Adds "extra fields" but at process scope (#1424)

* Adds "extra fields" but at process scope

fixes gh-1421

* Added changes following the review

* Added changes following the review

* Added changes following the review

docs/src/main/asciidoc/spring-cloud-sleuth.adoc

@@ -446,9 +446,10 @@ String countryCode = ExtraFieldPropagation.get(span.context(), "x-country-code")
 ```
 
 IMPORTANT: A difference from previous versions of Sleuth is that, with Brave, you must pass the list of baggage keys.
-There are two properties to achieve this.
+There are the following properties to achieve this.
 With the `spring.sleuth.baggage-keys`, you set keys that get prefixed with `baggage-` for HTTP calls and `baggage_` for messaging.
-You can also use the `spring.sleuth.propagation-keys` property to pass a list of prefixed keys that are whitelisted without any prefix.
+You can also use the `spring.sleuth.propagation-keys` property to pass a list of prefixed keys that are propagated to remote services without any prefix.
+You can also use the `spring.sleuth.local-keys` property to pass a list keys that will be propagated locally but will not be propagated over the wire.
 Notice that there's no `x-` in front of the header keys.
 
 In order to automatically set the baggage values to Slf4j's MDC, you have to set

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/autoconfig/SleuthProperties.java

@@ -62,6 +62,13 @@ public class SleuthProperties {
 	 */
 	private List<String> propagationKeys = new ArrayList<>();
 
+	/**
+	 * Same as {@link #propagationKeys} except that this field is not propagated to remote services.
+	 *
+	 * @see brave.propagation.ExtraFieldPropagation.FactoryBuilder#addRedactedField(String)
+	 */
+	private List<String> localKeys = new ArrayList<>();
+
 	public boolean isEnabled() {
 		return this.enabled;
 	}
@@ -102,4 +109,11 @@ public class SleuthProperties {
 		this.propagationKeys = propagationKeys;
 	}
 
+	public List<String> getLocalKeys() {
+		return this.localKeys;
+	}
+
+	public void setLocalKeys(List<String> localKeys) {
+		this.localKeys = localKeys;
+	}
 }

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/autoconfig/TraceAutoConfiguration.java

@@ -155,6 +155,11 @@ public class TraceAutoConfiguration {
 				factoryBuilder = factoryBuilder.addField(key);
 			}
 		}
+		if (!sleuthProperties.getLocalKeys().isEmpty()) {
+			for (String key : sleuthProperties.getLocalKeys()) {
+				factoryBuilder = factoryBuilder.addRedactedField(key);
+			}
+		}
 		return factoryBuilder.build();
 	}
 

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/log/Slf4jScopeDecorator.java

@@ -114,6 +114,9 @@ final class Slf4jScopeDecorator implements CurrentTraceContext.ScopeDecorator {
 			for (String key : whitelistedPropagationKeysWithValue(currentSpan)) {
 				MDC.put(key, ExtraFieldPropagation.get(currentSpan, key));
 			}
+			for (String key : whitelistedLocalKeysWithValue(currentSpan)) {
+				MDC.put(key, ExtraFieldPropagation.get(currentSpan, key));
+			}
 		}
 		else {
 			MDC.remove("traceId");
@@ -130,6 +133,9 @@ final class Slf4jScopeDecorator implements CurrentTraceContext.ScopeDecorator {
 			for (String s : whitelistedPropagationKeys()) {
 				MDC.remove(s);
 			}
+			for (String s : whitelistedLocalKeys()) {
+				MDC.remove(s);
+			}
 			previousMdc.clear();
 		}
 
@@ -165,6 +171,7 @@ final class Slf4jScopeDecorator implements CurrentTraceContext.ScopeDecorator {
 		List<AbstractMap.SimpleEntry<String, String>> previousMdc = new ArrayList<>();
 		List<String> keys = new ArrayList<>(whitelistedBaggageKeys());
 		keys.addAll(whitelistedPropagationKeys());
+		keys.addAll(whitelistedLocalKeys());
 		for (String key : keys) {
 			previousMdc.add(new AbstractMap.SimpleEntry<>(key, MDC.get(key)));
 		}
@@ -207,10 +214,18 @@ final class Slf4jScopeDecorator implements CurrentTraceContext.ScopeDecorator {
 		return whitelistedKeys(this.sleuthProperties.getPropagationKeys());
 	}
 
+	private List<String> whitelistedLocalKeys() {
+		return whitelistedKeys(this.sleuthProperties.getLocalKeys());
+	}
+
 	private List<String> whitelistedPropagationKeysWithValue(TraceContext context) {
 		return whitelistedKeysWithValue(context, whitelistedPropagationKeys());
 	}
 
+	private List<String> whitelistedLocalKeysWithValue(TraceContext context) {
+		return whitelistedKeysWithValue(context, whitelistedLocalKeys());
+	}
+
 	private void log(String text, TraceContext span) {
 		if (span == null) {
 			return;

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/log/Slf4JSpanLoggerTest.java

@@ -41,7 +41,8 @@ import static org.assertj.core.api.Assertions.assertThat;
 @SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.NONE, properties = {
 		"spring.sleuth.baggage-keys=my-baggage",
 		"spring.sleuth.propagation-keys=my-propagation",
-		"spring.sleuth.log.slf4j.whitelisted-mdc-keys=my-baggage,my-propagation" })
+		"spring.sleuth.local-keys=my-local",
+		"spring.sleuth.log.slf4j.whitelisted-mdc-keys=my-baggage,my-propagation,my-local" })
 @SpringBootConfiguration
 @EnableAutoConfiguration
 public class Slf4JSpanLoggerTest {
@@ -81,16 +82,20 @@ public class Slf4JSpanLoggerTest {
 		ExtraFieldPropagation.set(this.span.context(), "my-baggage", "my-value");
 		ExtraFieldPropagation.set(this.span.context(), "my-propagation",
 				"my-propagation-value");
+		ExtraFieldPropagation.set(this.span.context(), "my-local",
+				"my-local-value");
 		Scope scope = this.slf4jScopeDecorator.decorateScope(this.span.context(), () -> {
 		});
 
 		assertThat(MDC.get("my-baggage")).isEqualTo("my-value");
 		assertThat(MDC.get("my-propagation")).isEqualTo("my-propagation-value");
+		assertThat(MDC.get("my-local")).isEqualTo("my-local-value");
 
 		scope.close();
 
 		assertThat(MDC.get("my-baggage")).isNullOrEmpty();
 		assertThat(MDC.get("my-propagation")).isNullOrEmpty();
+		assertThat(MDC.get("my-local")).isNullOrEmpty();
 	}
 
 	@Test