fix: DSC contains actual SampleRate

src/Sentry/DynamicSamplingContext.cs

@@ -98,6 +98,24 @@ private DynamicSamplingContext(SentryId traceId,
 
     public BaggageHeader ToBaggageHeader() => BaggageHeader.Create(Items, useSentryPrefix: true);
 
+    public DynamicSamplingContext WithSampleRate(double sampleRate)
+    {
+        if (Items.TryGetValue("sample_rate", out var dscSampleRate))
+        {
+            if (double.TryParse(dscSampleRate, NumberStyles.Float, CultureInfo.InvariantCulture, out var rate))
+            {
+                if (Math.Abs(rate - sampleRate) > double.Epsilon)
+                {
+                    var items = Items.ToDictionary(kvp => kvp.Key, kvp => kvp.Value);
+                    items["sample_rate"] = sampleRate.ToString(CultureInfo.InvariantCulture);
+                    return new DynamicSamplingContext(items);
+                }
+            }
+        }
+
+        return this;
+    }
+
     public DynamicSamplingContext WithReplayId(IReplaySession? replaySession)
     {
         if (replaySession?.ActiveReplayId is not { } replayId || replayId == SentryId.Empty)

src/Sentry/Internal/Hub.cs

@@ -172,8 +172,8 @@ internal ITransactionTracer StartTransaction(
 
         bool? isSampled = null;
         double? sampleRate = null;
-        var sampleRand = dynamicSamplingContext?.Items.TryGetValue("sample_rand", out var dscsampleRand) ?? false
-            ? double.Parse(dscsampleRand, NumberStyles.Float, CultureInfo.InvariantCulture)
+        var sampleRand = dynamicSamplingContext?.Items.TryGetValue("sample_rand", out var dscSampleRand) ?? false
+            ? double.Parse(dscSampleRand, NumberStyles.Float, CultureInfo.InvariantCulture)
             : SampleRandHelper.GenerateSampleRand(context.TraceId.ToString());
 
         // TracesSampler runs regardless of whether a decision has already been made, as it can be used to override it.
@@ -196,6 +196,9 @@ internal ITransactionTracer StartTransaction(
         sampleRate ??= _options.TracesSampleRate ?? 0.0;
         isSampled ??= context.IsSampled ?? SampleRandHelper.IsSampled(sampleRand, sampleRate.Value);
 
+        // Ensure the actual sampleRate is set on the provided DSC (https://github.com/getsentry/team-sdks/issues/117)
+        dynamicSamplingContext = dynamicSamplingContext?.WithSampleRate(sampleRate.Value);
+
         // Make sure there is a replayId (if available) on the provided DSC (if any).
         dynamicSamplingContext = dynamicSamplingContext?.WithReplayId(_replaySession);
 

test/Sentry.AspNetCore.Tests/SentryTracingMiddlewareTests.cs

@@ -316,7 +316,7 @@ public async Task Baggage_header_propagates_to_outbound_requests(bool shouldProp
                 "sentry-trace_id=75302ac48a024bde9a3b3734a82e36c8, " +
                 "sentry-public_key=d4d82fc1c2c4032a83f3a29aa3a3aff, " +
                 "sentry-sample_rand=0.1234, " +
-                "sentry-sample_rate=0.5";
+                "sentry-sample_rate=1";
         }
         else
         {
@@ -395,13 +395,18 @@ public async Task Baggage_header_propagates_to_outbound_requests(bool shouldProp
     [Fact]
     public async Task Baggage_header_sets_dynamic_sampling_context()
     {
-        // incoming baggage header
-        const string baggage =
+        const string incomingBaggageHeader =
             "sentry-trace_id=75302ac48a024bde9a3b3734a82e36c8, " +
             "sentry-public_key=d4d82fc1c2c4032a83f3a29aa3a3aff, " +
             "sentry-sample_rand=0.1234, " +
             "sentry-sample_rate=0.5";
 
+        const string expectedBaggageHeader =
+            "sentry-trace_id=75302ac48a024bde9a3b3734a82e36c8, " +
+            "sentry-public_key=d4d82fc1c2c4032a83f3a29aa3a3aff, " +
+            "sentry-sample_rand=0.1234, " +
+            "sentry-sample_rate=1";
+
         // Arrange
         TransactionTracer transaction = null;
 
