From 753c4dfc872183126dcb7a04356b85d34d4762c1 Mon Sep 17 00:00:00 2001
From: Felix Barnsteiner <felix.barnsteiner@isys.de>
Date: Fri, 3 Nov 2017 12:53:34 +0100
Subject: [PATCH 1/3] Add Span#unwrap

---
 .../src/main/java/io/opentracing/Span.java      | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/opentracing-api/src/main/java/io/opentracing/Span.java b/opentracing-api/src/main/java/io/opentracing/Span.java
index 548ac4f8..50a78101 100644
--- a/opentracing-api/src/main/java/io/opentracing/Span.java
+++ b/opentracing-api/src/main/java/io/opentracing/Span.java
@@ -161,4 +161,21 @@ public interface Span {
      * @see Span#context()
      */
     void finish(long finishMicros);
+
+    /**
+     * Returns an object that is an instance of the given class to allow access to non-standard methods.
+     *
+     * <p> Using this method is highly preferred to type casts, especially because there might be a hierarchy of wrapper
+     * objects. </p>
+     *
+     * <p> If the class implementing this interface is an instance of the provided class, the <code>this</code>
+     * reference is returned. Otherwise, if the receiver is a wrapper, return the the result of calling
+     * <code>unwrap</code> recursively on the wrapped object. If the receiver is not a wrapper and is not an instance of
+     * the provided class, then <code>null</code> is returned.</p>
+     *
+     * @param clazz The Class that the result must be an instance of.
+     * @return an object that is an instance of the provided class, or <code>null</code> if there is no such class in
+     * the wrapper hierarchy.
+     */
+    <T> T unwrap(java.lang.Class<T> clazz);
 }

From 87a120ebde9a18b34629aeeeee48eeb909a9c320 Mon Sep 17 00:00:00 2001
From: Felix Barnsteiner <felix.barnsteiner@isys.de>
Date: Fri, 3 Nov 2017 13:15:50 +0100
Subject: [PATCH 2/3] Add implementation and test

---
 .../src/main/java/io/opentracing/mock/MockSpan.java |  9 +++++++++
 .../test/java/io/opentracing/mock/MockSpanTest.java |  8 ++++++++
 .../src/main/java/io/opentracing/noop/NoopSpan.java | 13 +++++++++++--
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/opentracing-mock/src/main/java/io/opentracing/mock/MockSpan.java b/opentracing-mock/src/main/java/io/opentracing/mock/MockSpan.java
index 859513aa..403bf705 100644
--- a/opentracing-mock/src/main/java/io/opentracing/mock/MockSpan.java
+++ b/opentracing-mock/src/main/java/io/opentracing/mock/MockSpan.java
@@ -115,6 +115,15 @@ public synchronized void finish(long finishMicros) {
         this.finished = true;
     }
 
+    @Override
+    public <T> T unwrap(Class<T> clazz) {
+        if (clazz.isInstance(this)) {
+            return clazz.cast(this);
+        } else {
+            return null;
+        }
+    }
+
     @Override
     public MockSpan setTag(String key, String value) {
         return setObjectTag(key, value);
diff --git a/opentracing-mock/src/test/java/io/opentracing/mock/MockSpanTest.java b/opentracing-mock/src/test/java/io/opentracing/mock/MockSpanTest.java
index b488f657..f0f05118 100644
--- a/opentracing-mock/src/test/java/io/opentracing/mock/MockSpanTest.java
+++ b/opentracing-mock/src/test/java/io/opentracing/mock/MockSpanTest.java
@@ -17,6 +17,7 @@
 import org.junit.Test;
 
 import io.opentracing.Span;
+import io.opentracing.Tracer;
 
 /**
  * @author Pavol Loffay
@@ -78,4 +79,11 @@ public void testAddBaggageAfterFinish() {
         }
         Assert.assertEquals(1, tracer.finishedSpans().get(0).generatedErrors().size());
     }
+
+    @Test
+    public void testUnwrap() throws Exception {
+        Tracer tracer = new MockTracer();
+        Span span = tracer.buildSpan("foo").startManual();
+        Assert.assertSame(span, span.unwrap(MockSpan.class));
+    }
 }
diff --git a/opentracing-noop/src/main/java/io/opentracing/noop/NoopSpan.java b/opentracing-noop/src/main/java/io/opentracing/noop/NoopSpan.java
index 7d503066..e42e5713 100644
--- a/opentracing-noop/src/main/java/io/opentracing/noop/NoopSpan.java
+++ b/opentracing-noop/src/main/java/io/opentracing/noop/NoopSpan.java
@@ -13,11 +13,11 @@
  */
 package io.opentracing.noop;
 
