Add sample_rand to propagation context

Author: solnic

sentry-ruby/lib/sentry/propagation_context.rb

@@ -3,6 +3,7 @@
 require "securerandom"
 require "sentry/baggage"
 require "sentry/utils/uuid"
+require "sentry/utils/sample_rand"
 
 module Sentry
   class PropagationContext
@@ -33,13 +34,17 @@ class PropagationContext
     # Please use the #get_baggage method for interfacing outside this class.
     # @return [Baggage, nil]
     attr_reader :baggage
+    # The propagated random value used for sampling decisions.
+    # @return [Float, nil]
+    attr_reader :sample_rand
 
     def initialize(scope, env = nil)
       @scope = scope
       @parent_span_id = nil
       @parent_sampled = nil
       @baggage = nil
       @incoming_trace = false
+      @sample_rand = nil
 
       if env
         sentry_trace_header = env["HTTP_SENTRY_TRACE"] || env[SENTRY_TRACE_HEADER_NAME]
@@ -61,6 +66,7 @@ def initialize(scope, env = nil)
                 Baggage.new({})
               end
 
+            @sample_rand = extract_sample_rand_from_baggage(@baggage)
             @baggage.freeze!
             @incoming_trace = true
           end
@@ -69,6 +75,7 @@ def initialize(scope, env = nil)
 
       @trace_id ||= Utils.uuid
       @span_id = Utils.uuid.slice(0, 16)
+      @sample_rand ||= generate_sample_rand
     end
 
     # Extract the trace_id, parent_span_id and parent_sampled values from a sentry-trace header.
@@ -123,6 +130,7 @@ def populate_head_baggage
 
       items = {
         "trace_id" => trace_id,
+        "sample_rand" => Utils::SampleRand.format(@sample_rand),
         "environment" => configuration.environment,
         "release" => configuration.release,
         "public_key" => configuration.dsn&.public_key
@@ -131,5 +139,30 @@ def populate_head_baggage
       items.compact!
       @baggage = Baggage.new(items, mutable: false)
     end
+
+    def extract_sample_rand_from_baggage(baggage)
+      return nil unless baggage&.items
+
+      sample_rand_str = baggage.items["sample_rand"]
+      return nil unless sample_rand_str
+
+      sample_rand = sample_rand_str.to_f
+      Utils::SampleRand.valid?(sample_rand) ? sample_rand : nil
+    end
+
+    def generate_sample_rand
+      if @incoming_trace && @parent_sampled && @baggage
+        sample_rate_str = @baggage.items["sample_rate"]
+        sample_rate = sample_rate_str&.to_f
+
+        if sample_rate && @parent_sampled != nil
+          Utils::SampleRand.generate_from_sampling_decision(@parent_sampled, sample_rate, @trace_id)
+        else
+          Utils::SampleRand.generate_from_trace_id(@trace_id)
+        end
+      else
+        Utils::SampleRand.generate_from_trace_id(@trace_id)
+      end
+    end
   end
 end