@@ -440,7 +445,7 @@ public async Task Baggage_header_sets_dynamic_sampling_context()
         {
             Headers =
             {
-                {"baggage", baggage}
+                {"baggage", incomingBaggageHeader}
             }
         };
 
@@ -449,7 +454,7 @@ public async Task Baggage_header_sets_dynamic_sampling_context()
         // Assert
         var dsc = transaction?.DynamicSamplingContext;
         Assert.NotNull(dsc);
-        Assert.Equal(baggage, dsc.ToBaggageHeader().ToString());
+        Assert.Equal(expectedBaggageHeader, dsc.ToBaggageHeader().ToString());
     }
 
     [Fact]

test/Sentry.OpenTelemetry.Tests/SentrySpanProcessorTests.cs

@@ -141,7 +141,8 @@ public void OnStart_Transaction_With_DynamicSamplingContext()
         {
             actual.Items["trace_id"].Should().Be(expected["trace_id"]);
             actual.Items["public_key"].Should().Be(expected["public_key"]);
-            actual.Items["sample_rate"].Should().Be(expected["sample_rate"]);
+            actual.Items["sample_rate"].Should().NotBe(expected["sample_rate"]);
+            actual.Items["sample_rate"].Should().Be(_fixture.Options.TracesSampleRate.ToString());
         }
     }
 

test/Sentry.Tests/HubTests.cs

@@ -681,6 +681,76 @@ public void StartTransaction_SameInstrumenter_SampledIn()
         transaction.IsSampled.Should().BeTrue();
     }
 