+import java.util.Map;
+
 import io.opentracing.Span;
 import io.opentracing.SpanContext;
 
-import java.util.Map;
-
 public interface NoopSpan extends Span {
     static final NoopSpan INSTANCE = new NoopSpanImpl();
 }
@@ -33,6 +33,15 @@ public void finish() {}
     @Override
     public void finish(long finishMicros) {}
 
+    @Override
+    public <T> T unwrap(Class<T> clazz) {
+        if (clazz.isInstance(this)) {
+            return clazz.cast(this);
+        } else {
+            return null;
+        }
+    }
+
     @Override
     public NoopSpan setTag(String key, String value) { return this; }
 

From f259b891ca753c0a6689573860c5db89b872747c Mon Sep 17 00:00:00 2001
From: Felix Barnsteiner <felix.barnsteiner@isys.de>
Date: Fri, 3 Nov 2017 13:22:22 +0100
Subject: [PATCH 3/3] Improve generic signature and add another test

---
 opentracing-api/src/main/java/io/opentracing/Span.java    | 2 +-
 .../src/main/java/io/opentracing/mock/MockSpan.java       | 2 +-
 .../src/test/java/io/opentracing/mock/MockSpanTest.java   | 8 ++++++++
 .../src/main/java/io/opentracing/noop/NoopSpan.java       | 2 +-
 4 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/opentracing-api/src/main/java/io/opentracing/Span.java b/opentracing-api/src/main/java/io/opentracing/Span.java
index 50a78101..f515a064 100644
--- a/opentracing-api/src/main/java/io/opentracing/Span.java
+++ b/opentracing-api/src/main/java/io/opentracing/Span.java
@@ -177,5 +177,5 @@ public interface Span {
      * @return an object that is an instance of the provided class, or <code>null</code> if there is no such class in
      * the wrapper hierarchy.
      */
-    <T> T unwrap(java.lang.Class<T> clazz);
+    <T extends Span> T unwrap(java.lang.Class<T> clazz);
 }
diff --git a/opentracing-mock/src/main/java/io/opentracing/mock/MockSpan.java b/opentracing-mock/src/main/java/io/opentracing/mock/MockSpan.java
index 403bf705..ffd7f6e6 100644
--- a/opentracing-mock/src/main/java/io/opentracing/mock/MockSpan.java
+++ b/opentracing-mock/src/main/java/io/opentracing/mock/MockSpan.java
@@ -116,7 +116,7 @@ public synchronized void finish(long finishMicros) {
     }
 
     @Override
-    public <T> T unwrap(Class<T> clazz) {
+    public <T extends Span> T unwrap(Class<T> clazz) {
         if (clazz.isInstance(this)) {
             return clazz.cast(this);
         } else {
diff --git a/opentracing-mock/src/test/java/io/opentracing/mock/MockSpanTest.java b/opentracing-mock/src/test/java/io/opentracing/mock/MockSpanTest.java
index f0f05118..b258b8ac 100644
--- a/opentracing-mock/src/test/java/io/opentracing/mock/MockSpanTest.java
+++ b/opentracing-mock/src/test/java/io/opentracing/mock/MockSpanTest.java
@@ -18,6 +18,7 @@
 
 import io.opentracing.Span;
 import io.opentracing.Tracer;
+import io.opentracing.noop.NoopSpan;
 
 /**
  * @author Pavol Loffay
@@ -86,4 +87,11 @@ public void testUnwrap() throws Exception {
         Span span = tracer.buildSpan("foo").startManual();
         Assert.assertSame(span, span.unwrap(MockSpan.class));
     }
+
+    @Test
+    public void testUnwrapWrongInstance() throws Exception {
+        Tracer tracer = new MockTracer();
+        Span span = tracer.buildSpan("foo").startManual();
+        Assert.assertNull(span.unwrap(NoopSpan.class));
+    }
 }
diff --git a/opentracing-noop/src/main/java/io/opentracing/noop/NoopSpan.java b/opentracing-noop/src/main/java/io/opentracing/noop/NoopSpan.java
index e42e5713..ec09dca7 100644
--- a/opentracing-noop/src/main/java/io/opentracing/noop/NoopSpan.java
+++ b/opentracing-noop/src/main/java/io/opentracing/noop/NoopSpan.java
@@ -34,7 +34,7 @@ public void finish() {}
     public void finish(long finishMicros) {}
 
     @Override
-    public <T> T unwrap(Class<T> clazz) {
+    public <T extends Span> T unwrap(Class<T> clazz) {
         if (clazz.isInstance(this)) {
             return clazz.cast(this);
         } else {