Decode the OTEL_RESOURCE_ATTRIBUTES environment variable according to the spec

src/OpenTelemetry.Api/Context/Propagation/BaggagePropagator.cs

@@ -1,10 +1,6 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
-#if NET
-using System.Diagnostics.CodeAnalysis;
-#endif
-using System.Net;
 using System.Text;
 using OpenTelemetry.Internal;
 
@@ -20,9 +16,6 @@ public class BaggagePropagator : TextMapPropagator
     private const int MaxBaggageLength = 8192;
     private const int MaxBaggageItems = 180;
 
-    private static readonly char[] EqualSignSeparator = ['='];
-    private static readonly char[] CommaSignSeparator = [','];
-
     /// <inheritdoc/>
     public override ISet<string> Fields => new HashSet<string> { BaggageHeaderName };
 
@@ -52,7 +45,7 @@ public override PropagationContext Extract<T>(PropagationContext context, T carr
             var baggageCollection = getter(carrier, BaggageHeaderName);
             if (baggageCollection?.Any() ?? false)
             {
-                if (TryExtractBaggage([.. baggageCollection], out var baggage))
+                if (PercentEncodingHelper.TryExtractBaggage([.. baggageCollection], out var baggage))
                 {
                     return new PropagationContext(context.ActivityContext, new Baggage(baggage!));
                 }
@@ -97,77 +90,12 @@ public override void Inject<T>(PropagationContext context, T carrier, Action<T,
                     continue;
                 }
 
-                baggage.Append(WebUtility.UrlEncode(item.Key)).Append('=').Append(WebUtility.UrlEncode(item.Value)).Append(',');
+                baggage.Append(PercentEncodingHelper.PercentEncodeBaggage(item.Key, item.Value));
+                baggage.Append(',');
             }
             while (e.MoveNext() && ++itemCount < MaxBaggageItems && baggage.Length < MaxBaggageLength);
             baggage.Remove(baggage.Length - 1, 1);
             setter(carrier, BaggageHeaderName, baggage.ToString());
         }
     }
-
-    internal static bool TryExtractBaggage(
-        string[] baggageCollection,
-#if NET
-        [NotNullWhen(true)]
-#endif
-        out Dictionary<string, string>? baggage)
-    {
-        int baggageLength = -1;
-        bool done = false;
-        Dictionary<string, string>? baggageDictionary = null;
-
-        foreach (var item in baggageCollection)
-        {
-            if (done)
-            {
-                break;
-            }
-
-            if (string.IsNullOrEmpty(item))
-            {
-                continue;
-            }
-
-            foreach (var pair in item.Split(CommaSignSeparator))
-            {
-                baggageLength += pair.Length + 1; // pair and comma
-
-                if (baggageLength >= MaxBaggageLength || baggageDictionary?.Count >= MaxBaggageItems)
-                {
-                    done = true;
-                    break;
-                }
-
-#if NET
-                if (pair.IndexOf('=', StringComparison.Ordinal) < 0)
-#else
-                if (pair.IndexOf('=') < 0)
-#endif
-                {
-                    continue;
-                }
-
-                var parts = pair.Split(EqualSignSeparator, 2);
-                if (parts.Length != 2)
-                {
-                    continue;
-                }
-
-                var key = WebUtility.UrlDecode(parts[0]);
-                var value = WebUtility.UrlDecode(parts[1]);
-
-                if (string.IsNullOrEmpty(key) || string.IsNullOrEmpty(value))
-                {
-                    continue;
-                }
-
-                baggageDictionary ??= [];
-
-                baggageDictionary[key] = value;
-            }
-        }
-
-        baggage = baggageDictionary;
-        return baggageDictionary != null;
-    }
 }

src/OpenTelemetry.Api/OpenTelemetry.Api.csproj

@@ -15,6 +15,7 @@
     <Compile Include="$(RepoRoot)\src\Shared\DiagnosticDefinitions.cs" Link="Includes\DiagnosticDefinitions.cs" />
     <Compile Include="$(RepoRoot)\src\Shared\ExceptionExtensions.cs" Link="Includes\ExceptionExtensions.cs" />
     <Compile Include="$(RepoRoot)\src\Shared\Guard.cs" Link="Includes\Guard.cs" />
+    <Compile Include="$(RepoRoot)\src\Shared\PercentEncodingHelper.cs" Link="Includes\PercentEncodingHelper.cs" />
     <Compile Include="$(RepoRoot)\src\Shared\SemanticConventions.cs" Link="Includes\SemanticConventions.cs" />
     <Compile Include="$(RepoRoot)\src\Shared\Shims\ExperimentalAttribute.cs" Link="Includes\Shims\ExperimentalAttribute.cs" />
     <Compile Include="$(RepoRoot)\src\Shared\Shims\Lock.cs" Link="Includes\Shims\Lock.cs" />

src/OpenTelemetry/CHANGELOG.md

@@ -18,6 +18,11 @@ Released 2025-Oct-01
   to a single `MeterProvider`, as required by the OpenTelemetry specification.
   ([#6458](https://github.com/open-telemetry/opentelemetry-dotnet/pull/6458))
 
