Take advantage of the Span<T> namespace changes

tracer/src/Datadog.Trace/Agent/StatsAggregator.cs

@@ -365,9 +365,7 @@ internal StatsAggregationKey BuildKey(Span span, List<PeerTagKey> peerTagKeys, o
         /// The <paramref name="keyPrefix"/> is a pre-encoded UTF-8 byte array (e.g. "tagKey:") and is
         /// hashed directly. Only the <paramref name="tagValue"/> needs UTF-8 encoding at call time.
         /// </summary>
-#if NETCOREAPP
-        [System.Runtime.CompilerServices.SkipLocalsInit]
-#endif
+        [SkipLocalsInit]
         private static ulong HashTag(byte[] keyPrefix, string tagValue, FnvHash64.Version version, ulong? initialHash = null)
         {
             // Hash the pre-encoded key prefix (e.g. "peer.service:") directly — no encoding needed
@@ -377,22 +375,35 @@ private static ulong HashTag(byte[] keyPrefix, string tagValue, FnvHash64.Versio
 
             // Now encode and hash just the tag value
             var maxByteCount = EncodingHelpers.Utf8NoBom.GetMaxByteCount(tagValue.Length);
-#if NETCOREAPP
             const int maxStackLimit = 256;
 
             if (maxByteCount <= maxStackLimit)
             {
                 Span<byte> buffer = stackalloc byte[maxStackLimit];
-                var written = EncodingHelpers.Utf8NoBom.GetBytes(tagValue, buffer);
+                int written;
+#if NETCOREAPP
+                written = EncodingHelpers.Utf8NoBom.GetBytes(tagValue, buffer);
+#else
+                unsafe
+                {
+                    var tagValueSpan = tagValue.AsSpan();
+                    fixed (char* tagValuePointer = tagValueSpan)
+                    {
+                        fixed (byte* bufferPointer = buffer)
+                        {
+                            written = EncodingHelpers.Utf8NoBom.GetBytes(tagValuePointer, tagValueSpan.Length, bufferPointer, buffer.Length);
+                        }
+                    }
+                }
+#endif
                 return FnvHash64.GenerateHash(buffer.Slice(0, written), version, hash);
             }
-#endif
 
             var rented = ArrayPool<byte>.Shared.Rent(maxByteCount);
             try
             {
                 var written = EncodingHelpers.Utf8NoBom.GetBytes(tagValue, charIndex: 0, charCount: tagValue.Length, rented, byteIndex: 0);
-                return FnvHash64.GenerateHash(rented, 0, written, version, hash);
+                return FnvHash64.GenerateHash(rented.AsSpan().Slice(0, written), version, hash);
             }
             finally
             {

tracer/src/Datadog.Trace/ClrProfiler/AutoInstrumentation/AWS/Shared/SpanPointers.cs

@@ -13,12 +13,6 @@
 using Datadog.Trace.ClrProfiler.AutoInstrumentation.AWS.DynamoDb;
 using Datadog.Trace.Util;
 
-#if NETCOREAPP3_1_OR_GREATER
-using System.Buffers;
-#else
-using Datadog.Trace.VendoredMicrosoftCode.System.Buffers;
-#endif
-
 namespace Datadog.Trace.ClrProfiler.AutoInstrumentation.AWS.Shared;
 
 /// <summary>

tracer/src/Datadog.Trace/DataStreamsMonitoring/Hashes/HashHelper.cs

@@ -61,24 +61,12 @@ public static NodeHash CalculateNodeHash(in NodeHashBase baseNodeHash, IEnumerab
         return new NodeHash(hash);
     }
 
-#if NETCOREAPP3_1_OR_GREATER
     [System.Runtime.CompilerServices.SkipLocalsInit]
-#endif
     public static PathwayHash CalculatePathwayHash(NodeHash nodeHash, PathwayHash parentHash)
     {
-#if NETCOREAPP3_1_OR_GREATER
         Span<byte> bytes = stackalloc byte[16];
-        System.Buffers.Binary.BinaryPrimitives.WriteUInt64LittleEndian(bytes, nodeHash.Value);
-        System.Buffers.Binary.BinaryPrimitives.WriteUInt64LittleEndian(bytes.Slice(8), parentHash.Value);
+        BinaryPrimitives.WriteUInt64LittleEndian(bytes, nodeHash.Value);
+        BinaryPrimitives.WriteUInt64LittleEndian(bytes.Slice(8), parentHash.Value);
         return new PathwayHash(FnvHash64.GenerateHash(bytes, HashVersion));
-#else
-        // annoyingly allocate-y, but meh
-        var bytes = new byte[8];
-        BinaryPrimitivesHelper.WriteUInt64LittleEndian(bytes, nodeHash.Value);
-        var hash = FnvHash64.GenerateHash(bytes, HashVersion);
-
-        BinaryPrimitivesHelper.WriteUInt64LittleEndian(bytes, parentHash.Value);
-        return new PathwayHash(FnvHash64.GenerateHash(bytes, HashVersion, hash));
-#endif
     }
 }

