Enable propagation and documented propagation interfaces... (#49)

* basic propagation, no tests

* implement basic tests

* getter works on multiple header values

* make tests to be part of the same class

Author: SergeyKanzhelev

build/Common.test.props

@@ -11,7 +11,6 @@
     <CodeAnalysisRuleSet>$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildProjectDirectory), 'OpenCensus.sln'))\build\OpenCensus.test.ruleset</CodeAnalysisRuleSet>
   </PropertyGroup>
 
-
   <ItemGroup>
     <AdditionalFiles Include="$(MSBuildThisFileDirectory)/stylecop.json" />
   </ItemGroup>

src/OpenCensus.Abstractions/Tags/TagValues.cs

@@ -16,9 +16,7 @@
 
 namespace OpenCensus.Tags
 {
-    using System;
     using System.Collections.Generic;
-    using OpenCensus.Utils;
     using OpenCensus.Utils.Abstractions;
 
     public sealed class TagValues

src/OpenCensus.Abstractions/Trace/Propagation/IGetter.cs

@@ -16,10 +16,19 @@
 
 namespace OpenCensus.Trace.Propagation
 {
+    /// <summary>
+    /// Configuration of wire protocol to use to extract and inject span context from the wire.
+    /// </summary>
     public interface IPropagationComponent
     {
+        /// <summary>
+        /// Gets the binary format propagator.
+        /// </summary>
         IBinaryFormat BinaryFormat { get; }
 
+        /// <summary>
+        /// Gets the text format propagator.
+        /// </summary>
         ITextFormat TextFormat { get; }
     }
 }

src/OpenCensus.Abstractions/Trace/Propagation/IPropagationComponent.cs

@@ -16,14 +16,38 @@
 
 namespace OpenCensus.Trace.Propagation
 {
+    using System;
     using System.Collections.Generic;
 
+    /// <summary>
+    /// Text format wire context propagator. Helps to extract and inject context from textual 
+    /// representation (typically http headers or metadata colleciton).
+    /// </summary>
     public interface ITextFormat
     {
+        /// <summary>
+        /// Gets the list of headers used by propagator. The use cases of this are:
+        ///   * allow pre-allocation of fields, especially in systems like gRPC Metadata
+        ///   * allow a single-pass over an iterator (ex OpenTracing has no getter in TextMap).
+        /// </summary>
         IList<string> Fields { get; }
 
-        void Inject<T>(ISpanContext spanContext, T carrier, ISetter<T> setter);
+        /// <summary>
+        /// Injects textual representation of span context to transmit over the wire.
+        /// </summary>
+        /// <typeparam name="T">Type of an object to set context on. Typically HttpRequest or similar.</typeparam>
+        /// <param name="spanContext">Span context to transmit over the wire.</param>
+        /// <param name="carrier">Object to set context on. Instance of this object will be passed to setter.</param>
+        /// <param name="setter">Action that will set name and value pair on the object.</param>
+        void Inject<T>(ISpanContext spanContext, T carrier, Action<T, string, string> setter);
 
-        ISpanContext Extract<T>(T carrier, IGetter<T> getter);
+        /// <summary>
+        /// Extracts span context from textual representation.
+        /// </summary>
+        /// <typeparam name="T">Type of object to extract context from. Typically HttpRequest or similar.</typeparam>
+        /// <param name="carrier">Object to extract context from. Instance of this object will be passed to the getter.</param>
+        /// <param name="getter">Function that will return string value of a key with the specified name.</param>
+        /// <returns>Span context from it's text representation.</returns>
+        ISpanContext Extract<T>(T carrier, Func<T, string, IEnumerable<string>> getter);
     }
 }

src/OpenCensus.Abstractions/Trace/Propagation/ISetter.cs

@@ -21,14 +21,17 @@ namespace OpenCensus.Collector.AspNetCore.Implementation
     using Microsoft.AspNetCore.Http.Features;
     using OpenCensus.Collector.Implementation.Common;
     using OpenCensus.Trace;
+    using OpenCensus.Trace.Propagation;
 
     internal class HttpInListener : ListenerHandler
     {
         private readonly PropertyFetcher startContextFetcher = new PropertyFetcher("HttpContext");
         private readonly PropertyFetcher stopContextFetcher = new PropertyFetcher("HttpContext");
+        private readonly IPropagationComponent propagationComponent;
 
-        public HttpInListener(ITracer tracer, ISampler sampler) : base("Microsoft.AspNetCore", tracer, sampler)
+        public HttpInListener(ITracer tracer, ISampler sampler, IPropagationComponent propagationComponent) : base("Microsoft.AspNetCore", tracer, sampler)
         {
+            this.propagationComponent = propagationComponent;
         }
 
         public override void OnStartActivity(Activity activity, object payload)
@@ -43,7 +46,12 @@ public override void OnStartActivity(Activity activity, object payload)
 
             var request = context.Request;
 
-            this.Tracer.SpanBuilder("HttpIn").SetSampler(this.Sampler).StartScopedSpan();
+            var ctx = this.propagationComponent.TextFormat.Extract<HttpRequest>(
+                request, 
+                (r, name) => r.Headers[name]
+            );
+
+            this.Tracer.SpanBuilderWithRemoteParent("HttpIn", ctx).SetSampler(this.Sampler).StartScopedSpan();
 
             var span = this.Tracer.CurrentSpan;
 

src/OpenCensus.Abstractions/Trace/Propagation/ITextFormat.cs

@@ -21,6 +21,7 @@ namespace OpenCensus.Collector.AspNetCore
     using OpenCensus.Collector.AspNetCore.Implementation;
     using OpenCensus.Collector.Implementation.Common;
     using OpenCensus.Trace;
+    using OpenCensus.Trace.Propagation;
 
