Address Bogdan's comments.

* Use Mockito in tests.

* Use HttpRequest local id generator for message event.

* Use Attribute in Annotation to record number of retry.

Author: HailongWen

google-http-client/src/main/java/com/google/api/client/http/HttpRequest.java

@@ -25,11 +25,14 @@
 import com.google.api.client.util.StringUtils;
 
 import io.opencensus.common.Scope;
+import io.opencensus.trace.Annotation;
+import io.opencensus.trace.AttributeValue;
 import io.opencensus.trace.Span;
 import io.opencensus.trace.Tracer;
 
 import java.io.IOException;
 import java.io.InputStream;
+import java.util.Collections;
 import java.util.concurrent.Callable;
 import java.util.concurrent.Executor;
 import java.util.concurrent.Executors;
@@ -866,8 +869,15 @@ public HttpResponse execute() throws IOException {
         .spanBuilder(OpenCensusUtils.SPAN_NAME_HTTP_REQUEST_EXECUTE)
         .setRecordEvents(OpenCensusUtils.isRecordEvent())
         .startSpan();
+    long idGenerator = 0L;
+
     do {
-      span.addAnnotation("retry #" + (numRetries - retriesRemaining));
+      span.addAnnotation(
+          Annotation.fromDescriptionAndAttributes(
+              "retry",
+              Collections.<String, AttributeValue>singletonMap(
+                  "number of retry",
+                  AttributeValue.longAttributeValue(numRetries - retriesRemaining))));
       // Cleanup any unneeded response from a previous iteration
       if (response != null) {
         response.ignore();
@@ -911,7 +921,7 @@ public HttpResponse execute() throws IOException {
           headers.setUserAgent(originalUserAgent + " " + USER_AGENT_SUFFIX);
         }
       }
-      OpenCensusUtils.propagateTracingContext(span, headers);
+      OpenCensusUtils.propagateTracingContext(span.getContext(), headers);
 
       // headers
       HttpHeaders.serializeHeaders(headers, logbuf, curlbuf, logger, lowLevelHttpRequest);
@@ -994,11 +1004,13 @@ public HttpResponse execute() throws IOException {
       lowLevelHttpRequest.setTimeout(connectTimeout, readTimeout);
       // switch tracing scope to current span
       Scope ws = tracer.withSpan(span);
-      OpenCensusUtils.recordSentMessageEvent(span, lowLevelHttpRequest.getContentLength());
+      OpenCensusUtils.recordSentMessageEvent(
+          span, idGenerator++, lowLevelHttpRequest.getContentLength());
       try {
         LowLevelHttpResponse lowLevelHttpResponse = lowLevelHttpRequest.execute();
         if (lowLevelHttpResponse != null) {
-          OpenCensusUtils.recordReceivedMessageEvent(span, lowLevelHttpResponse.getContentLength());
+          OpenCensusUtils.recordReceivedMessageEvent(
+              span, idGenerator++, lowLevelHttpResponse.getContentLength());
         }
         // Flag used to indicate if an exception is thrown before the response is constructed.
         boolean responseConstructed = false;

google-http-client/src/main/java/com/google/api/client/util/OpenCensusUtils.java

@@ -21,11 +21,11 @@
 import com.google.common.annotations.VisibleForTesting;
 
 import io.opencensus.contrib.http.util.HttpPropagationUtil;
-import io.opencensus.trace.BlankSpan;
 import io.opencensus.trace.EndSpanOptions;
 import io.opencensus.trace.NetworkEvent;
 import io.opencensus.trace.NetworkEvent.Type;
 import io.opencensus.trace.Span;
+import io.opencensus.trace.SpanContext;
 import io.opencensus.trace.Status;
 import io.opencensus.trace.Tracer;
 import io.opencensus.trace.Tracing;
@@ -60,11 +60,6 @@ public class OpenCensusUtils {
    */
   private static Tracer tracer = Tracing.getTracer();
 
-  /**
-   * Sequence id generator for message event.
-   */
-  private static AtomicLong idGenerator = new AtomicLong();
-
   /**
    * Whether spans should be recorded locally. Defaults to true.
    */
@@ -140,18 +135,18 @@ public static boolean isRecordEvent() {
   }
 
   /**
-   * Propagate information of current tracing context. This information will be injected into HTTP
+   * Propagate information of a given tracing context. This information will be injected into HTTP
    * header.
    *
-   * @param span the span to be propagated.
+   * @param spanContext the spanContext to be propagated.
    * @param headers the headers used in propagation.
    */
-  public static void propagateTracingContext(Span span, HttpHeaders headers) {
-    Preconditions.checkArgument(span != null, "span should not be null.");
+  public static void propagateTracingContext(SpanContext spanContext, HttpHeaders headers) {
+    Preconditions.checkArgument(spanContext != null, "spanContext should not be null.");
     Preconditions.checkArgument(headers != null, "headers should not be null.");
     if (propagationTextFormat != null && propagationTextFormatSetter != null) {
-      if (!span.equals(BlankSpan.INSTANCE)) {
-        propagationTextFormat.inject(span.getContext(), headers, propagationTextFormatSetter);
+      if (!spanContext.equals(SpanContext.INVALID)) {
+        propagationTextFormat.inject(spanContext, headers, propagationTextFormatSetter);
       }
     }
   }
@@ -201,21 +196,23 @@ public static EndSpanOptions getEndSpanOptions(@Nullable Integer statusCode) {
    * Note that the size represents the message size in application layer, i.e., content-length.
    *
    * @param span The {@code span} in which the send event occurs.
+   * @param id The id for the message, It is unique within an {@link HttpRequest}.
    * @param size Size of the request.
    */
-  public static void recordSentMessageEvent(Span span, long size) {
-    recordMessageEvent(span, size, Type.SENT);
+  public static void recordSentMessageEvent(Span span, long id, long size) {
+    recordMessageEvent(span, id, size, Type.SENT);
   }
 
   /**
    * Records a new message event which contains the size of the response content.
    * Note that the size represents the message size in application layer, i.e., content-length.
    *
    * @param span The {@code span} in which the receive event occurs.
+   * @param id The id for the message. It is unique within an {@link HttpRequest}.
    * @param size Size of the response.
    */
-  public static void recordReceivedMessageEvent(Span span, long size) {
-    recordMessageEvent(span, size, Type.RECV);
+  public static void recordReceivedMessageEvent(Span span, long id, long size) {
+    recordMessageEvent(span, id, size, Type.RECV);
   }
 
   /**
@@ -224,15 +221,16 @@ public static void recordReceivedMessageEvent(Span span, long size) {
    * releases.
    *
    * @param span The {@code span} in which the event occurs.
+   * @param id The id for the message.
    * @param size Size of the message.
    * @param eventType The {@code NetworkEvent.Type} of the message event.
    */
   @VisibleForTesting
-  static void recordMessageEvent(Span span, long size, Type eventType) {
+  static void recordMessageEvent(Span span, long id, long size, Type eventType) {
     Preconditions.checkArgument(span != null, "span should not be null.");
     if (size < 0) size = 0;
     NetworkEvent event = NetworkEvent
-        .builder(eventType, idGenerator.getAndIncrement())
+        .builder(eventType, id)
         .setUncompressedMessageSize(size)
         .build();
     span.addNetworkEvent(event);