initial seed propagation impl

Author: buenaflor

dart/lib/src/sentry_baggage.dart

@@ -1,11 +1,13 @@
 import 'package:meta/meta.dart';
-import 'scope.dart';
-import 'protocol.dart';
 
+import 'protocol.dart';
+import 'scope.dart';
 import 'sentry_options.dart';
 
 class SentryBaggage {
   static const String _sampleRateKeyName = 'sentry-sample_rate';
+  static const String _sampleRandKeyName = 'sentry-sample_rand';
+
   static const int _maxChars = 8192;
   static const int _maxListMember = 64;
 
@@ -194,6 +196,10 @@ class SentryBaggage {
     set(_sampleRateKeyName, value);
   }
 
+  void setSampleRand(String value) {
+    set(_sampleRandKeyName, value);
+  }
+
   void setSampled(String value) {
     set('sentry-sampled', value);
   }
@@ -207,6 +213,15 @@ class SentryBaggage {
     return double.tryParse(sampleRate);
   }
 
+  double? getSampleRand() {
+    final sampleRand = get(_sampleRandKeyName);
+    if (sampleRand == null) {
+      return null;
+    }
+
+    return double.tryParse(sampleRand);
+  }
+
   void setReplayId(String value) => set('sentry-replay_id', value);
 
   SentryId? getReplayId() {

dart/lib/src/sentry_trace_context_header.dart

@@ -1,7 +1,7 @@
 import 'package:meta/meta.dart';
 
-import 'protocol/sentry_id.dart';
 import 'protocol/access_aware_map.dart';
+import 'protocol/sentry_id.dart';
 import 'sentry_baggage.dart';
 import 'sentry_options.dart';
 
@@ -15,6 +15,7 @@ class SentryTraceContextHeader {
     this.userSegment,
     this.transaction,
     this.sampleRate,
+    this.sampleRand,
     this.sampled,
     this.unknown,
     this.replayId,
@@ -30,6 +31,7 @@ class SentryTraceContextHeader {
   final String? userSegment;
   final String? transaction;
   final String? sampleRate;
+  final String? sampleRand;
   final String? sampled;
 
   @internal
@@ -102,6 +104,9 @@ class SentryTraceContextHeader {
     if (sampleRate != null) {
       baggage.setSampleRate(sampleRate!);
     }
+    if (sampleRand != null) {
+      baggage.setSampleRate(sampleRand!);
+    }
     if (sampled != null) {
       baggage.setSampled(sampled!);
     }

dart/lib/src/sentry_tracer.dart

@@ -385,6 +385,7 @@ class SentryTracer extends ISentrySpan {
       transaction:
           _isHighQualityTransactionName(transactionNameSource) ? name : null,
       sampleRate: _sampleRateToString(_rootSpan.samplingDecision?.sampleRate),
+      sampleRand: _sampleRateToString(_rootSpan.samplingDecision?.sampleRand),
       sampled: _rootSpan.samplingDecision?.sampled.toString(),
     );
 

dart/lib/src/sentry_traces_sampler.dart

@@ -33,10 +33,7 @@ class SentryTracesSampler {
       try {
         final result = tracesSampler(samplingContext);
         if (result != null) {
-          return SentryTracesSamplingDecision(
-            _sample(result),
-            sampleRate: result,
-          );
+          return _sample2(result);
         }
       } catch (exception, stackTrace) {
         _options.logger(
@@ -64,10 +61,7 @@ class SentryTracesSampler {
     double? optionsOrDefaultRate = optionsRate ?? defaultRate;
 
     if (optionsOrDefaultRate != null) {
-      return SentryTracesSamplingDecision(
-        _sample(optionsOrDefaultRate),
-        sampleRate: optionsOrDefaultRate,
-      );
+      return _sample2(optionsOrDefaultRate);
     }
 
     return SentryTracesSamplingDecision(false);
@@ -78,8 +72,19 @@ class SentryTracesSampler {
     if (optionsRate == null || !tracesSamplingDecision.sampled) {
       return false;
     }
-    return _sample(optionsRate);
+    return _shouldSample(optionsRate);
   }
 
-  bool _sample(double result) => !(result < _random.nextDouble());
+  SentryTracesSamplingDecision _sample2(double sampleRate) {
+    final sampleRand = _random.nextDouble();
+    return SentryTracesSamplingDecision(
+        _shouldSample(sampleRate, sampleRand: sampleRand),
+        sampleRate: sampleRate,
+        sampleRand: sampleRand);
+  }
+
+  bool _shouldSample(double sampleRate, {double? sampleRand}) {
+    final rand = sampleRand ?? _random.nextDouble();
+    return rand <= sampleRate;
+  }
 }

dart/lib/src/sentry_traces_sampling_decision.dart

@@ -2,8 +2,10 @@ class SentryTracesSamplingDecision {
   SentryTracesSamplingDecision(
     this.sampled, {
     this.sampleRate,
+    this.sampleRand,
   });
 
   final bool sampled;
   final double? sampleRate;
+  final double? sampleRand;
 }

dart/lib/src/sentry_transaction_context.dart

@@ -1,8 +1,8 @@
 import 'package:meta/meta.dart';
-import 'sentry_trace_origins.dart';
 
 import 'protocol.dart';
 import 'sentry_baggage.dart';
+import 'sentry_trace_origins.dart';
 import 'tracing.dart';
 
 @immutable
@@ -35,6 +35,7 @@ class SentryTransactionContext extends SentrySpanContext {
     SentryBaggage? baggage,
   }) {
     final sampleRate = baggage?.getSampleRate();
+    final sampleRand = baggage?.getSampleRand();
     return SentryTransactionContext(
       name,
       operation,
@@ -44,6 +45,7 @@ class SentryTransactionContext extends SentrySpanContext {
           ? SentryTracesSamplingDecision(
               traceHeader.sampled!,
               sampleRate: sampleRate,
+              sampleRand: sampleRand,
             )
           : null,
       transactionNameSource: