Tracing: added request status codes and exceptions

After a request is completed, its status code (OK or ERROR) is added
to trace data, as well as exception information (if one occured).

Author: wprzytula

driver-core/src/main/java/com/datastax/driver/core/RequestHandler.java

@@ -281,6 +281,11 @@ private void setFinalResult(
         logServerWarnings(response.warnings);
       }
       callback.onSet(connection, response, info, statement, System.nanoTime() - startTime);
+
+      tracingInfo.setStatus(
+          response.type == Message.Response.Type.ERROR
+              ? TracingInfo.StatusCode.ERROR
+              : TracingInfo.StatusCode.OK);
       tracingInfo.tracingFinished();
     } catch (Exception e) {
       callback.onException(
@@ -290,6 +295,8 @@ private void setFinalResult(
           System.nanoTime() - startTime, /*unused*/
           0);
 
+      tracingInfo.setStatus(TracingInfo.StatusCode.ERROR, e.toString());
+      tracingInfo.recordException(e);
       tracingInfo.tracingFinished();
     }
   }
@@ -315,6 +322,8 @@ private void setFinalException(
 
     cancelPendingExecutions(execution);
 
+    tracingInfo.recordException(exception);
+    tracingInfo.setStatus(TracingInfo.StatusCode.ERROR, exception.toString());
     tracingInfo.tracingFinished();
 
     try {

driver-core/src/main/java/com/datastax/driver/core/tracing/NoopTracingInfoFactory.java

@@ -22,6 +22,15 @@ private static class NoopTracingInfo implements TracingInfo {
     @Override
     public void setNameAndStartTime(String name) {}
 
+    @Override
+    public void recordException(Exception exception) {}
+
+    @Override
+    public void setStatus(StatusCode code, String description) {}
+
+    @Override
+    public void setStatus(StatusCode code) {}
+
     @Override
     public void tracingFinished() {}
   }

driver-core/src/main/java/com/datastax/driver/core/tracing/TracingInfo.java

@@ -22,6 +22,12 @@
  */
 public interface TracingInfo {
 
+  /** Final status of the traced execution. */
+  enum StatusCode {
+    OK,
+    ERROR,
+  }
+
   /**
    * Starts a span corresponding to this {@link TracingInfo} object. Must be called exactly once,
    * before any other method, at the beginning of the traced execution.
@@ -30,6 +36,28 @@ public interface TracingInfo {
    */
   void setNameAndStartTime(String name);
 
+  /**
+   * Records in the trace that the provided exception occured.
+   *
+   * @param exception the exception to be recorded.
+   */
+  void recordException(Exception exception);
+
+  /**
+   * Sets the final status of the traced execution.
+   *
+   * @param code the status code to be set.
+   */
+  void setStatus(StatusCode code);
+
+  /**
+   * Sets the final status of the traced execution, with additional description.
+   *
+   * @param code the status code to be set.
+   * @param description the additional description of the status.
+   */
+  void setStatus(StatusCode code, String description);
+
   /** Must be always called exactly once at the logical end of traced execution. */
   void tracingFinished();
 }