+* Added decoding of the `OTEL_RESOURCE_ATTRIBUTES` variable according to the specification,
+  adhering to the [W3C Baggage](https://github.com/w3c/baggage/blob/main/baggage/HTTP_HEADER_FORMAT.md)
+  format.
+  ([#6461](https://github.com/open-telemetry/opentelemetry-dotnet/pull/6461))
+
 * Added `FormatMessage` configuration option to self-diagnostics feature. When
   set to `true` (default is false), log messages will be formatted by replacing
   placeholders with actual parameter values for improved readability.

src/OpenTelemetry/Resources/OtelEnvResourceDetector.cs

@@ -2,14 +2,13 @@
 // SPDX-License-Identifier: Apache-2.0
 
 using Microsoft.Extensions.Configuration;
+using OpenTelemetry.Internal;
 
 namespace OpenTelemetry.Resources;
 
 internal sealed class OtelEnvResourceDetector : IResourceDetector
 {
     public const string EnvVarKey = "OTEL_RESOURCE_ATTRIBUTES";
-    private const char AttributeListSplitter = ',';
-    private const char AttributeKeyValueSplitter = '=';
 
     private readonly IConfiguration configuration;
 
@@ -35,16 +34,12 @@ private static List<KeyValuePair<string, object>> ParseResourceAttributes(string
     {
         var attributes = new List<KeyValuePair<string, object>>();
 
-        string[] rawAttributes = resourceAttributes.Split(AttributeListSplitter);
-        foreach (string rawKeyValuePair in rawAttributes)
+        if (PercentEncodingHelper.TryExtractBaggage([resourceAttributes], out var baggage) && baggage != null)
         {
-            string[] keyValuePair = rawKeyValuePair.Split(AttributeKeyValueSplitter);
-            if (keyValuePair.Length != 2)
+            foreach (var kvp in baggage)
             {
-                continue;
+                attributes.Add(new KeyValuePair<string, object>(kvp.Key, kvp.Value));
             }
-
-            attributes.Add(new KeyValuePair<string, object>(keyValuePair[0].Trim(), keyValuePair[1].Trim()));
         }
 
         return attributes;

