Adding Opencensus c# headers when sending data to Stackdriver (#78)

* 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

* Fixed Stackdriver export interval propagation
Added Opencensus headers into every call into Stackdriver APIs
Added consts for resources that Stackdriver Exporter should auto-detect when running on GCP

* - Added test project for Stackdriver Exporter
- Added tests for StackdriverStatsConfiguration

* Trying to fix the tests that fail on CI as a result of wrong signing key for InternalVisibleTo

* Updating Travis build definition to latest .netcore sdk and running all tests

* Adding an option to set google cloud projectId in environment variable for testing purposes(Stackdriver exporter).

* Temporarily commenting out lines that read from a friend assembly as it doesn't work on a build server

* Added AssemblyInfo.cs into Stackdriver Exporter, so it's visible to tests on both signed and unsigned builds

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

* 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

* Fixed Stackdriver export interval propagation
Added Opencensus headers into every call into Stackdriver APIs
Added consts for resources that Stackdriver Exporter should auto-detect when running on GCP

* - Added test project for Stackdriver Exporter
- Added tests for StackdriverStatsConfiguration

* Trying to fix the tests that fail on CI as a result of wrong signing key for InternalVisibleTo

* Adding an option to set google cloud projectId in environment variable for testing purposes(Stackdriver exporter).

* Temporarily commenting out lines that read from a friend assembly as it doesn't work on a build server

* Added AssemblyInfo.cs into Stackdriver Exporter, so it's visible to tests on both signed and unsigned builds

* Rebasing origin to upstream

* Updated readme to include a link to Stackdriver package

* Update Stackdriver Exporter instructions and split the table of nuget packages for better visibility on various screen sizes

* Add user-agent header in Stackdriver metrics and trace exporters

* Protecting static constructor from exceptions, addressing comments

Author: Simon Zeltser

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

@@ -20,6 +20,8 @@ namespace OpenCensus.Exporter.Stackdriver.Implementation
 
     internal class Constants
     {
+        public const string PACKAGE_VERSION_UNDEFINED = "undefined";
+
         public const string LABEL_DESCRIPTION = "OpenCensus TagKey";
         public const string OPENCENSUS_TASK = "opencensus_task";
         public const string OPENCENSUS_TASK_DESCRIPTION = "Opencensus task identifier";

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

@@ -26,6 +26,8 @@ namespace OpenCensus.Exporter.Stackdriver.Implementation
     using System;
     using System.Collections.Generic;
     using System.Diagnostics;
+    using System.Linq;
+    using System.Reflection;
     using System.Threading;
     using System.Threading.Tasks;
 
@@ -45,9 +47,8 @@ internal class StackdriverStatsExporter
         private const string CUSTOM_METRIC_DOMAIN = "custom.googleapis.com/";
         private const string CUSTOM_OPENCENSUS_DOMAIN = CUSTOM_METRIC_DOMAIN + "opencensus/";
 
-        // TODO - zeltser - figure out how to extract OpenCensus package version
-        private const string USER_AGENT = "opencensus-csharp [0.0]";
         private const string USER_AGENT_KEY = "user-agent";
+        private static string USER_AGENT;
 
         private readonly string domain;
         private readonly string displayNamePrefix;
@@ -88,6 +89,19 @@ public StackdriverStatsExporter(
             displayNamePrefix = GetDisplayNamePrefix(configuration.MetricNamePrefix);
         }
 
+        static StackdriverStatsExporter()
+        {
+            try
+            {
+                string assemblyPackageVersion = typeof(StackdriverStatsExporter).GetTypeInfo().Assembly.GetCustomAttributes<AssemblyInformationalVersionAttribute>().First().InformationalVersion;
+                USER_AGENT = $"opencensus-csharp/{assemblyPackageVersion}";
+            }
+            catch (Exception)
+            {
+                USER_AGENT = $"opencensus-csharp/{Constants.PACKAGE_VERSION_UNDEFINED}";
+            }
+        }
+
         public void Start()
         {
             lock (locker)