tracer/src/Datadog.Trace/DataStreamsMonitoring/VarEncodingHelper.cs

@@ -70,7 +70,6 @@ public static int WriteVarLong(byte[] bytes, int offset, ulong value)
     public static int WriteVarLong(BinaryWriter writer, ulong value)
         => WriteVarLong(value, new BinaryWriterByteWriter(writer));
 
-#if NETCOREAPP3_1_OR_GREATER
     /// <summary>
     /// Serializes 64-bit unsigned integers 7 bits at a time,
     /// starting with the least significant bits. The most significant bit in each
@@ -95,7 +94,6 @@ public static int WriteVarLong(Span<byte> bytes, ulong value)
         bytes[length - 1] = (byte)(value);
         return length;
     }
-#endif
 
     /// <summary>
     /// Serializes 64-bit signed integers using zig-zag encoding,
@@ -122,7 +120,6 @@ public static int WriteVarLongZigZag(byte[] bytes, int offset, long value)
     public static int WriteVarLongZigZag(BinaryWriter writer, long value)
         => WriteVarLong(writer, ZigZag(value));
 
-#if NETCOREAPP3_1_OR_GREATER
     /// <summary>
     /// Serializes 64-bit signed integers using zig-zag encoding,
     /// which ensures small-scale integers are turned into unsigned integers
@@ -134,7 +131,6 @@ public static int WriteVarLongZigZag(BinaryWriter writer, long value)
     /// <returns>The number of bytes written</returns>
     public static int WriteVarLongZigZag(Span<byte> bytes, long value)
         => WriteVarLong(bytes, ZigZag(value));
-#endif
 
     /// <summary>
     /// Serializes 32-bit unsigned integers 7 bits at a time,
@@ -165,7 +161,6 @@ public static int WriteVarInt(byte[] bytes, int offset, uint value)
     public static int WriteVarInt(BinaryWriter writer, uint value)
         => WriteVarLong(value, new BinaryWriterByteWriter(writer));
 
-#if NETCOREAPP3_1_OR_GREATER
     /// <summary>
     /// Serializes 32-bit unsigned integers 7 bits at a time,
     /// starting with the least significant bits. The most significant bit in each
@@ -179,7 +174,6 @@ public static int WriteVarInt(BinaryWriter writer, uint value)
     /// <returns>The number of bytes written</returns>
     public static int WriteVarInt(Span<byte> bytes, uint value)
         => WriteVarLong(bytes, value);
-#endif
 
     /// <summary>
     /// Serializes 32-bit signed integers using zig-zag encoding,
@@ -206,7 +200,6 @@ public static int WriteVarIntZigZag(byte[] bytes, int offset, int value)
     public static int WriteVarIntZigZag(BinaryWriter writer, int value)
         => WriteVarLongZigZag(writer, value);
 
-#if NETCOREAPP3_1_OR_GREATER
     /// <summary>
     /// Serializes 32-bit signed integers using zig-zag encoding,
     /// which ensures small-scale integers are turned into unsigned integers
@@ -218,7 +211,6 @@ public static int WriteVarIntZigZag(BinaryWriter writer, int value)
     /// <returns>The number of bytes written</returns>
     public static int WriteVarIntZigZag(Span<byte> bytes, int value)
         => WriteVarLongZigZag(bytes, value);
-#endif
 
     /// <summary>
     /// Deserializes 64-bit unsigned integers that have been encoded using
@@ -252,7 +244,6 @@ public static int WriteVarIntZigZag(Span<byte> bytes, int value)
         return null;
     }
 
-#if NETCOREAPP3_1_OR_GREATER
     /// <summary>
     /// Deserializes 64-bit unsigned integers that have been encoded using
     /// <see cref="WriteVarLong(byte[],int,ulong)"/>
@@ -284,7 +275,6 @@ public static int WriteVarIntZigZag(Span<byte> bytes, int value)
         bytesRead = default;
         return null;
     }
-#endif
 
