Fixes AddCustomAttribute throws Newtonsoft.Json.JsonWriterException: Unsupported type error when used to add header values (newrelic#378)

* Added a test for Microsoft.Extensions.Primitives.StringValues

* Check for StringValues and explicitly tostring it

Author: jaffinito

src/Agent/NewRelic/Agent/Core/JsonConverters/JsonSerializerHelpers.cs

@@ -27,9 +27,19 @@ public static void WriteCollection(JsonWriter writer, IEnumerable<IAttributeValu
                     }
 
                     writer.WritePropertyName(attribVal.AttributeDefinition.Name);
-                    writer.WriteValue(outputValue);
+
+                    // Causes an exception since this type is unsupported by the JsonConverter
+                    if (outputValue.GetType().ToString() == "Microsoft.Extensions.Primitives.StringValues")
+                    {
+                        writer.WriteValue(outputValue.ToString());
+                    }
+                    else
+                    {
+                        writer.WriteValue(outputValue);
+                    }
                 }
             }
+
             writer.WriteEndObject();
         }
 

tests/Agent/UnitTests/CompositeTests/AgentApiTests.cs

@@ -17,6 +17,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using Microsoft.Extensions.Primitives;
 
 namespace CompositeTests
 {
@@ -2256,6 +2257,10 @@ public void SpanCustomAttributes()
             segment.AddCustomAttribute("key8", null);
             segment.AddCustomAttribute("", dtm2);
 
+            var singleStringValue = new StringValues("avalue");
+            var multiStringValue = new StringValues(new[] { "onevalue", "twovalue", "threevalue" });
+            segment.AddCustomAttribute("key9a", singleStringValue);
+            segment.AddCustomAttribute("key9b", multiStringValue);
 
             var expectedAttributes = new[]
             {
@@ -2265,7 +2270,9 @@ public void SpanCustomAttributes()
                 new ExpectedAttribute(){ Key = "key4", Value = 4.0d},
                 new ExpectedAttribute(){ Key = "key5", Value = true},
                 new ExpectedAttribute(){ Key = "key6", Value = dtm1.ToString("o")},
-                new ExpectedAttribute(){ Key = "key7", Value = dtm2.ToString("o")}
+                new ExpectedAttribute(){ Key = "key7", Value = dtm2.ToString("o")},
+                new ExpectedAttribute(){ Key = "key9a", Value = "avalue"},
+                new ExpectedAttribute(){ Key = "key9b", Value = "onevalue,twovalue,threevalue"}
             };
 
             var unexpectedAttributes = new[]

tests/Agent/UnitTests/CompositeTests/CompositeTests.csproj

@@ -10,6 +10,7 @@
     <PackageReference Include="Castle.Core" Version="3.3.0" />
     <PackageReference Include="Castle.Windsor" Version="3.3.0" />
     <PackageReference Include="JustMock" Version="2020.1.113.1" />
+    <PackageReference Include="Microsoft.Extensions.Primitives" Version="1.1.1" />
     <PackageReference Include="MoreLinq" Version="2.4.0" />
     <PackageReference Include="Newtonsoft.Json" Version="11.0.2" />
     <PackageReference Include="NUnit" Version="3.12.0" />