Add support single and dual span types (#68)

* adding support for single and dual span types

* merge conflicts

* renaming config to dualSpanMode instead of dualSpanType

* fixing bug: server span context created from extracted wire context does not carry extracted flag

Author: mchandramouli

core/src/main/java/com/expedia/www/haystack/client/Tracer.java

@@ -290,7 +290,10 @@ SpanContext createDependentContext() {
             // then we assume this is the first span in the server and so just return the parent context
             // with the same shared span ids
             if (!tracer.dualSpanMode && (isServerSpan() || parent.getContext().isExtractedContext())) {
-                return parent.getContext();
+                return createContext(parent.getContext().getTraceId(),
+                                     parent.getContext().getSpanId(),
+                                     parent.getContext().getParentId(),
+                                     baggage);
             }
 
             return createContext(parent.getContext().getTraceId(),

core/src/test/java/com/expedia/www/haystack/client/SpanBuilderTest.java

@@ -154,6 +154,52 @@ public void testChildOfWithSingleSpanTypeAndExtractedContext() {
                             serverSpan.context().getSpanId().toString());
     }
 
+    @Test
+    public void testChildOfSingleSpanTypeWithExtractedContextDoesNotPropagateExtractedContext() {
+        //create a client span
+        final Tracer clientTracer = new Tracer.Builder(new NoopMetricsRegistry(),
+                                                       "ClientService",
+                                                       dispatcher).build();
+        final Span clientSpan = clientTracer.buildSpan("Api_call")
+                .withTag(Tags.SPAN_KIND.getKey(), Tags.SPAN_KIND_CLIENT)
+                .start();
+        final MapBackedTextMap wireData = new MapBackedTextMap();
+        clientTracer.inject(clientSpan.context(), Format.Builtin.TEXT_MAP, wireData);
+
+        //create a server
+        final Tracer serverTracer = new Tracer.Builder(new NoopMetricsRegistry(),
+                                                       "ServerService",
+                                                       dispatcher).build();
+        final SpanContext wireContext = serverTracer.extract(Format.Builtin.TEXT_MAP, wireData);
+        final Span serverSpan = serverTracer.buildSpan("Api")
+                .asChildOf(wireContext)
+                .start();
+
+        //make sure client and server have the same span-ids for single span type
+        Assert.assertEquals("trace-ids are not matching",
+                            clientSpan.context().getTraceId().toString(),
+                            serverSpan.context().getTraceId().toString());
+        Assert.assertEquals("server - client span-ids do not match",
+                            clientSpan.context().getSpanId().toString(),
+                            serverSpan.context().getSpanId().toString());
+
+        //not create another child of server span
+        final Span childOfServerSpan = serverTracer.buildSpan("child_operation")
+                .asChildOf(serverSpan)
+                .start();
+
+        //make sure server span and child span have the same trace-ids but different span-ids
+        Assert.assertEquals("trace-ids are not matching",
+                            serverSpan.context().getTraceId().toString(),
+                            childOfServerSpan.context().getTraceId().toString());
+        Assert.assertNotEquals("server - childOfServerSpan span-ids match - they should not",
+                            serverSpan.context().getSpanId().toString(),
+                            childOfServerSpan.context().getSpanId().toString());
+        Assert.assertEquals("server's span id - childOfServerSpan's parent id do not match",
+                            serverSpan.context().getSpanId().toString(),
+                            childOfServerSpan.context().getParentId().toString());
+    }
+
     @Test
     public void testWithTags() {
         Span child = tracer.buildSpan("child")