     /// <summary>
     /// Deserializes 64-bit unsigned integers that have been encoded using
@@ -297,7 +287,6 @@ public static int WriteVarIntZigZag(Span<byte> bytes, int value)
     public static long? ReadVarLongZigZag(byte[] bytes, int offset, out int bytesRead)
         => ReadVarLong(bytes, offset, out bytesRead) is { } decoded ? UnZigZag(decoded) : null;
 
-#if NETCOREAPP3_1_OR_GREATER
     /// <summary>
     /// Deserializes 64-bit unsigned integers that have been encoded using
     /// <see cref="WriteVarLongZigZag(byte[],int,long)"/>
@@ -307,7 +296,6 @@ public static int WriteVarIntZigZag(Span<byte> bytes, int value)
     /// <returns>The decoded value, or null if decoding failed</returns>
     public static long? ReadVarLongZigZag(Span<byte> bytes, out int bytesRead)
         => ReadVarLong(bytes, out bytesRead) is { } decoded ? UnZigZag(decoded) : null;
-#endif
 
     /// <summary>
     /// Deserializes 32-bit unsigned integers that have been encoded using
@@ -322,7 +310,6 @@ public static int WriteVarIntZigZag(Span<byte> bytes, int value)
             ? (uint)decoded
             : null;
 
-#if NETCOREAPP3_1_OR_GREATER
     /// <summary>
     /// Deserializes 64-bit unsigned integers that have been encoded using
     /// <see cref="WriteVarInt(byte[],int,uint)" />
@@ -334,7 +321,6 @@ public static int WriteVarIntZigZag(Span<byte> bytes, int value)
         => ReadVarLong(bytes, out bytesRead) is { } decoded and <= int.MaxValue
             ? (uint)decoded
             : null;
-#endif
 
     /// <summary>
     /// Deserializes 64-bit unsigned integers that have been encoded using
@@ -349,7 +335,6 @@ public static int WriteVarIntZigZag(Span<byte> bytes, int value)
             ? (int)decoded
             : null;
 
-#if NETCOREAPP3_1_OR_GREATER
     /// <summary>
     /// Deserializes 64-bit unsigned integers that have been encoded using
     /// <see cref="WriteVarIntZigZag(byte[],int,int)" />
@@ -361,7 +346,6 @@ public static int WriteVarIntZigZag(Span<byte> bytes, int value)
         => ReadVarLongZigZag(bytes, out bytesRead) is { } decoded and >= int.MinValue and <= int.MaxValue
             ? (int)decoded
             : null;
-#endif
 
     /// <summary>
     /// Returns the number of bytes that <see cref="WriteVarIntZigZag(byte[],int,int)"/> encodes a value into.

tracer/src/Datadog.Trace/Debugger/Helpers/StringExtensions.cs

@@ -32,11 +32,7 @@ public static string ToUUID(this string input)
             // note that we _could_ get a UUID from these bytes by trivially doing
             // new Guid(bytes).ToString("d") but that uses a slightly different
             // layout of the bytes, which would cause a different UUID to be generated
-#if NETCOREAPP
             Span<char> chars = stackalloc char[36];
-#else
-            var chars = new char[36];
-#endif
             var targetIndex = 0;
 
             for (var sourceIndex = 0; sourceIndex < 16; sourceIndex++)
@@ -51,7 +47,11 @@ public static string ToUUID(this string input)
                 chars[targetIndex++] = Hex[sourceByte & 0xF];
             }
 
+#if NETCOREAPP
             return new string(chars);
+#else
+            return chars.ToString();
+#endif
         }
     }
 }

tracer/src/Datadog.Trace/DiagnosticListeners/AspNetCoreResourceNameHelper.cs

@@ -11,7 +11,6 @@
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
-using System.Text;
 using Datadog.Trace.DuckTyping;
 using Datadog.Trace.SourceGenerators;
 using Datadog.Trace.Util;
@@ -128,14 +127,9 @@ internal static string SimplifyRoutePattern(
                     + (string.IsNullOrEmpty(actionName) ? 0 : Math.Max(actionName!.Length - 6, 0)) // "action".Length
                     + 1; // '/' prefix
 
-#if NETCOREAPP
         var sb = maxSize < 512
                      ? new ValueStringBuilder(stackalloc char[512])
                      : new ValueStringBuilder(); // too big to use stackallocation, so use array builder
-#else
-        // In .NET Core 2.1, the ValueStringBuilder doesn't actually improve anything
-        var sb = StringBuilderCache.Acquire(maxSize);
-#endif
 
         foreach (var pathSegment in routePattern.PathSegments)
         {
@@ -227,23 +221,13 @@ internal static string SimplifyRoutePattern(
             }
         }
 