src/Shared/PercentEncodingHelper.cs

@@ -0,0 +1,146 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#if NET
+using System.Diagnostics.CodeAnalysis;
+#endif
+using System.Text;
+using System.Text.RegularExpressions;
+
+namespace OpenTelemetry.Internal;
+
+/// <summary>
+/// Helper methods for percent-encoding and decoding baggage values.
+/// See https://w3c.github.io/baggage/.
+/// </summary>
+internal static partial class PercentEncodingHelper
+{
+    private const int MaxBaggageLength = 8192;
+    private const int MaxBaggageItems = 180;
+    private const char KeyValueSplitter = '=';
+    private const char ListSplitter = ',';
+
+    internal static bool TryExtractBaggage(
+        string[] baggageCollection,
+#if NET
+        [NotNullWhen(true)]
+#endif
+        out Dictionary<string, string>? baggage)
+    {
+        Dictionary<string, string>? baggageDictionary = null;
+        int baggageLength = -1; // Start with -1 to account for no leading comma on first item
+
+        foreach (var baggageList in baggageCollection.Where(h => !string.IsNullOrEmpty(h)))
+        {
+            foreach (string keyValuePair in baggageList.Split(ListSplitter))
+            {
+                baggageLength += keyValuePair.Length + 1; // pair length + comma
+                if (ExceedsMaxBaggageLimits(baggageLength, baggageDictionary?.Count))
+                {
+                    baggage = baggageDictionary;
+                    return baggageDictionary != null;
+                }
+#if NET
+                var indexOfFirstEquals = keyValuePair.IndexOf(KeyValueSplitter, StringComparison.Ordinal);
+#else
+                var indexOfFirstEquals = keyValuePair.IndexOf(KeyValueSplitter);
+#endif
+                if (indexOfFirstEquals < 0)
+                {
+                    continue;
+                }
+
+                var splitKeyValue = keyValuePair.Split([KeyValueSplitter], 2);
+                var key = splitKeyValue[0].Trim();
+                var value = splitKeyValue[1].Trim();
+
+                if (!IsValidKeyValuePair(key, value))
+                {
+                    continue;
+                }
+
+                var decodedValue = PercentDecodeBaggage(value);
+
+                baggageDictionary ??= [];
+                baggageDictionary[key] = decodedValue;
+            }
+        }
+
+        baggage = baggageDictionary;
+        return baggageDictionary != null;
+    }
+
+    /// <summary>
+    /// As per the specification, only the value is percent-encoded.
+    /// "Uri.EscapeDataString" encodes code points which are not required to be percent-encoded.
+    /// </summary>
+    /// <param name="key"> The baggage key. </param>
+    /// <param name="value"> The baggage value. </param>
+    /// <returns> The percent-encoded baggage item. </returns>
+    internal static string PercentEncodeBaggage(string key, string value) => $"{key.Trim()}={Uri.EscapeDataString(value.Trim())}";
+
+    private static string PercentDecodeBaggage(string baggageEncoded)
+    {
+        var bytes = new List<byte>();
+        for (int i = 0; i < baggageEncoded.Length; i++)
+        {
+            if (baggageEncoded[i] == '%' && i + 2 < baggageEncoded.Length && IsHex(baggageEncoded[i + 1]) && IsHex(baggageEncoded[i + 2]))
+            {
+                var hex = baggageEncoded.AsSpan(i + 1, 2);
+#if NET
+                bytes.Add(byte.Parse(hex, System.Globalization.NumberStyles.HexNumber, System.Globalization.CultureInfo.InvariantCulture));
+#else
+                bytes.Add(Convert.ToByte(hex.ToString(), 16));
+#endif
+
+                i += 2;
+            }
+            else if (baggageEncoded[i] == '%')
+            {
+                return baggageEncoded; // Bad percent triplet -> return original value
+            }
+            else
+            {
+                if (!IsBaggageOctet(baggageEncoded[i]))
+                {
+                    return baggageEncoded; // non-encoded character not baggage octet encoded -> return original value
+                }
+
+                bytes.Add((byte)baggageEncoded[i]);
+            }
+        }
+
+        return new UTF8Encoding(false, false).GetString(bytes.ToArray());
+    }
+
+#if NET
+    [GeneratedRegex(@"^[!#$%&'*+\-\.^_`|~0-9A-Z]+$", RegexOptions.IgnoreCase)]
+    private static partial Regex TokenRegex();
+#else
+
+#pragma warning disable SA1201 // A field should not follow a method
+    private static readonly Regex TokenRegexField = new(
+        @"^[!#$%&'*+\-\.^_`|~0-9A-Z]+$", RegexOptions.IgnoreCase | RegexOptions.Compiled);
+#pragma warning restore SA1201 // A field should not follow a method
+
+    private static Regex TokenRegex() => TokenRegexField;
+#endif
+
+    private static bool ExceedsMaxBaggageLimits(int currentLength, int? currentItemCount) =>
+        currentLength >= MaxBaggageLength || currentItemCount >= MaxBaggageItems;
+
+    private static bool IsValidKeyValuePair(string key, string value) =>
+        !string.IsNullOrEmpty(key) && !string.IsNullOrEmpty(value) && TokenRegex().IsMatch(key);
+
+    private static bool IsHex(char c) =>
+        (c >= '0' && c <= '9') ||
+        (c >= 'a' && c <= 'f') ||
+        (c >= 'A' && c <= 'F');
+
+    private static bool IsBaggageOctet(char c) =>
+        c == 0x21 ||
+        (c >= 0x23 && c <= 0x2B) ||
+        (c >= 0x2D && c <= 0x3A) ||
+        (c >= 0x3C && c <= 0x5B) ||
+        (c >= 0x5D && c <= 0x7E);
+}

test/OpenTelemetry.Api.Tests/Context/Propagation/BaggagePropagatorTests.cs

@@ -152,14 +152,14 @@ public void ValidateSpecialCharsBaggageExtraction()
 
         Assert.Equal(3, actualBaggage.Count);
 
-        Assert.True(actualBaggage.ContainsKey("key 1"));
-        Assert.Equal("value 1", actualBaggage["key 1"]);
+        Assert.True(actualBaggage.ContainsKey("key+1"));
+        Assert.Equal("value+1", actualBaggage["key+1"]);
 
         Assert.True(actualBaggage.ContainsKey("key2"));
         Assert.Equal("!x_x,x-x&x(x\");:", actualBaggage["key2"]);
 
-        Assert.True(actualBaggage.ContainsKey("key()3"));
-        Assert.Equal("value()!&;:", actualBaggage["key()3"]);
+        Assert.True(actualBaggage.ContainsKey("key%28%293"));
+        Assert.Equal("value()!&;:", actualBaggage["key%28%293"]);
     }
 
     [Fact]
@@ -204,6 +204,6 @@ public void ValidateSpecialCharsBaggageInjection()
         this.baggage.Inject(propagationContext, carrier, Setter);
 
         Assert.Single(carrier);
-        Assert.Equal("key+1=value+1,key2=!x_x%2Cx-x%26x(x%22)%3B%3A", carrier[BaggagePropagator.BaggageHeaderName]);
+        Assert.Equal("key 1=value%201,key2=%21x_x%2Cx-x%26x%28x%22%29%3B%3A", carrier[BaggagePropagator.BaggageHeaderName]);
     }
 }