+    [Fact]
+    public void StartTransaction_DynamicSamplingContextWithSampleRate_UsesSampleRate()
+    {
+        // Arrange
+        var transactionContext = new TransactionContext("name", "operation");
+        var dsc = BaggageHeader.Create(new List<KeyValuePair<string, string>>
+        {
+            {"sentry-trace_id", "43365712692146d08ee11a729dfbcaca"},
+            {"sentry-public_key", "d4d82fc1c2c4032a83f3a29aa3a3aff"},
+            {"sentry-sample_rate", "0.5"},
+            {"sentry-sample_rand", "0.1234"},
+        }).CreateDynamicSamplingContext();
+
+        _fixture.Options.TracesSampler = _ => 0.5;
+        _fixture.Options.TracesSampleRate = 0.5;
+
+        var hub = _fixture.GetSut();
+
+        // Act
+        var transaction = hub.StartTransaction(transactionContext, new Dictionary<string, object>(), dsc);
+
+        // Assert
+        var transactionTracer = transaction.Should().BeOfType<TransactionTracer>().Subject;
+        transactionTracer.SampleRate.Should().Be(0.5);
+        transactionTracer.DynamicSamplingContext.Should().BeSameAs(dsc);
+    }
+
+    [Theory]
+    [InlineData(true, true)]
+    [InlineData(true, false)]
+    [InlineData(false, true)]
+    [InlineData(false, false)]
+    public void StartTransaction_DynamicSamplingContextWithSampleRate_UsesActualSampleRate(bool useTracesSampler, bool useTracesSampleRate)
+    {
+        // Arrange
+        var transactionContext = new TransactionContext("name", "operation");
+        var dsc = BaggageHeader.Create(new List<KeyValuePair<string, string>>
+        {
+            {"sentry-trace_id", "43365712692146d08ee11a729dfbcaca"},
+            {"sentry-public_key", "d4d82fc1c2c4032a83f3a29aa3a3aff"},
+            {"sentry-sample_rate", "0.5"},
+            {"sentry-sample_rand", "0.1234"},
+        }).CreateDynamicSamplingContext();
+
+        _fixture.Options.TracesSampler = useTracesSampler ? _ => 0.3 : _ => null;
+        _fixture.Options.TracesSampleRate = useTracesSampleRate ? 0.4 : null;
+
+        var hub = _fixture.GetSut();
+
+        // Act
+        var transaction = hub.StartTransaction(transactionContext, new Dictionary<string, object>(), dsc);
+
+        // Assert
+        if (useTracesSampler || useTracesSampleRate)
+        {
+            var expectedSampleRate = useTracesSampler ? 0.3 : 0.4;
+            var transactionTracer = transaction.Should().BeOfType<TransactionTracer>().Subject;
+            transactionTracer.SampleRate.Should().Be(expectedSampleRate);
+            transactionTracer.DynamicSamplingContext.Should().NotBeSameAs(dsc);
+            transactionTracer.DynamicSamplingContext.Should().BeEquivalentTo(dsc.ReplaceSampleRate(expectedSampleRate));
+        }
+        else
+        {
+            var unsampledTransaction = transaction.Should().BeOfType<UnsampledTransaction>().Subject;
+            unsampledTransaction.SampleRate.Should().Be(0.0);
+            unsampledTransaction.DynamicSamplingContext.Should().NotBeSameAs(dsc);
+            unsampledTransaction.DynamicSamplingContext.Should().BeEquivalentTo(dsc.ReplaceSampleRate(0));
+        }
+    }
+
     [Theory]
     [InlineData(true)]
     [InlineData(false)]
@@ -711,22 +781,15 @@ public void StartTransaction_DynamicSamplingContextWithReplayId_UsesActiveReplay
         var transactionTracer = transaction.Should().BeOfType<TransactionTracer>().Subject;
         transactionTracer.IsSampled.Should().BeTrue();
         transactionTracer.DynamicSamplingContext.Should().NotBeNull();
-        foreach (var dscItem in dsc!.Items)
+
+        var expectedDsc = dsc.ReplaceSampleRate(_fixture.Options.TracesSampleRate.Value);
+        if (replaySessionIsActive)
         {
-            if (dscItem.Key == "replay_id")
-            {
-                transactionTracer.DynamicSamplingContext!.Items["replay_id"].Should().Be(replaySessionIsActive
-                    // We overwrite the replay_id when we have an active replay session
-                    ? _fixture.ReplaySession.ActiveReplayId.ToString()
-                    // Otherwise we propagate whatever was in the baggage header
-                    : dscItem.Value);
-            }
-            else
-            {
-                transactionTracer.DynamicSamplingContext!.Items.Should()
-                    .Contain(kvp => kvp.Key == dscItem.Key && kvp.Value == dscItem.Value);
-            }
+            // We overwrite the replay_id when we have an active replay session
+            // Otherwise we propagate whatever was in the baggage header
+            expectedDsc = expectedDsc.ReplaceReplayId(_fixture.ReplaySession);
         }
+        transactionTracer.DynamicSamplingContext.Should().BeEquivalentTo(expectedDsc);
     }
 
     [Theory]
@@ -822,7 +885,8 @@ public void StartTransaction_DynamicSamplingContextWithSampleRand_InheritsSample
         transactionTracer.IsSampled.Should().BeTrue();
         transactionTracer.SampleRate.Should().Be(0.4);
         transactionTracer.SampleRand.Should().Be(0.1234);
-        transactionTracer.DynamicSamplingContext.Should().Be(dsc);
+        transactionTracer.DynamicSamplingContext.Should().NotBeSameAs(dsc);
+        transactionTracer.DynamicSamplingContext.Should().BeEquivalentTo(dsc.ReplaceSampleRate(0.4));
     }
 
     [Theory]
@@ -855,15 +919,17 @@ public void StartTransaction_TraceSampler_UsesSampleRand(double sampleRate, bool
             transactionTracer.IsSampled.Should().BeTrue();
             transactionTracer.SampleRate.Should().Be(sampleRate);
             transactionTracer.SampleRand.Should().Be(0.1234);
-            transactionTracer.DynamicSamplingContext.Should().Be(dsc);
+            transactionTracer.DynamicSamplingContext.Should().NotBeSameAs(dsc);
+            transactionTracer.DynamicSamplingContext.Should().BeEquivalentTo(dsc.ReplaceSampleRate(sampleRate));
         }
         else
         {
             var unsampledTransaction = transaction.Should().BeOfType<UnsampledTransaction>().Subject;
             unsampledTransaction.IsSampled.Should().BeFalse();
             unsampledTransaction.SampleRate.Should().Be(sampleRate);
             unsampledTransaction.SampleRand.Should().Be(0.1234);
-            unsampledTransaction.DynamicSamplingContext.Should().Be(dsc);
+            unsampledTransaction.DynamicSamplingContext.Should().NotBeSameAs(dsc);
+            unsampledTransaction.DynamicSamplingContext.Should().BeEquivalentTo(dsc.ReplaceSampleRate(sampleRate));
         }
     }
 