-#if NETCOREAPP
         if (sb.Length <= 1)
         {
             sb.Dispose();
             return "/";
         }
 
         return sb.ToString();
-#else
-        if (sb.Length <= 1)
-        {
-            StringBuilderCache.Release(sb);
-            return "/";
-        }
-
-        return StringBuilderCache.GetStringAndRelease(sb).ToLowerInvariant();
-#endif
     }
 
     internal static string SimplifyRouteTemplate(
@@ -261,14 +245,9 @@ internal static string SimplifyRouteTemplate(
                     + (string.IsNullOrEmpty(actionName) ? 0 : Math.Max(actionName!.Length - 6, 0)) // "action".Length
                     + 1; // '/' prefix
 
-#if NETCOREAPP
         var sb = maxSize < 512
                      ? new ValueStringBuilder(stackalloc char[512])
                      : new ValueStringBuilder(); // too big to use stackallocation, so use array builder
-#else
-        // In .NET Core 2.1, the ValueStringBuilder doesn't actually improve anything
-        var sb = StringBuilderCache.Acquire(maxSize);
-#endif
 
         // Remove the boxing of the enumerator
         // In all versions of .NET, this is implemented as a List<TemplateSegment>
@@ -367,23 +346,13 @@ internal static string SimplifyRouteTemplate(
         }
 
         // We never added anything, or we just added the first `/`, no need for explicit ToString()
-#if NETCOREAPP
         if (sb.Length <= 1)
         {
             sb.Dispose();
             return "/";
         }
 
         return sb.ToString();
-#else
-        if (sb.Length <= 1)
-        {
-            StringBuilderCache.Release(sb);
-            return "/";
-        }
-
-        return StringBuilderCache.GetStringAndRelease(sb).ToLowerInvariant();
-#endif
     }
 
     [TestingAndPrivateOnly]
@@ -412,10 +381,5 @@ internal static bool IsIdentifierSegment(object? value, out string? valueAsStrin
 
         return UriHelpers.IsIdentifierSegment(valueAsString, 0, valueAsString.Length);
     }
-
-#if !NETCOREAPP
-    // .NET Core 2.1 helper which doesn't _actually_ append as lower invariant, and just does it all at the end instead
-    private static void AppendAsLowerInvariant(this StringBuilder sb, string? value) => sb.Append(value);
-#endif
 }
 #endif

tracer/src/Datadog.Trace/Propagators/B3SingleHeaderContextPropagator.cs

@@ -62,7 +62,6 @@ public bool TryExtract<TCarrier, TCarrierGetter>(TCarrier carrier, TCarrierGette
                     return false;
                 }
 
-#if NETCOREAPP
                 ReadOnlySpan<char> rawTraceId;
                 ReadOnlySpan<char> rawSpanId;
                 char rawSampled;
@@ -100,45 +99,6 @@ public bool TryExtract<TCarrier, TCarrierGetter>(TCarrier carrier, TCarrierGette
 
                 var samplingPriority = rawSampled == '1' ? 1 : 0;
                 var spanContext = new SpanContext(traceId, parentId, samplingPriority, serviceName: null, null, rawTraceId.ToString(), rawSpanId.ToString(), isRemote: true);
-#else
-                string? rawTraceId;
-                string? rawSpanId;
-                char rawSampled;
-
-                if (brValue.Length > 50 && brValue[32] == '-' && brValue[49] == '-')
-                {
-                    // 128-bit trace id
-                    rawTraceId = brValue.Substring(0, 32);
-                    rawSpanId = brValue.Substring(33, 16);
-                    rawSampled = brValue[50];
-                }
-                else if (brValue.Length > 34 && brValue[16] == '-' && brValue[33] == '-')
-                {
-                    // 64-bit trace id
-                    rawTraceId = brValue.Substring(0, 16);
-                    rawSpanId = brValue.Substring(17, 16);
-                    rawSampled = brValue[34];
-                }
-                else
-                {
-                    return false;
-                }
-
-                var success = HexString.TryParseTraceId(rawTraceId, out var traceId);
-
-                if (!success || traceId == TraceId.Zero)
-                {
-                    return false;
-                }
-
-                if (!HexString.TryParseUInt64(rawSpanId, out var parentId))
-                {
-                    parentId = 0;
-                }
-
-                var samplingPriority = rawSampled == '1' ? 1 : 0;
-                var spanContext = new SpanContext(traceId, parentId, samplingPriority, serviceName: null, null, rawTraceId, rawSpanId, isRemote: true);
-#endif
 
                 context = new PropagationContext(spanContext, baggage: null);