     /// <summary>
     /// Dependencies collector.
@@ -35,11 +36,12 @@ public class RequestsCollector : IDisposable
         /// <param name="options">Configuration options for dependencies collector.</param>
         /// <param name="tracer">Tracer to record traced with.</param>
         /// <param name="sampler">Sampler to use to sample dependnecy calls.</param>
-        public RequestsCollector(RequestsCollectorOptions options, ITracer tracer, ISampler sampler)
+        /// <param name="propagationComponent">Wire context propagation component.</param>
+        public RequestsCollector(RequestsCollectorOptions options, ITracer tracer, ISampler sampler, IPropagationComponent propagationComponent)
         {
             this.diagnosticSourceSubscriber = new DiagnosticSourceSubscriber(
                 new Dictionary<string, Func<ITracer, ISampler, ListenerHandler>>()
-                { {"Microsoft.AspNetCore", (t, s) => new HttpInListener(t, s) } }, 
+                { {"Microsoft.AspNetCore", (t, s) => new HttpInListener(t, s, propagationComponent) } }, 
                 tracer, 
                 sampler);
             this.diagnosticSourceSubscriber.Subscribe();

src/OpenCensus.Collector.AspNetCore/Implementation/HttpInListener.cs

@@ -21,6 +21,7 @@ namespace OpenCensus.Collector.Dependencies
     using OpenCensus.Collector.Dependencies.Implementation;
     using OpenCensus.Collector.Implementation.Common;
     using OpenCensus.Trace;
+    using OpenCensus.Trace.Propagation;
 
     /// <summary>
     /// Dependencies collector.
@@ -35,11 +36,11 @@ public class DependenciesCollector : IDisposable
         /// <param name="options">Configuration options for dependencies collector.</param>
         /// <param name="tracer">Tracer to record traced with.</param>
         /// <param name="sampler">Sampler to use to sample dependnecy calls.</param>
-        public DependenciesCollector(DependenciesCollectorOptions options, ITracer tracer, ISampler sampler)
+        public DependenciesCollector(DependenciesCollectorOptions options, ITracer tracer, ISampler sampler, IPropagationComponent propagationComponent)
         {
             this.diagnosticSourceSubscriber = new DiagnosticSourceSubscriber(
                 new Dictionary<string, Func<ITracer, ISampler, ListenerHandler>>()
-                { {"HttpHandlerDiagnosticListener", (t, s) => new HttpHandlerDiagnosticListener(t, s) } },
+                { {"HttpHandlerDiagnosticListener", (t, s) => new HttpHandlerDiagnosticListener(t, s, propagationComponent) } },
                 tracer, 
                 sampler);
             this.diagnosticSourceSubscriber.Subscribe();

src/OpenCensus.Collector.AspNetCore/RequestsCollector.cs

@@ -17,13 +17,15 @@
 namespace OpenCensus.Collector.Dependencies.Implementation
 {
     using System;
+    using System.Collections.Generic;
     using System.Diagnostics;
     using System.Linq;
     using System.Net;
     using System.Net.Http;
     using System.Threading.Tasks;
     using OpenCensus.Collector.Implementation.Common;
     using OpenCensus.Trace;
+    using OpenCensus.Trace.Propagation;
 
     internal class HttpHandlerDiagnosticListener : ListenerHandler
     {
@@ -32,8 +34,11 @@ internal class HttpHandlerDiagnosticListener : ListenerHandler
         private readonly PropertyFetcher stopExceptionFetcher = new PropertyFetcher("Exception");
         private readonly PropertyFetcher stopRequestStatusFetcher = new PropertyFetcher("RequestTaskStatus");
 
-        public HttpHandlerDiagnosticListener(ITracer tracer, ISampler sampler) : base("HttpHandlerDiagnosticListener", tracer, sampler)
+        private readonly IPropagationComponent propagationComponent;
+
+        public HttpHandlerDiagnosticListener(ITracer tracer, ISampler sampler, IPropagationComponent propagationComponent) : base("HttpHandlerDiagnosticListener", tracer, sampler)
         {
+            this.propagationComponent = propagationComponent;
         }
 
         public override void OnStartActivity(Activity activity, object payload)
@@ -56,7 +61,10 @@ public override void OnStartActivity(Activity activity, object payload)
             span.PutHttpMethodAttribute(request.Method.ToString());
             span.PutHttpHostAttribute(request.RequestUri.Host, request.RequestUri.Port);
             span.PutHttpPathAttribute(request.RequestUri.AbsolutePath);
-            span.PutHttpUserAgentAttribute(request.Headers.GetValues("User-Agent").FirstOrDefault());
+            request.Headers.TryGetValues("User-Agent", out IEnumerable<string> userAgents);
+            span.PutHttpUserAgentAttribute(userAgents?.FirstOrDefault());
+
+            this.propagationComponent.TextFormat.Inject<HttpRequestMessage>(span.Context, request, (r, k, v) => r.Headers.Add(k, v));
         }
 
         public override void OnStopActivity(Activity activity, object payload)