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

@@ -16,9 +16,13 @@
 
 namespace OpenCensus.Exporter.Stackdriver.Implementation
 {
+    using System;
     using System.Collections.Generic;
     using System.Linq;
+    using System.Reflection;
+    using Google.Api.Gax.Grpc;
     using Google.Cloud.Trace.V2;
+    using Grpc.Core;
     using OpenCensus.Exporter.Stackdriver.Utils;
     using OpenCensus.Trace;
     using OpenCensus.Trace.Export;
@@ -139,24 +143,67 @@ public static Google.Cloud.Trace.V2.AttributeValue ToAttributeValue(this IAttrib
     /// </summary>
     internal class StackdriverTraceExporter : IHandler
     {
-        private Google.Api.Gax.ResourceNames.ProjectName googleCloudProjectId;
+        private static string STACKDRIVER_EXPORTER_VERSION;
+        private static string OPENCENSUS_EXPORTER_VERSION;
+
+        private readonly Google.Api.Gax.ResourceNames.ProjectName googleCloudProjectId;
+        private readonly TraceServiceSettings traceServiceSettings;
 
         public StackdriverTraceExporter(string projectId)
         {
             googleCloudProjectId = new Google.Api.Gax.ResourceNames.ProjectName(projectId);
 
+            // Set header mutation for every outgoing API call to Stackdriver so the BE knows
+            // which version of OC client is calling it as well as which version of the exporter
+            CallSettings callSettings = CallSettings.FromHeaderMutation(StackDriverCallHeaderAppender);
+            traceServiceSettings = new TraceServiceSettings();
+            traceServiceSettings.CallSettings = callSettings;
+        }
+
+        static StackdriverTraceExporter()
+        {
+            try
+            {
+                string assemblyPackageVersion = typeof(StackdriverTraceExporter).GetTypeInfo().Assembly.GetCustomAttributes<AssemblyInformationalVersionAttribute>().First().InformationalVersion;
+                STACKDRIVER_EXPORTER_VERSION = assemblyPackageVersion;
+            }
+            catch (Exception)
+            {
+                STACKDRIVER_EXPORTER_VERSION = $"{Constants.PACKAGE_VERSION_UNDEFINED}";
+            }
+
+            try
+            {
+                OPENCENSUS_EXPORTER_VERSION = Assembly.GetCallingAssembly().GetName().Version.ToString();
+            }
+            catch (Exception)
+            {
+                OPENCENSUS_EXPORTER_VERSION = $"{Constants.PACKAGE_VERSION_UNDEFINED}";
+            }
         }
 
         public void Export(IList<ISpanData> spanDataList)
         {
-            TraceServiceClient traceWriter = TraceServiceClient.Create();
+            TraceServiceClient traceWriter = TraceServiceClient.Create(settings: traceServiceSettings);
+            
             var batchSpansRequest = new BatchWriteSpansRequest
             {
                 ProjectName = googleCloudProjectId,
                 Spans = { spanDataList.Select(s => s.ToSpan(googleCloudProjectId.ProjectId)) },
             };
+            
+            traceWriter.BatchWriteSpansAsync(batchSpansRequest);
+        }
 
-            traceWriter.BatchWriteSpans(batchSpansRequest);
+        /// <summary>
+        /// Appends OpenCensus headers for every outgoing request to Stackdriver Backend
+        /// </summary>
+        /// <param name="metadata">The metadata that is sent with every outgoing http request</param>
+        private static void StackDriverCallHeaderAppender(Metadata metadata)
+        {
+            
+            metadata.Add("AGENT_LABEL_KEY", "g.co/agent");
+            metadata.Add("AGENT_LABEL_VALUE_STRING", $"{OPENCENSUS_EXPORTER_VERSION}; stackdriver-exporter {STACKDRIVER_EXPORTER_VERSION}");
         }
     }
 }