fix span error tagging in grpc server interceptor

dd-java-agent/instrumentation/grpc-1.5/src/main/java/datadog/trace/instrumentation/grpc/server/GrpcServerDecorator.java

@@ -2,6 +2,9 @@ package datadog.trace.instrumentation.grpc.server;
 
 import datadog.trace.agent.decorator.ServerDecorator;
 import datadog.trace.api.DDSpanTypes;
+import io.grpc.Status;
+import io.opentracing.Span;
+import io.opentracing.tag.Tags;
 
 public class GrpcServerDecorator extends ServerDecorator {
   public static final GrpcServerDecorator DECORATE = new GrpcServerDecorator();
@@ -20,4 +23,17 @@ public class GrpcServerDecorator extends ServerDecorator {
   protected String component() {
     return "grpc-server";
   }
+
+  public Span onClose(final Span span, final Status status) {
+
+    span.setTag("status.code", status.getCode().name());
+    span.setTag("status.description", status.getDescription());
+
+    onError(span, status.getCause());
+    if (!status.isOk()) {
+      Tags.ERROR.set(span, true);
+    }
+
+    return span;
+  }
 }

dd-java-agent/instrumentation/grpc-1.5/src/main/java/datadog/trace/instrumentation/grpc/server/TracingServerInterceptor.java

@@ -90,6 +90,27 @@ public class TracingServerInterceptor implements ServerInterceptor {
       this.span = span;
     }
 
+    @Override
+    public void onClose(final Status status, final Metadata trailers) {
+      DECORATE.onClose(span, status);
+      // Finishes span.
+      try (final Scope scope = tracer.scopeManager().activate(span, false)) {
+        if (scope instanceof TraceScope) {
+          ((TraceScope) scope).setAsyncPropagation(true);
+        }
+        delegate().onClose(status, trailers);
+        if (scope instanceof TraceScope) {
+          ((TraceScope) scope).setAsyncPropagation(false);
+        }
+      } catch (final Throwable e) {
+        DECORATE.onError(span, e);
+        throw e;
+      } finally {
+        DECORATE.beforeFinish(span);
+        span.finish();
+      }
+    }
+
     @Override
     public void onMessage(final ReqT message) {
       final Scope scope =
@@ -178,6 +199,7 @@ public class TracingServerInterceptor implements ServerInterceptor {
       }
     }
 
+
     @Override
     public void onReady() {
       try (final Scope scope = tracer.scopeManager().activate(span, false)) {