[zipkin] Switch to TagWriter for handling of tags/attributes (#5590)

Author: CodeBlanch

src/OpenTelemetry.Exporter.Zipkin/Implementation/ZipkinSpan.cs

@@ -153,26 +153,22 @@ public void Write(Utf8JsonWriter writer)
             writer.WritePropertyName(ZipkinSpanJsonHelper.TagsPropertyName);
             writer.WriteStartObject();
 
-            // this will be used when we convert int, double, int[], double[] to string
+            // Note: The spec says "Primitive types MUST be converted to string using en-US culture settings"
+            // https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/sdk_exporters/zipkin.md#attribute
+
             var originalUICulture = Thread.CurrentThread.CurrentUICulture;
             Thread.CurrentThread.CurrentUICulture = CultureInfo.InvariantCulture;
 
             try
             {
                 foreach (var tag in this.LocalEndpoint.Tags ?? Enumerable.Empty<KeyValuePair<string, object>>())
                 {
-                    if (ZipkinTagTransformer.Instance.TryTransformTag(tag, out var result))
-                    {
-                        writer.WriteString(tag.Key, result);
-                    }
+                    ZipkinTagWriter.Instance.TryWriteTag(ref writer, tag);
                 }
 
                 foreach (var tag in this.Tags)
                 {
-                    if (ZipkinTagTransformer.Instance.TryTransformTag(tag, out var result))
-                    {
-                        writer.WriteString(tag.Key, result);
-                    }
+                    ZipkinTagWriter.Instance.TryWriteTag(ref writer, tag);
                 }
             }
             finally

src/OpenTelemetry.Exporter.Zipkin/Implementation/ZipkinTagTransformer.cs

@@ -0,0 +1,69 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#nullable enable
+
+using System.Buffers.Text;
+using System.Globalization;
+using System.Text.Json;
+using OpenTelemetry.Internal;
+
+namespace OpenTelemetry.Exporter.Zipkin.Implementation;
+
+internal sealed class ZipkinTagWriter : JsonStringArrayTagWriter<Utf8JsonWriter>
+{
+    public const int StackallocByteThreshold = 256;
+
+    private ZipkinTagWriter()
+    {
+    }
+
+    public static ZipkinTagWriter Instance { get; } = new();
+
+    protected override void WriteIntegralTag(ref Utf8JsonWriter writer, string key, long value)
+    {
+        Span<byte> destination = stackalloc byte[StackallocByteThreshold];
+        if (Utf8Formatter.TryFormat(value, destination, out int bytesWritten))
+        {
+            writer.WriteString(key, destination.Slice(0, bytesWritten));
+        }
+        else
+        {
+            writer.WriteString(key, value.ToString(CultureInfo.InvariantCulture));
+        }
+    }
+
+    protected override void WriteFloatingPointTag(ref Utf8JsonWriter writer, string key, double value)
+    {
+        Span<byte> destination = stackalloc byte[StackallocByteThreshold];
+        if (Utf8Formatter.TryFormat(value, destination, out int bytesWritten))
+        {
+            writer.WriteString(key, destination.Slice(0, bytesWritten));
+        }
+        else
+        {
+            writer.WriteString(key, value.ToString(CultureInfo.InvariantCulture));
+        }
+    }
+
+    protected override void WriteBooleanTag(ref Utf8JsonWriter writer, string key, bool value)
+        => writer.WriteString(key, value ? "true" : "false");
+
+    protected override void WriteStringTag(ref Utf8JsonWriter writer, string key, string value)
+        => writer.WriteString(key, value);
+
+    protected override void WriteArrayTag(ref Utf8JsonWriter writer, string key, ArraySegment<byte> arrayUtf8JsonBytes)
+    {
+        writer.WritePropertyName(key);
+        writer.WriteStringValue(arrayUtf8JsonBytes);
+    }
+
+    protected override void OnUnsupportedTagDropped(
+        string tagKey,
+        string tagValueTypeFullName)
+    {
+        ZipkinExporterEventSource.Log.UnsupportedAttributeType(
+            tagValueTypeFullName,
+            tagKey);
+    }
+}

src/OpenTelemetry.Exporter.Zipkin/Implementation/ZipkinTagWriter.cs

@@ -23,8 +23,7 @@
     <Compile Include="$(RepoRoot)\src\Shared\Shims\NullableAttributes.cs" Link="Includes\Shims\NullableAttributes.cs" />
     <Compile Include="$(RepoRoot)\src\Shared\SpanAttributeConstants.cs" Link="Includes\SpanAttributeConstants.cs" />
     <Compile Include="$(RepoRoot)\src\Shared\StatusHelper.cs" Link="Includes\StatusHelper.cs" />
-    <Compile Include="$(RepoRoot)\src\Shared\TagTransformer.cs" Link="Includes\TagTransformer.cs" />
-    <Compile Include="$(RepoRoot)\src\Shared\TagTransformerJsonHelper.cs" Link="Includes\TagTransformerJsonHelper.cs" />
+    <Compile Include="$(RepoRoot)\src\Shared\TagWriter\*.cs" Link="Includes\TagWriter\%(Filename).cs" />
   </ItemGroup>
 
   <ItemGroup>