@@ -897,15 +963,17 @@ public void StartTransaction_StaticSampler_UsesSampleRand(double sampleRate, boo
             transactionTracer.IsSampled.Should().BeTrue();
             transactionTracer.SampleRate.Should().Be(sampleRate);
             transactionTracer.SampleRand.Should().Be(0.1234);
-            transactionTracer.DynamicSamplingContext.Should().Be(dsc);
+            transactionTracer.DynamicSamplingContext.Should().NotBeSameAs(dsc);
+            transactionTracer.DynamicSamplingContext.Should().BeEquivalentTo(dsc.ReplaceSampleRate(sampleRate));
         }
         else
         {
             var unsampledTransaction = transaction.Should().BeOfType<UnsampledTransaction>().Subject;
             unsampledTransaction.IsSampled.Should().BeFalse();
             unsampledTransaction.SampleRate.Should().Be(sampleRate);
             unsampledTransaction.SampleRand.Should().Be(0.1234);
-            unsampledTransaction.DynamicSamplingContext.Should().Be(dsc);
+            unsampledTransaction.DynamicSamplingContext.Should().NotBeSameAs(dsc);
+            unsampledTransaction.DynamicSamplingContext.Should().BeEquivalentTo(dsc.ReplaceSampleRate(sampleRate));
         }
     }
 
@@ -2108,3 +2176,67 @@ internal partial class HubTestsJsonContext : JsonSerializerContext
 {
 }
 #endif
+
+#nullable enable
+file static class DynamicSamplingContextExtensions
+{
+    public static DynamicSamplingContext ReplaceSampleRate(this DynamicSamplingContext? dsc, double sampleRate)
+    {
+        Assert.NotNull(dsc);
+
+        var value = sampleRate.ToString(CultureInfo.InvariantCulture);
+        return dsc.Replace("sentry-sample_rate", value);
+    }
+
+    public static DynamicSamplingContext ReplaceReplayId(this DynamicSamplingContext? dsc, IReplaySession replaySession)
+    {
+        Assert.NotNull(dsc);
+
+        if (!replaySession.ActiveReplayId.HasValue)
+        {
+            throw new InvalidOperationException($"No {nameof(IReplaySession.ActiveReplayId)}.");
+        }
+
+        var value = replaySession.ActiveReplayId.Value.ToString();
+        return dsc.Replace("sentry-replay_id", value);
+    }
+
+    private static DynamicSamplingContext Replace(this DynamicSamplingContext dsc, string key, string newValue)
+    {
+        var items = dsc.ToBaggageHeader().Members.ToList();
+        var index = items.FindSingleIndex(key);
+
+        var oldValue = items[index].Value;
+        if (oldValue == newValue)
+        {
+            throw new InvalidOperationException($"{key} already is {oldValue}.");
+        }
+
+        items[index] = new KeyValuePair<string, string>(key, newValue);
+
+        var baggage = BaggageHeader.Create(items);
+        var dynamicSamplingContext = DynamicSamplingContext.CreateFromBaggageHeader(baggage, null);
+        if (dynamicSamplingContext is null)
+        {
+            throw new InvalidOperationException($"Invalid {nameof(BaggageHeader)}: {baggage}");
+        }
+
+        return dynamicSamplingContext;
+    }
+
+    private static int FindSingleIndex(this List<KeyValuePair<string, string>> items, string key)
+    {
+        var index = items.FindIndex(item => item.Key == key);
+        if (index == -1)
+        {
+            throw new InvalidOperationException($"{key} not found.");
+        }
+
+        if (items.FindLastIndex(item => item.Key == key) != index)
+        {
+            throw new InvalidOperationException($"Duplicate {key} found.");
+        }
+
+        return index;
+    }
+}