[shared] Add TagWriter implementation

OpenTelemetry.sln

@@ -348,6 +348,13 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Configuration", "Configurat
 		src\Shared\Configuration\OpenTelemetryConfigurationExtensions.cs = src\Shared\Configuration\OpenTelemetryConfigurationExtensions.cs
 	EndProjectSection
 EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "TagWriter", "TagWriter", "{993E65E5-E71B-40FD-871C-60A9EBD59724}"
+	ProjectSection(SolutionItems) = preProject
+		src\Shared\TagWriter\ArrayTagWriter.cs = src\Shared\TagWriter\ArrayTagWriter.cs
+		src\Shared\TagWriter\JsonStringArrayTagWriter.cs = src\Shared\TagWriter\JsonStringArrayTagWriter.cs
+		src\Shared\TagWriter\TagWriter.cs = src\Shared\TagWriter\TagWriter.cs
+	EndProjectSection
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -694,6 +701,7 @@ Global
 		{7BE494FC-4B0D-4340-A62A-9C9F3E7389FE} = {A115CE4C-71A8-4B95-96A5-C1DF46FD94C2}
 		{19545B37-8518-4BDD-AD49-00C031FB3C2A} = {3862190B-E2C5-418E-AFDC-DB281FB5C705}
 		{87A20A76-D524-4AAC-AF92-8725BFED0415} = {A49299FB-C5CD-4E0E-B7E1-B7867BBD67CC}
+		{993E65E5-E71B-40FD-871C-60A9EBD59724} = {A49299FB-C5CD-4E0E-B7E1-B7867BBD67CC}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {55639B5C-0770-4A22-AB56-859604650521}

src/Shared/TagWriter/ArrayTagWriter.cs

@@ -0,0 +1,24 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#nullable enable
+
+namespace OpenTelemetry.Internal;
+
+internal abstract class ArrayTagWriter<TArrayState>
+    where TArrayState : notnull
+{
+    public abstract TArrayState BeginWriteArray();
+
+    public abstract void WriteNullValue(ref TArrayState state);
+
+    public abstract void WriteIntegralValue(ref TArrayState state, long value);
+
+    public abstract void WriteFloatingPointValue(ref TArrayState state, double value);
+
+    public abstract void WriteBooleanValue(ref TArrayState state, bool value);
+
+    public abstract void WriteStringValue(ref TArrayState state, string value);
+
+    public abstract void EndWriteArray(ref TArrayState state);
+}

src/Shared/TagWriter/JsonStringArrayTagWriter.cs

@@ -0,0 +1,99 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#nullable enable
+
+using System.Diagnostics;
+using System.Text.Json;
+
+namespace OpenTelemetry.Internal;
+
+internal abstract class JsonStringArrayTagWriter<TTagState> : TagWriter<TTagState, JsonStringArrayTagWriter<TTagState>.JsonArrayTagWriterState>
+    where TTagState : notnull
+{
+    protected JsonStringArrayTagWriter()
+        : base(new JsonArrayTagWriter())
+    {
+    }
+
+    protected sealed override void WriteArrayTag(ref TTagState writer, string key, ref JsonArrayTagWriterState array)
+    {
+        var result = array.Stream.TryGetBuffer(out var buffer);
+
+        Debug.Assert(result, "result was false");
+
+        this.WriteArrayTag(ref writer, key, buffer);
+    }
+
+    protected abstract void WriteArrayTag(ref TTagState writer, string key, ArraySegment<byte> arrayUtf8JsonBytes);
+
+    internal readonly struct JsonArrayTagWriterState(MemoryStream stream, Utf8JsonWriter writer)
+    {
+        public MemoryStream Stream { get; } = stream;
+
+        public Utf8JsonWriter Writer { get; } = writer;
+    }
+
+    internal sealed class JsonArrayTagWriter : ArrayTagWriter<JsonArrayTagWriterState>
+    {
+        [ThreadStatic]
+        private static MemoryStream? threadStream;
+
+        [ThreadStatic]
+        private static Utf8JsonWriter? threadWriter;
+
+        public override JsonArrayTagWriterState BeginWriteArray()
+        {
+            var state = EnsureWriter();
+            state.Writer.WriteStartArray();
+            return state;
+        }
+
+        public override void EndWriteArray(ref JsonArrayTagWriterState state)
+        {
+            state.Writer.WriteEndArray();
+            state.Writer.Flush();
+        }
+
+        public override void WriteBooleanValue(ref JsonArrayTagWriterState state, bool value)
+        {
+            state.Writer.WriteBooleanValue(value);
+        }
+
+        public override void WriteFloatingPointValue(ref JsonArrayTagWriterState state, double value)
+        {
+            state.Writer.WriteNumberValue(value);
+        }
+
+        public override void WriteIntegralValue(ref JsonArrayTagWriterState state, long value)
+        {
+            state.Writer.WriteNumberValue(value);
+        }
+
+        public override void WriteNullValue(ref JsonArrayTagWriterState state)
+        {
+            state.Writer.WriteNullValue();
+        }
+
+        public override void WriteStringValue(ref JsonArrayTagWriterState state, string value)
+        {
+            state.Writer.WriteStringValue(value);
+        }
+
+        private static JsonArrayTagWriterState EnsureWriter()
+        {
+            if (threadStream == null)
+            {
+                threadStream = new MemoryStream();
+                threadWriter = new Utf8JsonWriter(threadStream);
+                return new(threadStream, threadWriter);
+            }
+            else
+            {
+                threadStream.SetLength(0);
+                threadWriter!.Reset(threadStream);
+                return new(threadStream, threadWriter);
+            }
+        }
+    }
+}