From e316e8bc3d853213aadbb4dd4ca9b2f2c7294c09 Mon Sep 17 00:00:00 2001
From: Marcin Grzejszczak <marcin@grzejszczak.pl>
Date: Mon, 10 Apr 2017 16:48:50 +0200
Subject: [PATCH] Stopped producing warnings if the current span is null

fixes #552
---
 .../cloud/sleuth/trace/DefaultTracer.java        | 16 +++++++++++-----
 .../cloud/sleuth/trace/DefaultTracerTests.java   | 15 +++++++++++++++
 2 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/trace/DefaultTracer.java b/spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/trace/DefaultTracer.java
index b5728856a..40c2f104b 100644
--- a/spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/trace/DefaultTracer.java
+++ b/spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/trace/DefaultTracer.java
@@ -16,9 +16,12 @@
 
 package org.springframework.cloud.sleuth.trace;
 
+import java.lang.invoke.MethodHandles;
 import java.util.Random;
 import java.util.concurrent.Callable;
 
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
 import org.springframework.cloud.sleuth.Sampler;
 import org.springframework.cloud.sleuth.Span;
 import org.springframework.cloud.sleuth.SpanNamer;
@@ -38,6 +41,8 @@ import org.springframework.cloud.sleuth.util.SpanNameUtil;
  */
 public class DefaultTracer implements Tracer {
 
+	private static final Log log = LogFactory.getLog(MethodHandles.lookup().lookupClass());
+
 	private static final int MAX_CHARS_IN_SPAN_NAME = 50;
 
 	private final Sampler defaultSampler;
@@ -102,17 +107,18 @@ public class DefaultTracer implements Tracer {
 		return continueSpan(span);
 	}
 
-	private String shortenNameIfNecessary(String name) {
-		int maxLength = name.length() > MAX_CHARS_IN_SPAN_NAME ? MAX_CHARS_IN_SPAN_NAME : name.length();
-		return name.substring(0, maxLength);
-	}
-
 	@Override
 	public Span detach(Span span) {
 		if (span == null) {
 			return null;
 		}
 		Span cur = SpanContextHolder.getCurrentSpan();
+		if (cur == null) {
+			if (log.isTraceEnabled()) {
+				log.trace("Span in the context is null so something has already detached the span. Won't do anything about it");
+			}
+			return null;
+		}
 		if (!span.equals(cur)) {
 			ExceptionUtils.warn("Tried to detach trace span but " + "it is not the current span: " + span
 					+ ". You may have forgotten to close or detach " + cur);
diff --git a/spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/trace/DefaultTracerTests.java b/spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/trace/DefaultTracerTests.java
index 8bcd56b0f..eb19e9115 100644
--- a/spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/trace/DefaultTracerTests.java
+++ b/spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/trace/DefaultTracerTests.java
@@ -22,9 +22,11 @@ import java.util.Random;
 
 import org.junit.After;
 import org.junit.Before;
+import org.junit.Rule;
 import org.junit.Test;
 import org.mockito.ArgumentCaptor;
 import org.mockito.Mockito;
+import org.springframework.boot.test.rule.OutputCapture;
 import org.springframework.cloud.sleuth.DefaultSpanNamer;
 import org.springframework.cloud.sleuth.Span;
 import org.springframework.cloud.sleuth.SpanNamer;
@@ -54,6 +56,7 @@ public class DefaultTracerTests {
 	private SpanNamer spanNamer = new DefaultSpanNamer();
 	private SpanLogger spanLogger = Mockito.mock(SpanLogger.class);
 	private SpanReporter spanReporter = Mockito.mock(SpanReporter.class);
+	@Rule public OutputCapture capture = new OutputCapture();
 
 	@Before
 	public void setup() {
@@ -206,6 +209,18 @@ public class DefaultTracerTests {
 		then(child.getName().length()).isEqualTo(50);
 	}
 
+	@Test
+	public void shouldNotProduceAWarningMessageWhenThereIsNoSpanInContextAndWeDetachASpan() {
+		DefaultTracer tracer = new DefaultTracer(new AlwaysSampler(), new Random(),
+				this.spanNamer, this.spanLogger, this.spanReporter);
+		Span span = Span.builder().name("foo").traceId(1L).spanId(1L).build();
+
+		Span child = tracer.detach(span);
+
+		then(child).isNull();
+		then(this.capture.toString()).doesNotContain("Tried to detach trace span");
+	}
+
 	private String bigName() {
 		StringBuilder sb = new StringBuilder();
 		for (int i = 0; i < 60; i++) {