create scope for servlet request. (#1699)

Author: rghetia

contrib/http_servlet/src/main/java/io/opencensus/contrib/http/servlet/OcHttpServletFilter.java

@@ -18,6 +18,7 @@
 
 import com.google.common.annotations.VisibleForTesting;
 import io.opencensus.common.ExperimentalApi;
+import io.opencensus.common.Scope;
 import io.opencensus.contrib.http.HttpRequestContext;
 import io.opencensus.contrib.http.HttpServerHandler;
 import io.opencensus.trace.Tracing;
@@ -96,7 +97,12 @@ public void doFilter(ServletRequest request, ServletResponse response, FilterCha
         handler.handleMessageReceived(context, length);
       }
 
-      chain.doFilter(httpReq, httpResp);
+      Scope scope = Tracing.getTracer().withSpan(handler.getSpanFromContext(context));
+      try {
+        chain.doFilter(httpReq, httpResp);
+      } finally {
+        scope.close();
+      }
 
       if (httpReq.isAsyncStarted()) {
         OcHttpServletListener listener = new OcHttpServletListener(handler, context);

contrib/http_servlet/src/main/java/io/opencensus/contrib/http/servlet/OcHttpServletListener.java

@@ -19,9 +19,12 @@
 import static com.google.common.base.Preconditions.checkNotNull;
 
 import io.opencensus.common.ExperimentalApi;
+import io.opencensus.common.Scope;
 import io.opencensus.contrib.http.HttpRequestContext;
 import io.opencensus.contrib.http.HttpServerHandler;
+import io.opencensus.trace.Tracing;
 import java.io.Closeable;
+import javax.annotation.Nullable;
 import javax.servlet.AsyncContext;
 import javax.servlet.AsyncEvent;
 import javax.servlet.AsyncListener;
@@ -37,6 +40,7 @@ public final class OcHttpServletListener implements Closeable, AsyncListener {
   private final HttpRequestContext context;
   private final HttpServerHandler<HttpServletRequest, HttpServletResponse, HttpServletRequest>
       handler;
+  @Nullable private Scope scope = null;
 
   OcHttpServletListener(
       HttpServerHandler<HttpServletRequest, HttpServletResponse, HttpServletRequest> handler,
@@ -56,6 +60,9 @@ public void onComplete(AsyncEvent event) {
     if (response instanceof HttpServletResponse) {
       OcHttpServletUtil.recordMessageSentEvent(handler, context, (HttpServletResponse) response);
     }
+    if (scope != null) {
+      scope.close();
+    }
     handler.handleEnd(
         context,
         (HttpServletRequest) event.getSuppliedRequest(),
@@ -66,6 +73,9 @@ public void onComplete(AsyncEvent event) {
 
   @Override
   public void onError(AsyncEvent event) {
+    if (scope != null) {
+      scope.close();
+    }
     handler.handleEnd(
         context,
         (HttpServletRequest) event.getSuppliedRequest(),
@@ -74,15 +84,21 @@ public void onError(AsyncEvent event) {
   }
 
   @Override
+  @SuppressWarnings(
+      "MustBeClosedChecker") // Close will happen in onTimeout or onError or onComplete method
   public void onStartAsync(AsyncEvent event) {
     AsyncContext eventAsyncContext = event.getAsyncContext();
     if (eventAsyncContext != null) {
+      this.scope = Tracing.getTracer().withSpan(handler.getSpanFromContext(context));
       eventAsyncContext.addListener(this, event.getSuppliedRequest(), event.getSuppliedResponse());
     }
   }
 
   @Override
   public void onTimeout(AsyncEvent event) {
+    if (scope != null) {
+      scope.close();
+    }
     handler.handleEnd(
         context,
         (HttpServletRequest) event.getSuppliedRequest(),