StartScopeSpan out param (#95)

* StartScopeSpan out param

* Fact test added for out param case

* Improved by declaring the out var inline

Author: sandeshp

src/OpenCensus.Abstractions/Trace/ISpanBuilder.cs

@@ -57,5 +57,13 @@ public interface ISpanBuilder
         /// <returns>Scoped event to control the scope of span in the context.
         /// Dispose to stop the span and disassiciate it from the current context.</returns>
         IScope StartScopedSpan();
+
+        /// <summary>
+        /// Starts the span and set it as a current on the current context, setting the out param to current span.
+        /// </summary>
+        /// <param name="currentSpan">Current span.</param>
+        /// <returns>Scoped event to control the scope of span in the context.
+        /// Dispose to stop the span and disassiciate it from the current context.</returns>
+        IScope StartScopedSpan(out ISpan currentSpan);
     }
 }

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

@@ -61,23 +61,24 @@ public override void OnStartActivity(Activity activity, object payload)
 
             string path = (request.PathBase.HasValue || request.Path.HasValue) ? (request.PathBase + request.Path).ToString() : "/";
 
-            this.Tracer.SpanBuilderWithRemoteParent(path, ctx).SetSampler(this.Sampler).StartScopedSpan();
-
-            var span = this.Tracer.CurrentSpan;
-
-            if (span != null)
+            ISpan span = null;
+            this.Tracer.SpanBuilderWithRemoteParent(path, ctx).SetSampler(this.Sampler).StartScopedSpan(out span);
+            if (span == null)
             {
-                // Note, route is missing at this stage. It will be available later
+                // Debug.WriteLine("span is null");
+                return;
+            }
 
-                span.PutServerSpanKindAttribute();
-                span.PutHttpHostAttribute(request.Host.Host, request.Host.Port ?? 80);
-                span.PutHttpMethodAttribute(request.Method);
-                span.PutHttpPathAttribute(path);
+            // Note, route is missing at this stage. It will be available later
 
-                var userAgent = request.Headers["User-Agent"].FirstOrDefault();
-                span.PutHttpUserAgentAttribute(userAgent);
-                span.PutHttpRawUrlAttribute(GetUri(request));
-            }
+            span.PutServerSpanKindAttribute();
+            span.PutHttpHostAttribute(request.Host.Host, request.Host.Port ?? 80);
+            span.PutHttpMethodAttribute(request.Method);
+            span.PutHttpPathAttribute(path);
+
+            var userAgent = request.Headers["User-Agent"].FirstOrDefault();
+            span.PutHttpUserAgentAttribute(userAgent);
+            span.PutHttpRawUrlAttribute(GetUri(request));
         }
 
         public override void OnStopActivity(Activity activity, object payload)

src/OpenCensus.Collector.Dependencies/Implementation/HttpHandlerDiagnosticListener.cs

@@ -56,8 +56,7 @@ public override void OnStartActivity(Activity activity, object payload)
                 return;
             }
 
-            this.Tracer.SpanBuilder(request.RequestUri.AbsolutePath).SetSampler(this.Sampler).StartScopedSpan();
-            var span = this.Tracer.CurrentSpan;
+            this.Tracer.SpanBuilder(request.RequestUri.AbsolutePath).SetSampler(this.Sampler).StartScopedSpan(out ISpan span);
             span.PutClientSpanKindAttribute();
             span.PutHttpMethodAttribute(request.Method.ToString());
             span.PutHttpHostAttribute(request.RequestUri.Host, request.RequestUri.Port);

src/OpenCensus/Trace/SpanBuilderBase.cs

@@ -33,5 +33,11 @@ public IScope StartScopedSpan()
         {
             return CurrentSpanUtils.WithSpan(this.StartSpan(), true);
         }
+
+        public IScope StartScopedSpan(out ISpan currentSpan)
+        {
+            currentSpan = this.StartSpan();
+            return CurrentSpanUtils.WithSpan(currentSpan, true);
+        }
     }
 }

src/Samples/TestZipkin.cs

@@ -58,11 +58,9 @@ private static void DoWork(int i)
             // 7. Start another span. If another span was already started, it'll use that span as the parent span.
             // In this example, the main method already started a span, so that'll be the parent span, and this will be
             // a child span.
-            using (OpenCensus.Common.IScope scope = tracer.SpanBuilder("DoWork").StartScopedSpan())
+            using (OpenCensus.Common.IScope scope = tracer.SpanBuilder("DoWork").StartScopedSpan(out ISpan span))
             {
                 // Simulate some work.
-                ISpan span = tracer.CurrentSpan;
-
                 try
                 {
                     Console.WriteLine("Doing busy work");

test/OpenCensus.Tests/Impl/Trace/SpanBuilderBaseTest.cs

@@ -49,5 +49,23 @@ public void StartScopedSpan()
             span.Verify(s => s.End(EndSpanOptions.Default));
             Assert.Same(BlankSpan.Instance, tracer.CurrentSpan);
         }
+
+        [Fact]
+        public void StartScopedSpan_WithParam()
+        {
+            Assert.Same(BlankSpan.Instance, tracer.CurrentSpan);
+
+            IScope scope = spanBuilder.Object.StartScopedSpan(out ISpan outSpan);
+            try
+            {
+                Assert.Same(outSpan, tracer.CurrentSpan);
+            }
+            finally
+            {
+                scope.Dispose();
+            }
+            span.Verify(s => s.End(EndSpanOptions.Default));
+            Assert.Same(BlankSpan.Instance, tracer.CurrentSpan);
+        }
     }
 }