.NET Framework HttpClient Instrumentation: Fix missing events on instances created before TracerProvider (Part 2) (#2375)

* CHANGELOG update.

* Test and bug fixes.

* Update src/OpenTelemetry.Instrumentation.Http/CHANGELOG.md

Co-authored-by: Robert Pająk <pellared@hotmail.com>

* Lint

Co-authored-by: Cijo Thomas <cithomas@microsoft.com>
Co-authored-by: Robert Pająk <pellared@hotmail.com>

src/OpenTelemetry.Instrumentation.Http/CHANGELOG.md

@@ -5,6 +5,10 @@
 * Removes .NET Framework 4.5.2 support. The minimum .NET Framework
   version supported is .NET 4.6.1. ([#2138](https://github.com/open-telemetry/opentelemetry-dotnet/issues/2138))
 
+* `HttpClient` instances created before `AddHttpClientInstrumentation` is called
+  on .NET Framework will now also be instrumented
+  ([#2364](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2364))
+
 ## 1.0.0-rc7
 
 Released 2021-Jul-12

src/OpenTelemetry.Instrumentation.Http/Implementation/HttpWebRequestActivitySource.netfx.cs

@@ -492,10 +492,29 @@ namespace OpenTelemetry.Instrumentation.Http.Implementation
                 ArrayList originalArrayList = connectionListField.GetValue(value) as ArrayList;
                 ConnectionArrayList newArrayList = new ConnectionArrayList(originalArrayList ?? new ArrayList());
 
+                foreach (object connection in originalArrayList)
+                {
+                    HookConnection(connection);
+                }
+
                 connectionListField.SetValue(value, newArrayList);
             }
         }
 
+        private static void HookConnection(object value)
+        {
+            if (connectionType.IsInstanceOfType(value))
+            {
+                // Replace the HttpWebRequest arraylist inside this Connection object,
+                // which allows us to intercept each new HttpWebRequest object added under
+                // this Connection.
+                ArrayList originalArrayList = writeListField.GetValue(value) as ArrayList;
+                HttpWebRequestArrayList newArrayList = new HttpWebRequestArrayList(originalArrayList ?? new ArrayList());
+
+                writeListField.SetValue(value, newArrayList);
+            }
+        }
+
         private static Func<TClass, TField> CreateFieldGetter<TClass, TField>(string fieldName, BindingFlags flags)
             where TClass : class
         {
@@ -968,17 +987,7 @@ namespace OpenTelemetry.Instrumentation.Http.Implementation
 
             public override int Add(object value)
             {
-                if (connectionType.IsInstanceOfType(value))
-                {
-                    // Replace the HttpWebRequest arraylist inside this Connection object,
-                    // which allows us to intercept each new HttpWebRequest object added under
-                    // this Connection.
-                    ArrayList originalArrayList = writeListField.GetValue(value) as ArrayList;
-                    HttpWebRequestArrayList newArrayList = new HttpWebRequestArrayList(originalArrayList ?? new ArrayList());
-
-                    writeListField.SetValue(value, newArrayList);
-                }
-
+                HookConnection(value);
                 return base.Add(value);
             }
         }

test/OpenTelemetry.Instrumentation.Http.Tests/HttpWebRequestTests.Basic.netfx.cs

@@ -264,6 +264,24 @@ namespace OpenTelemetry.Instrumentation.Http.Tests
                 })
                 .Build();
         }
+
+        [Fact]
+        public async Task HttpWebRequestInstrumentationOnExistingInstance()
+        {
+            using HttpClient client = new HttpClient();
+
+            await client.GetAsync(this.url).ConfigureAwait(false);
+
+            var activityProcessor = new Mock<BaseProcessor<Activity>>();
+            using var shutdownSignal = Sdk.CreateTracerProviderBuilder()
+                .AddProcessor(activityProcessor.Object)
+                .AddHttpClientInstrumentation()
+                .Build();
+
+            await client.GetAsync(this.url).ConfigureAwait(false);
+
+            Assert.Equal(3, activityProcessor.Invocations.Count);  // SetParentProvider/Begin/End called
+        }
     }
 }
 #endif