sentry-ruby/spec/sentry/propagation_context/sample_rand_spec.rb

@@ -0,0 +1,196 @@
+# frozen_string_literal: true
+
+RSpec.describe Sentry::PropagationContext do
+  before do
+    perform_basic_setup
+  end
+
+  let(:scope) { Sentry.get_current_scope }
+
+  describe "sample_rand integration" do
+    describe "#initialize" do
+      it "generates sample_rand when no incoming trace" do
+        context = described_class.new(scope)
+
+        expect(context.sample_rand).to be_a(Float)
+        expect(context.sample_rand).to be >= 0.0
+        expect(context.sample_rand).to be < 1.0
+      end
+
+      it "generates deterministic sample_rand from trace_id" do
+        context1 = described_class.new(scope)
+        context2 = described_class.new(scope)
+
+        # Different contexts should have different trace_ids and thus different sample_rand
+        expect(context1.sample_rand).not_to eq(context2.sample_rand)
+
+        # But same trace_id should generate same sample_rand
+        trace_id = context1.trace_id
+        allow(Sentry::Utils).to receive(:uuid).and_return(trace_id)
+        context3 = described_class.new(scope)
+
+        expect(context3.sample_rand).to eq(context1.sample_rand)
+      end
+
+      context "with incoming trace" do
+        let(:env) do
+          {
+            "HTTP_SENTRY_TRACE" => "771a43a4192642f0b136d5159a501700-7c51afd529da4a2a-1",
+            "HTTP_BAGGAGE" => "sentry-trace_id=771a43a4192642f0b136d5159a501700,sentry-sample_rand=0.123456"
+          }
+        end
+
+        it "uses sample_rand from incoming baggage" do
+          context = described_class.new(scope, env)
+
+          expect(context.sample_rand).to eq(0.123456)
+          expect(context.incoming_trace).to be true
+        end
+      end
+
+      context "with incoming trace but no sample_rand in baggage" do
+        let(:env) do
+          {
+            "HTTP_SENTRY_TRACE" => "771a43a4192642f0b136d5159a501700-7c51afd529da4a2a-1",
+            "HTTP_BAGGAGE" => "sentry-trace_id=771a43a4192642f0b136d5159a501700,sentry-sample_rate=0.5"
+          }
+        end
+
+        it "generates sample_rand based on sampling decision" do
+          context = described_class.new(scope, env)
+
+          expect(context.sample_rand).to be_a(Float)
+          expect(context.sample_rand).to be >= 0.0
+          expect(context.sample_rand).to be < 1.0
+          expect(context.incoming_trace).to be true
+
+          # For sampled=true and sample_rate=0.5, sample_rand should be < 0.5
+          expect(context.sample_rand).to be < 0.5
+        end
+
+        it "is deterministic for same trace" do
+          context1 = described_class.new(scope, env)
+          context2 = described_class.new(scope, env)
+
+          expect(context1.sample_rand).to eq(context2.sample_rand)
+        end
+      end
+
+      context "with incoming trace but no baggage" do
+        let(:env) do
+          {
+            "HTTP_SENTRY_TRACE" => "771a43a4192642f0b136d5159a501700-7c51afd529da4a2a-1"
+          }
+        end
+
+        it "generates deterministic sample_rand from trace_id" do
+          context = described_class.new(scope, env)
+
+          expect(context.sample_rand).to be_a(Float)
+          expect(context.sample_rand).to be >= 0.0
+          expect(context.sample_rand).to be < 1.0
+          expect(context.incoming_trace).to be true
+
+          # Should be deterministic based on trace_id
+          expected = Sentry::Utils::SampleRand.generate_from_trace_id("771a43a4192642f0b136d5159a501700")
+          expect(context.sample_rand).to eq(expected)
+        end
+      end
+    end
+
+    describe "#get_baggage" do
+      it "includes sample_rand in baggage" do
+        context = described_class.new(scope)
+        baggage = context.get_baggage
+
+        expect(baggage.items["sample_rand"]).to eq(Sentry::Utils::SampleRand.format(context.sample_rand))
+      end
+
+      context "with incoming baggage containing sample_rand" do
+        let(:env) do
+          {
+            "HTTP_SENTRY_TRACE" => "771a43a4192642f0b136d5159a501700-7c51afd529da4a2a-1",
+            "HTTP_BAGGAGE" => "sentry-trace_id=771a43a4192642f0b136d5159a501700,sentry-sample_rand=0.654321"
+          }
+        end
+
+        it "preserves incoming sample_rand in baggage" do
+          context = described_class.new(scope, env)
+          baggage = context.get_baggage
+
+          expect(baggage.items["sample_rand"]).to eq("0.654321")
+        end
+      end
+    end
+
+    describe "extract_sample_rand_from_baggage" do
+      it "extracts valid sample_rand from baggage" do
+        baggage = Sentry::Baggage.new({ "sample_rand" => "0.123456" })
+        context = described_class.new(scope)
+
+        sample_rand = context.send(:extract_sample_rand_from_baggage, baggage)
+        expect(sample_rand).to eq(0.123456)
+      end
+
+      it "returns nil for invalid sample_rand" do
+        baggage = Sentry::Baggage.new({ "sample_rand" => "1.5" })  # > 1.0 is invalid
+        context = described_class.new(scope)
+
+        sample_rand = context.send(:extract_sample_rand_from_baggage, baggage)
+        expect(sample_rand).to be_nil
+      end
+
+      it "returns nil when no sample_rand in baggage" do
+        baggage = Sentry::Baggage.new({ "trace_id" => "abc123" })
+        context = described_class.new(scope)
+
+        sample_rand = context.send(:extract_sample_rand_from_baggage, baggage)
+        expect(sample_rand).to be_nil
+      end
+
+      it "returns nil when baggage is nil" do
+        context = described_class.new(scope)
+
+        sample_rand = context.send(:extract_sample_rand_from_baggage, nil)
+        expect(sample_rand).to be_nil
+      end
+    end
+
+    describe "generate_sample_rand" do
+      context "with incoming trace and sampling decision" do
+        let(:context) do
+          ctx = described_class.new(scope)
+          ctx.instance_variable_set(:@incoming_trace, true)
+          ctx.instance_variable_set(:@parent_sampled, true)
+          ctx.instance_variable_set(:@baggage, Sentry::Baggage.new({ "sample_rate" => "0.5" }))
+          ctx.instance_variable_set(:@trace_id, "771a43a4192642f0b136d5159a501700")
+          ctx
+        end
+
+        it "generates sample_rand based on sampling decision" do
+          sample_rand = context.send(:generate_sample_rand)
+
+          expect(sample_rand).to be_a(Float)
+          expect(sample_rand).to be >= 0.0
+          expect(sample_rand).to be < 0.5
+        end
+      end
+
+      context "without incoming trace" do
+        let(:context) do
+          ctx = described_class.new(scope)
+          ctx.instance_variable_set(:@incoming_trace, false)
+          ctx.instance_variable_set(:@trace_id, "771a43a4192642f0b136d5159a501700")
+          ctx
+        end
+
+        it "generates deterministic sample_rand from trace_id" do
+          sample_rand = context.send(:generate_sample_rand)
+          expected = Sentry::Utils::SampleRand.generate_from_trace_id("771a43a4192642f0b136d5159a501700")
+
+          expect(sample_rand).to eq(expected)
+        end
+      end
+    end
+  end
+end

sentry-ruby/spec/sentry/propagation_context_spec.rb

@@ -119,6 +119,7 @@
       expect(baggage.mutable).to eq(false)
       expect(baggage.items).to eq({
         "trace_id" => subject.trace_id,
+        "sample_rand" => Sentry::Utils::SampleRand.format(subject.sample_rand),
         "environment" => "test",
         "release" => "foobar",
         "public_key" => Sentry.configuration.dsn.public_key