Basic working version of Stackdriver stats exporter (#63)

* Introducing Stackdriver Exporter for Opencensus C# library

- Current implementation can only store string values
- Added the exporter and trace handler only
- The exporter relies on newest Trace API from Stackdriver.

* Updating translation from ISpan to Stackdriver's Span to cover more fields

* Fixing the issue that prevented Stackdriver API call to succeed:
now construction of Span resource is taken care of by SpanName class that
is part of Stackdriver Trace V2 API.

* - Added support for capturing all types of trace spans (long/bool/string)
- Fixed csproj, so it produces both .NET Core and .NET versions. It also means signing the assembly using the same mechanism as other assemblies in the solution

* - Added support for storing links
- Minor fixes to proto<->opencensus translation methods

* Fixing merge issue

* Added command line support for the Samples project.
This will make it easier to script testing multiple exporters as
well as prevent commenting and uncommenting different test procedures
for different exporters. Finally, it will making test code cleaner for
showing samples embedded in documentation website.

In order to test the exporter, you can either execute it from the command line:
samples.dll prometheus
or to debug using Visual Studio:
Debug => Sample Properties => Debug.
Now create a profile for your testing execution and fill application arguments
if needed.
Now choose your profile in running configuration of Visual Studio.
Running settings are local to the machine and are ignored in PRs.

* Adding sceleton of metrics support in Stackdriver Exporter.

Currently we can't detect all types of monitoring resources but we
can ship the batches of metrics with time series to Stackdriver.
Thorough testing TBD

* Fixing a few bugs in Stackdriver metrics exporter

- Small refactoring
- Assinging default values for time intervals

* - Fixing a few bugs around metric creation and labels
- Refactoring MetricsConversions
- Fixing stackdriver stats configuration - population of default resource and projects

* First working version of Stackdriver Stats Exporter.

1) Fixed bugs related to Stackdriver Metrics Descriptor creation
2) Renamed Metrics Exporter to Stats Exporter to follow Opencensus terminology
3) Cache Stackdriver Metrics Descriptors locally so it's easy which descriptor holds the time series to upload
4) Fixed test code that was producing the metrics using Opencensus and uploading it to Stackdriver
5) Minor refactoring

Current limitations:

1) Supporting only string labels
2) We support only "Global" monitored resource. We need to detect dynamically where the code is running and attach
corresponding labels to the monitored resource, so metrics are stored correctly
3) More Tests

* Removing commented lines

Author: Simon Zeltser

src/OpenCensus.Exporter.Stackdriver/Implementation/Constants.cs

@@ -17,16 +17,20 @@
 namespace OpenCensus.Exporter.Stackdriver.Implementation
 {
     using System;
+    using System.Collections.Generic;
+    using System.Collections.Specialized;
 
     internal class Constants
     {
         public const string LABEL_DESCRIPTION = "OpenCensus TagKey";
         public const string OPENCENSUS_TASK = "opencensus_task";
         public const string OPENCENSUS_TASK_DESCRIPTION = "Opencensus task identifier";
+
         public const string GCP_GKE_CONTAINER = "k8s_container";
         public const string GCP_GCE_INSTANCE = "gce_instance";
         public const string AWS_EC2_INSTANCE = "aws_ec2_instance";
         public const string GLOBAL = "global";
+
         public const string PROJECT_ID_LABEL_KEY = "project_id";
         public static readonly string OPENCENSUS_TASK_VALUE_DEFAULT = generateDefaultTaskValue();
 

…ackdriver/Implementation/MetricsUtils.cs …plementation/GoogleCloudResourceUtils.cssrc/OpenCensus.Exporter.Stackdriver/Implementation/MetricsUtils.cs renamed to src/OpenCensus.Exporter.Stackdriver/Implementation/GoogleCloudResourceUtils.cs src/OpenCensus.Exporter.Stackdriver/Implementation/MetricsUtils.cs renamed to src/OpenCensus.Exporter.Stackdriver/Implementation/GoogleCloudResourceUtils.cs

@@ -17,12 +17,27 @@
 namespace OpenCensus.Exporter.Stackdriver.Implementation
 {
     using Google.Api;
+    using System.Collections.Generic;
 
     /// <summary>
-    /// Utility methods for metrics
+    /// Utility methods for working with Google Cloud Resources
     /// </summary>
-    public static class MetricsUtils
+    public static class GoogleCloudResourceUtils
     {
+        private static Dictionary<string, string> gcpResourceLabelMappings = new Dictionary<string, string>()
+        {
+            { "project_id", Constants.PROJECT_ID_LABEL_KEY },
+            { "instance_id", Constants.GCP_GCE_INSTANCE },
+            { "zone", null }
+        };
+
+        /// <summary>
+        /// Detects Google Cloud ProjectId based on the environment on which the code runs.
+        /// Supports GCE/GKE/GAE
+        /// In case the code runs in a different environment,
+        /// the method returns null
+        /// </summary>
+        /// <returns>Google Cloud Project ID</returns>
         public static string GetProjectId()
         {
             var instance = Google.Api.Gax.Platform.Instance();
@@ -37,29 +52,14 @@ public static string GetProjectId()
         /// <returns>Stackdriver Monitored Resource</returns>
         public static MonitoredResource GetDefaultResource(string projectId)
         {
-            var builder = new MonitoredResource();
-            builder.Type = Constants.GLOBAL;
-            builder.Labels.Add(Constants.PROJECT_ID_LABEL_KEY, projectId);
+            var resource = new MonitoredResource();
+            resource.Type = Constants.GLOBAL;
+            resource.Labels.Add(Constants.PROJECT_ID_LABEL_KEY, projectId);
 
             // TODO - zeltser - setting monitored resource labels for detected resource
             // along with all the other metadata
 
-            return builder;
-        }
-
-        public static string GetLabelKey(string label)
-        {
-            return label.Replace('/', '_');
-        }
-
-        public static string GenerateTypeName(string viewName, string domain)
-        {
-            return domain + viewName;
-        }
-
-        public static string GetDisplayName(string viewName, string displayNamePrefix)
-        {
-            return displayNamePrefix + viewName;
+            return resource;
         }
     }
 }