if (null != value) {
+      return value;
+    }
+
+    return defaultValue;
   }
 
   /** @deprecated This method should only be used internally. Use the explicit getter instead. */
   private static Map<String, String> getMapSettingFromEnvironment(
       final String name, final String defaultValue) {
-    return parseMap(getSettingFromEnvironment(name, defaultValue), PREFIX + name);
+    return parseMap(
+        getSettingFromEnvironment(name, defaultValue), propertyNameToSystemPropertyName(name));
   }
 
   /**
@@ -674,8 +702,28 @@ private Set<Integer> getIntegerRangeSettingFromEnvironment(
     }
   }
 
-  private static String propertyToEnvironmentName(final String name) {
-    return ENV_REPLACEMENT.matcher(name.toUpperCase()).replaceAll("_");
+  /**
+   * Converts the property name, e.g. 'service.name' into a public environment variable name, e.g.
+   * `DD_SERVICE_NAME`.
+   *
+   * @param setting The setting name, e.g. `service.name`
+   * @return The public facing environment variable name
+   */
+  private static String propertyNameToEnvironmentVariableName(final String setting) {
+    return ENV_REPLACEMENT
+        .matcher(propertyNameToSystemPropertyName(setting).toUpperCase())
+        .replaceAll("_");
+  }
+
+  /**
+   * Converts the property name, e.g. 'service.name' into a public system property name, e.g.
+   * `dd.service.name`.
+   *
+   * @param setting The setting name, e.g. `service.name`
+   * @return The public facing system property name
+   */
+  private static String propertyNameToSystemPropertyName(String setting) {
+    return PREFIX + setting;
   }
 
   private static Map<String, String> getPropertyMapValue(
@@ -830,6 +878,50 @@ private static <V extends Enum<V>> Set<V> convertStringSetToEnumSet(
     return Collections.unmodifiableSet(result);
   }
 
+  /**
+   * Loads the optional configuration properties file into the global {@link Properties} object.
+   *
+   * @return The {@link Properties} object. the returned instance might be empty of file does not
+   *     exist or if it is in a wrong format.
+   */
+  private static Properties loadConfigurationFile() {
+    Properties properties = new Properties();
+
+    // Reading from system property first and from env after
+    String configurationFilePath =
+        System.getProperty(propertyNameToSystemPropertyName(CONFIGURATION_FILE));
+    if (null == configurationFilePath) {
+      configurationFilePath =
+          System.getenv(propertyNameToEnvironmentVariableName(CONFIGURATION_FILE));
+    }
+    if (null == configurationFilePath) {
+      return properties;
+    }
+
+    // Normalizing tilde (~) paths for unix systems
+    configurationFilePath =
+        configurationFilePath.replaceFirst("^~", System.getProperty("user.home"));
+
+    // Configuration properties file is optional
+    File configurationFile = new File(configurationFilePath);
+    if (!configurationFile.exists()) {
+      log.error("Configuration file '{}' not found.", configurationFilePath);
+      return properties;
+    }
+
+    try {
+      FileReader fileReader = new FileReader(configurationFile);
+      properties.load(fileReader);
+    } catch (FileNotFoundException fnf) {
+      log.error("Configuration file '{}' not found.", configurationFilePath);
+    } catch (IOException ioe) {
+      log.error(
+          "Configuration file '{}' cannot be accessed or correctly parsed.", configurationFilePath);
+    }
+
+    return properties;
+  }
+
   /**
    * Returns the detected hostname. This operation is time consuming so if the usage changes and
    * this method will be called several times then we should implement some sort of caching.

@@ -8,6 +8,7 @@ import spock.lang.Specification
 import static datadog.trace.api.Config.AGENT_HOST
 import static datadog.trace.api.Config.AGENT_PORT_LEGACY
 import static datadog.trace.api.Config.AGENT_UNIX_DOMAIN_SOCKET
+import static datadog.trace.api.Config.CONFIGURATION_FILE
 import static datadog.trace.api.Config.DB_CLIENT_HOST_SPLIT_BY_INSTANCE
 import static datadog.trace.api.Config.DEFAULT_JMX_FETCH_STATSD_PORT
 import static datadog.trace.api.Config.GLOBAL_TAGS
@@ -725,4 +726,65 @@ class ConfigTest extends Specification {
     then:
     config.localRootSpanTags.get('_dd.hostname') == InetAddress.localHost.hostName
   }
+
+  def "verify fallback to properties file"() {
+    setup:
+    System.setProperty(PREFIX + CONFIGURATION_FILE, "src/test/resources/dd-java-tracer.properties")
+
+    when:
+    def config = new Config()
+
+    then:
+    config.serviceName == "set-in-properties"
+
+    cleanup:
+    System.clearProperty(PREFIX + CONFIGURATION_FILE)
+  }
+
+  def "verify fallback to properties file has lower priority than system property"() {
+    setup:
+    System.setProperty(PREFIX + CONFIGURATION_FILE, "src/test/resources/dd-java-tracer.properties")
+    System.setProperty(PREFIX + SERVICE_NAME, "set-in-system")
+
+    when:
+    def config = new Config()
+
+    then:
+    config.serviceName == "set-in-system"
+
+    cleanup:
+    System.clearProperty(PREFIX + CONFIGURATION_FILE)
+    System.clearProperty(PREFIX + SERVICE_NAME)
+  }
+
+  def "verify fallback to properties file has lower priority than env var"() {
+    setup:
+    System.setProperty(PREFIX + CONFIGURATION_FILE, "src/test/resources/dd-java-tracer.properties")
+    environmentVariables.set("DD_SERVICE_NAME", "set-in-env")
+
+    when:
+    def config = new Config()
+
+    then:
+    config.serviceName == "set-in-env"
+
+    cleanup:
+    System.clearProperty(PREFIX + CONFIGURATION_FILE)
+    System.clearProperty(PREFIX + SERVICE_NAME)
+    environmentVariables.clear("DD_SERVICE_NAME")
+  }
+
+  def "verify fallback to properties file that does not exist does not crash app"() {
+    setup:
+    System.setProperty(PREFIX + CONFIGURATION_FILE, "src/test/resources/do-not-exist.properties")
+
+    when:
+    def config = new Config()
+
+    then:
+    config.serviceName == 'unnamed-java-app'
+
+    cleanup:
+    System.clearProperty(PREFIX + CONFIGURATION_FILE)
+  }
 }
@@ -0,0 +1 @@
+dd.service.name=set-in-properties