Simplify stats::StackdriverExporter. (census-instrumentation#180)

This makes it look more like trace::StackdriverExporter, and reduces
includes.

Author: g-easy

examples/grpc/BUILD

@@ -55,6 +55,7 @@ cc_binary(
         "@com_github_grpc_grpc//:grpc++",
         "@com_github_grpc_grpc//:grpc_opencensus_plugin",
         "@com_google_absl//absl/strings",
+        "@com_google_absl//absl/time",
     ],
 )
 

examples/grpc/hello_client.cc

@@ -20,6 +20,7 @@
 #include <grpcpp/grpcpp.h>
 #include <grpcpp/opencensus.h>
 
+#include "absl/time/clock.h"
 #include "examples/grpc/hello.grpc.pb.h"
 #include "examples/grpc/hello.pb.h"
 #include "examples/grpc/stackdriver.h"

opencensus/exporters/stats/stackdriver/README.md

@@ -35,7 +35,7 @@ that key.
 
 Please refer to the [Stats access controls](https://cloud.google.com/monitoring/access-control)
 and [Trace access controls](https://cloud.google.com/trace/docs/iam)
-documentation for configuring roles.
+documentation for configuring roles. The "Monitoring Editor" role is required.
 
 ### Register the exporter
 

opencensus/exporters/stats/stackdriver/internal/stackdriver_exporter.cc

@@ -41,10 +41,7 @@ constexpr char kProjectIdPrefix[] = "projects/";
 // Stackdriver limits a single CreateTimeSeries request to 200 series.
 constexpr int kTimeSeriesBatchSize = 200;
 
-}  // namespace
-
-class StackdriverExporter::Handler
-    : public ::opencensus::stats::StatsExporter::Handler {
+class Handler : public ::opencensus::stats::StatsExporter::Handler {
  public:
   Handler(absl::string_view project_id, absl::string_view opencensus_task);
 
@@ -70,15 +67,15 @@ class StackdriverExporter::Handler
       registered_descriptors_ GUARDED_BY(mu_);
 };
 
-StackdriverExporter::Handler::Handler(absl::string_view project_id,
-                                      absl::string_view opencensus_task)
+Handler::Handler(absl::string_view project_id,
+                 absl::string_view opencensus_task)
     : project_id_(absl::StrCat(kProjectIdPrefix, project_id)),
       opencensus_task_(opencensus_task),
       stub_(google::monitoring::v3::MetricService::NewStub(
           ::grpc::CreateChannel(kGoogleStackdriverStatsAddress,
                                 ::grpc::GoogleDefaultCredentials()))) {}
 
-void StackdriverExporter::Handler::ExportViewData(
+void Handler::ExportViewData(
     const std::vector<std::pair<opencensus::stats::ViewDescriptor,
                                 opencensus::stats::ViewData>>& data) {
   // TODO: refactor to avoid copying the timeseries.
@@ -131,7 +128,7 @@ void StackdriverExporter::Handler::ExportViewData(
   }
 }
 
-bool StackdriverExporter::Handler::MaybeRegisterView(
+bool Handler::MaybeRegisterView(
     const opencensus::stats::ViewDescriptor& descriptor) {
   const auto& it = registered_descriptors_.find(descriptor.name());
   if (it != registered_descriptors_.end()) {
@@ -161,11 +158,13 @@ bool StackdriverExporter::Handler::MaybeRegisterView(
   return true;
 }
 
+}  // namespace
+
 // static
 void StackdriverExporter::Register(absl::string_view project_id,
                                    absl::string_view opencensus_task) {
-  opencensus::stats::StatsExporter::RegisterPushHandler(absl::WrapUnique(
-      new StackdriverExporter::Handler(project_id, opencensus_task)));
+  opencensus::stats::StatsExporter::RegisterPushHandler(
+      absl::WrapUnique(new Handler(project_id, opencensus_task)));
 }
 
 }  // namespace stats

opencensus/exporters/stats/stackdriver/stackdriver_exporter.h

@@ -16,37 +16,26 @@
 #define OPENCENSUS_EXPORTERS_STATS_STACKDRIVER_STACKDRIVER_EXPORTER_H_
 
 #include "absl/strings/string_view.h"
-#include "opencensus/stats/stats.h"
 
 namespace opencensus {
 namespace exporters {
 namespace stats {
 
 // Exports stats for registered views (see opencensus/stats/stats_exporter.h) to
-// Stackdriver.
-// StackdriverExporter is thread-safe.
-class StackdriverExporter : public ::opencensus::stats::StatsExporter::Handler {
+// Stackdriver. StackdriverExporter is thread-safe.
+class StackdriverExporter {
  public:
-  // Registers the exporter and sets the project ID and task value. The
-  // following are required to communicate with stackdriver: a valid project ID,
-  // a valid authentication key which has been generated for that project (with
-  // the "Monitoring Editor" role), and the server security credentials. An
-  // authentication key can be generated for your project in the gcp/stackdriver
-  // settings for your account. Grpc will look for the key using the path
-  // defined by GOOGLE_APPLICATION_CREDENTIALS environment variable (export
-  // GOOGLE_APPLICATION_CREDENTIALS=<path_to_key>). The server security
-  // credentials located in <grpc_path>/etc/roots.pem needs to be copied to
-  // /usr/share/grpc/roots.pem
-  // project_id should be the exact id of the project, as in the GCP console,
-  // with no prefix--e.g. "sample-project-id". opencensus_task is used to
-  // uniquely identify the task in Stackdriver. The recommended format is
+  // Registers the exporter and sets the project ID and task value. project_id
+  // should be the exact id of the project, as in the GCP console, with no
+  // prefix--e.g. "sample-project-id". opencensus_task is used to uniquely
+  // identify the task in Stackdriver. The recommended format is
   // "{LANGUAGE}-{PID}@{HOSTNAME}"; if {PID} is not available a random number
   // may be used.
   static void Register(absl::string_view project_id,
                        absl::string_view opencensus_task);
 
  private:
-  class Handler;
+  StackdriverExporter() = delete;
 };
 
 }  // namespace stats